TECHNOLOGICAL FIELD

Embodiments of the present invention relate to an optical arrangement. In particular, an optical arrangement that guides a light path.

BACKGROUND

The optical arrangements used in larger optical apparatus, for example cameras, to guide a light path may not be suitable for miniaturization. For example, they often use relatively large, heavy or expensive optical elements. BRIEF SUMMARY

According to various, but not necessarily all, embodiments of the invention there is provided an apparatus comprising: a light guide extending in a first direction comprising a first region and a second region separated in the first direction, wherein the first region comprises at least an in-coupling element for coupling light into the light guide and the second region comprises at least an out-coupling element for coupling light from the light guide; a light source; and a reflective element; wherein the light guide, the light source and the reflective element are configured to provide a light path from the light source to the reflective element via the first region of the light guide and from the reflective element to the in-coupling element.

According to various, but not necessarily all, embodiments of the invention there is provided an apparatus comprising: a light source; a reflective element; a light-input light guide comprising at least an in-coupling element for coupling light into the light-input light guide and at least an out-coupling element coupling light from the light-input light guide, configured to provide a portion of a light path from the light source to the reflective element; and an exit pupil light guide comprising at least an in-coupling element for coupling into the exit pupil light guide and an out-coupling element for coupling light from the exit pupil light guide, configured to provide a portion of the light path reflected from the reflective element. According to various, but not necessarily all, embodiments of the invention there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

For a better understanding of various examples that are useful for understanding the detailed description, reference will now be made by way of example only to the accompanying drawings in which:

Figs 1 , 2, 3 illustrate different examples of an apparatus comprising at least a light source, a reflective element and an exit pupil light guide;

Figs 4 and 5 illustrate different examples of the apparatus in two-eye configurations.

DETAILED DESCRIPTION The Figures illustrate an apparatus 10 that may be used, for example as a module for eyewear or as eyewear. The apparatus 10 may be used, for example, to enable a near- eye display system and/or a head up display. The apparatus 10 is an example of an optical arrangement for guiding a light path 42. The apparatus 10 comprises at least a light source 40, a reflective element 50 and an exit pupil light guide 20. In some, but not necessarily all examples, it may also comprise a light- input light guide 60.

The light source 40 may be any suitable light source. It may for example comprise one or more light emitting diodes. Optics 82 may be used to collimate light from the light source 40.

The reflective element 50 reflects light produced by the light source 40. It may selectively modulate the reflected light. It may, for example, be a reflective display such as a reflective pixelated display. Examples of reflective displays include, but are not limited to, liquid crystal on silicon (LCoS) displays and digital light processing (DLP) displays.

A LCoS display is a miniature reflective active-matrix liquid crystal display comprising a liquid crystal layer and a silicon backplane, each pixel is controlled by a transistor. If plane polarized light (e.g. a first linear polarization state) is incident on a pixel of the LCoS display it is controllably polarized when reflected to have a linear polarization vector. That vector can be defined by a component (which may be zero) of the first linear polarization state and a component (which may be zero) of a second linear polarization state that is orthogonal to the first linear polarization state. The orientation of the vector represents the pixel value. A DLP display comprises a matrix of movable micromirrors, each pixel is controlled by a position of a micromirror. .

The exit pupil light guide 20 extends in a first direction 21 and comprises a first region 24 and a second region 26 separated in the first direction 21. The first region 24 comprises an in-coupling element 34 for coupling light into the exit pupil light guide 20 and the second region 26 comprises an out-coupling element 36 for coupling light from the exit pupil light guide 20. The out-coupling element 36 forms the exit pupil of the exit pupil light guide 20.

In some but not necessarily all examples, the exit pupil light guide 20 operates as an exit pupil expander because the in-coupling element 34 is smaller in area than the out-coupling element 36. The length of the in-coupling element 34 in the first direction 22 is less than the length of the out-coupling element 36 in the first direction.

