Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
LIGHT DIRECTING ARTICLE WITH A PATTERNED RETARDER
Document Type and Number:
WIPO Patent Application WO/2019/135197
Kind Code:
A1
Abstract:
The disclosed light directing article comprising a plurality of optical elements, a first continuous region comprising having a first light directing property, a plurality of second discontinuous regions, surrounded at least in part by the first continuous region. The second discontinuous regions have a second light directing property different from the first light directing property. One of the first continuous region or second discontinuous regions comprise a retarder.

Inventors:
SHAVER, Jonah (3M Center, Post Office Box 33427Saint Paul, Minnesota, 55133-3427, US)
WHEATLEY, John A. (3M Center, Post Office Box 33427Saint Paul, Minnesota, 55133-3427, US)
WHITING, Tien Yi T. H. (3M Center, Post Office Box 33427Saint Paul, Minnesota, 55133-3427, US)
CLEAR, Susannah C. (3M Center, Post Office Box 33427Saint Paul, Minnesota, 55133-3427, US)
LOGA, Joshua J. (3M Center, Post Office Box 33427Saint Paul, Minnesota, 55133-3427, US)
TOY, Michelle L. (3M Center, Post Office Box 33427Saint Paul, Minnesota, 55133-3427, US)
BARNES, Carla H. (3M Center, Post Office Box 33427Saint Paul, Minnesota, 55133-3427, US)
Application Number:
IB2019/050070
Publication Date:
July 11, 2019
Filing Date:
January 04, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
3M INNOVATIVE PROPERTIES COMPANY (3M Center, Post Office Box 33427Saint Paul, Minnesota, 55133-3427, US)
International Classes:
H01S3/10; H01S3/02
Foreign References:
US20140036943A12014-02-06
US20060198404A12006-09-07
US5082354A1992-01-21
US20040263974A12004-12-30
US8553187B22013-10-08
Attorney, Agent or Firm:
TÉLLEZ, Carlos M. et al. (3M Center, Office of Intellectual Property CounselPost Office Box 3342, Saint Paul Minnesota, 55133-3427, US)
Download PDF:
Claims:
What is claimed is:

1. A light directing article comprising:

a plurality of optical elements;

a first continuous region comprising having a first light directing property;

a plurality of second discontinuous regions, surrounded at least in part by the first continuous region, wherein the second discontinuous regions have a second light directing property different from the first light directing property;

wherein one of the first continuous region or second discontinuous regions comprise a retarder.

2. The light directing article of any of claim 1, wherein the optical element comprises a bead, prism, or microstructure comprising a cube comer.

3. The light directing article of any of the preceding claims, further comprising a phase reversing optical reflector.

4. The light directing article of any of the preceding claims, wherein the phase reversing optical reflector comprises a metalized layer or a dielectric stack.

5. The light directing article of any of the preceding claims, wherein the light directing article is a retroreflective article.

6. The light directing article of any of the preceding claims, wherein the first continuous region forms a thickness above the second discontinuous continuous regions.

7. The light directing article of any of the preceding claims, wherein the second discontinuous regions form a thickness above the first continuous region.

8. The light directing article of any of the preceding claims, further comprising an encapsulation material at least partially filling the thickness between the first continuous region and second discontinuous regions.

9. The light directing article of any of the preceding claims, wherein the encapsulation material has an overall refractive index substantially similar to the overall refractive index of the retarder.

10. The light directing article of any of the preceding claims, wherein the first light directing property is one or more of a light wavelength, redirected light, retroreflected light, polarized light.

11. The light directing article of any of the preceding claims, wherein the second light directing property is one or more of a light wavelength, redirected light, retroreflected light, polarized light, different from the first light directing property.

12. The light directing article of any of the preceding claims, wherein the retarder is one of a quarter wave, 1/8 wave, or 3/8 wave retarder for at least one wavelength in the near infrared range or visible light range.

13. The light directing article of any of the preceding claims, wherein the first continuous region and the second discontinuous regions are arranged to form an optical signature.

14. The light directing article of any of the preceding claims, wherein the optical signature has a specific wavelength or polarization state.

15. The light directing article of any of the preceding claims, wherein the optical signature forms a code, detectable by modulating different polarization states.

16. The light directing article of any of the preceding claims, further comprises a protecting layer at an outermost surface of the light directing article and wherein the retarder is positioned between the protective layer and the optical elements.

17. The light directing article of any one of the preceding claims, wherein the retarder is transparent under the visible light spectrum.

18. The light directing article of any one of the preceding claims, further comprising a wavelength selective absorber, wavelength selective reflector, or wavelength selective dowconverter.

