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Title:
DISPLAY WHICH HAS A SELECTABLE VIEWING SECTOR
Document Type and Number:
WIPO Patent Application WO/2022/090615
Kind Code:
A1
Abstract:
A display apparatus comprises:- at least one backlight unit to project first deflected light to a first angular range,and to project second deflected light to a second different angular range, and - a spatial modulator array to form first modulated light from the first deflected light, and to form second modulated light from the second deflected light,wherein the apparatus is arranged to form the first deflected light by guiding and deflecting light obtained from one or more first light sources, wherein the apparatus is arranged to form the second deflected light by guiding and deflecting light obtained from one or more second light sources.

Inventors:
RUOTSALAINEN TEEMU (FI)
MÄKELÄ TAPIO (FI)
SNECK ASKO (FI)
Application Number:
PCT/FI2021/050711
Publication Date:
May 05, 2022
Filing Date:
October 25, 2021
Export Citation:
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Assignee:
TEKNOLOGIAN TUTKIMUSKESKUS VTT OY (FI)
International Classes:
G02F1/13357; F21V8/00
Domestic Patent References:
WO2017065745A12017-04-20
Foreign References:
US20120069550A12012-03-22
US20170261672A12017-09-14
US20190004236A12019-01-03
Attorney, Agent or Firm:
BERGGREN OY (FI)
Download PDF:
Claims:
CLAIMS

1 . A display apparatus (500), comprising:

- at least one backlight unit ( BLU2 ) to project first deflected light (B2b) to a first angular range (RNG2) and to project second deflected light (B2c) to a second different angular range (RNG3),

- a spatial modulator array (SMA1 ) to form first modulated light (VOb) from the first deflected light (B2b), and to form second modulated light (VOc) from the second deflected light (B2c), wherein the apparatus (500) is arranged to form the first deflected light (B2b) by guiding and deflecting light obtained from one or more first light sources (LED1 b), wherein the apparatus (500) is arranged to form the second deflected light (B2c) by guiding and deflecting light obtained from one or more second light sources (LED1 c), wherein a first backlight unit ( BLU2 ) of the apparatus (500) comprises:

- the one or more first light sources (LED1 b) to provide first input light (BOb),

- the one or more second light sources (LED1 c) to provide second input light (B0c),

- a first waveguiding substrate ( BLU2 ),

- a plurality of light-deflecting grooves (G2) implemented on the substrate (SUB2), wherein the first backlight unit ( BLU2 ) is arranged to form first guided light (B1 b) by coupling the first input light (BOb) into the substrate (SLIB2) through a first edge (EDG1 b) of the substrate ( BLU2 ), wherein the grooves (G2) of the substrate ( BLU2 ) are arranged to form the first deflected light (B2b) by coupling the first guided light (B1 b) out of the substrate (SLIB2), where in an area covered by the grooves (G2) within an out-coupling region (REG1 ) of the substrate (SLIB2) is selected to be smaller than 5% of the area of the out- coupling region (REG1 ) such that average optical attenuation (AIBI I/IBI 1) in the out-coupling region (REG1 ) is smaller than 20% for visible light (B11 ), which is transmitted through the substrate (SLIB2), wherein the average optical attenuation (AIBI I/IBI 1) is the average value of optical attenuation over the out- coupling region (REG1 ), characterized in that the first backlight unit (BLLI2) is arranged to form second guided light (B1 c) by coupling the second input light (BOc) into the substrate (SLIB2) through a second edge (EDG1 c) of the substrate (SLIB2), wherein the grooves (G2) are arranged to form the second deflected light (B2c) by coupling the second guided light (B1 c) out of the first substrate (SLIB2).

2. The display apparatus (500) of claim 1 , comprising a second backlight unit (BLLI1 ) comprising a second substrate (SLIB1 ), which has grooves (G1 ) to project third deflected light (B2a) to a third angular range (RNG1 ), wherein the second backlight unit (BLLI1 ) comprises one or more third light sources (LED1 a) to provide third input light (BOa), wherein the second backlight unit (BLLI1 ) is arranged to form third guided light (B1 a) by coupling the third input light (BOa) into the second substrate (SLIB1 ), wherein the grooves (G1 ) of the second substrate (SLIB1 ) are arranged to project the third deflected light (B2a) into the third angular range (RNG1 ) by coupling the third guided light (B1 a) out of the second substrate (SLIB1 ) wherein the first backlight unit (BLLI2) is positioned between the second backlight unit (BLLI1 ) and the spatial modulator array (SMA1 ), or the second backlight unit (BLLI1 ) is positioned between the first backlight unit ( BLU2 ) and the spatial modulator array (SMA1 )

3. The apparatus (500) of claim 1 or 2, wherein the width (WG2) of the grooves (G2) of the first substrate (SLIB2) is in the range of 0.5 m to 10 pm, and wherein the depth (hG2) of the grooves (G2) of the first substrate (SLIB2) is in the range of 0.5 pm to 5 pm.

4. The apparatus (500) according to any of the claims 1 to 3, wherein an average distance (e2) between grooves (G2) of the first substrate (SLIB2) is smaller than 0.6 mm.

5. The apparatus (500) according to any of the claims 1 to 4, wherein the apparatus (500) is arranged to display first information (INFO2) to a first viewing region (ZONE2) and to display second information (INFO3) to a second viewing region (ZONE3), wherein the spatial modulator array (SMA1 ) is arranged to sequentially display the first information (INFO2) and the second information (INFO3), wherein the one or more first light sources (LED1 b) are arranged to emit first light pulses (BOb) during displaying the first information (INFO2), and wherein the one or more second light sources (LED1 c) are arranged to emit second light pulses (BOc) during displaying the second information (INFO3).

6. The apparatus (500) according to any of the claims 1 to 5, comprising a first subset (GRP1 ) of light sources (LED1 b) to form a first partial guided beam (B1 bn), and a second independently controllable subset (GRP2) of light sources (LED1 b) to form a second partial guided beam (B1 bi2), wherein the first subset (GRP1 ) is positioned at the first edge (EDG1 ) of the first substrate (SLIB2), and wherein the second subset (GRP2) is positioned at the same first edge (EDG1 ) of the first substrate (SUB1)1

). The apparatus (500) of claim 6, comprising a first partial region (REG11 ) of the first substrate (SLIB2) to project deflected light (B2b) by coupling light of the first partial guided beam (B1 bn) out of the first substrate (SLIB2), and a second partial region (REG12) of the fist substrate (SLIB2) to project deflected light (B2b) by coupling light of the second partial guided beam (B1 bi2) out of the first substrate (SLIB2), wherein the second partial region (REG12) is not arranged to couple light of the first partial guided beam (B1 bn) out of the first substrate (SUB2).

8. The apparatus (500) according to any of the claims 1 to 7, comprising a masking unit (MSK1 ) positioned above the modulator array (SMA1 ), wherein the masking unit (MSK1 ) comprises:

- one or more light sources (LED1f) to provide auxiliary input light,

- a third waveguiding substrate (SLIB3),

- a plurality of light-deflecting grooves (G3) implemented on the third substrate (SUB3), wherein the masking unit (MSK1 ) is arranged to form auxiliary guided light (B1f) by coupling the auxiliary input light into the third substrate (SLIB3), wherein the grooves (G3) of the third substrate (SLIB3) are arranged to form masking light (B2f) by coupling the auxiliary guided light (B1f) out of the third substrate (SUB3).

9. The apparatus (500) according to any of the claims 1 to 8, comprising a user interface (LIIF1 ) for receiving user input, wherein the apparatus (500) is arranged to control operation of the one or more light sources (LED1 b, LED1 c) based on the user input.

10. The apparatus (500) according to any of the claims 1 to 9, wherein the spatial modulator array (SMA1 ) comprises a liquid crystal layer (CRY1 ).

11. A method for displaying information (INFO2, INFO3), the method comprising:

- projecting first deflected light (B2b) to a first angular range (RNG2),

- projecting second deflected light (B2c) to a second different angular range (RNG3),

- forming first modulated light (VOb) from the first deflected light (B2b) by using a spatial modulator array (SMA1 ),

- forming second modulated light (VOc) from the second deflected light (B2c) by using the modulator array (SMA1 ),

- using the modulator array (SMA1 ) to display first information (INFO2) in a situation where projecting of the first deflected light (B2b) is enabled and projecting of the second deflected light (B2c) is disabled, and

- using the modulator array (SMA1 ) to display second information (INFO3) in a situation where projecting of the second deflected light (B2c) is enabled, characterized in that the method comprises projecting the deflected light (B2b, B2c) and displaying the information (INFO2, INFO3) by using the apparatus (500) according to any of the claims 1 to 10.

12. The method of claim 11 , comprising using the modulator array (SMA1 ) to display the second information (INFO3) in a situation where projecting of the first deflected light (B2b) is disabled.

13. A method for producing the apparatus (500) according to any of the claims 1 to 10, the method comprising producing at least one substrate (SLIB1 , SLIB2) by embossing.

Description:
DISPLAY WHICH HAS A SELECTABLE VIEWING SECTOR

FIELD

The present invention relates to controlling visibility of displayed information.

BACKGROUND

A user may use display device to display confidential information. The display device may be e.g. a phone or a portable computer. The display device may be used e.g. together with a screen protector film, which allows the user to view the confidential information from a first viewing point, but which may prevent a second person from viewing the confidential information from a second different viewing point. The display device may display the information by emitting light. The protector film may comprise e.g. microscopic louvres, which allow light emitted from the display device to pass through the screen protector element only when the direction of propagation of the emitted light is in a predetermined angular range. The line of sight from the second viewing point to the display device may be outside the predetermined angular range, and the protector film may prevent propagation of emitted light from the display device to the second viewing point. The protector film may prevent propagation of emitted light to directions which are outside the predetermined angular range. The screen protector element may appear as a dark area to the second person. Thus, the second person viewing the screen protector element from the second viewing point cannot see the displayed confidential information.

SUMMARY

Some variations relate to a display apparatus, which has a selectable viewing sector. Some variations relate to a display apparatus, which has a controllable viewing sector. Some variations relate to a method for controlling visibility of displayed information. Some variations relate to a transparent display apparatus. Some variations relate to a method for producing a display apparatus.

According to an aspect, there is provided a display apparatus of claim 1 .

Further embodiments are defined in the other claims.

According to an aspect, there is provided a display apparatus comprising:

- at least one backlight unit to project first deflected light to a first angular range and to project second deflected light to a second angular range,

- a spatial modulator array to form first modulated light from the first deflected light, and to form second modulated light from the second deflected light, wherein the apparatus is arranged to form the first deflected light by guiding and deflecting light obtained from one or more first light sources, wherein the apparatus is arranged to form the second deflected light by guiding and deflecting light obtained from one or more second light sources, wherein a first backlight unit of the apparatus (500) comprises:

- one or more first light sources to provide first input light,

- a first waveguiding substrate,

- a plurality of light-deflecting grooves implemented on the substrate, wherein the first backlight unit is arranged to form first guided light by coupling the first input light into the substrate, wherein the grooves of the substrate are arranged to form the first deflected light by coupling the guided light out of the substrate.

According to an aspect, there is provided a display apparatus, comprising:

- at least one backlight unit to project first deflected light to a first angular range and to project second deflected light to a second different angular range,

- a spatial modulator array to form first modulated light from the first deflected light, and to form second modulated light from the second deflected light, wherein the apparatus is arranged to form the first deflected light by guiding and deflecting light obtained from one or more first light sources, wherein the apparatus is arranged to form the second deflected light by guiding and deflecting light obtained from one or more second light sources, wherein a first backlight unit of the apparatus comprises:

- the one or more first light sources to provide first input light, - the one or more second light sources to provide second input light,

- a first waveguiding substrate,

- a plurality of light-deflecting grooves implemented on the substrate, wherein the first backlight unit is arranged to form first guided light by coupling the first input light into the substrate through a first edge of the substrate, wherein the first backlight unit is arranged to form second guided light by coupling the second input light into the substrate through a second edge of the substrate, wherein the grooves of the substrate are arranged to form the first deflected light by coupling the first guided light out of the substrate, wherein the grooves are arranged to form the second deflected light by coupling the second guided light (B1 c) out of the first substrate (SLIB2), wherein an area covered by the grooves within an out-coupling region of the substrate is selected to be smaller than 5% of the area of the out-coupling region such that average optical attenuation in the out-coupling region is smaller than 20% for visible light, which is transmitted through the substrate, wherein the average optical attenuation is the average value of optical attenuation over the out- coupling region.

The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

In an embodiment, the display apparatus may be set to operate e.g. in a free view mode (MODE2) or in a privacy mode (MODE1 ). The viewing sector of the display apparatus may be restricted by providing reduced brightness into one or more angular ranges. The display apparatus may have a first operating mode (MODE1 ) where displayed information may be viewed only from a narrow viewing sector. The display apparatus may have a second operating mode (MODE2) where displayed information may be viewed from a wide viewing sector. The display apparatus may be arranged to operate in the first operating mode (MODE1 ) e.g. in order to protect confidential information, which is displayed on the display apparatus. The second operating mode (MODE2) may be used e.g. in order to display non-confidential information to several persons. The operating mode of the display apparatus may be changed e.g. by electrically switching light sources on or off.

When used in the first operating mode, the display apparatus may provide privacy e.g. in a situation where a user of the display apparatus is attending a meeting or traveling with other people e.g. in an airplane. The restricted viewing sector of the display apparatus may protect confidential information displayed on the display apparatus.

The display apparatus may be e.g. a phone, a tablet, or a portable computer. The display apparatus may be a part of a phone, a tablet, or a portable computer.

The display apparatus may comprise a first backlight unit to provide first deflected light, a second backlight unit to provide second deflected light, and a spatial modulator array to display information by spatially modulating the intensity of the first deflected light and the second deflected light. The spatial modulator array may be e.g. an LCD panel, which comprises a liquid crystal layer. The spatial modulator array may form first modulated light by modulating the first deflected light. The spatial modulator array may form second modulated light by modulating the second deflected light. The display apparatus may project the first modulated light to a first viewing region. The display apparatus may project the second modulated light to a second viewing region.