In some but not necessarily all examples, the exit pupil light guide 20 is a diffractive light guide. The in-coupling element 34 is an in-coupling diffractive element such as, for example a diffraction grating and the out-coupling element 36 is an out-coupling diffractive element such as, for example, an out-coupling diffraction grating. The in-coupling diffraction grating 34 and the out-coupling diffraction grating 36 may have the same diffraction properties and provide similar diffraction effects. In this scenario, the angle at which a light ray enters the in-coupling element 34 is also the angle at which the light ray exits the out-coupling element 36. As an example, the diffraction gratings may have the same cross-sectional profile, separation distance/density and grating orientation.

In some but not necessarily all examples, the exit pupil light guide 20 operates as a diffractive exit pupil expander because the number of grating lines of the out-coupling diffraction grating 36 is greater than the number of grating lines of the in-coupling diffraction grating 34.

A light path 42 extends from the light source 40 to the reflective element 50, reflects from the reflective element 50 and extends to the in-coupling element 34 of the exit pupil light guide 20. The light path 42 is guided by total internal reflection along the exit pupil light guide 20 and exits from the out-coupling element 36 of the exit pupil light guide 20.

In all the examples illustrated, a portion of the light path 42 from the reflective element 50 is guided along the exit pupil light guide 20 to the out-coupling element 36.

However, the portion of the light path 42 from the light source 40 to the reflective element 50 may be different in different examples. A beam splitter is not used or required in the light path 42 from the light source 40 to the reflective element 50 saving space and/or cost.

In some examples (e.g. Figs 1 and 2), a portion of the light path 42 from the light source 40 to the reflective element 50 is via the exit pupil light guide 20. The term 'via' should be understood to mean that this portion of the light path 42 passes through (intersects with) the exit pupil light guide 20 but is not guided along the exit pupil light guide by total internal reflection. Alternatively, in some examples (e.g. Fig 3), no portion of the light path 42 from the light source 40 to the reflective element 50 is via the exit pupil light guide 20.

In some examples (e.g. Figs 2 and 3), a portion of the light path 42 from the light source 40 to the reflective element 50 is guided along a light-input light guide 60 by total internal reflection. Alternatively, in some examples (e.g. Fig 1 ), a light-input light guide 60 is not used.

In some examples (e.g. Fig 2), the portion of the light path 42 from the light source 40 to the reflective element 50 is guided along a light-input light guide 60 by total internal reflection and is also via the exit pupil light guide 20.

The light-input light guide 60 may comprise an in-coupling element 64 for coupling light into the light-input light guide 60 and an out-coupling element 66 for coupling light from the light- input light guide 60. It provides a portion of the light path 42 from the light source 40 to the reflective element 50.

In some but not necessarily all examples, the light-input light guide 60 is a diffractive light guide. The in-coupling element 64 is an in-coupling diffraction grating and the out-coupling element 66 is an out-coupling diffraction grating. The in-coupling diffraction grating 64 and the out-coupling diffraction grating 66 may have the same diffraction properties. For example, the diffraction gratings may have the same cross-sectional profile, separation distance/density and grating orientation.

In the three examples described below with reference to Figs 1 , 2 and 3, the light guide whether an exit pupil light guide 20 or a light-input light guide 60 is polarization selective. An in-coupling element is configured to in-couple light of a particular polarization state and not in-couple light of a polarization state orthogonal to that particular polarization state. This can be used to selectively either pass or guide incident light by controlling the polarization state of the incident light. For example, it can be used to direct light with one polarization state to the reflective element 50 and then direct light with an orthogonal polarization state from the reflective element 50.

Polarization-selectivity may be controlled by varying an orientation angle of parallel diffraction gratings within the plane of the grating. Diffractive grating parameters such as grating pitch, depth, and fill ratio can be optimized for high polarization-selectivity. Similar polarization-selectivity in the diffractive gratings of out-coupling element 26 further improves the polarization-selectivity of the out-coupled light. Additional components such as polarizers or liquid crystal shutters can be placed on the optical path to further improve the polarization-selectivity. For example, a linear polarizer can be placed between the eye and the out-coupling element 26 to further improve the polarization selectivity of the out-coupled light.