Description:
LIGHT DIRECTING ARTICLE WITH A PATTERNED RETARDER

Technical Field

[0001] The present disclosure relates to a light directing article with a patterned retarder.

Background

[0002] Light directing articles have an ability to manipulate incoming light and typically include an optical element such as a bead or prism. Retroreflective articles are light directing articles that include at least a retroreflecting element. Retroreflective elements reflect incident light back towards the light source. Retroreflecting elements include cube-comer prismatic retroreflectors and beaded retroreflectors. Retarders slow one of the orthogonal components of an incident propagating electromagnetic wave more than the other orthogonal components, creating a phase difference resulting in a change - for polarized incident light - in polarization state.

Summary

[0003] The disclosed light directing article comprising a plurality of optical elements, a first continuous region comprising having a first light directing property, a plurality of second discontinuous regions, surrounded at least in part by the first continuous region. The second discontinuous regions have a second light directing property different from the first light directing property. One of the first continuous region or second discontinuous regions comprise a retarder.

[0004] In one embodiment, the optical element comprises a bead, prism, or microstructure comprising a cube comer. In one embodiment, the light directing article further comprising a phase reversing optical reflector. In one embodiment, the phase reversing optical reflector comprises a metalized layer or a dielectric stack. In one embodiment, the light directing article is a retroreflective article. In one embodiment, the first continuous region forms a thickness above the second discontinuous continuous regions. In one embodiment, the second discontinuous regions form a thickness above the first continuous region. In one embodiment, the light directing further comprises an encapsulation material at least partially filling the thickness between the first continuous region and second discontinuous regions. In one embodiment, the encapsulation material has an overall refractive index substantially similar to the overall refractive index of the retarder. In one embodiment, the first light directing property is one or more of a light wavelength, redirected light, retroreflected light, polarized light. In one embodiment, the second light directing property is one or more of a light wavelength, redirected light, retroreflected light, polarized light, different from the first light directing property. In one embodiment, the retarder is one of a quarter wave, 1/8 wave, or 3/8 wave retarder for at least one wavelength in the near infrared range or visible light range. In one embodiment, the first continuous region and the second discontinuous regions are arranged to form an optical signature. In one embodiment, the optical signature has a specific wavelength or polarization state. In one embodiment, the optical signature forms a code, detectable by modulating different polarization states. In one embodiment, the light directing further comprises a protecting layer at an outermost surface of the light directing article and wherein the retarder is positioned between the protective layer and the optical elements. In one embodiment, the retarder is transparent under the visible light spectrum. In one embodiment, the light directing further comprises a wavelength selective absorber, wavelength selective reflector, or wavelength selective dowconverter.

Brief Description of Drawings

[0005] FIG. 1 shows one embodiment of a side sectional view of a light directing article;

[0006] FIG. 2 shows a top view of the light directing article of FIG. 1 ;

[0007] FIG. 3 shows another embodiment of a side sectional view of a light directing article;

[0008] FIG. 4 shows a top view of the light directing article of FIG. 3.

[0009] FIG. 5 shown an embodiment of an intermediate in forming a light directing article;

[0010] FIG. 6 shows an embodiment of an intermediate in forming a light directing article;

[0011] FIG. 7 shown another embodiment of a side sectional view of a light directing article.

[0012] While the above-identified drawings and figures set forth embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this invention. The figures may not be drawn to scale.

Detailed Description

[0013] Light directing articles and retroreflecting articles like the ones described herein may be useful in certain machine vision detection and sensing systems. As one example, as transportation infrastructure becomes more complicated, vehicles are gaining more driving autonomy. To navigate safely and effectively, sensing modules are increasingly incorporated into these vehicles to perform tasks from parking assistance, self-regulating cruise control and lane deviation warning, to fully autonomous navigation and driving, including collision avoidance and traffic sign interpretation.

[0014] To sense the world around them, vehicles use a set of sensors that emit one or more points of light. For example, a lidar (light detection and ranging) system may use a constellation of points of light that move through the environment to detect potential obstacles or informational objects. These interrogating light beams may use a narrow wavelength band, for example, 2-20 nm, or may use a broad wavelength band, for example, 100 nm or more.

[0015] FIG. 1 is a side sectional view of a light directing article 100 with a retarder 120. FIG. 2 shows a top view of the light directing article 100 of FIG. 1. Light directing article 100 includes light directing layer 110 and retarder 120. In this embodiment, the light directing layer 110 is a retroreflective layer.