The first backlight unit may be arranged to operate as a rear unit, wherein the second backlight unit may be arranged to operate as an intermediate unit, which is located between the rear unit and the modulator array. Alternatively, the first backlight unit may be arranged to operate as the intermediate unit, wherein the second backlight unit may be arranged to operate as the rear unit. The light-deflecting grooves of the intermediate backlight unit may be implemented such that the intermediate backlight unit is substantially transparent for deflected light, which is projected from the rear backlight unit to the modulator array. The first backlight unit may be arranged to project first deflected light to first angular range, and the second backlight unit may be arranged to project second deflected light to second different angular range. The direction of the center of the first angular range may be e.g. substantially parallel with the normal direction (SZ) of the substrate of the first backlight unit. The direction of the center of the second angular range may be e.g. inclined with respect to said normal direction (SZ). In particular, the first backlight unit may be arranged to project a maximum intensity to a first direction, which is substantially parallel with the normal direction (SZ), and the second backlight unit may be arranged to project a maximum intensity to a second direction, which is inclined with respect to the normal direction (SZ).

The first backlight unit may provide deflected light for providing a narrow viewing sector. The second backlight unit may provide deflected light for providing a wide viewing sector, when used together with the first deflected light. A first person located in the first viewing region and may observe the displayed information in the first operating mode and in the second operating mode. A second person located in the second viewing region may observe the displayed information in the second operating mode, but not in the first operating mode. The first viewing region may represent a narrow angular range. The display apparatus may have a narrow viewing sector in a situation where only the first backlight unit projects deflected light to the modulator array. The first viewing region and the second viewing region may together represent a wider viewing region in a situation where both backlight units simultaneously project deflected light to the modulator array.

The first backlight unit may comprise first light sources, and a waveguiding substrate. The waveguiding substrate may be e.g. a plastic film or a glass plate. The light sources may be e.g. light emitting diodes (LED). The first backlight unit may form first guided light by coupling light of the first light sources into the substrate. The first guided light may propagate within the substrate such that the guided light is confined to the substrate by total internal reflection. The substrate may comprise a plurality of light-deflecting features to couple the first guided light out of the substrate. The first backlight unit may form first deflected light by using the light-deflecting features to couple the first guided light out of the substrate. The first backlight unit may be arranged to project first deflected light into a first angular range, which may correspond to a first viewing region.

The second backlight unit may comprise second light sources, and a second waveguiding substrate. The second backlight unit may form second guided light by coupling light of the second light sources into the substrate. The second guided light may propagate within the second substrate such that the guided light is confined to the substrate by total internal reflection. The second substrate may comprise a plurality of light-deflecting features to couple the second guided light out of the substrate. The second backlight unit may form second deflected light by using the light-deflecting features to couple the second guided light out of the substrate. The second backlight unit may be arranged to project second deflected light into a second angular range, which may correspond to a second viewing region.

The second backlight unit may also comprise third light sources. The second backlight unit may form third guided light by coupling light of the third light sources into the substrate. The third guided light may propagate within the substrate. The second backlight unit may form third deflected light by using the light-deflecting features to couple the third guided light out of the substrate. The second backlight unit may be arranged to project third deflected light into a third angular range, which may correspond to a third viewing region.

The first viewing region may be located between the second viewing region and the third viewing region. The first viewing region, the second viewing region, and the third viewing region may together represent a wide viewing region in a situation where both backlight units simultaneously project deflected light to the modulator array.

In an embodiment, the display apparatus may also have an operating mode where only the second backlight unit projects deflected light to the modulator array such that the first backlight unit does not project deflected light to the modulator array. In that case, the display apparatus may provide reduced visibility for the first viewing region. In an embodiment, the backlight units of the display apparatus may be produced with low production costs.

The display apparatus may be arranged to operate such that structural layers do not attenuate light emitted from the display apparatus. The angular width of the viewing sector of the display apparatus may be changed without manually removing one or more layers from the display apparatus.

As a comparative example, a micro louvre film may be temporarily disposed on a display in order to provide a narrow viewing sector, but the micro louvre film may need to be removed manually.

As a comparative example, a micro louvre film may be disposed on a display in order to provide a narrow viewing sector, but the micro louvre film may reduce the maximum brightness of the display and may cause loss of light also in the desired narrow viewing sector.

In an embodiment, the display apparatus may be arranged to operate as a transparent display, which allows viewing an object through the display apparatus. The object may be located behind the display apparatus, and light reflected from the object may be transmitted to the eye of an observer through the backlight units and through the modulator array. The display apparatus may allow viewing the object in addition to viewing the information displayed on the display apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following examples, several variations will be described in more detail with reference to the appended drawings, in which

Fig. 1a shows, by way of example, in a cross-sectional side view, a display apparatus,

Fig. 1 b shows, by way of example, method steps for controlling operation of the display apparatus, Fig. 1c shows, by way of example, method steps for displaying first information to a first direction, and displaying second information to a second direction,

Fig. 1d shows, by way of example, a timing diagram for displaying first information to a first direction, and for displaying second information to a second direction,

Fig. 2a shows, by way of example, in a cross-sectional side view, coupling of light into the substrate and out of the substrate,

Fig. 2b shows, by way of example, in a cross-sectional side view, light- deflecting grooves implemented on a waveguiding substrate,

Fig. 2c shows, by way of example, in a cross-sectional side view, coupling of light into the substrate and out of the substrate,

Fig. 2d shows, by way of example, in a cross-sectional side view, coupling of light into the substrate and out of the substrate,

Fig. 2e shows, by way of example, in a cross-sectional side view, projecting deflected light to an inclined direction,

Fig. 2f shows, by way of example, in a cross-sectional side view, projecting deflected light to an inclined direction,

Fig. 2g shows, by way of example, in a cross-sectional side view, light- deflecting grooves implemented on a waveguiding substrate,

Fig. 2h shows, by way of example, in a cross-sectional side view, a groove which has refractive facets,

Fig. 2i shows, by way of example, in a cross-sectional side view, a groove which has trapezoidal cross section. Fig. 3a shows, by way of example, in a cross-sectional side view, input angle of an input light ray, and an output angle of an output light ray,

Fig. 3b shows, by way of example, angular intensity distribution of input light,

Fig. 3c shows, by way of example, angular intensity distribution of deflected output light,

Fig. 4a shows, by way of example, angular intensity distribution of first deflected light projected from a first backlight unit, and angular intensity distributions of second and third deflected lights projected from a second backlight unit,

Fig. 4b shows, by way of example, angular intensity distribution of first deflected light, angular intensity distribution of second deflected light, and angular intensity distribution of third deflected light,

Fig. 4c shows, by way of example, angular intensity distribution of second deflected light, and angular intensity distribution of third deflected light,

Fig. 4d shows, by way of example, angular intensity distribution of second deflected light, and angular intensity distribution of third deflected light,

Fig. 5a shows, by way of example, in a top view, a backlight unit for providing second deflected light and third deflected light,

Fig. 5b shows, by way of example, in a top view, projecting second deflected light to a first azimuth range, and projecting third deflected light to a second azimuth range, Fig. 5c shows, by way of example, in a top view, a backlight unit for providing second deflected light, third deflected light, fourth deflected light, and fifth deflected light,

Fig. 5d shows, by way of example, in a top view, projecting second deflected light to a first azimuth range, projecting third deflected light to a second azimuth range, projecting fourth deflected light to a third azimuth range, projecting fifth deflected light to a fourth azimuth range,

Fig. 6a shows, by way of example, in a cross-sectional side view, a first backlight unit, a second backlight unit, a spatial modulator array, and a backlight reflector,

Fig. 6b shows, by way of example, in a cross-sectional side view, a display apparatus,

Fig. 6c shows, by way of example, in a cross-sectional side view, a display apparatus,

Fig. 7a shows, by way of example, in a three-dimensional view, a first backlight unit, a second backlight unit, and a spatial modulator array,

Fig. 7b shows, by way of example, in a three-dimensional view, a display apparatus,

Fig. 7c shows, by way of example, functional units of a display apparatus,

Fig. 7d shows, by way of example, in a top view, light valve pixels of the modulator array,

Fig. 8a shows, by way of example, in a cross-sectional side view, coupling of light into the substrate via an edge of a substrate, Fig. 8b shows, by way of example, in a cross-sectional side view, coupling of light into the substrate via a major surface of the substrate, by using an in-coupling element,

Fig. 8c shows, by way of example, in a cross-sectional side view, coupling of light into the substrate via a major surface of the substrate, by using an in-coupling prism,

Fig. 9 shows, by way of example, in a cross-sectional side view, a display apparatus, which comprises a masking unit,

Fig. 10a shows, by way of example, in a top view, short grooves implemented on a substrate,

Fig. 10b shows, by way of example, in a top view, a substrate which comprises grooves which have different orientations,

Fig. 10c shows, by way of example, in a top view, a substrate which comprises nonlinear grooves,

Fig. 10d shows by way of example, in a top view, a substrate which comprises a first out-coupling portion and a second portion,

Fig. 10e shows by way of example, in a top view, a first group of light sources at a first edge, and a second group of light sources at the same first edge,

Fig. 10f shows by way of example, in a top view, a situation where operation of the light sources of the first group is enabled and the operation of the light sources of the second group is disabled,

Fig. 1 1 a shows, by way of example, in a cross-sectional side view, a transparent display apparatus,

Fig. 1 1 b shows, by way of example, in a cross-sectional side view, a transparent display apparatus, Fig. 12 shows, by way of example, in a three-dimensional view, forming a substrate by embossing,

Fig. 13a shows, by way of example, in a front view, a substrate which comprises short grooves,

Fig. 13b shows, by way of example, in a cross-sectional view, a groove which has non-uniform depth, and

Fig. 13c shows, by way of example, in a cross-sectional view, a groove which has curved light-deflecting facets, and

Fig. 14 shows, by way of example, a curved planar waveguiding substrate.

DETAILED DESCRIPTION

Referring to Fig. 1 , a display apparatus (500) may comprise:

- a first backlight unit (BLLI1 ) to project first deflected light (B2a) to a first angular range (RNG1 ),

- a second backlight unit (BLLI2) to project second deflected light (B2b) to a second different angular range (RNG2), and

- a spatial modulator array (SMA1 ) to form first modulated light (VOa) by modulating the first deflected light (B2a), and to form second modulated light (VOb) by modulating the second deflected light (B2b).

The display apparatus 500 may be e.g. phone, a tablet, or a computer. The display apparatus 500 may be e.g. a computer screen, vehicle screen, or a television. The display apparatus 500 may be e.g. a part of a computer system.

The display apparatus may be arranged to display confidential information. The display apparatus may be arranged to operate as a display of a point of sales terminal, a display of a banking terminal, a display of a check-in terminal, or a display of a postal terminal. The terminal may comprise the display apparatus. The display apparatus may be arranged to display visual information of a game, e.g. at a gambling casino. The display apparatus may be arranged to display visual information of a quiz, where one or more persons attempt to answer questions correctly.

The spatial modulator array SMA1 may be e.g. a liquid crystal panel, which may be arranged to operate e.g. in the TN configuration or in the IPS configuration. TN means Twisted Nematic. IPS means In Plane Switching. The spatial modulator array SMA1 may comprise a two-dimensional array of microscopic light valves to control local transmittance of light through the spatial modulator array SMA1 . Each pixel of the spatial modulator array SMA1 may comprise an independently controllable light valve (i.e. an intensity modulator). The modulator array SMA1 may comprise a two-dimensional array of transmissive modulators to modulate spatial intensity distribution of the projected modulated light VOa, VOb, VOc.

The display apparatus 500 may be arranged to display information INFO1 by projecting first modulated light VOa to a first viewing region ZONE1. The display apparatus 500 may be arranged to display the same information INFO1 by projecting second modulated light VOb to a second viewing region ZONE2. The information may be in graphical form, e.g. text, numbers, a photo, and/or a video. The apparatus 500 may be arranged to display graphical information INFO1. For example, the information INFO1 may be displayed as an image, photo, video and/or text. The information INFO1 may be e.g. a graphical image. The information may be in visually observable form, where an observer EYE1 may observe the information with unaided naked eye. The modulated light VOa, VOb may carry the information to the eye of an observer EYE1 , EYE2. The apparatus 500 may project information-carrying modulated light VOa, VOb, VOc, which represents the displayed information INFO1. The information-carrying light VOa, VOb, VOc may carry the displayed information INFO1 to the eye of an observer EYE1 , EYE2, EYE3. An observer EYE1 , EYE2, EYE3 may observe the displayed information INFO1 when the information-carrying light V0 impinges on the eye of said observer.

An observer EYE1 located in the first viewing region ZONE1 may observe the displayed information INFO1 when the first modulated light VOa impinges on the eye of the observer EYE1 . An observer EYE2 located in the second viewing region ZONE2 may observe the displayed information INFO1 when the second modulated light VOb impinges on the eye of the observer EYE2.

The first backlight unit BLLI1 may comprise:

- one or more first light sources LED1 a to provide first input light BOa,

- a first waveguiding substrate SLIB1 , and

- a plurality of light-deflecting grooves G1 implemented on the first substrate SUB1.

The first backlight unit BLLI1 may be arranged to form first guided light B1 a by coupling the first input light BOa into the first substrate SLIB1 . The grooves G1 of the first substrate SLIB1 may be arranged to form the first deflected light B2a by coupling the first guided light B1 a out of the first substrate SLIB1 .

The second backlight unit BLLI2 may comprise:

- one or more second light sources LED1 b to provide second input light BOb,

- a second waveguiding substrate SLIB2, and

- a plurality of light-deflecting grooves G2 implemented on the second substrate SUB2.

The second backlight unit BLLI2 may be arranged to form second guided light B1 b by coupling the second input light BOb into the second substrate SLIB2. The grooves G2 of the second substrate SLIB2 may be arranged to form the second deflected light B2b by coupling the second guided light B1 b out of the second substrate SUB2.

The second backlight unit BLLI2 may be arranged to operate as a rear backlight unit, wherein the first backlight unit BLLI1 may be arranged to operate as an intermediate backlight unit, which is located between the rear backlight unit and the modulator array SMA1 . The first substrate SLIB1 may be located between the second substrate SLIB2 and the modulator array SMA1 . The first substrate SLIB1 , the second substrate SLIB2, and the modulator array SMA1 may together form a stack. The modulator array may be located above the first substrate, and the second substrate may be located below the first substrate. The apparatus 500 may project the second deflected light B2b and/or the third deflected light B2c through the substrate (SLIB1 ) of the intermediate backlight unit to the modulator array SMA1. The substrate (SLIB1 ) of the intermediate backlight unit may be substantially transparent.