Although in the three examples described below in relation to Figs 1 , 2 and 3 the light guides are polarization selective for linearly polarized light, this is not essential. They may alternatively be polarization-selective for circularly polarized light.

A quarter waveplate converts light having a first plane polarized state to light having a first circular polarization sate (and vice versa) and converts light having a second linear polarization state to light having a second circular polarization state (and vice versa). It may therefore be used to convert plane-polarization selectivity of a light guide to circular- polarization selectivity (and vice versa).

The reflective element 50 with or without additional polarization elements such as a quarter waveplate may control the polarization state of light. Although in the three examples described below in relation to Figs 1 , 2 and 3 the reflective element 50 is a LCoS display that changes a polarization vector of linearly polarized light, the use of an LCoS display is not essential. For example, a DLP display or suitable DLP based display may be used instead. .

Although three examples are described in detail below in relation to Figs 1 to 3, it should be understood that these examples are not the only examples of the apparatus 10. Different configurations may, for example be created by having the in-coupling element 34 and the out-coupling element 36 of the exit pupil light guide 20 on the same side of the exit pupil light guide 20 (as illustrated) or on opposite sides of the exit pupil light guide 20. Different configurations may, for example be created by having the in-coupling element 64 and the out-coupling element 66 of the light-input light guide 60 on the same side of the exit pupil light guide 20 (as illustrated in Figs 2 and 3 ) or on opposite sides of the exit pupil light guide 20. It may therefore be a design choice whether or not the light source 40 and the reflective element 50 are on the same side of the exit pupil light guide 20 or on opposite sides of the exit pupil light guide 20 with the exit pupil light guide 20 between them.

In the first and second examples (Figs 1 and 2), a portion of the light path 42 from the light source 40 to the reflective element 50 is via (through, as opposed to along) the exit pupil light guide 20. A portion of the light path 42 from the reflective element 50 is guided along the exit pupil light guide 20. In the third example (Fig 3), no portion of the light path 42 from the light source 40 to the reflective element 50 is via the exit pupil light guide 20.

In the second and third examples (Figs 2 and 3), a portion of the light path 42 from the light source 40 to the reflective element 50 is guided along a light-input light guide 60. A portion of the light path 42 from the reflective element 50 is guided along the exit pupil light guide 20. In the first example (Fig 1 ), a light-input light guide is not used.

It will therefore be appreciated, that in some examples (e.g. Figs 1 and 2), the apparatus 10 comprises: a light guide 20 extending in a first direction 22 and comprising a first region 24 and a second region 26 separated in the first direction 22, wherein the first region 24 comprises at least an in-coupling element 34 for coupling light into the light guide 20 and the second region 26 comprises at least an out-coupling element 36 for coupling light from the light guide 20; a light source 40; and a reflective element 50, wherein the light guide 20, the light source 40 and the reflective element 50 are mutually configured to provide a light path 42 from the light source 40 to the reflective element via the first region 24 of the light guide 20 and from the reflective element 50 to the in-coupling element 34 of the light guide 20.

It will therefore be appreciated, that in some examples, the apparatus 10 comprises: a light source 40; a reflective element 50; a light-input light guide 60, comprising at least an in- coupling element 64 for coupling light into the light-input light guide 60 and at least an out- coupling element 66 for coupling light from the light-input light guide 60, configured to provide a portion of a light path 42 from the light source 40 to the reflective element 50; and an exit pupil light guide 20 comprising at least an in-coupling element 34 for coupling light into the exit pupil light guide 20 and an out-coupling element 36 for coupling light from the exit pupil light guide 20, configured to provide a portion of the light path 42 reflected from the reflective element 50.

Example 1

In the example illustrated in Fig 1 , the apparatus 10 comprises a light source 40, a reflective element 50 and an exit pupil light guide 20. The exit pupil light guide 20 lies between the light source 40 and the reflective element 50. The light path 42 extends from the light source 40 via optics 80 to the first portion 24 of the exit pupil light guide 20. The optics comprise a collimator 82, for example a lens or combination of lenses, that collimates the light from the light source 40 to form a light beam and a polarizer 84. The polarizer 84 is a polarizer that passes light of a first polarization state P1 and does not pass light of a second polarization state P2 that is orthogonal to the first linear polarization state P1.