[0016] The light directing article 100, which is shown in FIGS. 1 and 2, has a first continuous region 122 and second discontinuous regions 124. In this embodiment, the second discontinuous regions 124 comprise the retarder 120. As shown in this embodiment, there are at least two discontinuous regions 124 that are separated from one another by the first continuous region 122. A discontinuous region 124 may be at least partially or entirely surrounded by the first continuous region 122. As shown in this embodiment, the first continuous region 122 does not include a retarder.

[0017] The first continuous region 122 has a first light directing property. The second discontinuous regions 124 have a second light directing property, which is different from the first light directing property. A light directing property maybe directing a particular wavelength or wavelength range, the angle of light direction, retroreflected light, polarization state of light, absorbing light.

[0018] Referring to FIG. 3, first incident ray 130 and first retroreflected ray 140 and second incident ray 150 and second retroreflected ray 160 illustrate the general functionality of the light directing article 100, which will be described further below.

[0019] FIG. 3 is a side sectional view of a second embodiment of a light directing article 100 with a retarder 120. FIG. 4 shows a top view of the light directing article 100 of FIG. 3. The embodiment in FIG. 3 and 4 is substantially similar to the embodiment in FIG. 1 and 2, with the same reference numbers to indicate common parts. However, in the embodiment shown in FIG. 3 and 4, the first continuous region 122 comprises the retarder 120. As shown in this embodiment, the second discontinuous regions 124 do not include a retarder. The first continuous region 122 has a first light directing property. The second discontinuous regions 124 have a second light directing property, which is different from the first light directing property. A light directing property maybe directing a particular wavelength or wavelength range, the angle of light direction, retroreflected light, polarization state of light, absorbing light

[0020] For light directing articles, various layers in a stack can create areas that become obvious to the eye. For example, when desiring a transparent stack, added layers can limit the amount the material is transparent to a human eye. This may be desirable if one wants to conceal the presence of the pattern made by the two regions. The encapsulation material may also serve to envelope the retarding material in a protection layer. In order to maintain the retardance of the article, the encapsulation material should be optically isotropic, that is have negligible birefringence. For example, in the embodiment in FIG. 1 and 3, the applied retarder 120 can become visually apparent because of the thickness created by the retarder 120 above the light directing layer 110. An encapsulation material may be included to at least partially fill in a portion of the thickness formed between the light directing layer 110 and the applied retarder 120.

Regardless of whether the retarder 120 is located at the second discontinuous region 124 (like shown in FIG. 1) or the first continuous region 122 (like shown in FIG. 3), an encapsulation material 190 may be included. To further minimize the conspicuity of the retarder 120, the encapsulation material 190 can have a refractive index substantially similar to the retarder 120. In one embodiment, the encapsulation material 190 has a refractive index within 20% of the retarder 120.

[0021] FIG. 7 is a side sectional view of a light directing article 100 with a retarder 120. Light directing article 100 includes light directing layer 110 and retarder 120. The embodiment in FIG. 7 is substantially similar to the embodiment in FIG. 1 and 1, but that an encapsulation material 190 entirely fills in the thickness formed between the light directing layer 110 and the applied retarder 120. [0022] Light directing article 100 as described herein may further comprise a protecting layer at an outermost surface of the light directing article. A protective layer can protect the underlying optical elements, retarder, and optional phase reversing optical reflector. FIG. 7 shows a protective layer 140 applied to the light directing article 100. Any of the embodiments, can include protective layer 140.

[0023] First incident ray 130 and second incident ray 150 may each be considered to be left-hand circularly polarized light. First incident ray 130 and second incident ray 150 are each incident on regions of retroreflecting article 100 having different retardation properties. For the purposes of this example, it is assumed that retroreflecting layer 110 has the property of being circular polarization flipping (though not depolarizing); for example, left-hand circularly polarized light is converted to right-hand circularly polarized light, but linearly polarized light is not converted to light having an orthogonal polarization orientation. Further, it is assumed that retarder 120 is configured at least in some regions as a quarter wave retarder, at least for the wavelength of the incident rays and at their incident angles.

[0024] First incident ray 130 is left hand circularly polarized and incident on a region of the light directing article 100 without the retarder 120. In the embodiment shown in FIGS. 1 and 2, the first continuous region 122 does not have the retarderl20. In the embodiment shown in FIGS. 3 and 4, the second discontinuous regions 124 do not have the retarder 120. The handedness of first incident ray 130 is flipped when retroreflected by a polarization preserving, phase reversing retroreflecting layer 110. First retroreflected ray 140 is right-hand circularly polarized light, and therefore for a detector passing left- hand circularly polarized light the first retroreflected ray 140 would not be detected and would appear dark.