Alternatively, the vertical positions of the backlight units BLLI1 , BLLI2 may be interchanged. The first backlight unit BLLI1 may be arranged to operate as the rear backlight unit, and the second backlight unit BLLI2 may be arranged to operate as the intermediate backlight unit, which is located between the rear backlight unit and the modulator array SMA1 . The second substrate SLIB2 may be located between the first substrate SLIB1 and the modulator array SMA1. The modulator array may be located above the second substrate, and the first substrate may be located below the second substrate. The apparatus 500 may project the first deflected light B2a through the substrate (SLIB2) of the intermediate backlight unit to the modulator array SMA1 . The substrate (SLIB2) of the intermediate backlight unit may be substantially transparent.

Projecting of the second modulated light VOb may be controlled by controlling operation of the second light sources LED1 b. Projecting of the second modulated light VOb may be enabled and disabled by switching the second light sources LED1 b on and off. Projecting of the second modulated light VOb may be disabled so as to make it difficult or impossible for an observer EYE2 located in the second viewing region ZONE2 to observe the information INFO1 displayed on the display apparatus 500.

The display apparatus 500 may have a first operating mode (MODE1 ) where projecting of the first modulated light VOa is enabled and projecting of the second modulated light VOb is disabled such that the observer EYE1 located in the first viewing region ZONE1 may observe the displayed information INFO1 , but the second observer EYE2 located in the second viewing region ZONE2 cannot observe the displayed information INFO1 .

The display apparatus 500 may have a second operating mode (MODE2) where projecting of the first modulated light VOa and the second modulated light V02b is enabled such that the observer EYE1 located in the first viewing region ZONE1 and the observer EYE2 located in the second viewing region ZONE2 may observe the displayed information INFO1. An observer EYE1 located in the first viewing region ZONE1 may see the information INFO1 displayed on the display apparatus 500 in the first operating mode MODE1 and also in the second operating mode MODE2.

An observer EYE2 located in the second viewing region ZONE2 may see the information INFO1 displayed on the display apparatus 500 in the second operating mode MODE2, wherein the observer EYE2 located in the second viewing region ZONE2 cannot see the information INFO1 displayed on the display apparatus 500 in first operation mode MODE1 .

The second backlight unit BLLI2 may also be arranged to project third deflected light (B2c) to a third angular range (RNG3). The spatial modulator array SMA1 may form third modulated light (VOc) by modulating the third deflected light B2c. The display apparatus 500 may be arranged to display information INFO1 by projecting the third modulated light VOc to a third viewing region ZONE3. An observer EYE3 located in the third viewing region ZONE3 may observe the displayed information INFO1 when the third modulated light VOc impinges on the eye of the observer EYE3.

The second backlight unit BLLI2 may comprise one or more third light sources LED1 c to provide third input light BOc. The second backlight unit BLLI2 may be arranged to form third guided light B1 c by coupling the third input light BOc into the second substrate SLIB2. The grooves G2 of the second substrate SLIB2 may be arranged to form the third deflected light B2c by coupling the third guided light B1 c out of the second substrate SLIB2.

Projecting of the third modulated light VOc may be controlled by controlling the operation of the third light sources LED1 c. Projecting of the third modulated light VOc may be enabled and disabled by switching the third light sources LED1 c on and off. Projecting of the third modulated light VOc may be disabled so as to make it difficult or impossible for an observer EYE3 located in the third viewing region ZONE3 to observe the information INFO1 displayed on the display apparatus 500. In an embodiment, projecting of the first modulated light VOa, the second modulated light VOb, and the third modulated light VOc may be controlled independently for each viewing region ZONE1 , ZONE2, ZONE3 of the display apparatus 500.

The display apparatus 500 may have two or more operating modes e.g. as indicated in the table 1 .

Table 1 : Operating modes of the display apparatus 500. "on" = projection enabled, "off - projection disabled.

The display apparatus 500 may have a narrow (or narrower) total viewing sector in the first operating mode (MODE1 ). Projecting of the first modulated light (VOa) may be enabled in the first operating mode MODE1 , wherein projecting of the second and third modulated light (VOb, VOc) may be disabled in the first operating mode (MODE1 ).

The display apparatus 500 may have a wide (or wider) total viewing sector in the second operating mode (MODE2). Projecting of the first, second and third modulated light (VOa, VOb, VOc) may be enabled in the second operating mode (MODE2).

The first substrate SLIB1 of the first backlight unit BLLI1 may comprise a first major surface SRF1 and a second major surface SRF2. The major surfaces SRF1 , SRF2 may be substantially flat, and the major surfaces SRF1 , SRF2 may be substantially parallel with each other. The first substrate SLIB1 may comprise a plurality of first light-deflecting grooves G1 .

The second substrate SLIB2 of the second backlight unit BLLI2 may comprise a first major surface SRF1 and a second major surface SRF2. The major surfaces SRF1 , SRF2 may be substantially flat, and the major surfaces SRF1 , SRF2 may be substantially parallel with each other. The second substrate SLIB2 may comprise a plurality of second light-deflecting grooves G2.

SX, SY and SZ denote orthogonal directions. The apparatus 500 may be used in any position. The directions SX, SY and SZ do not need to be fixed with respect to the direction of gravity. The apparatus 500 may have an arbitrary orientation with respect to the direction of gravity.

The rear backlight unit may also be called e.g. as a distal backlight unit, and the intermediate backlight unit may also be called e.g. as a proximal backlight unit.

The rear backlight unit may also be called e.g. as a lower backlight unit, and the intermediate backlight unit may also be called e.g. as an upper backlight unit. The upper backlight unit does not need to be above the lower backlight unit with respect to the direction of gravity.

The first major surface SRF1 and the second major surface SRF2 of the first substrate SLIB1 may be substantially parallel with a plane defined by the directions SX and SY. The first major surface SRF1 and the second major surface SRF2 of the second substrate SLIB2 may be substantially parallel with a plane defined by the directions SX and SY. The spatial modulator array SMA1 may be substantially parallel with a plane defined by the directions SX and SY. The substrates SLIB1 , SLIB2 and the spatial modulator array SMA1 may be perpendicular to the direction SZ.

The first viewing region ZONE1 may be above a center CNT1 of the spatial modulator array SMA1. The first viewing region ZONE1 may include viewing positions POS1 , which are on the centerline CLIN1 , which is parallel with the direction SZ. The centerline CLIN1 intersects the center CNT1 of the spatial modulator array SMA1 .

The first deflected light B2a and the first modulated light VOa may have an angular intensity maximum in a first direction DIR2a. The first direction DIR2a may be e.g. parallel with the normal direction SZ. The normal direction SZ may be perpendicular to the major surface SRF2 of the substrate SLIB1 . An angle (<PDiR2a) between the normal direction SZ and the first direction DIR2a may be substantially equal to zero.

The second deflected light B2b and the second modulated light VOb may have an angular intensity maximum in a second direction DIR2b. The third deflected light B2c and the third modulated light VOc may have an angular intensity maximum in a third direction DIR2c.

The symbol ( oiR2b denotes an angle between the normal direction SZ and the projecting direction DIR2b. The symbol ( DIR2C denotes an angle between the normal direction SZ and the projecting direction DIR2c. The angle ( oiR2b may be e.g. in the range of 40° to 70°. The angle ( DIR2C may be e.g. in the range of 40° to 70°. The angle ( DIR2C may be equal to the angle ( oiR2b, or the angle < DIR2C may be different from the angle ( oiR2b. The direction DIR2a, DIR2b and/or DIR2c may be e.g. in a plane defined by directions SX and SZ.

The light source LED1 a, LED1 b, LED1 c may emit e.g. substantially white light. The light source LED1 a, LED1 b, LED1 c may emit e.g. single color light (e.g. red, green or blue).

The light source LED1 a, LED1 b, LED1 c may be e.g. a light-emitting diode, a cold cathode fluorescent lamp, or a laser light source. Light emitting diodes may have small size and high efficiency for converting electrical power into visible light. The light emitted from light emitting diodes may be easily coupled e.g. to an edge of the substrate. The light source LED1 a, LED1 b, LED1 c may also be e.g. a cold cathode fluorescent lamp or a laser light source.

Fig. 1 b shows, by way of example, method steps for controlling visibility of information (INFO1 ) displayed on the display DISP1 . User input or control signal (SMODE) may be received in step 2010. The user input may be received e.g. via a user interface (UIF1 , see Fig. 7c)). A control signal (SMODE) may also be received e.g. via a communication unit (RXTX1 , see Fig. 7c).

Operation of one or more light sources LED1 a, LED1 b, LED1 c may be controlled according to the user input or control signal in step 2020. The apparatus 500 may be arranged to start operation in an operating mode MODE1 (step 2021 ), MODE2 (step 2022), MODE3 (step 2023), MODE4 (step 2024), MODE5 (step 2025), MODE6 (step 2026), MODE7 (step 2027), or MODEO (step 2030), as indicated by the user input or control signal SMODE.

Referring to Figs. 1 c and 1d, the apparatus 500 may be arranged to display different information (INFO1 , INFO2) to different directions (DIR2a, DIR2b). In this case, the modulator array SMA1 may be controlled at a high refresh rate to alternate between displaying first information INFO1 and displaying second information INFO2. The first light sources LED1 a may be arranged to emit first light pulses BOa during displaying the first information INFO1 , and the second light sources LED1 b may be arranged to emit second light pulses BOb during displaying the second information INFO2. The modulator array SMA1 may display the first information INFO1 so that the modulator array SMA1 does not display the second information INFO2 during displaying the first information INFO1 . The modulator array SMA1 may display the second information INFO2 so that the modulator array SMA1 does not display the first information INFO1 during displaying the second information INFO2.

The modulator array SMA1 may sequentially display first information INFO1 and second information INFO2, wherein the first light sources LED1 a may be arranged to emit first light pulses BOa during displaying the first information INFO1 , and wherein the second light sources LED1 b may be arranged to emit second light pulses BOb during displaying the second information INFO2. The repetition rate of the light pulses BOa may be e.g. greater than 20 pulses/second so as to reduce or eliminate visually detectable flicker of the displayed information INFO1 . The light pulses BOa, BOb may be interlaced at a high repetition rate so that the first information INFO1 and the second information INFO2 may visually appear to be displayed at the same time.

The refresh rate of the modulator array SMA1 may be e.g. higher than 50 Hz, higher than 100 Hz, or even higher than 200 Hz. The light sources LED1 a, LED1 b may be operated in a pulsed manner. The pulsed operation of the light sources LED1 a, LED1 b may be synchronized with the operation of the modulator array SMA1 so that the first information INFO1 may be observed e.g. only from the first viewing region ZONE1 , and such that the second information INFO2 may be observed e.g. only from the second viewing region ZONE2.

The operating mode of the apparatus 500 may be changed sequentially, wherein the information displayed on the modulator array SMA1 may be changed in a synchronized manner. Different information (e.g. INFO1 , INFO2) may be displayed in each operating mode (e.g. MODE1 , MODE5)

For example, the apparatus 500 may display first information INFO1 such that the first information INFO1 may be observed only from the first viewing region ZONE1. For example, the apparatus 500 may display second information INFO2 such that the second information INFO2 may be observed only from the second viewing region ZONE2. For example, the apparatus 500 may display third information INFO3 such that the third information INFO3 may be observed only from the third viewing region ZONE3. The first information INFO1 may be e.g. a first text "ABC". The second information INFO2 may be e.g. a second text "DEF". The third information may be e.g. a third text "GHI".

For example, first information INFO1 may be displayed in mode MODE1 in step 2041 , second information INFO2 may be displayed in mode MODE5 in step 2042, and third information INFO3 may be displayed in mode MODE6 in step 2043. The duration of an individual displaying step (2041 , 2042, 2043) may be e.g. shorter than 50 ms (milliseconds), or even shorter than 10 ms. The sequence of steps 2041 , 2042, 2043 may be cyclically repeated during a time period, which may be e.g. longer than 1 second, longer than 1 minute, or longer than 1 hour. The method may comprise e.g. using one of the following sequences of modes (MODE1 , MODE5), (MODE1 , MODE6), (MODE6, MODE7), (MODE1 , MODE6, MODE6), (MODE4, MODE5), or (MOD3, MODE6).

The first information INFO1 may be e.g. a first graphical image. The second information INFO2 may be e.g. a second graphical image. The third information may be e.g. a third graphical image. The second image may be different from the first image. The third image may be different from the first image and different from the second image.

Fig. 1d shows, by way of example, a timing diagram for displaying first information INFO1 so that the first information INFO1 may be observed only from the first viewing region ZONE1 , and displaying second information INFO2 so that the second information INFO2 may be observed only from the second viewing region ZONE2.

The modulator array SMA1 may start displaying first information INFO1 at a time ti,i, and the first light source LED1 a may be switched on at the time ti,i . The modulator array SMA1 may stop displaying first information INFO1 at a time t'1,1 , and the first light source LED1 a may be switched off at the time t'1,1.

TFLASH may denote the duration between the start time ti,i and the stop time t'1,1. TFLASH may be the duration of a light pulse emitted from the first light source LED1 a. AFTR may denote a transition time of the modulator array SMA1 for changing the state of the light valves (i.e. pixels).

The modulator array SMA1 may start displaying second information INFO2 at a time ti,2, and the second light source LED1 b may be switched on at the time ti ,2. The modulator array SMA1 may stop displaying second information INFO2 at a time t'1,2, and the second light source LED1 b may be switched off at the time t'1,2.

The modulator array SMA1 may start displaying third information INFO3 at a time ti,3, and the third light source LED1 c may be switched on at the time ti,3. The modulator array SMA1 may stop displaying third information INFO3 at a time t'1,3, and the first light source LED1 c may be switched off at the time t'1,3. The sequence of displaying the different information with the different light sources may be cyclically repeated. The modulator array SMA1 may start displaying first information INFO1 again at a time t2,i , and the first light source LED1 a may be switched on again at the time t2,i . TCYCLE may denote duration between the times ti,i, t2,i .

The method may comprise driving the modulator array (SMA1 ) to change the displayed information (INFO1 , INFO2), using a first light source (LED1 a) to provide first light pulses (BOa), and using a second light source (LED1 b) to provide second light pulses (BOb), wherein the operation of the light sources (LED1 , LED1 b) may be synchronized with the operation of the modulator array (SMA1 ) such that first displayed information (INFO1 ) is observable from a first viewing region (ZONE1 ) but not from a second viewing region (ZONE2), and such that second different displayed information (INFO2) is observable from the second viewing region (ZONE2) but not from the first viewing region (ZONE1 ).