The light path 42 passes through the first portion 24 of the exit pupil light guide 20 to the reflection element 50. The in-coupling element 34 at the first portion 24 of the exit pupil light guide 20 is configured to be polarization selective. It in-couples light of the second polarization state P2 more than light of the first polarization state P1 . It may in-couple light of the second polarization state P2 but not light of the first polarization state P1 .

The light passed by the polarizer 84 is in the first polarization state P1 and is therefore not in-coupled by the in-coupling element 34 and passes through to the reflection element 50. The light 42 is at least partially reflected from the reflective element 50 back towards the first portion 24 of the exit pupil light guide 20. The reflection changes the polarization state of the light 42 and the reflected light may comprise light that has a second polarization state P2.

The light 42 in the second polarization state P2 is in-coupled to the exit pupil light guide 20 by the in-coupling element 34 at the first portion 24 of the exit pupil light guide 20. The in- coupled light 42 is guided along the exit pupil light guide 20 by total internal reflection and is out-coupled from the out-coupling element 36 at the second portion 26 of the exit pupil light guide 20.

Additional collimator optics 86 may be positioned between the exit pupil light guide 20 and the reflective element 50. The light path 42 from the light source 40 to the reflective element 50 via the exit pupil light guide 20 is rectilinear.

In this example, the in-coupling element 34 at the first portion 24 of the exit pupil light guide 20 is configured to be polarization selective so that is passes light of the first polarization state P1 from the light source 40 and in-couples light of the second polarization state P2 from the reflective element 50. This may be achieved by using a slanted diffraction grating as the in-coupling element 34. A diffraction grating may have a common cross-sectional profile shape for any vertical cross-section taken along a 'profile' vector. A diffraction grating may have common profile features that extend in parallel in a direction perpendicular to a 'grating' vector. In an un-slanted diffraction grating, the 'profile' vector and the 'grating' vector are aligned (coincident). In a slanted diffraction grating the 'profile' vector and the 'grating' vector are mis-aligned (off-set) in the horizontal plane. In this example, the 'profile' vector remains aligned with the first direction 22 while the 'grating' vector is rotated out of alignment. The diffraction grating has a common cross-sectional profile shape for any vertical cross-section taken along the first direction 22, but the common profile features that extend in parallel no longer extend in a direction perpendicular to the first direction 22.

In this example, the reflective element 50 is a pixelated LCoS display. The first polarization state is a first linear polarization state and the second polarization state is a second linear polarization state. Example 2

In the example illustrated in Fig 2, the apparatus 10 comprises a light source 40, a reflective element 50, an exit pupil light guide 20 and a light-input light guide 60.

In this example, the exit pupil light guide 20 lies between the light source 40 and the reflective element 50. However, in other examples, the light source 40 and the reflective element 50 may be on the same side of the exit pupil light guide 20.

The light path 42 extends from the light source 40 via optics 80 to the in-coupling element 64 of the light-input light guide 60. The optics comprise a collimator 82, for example a lens or combination of lenses, that integrates and steers the light from the light source 40 to form a light beam with certain designed divergence.

The light path 42 is at least partially in-coupled in to the light-input light guide 60 by the in- coupling element 64.

The in-coupling element 64 of the light-input light guide 60 is configured to be polarization selective. It in-couples light of the first polarization state P1 more than light of the second polarization state P2, orthogonal to the first polarization state. It may in-couple light of the first polarization state P1 but not light of the second polarization state P2.

The light 42 in the first polarization state P1 incident on the in-coupling element 64 is in- coupled to the light-input light guide 60 by the in-coupling element 64.

The light 42 in the second polarization state P2 incident on the in-coupling element 64 is not in-coupled to the light-input light guide 60 by the in-coupling element 64 and passes through the light-input light guide 60.