[0025] Second incident ray 150 is left hand circularly polarized and is incident on a region of the light directing article 100, which comprises the retarder 120. In the embodiment shown in FIGS. 1 and 2, the second discontinuous regions 124 have the retarderl20. In the embodiment shown in FIGS. 3 and 4, the first continuous region 122 has the retarder 120. Second incident ray 150 is converted from left-hand circularly polarized light to linearly polarized light, and is preserved in its linearly polarized state while retroreflecting. Upon retroreflection, it is converted back into circularly polarized light having the same handedness as the incident light. A detector passing left-hand circularly polarized light would detect second retroreflected ray 160 and would appear bright.

[0026] The region comprising the retarder 120, would return light and appear bright.

[0027] Light directing layer 110 may be any suitable layer or combination of layers for directing incident light with optical elements. In embodiments where the light directing layer is a retroreflecting layer 110, the retroreflecting layer may be any suitable retroreflector that does not substantially depolarize polarized light. Suitable retroreflectors include optical elements and a phase reversing optical reflector.

[0028] For example, suitable retroreflectors include substantially non-depolarizing retroreflectors. For example, a non-depolarizing retroreflector retroreflects an incident left-handed circularly polarized light to either a left-handed circularly polarized light or a right-handed circularly polarized light. Depending on the application, some degree of depolarization may be acceptable and to some degree is inevitable based on spatial non-uniformities, from real-world manufacturing conditions, or otherwise. Depolarization may also be dependent to some degree on the angle of incidence for polarized light or the wavelength of the incident polarized light. In many cases, however, and for the purposes of this description, depolarizing retroreflectors neither flip nor maintain the polarization of incident polarized light. For example, incident left-handed circularly polarized light may return a small portion of left-handed circularly polarized light as part of a larger generally randomized polarization. In other examples using depolarizing retroreflectors, incident left-handed circularly polarized light may be returned as elliptically polarized light or substantially non-polarized light. Again, for the purposes of this description, these types of retroreflectors should not be considered non-depolarizing retroreflectors.

[0029] Suitable retroreflectors that do not depolarize polarized light (at least to a degree potentially applicable for the current description) and include a phase reversing optical reflector with the optical element, include, for example, a metal-backed prism (cube-comer) retroreflectors, metal-backed beaded retroreflectors, and beaded retroreflectors partially immersed in binder optionally including, for example, nacreous or other reflective flake material. Metal or a dielectric stack may be used with a prism or a bead for achieving retroreflection that does not depolarize polarized light. Air-backed prisms that rely on total- internal reflection to retroreflect incident light were observed to depolarize incident light.

[0030] The retroreflecting layer may be any suitable size and have any suitable size optical elements. For example, prisms or beads used in the retroreflecting layer may be on the order of several micrometers in size (width or diameter), tens of micrometers in size, hundreds of micrometers in size, or several millimeters in size, or even several centimeters in size. Beads of multiple different sizes and size distributions may be utilized as appropriate and suitable for the application. Depending on the retroreflected wavelength of interest, there may be a certain practical minimum feature size in order to prevent diffractive and other sub-wavelength feature effects from influencing or even dominating the desired optical performance.

[0031] For beaded retroreflectors, glass beads are commonly used, but any substantially spherical and substantially transparent material can be used. Other examples of bead materials include nanocrystalline ceramic oxides. The materials may be selected based on durability, environmental robustness, manufacturability, index of refraction, wavelength transparency, coatability, or any other physical, optical, or material property. The beads may be partially submerged into a reflective binder, containing, for example, nacreous or metal flake, or they may be partially metallized through vapor coating, sputter coating, or any other suitable process. In some embodiments, the beads may be coated with a dielectric material. In some embodiments, a metalized or dielectric mirror containing film may be laminated or otherwise attached to the bead surface. In some embodiments, the coating or layer may be a spectrally selective reflector. In some embodiments, beads may create an optical path, through a non-reflective binder, between the light incident surface of a retroreflector and the optical reflector. The non-reflective binder may have any physical properties and may impart certain desired properties to the retroreflecting layer. For example, the binder may include a pigment or dye to impart wavelength selective absorption, which can optionally provide a colored or fluorescent effect to the retroreflective article.