Referring to Fig. 2a, the first backlight unit BLLI1 may comprise a plurality of light-deflecting grooves G1 implemented on at least one major surface SRF1 , SRF2 of the substrate SLIB1 . The first backlight unit BLII1 may comprise one or more first light sources LED1a to provide first input light BOa, which may be coupled into the substrate SLIB1 to form first guided light B1 a. The one or more first light sources LED1 a may be positioned e.g. outside the substrate SLIB1. The first input light BOa may be coupled to the substrate SLIB1 e.g. through an edge EDG1 a of the substrate SLIB1. The substrate SLIB1 may operate as a planar waveguide for the guided light B1 a. The waveguided light B1 a may be confined to the substrate SLIB1 by total internal reflection (TIR), which takes place at the major surfaces SRF1 , SRF2 of the substrate SLIB1. The waveguided light B1 a may also be called simply as guided light. The waveguiding substrate operates as a light guide. The guided light may propagate within the substrate in one or more transverse directions (e.g. in the direction SX and/or -SX).

Waveguided light B1 a propagating within the substrate SLIB1 is trapped within the substrate by total internal reflection (TIR) until the guided light encounters a light-deflecting groove G1. When the guided light encounters a lightdeflecting groove, a part of the guided light may be deflected out of the substrate. The light-deflecting grooves G1 may form a deflected light beam B2a by reflecting, refracting and/or scattering the waveguided light B1 a. The grooves G1 may direct the deflected light beam B2a towards the spatial modulating array SMA1 . The light-deflecting grooves G1 of the first substrate SLIB1 may couple the first guided light B1 a out of the substrate SLIB1 so as to form first deflected light B2a into a first angular range RNG1 (Fig. 4b). The angular intensity distribution lB2a(c ) of the deflected light B2a may have a maximum in the direction DIR2a.

Referring to Fig. 2b, the grooves G1 may have a width WGI and a depth hd. The grooves G1 may have e.g. a triangular or trapezoidal cross section. The grooves G1 may have light-scattering facets FACET1 , FACET2. An angle 0n may denote an orientation angle between a first facet FACET1 and the major surface SRF1. An angle 012 may denote an orientation angle between a second facet FACET2 and the major surface SRF1 . The apex angle a1 of the groove G1 may be equal to 180°- (0n+0i2). The angle 0n may also denote the angle between the surface normal of the facet FACET1 and the surface normal of the major surface SRF1 . The substrate SLIB1 may have a thickness tsUB1.

The substrate SLIB1 may comprise a plurality of grooves G1 implemented on the first major surface SRF1 . The grooves G1 of the first major surface SRF1 may be arranged to form the deflected light B2a by using reflective facets FACET1 , FACET2. The orientation angles 011 of reflective facets FACET1 may be e.g. in the range of 10° to 30°. The orientation angles 012 of reflective facets FACET2 may be e.g. in the range of 10° to 30°. The reflective facets FACET 1 , FACET2 may be arranged to reflect the guided light e.g. by total internal reflection.

In an embodiment, the first substrate SLIB1 may be positioned e.g. between the second substrate SLIB2 and the modulator array SMA1 . The first backlight unit BLLI1 may operate as an intermediate backlight unit, which may be located above the rear (second) backlight unit BLLI2 in the direction SZ. The modulator array SMA1 may be positioned above the intermediate (first) backlight unit BLU1.

The grooves G1 of the first substrate SLIB1 may be so narrow that they do not significantly obstruct the deflected light B2b, B2c projected from the second substrate SLIB2 to the modulator array SMA1 through the first substrate SLIB1 . The substrate SLIB1 may comprise a plurality of substantially flat clear viewing portions C1 between adjacent grooves G1 so that the substrate SLIB2 may operate as a transparent optical element. The total area of covered by the grooves G1 of the first substrate SLIB1 may be e.g. smaller than 5% of the area of the major surface SRF1 , SRF2. The clear portions C1 between adjacent grooves G1 may ensure effective distribution of guided light B1 a within the substrate SLIB1 by total internal reflection (TIR). The average distance ei between adjacent grooves G1 of the first substrate SLIB1 may be e.g. smaller than 0.6 mm, so as to effectively illuminate the modulator array SMA1 with the projected deflected light B2a. The adjacent grooves G1 of the first substrate SLIB1 may together appear as a substantially uniform luminous region. The width WGI of the grooves G1 of the first substrate SLIB1 may be e.g. in the range of 0.5 m to 10 pm, and the depth hd of the grooves G1 of the first substrate SLIB1 may be e.g. in the range of 0.5 pm to 5 pm.

Referring to Fig. 2c, the second backlight unit BLLI2 may comprise a plurality of light-deflecting grooves G2 implemented on at least one major surface SRF1 , SRF2 of the substrate SLIB2. The second backlight unit BLLI2 may comprise one or more second light sources LED1 b to provide second input light BOb, which may be coupled into the substrate SLIB2 to form second guided light B1 b. The second input light B1 b may be coupled to the substrate SLIB2 e.g. through an edge EDG1 b of the substrate SLIB2. The substrate SLIB2 may operate as a planar waveguide for the guided light B1 b. The guided light B1 b may propagate within the substrate in a transverse direction (e.g. in the direction SX).

Referring to Fig. 2d, the second backlight unit BLLI2 may comprise one or more third light sources LED1 c to provide third input light BOc, which may be coupled into the substrate SLIB2 to form third guided light B1 c. The third input light B1 c may be coupled to the substrate SLIB2 e.g. through an edge EDG1 c of the substrate SLIB2. The substrate SLIB2 may operate as a planar waveguide for the guided light B1 c. The guided light B1 c may propagate within the substrate in a transverse direction (e.g. in the direction -SX).

Referring to Fig. 2e, the second backlight unit BLLI2 may form second guided light B1 b, which may propagate e.g. substantially in the direction SX. Waveguided light B1 b propagating within the substrate SLIB2 is trapped within the substrate by total internal reflection (TIR) until the guided light encounters a light-deflecting groove G2. When the guided light encounters a lightdeflecting groove, a part of the guided light may be deflected out of the substrate. The light-deflecting grooves G2 may form a deflected light beam B2b by reflecting, refracting and/or scattering the waveguided light B1 b. The light-deflecting grooves G2 of the second substrate SLIB2 may couple the second guided light B1 b out of the substrate SLIB2 so as to form second deflected light B2b into a second angular range RNG2 (Fig. 4b). The grooves G2 may direct the deflected light beam B2b towards the spatial modulating array SMA1 . The angular intensity distribution lB2b(cp) of the deflected light B2b may have a maximum in the direction DIR2b.

Referring to Fig. 2f, the second backlight unit BLLI2 may form third guided light B1 c, which may propagate e.g. substantially in the direction -SX. Waveguided light B1 c propagating within the substrate SLIB2 is trapped within the substrate by total internal reflection (TIR) until the guided light encounters a lightdeflecting groove G2. When the guided light encounters a light-deflecting groove, a part of the guided light may be deflected out of the substrate. The light-deflecting grooves G2 may form a deflected light beam B2c by reflecting, refracting and/or scattering the waveguided light B1 c. The light-deflecting grooves G2 of the second substrate SLIB2 may couple the third guided light B1 c out of the substrate SLIB2 so as to form third deflected light B2c into a third angular range RNG3 (Fig. 4b). The grooves G2 may direct the deflected light beam B2c towards the spatial modulating array SMA1. The angular intensity distribution IB2C(< ) of the deflected light B2c may have a maximum in the direction DIR2c.

Referring to Fig. 2g, the grooves G2 may have a width WG2 and a depth hG2. The grooves G2 may have e.g. a triangular or trapezoidal cross section. The U grooves G2 may have light-scattering facets FACET1 , FACET2. An angle 021 may denote an orientation angle between a first facet FACET1 and the major surface SRF1. An angle P22 may denote an orientation angle between a second facet FACET2 and the major surface SRF1 . The apex angle a2 of the groove G2 may be equal to 180°- (P21+P22). The substrate SUB2 may have a thickness tsuB2.

The substrate SLIB2 may comprise a plurality of grooves G2 implemented on the first major surface SRF1 . The grooves G2 of the first major surface SRF1 may be arranged to form the deflected light B2b, B2c by using reflective facets FACET 1 , FACET2. The orientation angles P21 of reflective facets FACET 1 may be e.g. in the range of 10° to 30°. The orientation angles P22 of reflective facets FACET2 may be e.g. in the range of 10° to 30°. The reflective facets FACET 1 , FACET2 may be arranged reflect the guided light e.g. by total internal reflection.

In an embodiment, the second substrate SLIB2 may be positioned e.g. between the first substrate SLIB1 and the modulator array SMA1 . The second backlight unit BLLI2 may operate as an intermediate backlight unit, which is located above the rear (first) backlight unit BLLI1 in the direction SZ. The grooves G2 of the second substrate SLIB2 may be so narrow that they do not significantly obstruct the deflected light B2a projected from the first substrate SLIB1 to the modulator array SMA1 through the second substrate SLIB2. The substrate SLIB2 may comprise a plurality of substantially flat clear viewing portions C2 between adjacent grooves G2 so that the substrate SLIB2 may operate as a transparent optical element. The total area of covered by the grooves G2 of the second substrate SLIB2 may be e.g. smaller than 5% of the area of the major surface SRF1 , SRF2. The clear portions C2 between adjacent grooves G2 may ensure effective distribution of guided light B1 b, B1 c within the substrate SLIB2 by total internal reflection (TIR). The average distance 62 between adjacent grooves G2 of the second substrate SLIB2 may be e.g. smaller than 0.6 mm, so as to effectively illuminate the modulator array SMA1 with the projected deflected light B2b and B2c. The adjacent grooves G2 of the second substrate SLIB2 may together appear as a substantially uniform luminous region. The width WG2 of the grooves G2 of the second substrate SLIB2 may be e.g. in the range of 0.5 m to 10 pm, and the depth hG2 of the grooves G2 of the second substrate SLIB2 may be e.g. in the range of 0.5 Lim to 5 |nm.

The angle P22 may be substantially equal to the angle P21, or the angle P22 may be different from the angle P21. The angle P21 may be selected to provide a desired angular intensity distribution lB2b(c ) of the second deflected light B2b. The angle P22 may be selected to provide a desired angular intensity distribution IB2C(< ) of the third deflected light B2c.

Referring to Fig. 2h, the second major surface SRF2 of the substrate SLIB2 may comprise a plurality of light-deflecting grooves G2, which have refractive facets FACET 1 , FACET2. A groove G2 may be arranged to couple guided light B1 b, B1 c out of the substrate SLIB2 by refraction.

A plurality of grooves G2 may be implemented on the second major surface SRF2 to refract guided light B1 b and/or B1 c out of the substrate SLIB2. The refractive grooves G2 may be arranged to provide an angular intensity distribution lB2b(cp) where the intensity maximum is in a direction (DIR2b), which is different from the perpendicular direction SZ. The refractive grooves G2 may be arranged to provide an angular intensity distribution IB2C(< ) where the intensity maximum is in a direction (DIR2c), which is different from the perpendicular direction SZ. The orientation angles P21, P22 of the refractive facets may be e.g. in the range of 50° to 70°, advantageously in the range of 60° to 65°. The apex angle a2 of the grooves G2 implemented on the output surface SRF2 may be e.g. in the range of 40° to 70°, advantageously in the range of 50° to 60°. Maximum intensity of the deflected light B2b may be attained when the apex angle a2 is e.g. in the range of 50° to 60°.

Referring to Fig. 2i, the cross-sectional shape of the light-deflecting grooves G1 , G2 may also be e.g. trapezoidal.

Thanks to the small area covered by the grooves, the optical transmittance of the waveguiding substrate SLIB1 and/or SLIB2 may be high. Consequently, the deflected light projected from the rear backlight unit may be transmitted through the intermediate backlight light unit to the modulator array SMA1 with low losses. The spatially averaged optical transmittance of the waveguiding substrate SLIB1 or SLIB2 for the light transmitted through the waveguiding substrate in the direction SZ may be e.g. greater than 80% in the visible range of wavelengths from 400 nm to 760 nm. The grooves may reduce the optical transmittance by reflecting, refracting and scattering light. The spatially averaged optical transmittance of the waveguiding substrate takes into account the intensity-reducing effect of the grooves, the effect of reflection losses at the surfaces SRF1 , SRF2, and the effect of absorption of light inside the substrate.

The substrate SLIB1 and/or the substrate SLIB2 may comprise one or more out-coupling regions REG1 (see e.g. Fig. 10d). A plurality of grooves G1 , G2 may be implemented on the major surface SRF1 and/or SRF2. The area of the coupling region REG1 may also be smaller than or equal to the area of the major surface SRF1 , SRF2. The out-coupling region REG1 is a spatial area, which comprises a plurality of grooves G1 , G2 implemented on the first major surface SRF1 and/or on the second major surface SRF2.

For example, the substrate SLIB1 and/or the substrate SLIB2 may comprise at least one region REG1 , which comprises a plurality of light-deflecting grooves such that the width of the grooves is e.g. in the range of 0.5 m to 10 m, and the depth of the grooves may be in the range of 0.5 pm to 5 pm. The average distance between adjacent grooves in said region REG1 may be e.g. smaller than 0.6 mm. The total area covered by the grooves may be e.g. smaller than 5% of the area of said region REG1 .

For example, an out-coupling region REG1 of the substrate SLIB1 , SLIB2 may comprise a plurality of light-deflecting grooves such that the width of the grooves is e.g. in the range of 0.5 pm to 10 pm, and the depth hd of the grooves may be in the range of 0.5 pm to 5 pm. The average distance between adjacent grooves may be e.g. smaller than 0.6 mm. The total area covered by the grooves of the out-coupling region REG1 may be e.g. smaller than 5% of the area of the out-coupling region REG1 . The average number density of the grooves in the out-coupling region REG1 may be e.g. in the range of 1.6 grooves per mm to 20 grooves per mm. The dimensions LI REGI and L2REGI of the region REG1 may be e.g. greater than 5 cm. The size of the region REG1 may be e.g. greater than 5 cm x 5 cm. The grooves G1 may together cover a fraction FGI of the area of the out- coupling region REGI . The fraction FGI may be defined by the equation FGI=AGI/AREGI , where AGI denotes the total area covered by the grooves G1 within the out-coupling region REG1 , and AREGI denotes the area of the out- coupling region REGI . The fraction FGI may also be called as the coverage ratio of the grooves G1 . The area Aci covered by the flat smooth regions C1 within the out-coupling region REG1 is equal to AREGI - AGI . The flat smooth regions C1 may together cover a fraction Fci of the out-coupling region REG1 . The fraction Fci may be defined by the equation FCI=1 -AGI/AREGI . The fraction Fci may also be called as the coverage ratio of the flat regions C1 . The sum of the coverage ratio FGI of the grooves G1 and the coverage ratio Fci of the flat regions C1 may be equal to one.