If the first polarization state P1 is a first linear polarization state and the second polarization state is a second linear polarization state, orthogonal to the first linear polarization state, then a combination of a quarter waveplate 70 and mirror 72 may, optionally, be used to change the light 42 of the second polarization state P2 to the first polarization state P1 and return it to the in-coupling element 64 where it is in-coupled to the light-input light guide 60 by the in-coupling element 64. The quarter waveplate 70 changes the second linear polarization state P2 to a second circular polarization state, which on reflection at mirror 72 turns into a first circular polarization state orthogonal to the second circular polarization state, and then on passing through the quarter waveplate 70 is converted to the first linear polarization state P1 .

The in-coupled light 42 is guided along the light-input light guide 60 by total internal reflection and is out-coupled from the out-coupling element 66 of the light-input light guide 60. The light-input light guide 60 in this example comprises reflective surfaces 68 at both ends.

The out-coupling element 66 of the light-input light guide 60 may be adjacent the in-coupling element 34 of the exit pupil light guide 20.

The light path 42 passes through the first portion 24 of an exit pupil light guide 20 to the reflection element 50. The in-coupling element 34 at the first portion 24 of the exit pupil light guide 20 is configured to be polarization selective. It in-couples light of the second polarization state P2 more than light of the first polarization state P1 . It may in-couple light of the second polarization state P2 but not light of the first polarization state P1 . The light produced by the out-coupling element 66 of the light-input light guide 60 is in the first polarization state P1 and is therefore not in-coupled by the in-coupling element 34 and passes through to the reflection element 50.

The light 42 is at least partially reflected from the reflective element 50 back towards the first portion 24 of the exit pupil light guide 20. The reflection may change the polarization state of the light 42 and the reflected light may comprise light that has a second polarization state P2.

The light 42 in the second polarization state P2 is in-coupled to the exit pupil light guide 20 by the in-coupling element 34 at the first portion 24 of the exit pupil light guide 20. The in- coupled light 42 is guided along the exit pupil light guide 20 by total internal reflection and is out-coupled from the out-coupling element 36 at the second portion 26 of the exit pupil light guide 20. Additional collimator optics 86 may be positioned between the exit pupil light guide 20 and the reflective element 50. The light path 42 from the light source 40 to the reflective element 50 via the exit pupil light guide 20 is not rectilinear but off-set by the light-input light guide 60. In this example, as in Fig 1 , the in-coupling element 34 at the first portion 24 of the exit pupil light guide 20 is configured to be polarization selective so that is passes light of the first polarization state P1 from the light source 40 and in-couples light of the second polarization state P2 from the reflective element 50. In this example, as in Fig 1 , the reflective element 50 is a pixelated LCoS display. The first polarization state is a first linear polarization state and the second polarization state is a second linear polarization state.

Example 3

In the example illustrated in Fig 3, the apparatus 10 comprises a light source 40, a reflective element 50, an exit pupil light guide 20 and a light-input light guide 60.

In this example, the exit pupil light guide 20 does not lie between the light source 40 and the reflective element 50.

In this example, the light source 40 and the reflective element 50 are on the same side of the light input guide 60. However, in other examples, the light source 40 and the reflective element 50 may be on opposite sides of the light input guide 60.

The light path 42 extends from the light source 40 via optics 80 to the in-coupling element 64 of the light-input light guide 60. The optics comprise a collimator 82, for example a lens or combination of lenses, that collimates the light from the light source 40 to form a light beam.

The light path 42 is at least partially in-coupled in to the light-input light guide 60 by the in- coupling element 64.

The in-coupling element 64 of the light-input light guide 60 is configured to be polarization selective. It in-couples light of the first polarization state P1 more than light of the second polarization state P2, orthogonal to the first polarization state. It may in-couple light of the first polarization state P1 but not light of the second polarization state P2.

The light 42 in the first polarization state P1 incident on the in-coupling element 64 is in- coupled to the light-input light guide 60 by the in-coupling element 64.

The light 42 in the second polarization state P2 incident on the in-coupling element 64 is not in-coupled to the light-input light guide 60 by the in-coupling element 64 and passes through the light-input light guide 60.