[0032] For prismatic retroreflectors, any suitable prismatic shape may be microreplicated or otherwise formed in a transparent (at least transparent to the wavelength of interest) medium. For example, right angle linear prisms, such as those in Brightness Enhancing Film (BEF), may be used, although such prism would not be retroreflecting over a very wide range of angles. Microstructures with a cube comer, such as a truncated cube or a full cube, are widely used as a retroreflecting prismatic shape, where each incident light ray is reflected three times before being returned to the incident direction. Other surfaces having more facets may be used as a prismatic retroreflector. Any suitable resins may be used; thermoplastic material or resins that may be applied in a liquid or flowable form and then subsequently cured and removed from a tool may be used. The tool can be formed through any suitable process, including etching (chemical or reactive ion etching), diamond turning, and others. In some embodiments, the tool can be a fused or otherwise attached collection of multiple parts to cover a full prismatic sheet surface pattern. Curing may take place through the addition of heat or electromagnetic radiation. UV-curable resins or resins that are curable through atypical ambient conditions may be chosen as to not unintentionally partially or fully cure during handling or pre-cure processing. In some embodiments, additive or subtractive manufacturing processes may be used to form either a tool surface for microreplication or the prismatic surface itself.

[0033] Retarder 120 may be any suitable retardation layer that selectively slows one of the orthogonal components of light to change its polarization. In some embodiment, the retarder is transparent under the visible light spectrum. In some embodiments, retarder 120 may be configured as a quarter wave retarder. A quarter wave retarder has a retardance that, for a certain wavelength of interest l, has a retardance of l/4. A quarter wave retarder for a given wavelength of light will convert it from circularly polarized light to linear polarized light or vice versa. In some applications, a quarter wave retarder may function acceptably without having perfect l/4 retardance. For some applications, using an achromatic retarder may permit substantially quarter wave retardance to be maintained over a range of wavelengths; for example, a range of wavelengths spanning 2 nm, 10 nm, 20 nm, 40 nm, 50 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, or even 500 nm. In some embodiments, the quarter wave retarder has substantially quarter wave retardance over the entire near-infrared wavelength range, for example, 700 to 1400 nm. In some embodiments, the quarter wave retarder has substantially quarter wave retardance over the entire visible wavelength range, for example, 400 to 700 nm. In some embodiments, the quarter wave retarder has substantially quarter wave retardance over both the near-infrared and visible range.

[0034] In some embodiments, retarder 120 may provide substantially similar retardance values over a wide range of incidence angles. In some embodiments, the retardance may not vary by more than 10% over a 30 degree half-angle cone, may not vary by more than 10% over a 45 degree half-angle cone, or may not vary by more than 10% over a 60 degree half-angle cone. For some applications, not varying more than 20% over a 30, 45, or 60 degree half angle cone may be acceptable. [0035] Retarder 120 may include any suitable retarding material or materials. In some embodiments, retardation layer 120 includes or is a liquid crystal retarder. In some embodiments, retarder 120 includes an oriented birefringent polymer film. Depending on the birefringence of the chosen polymer set, suitable thickness may be chosen to obtain the desired retardance values. In some embodiments, retarder 120 may include a compensation film or other additional film with low retardance (for example, less than 100 nm of retardance) to enhance or preserve circularly polarized light over a wide range of angles for a wavelength or wavelength range of interest.

[0036] Typically, the light directing layer 110 is planar and the retarder 120 is also planar. The retarder 120 may be a coating or a film. In some embodiments, the retarder 120 has substantially uniform thickness. Uniform thickness is a thickness having general uniformity within manufacturing tolerances and may include situations with the retarder might ripple, crack, crimp, fold onto itself. In one embodiment, the retarder 120 is in direct contact with the optical element. In one embodiment, additional layers or materials may be adjacent to the retarder 120 and positioned between the retarder 120 and light directing layer 110 or covering the retarder 120, such as, for example, adhesive, primer, interlayer, color layer, acrylate layer. These additional layers desirably would not interfere with the properties of the incoming and outgoing light (and is not birefringent).

[0037] The retarder 120, which is at either the first continuous region 122 or second discontinuous regions 124 maybe patterned such as described in US Patent Application 62/461,177 filed February 20, 2017 (attorney docket number 79275US002).

[0038] In one embodiment, the light directing article itself, regardless of the location of the retarder, spatially variant. For example, portions of the optical elements may be intentionally nonfunctional to partially or completely block light in regions, such the first continuous region 122 or second

discontinuous regions 124. A spatially variant light directing article, along with the retarder, would create optical patterns and optical signatures.

[0039] When the light directing article includes a first continuous region 122 and second discontinuous regions 124, at least one of which comprises a retarder 120, the retarder regions can be arranged relative to one another to form an optical pattern. An optical pattern can create an optical signature, which is a wavelength or polarization characteristic of the light sent from the light directing article to a detector. A spatially variant article, can have wavelength and polarization characteristics that vary across the area of the article. If the size of the regions is large enough to be individually resolved at a given observation distance these areas and their respective wavelength and polarization states can be individually detected. If the size of the regions is too small to be individually resolved at a given observation distance, the detector detects the combined signature of the different regions as composite optical signature. Such optical patterns and signatures may be useful for creating a code. The information may be human readable, machine readable, or both human and machine readable.

[0040] Uight directing article 100 may enable particular sensor systems to operate with a high degree of fidelity. For example, a sensor that detects circularly polarized light (for example, a charge coupled device or CMOS used in conjunction with a filter that passes left-handed circularly polarized light) may be a useful sensor configuration. Interrogated with left-handed circularly polarized light, for example, retroreflecting article 100 may provide certain portions (depending on the configuration and optics of retroreflecting layer 110 and retarder 120) that retroreflect left-hand circularly polarized light. These may appear bright or be otherwise detectable with such a sensor configuration. In other portions of retroreflecting article 100, the left-hand circularly polarized interrogation light may be absorbed, or flipped to right-hand circularly polarized light. Such regions would appear dark or be difficult to detect with such a sensor configuration. Retroreflecting articles 100 may be used with a system described in U.S. Patent Application 62/578,151 (attorney docket number 80107US002), filed October 27, 2017.

[0041] Wavelength selective absorbers or reflectors can be incorporated into any material in the optical path, including the retarder. A wavelength selective absorber or reflectors maybe used to absorb or reflect, respectively, wavelengths in the visible, near-infrared, or mid-infrared light.

[0042] In some embodiments, by utilizing circularly polarized light, several potential advantages may be realized. In particular, circularly polarized light tends to be rare in nature, reducing the probability of a false positive signal or other interference.

[0043] Various configurations for a retroreflective material containing a non-depolarizing reflector are described in the following table. A polarized light source could emit different polarization states such as horizontal linearly polarized light (denoted as Linear H), vertical linear polarized light (denoted as Linear V), left circularly polarized light (Left CP), or right circularly polarized light (Right CP) as indicated on the left hand side of the table. The retroreflector can be designed to return different polarization states to a transceiver which include Linear H, Linear V, Left CP, and Right CP. The state of light that is returned to the transceiver depends on the properties of the retarder as indicated in the cells of the table. For example, if Linear H light is incident on a retroreflector having a 1/4 wave retarder, the retroreflector will rotate the polarization of the light 90 degrees and return Linear V. Another example is if Left CP light is incident on a retroreflector having 1/4 wave retarder, the retroreflector will return Left CP light. Another example is if Linear H light is incident on a retroreflector having an 1/8 wave retarder, the retroreflector will return Left CP light. Conversely to have incident Linear H light and have the retroreflector return Right CP light, the retarder should be 3/8 wave. The Table 1 below is for the case of the retarder slow axis at 45 degrees from vertical.

[0044] TABLE 1

[0045] If the retarder slow axis is -45 degrees from vertical, some of the retarder requirements change as indicated in Table 2 below.

[0046] TABLE 2

[0047] Though not intended to be limiting, this shows that retardation levels of 1/8, 1/4, and 3/8 are useful if the objective is to utilize circularly polarized light in the emission from the transceiver and/or the return of light from the retroreflector to the transceiver.

[0048] In some embodiments, retroreflecting article 100 may be configured to operate in the near- infrared wavelength range. Certain sensor systems utilize near-infrared light in order to operate within wavelengths that are invisible to humans. In some embodiments, retroreflecting article 100 may include a retroreflecting layer 110 that retroreflects near-infrared light, and a retardation layer 120 that is configured as a quarter wave retarder for at least one wavelength in the near-infrared wavelength range.

[0049] In one portion, because the handedness of the incident light is preserved, and because the light pass handedness of the polarizing filter is the same as the incident light, the retroreflecting article appears bright. Naturally, other combinations of components such as the incident light polarization, retroreflector type (for example, handedness-preserving or handedness-reversing), and pass-handedness of the circular polarizing filter apparent to the skilled person may be utilized to result in the retroreflecting article’s bright appearance in select regions.

[0050] An advantage of utilizing circularly polarized light and a retroreflective material containing a quarter wave retarder is that the visibility of the retroreflective light is largely invariant as a function of polar and azimuthal alignment between the polarizer that creates or detects the circular polarized light and the quarter wave retarder. In other words, such a retarder may be rotationally invariant with respect to the polarizer that creates or detects the circular polarized light. In some embodiments, this means that the retroreflecting layer has a retroreflective efficiency of not less than 70% of a maximum value as the retarder is rotating about the azimuth. For purposes of illustration, retroreflecting article 100 is assumed to be illuminated and detected under conditions that allow the pattern on the arbitrarily-aligned film to be visible (i.e., in certain embodiments the pattern would be invisible if not illuminated with circularly polarized light or even at all to human eyes). Applications related to this advantage include permanently or temporarily attachable stickers or decals that can be placed on signs, clothing, vehicles, horizontal surfaces, vertical surfaces, infrastructure, buildings, or the like. Because the quarter wave retarder does not need to be carefully aligned with the polarizer on either a light source or a detector, such decals may be easily attached without worry of misorientation or misalignment causing faulty or incomplete detection. Such decals or stickers may be temporarily attached to provide new machine-readable meanings to signs, clothing, or any other attachable surface.

[0051] FIGS. 5, 6, and 7 show one embodiment of making a light directing article 100 comprising a patterned retarder 120. First, a stack of materials is formed comprising the retarder 120 and a carrier 180. In that stack, the retarder 120 and portion of the carrier 180 are precision cut, such as by a laser. Other examples of cutting include laser cutting, die cutting, water jet cutting. As shown in FIG. 5, a weed 170 is applied to the retarder 120. The weed 170 and cut portions are removed leaving discontinuous portions of retarder 120. As shown in FIG. 6, the retarder 120 is applied to a protective layer 140. After application of the retarder 120 to the protective layer, the carrier 180 is removed leaving the retarder 120 on the protective layer 140. As shown in FIG. 7, the retarder 120 is applied to a light directing layer 110.

Between adjacent layers of the various materials shown in FIGS. 5, 6, and 7 adhesives or release materials can be included to aid in attachment or separation.

[0052] FIG. 7 shows a light directing article 100 comprising discontinuous retarder 120 and an overlying protective layer 140. In the embodiment shown in FIG. 7, an encapsulation material 190 is included. In one embodiment, the surface of the light directing layer 110 can be coated with an encapsulation material 190 followed by application of the protective layer 140 and retarder 120. In another embodiment, the retarder 120 can be coated with an encapsulation material 190, followed by application of the retarder 120 and protective layer 140 being applied to the light directing layer 110.

[0053] Light directing articles may be useful for traffic control signs and directional/navigational infrastructure. In some embodiments, retroreflecting articles as described herein may be useful as rigid signs. In some embodiments, these articles may be or included in temporary traffic control devices, such as cones or flags or portable signs. In some embodiments, these articles may be used or incorporated into clothing or wearable items, such as conspicuity vests, helmets, or other safety equipment. In some embodiments, the retroreflecting articles may be conformable, washable, breathable, bendable, rollable, or foldable. In some embodiments, a light directing article is a window film. In some embodiments, these articles may be attached to any type of vehicle, such as a car, motorcycle, airplane, bicycle, boat, or any other vehicle. In some embodiments, these articles can be used for material handling and inventory control in a warehouse, train yard, shipyard, or distribution center, allowing, for example, for the automated identification of the content of shelves, boxes, shipping containers, or the like. They can be used for augmented reality (AR) where the AR system can detect the film for wayfmding or to read a code.

[0054] Retroreflecting articles as described herein may be any suitable size, from small decals or stickers including pressure sensitive adhesive to large, highly visible traffic signs. Substrates to provide rigidity or easy adhesion (for example, pressure sensitive adhesion) may be also included behind the retroreflecting layer without affecting the optics of the retroreflecting article.

[0055] In one aspect, the disclosed application may be used to uniquely identify light directing articles with an optical sensor system modulating polarization states of circular polarizers on light source and/or camera, such as described in U.S. patent application 62/578,151 fded on October 27, 2017. For example, a light directing article would appear bright in the presence of a system having setup 2 and dark in a system having setup 3. In comparison, a light directing article 100 with a phase-reversing reflector, but without retarder, would appear dark in the presence of a system having setup 2 and bright in a system having setup 3, while a light directing article 100 with a depolarizing reflector would appear bright in the presence of both systems. By having different appearances in setups 2 and 3, a light directing article 100 could be uniquely identified and detected when in the presence of light directing articles 100 that did not include retarders (e.g., retroreflective articles commonly found on roads such as, for example, existing traffic signs or license plates).

[0056] The light directing article 100 may be used to create optical signatures that are detectable by modulating different polarization states in the visible spectrum. Cameras on a vehicle may be used in identifying such optical signatures. In one embodiment, the optical signature is created by the retarder so that it forms a code. In other aspect, the light directing article 100 may be used to create optical signatures that are detectable by modulating different polarization states in the near-IR spectrum.

[0057] In one embodiment, the retarder 120 is an adhesive backed sticker, which can then be applied to an underlying light directing layer 110. In one embodiment, the retarder 120 is a continuous arrangement with regions of discontinuity and when applied to the light directing layer 110, the retarder 120 forms the first continuous region 120 and these regions of discontinuity allow the underlying light directing layer 110 to form the second discontinuous regions 124. In one embodiment, the retarder 120 is a discrete elements and when applied to the light directing layer 110, the retarder 120 forms the second

discontinuous regions 124 and these underlying light directing layer 110 forms the first continuous regions 122.

[0058] In one aspect, the present application relates to a system for identifying a light directing article 100. In one embodiment, the system setup includes a light source with a circular polarizer disposed on the optical path of the light source (i.e., light passes through the circular polarizer), a light directing article 100 including a retarder, and a receiving unit capable of receiving light directed to it by the light directing article. In some embodiments, the receiving unit is a camera. In some embodiments, a circular polarizer is disposed on the receiving unit in a direction parallel to the circular polarizer for the light source. In other embodiments, a circular polarizer is disposed on the receiving unit in a direction orthogonal to the circular polarizer for the light source.

[0059] In some embodiments, at least two receiving units are part of the system. In one embodiment, a first receiving unit includes a first circular polarizer disposed thereon, so that the first circular polarizer is in a direction that is parallel to the light source. A second receiving unit includes a second circular polarizer disposed thereon, so that the second circular polarizer is in a direction orthogonal to the light source.

[0060] In some embodiments, the system further includes a processor for processing information obtained by the receiving unit. In one embodiment, the first receiving unit generates a first output obtained under a first set of conditions. The second receiving unit generates a second output, obtained under a second set of conditions, different from the first set of conditions. In some embodiments, the processor compares the first and second output and provides a response or command.

[0061] In some embodiments, the first and second receiving units are cameras, the first and second outputs are images, and the first and second conditions are different polarization states. In some embodiments, the cameras operate in visible wavelengths (e.g., 400 700 nm). In other embodiments, the cameras operate in near infrared wavelengths (e.g., 700 1400 nm).

[0062] In some embodiments, an autonomous vehicle includes a light source having a circular polarizer disposed thereon and at least one receiving unit having a first and second circular polarizers disposed thereon so that the first circular polarizer is in a direction parallel to the circular polarizer in the light source and the second circular polarizer is in a direction orthogonal to the circular polarizer in the light source. The autonomous vehicle further includes a processor capable of analyzing outputs from the receiving unit. The processor subsequently generates a response based on the analysis performed on the outputs of the receiving unit.

[0063] In some embodiments, the receiving unit produces a first output and a second output, wherein the first and second outputs are generated under different conditions. In one embodiment, the first output is an image taken under a first polarization state and the second image is an image taken under a second polarization state, wherein the first polarization state is different from the second polarization state.

[0064] In one embodiment, the processor compares the first and second images and produces a response. In some embodiments, the response is a command to an autonomous vehicle. Exemplary commands include reducing vehicle speed, changing vehicle direction, changing level of autonomy, and modifying driving pattern.

[0065] In one embodiment, the processor compares first and second images and determines based on differences between the images that a detected article includes a light directing article according to the present application. In some embodiments, the light directing article includes an optical signature that conveys information to the autonomous vehicle. The processor detects the optical signature, interprets the conveyed information and generates a command to the vehicle in response to the information provided.

[0066] An exemplary method for detecting light directing articles according to the present application includes: providing a light directing article having optical elements and a retarder that contours at least some of the optical elements, illuminating the light directing article using a light source that includes a circular polarizer disposed on the optical path of the light, and providing a first receiving unit and a second receiving unit, wherein the first receiving unit includes a first circular polarizer disposed on it in a direction that is parallel to the circular polarizer in the light source, and wherein the second receiving unit includes a second circular polarizer disposed on it in a direction that is orthogonal to the circular polarizer in the light source. In some cases, the light source of a transceiver may be inherently polarized such as with laser based sources. In this case a circular polarizer may not be required on the source but rather, a way of converting the linearly polarized laser source to circularly polarized. One way of doing this would be a to use a % wave retarder to convert the emitted laser light to circular.

[0067] Although specific embodiments have been shown and described herein, it is understood that these embodiments are merely illustrative of the many possible specific arrangements that can be devised in application of the principles of the invention. Numerous and varied other arrangements can be devised in accordance with these principles by those of skill in the art without departing from the spirit and scope of the invention. The scope of the present invention should not be limited to the structures described in this application, but only by the structures described by the language of the claims and the equivalents of those structures.