The grooves G1 may cause a loss AlB2b of intensity lB2b of light B2b, which is transmitted through the substrate SLIB1. The grooves G1 may cause optical attenuation (AlB2b/lB2b).

To the first approximation, the optical attenuation (AlB2b/lB2b) caused by the grooves G1 may be e.g. approximately equal to 2- FGI . TO the first approximation, the extinction cross section of a single groove may be approximately equal to two times the area covered by said single groove. The area covered by a single groove G1 within the region REG1 is equal to the width WGI of the groove G1 multiplied by the length (LGI ) of said groove G1 within said region REGI .

Thanks to the small surface coverage ratio FGI of the grooves G1 , the optical attenuation caused by the grooves may be low. Thanks to the small surface coverage ratio FGI of the grooves G1 , the optical transmittance of the waveguiding substrate may be high, respectively.

In an embodiment, the second backlight unit BLLI2 may be arranged to operate as the rear backlight unit, and the first backlight unit BLLI1 may be arranged to operate as the intermediate backlight unit. The intermediate backlight unit may be positioned between the rear backlight unit and the modulator array SMA1 . The substrate SLIB1 of the intermediate backlight unit may have high transmittance for light B2b, B2c projected from the rear backlight unit to the modulator array SMA1 through the substrate SLIB1 .

The area covered by the grooves G1 within the out-coupling region REG1 of the substrate SLIB1 may be e.g. smaller than 5% of the area of the out-coupling region REG1 , such that average optical attenuation (AlB2b/lB2b) in the out- coupling region REG1 may be e.g. smaller than 20% for visible light (B2b), which is transmitted through the substrate SLIB1. Said average optical attenuation (AlB2b/lB2b) may be the average value of optical attenuation over the out-coupling region REG1. The average optical attenuation may also be called as the spatially averaged optical attenuation. The average attenuation may be e.g. smaller than 20% in the visible range of wavelengths from 400 nm to 760 nm. The average attenuation may include attenuation caused by the grooves, attenuation caused by reflection loss at the first major surface SRF1 , and attenuation caused by reflection loss at the second major surface SRF2.

The average optical transmittance may be e.g. greater than 80%, respectively. The average optical transmittance of the waveguiding substrate SLIB1 for visible light B2b transmitted through the waveguiding substrate SLIB1 may be e.g. greater than 80% in the visible range of wavelengths from 400 nm to 760 nm. The average optical transmittance may be the average value of optical transmittance over the out-coupling region REG1 . The average transmittance may be e.g. greater than 80% in the visible range of wavelengths from 400 nm to 760 nm. The average optical transmittance may take into account the optical attenuation caused by the grooves, attenuation caused by reflection loss at the first major surface SRF1 , and attenuation caused by reflection loss at the second major surface SRF2.

In an embodiment, the first backlight unit BLLI1 may be arranged to operate as the rear backlight unit, and the second backlight unit BLLI2 may be arranged to operate as the intermediate backlight unit. The substrate SLIB2 of the intermediate backlight unit may have high transmittance for light B2a projected from the rear backlight unit. For example, the area covered by the grooves G1 within an out-coupling region REG1 of the substrate SLIB2 may be e.g. smaller than 5% of the area of the out-coupling region REG1 , such that average optical attenuation (AlB2a/lB2a) in the out-coupling region REG1 may be e.g. smaller than 20% for visible light (B2a), which is transmitted from the rear backlight unit BLLI1 to the modulator array SMA1 through the substrate SLIB2.

The substrate SLIB1 , SLIB2 may be substantially rectangular, when viewed in a direction SZ, which is perpendicular to the major surfaces SRF1 , SRF2.

The substrate SLIB1 may have a dimension LI SUBI in the direction SX, and a dimension L2SUBI in the direction SY. The dimension LI SUBI may be e.g. the length of the substrate SLIB1 , and the dimension L2SUBI may e.g. the width of the substrate SUB1 . The dimensions (LI SUBI , L2SUBI ) may be e.g. in the range of 0.05 m to 2 m. The size of the second substrate SLIB2 may be substantially equal to the size of the first substrate SLIB1 .

The substrate SLIB1 , SLIB2 may be a flat planar waveguiding plate, which has two substantially parallel major surfaces SRF1 , SRF2. The substrate SLIB1 , SLIB2 may confine the guided light B1 by total internal reflection, which takes place on the major surfaces SRF1 , SRF2. The substrate SLIB1 , SLIB2 may have constant thickness, or the substrate SLIB1 , SLIB2 may be tapered.

The substrate SLIB1 , SLIB2 may comprise optically transparent material. For example, the substrate SLIB1 , SLIB2 may comprise or consist of plastic, glass, silica (SiC>2) or sapphire (AI2O3).

The substrate SLIB1 , SLIB2 may comprise or consist of Poly(methyl methacrylate) (PMMA). The substrate SLIB1 , SLIB2 may comprise or consist of polycarbonate. The substrate SLIB1 , SLIB2 may comprise or consist of polyethylene terephthalate (PET).

The light-deflecting grooves G1 , G2 may be formed e.g. by embossing, hot embossing, molding, injection molding, immolding, etching, machining, laser processing, laser engraving, mechanical engraving, chemical etching, mechanical etching, printing, nanoimprinting, ablative manufacturing and/or additive manufacturing. The substrates SLIB1 , SLIB2 may be produced in large scale e.g. by forming the microscopic grooves G1 , G2 on a plastic substrate. The grooves G1 , G2 may be formed on the substrate e.g. in a roll-to-roll process. An embossing tool or a mold may comprise microscopic protrusions, which may form the grooves G1 , G2 on the substrate SLIB1 , SLIB2 when pressed against the substrate. The embossing tool or the mold may be formed e.g. by photolithography, electron beam lithography, etching, chemical etching, electron beam etching, electroplating, laser engraving, mechanical engraving, machining, laser processing, electron beam, ablative manufacturing and/or additive manufacturing.

The features G1 , G2 may deflect light e.g. scattering, reflection, refraction and/or diffraction. The substrate SLIB1 , SLIB2 may comprise e.g. a plurality of light-deflecting grooves G1 , G2 implemented on at least one major surface SRF1 , SRF2 of the substrate.

In particular, the width WGI , WG2 of the grooves G1 , G2 may be slightly greater than the wavelength A. of visible light, and forming the deflected light B2 may be modeled by the Rigorous theory of scattering.

In an embodiment, the distances ei, e2 between adjacent grooves G1 ,G2 may exhibit variation so as to reduce or avoid diffraction effects. The diffraction may cause a colorful "rainbow" effect, which may disturb vision of an observer (EYE1 ).

Referring to Fig. 3a, a light source LED1 b may provide an input light beam BOb, which may be coupled into the substrate SLIB2. The guided light B1 b propagating inside the substrate SLIB2 may be formed by coupling the input light BOb into the substrate SLIB2. The input light BOb may be coupled into the substrate SLIB2 e.g. through an edge EDG1 b of the substrate SLIB2.

The input light beam BOb may be used as input light for the substrate SLIB2. The input light BOb may have an angular intensity distribution lsob(<|)). The angular intensity distribution lsob(<|)) may have an angular width A(|)B0b. The input light beam BOb may be formed of light rays LRO, which propagate in different directions (<|)) with different angular intensities. The input angle <|) may denote an angle between the direction of propagation of a light ray LRO and a reference plane REFO. The reference plane REFO may be e.g. parallel with the first major surface SRF1 of the substrate SLIB2. The reference plane REFO may be perpendicular to the input edge EDG1 b of the substrate SLIB1 .

The light-deflecting grooves G2 may form deflected light B2b by reflecting refracting and/or scattering guided light B1 b, which propagates within the substrate SLIB2. The deflected output light B2b may have an angular intensity distribution lB2b(cp). The angular intensity distribution lB2b(cp) may have an angular width A( B2b.

The deflected light B2b may be formed of light rays LR2, which propagate in different directions (9) with different angular intensities. The output angle 9 may denote an angle between the direction of propagation of a light ray LR2 and a reference plane REF2. The reference plane REF2 may be perpendicular to the first major surface SRF1 of the substrate SLIB1. The reference plane REF2 may be parallel with an input edge EDG1 b of the substrate SLIB1.

The substrate SLIB1 may map the angular intensity distribution lsoa(<|)) of the input light BOa into the angular intensity distribution lB2a(9) of the deflected light B2a.

The substrate SLIB2 may map the angular intensity distribution lsob(<|)) of the input light BOb into the angular intensity distribution lB2b(9) of the deflected light B2b.

The substrate SLIB2 may map the angular intensity distribution IBOC(<|)) of the input light BOc into the angular intensity distribution IB2C(9) of the deflected light B2c.

Referring to Fig. 4a, the modulator array SMA1 may form first modulated light VOa from the first deflected light B2a, second modulated light VOb from the second deflected light B2b, and third modulated light VOc from the third deflected light B2c. The first modulated light VOa projected to the first viewing region ZONE1 may have a first angular intensity distribution lvoa(9). The second modulated light VOb projected to the second viewing region ZONE2 may have a second angular intensity distribution lvob(9). The third modulated light VOc projected to the third viewing region ZONE3 may have a third angular intensity distribution lvoc(φ ).

Referring to Fig. 4b, the first backlight unit BLUI1 may project first deflected light B2a to a first angular range RNG1 . The first deflected light B2a may have a first angular intensity distribution lB2a(φ ). The first angular range RNG1 may include the direction SZ, which is perpendicular to the first substrate SU B1. The first angular intensity distribution lB2a(φ ) may have a maximum MAX2a in the direction DIR2a. 2 DIRa2 denotes the angle between the normal direction SZ and the direction DIR2a. The direction angle φ DIR2a may be substantially equal to zero.

The second backlight unit BLU2 may project second deflected light B2b to a second angular range RNG2. The second deflected light B2b may have a second angular intensity distribution lB2b(φ ). The second angular intensity distribution lB2b(φ ) may have a maximum MAX2b in the direction DIR2b specified by the direction angle φ DIR2. b

The second backlight unit BLU2 may project third deflected light B2c to a third angular range RNG3. The third deflected light B2c may have a third angular intensity distribution IB2C(φ ). The third angular intensity distribution IB2C(φ ) may have a maximum MAX2c in the direction DIR2c specified by the direction angle φDIR2c.

Fig. 4c shows, by way of example, angular intensity distributions lB2b(φ ) and IB2C(φ ) in a situation where the orientation angles β21 and β22 of reflective facets FACET1 , FACET2 of the grooves G1 are equal to 25°, i.e. β21 = β22 = 25°.

Fig. 4d shows, by way of example, angular intensity distributions lB2b(φ ) and IB2C(φ ) in a situation where the orientation angles β21 and β22 of reflective facets FACET1 , FACET2 of the grooves G1 are equal to 15°, i.e. β21 = β22 = 15°.

Referring to Fig. 5a, the second backlight unit BLU2 may comprise second light sources LED1 b for forming second deflected light B2b. The second backlight unit BLU2 may comprise third light sources LED1 c for forming third deflected light B2c. The second light sources LED1 b may be disposed at a first edge EDG1 b of the substrate SLIB2, and the third light sources LED1 c may be disposed at a second (opposite) edge EDG1 c of the substrate SUB2. The second backlight unit BLLI2 may be arranged to form second guided light B1 b by coupling light of the second light sources LED1 b into the substrate SLIB2. The second backlight unit BLLI2 may be arranged to form third guided light B1 c by coupling light of the third light sources LED1 c into the substrate SLIB2. The second guided light B1 b may propagate e.g. in the direction SX. The third guided light B1 c may propagate e.g. in the direction -SX. The direction of propagation of the third guided light B1 c may be opposite to the direction of propagation of the second guided light B1 b. The substrate SLIB2 may comprise a plurality of light-deflecting grooves G2. The light-deflecting grooves G2 may form the second deflected light B2b by coupling the second guided light B1 b out of the substrate SLIB2. The light-deflecting grooves G2 may form the third deflected light B2c by coupling the third guided light B1 c out of the substrate SUB2.

Projecting of the second deflected light B2b may be enabled and disabled by switching the second light sources LED1 b on and off. Projecting of the third deflected light B2c may be enabled and disabled by switching the third light sources LED1 c on and off.

Referring to Fig. 5b, the second deflected light B2b may be projected to a first azimuth range SEC2b. The directions of propagation of the second deflected light B2b may be within a range SEC2b of azimuth angles. The third deflected light B2c may be projected to a second azimuth range SEC2c.

Referring to Fig. 5c, the second backlight unit BLLI2 may further comprise fourth light sources LED1d for forming fourth deflected light B2d. The second backlight unit BLLI2 may comprise fifth light sources LED1 e for forming fifth deflected light B2e. The fourth light sources LED1 b may be disposed at a third edge EDG1d of the substrate SLIB2, and the fifth light sources LED1 e may be disposed at a fourth (opposite) edge EDG1e of the substrate SUB2. The second backlight unit BLLI2 may be arranged to form fourth guided light Bid by coupling light of the fourth light sources LED1 e into the substrate SLIB2. The second backlight unit BLLI2 may be arranged to form fifth guided light B1 e by coupling light of the fifth light sources LED1 e into the substrate SLIB2. The fourth guided light B1 b may propagate e.g. in the direction SY. The fifth guided light B1 e may propagate e.g. in the direction -SY. The direction of propagation of the fifth guided light B1 e may be opposite to the direction of propagation of the fourth guided light Bid. The substrate SLIB2 may comprise a plurality of light-deflecting grooves G2b, G2d. The light-deflecting grooves G2b may form the deflected light B2b and B2c by coupling the guided light B1 b and B1 c out of the substrate SLIB2. The light-deflecting grooves G2d may form the fourth deflected light B2d by coupling the fourth guided light Bid out of the substrate SUB2. The light-deflecting grooves G2d may form the fifth deflected light B2e by coupling the fifth guided light B1 e out of the substrate SLIB2. The orientation of the light-deflecting grooves G2d may be e.g. substantially perpendicular to the orientation of the light-deflecting grooves G2b. Projecting of the deflected light B2d may be enabled and disabled by switching the light sources LED1d on and off. Projecting of the deflected light B2e may be enabled and disabled by switching the light sources LED1 e on and off.

Referring to Fig. 5d, the deflected light B2b may be projected to an azimuth range SEC2b. The deflected light B2c may be projected to an azimuth range SEC2c. The deflected light B2d may be projected to an azimuth range SEC2d. The deflected light B2e may be projected to an azimuth range SEC2e.

Referring to Figs. 6a and 6b, the modulator array SMA1 may comprise a liquid crystal layer CRY1 , one or more electrode layers ELEC1 , a first polarizer layer POL1 , and a second polarizer layer POL2. The modulator array SMA1 may optionally comprise a color filter array CFIL1 for displaying color images. Using the liquid crystal layer CRY1 together with the color filter array CFIL1 may provide spatially separate green, red and blue display pixels. The modulator array SMA1 may optionally comprise transparent substrates GLAS1 , GLAS2 to provide mechanical stability. For example, the electrodes of the electrode layer ELEC1 may be attached to the substrate GLAS1. The modulator array SMA1 may comprise an array of thin film transistors (TFT matrix) to drive the electrodes.

The first backlight unit BLU1 may comprise cladding layers CLAD1 , CLAD2 to ensure total internal reflection at the first major surface SRF1 and/or at the second major surface SRF2 of the substrate SUB1 . The substrate SUB1 may be stacked between the cladding layers CLAD1 , CLAD2. A first cladding layer CLAD1 may be in contact with the first major surface SRF1 of the substrate SUB1. A second cladding layer CLAD2 may be in contact with the second major surface SRF2 of the substrate SLIB1 . The substrate SLIB1 may have a refractive index HSUBI . The first cladding layer CLAD1 may have a refractive index HCLADI . The second cladding layer CLAD2 may have a refractive index ncLAD2. The refractive index nsuBi may be higher than the refractive indices ncLADi, ncLAD2 in order to provide the total internal reflection at the surfaces SRF1 , SRF2. The cladding layer CLAD1 and/or CLAD2 may comprise e.g. transparent plastic or transparent adhesive to provide a refractive index (ncLADi, ncLAD2), which is lower than the refractive index nsuBi of the substrate SUB1.

The second backlight unit BLLI2 may comprise cladding layers CLAD3, CLAD4 to ensure total internal reflection at the first major surface SRF1 and/or at the second major surface SRF2 of the substrate SLIB2.

The first backlight unit BLLI1 and the second backlight unit BLLI2 may also comprise the same cladding layer CLAD1 (Fig. 6b).

The apparatus 500 may optionally comprise a bottom reflector MIR1 to reflect escaping light back towards the modulator array SMA1 . The second substrate SLIB2 may be located between the first substrate SLIB1 and the bottom reflector MIR1 .

Referring to 6c, the apparatus 500 may comprise a plurality of (narrow) spacer elements SPC1 to define one or more gaps GAP1 , GAP2, GAP3. The gap GAP1 , GAP2, GAP3 may be filled with a substance, which provides total internal reflection at the surface SRF1 , SRF2. The refractive index of the substance may be smaller than the refractive index of the substrate. The substance may be e.g. gas, liquid or gel. The substance may be e.g. nitrogen or silicone oil.

A gap GAP1 may be defined between the rear substrate (SLIB2 or SLIB1 ) and an auxiliary layer 110. The auxiliary layer 110 may optionally operate as reflective layer. A gap GAP2 may be defined between the rear substrate (SLIB2 or SLIB1 ) and the intermediate substrate (SLIB1 or SLIB2). A gap GAP3 may be defined between the intermediate substrate (SLIB1 or SLIB2) and the modulator array SMA1 .

Referring to Figs. 7a and 7b, the display apparatus 500 may comprise a user interface LIIF1 for receiving user input for setting the operating mode (MODE1 , MODE2, ...) of the display apparatus 500. The user interface LIIF1 may comprise e.g. one or more real or virtual keys KEY1 , KEY2 for receiving user input for setting the operating mode. The operating mode of the apparatus 500 may be set e.g. by one or more electronic switches.

In an embodiment, the display apparatus 500 may comprise a sensor layer, which may be arranged to operate as the user interface LIIF1 for receiving user input for setting the operating mode. The display apparatus 500 may be arranged to operate e.g. as a capacitive touch screen or as a pressuresensitive touch screen. The display apparatus 500 may be configured to execute program code (application) to implement a user interface LIIF1 for receiving user input for setting the operating mode of the display apparatus 500.

The display apparatus 500 may comprise driver electronics (DRV1 ) for driving the light sources LED1 a, LED1 b, LED1 c according to the selected operating mode. The driver electronics may comprise e.g. relays, transistors or mechanical switches to connect an electric operating current to the light sources LED1 a, LED1 b, LED1 c according to the selected operating mode. The apparatus 500 may optionally comprise e.g. a battery, a power connector, and/or a power receiving coil to provide electrical operating power for the light sources LED1 a, LED1 b, LED1 c. Operating current may be conducted to the light sources via electrical conductors.

Referring to Fig. 7b, the display apparatus 500 may be arranged to display information INFO1 in graphical form (e.g. the text "ABC"). The display apparatus 500 may be arranged to display the information INFO1 in graphical form e.g. by displaying a pattern, text, numbers, a picture and/or a video. Referring to Fig. 7c, the apparatus 500 may comprise a control unit CNT1 for controlling operation of the apparatus 500, a display driver unit GPII1 to drive the modulator array SMA1 , and a driving unit DRV1 to drive the light sources LED1 a, LED1 b, LED1 c. The apparatus may comprise a memory MEM1 for storing program code PROC1 , a memory MEM2 for storing information data DATA1 , and/or a memory MEM3 for storing operating parameter data PAR1 . The apparatus may comprise a memory MEM4 for storing one or more values of a mode control signal SMODE. The apparatus 500 may comprise a user interface LIIF1 for receiving user input from a user. The apparatus 500 may comprise a communication unit RXTX1 e.g. for receiving information data DATA1 from the Internet or from another device.

The control unit CNT1 may comprise one or more data processors for controlling displaying the information INFO1 , INFO2, INFO3 and for controlling operation of the light sources LED1 a, LED1 b, LED1 c. The control unit CNT1 may control displaying the information and control operation of the light sources by executing the program code PROC1 .

The control unit CNT1 may provide instructions SDRVI for the light source driving unit DRV1. The light source driving unit DRV1 may control operating currents of the light sources LED1 a, LED1 b, LED1 c according to the instructions SDRVI . The operating parameter data PAR1 may e.g. specify operating current values for driving the light sources.

The control unit CNT 1 may provide instructions SGPUI for the display driver unit GPII1 according to the information data DATA1 , and the display driver unit GPII1 may drive the modulator array SMA1 according to instructions SGPUI received from the control unit CNT 1 . For example, the information data DATA1 may comprise text data, image data and/or video data, wherein the control unit CNT1 and the display driver unit GPLI1 may control operation of the light valves of the modulator array SMA1 so as to display a text, an image, and/or a video according to the information data DATA1 . The information data DATA1 may comprise data for displaying information INFO1 , INFO2, INFO3. The information INFO1 may be e.g. an image, photo, video and/or text. The information INFO2 may be e.g. an image, photo, video and/or text. The information INFO3 may be e.g. an image, photo, video and/or text.

The display apparatus 500 may comprise a display driver unit GPU1 to drive the modulator array SMA1 according to digital image data (SGPUI ,DATA1 ). The digital image data may be received e.g. from the memory MEM2 and/or via the communication unit RXTX1 . The communication unit may receive image data e.g. from a server via the Internet, e.g. by using a local area network (e.g. WiFi), or by using a mobile communications network (e.g. UMTS, LTE, 4G, 5G). The communication unit may also comprise e.g. an electric connector (e.g. HDMI) to receive digital image data.

The apparatus 500 may be arranged to control operation of the light sources LED1 a, LED1 b, LED1 c according to user input received via the user interface UIF1 . For example, the apparatus 500 may be set to provide a narrow viewing sector (e.g. in the operating MODE1 ) during a first time period. For example, the apparatus 500 may be set to provide a wide viewing sector (e.g. in the operating MODE2) during a second time period. For example, the apparatus 500 may be set to provide a narrow viewing sector when displaying confidential information (e.g. an email message). For example, the apparatus 500 may be set to provide a wide viewing sector when displaying a public video to several persons.

In an embodiment, the control unit CNT1 may be arranged to form a mode control signal SMODEI by executing the program code PROC1 .

For example, the program code PROC1 , when executed by one or more data processors CNT1 , may cause the apparatus 500 to:

- form a first mode control signal (SMODE.I ) for setting the apparatus 500 to operate in a first operating mode (e.g. MODE1 ),

- control operation of the light sources (LED1a, LED1 b, LED1 c) according to the first mode control signal (SMODE.I ), and

- display first information INFO1 on the display DISP1 when the light sources (LED1 a, LED1 b, LED1 c) operate according to the first mode control signal (SMODE.I ), - form a second mode control signal (SMODEJ) for setting the apparatus 500 to operate in a second operating mode (e.g. MODE2),

- control operation of the light sources (LED1a, LED1 b, LED1 c) according to the second mode control signal (SMODE.2), and

- display second information INFO2 on the display DISP1 when the light sources (LED1 a, LED1 b, LED1 c) operate according to the second mode control signal (SMODE ).

In an embodiment, the apparatus 500 may control the light sources LED1 a, LED1 b and the light valves of the modulator array SMA1 at a high rate in a synchronized manner, so as to display different information INFO1 , INFO2 to different viewing regions ZONE1 , ZONE2. The apparatus may display first information INFO1 to the first viewing region ZONE1 such that the first information INFO1 cannot be observed from the second viewing region ZONE2. The apparatus may display second information INFO2 to the second viewing region ZONE2 such that the second information INFO2 cannot be observed from the first viewing region ZONE1 .

For example, the program code PROC1 , when executed by one or more data processors CNT1 , may cause the apparatus 500 to repetitively perform a sequence, which comprises at least a first step and a second step, wherein the first step comprises:

- causing at least a first light source LED1 a to emit a first light pulse BOa when operation of a second light source LED1 b is disabled, and

- causing the modulator array SMA1 to display first information INFO1 during emission of the first light pulse BOa, wherein the second step comprises:

- causing at least the second light source LED1 b to emit a second light pulse BOb when operation of the first light source LED1 a is disabled, and

- causing the modulator array SMA1 to display second information INFO2 during emission of the second light pulse BOb.

Referring to Fig.7d, the modulator array SMA1 may comprise a two- dimensional array of individually controllable light valves Pu, ...PM,N. The valves Pu, ...PM,N. may also be called as the pixels. The modulator array SMA1 may comprise e.g. more than 10 6 pixels. The apparatus 500 may provide e.g. full HD resolution with 1920^1080 pixels. The apparatus 500 may provide e.g. 4K resolution with 3840 x 2160 pixels

Referring to Fig. 8a, input light BOb obtained from a light source LED1 b may be coupled into the substrate SLIB2 e.g. through an edge EDG1 b of the substrate. The edge EDG1 b may operate as an in-coupling structure INC1 .

Input light BOb may be directly coupled from a light source LED1 b to the edge EDG1 b.

The apparatus 500 may optionally comprise e.g. focusing optics to focus input light BOb to the edge EDG1 b. The apparatus 500 may comprise refractive and/or reflective focusing optics. For example, the apparatus 500 may comprise an elliptical reflector to focus input light BOa from a linear cold cathode fluorescent lamp to an edge of the substrate SLIB2.

Coupling of light BOb into the edge EDG1 b may be difficult in a situation where the thickness tsuB2 of the substrate SLIB2 is small when compared with the smallest dimension of the light emitter.

Referring to Fig. 8b, the input light BOb may also be coupled into the substrate SLIB2 via the major surface SRF1 and/or SRF2, by using an in-coupling element INC1 . The in-coupling element INC1 may comprise e.g. one or more grooves GO, which are arranged to form guided light B1 b by reflecting input light BOb received from a light source LED1 b.

Referring to Fig. 8c, the input light BOb may also be coupled into the substrate SLIB2 by using an in-coupling prism PRISM1. The in-coupling prism PRISM1 may comprise an input facet FACE00 to form the guided light B1 b by coupling the input light BOb into the prism PRISM1. The prism PRISM1 may comprise a second coupling facet FACE01 to couple the guided light B1 b from the prism PRISM1 to the substrate SLIB2 through the major surface SRF1 or SRF2. The coupling facet FACE01 may be in contact with the major surface SRF1 or SRF2. Input light BOa from a light source LED1 a may also be coupled to the substrate SLIB1 through an edge EDG1 a, via the major surface SRF1 and/or SRF2 of the substrate SLIB1 by using an in-coupling element INC1 , or by using an incoupling prism PRISM1.

The in-coupling arrangement of Fig. 8b or 8c may be used e.g. in a situation where the light emitter (LED1) is large when compared with the thickness tsuBi tsuB2 of the substrate SUB1 , SUB2.

Referring to Fig. 9, an observer EYE2 located in the second viewing region ZONE2 may sometimes observe the displayed information INFO1 also in a situation where projecting of the second modulated light VOb to the second viewing region ZONE2 is disabled. For example, the intensity of the first modulated light VOa may be greater than zero in the second viewing region ZONE2. For example, ambient light may be reflected back from the apparatus 500.

The display apparatus 500 may optionally comprise a masking unit MSK1 to provide dazzling light B2f to the second viewing region ZONE2 e.g. in the first operating mode MODE1 . The masking unit MSK1 may be positioned above the modulator array SMA1 in the direction SZ.

The display apparatus 500 may allow an observer EYE1 located in the first viewing region ZONE1 to observe the displayed information in the first operating mode MODE1 , wherein the dazzling light B2f may make it difficult or impossible for the observer EYE2 located in the second viewing region ZONE2 to observe the displayed information INFO1. Projecting of the second modulated light VOb to the second viewing region ZONE2 may be disabled in the first operating mode MODE1. The dazzling light B2f may reduce visual contrast in the second viewing region ZONE2, so as to prevent visually observing the displayed information INFO1.

The masking unit MSK1 may comprise a substrate SLIB3 and light sources LED1f, LED1g to provide input light BOf, BOg. The input light BOf, BOg may be coupled into the substrate SLIB3 to form guided light B1f, B1g. The substrate SLIB3 may comprise light-deflecting grooves G3 to form dazzling light B2f, B2g by coupling the guided light B1f, B1g out of the substrate SLIB3. The masking unit MSK1 may project dazzling light B2f to the second viewing region ZONE2 and/or the masking unit MSK1 may project dazzling light B2g to the third viewing region ZONE3. Projecting of the dazzling light B2f may be enabled and disabled by switching the light sources LED1f on and off. Projecting of the dazzling light B2g may be enabled and disabled by switching the light sources LED1g on and off. The dazzling light B2f, B2g may also be called e.g. masking light.

Referring to Fig. 10a the substrate SLIB1 may also comprise grooves G1 , which are shorter than the lateral dimensions (LI SUBI , L2SUB2) of the substrate SLIB1 . The grooves G1 do not need to continuously extend from one edge of the substrate to another edge of the substrate. The length LGI of each groove G1 may be e.g. greater than 5 times the width WGI of said groove G1 .

The lengths LGI of the grooves G1 , the depths hd of the grooves G1 and/or the positions (x,y) of the grooves G1 may be selected to provide a desired spatial intensity distribution lB2a(x,y). In particular, the lengths LGI of the grooves G1 , the depths hd of the grooves G1 and/or the positions (x,y) of the grooves G1 may be selected to provide a substantially even spatial intensity distribution lB2a(x,y). x denotes a position coordinate in the direction SX. y denotes a position coordinate in the direction SY.

The substrate SLIB2 may also comprise grooves G2, which are shorter than the lateral dimensions (L1 SUB2, L2SUB2) of the substrate SUB2.

Referring to Fig. 10b, the substrate SLIB1 may comprise a plurality of grooves G1 which have different orientations. The substrate SLIB1 may comprise a plurality of grooves G1 which have a first orientation and a plurality of grooves G1 which have a second different orientation. The orientations of the grooves G1 may be selected e.g. in order to provide a desired angular intensity distribution lB2a((p).

The substrate SLIB2 may comprise a plurality of grooves G2 which have different orientations. Referring to Fig. 10c, the substrate SLIB1 may comprise a plurality of curved grooves G1 .

The substrate SLIB2 may comprise a plurality of curved grooves G2.

Referring to Fig. 10d, the substrate SLIB1 may comprise an out-coupling region REG1 , which comprises a plurality of grooves G1 to couple guided light out of the substrate SLIB1 . The out-coupling region REG1 may be covered with a pattern of grooves G1 . The entire area of the out-coupling region REG1 may be patterned with the grooves G1 such that the grooves G1 cover e.g. less than 5% of the area of the out-coupling region REG1 . However, the entire area of the substrate SLIB1 does not need to be patterned with the grooves G1 . The area of the out-coupling region REG1 may be smaller than or equal to the area of the major surface SRF1 , SRF2. The dimension LI REGI of the out-coupling region REG1 in the direction SX may be equal to or smaller than the corresponding dimension LI SUBI of the substrate SLIB1 , and/or the dimension L2REGI of the out-coupling region REG1 in the direction SY may be equal to or smaller than the corresponding dimension L2SUBI of the substrate SLIB1. The substrate SLIB1 may also comprise an outer region REGO, which is not arranged to couple light out of the substrate. The outer region REGO may be optionally covered e.g. with a frame and/or with an opaque covering layer.

In the similar manner, the substrate SLIB2 of the second backlight unit BLLI2 may comprise an out-coupling region REG1 covered with a pattern of grooves G2. The entire area of the out-coupling region REG1 may be patterned with the grooves G2 such that the grooves G2 cover e.g. less than 5% of the area of the out-coupling region REGI .

Referring to Figs. 10e and 10f , input light BOb emitted from several light sources LED1 b may be coupled into the substrate SLIB2 through the same edge EDG1 of the substrate SLIB2. The light sources LED1 b may be partitioned into a first group GRP1 and a second group GRP2. The light sources LED1 b of the first group GRP1 and the second group GRP2 may be positioned at the same edge EDG1 . The first group GRP1 may comprise one or more light sources LED1 b. The first group GRP1 may also be called as a first subset of the light sources LED1 b. The second group GRP2 may comprise one or more light sources LED1 b. The second group GRP2 may also be called as a second subset of the light sources LED1 b.

The apparatus 500 may comprise a first subset GRP1 of (the second) light sources LED1 b positioned at a first edge EDG1 of the substrate SLIB2 and a second independently controllable subset GRP2 of (the second) light sources LED1 b positioned at the same first edge EDG1 of the substrate SLIB2.

The light (BOb) of the light sources of the first group GRP1 may form a first partial guided light beam B1 bn, when coupled into the substrate SLIB2. The spatial intensity distribution of the guided beam B1 bn may be non-uniform in the direction SY of the edge EDG1 . The guided beam B1 bn may be coupled out of the substrate SLIB2 by grooves G2, which are within a first partial region REG11 of the substrate SLIB2. The dimension L2n of the first partial region REG1 1 may be substantially smaller than the corresponding dimension L2SUB2 of the substrate SLIB2. The dimensions L2n, L2SUB2 may be defined e.g. in the direction SY. The guided beam B1 bn may have an angular divergence A0n. The angular divergence A0n of the guided beam B1 bn may be e.g. smaller than 30° in order to define a visually detectable boundary BND11 of the region REG1 1 . The angular divergence A0n may be e.g. smaller than 10° to provide a substantially sharp boundary BND11 .

The light (BOb) of the light sources of the second group GRP2 may form a second partial guided light beam B1 bi2, when coupled into the substrate SUB2. The spatial intensity distribution of the guided beam B1 bi2 may be non- uniform in the direction SY of the edge EDG1 . The guided beam B1 bi2 may be coupled out of the substrate SLIB2 by grooves G2, which are within a second partial region REG12 of the substrate SLIB2. The dimension L2i2 of the second partial region REG12 may be substantially smaller than the corresponding dimension L2SUB2 of the substrate SUB2. The dimensions L2i2, L2SUB2 may be defined e.g. in the direction SY. The dimension L2i2 of the second partial region REG12 may be e.g. greater than or equal to 50% of the dimension L2SUB2 of the substrate SLIB2 in the direction (SY) of the edge EDG1 .

The apparatus 500 may comprise a first partial region REG11 to project deflected light B2b by coupling light of the first partial guided beam B1 bn out of the substrate SLIB2, and a second partial region REG12 to project deflected light B2b by coupling light of the second partial guided beam B1 bi2 out of the substrate SLIB2, wherein the second partial region REG12 is not arranged to couple light of the first partial guided beam B1 bn out of the substrate SLIB2.

The regions REG11 , REG12 may be partial regions of the out-coupling region REG1 shown in Fig. 10d, for example.

The masking apparatus 500 may have a first additional operation mode (e.g. MODE11 ) where the light sources of the first group GRP1 are switched on, and where the light sources of the second group GRP2 are switched off. The substrate may have a first partial region REG11 where the intensity of the first guided partial beam B1 bn is high (higher), and the substrate may have a second partial region REG12 where the intensity of the second guided partial beam B1 bi2 is low (lower) or zero.

The first partial region REG11 may project deflected light B2b, whereas the second partial region REG12 does not project deflected light B2b. Partitioning the light sources into two or more groups GRP1 , GRP2, and independent controlling of the groups GRP1 , GRP2 may provide one or more independently controllable spatial regions REG11 , REG12 of the substrate SLIB2.

In the first additional operating mode (MODE11 ), the projected deflected light B2b may allow observing first information INFO1 displayed within the first partial region REG11 , when viewed from the second viewing region ZONE2. In the first additional operating mode (MODE11 ), second information INFO2 displayed within the second partial region REG12 cannot be observed, when viewed from the second viewing region ZONE2.

The apparatus 500 may have a second additional operating mode (MODE12) where the light sources of the first group GRP1 are switched off, and where the light sources of the second group GRP2 are switched on.

In the second additional operating mode (MODE12), first information INFO1 displayed within the first partial region REG11 cannot be observed, when viewed from the second viewing region ZONE2. In the second additional operating mode (MODE12), the projected deflected light B2b may allow observing second information INFO2 displayed within the second partial region REG12, when viewed from the second viewing region ZONE2.

The operation of the second group GRP2 may be enabled and disabled in a situation where the operation of the first group GRP1 remains enabled. The apparatus 500 may be arranged to switch the light sources LED1 b of the second group GRP2 on and off in a situation where the light sources LED1 b of the first group GRP1 remain switched on.

The apparatus 500 may also comprise a first subset GRP1 of first light sources LED1 a positioned at a first edge EDG1 of the substrate SLIB1 and a second independently controllable subset GRP2 of first light sources LED1 a positioned at the same first edge EDG1 of the substrate SLIB1 .

Referring to Figs. 11 a and 11 b, the apparatus 500 may be substantially transparent. The transparent apparatus 500 may allow observing an object OBJ1 through the apparatus 500, in addition to observing the information INFO1 displayed on the apparatus 500. Visible light B11 provided from the object OBJ1 may be transmitted through the substrate of the backlight unit and through the modulator array to the eye of an observer EYE1 , so that the observer EYE1 may observe the object OBJ1. The object OBJ1 may be e.g. an item, a product, a person, a vehicle, or a building.

The apparatus 500 may comprise one or more backlight units BLLI1 , BLLI2, wherein the substrates SLIB1 , SLIB2 of the backlight units BLII1 , BLLI2 of the apparatus 500 may be substantially transparent, so as to allow observing the object OBJ1 through the apparatus 500.

The apparatus 500 may comprise

- a backlight unit (BLLI1 , BLLI2) to project deflected light (B2a, B2b, B2c),

- a spatial modulator array (SMA1 ) to form modulated light (V0a,V0b, VOc) from the deflected light (B2a, B2b, B2c), wherein the backlight unit (BLLI1 ,BLU2) comprises:

- one or more first light sources (LED1 a, LED1 b,LED1 c) to provide input light (BOa, BOb, BOc), - a waveguiding substrate (SLIB1 , SLIB2),

- a plurality of light-deflecting grooves (G1 , G2) implemented on the substrate (SUB1 , SUB2).

The backlight unit (BLLI1 , BLLI2) may be arranged to form guided light (B1 a, B1 b, B1 c) by coupling the input light (BOa, BOb, BOc) into the substrate (SLIB1 ,SUB2), wherein the grooves (G1 , G2) of the substrate (SLIB1 , SLIB2) are arranged to form the deflected light (B2a, B2b,B2c) by coupling the guided light (B1 a, B1 b,B1 c) out of the substrate (SLIB1 ,SUB2).

The substrate may be substantially transparent for visible light B11 provided from the object OBJ1 . An area covered by the grooves (G1 , G2) within an out- coupling region (REG1 ) of the substrate (SLIB1 , SLIB2) may be smaller than 5% of the area of the out-coupling region (REG1 ) such that average optical attenuation (AIBH/IBI 1) in the out-coupling region (REG1 ) is smaller than 20% for visible light (B11 ), which is transmitted through the substrate (SLIB1 ), wherein the average optical attenuation (AIBH/IBU) is the average value of optical attenuation over the out-coupling region (REG1 ).

The apparatus 500 may have a selectable viewing sector also in a situation where the apparatus comprises only one backlight unit (e.g. BLLI2). The apparatus 500 may have a several operating modes also in a situation where the apparatus comprises only one backlight unit (BLLI2). For example, the light sources LED1 b, LED1 c may be independently controllable.

The apparatus 500 may comprise:

- at least one backlight unit BLLI1 , BLLI2 to project first deflected light (B2a,B2b) to a first angular range RNG1 and to project second deflected light (B2b,B2c) to a second angular range RNG2,

- the spatial modulator array SMA1 to form first modulated light (V0a,V0b) from the first deflected light (B2a,B2b), and to form second modulated light (V0b,V0c) from the second deflected light (B2b,B2c), wherein the apparatus 500 may be arranged to form the first deflected light (B2a,B2b) by guiding and deflecting light obtained from one or more first light sources (LED1 a,LED1 b), and wherein the apparatus 500 may be arranged to form the second deflected light (B2b,B2c) by guiding and deflecting light obtained from one or more second light sources (LED1 b,LED1 c).

In an embodiment, the apparatus 500 may also comprise three or more backlight units (BLLI1 , BLLI2), which form a stack together with the modulator array SMA1 .

Referring to Fig. 12, the substrate SLIB1 , SLIB2 may be produced e.g. by embossing on a material MAT1. An embossing tool EMB1 may comprise microscopic protrusions RIB1 , which may form the grooves G1 , G2 on the substrate SLIB1 , SLIB2 when pressed against the material MAT1 of the substrate. The grooves G1 , G2 may be formed e.g. by using a rotating embossing roll EMB1 , which may be pressed against the material MAT1 . The material MAT1 and the substrate SLIB1 , SLIB2 may move at a velocity vi with respect to the embossing tool EMB1 . The rotating embossing tool EMB1 may allow producing the substrate SLIB1 , SLIB2 in a roll-to-roll process.

Forming the grooves G1 , G2 by embossing may facilitate mass production of a large quantity of substrates SLIB1 , SLIB2. Forming the grooves G1 , G2 by embossing may facilitate producing a substrate SLIB1 , SLIB2 which has a large surface area. Forming the grooves G1 , G2 by embossing may facilitate producing a substrate SLIB1 , SLIB2 which has a large width and/or length (LI SUBI , L2SUBI , L1 SUB2, L2SUB2).

The grooves G1 , G2 may be formed by hot embossing, wherein the embossing tool EMB1 and/or the material MAT1 may be heated above a glass transition temperature of the material MAT1 . The shape of the grooves G1 , G2 may be subsequently stabilized by cooling the material MAT1 .

The shape of the grooves G1 , G2 may also be stabilized e.g. by curing UV- curable material MAT1 with ultraviolet radiation. UV means ultraviolet radiation.

The embossing tool EMB1 may be formed e.g. by mechanical machining. In particular, the embossing tool EMB1 may be formed by mechanical machining by using a lathe. The protrusions RIB1 may be formed e.g. by cutting with a diamond edge. Forming the embossing tool EMB1 in the lathe may facilitate producing an embossing roll EMB1 , which has a large dimension DEMBI and/or a large dimension LI EMBI . The symbol DEMBI may denote the diameter of the embossing roll EMB1. The symbol LI EMBI may denote the length of the embossing roll EMB1.