If the first polarization state P1 is a first linear polarization state and the second polarization state is a second linear polarization state, orthogonal to the first linear polarization state, then a combination of a quarter waveplate 70 and mirror 72 may, optionally, be used to change the light 42 of the second polarization state P2 to the first polarization state P1 and return it to the in-coupling element 64 where it is in-coupled to the light-input light guide 60 by the in-coupling element 64. The quarter waveplate 70 changes the second linear polarization state P2 to a second circular polarization state, which on reflection at mirror 72 turns into a first circular polarization state orthogonal to the second circular polarization state, and then on passing through the quarter waveplate 70 is converted to the first linear polarization state P2.

The in-coupled light 42 is guided along the light-input light guide 60 by total internal reflection and is out-coupled from the out-coupling element 66 of the light-input light guide 60. The light-input light guide 60 in this example comprises reflective surfaces 68 at both ends.

The out-coupling element 66 of the light-input light guide 60 may be adjacent to the in- coupling element 34 of the exit pupil light guide 20 but the light path 42 to the reflection element 50 does not pass through the first portion 24 of the exit pupil light guide 20.

The light is at least partially reflected from the reflective element 50 back towards out- coupling element 66 of the light-input light guide 60 and the first portion 24 of the exit pupil light guide 20. The reflection changes the polarization state of the light and the reflected light may comprise light that has a second polarization state P2 which is not in-coupled by the out-coupling element 64 of the light input light guide 60 and passes through to the first portion 24 of the exit pupil light guide 20 where it is in-coupled by the in-coupling element 34 of the exit pupil light guide 20.

The in-coupling element 34 at the first portion 24 of the exit pupil light guide 20 may be configured to be polarization selective. It may in-couple light of the second polarization state P2 more than light of the first polarization state P1 . It may in-couple light of the second polarization state P2 but not light of the first polarization state P1 .

The light 42 in the second polarization state P2 is in-coupled to the exit pupil light guide 20 by the in-coupling element 34 at the first portion 24 of the exit pupil light guide 20. The in- coupled light is guided along the exit pupil light guide 20 by total internal reflection and is out-coupled from the out-coupling element 36 at the second portion 26 of the exit pupil light guide 20.

Additional collimator optics 86 may be positioned between the exit pupil light guide 20 and the reflective element 50.

The light path 42 from the light source 40 to the reflective element 50 via the exit pupil light guide 20 is not rectilinear but off-set by the light-input light guide 60.

In this example, as in Fig 1 and 2, the in-coupling element 34 at the first portion 24 of the exit pupil light guide 20 is configured to be polarization selective so that is passes light of the first polarization state P1 and in-couples light of the second polarization state P2 from the reflective element 50.

In this example, as in Fig 1 and 2, the reflective element 50 is a pixelated LCoS display. The first polarization state is a first linear polarization state and the second polarization state is a second linear polarization state.

In this example, no portion of the light path 42 from the light source 40 to the reflective element 50 is via or intersects the exit pupil light guide 20. Figs 1 , 2 and 3 are examples of the apparatus 10 arranged in a monocular configuration of eyewear (near eye display). The out-coupling element 36 of the exit pupil light guide 20 is arranged so that the light path 42 from the out-coupling element 36 enters a pupil 106 of an eye 102 of a user 100. The out-coupling element 36 of the exit pupil light guide 20 is nearer to the user's nose 104 than the in-coupling element 34 of the exit pupil light guide 20. The light source 40 and the reflective element 50 may be off-set laterally adjacent to the head 108 of the user 100 substantially out of the field of vision of the eye 102.

Figs 4 and 5 are examples of the apparatus 10 arranged in a two-eye configuration of eyewear (near eye display). They may be or be part of a head up display (HUD).

In Fig 4, the exit pupil light guide 20 comprises two distinct out-coupling elements 36.

A first out-coupling element 36i of the exit pupil light guide 20 is arranged so that the light path 42i from the first out-coupling element 36i enters a pupil 106 of a left eye 102i of a user 100. The first out-coupling element 36i of the exit pupil light guide 20 is further from the user's nose 104 than the in-coupling element 34 of the exit pupil light guide 20.