A groove G1 , G2 may have e.g. substantially uniform width WGI , WG2 and/or substantially uniform depth hd, hG2. A groove G1 , G2 may have e.g. substantially rectangular shape when viewed in the direction (SZ), which is perpendicular to the first major surface SRF1 . The grooves may have the same width or different widths. The grooves may have the same depth or different depths.

Referring to Figs. 13a and 13b, the grooves G1 , G2 may also have non-uniform width WGI , WG2 and/or non-uniform depth hd, hG2. A groove G1 , G2 may have e.g. substantially elliptical shape when viewed in the direction (SZ), which is perpendicular to the first major surface SRF1 .

The ratio (LGI/WGI ) of the length LGI of a groove G1 to the width WGI of the groove G1 may be e.g. greater than 2.0 in order to provide directional light- deflecting properties. The ratio (LGI/WGI ) may be e.g. greater than 2.0, greater than 5.0, or even greater than 10.0.

The ratio (LG2/WG2) of the length LG2 of a groove G2 to the width WG2 of the groove G2 may be e.g. greater than 2.0 in order to provide directional light- deflecting properties. The ratio (LG2/WG2) may be e.g. greater than 2.0, greater than 5.0, or even greater than 10.0.

The facets FACET1 , FACET2 of a groove G1 may be flat or curved. The facets FACET1 , FACET2 of a groove G2 may be flat or curved. Fig. 13c shows, by way of example, a groove G1 which has curved facets.

Referring to Fig. 14, the planar waveguiding substrate may also be curved. The radius RSRFI of curvature of the first major surface SRF1 of the substrate SLIB1 or SLIB2 may be e.g. greater than 50 times the thickness tsuBi of the substrate SLIB1. The major surfaces SRF1 , SRF2 of a curved planar waveguide SLIB1 , SLIB2 may be singly curved, i.e. they may be e.g. cylindrical surfaces. The major surfaces SRF1 , SRF2 of a curved planar waveguide may be doubly curved, i.e. they may be e.g. spherical surfaces.

In an embodiment, the curved planar waveguiding substrate SLIB1 , SLIB2 may be formed by forming a plurality of grooves G1 on a flat substrate, and converting the flat substrate into the curved substrate after the grooves have been formed.

A curved display apparatus 500 may comprise a first backlight unit BLLI1 , which comprises a curved substrate SLIB1 , a second backlight unit BLLI2, which comprises a curved substrate SLIB2, and a curved modulator array SMA1 . The curved display apparatus 500 may be used e.g. as an aerodynamic component of a vehicle, for displaying information.

Various aspects are illustrated by the following examples.

Example 1 . A display apparatus (500), comprising:

- at least one backlight unit (BLLI1 , BLLI2) to project first deflected light (B2a) to a first angular range (RNG1 ) and to project second deflected light (B2b) to a second angular range (RNG2),

- a spatial modulator array (SMA1 ) to form first modulated light (VOa) from the first deflected light (B2a), and to form second modulated light (VOb) from the second deflected light (B2b), wherein the apparatus (500) is arranged to form the first deflected light (B2a) by guiding and deflecting light obtained from one or more first light sources (LED1 a), wherein the apparatus (500) is arranged to form the second deflected light (B2b) by guiding and deflecting light obtained from one or more second light sources (LED1 b), wherein a first backlight unit (BLII1 ) of the apparatus (500) comprises:

- one or more first light sources (LED1a) to provide first input light (BOa),

- a first waveguiding substrate (SLIB1 ),

- a plurality of light-deflecting grooves (G1 ) implemented on the substrate (SUB1 ), wherein the first backlight unit (BLLI1 ) is arranged to form first guided light (B1 a) by coupling the first input light (BOa) into the substrate (SLIB1 ), wherein the grooves (G1 ) of the substrate (SLIB1 ) are arranged to form the first deflected light (B2a) by coupling the guided light (B1 a) out of the substrate (SUB1 ), wherein an area covered by the grooves (G1 ) within an out-coupling region (REG1 ) of the substrate (SLIB1 ) is smaller than 5% of the area of the out- coupling region (REG1 ) such that average optical attenuation (AIBI I/IBI 1) in the out-coupling region (REG1 ) is smaller than 20% for visible light (B11 ), which is transmitted through the substrate (SLIB1 ), wherein the average optical attenuation (AIBI I/IBI 1) is the average value of optical attenuation over the out- coupling region (REG1 ).

Example 2. The display apparatus (500) of example 1 , comprising:

- an intermediate backlight unit (BLLI1 ) to project first deflected light (B2a) to a first angular range (RNG1 ),

- a rear backlight unit (BLLI2) to project second deflected light (B2b) to a second different angular range (RNG2),

- a spatial modulator array (SMA1 ) to form first modulated light (VOa) from the first deflected light (B2a), and to form second modulated light (VOb) from the second deflected light (B2b), wherein the intermediate backlight unit (BLLI1 ) comprises:

- one or more first light sources (LED1a) to provide first input light (BOa),

- a first waveguiding substrate (SLIB1 ),

- a plurality of light-deflecting grooves (G1 ) implemented on the first substrate (SUB1 ), wherein the intermediate backlight unit (BLLI1 ) is arranged to form first guided light (B1 a) by coupling the first input light (BOa) into the first substrate (SLIB1 ), wherein the grooves (G1 ) of the first substrate (SLIB1 ) are arranged to form the first deflected light (B2a) by coupling the first guided light (B1 a) out of the first substrate (SLIB1 ), wherein the rear backlight unit (BLLI2) comprises:

- one or more second light sources (LED1 b) to provide second input light (BOb),

- a second waveguiding substrate (SLIB2),

- a plurality of light-deflecting grooves (G2) implemented on the second substrate (SUB2), wherein the rear backlight unit (BLLI2) is arranged to form second guided light (B1 b) by coupling the second input light (BOb) into the second substrate (SLIB2), wherein the grooves (G2) of the second substrate (SLIB2) are arranged to form the second deflected light (B2b) by coupling the second guided light (B1 b) out of the second substrate (SLIB2), wherein the intermediate backlight unit (BLLI1 ) is located between the rear backlight unit (BLLI2) and the spatial modulator array (SMA1 ) such that the second deflected light (B2b) is transmitted from the rear backlight unit (BLLI2) to the modulator array (SMA1 ) through the substrate (SLIB1 ) of the intermediate backlight unit (BLLI1 ), wherein an area covered by the grooves (G1 ) within an out-coupling region (REG1 ) of the substrate (SLIB1 ) of the intermediate backlight unit (BLLI1 ) is smaller than 5% of the area of the out-coupling region (REG1 ) such that average optical attenuation (AlB2b/lB2b) in the out-coupling region (REG1 ) is smaller than 20% for visible light (B2b), which is transmitted from the rear backlight unit (BLLI2) to the modulator array (SMA1 ) through the substrate (SUB1 ), wherein the average optical attenuation (AlB2b/lB2b) is the average value of optical attenuation over the out-coupling region (REG1 ).

Example 3. The apparatus (500) of example 1 or 2, wherein the width (WGI) of the grooves (G1 ) of the first substrate (SLIB1 ) is in the range of 0.5 m to 10 pm, and wherein the depth (hd) of the grooves (G1 ) of the first substrate (SUB1 ) is in the range of 0.5 pm to 5 pm.

Example 4. The apparatus (500) according to any of the examples 1 to 3, wherein an average distance (ei) between grooves (G1 ) of the first substrate (SLIB1 ) is smaller than 0.6 mm.

Example 5. The apparatus (500) according to any of the examples 1 to 4, wherein the apparatus (500) is arranged to display first information (INFO1 ) to a first viewing region (ZONE1 ) and to display second information (INFO2) to a second viewing region (ZONE2), wherein the spatial modulator array (SMA1 ) is arranged to sequentially display the first information (INFO1 ) and the second information (INFO2), wherein the one or more first light sources (LED1 a) are arranged to emit first light pulses (BOa) during displaying the first information (INFO1 ), and wherein the one or more second light sources (LED1 b) are arranged to emit second light pulses (BOb) during displaying the second information (INFO2).

Example 6. The apparatus (500) according to any of the examples 1 to 5, comprising a first subset (GRP1 ) of light sources (LED1 a,LED1 b) to form a first partial guided beam (B1 an, B1 bn), and a second independently controllable subset (GRP2) of light sources (LED1 a,LED1 b) to form a second partial guided beam (B1 ai2, B1 bi2), wherein the first subset (GRP1 ) is positioned at a first edge (EDG1 ) of the substrate (SUB1 ,SUB2) of a backlight unit (BLU1 , BLU2), and wherein the second subset (GRP2) is positioned at the same edge (EDG1 ).

Example 7. The apparatus (500) of example 6, comprising a first partial region (REG11 ) of the substrate (SLIB1 ,SUB2) to project deflected light (B2a, B2b) by coupling light of the first partial guided beam (B1 an, B1 bn) out of the substrate (SLIB1 ,SUB2), and a second partial region (REG12) of the substrate (SLIB1 ,SUB2) to project deflected light (B2a, B2b) by coupling light of the second partial guided beam (B1 ai2, B1 bi2) out of the substrate (SUB1 ,SUB2), wherein the second partial region (REG12) is not arranged to couple light of the first partial guided beam (B1 an, B1 bn) out of the substrate (SUB1 ,SUB2).

Example 8. The apparatus (500) according to any of the examples 1 to 7, comprising a masking unit (MSK1 ) positioned above the modulator array (SMA1 ), wherein the masking unit (MSK1 ) comprises:

- one or more light sources (LED1f) to provide auxiliary input light (BOf),

- a third waveguiding substrate (SLIB3),

- a plurality of light-deflecting grooves (G3) implemented on the third substrate (SLIB3), wherein the masking unit (MSK1 ) is arranged to form auxiliary guided light (B1f) by coupling the auxiliary input light (BOf) into the third substrate (SLIB3), wherein the grooves (G3) of the third substrate (SLIB3) are arranged to form masking light (B2f) by coupling the auxiliary guided light (B1f) out of the third substrate (SUB3).

Example 9. The apparatus (500) according to any of the examples 1 to 8, comprising a user interface (LIIF1 ) for receiving user input, wherein the apparatus (500) arranged to control operation of the one or more light sources (LED1 a, LED1 b) based on the user input.

Example 10. The apparatus (500) according to any of the examples 1 to 9, wherein the rear backlight unit (BLLI2) comprises one or more third light sources (LED1 c) to provide third input light (BOc), wherein the rear backlight unit (BLLI2) is arranged to form third guided light (B1 c) by coupling the third input light (BOc) into the second substrate (SLIB2), wherein the grooves (G2) of the second substrate (SLIB2) are arranged to project third deflected light (B2c) into a third angular range (RNG3) by coupling the third guided light (B1 c) out of the second substrate (SUB2).

Example 11. The apparatus (500) according to any of the examples 1 to 10, wherein the intermediate backlight unit comprises one or more third light sources (LED1 c) to provide third input light (BOc), wherein the intermediate backlight unit is arranged to form third guided light (B1 c) by coupling the third input light (BOc) into the substrate (SLIB1 , SLIB2) of the intermediate backlight unit, wherein the grooves of the substrate of the intermediate backlight unit are arranged to project third deflected light (B2c) into a third angular range (RNG3) by coupling the third guided light (B1 c) out of the substrate of the intermediate backlight unit.

Example 12. The apparatus (500) according to any of the examples 1 to 11 , wherein the spatial modulator array (SMA1 ) comprises a liquid crystal layer (CRY1 ).

Example 13. A method for displaying information (INFO1 , INFO2) by using the apparatus (500) according to any of the examples 1 to 10, the method comprising:

- using the modulator array (SMA1 ) to display first information (INFO1 ) in situation where projecting of the first deflected light (B2a) is enabled and projecting of the second deflected light (B2b) is disabled, and

- using the modulator array (SMA1 ) to display second information (INFO2) in a situation where projecting of the second deflected light (B2b) is enabled. Example 14. The method of example 13, comprising using the modulator array (SMA1 ) to display the second information (INFO2) in a situation where projecting of the first deflected light (B2b) is disabled.

Example 15. A method for producing the apparatus (500) according to any of the examples 1 to 12, the method comprising producing at least one substrate (SLIB1 , SLIB2) by embossing.

Example 16. A display apparatus (500), comprising:

- a backlight unit (BLLI1 , BLLI2) to project deflected light (B2a, B2b, B2c),

- a spatial modulator array (SMA1 ) to form modulated light (V0a,V0b, VOc) from the deflected light (B2a, B2b, B2c), wherein the backlight unit (BLLI1 , BLLI2) comprises:

- one or more light sources (LED1 a, LED1 b, LED1 c) to provide input light (BOa, B0b,B0c),

- a waveguiding substrate (SLIB1 , SLIB2),

- a plurality of light-deflecting grooves (G1 , G2) implemented on the substrate (SUB1 , SUB2), wherein the backlight unit (BLLI1 , BLLI2) is arranged to form guided light (B1 a, B1 b,B1 c) by coupling the input light (BOa, BOb, BOc) into the substrate (SLIB1 ,SUB2), wherein the grooves (G1 , G2) of the substrate (SLIB1 , SLIB2) are arranged to form the deflected light (B2a, B2b,B2c) by coupling the guided light (B1 a, B1 b,B1 c) out of the substrate (SLIB1 ,SUB2), wherein an area covered by the grooves (G1 , G2) within an out-coupling region (REG1 ) of the substrate (SLIB1 , SLIB2) is smaller than 5% of the area of the out-coupling region (REG1 ) such that average optical attenuation (AIBI I/IBI 1 ) in the out-coupling region (REG1 ) is smaller than 20% for visible light (B11 ), which is transmitted through the substrate (SLIB1 ), wherein the average optical attenuation (AIBI I/IBI 1) is the average value of optical attenuation over the out- coupling region (REG1 ).

Terms may also be substituted e.g. according to the following table, so as to take into account embodiments where the apparatus comprises the backlight unit BLLI2 for providing light B2b, B2c without using the backlight unit BLLI1. For example, the backlight unit BLLI2 may also be called as the "first" backlight unit BLU2. Light B2b and B2c provided by the backlight unit BLLI2 may be called as the "first" deflected light B2b and the "second" deflected light B2c, respectively.

Table 1 : Terms associated with the reference markings.

For the person skilled in the art, it will be clear that modifications and variations of the systems, products, apparatuses, devices and methods according to the present invention are perceivable. The figures are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the invention, which is defined by the appended claims.