A second out-coupling element 362 of the exit pupil light guide 20 is arranged so that the light path 422 from the second out-coupling element 362 enters a pupil 106 of a right eye 1022 of a user 100. The second out-coupling element 362 of the exit pupil light guide 20 is further from the user's nose 104 than the in-coupling element 34 of the exit pupil light guide 20. The light source 40, the reflective element 50 and in-coupling element 34 of the exit pupil light guide 20 are centrally located adjacent to the nose 104 of the user 100 substantially out of the field of vision of the eye 102.

In the example of Fig 4, no light input light guide 60 is used. The apparatus 10 operates as described with reference to Fig 1. There is a single light source 40, single reflective element 50 and single in-coupling element 34.

The arrangement provides the same image to both eyes and may be described as biocular. In Fig 5, there are two exit pupil light guides 20, fed by a single light-input light guide 60 comprising one in-coupling element 64 and two distinct out-coupling elements 661, 662. Each out-coupling element 661, 662 is associated with a respective reflection element 50i, 5Ο2 and distinct exit pupil light guide 20ι, 2Ο2.

An out-coupling element 36i of a first exit pupil light guide 20i is arranged so that the light path 42i from the out-coupling element 36i enters a pupil 106 of a left eye 102i of a user 100. The out-coupling element 36i of the first exit pupil light guide 20i is further from the user's nose 104 than the in-coupling element 34i of the first exit pupil light guide 20i. A first out-coupling element 661 of the light-input light guide 60, adjacent to a first reflective element 50i, provides light to the in-coupling element 34i of the first exit pupil light guide 2d.

An out-coupling element 362 of a second exit pupil light guide 2Ο2 is arranged so that the light path 422 from the out-coupling element 362 enters a pupil 106 of a right eye 1022 of the user 100. The out-coupling element 362 of the second exit pupil light guide 2Ο2 is further from the user's nose 104 than the in-coupling element 342 of the second exit pupil light guide 2Ο2. A second out-coupling element 662 of the light-input light guide 60, adjacent to a second reflective element 5Ο2 provides light to the in-coupling element 342 of the second exit pupil light guide 2Ο2. The light-input light guide 60 bridges the nose 104 of the user. The light source 40 and in- coupling element 64 of the light-input light guide 60 are centrally located adjacent to the nose 104 of the user 100 substantially out of the field of vision of the eyes 102.

The apparatus 10 operates in a manner similar to that described with reference to Fig 3. However, the orientation of the exit pupil light guides 20 are reversed so that the light paths 42 are towards the user's eyes 102.

The apparatus 10 illustrated in Fig 5 uses a single light source but two distinct reflective elements 50. One reflective element 50i provides a pixelated image to the left eye 102i. One reflective element 5Ο2 provides a pixelated image to the right eye 1022 that may be independently controlled. This may create a stereoscopic (three-dimensional) image for the user 100 which may be used for mediated reality, for example, augmented reality.

The arrangement provides different images to both eyes and may be described as binocular. It should be appreciated that additional or alternative optical elements to those illustrated may be used for controlling the light rays, such as intermediate optical elements for expanding the exit pupil It should be appreciated that different configuration of light guides 20, 60 other than those illustrated may be used. For example, a light guide 20, 60 may be a stacked arrangement of light guides, a double sided light guide with in-coupling and out-coupling elements on different sides or with multiple in-coupling/out-coupling elements on the same side. Intermediate grating areas may be provided for exit pupil extension or beam division. A single light guide 20, 60 may have multiple in-coupling/out-coupling elements for different frequencies of light, for example, one for visible light and one for infrared light.

The light guides 20, 60 may comprise reflective surfaces at one or both ends. Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

The term 'comprise' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use 'comprise' with an exclusive meaning then it will be made clear in the context by referring to "comprising only one" or by using "consisting". In this brief description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term 'example' or 'for example' or 'may' in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus 'example', 'for example' or 'may' refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example but does not necessarily have to be used in that other example. Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that

modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

I/we claim: