Optical system and optical waveguide

Abstract

An optical waveguide includes an optical film disposed between opposing first and second major surfaces of the optical waveguide. The optical film is positioned relative to a thickness direction of the optical waveguide so that for a light ray that enters the optical waveguide and is incident on the optical film, for non-overlapping continuous first range of larger angles and continuous second range of smaller angles, each of the first and second ranges of angles being at least 10 degrees wide, for at least a first polarization state, and for each of blue, green, and red wavelength ranges, for each first angle in the continuous first range, the optical film reflects less than about 20% of the incident light ray and for each second angle in the continuous second range, the optical film reflects at least 70% of the incident light ray.

Description

OPTICAL SYSTEM AND OPTICAL WAVEGUIDETechnical Field

[0001] The present disclosure relates to an optical system and an optical waveguide.Background

[0002] Typically, optical systems for applications, such as augmented reality (AR), commonly use reflective waveguides including a mirror to couple an image light into the reflective waveguide. However, dual reflections on the mirror may cause undesired stray light. A prism coupler with an absorber on an opposite side may be introduced to eliminate this type of stray light. However, the prism coupler may add up weight and volume to the optical systems that is not desired for wearable devices.

[0003] Therefore, an improved reflective waveguide is desired to eliminate the stray light without adding extra weight and volume to the optical system.Summary

[0004] In a first aspect, the present disclosure provides an optical waveguide. The optical waveguide includes an optical core and an input light coupler embedded in the optical core between substantially parallel opposing first and second major surfaces of the optical core. The input light coupler makes an oblique angle of between about 10 to about 60 degrees with the first and second major surfaces. The input light coupler is configured to reflect at least a portion of an incident light ray that enters the optical core through one of the first and second major surfaces of the optical core so that, a reflected light ray propagates along an in-plane length-direction of the optical core by undergoing total internal reflections at each of the first and second major surfaces of the optical core. For a substantially collimated light incident from within the optical core, a first incident angle of less than about 10 degrees and a second incident angle of greater than about 30 degrees, for at least one continuous wavelength range that is at least 10 nanometers (nm) wide and lies in a visible wavelength range extending from about 420 nm to about 680 nm, and for at least one of mutually orthogonal first and second polarization states, the input light coupler has a first average reflectance R1 for the first incident angle and a second average reflectance R2 for the second incident angle. A ratio of the first average reflectance R1 and the second average reflectance R2 is greater than about 1.5, i.e., R1 / R2 is greater than about 1.5.

[0005] In a second aspect, the present disclosure provides an optical waveguide. The optical waveguide includes an optical film disposed between opposing first and second major surfaces of the optical waveguide. The optical film is positioned relative to a thickness direction of the optical waveguide so that for a light ray that enters the optical waveguide and is incident on the optical film, for non-overlapping continuous first range of larger angles and continuous second range of smallerangles, each of the first and second ranges of angles being at least 10 degrees wide, for at least a first polarization state, and for each of a blue wavelength range extending from about 455 nanometers (nm) to about 475 nm, a green wavelength range extending from about 520 nm to about 540 nm, and a red wavelength range extending from about 615 nm to about 635 nm, for each first angle in the continuous first range of larger angles, the optical film reflects less than about 20% of the incident light ray and for each second angle in the continuous second range of smaller angles, the optical film reflects at least 70% of the incident light ray. The reflected light ray propagates along a lengthdirection of the optical waveguide by undergoing a plurality of total internal reflections.

[0006] In a third aspect, the present disclosure provides an optical system. The optical system includes a display configured to form and emit an image including an emitted image light. The optical system further includes an optical waveguide including an optical core, an input light coupler, and an output light coupler. The input light coupler is embedded in the optical core between opposing first and second major surfaces of the optical core. Further, the input light coupler is configured to receive at least a portion of the emitted image light that enters the optical core. The received image light propagates towards the output light coupler by undergoing multiple reflections at each of the first and second major surfaces of the optical core. The output light coupler is configured to extract at least a portion of the propagating image light out of the optical core for viewing by a viewer. For a substantially collimated light incident from within the optical core, for at least a first polarization state, and for at least one continuous wavelength range that is at least 10 nanometers (nm) wide and lies in a visible wavelength range that extends from about 420 nm to about 680 nm, a plot of an average reflectance of the input light coupler versus angle of incidence has a band edge where the average reflectance of the input light coupler decreases with increasing incident angle, such that along the band edge, the average reflectance decreases by at least 30 percentage points when the incident angle increases by no more than about 10 degrees.

[0007] The details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.Brief Description of the Drawings

[0008] Exemplary embodiments disclosed herein may be more completely understood in consideration of the following detailed description in connection with the following figures. The figures are not necessarily drawn to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

[0009] FIG. 1 A shows a schematic sectional view of an optical system including an optical waveguide, according to an embodiment of the present disclosure;

[0010] FIG. IB shows a schematic sectional view of the optical system further including a collimating lens, according to an embodiment of the present disclosure.

[0011] FIG. 2 shows a schematic perspective view of an optical core, according to an embodiment of the present disclosure;

[0012] FIG. 3 shows a detailed schematic view of a display, according to an embodiment of the present disclosure;

[0013] FIG. 4 shows a schematic sectional view of an input light coupler, according to an embodiment of the present disclosure;

[0014] FIG. 5 shows a schematic top view of the optical waveguide, according to an embodiment of the present disclosure;

[0015] FIG. 6 shows a detailed schematic sectional view of the input light coupler, according to an embodiment of the present disclosure;

[0016] FIG. 7 A shows a graph depicting optical reflectance verses wavelength of the input light coupler for different incident angles and a first polarization state, according to an embodiment of the present disclosure;

[0017] FIG. 7B shows a graph depicting optical reflectance verses wavelength of the input light coupler for different incident angles and a second polarization state, according to an embodiment of the present disclosure;

[0018] FIG. 8A shows a graph depicting optical reflectance verses incident angle of the input light coupler for the first polarization state, according to an embodiment of the present disclosure;

[0019] FIG. 8B shows a graph depicting optical reflectance verses incident angle of the input light coupler for the second polarization state, according to an embodiment of the present disclosure;

[0020] FIG. 9A shows an exemplary graph depicting layer thickness verses layer number for a first and second polymeric layers of the input light coupler;

[0021] FIG. 9B shows a magnified graph depicting the layer thickness verses layer number for the first and second polymeric layers of the input light coupler; and

[0022] FIG. 10 shows an exemplary graph depicting index verses wavelength for the first and second polymeric layers of the input light coupler.Detailed Description

[0023] In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

[0024] In the following disclosure, the following definitions are adopted.

[0025] As used herein, all numbers should be considered modified by the term “about”. As used herein, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably.

[0026] As used herein as a modifier to a property or attribute, the term “generally”, unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within + / - 20 % for quantifiable properties).

[0027] The term “substantially”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / - 10% for quantifiable properties) but again without requiring absolute precision or a perfect match.

[0028] The term “about”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / - 5% for quantifiable properties) but again without requiring absolute precision or a perfect match.

[0029] As used herein, the terms “first” and “second” are used as identifiers. Therefore, such terms should not be construed as limiting of this disclosure. The terms “first” and “second” when used in conjunction with a feature or an element can be interchanged throughout the embodiments of this disclosure.

[0030] As used herein, “at least one of A and B” should be understood to mean “only A, only B, or both A and B”.

[0031] Typically, optical systems for applications, such as augmented reality (AR), commonly use a reflective waveguide including a mirror to couple an image light into the reflective waveguide. However, dual reflections on the mirror may cause undesired stray light. A prism coupler with an absorber on an opposite side may be introduced to eliminate this type of stray light. However, the prism coupler may add up weight and volume to the optical systems that is not desired for wearable devices.

[0032] Therefore, an improved reflective waveguide is desired to eliminate the stray light without adding extra weight and volume to the optical system.

[0033] The present disclosure relates to an optical system and an optical waveguide. The optical waveguide includes an optical core and an input light coupler embedded in the optical core between substantially parallel opposing first and second major surfaces of the optical core. The input light coupler makes an oblique angle of between about 10 to about 60 degrees with the first and second major surfaces. The input light coupler is configured to reflect at least a portion of an incident light ray that enters the optical core through one of the first and second major surfaces of the optical core so that, a reflected light ray propagates along an in-plane length-direction of the optical core by undergoing total internal reflections at each of the first and second major surfaces of the optical core. For a substantially collimated light incident from within the optical core, a first incident angle of less than about 10 degrees and a second incident angle of greater than about 30 degrees, for at least one continuous wavelength range that is at least 10 nanometers (nm) wide and lies in a visible wavelengthrange extending from about 420 nm to about 680 nm, and for at least one of mutually orthogonal first and second polarization states, the input light coupler has a first average reflectance R1 for the first incident angle and a second average reflectance R2 for the second incident angle. A ratio of the first average reflectance R1 and the second average reflectance R2 is greater than about 1.5, i.e., R1 / R2 is greater than about 1.5.

[0034] Typically, correct or intended light rays are incident on the input light coupler at smaller angles (i.e., the first incident angle less than about 10 degrees) and the stray light rays (which may be caused due to the dual reflections on the input light coupler) are incident on the input light coupler at larger angles (i.e., the second incident angle greater than about 30 degrees). As R1 / R2 is greater than about 1.5, the input light coupler has a lower average reflectance for light incident at the greater angles (i.e., the stray light rays).

[0035] Since the input light coupler has the lower average reflectance for the stray light rays, the stray light rays may substantially transmit through the input light coupler and therefore may not propagate along the in-plane length-direction of the optical core. Thus, the undesired stray light may be eliminated and may not reach a viewer.

[0036] Referring now to figures, FIG. 1 A shows a schematic sectional view of an optical system 400 including an optical waveguide 300, according to an embodiment of the present disclosure.

[0037] A coordinate system including mutually perpendicular x, y, and z-axes is also illustrated in FIG. 1 A. The x and y-axes are in-plane axes of the optical system 400, while the z-axis is a transverse axis disposed along a thickness of the optical system 400. In other words, the x and y-axes are along a plane of the optical system 400 defining a x-y plane, and the z-axis is perpendicular to the x-y plane of the optical system 400.

[0038] The optical system 400 includes a display 30. The display 30 is configured to form and emit an image 30i including an emitted image light 30b, 30r. In some embodiments, the image 30i further includes an emitted image light 30g (shown in FIG. 3).

[0039] In some embodiments, the display 30 includes one or more of a light emitting diode display (LED), an organic light emitting diode display (OLED), a liquid crystal display (LCD), and an electroluminescent display (EL).

[0040] As discussed above, the optical system 400 further includes the optical waveguide 300. The optical waveguide 300 includes an input light coupler 20. In some embodiments, the input light coupler 20 includes an optical film. In such embodiments, the input light coupler 20 may be interchangeably referred to as “the optical film 20” herein.

[0041] In some embodiments, the optical waveguide 300 further includes an optical core 10 and an output light coupler 80.

[0042] In the illustrated embodiment of FIG. 1 A, the output light coupler 80 is embedded in the optical waveguide 300.

[0043] In some embodiments, the optical core 10 includes one or more of a glass, a dielectric, and a polymer.

[0044] Another coordinate system including mutually perpendicular x’, y’, and z’-axes is also illustrated in FIG. 1A. The x’ and y’-axes are in-plane axes of the input light coupler 20, while the z’ -axis is a transverse axis disposed along a thickness of the input light coupler 20. In other words, the x’ and y’-axes are along a plane of the input light coupler 20 defining a x’-y’ plane, and the z’-axis is perpendicular to the x’-y’ plane of the input light coupler 20. In some cases, the y-axis of the optical system 400 and the y’-axis of the input light coupler 20 may be substantially along a same direction.

[0045] The optical film 20 is disposed between opposing first and second major surfaces 301, 302 of the optical waveguide 300. As shown in FIG. 1A, the input light coupler 20 is embedded in the optical core 10 between opposing first and second major surfaces 11, 12 of the optical core 10.

[0046] In some embodiments, the first and second major surfaces 11, 12 of the optical core 10 are substantially parallel to each other. In some embodiments, at least one of the first and second major surfaces 11, 12 of the optical core 10 is an outermost major surface of the optical core 10. As shown in FIG. 1A, in some embodiments, the input light coupler 20 is substantially planar.

[0047] The input light coupler 20 is configured to receive at least a portion 31b, 31r of the emitted image light 30b, 30r that enters the optical core 10. In some embodiments, the portion 3 lb, 3 Ir of the emitted image light 30b, 30r may be interchangeably referred to as “the incident light ray 31b, 31r” or “the light ray 31b, 31r” herein.

[0048] In some embodiments, the incident light ray 31b, 31r enters the optical core 10 through a region 91 of the one of the first and second major surfaces 11, 12, such that in a plan top view in a thickness direction of the optical waveguide 300, the region 91 corresponds to the input light coupler 20. In some embodiments, the thickness direction of the optical waveguide 300 may be substantially along the z-axis.

[0049] In some embodiments, the input light coupler 20 extends across at least 70% of an entire thickness of the optical core 10. The thickness of the optical core 10 may be substantially along the z-axis. In some embodiments, the input light coupler 20 extends across at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the entire thickness of the optical core 10. In the illustrated embodiment of FIG. 1 A, the input light coupler 20 extends across at least 100% of the entire thickness of the optical core 10.

[0050] The optical film 20 is positioned relative to the thickness direction (i.e., substantially along the z-axis) of the optical waveguide 300 so that the light ray 31b, 31r that enters the optical core 10 is incident on the optical film 20.

[0051] The received image light 3 lb, 3 Ir propagates toward the output light coupler 80 by undergoing multiple reflections at each of the first and second major surfaces 11, 12 of the optical core 10. Specifically, the received image light 31b, 31r propagates toward the output light coupler 80 by undergoing multiple reflections at each of the first and second major surfaces 11, 12 of the opticalcore 10 as propagating image light 32b, 32r. The propagating image light 32b, 32r may be interchangeably referred to as “the reflected light ray 32b, 32r” herein.

[0052] The reflected light ray 32b, 32r propagates along a length-direction of the optical waveguide 300 by undergoing a plurality of total internal reflections. In some embodiments, the length-direction of the optical waveguide 300 is an in-plane length-direction. The length-direction or in-plane length-direction may be substantially along the x-axis.

[0053] In other words, the input light coupler 20 is configured to reflect at least a portion of the incident light ray 31b, 31r that enters the optical core 10 through one of the first and second major surfaces 11, 12 of the optical core 10 so that the reflected light ray 32b, 32r propagates along the inplane length-direction of the optical core 10 by undergoing total internal reflections at each of the first and second major surfaces 11, 12 of the optical core 10. In some embodiments, the portion of the incident light ray 31b, 31r enters the optical core 10 through the first major surface 11 of the optical core 10.

[0054] As shown in FIG. 1A, the input light coupler 20 makes an oblique angle al of between about 10 degrees to about 60 degrees with the first and second major surfaces 11, 12. In some embodiments, the input light coupler 20 makes the oblique angle al of between about 15 degrees to about 50 degrees, between about 20 degrees to about 40 degrees, or between about 20 degrees to about 30 degrees with the first and second major surfaces 11, 12. In some embodiments, the input light coupler 20 makes the oblique angle al of about 25 degrees.

[0055] The output light coupler 80 is configured to extract at least a portion 33b, 33r of the propagating image light 32b, 32r out of the optical core 10 for viewing by a viewer 90.

[0056] In some embodiments, the optical waveguide 300 further includes an optical cladding 70 disposed on and covering substantially an entirety of, at least one of the opposing first and second major surfaces 11, 12 of the optical core 10. As shown in FIG. 1A, in some embodiments, the optical cladding 70 is disposed on and covers substantially the entirety of, at least one of the opposing first and second major surfaces 11, 12 of the optical core 10.

[0057] In some embodiments, the optical cladding 70 has an index of refraction less than an index of refraction of the optical core 10 for at least one same wavelength in a visible wavelength range 42v (shown in FIG. 7B) extending from about 420 nanometers (nm) to about 680 nm.

[0058] In some embodiments, for at least one wavelength in the visible wavelength range 42v, the optical core 10 has the index of refraction of between about 1.05 and about 2.5. In some embodiments, for the at least one wavelength in the visible wavelength range 42v, the optical core 10 has the index of refraction of between about 1.2 and about 2.4, between about 1.3 and about 2.3, or between about 1.4 and about 2.2.

[0059] In some embodiments, for the at least one wavelength in the visible wavelength range 42v, the optical core 10 has the index of refraction of between about 1.3 and about 1.8. In someembodiments, for the at least one wavelength in the visible wavelength range 42v, the optical core 10 has the index of refraction of about 1.52.

[0060] In the illustrated embodiment of FIG. 1 A, the optical core 10 has an average thickness tl and the optical film 20 has an average thickness t2. In some embodiments, a ratio of the average thickness t2 and the average thickness tl is less than about 0.5, i.e., t2 / tl is less than about 0.5. In some embodiments, t2 / tl is less than about 0.4, less than about 0.3, less than about 0.2, less than about 0.1, less than about 0.05, less than about 0.01, less than about 0.005, or less than about 0.001.

[0061] FIG. IB shows a schematic sectional view of an optical system 401, according to an embodiment of the present disclosure.

[0062] In some embodiments, the optical system 401 of FIG. IB is substantially similar to the optical system 400 of FIG. 1 A, with like elements designated by like reference characters. However, the optical system 401 of FIG. IB has a different configuration. Specifically, the optical system 401 includes a collimating lens 25 disposed between the display 30 and the optical waveguide 300. In some embodiments, the collimating lens 25 may be configured to collimate the emitted image light 30b, 30r before it enters the optical waveguide 300.

[0063] FIG. 2 shows a schematic perspective view of the optical core 10, according to an embodiment of the present disclosure.

[0064] In some embodiments, the optical core 10 is substantially a one-dimensional optical core having a thickness Hl and a width W 1 along respective thickness and width directions of the optical core 10. In such embodiments, the width W1 is greater than the thickness Hl by at least a factor of 10. In some embodiments, the width W1 is larger than the thickness Hl by at least a factor of 50, a factor of 100, a factor of 500, or a factor of 1000.

[0065] In some embodiments, the optical core 10 is substantially a two-dimensional optical core having the thickness Hl and the width W 1 along the respective thickness and width directions of the optical core 10. In such embodiments, the width W1 and the thickness Hl are within a factor of 5 of each other. In some embodiments, the width W 1 and the thickness Hl are within a factor of 4, a factor of 3, a factor of 2, a factor of 1.5, a factor of 1.2, or a factor of 1.1 of each other.

[0066] In some embodiments, the thickness direction of the optical core 10 may be substantially along the z-axis and the width direction of the optical core 10 may be substantially along the y-axis.

[0067] In some embodiments, the thickness Hl may be interchangeably referred to as “the total thickness Hl” herein. In some embodiments, the total thickness Hl is between 0.1 millimeters (mm) and 10 mm, i.e., 0.1 mm < Hl < 10 mm. In some embodiments, the total thickness Hl is between 0.2 mm and 5 mm, i.e., 0.2 mm < Hl < 5 mm.

[0068] In some embodiments, the optical core 10 has a length LI along the length direction. In some embodiments, the length LI is greater than each of the thickness Hl and the width Wl.

[0069] FIG. 3 shows a detailed schematic view of the display 30, according to an embodiment of the present disclosure.

[0070] In some embodiments, the display 30 includes a plurality of blue, green, and red light emitting pixels 34b, 34g, 34r configured to emit the image 30i including the emitted image light 30b, 30g, 30r including at least one emitted blue image light 30b having a blue wavelength in a blue wavelength range 42b (shown in FIG. 7A) extending from about 455 nm to about 475 nm, at least one emitted green image light 30g having a green wavelength in a green wavelength range 42g (shown in FIG. 7A) extending from about 520 nm to about 540 nm, and at least one emitted red image light 30r having a red wavelength in a red wavelength range 42r (shown in FIG. 7A) extending from about 615 nm to about 635 nm.

[0071] In some embodiments, the emitted image light 30b, 30g, 30r includes at least one wavelength in each of the blue wavelength range 42b, the green wavelength range 42g, and the red wavelength range 42r.

[0072] In some embodiments, the display 30 further includes plurality of white light emitting pixels 34w configured to emit white light. In some embodiments, the emitted image light 30b, 30g, 30r is substantially white light.

[0073] FIG. 4 shows a schematic view of the input light coupler 20, according to an embodiment of the present disclosure. FIG. 4 further illustrates a substantially collimated light 40, 41 is incident on the input light coupler 20 from within the optical core 10 (shown in FIGS. 1A and IB).

[0074] In some embodiments, the substantially collimated light 40 is incident on the input light coupler 20 from within the optical core 10 at a first incident angle bl of less than about 10 degrees.

[0075] In some embodiments, the substantially collimated light 40 is incident on the input light coupler 20 from within the optical core 10 at the first incident angle bl of less than about 8 degrees, less than about 6 degrees, less than about 4 degrees, less than about 2 degrees, less than about 1 degree, less than about 0.5 degree, or less than about 0 degree. In some embodiments, the substantially collimated light 40 is incident on the input light coupler 20 from within the optical core 10 at the first incident angle bl of about 0 degree.

[0076] In some embodiments, the substantially collimated light 41 is incident on the input light coupler 20 from within the optical core 10 at a second incident angle b2 of greater than about 30 degrees.

[0077] In some embodiments, the substantially collimated light 41 is incident on the input light coupler 20 from within the optical core 10 at the second incident angle b2 of greater than about 35 degrees, greater than about 40 degrees, greater than about 45 degrees, greater than about 50 degrees, greater than about 55 degrees, greater than about 60 degrees, greater than about 65 degrees, greater than about 70 degrees, greater than about 75 degrees, or greater than about 80 degrees. In some embodiments, the substantially collimated light 41 is incident on the input light coupler 20 from within the optical core 10 at the second incident angle b2 is about 65 degrees.

[0078] FIG. 5 shows a schematic top view of the optical waveguide 300, according to an embodiment of the present disclosure.

[0079] In the illustrated embodiment of FIG. 5, the optical core 10 and the optical cladding 70 are substantially co-extensive with each other in length L2 and width W2. In some embodiments, the length L2 may be substantially along the x-axis and the width W2 may be substantially along the y-axis.

[0080] FIG. 6 shows a detailed schematic sectional view of the input light coupler 20 including the optical film 20, according to an embodiment of the present disclosure.

[0081] In some embodiments, the optical film 20 includes a plurality of polymeric layers 21, 22 numbering at least 5 in total. In some embodiments, the optical film 20 includes the plurality of polymeric layers 21, 22 numbering at least 10, at least 20, at least 50, at least 100, at least 150, at least 200, at least 250, at least 300, at least 350, at least 400, at least 450, or at least 500 in total.

[0082] In some embodiments, each of the polymeric layers 21, 22 has an average thickness t of less than about 1000 nm and greater than about 10 nm. The term “average thickness t”, as used herein, refers to an average of thicknesses measured at multiple points across a plane of each of the polymeric layers 21, 22. In some embodiments, each of the polymeric layers 21, 22 has the average thickness t of less than about 900 nm, less than about 800 nm, less than about 700 nm, less than about 600 nm, or less than about 500 nm and greater than about 20 nm, greater than about 30 nm, greater than about 40 nm, or greater than about 50 nm.

[0083] In some embodiments, the plurality of polymeric layers 21, 22 includes a plurality of alternating first and second polymeric layers 21, 22. In some embodiments, the first polymeric layers 21 and the second polymeric layers 22 have different indices of refraction from each other for at least one wavelength in the visible wavelength range 42v (shown in FIG. 7B).

[0084] In the illustrated embodiment of FIG. 6, the optical film 20 further includes at least one skin layer 23 disposed on the plurality of polymeric layers 21, 22 and having an average thickness st of greater than about 500 nm. The term “average thickness st”, as used herein, refers to an average of thicknesses measured at multiple points across a plane of the at least one skin layer 23. In some embodiments, the at least one skin layer 23 has the average thickness st of greater than about 750 nm, greater than about 1000 nm, greater than about 1500 nm, or greater than about 2000 nm.

[0085] The at least one skin layer 23 may protect the plurality of polymeric layers 21, 22 and may also provide mechanical stability to the optical film 20. In some cases, the at least one skin layer 23 may act as a protective boundary layer (PBL).

[0086] FIG. 7 A shows a graph 800 depicting optical reflectance verses wavelength of the input light coupler 20 for different incident angles and a first polarization state, according to an embodiment of the present disclosure. FIG. 7B shows a graph 810 depicting optical reflectance verses wavelength of the input light coupler 20 for the different incident angles and a second polarization state, according to an embodiment of the present disclosure.

[0087] In the graphs 800, 810, the wavelength is expressed in nanometers (nm) in the abscissa and the optical reflectance is expressed in percentage (%) in the ordinate.

[0088] The graph 800 includes a curve 802p depicting the optical reflectance verses wavelength of the input light coupler 20 for a light incident at 0 degree and having the first polarization state.

[0089] The graph 800 further includes a curve 804p depicting the optical reflectance verses wavelength of the input light coupler 20 for a light incident at 35 degrees and having the first polarization state.

[0090] Further, the graph 800 includes a curve 806p depicting the optical reflectance verses wavelength of the input light coupler 20 for a light incident at 65 degrees and having the first polarization state.

[0091] Furthermore, the graph 800 includes a curve 808p depicting the optical reflectance verses wavelength of the input light coupler 20 for a light incident at 85 degrees and having the first polarization state.

[0092] The graph 810 includes a curve 802s depicting the optical reflectance verses wavelength of the input light coupler 20 for a light incident at 0 degree and having the second polarization state.

[0093] The graph 810 further includes a curve 804s depicting the optical reflectance verses wavelength of the input light coupler 20 for a light incident at 35 degrees and having the second polarization state.

[0094] Further, the graph 810 includes a curve 806s depicting the optical reflectance verses wavelength of the input light coupler 20 for a light incident at 65 degrees and having the second polarization state.

[0095] Furthermore, the graph 810 includes a curve 808s depicting the optical reflectance verses wavelength of the input light coupler 20 for a light incident at 85 degrees and having the second polarization state.

[0096] Referring to FIGS. 4, 7 A, and 7B, for the substantially collimated light 40, 41 incident from within the optical core 10, the first incident angle bl of less than about 10 degrees and the second incident angle b2 of greater than about 30 degrees, for at least one continuous wavelength range that is at least 10 nm wide and lies in the visible wavelength range 42v, and for the at least one of mutually orthogonal first and second polarization states, the input light coupler 20 has a first average reflectance R1 for the first incident angle bl and a second average reflectance R2 for the second incident angle b2.

[0097] In some embodiments, the at least one continuous wavelength range includes at least the green wavelength range 42g and the red wavelength range 42r. In some embodiments, the at least one continuous wavelength range includes at least the blue wavelength range 42b.

[0098] In some embodiments, the at least one continuous wavelength range is at least 15 nm, at least 20 nm, at least 25 nm, or at least 30 nm wide. In some embodiments, the at least one continuous wavelength range (e.g., the green wavelength range 42g and the red wavelength range 42r) is about 20 nm wide.

[0099] In some embodiments, the first polarization state extends substantially along the x-axis and the orthogonal second polarization state extends substantially along the y-axis. In some embodiments, the first polarization state may correspond to a p-polarization state, while the second polarization state may correspond to an s-polarization state. In some embodiments, the at least one of the mutually orthogonal first and second polarization states includes the p-polarization state. In some embodiments, the at least one of the mutually orthogonal first and second polarization states includes the s-polarization state.

[0100] As is apparent from FIGS. 7 A and 7B, a ratio of the first average reflectance R1 and the second average reflectance R2 is greater than about 1.5, i.e., R1 / R2 is greater than about 1.5.

[0101] In some embodiments, R1 / R2 is greater than about 2, greater than about 2.5, greater than about 3, greater than about 3.5, greater than about 4, greater than about 4.5, greater than about 5, greater than about 5.5, greater than about 6, greater than about 7, greater than about 7.5, greater than about 10, greater than about 20, greater than about 30, greater than about 40, greater than about 50, greater than about 60, or greater than about 70.

[0102] As is apparent from the curve 802p, for the substantially collimated light 40 incident from within the optical core 10, for the first incident angle bl of about 0 degree, for the green wavelength range 42g, and for the first polarization state, the input light coupler 20 has the first average reflectance R1 of about 97.6%.

[0103] Further, as is apparent from the curve 802s, for the substantially collimated light 40 incident from within the optical core 10, for the first incident angle bl of about 0 degree, for the green wavelength range 42g, and for the second polarization state, the input light coupler 20 has the first average reflectance R1 of about 97.7%.

[0104] As is apparent from the curves 802p, 802s, for the substantially collimated light 40 incident from within the optical core 10, for the first incident angle bl of about 0 degree, for the red wavelength range 42r, and for the first and second polarization states, the input light coupler 20 has the first average reflectance R1 of about 97.5%.

[0105] Further, as is apparent from the curve 806p, for the substantially collimated light 41 incident from within the optical core 10, for the second incident angle b2 of about 65 degrees, and for the first polarization state, the input light coupler 20 has the second average reflectance R2 of about 1.9% for the green wavelength range 42g, and the second average reflectance R2 of about 1.3% for the red wavelength range 42r.

[0106] As is apparent from the curve 806s, for the substantially collimated light 41 incident from within the optical core 10, for the second incident angle b2 of about 65 degrees, and for the second polarization state, the input light coupler 20 has the second average reflectance R2 of about 21.6% for the green wavelength range 42g, and the second average reflectance R2 of about 13.5% for the red wavelength range 42r.

[0107] Therefore, in some embodiments, R1 / R2 is greater than about 30 (e.g., when the at least one of the first and second polarization states includes the first polarization state or the p-polarization state). In some embodiments, R1 / R2 is greater than about 35, greater than about 40, greater than about 45, greater than about 50, greater than about 55, greater than about 60, greater than about 65, greater than about 70, greater than about 75, or greater than about 80.

[0108] As is apparent from the curves 802p and 806p, in some embodiments, for the first polarization state, R1 / R2 is about 52.7 for the green wavelength range 42g and about 76.9 for the red wavelength range 42r. Further, as is apparent from the curves 802s and 806s, in some embodiments, for the second polarization state, R1 / R2 is about 4.5 for the green wavelength range 42g and about 7.2 for the red wavelength range 42r.

[0109] In some embodiments, the at least one continuous wavelength range includes at least the blue wavelength range 42b, and R1 / R2 is greater than about 5 (e.g., for the first polarization state). In some embodiments, R1 / R2 for the blue wavelength range 42b is greater than about 10, greater than about 15, or greater than about 18. As is apparent from the curves 802p and 806p, in some embodiments, for the first polarization state, R1 / R2 is about 18.4 for the blue wavelength range 42b.

[0110] Table. 1 provided below summarizes the first and second average reflectances Rl, R2 of the input light coupler 20 for different wavelength ranges and the first and second polarization states.Table 1

[0111] Table. 2 provided below summarizes the first and second average reflectances R1 / R2 of the input light coupler 20 for the different wavelength ranges and the first and second polarization states.Table 2

[0112] Referring to FIGS. 4 and 7A, in some embodiments, for the substantially collimated light 40, 41 incident from within the optical core 10, and for the at least one of the mutually orthogonal first and second polarization states, a plot of the reflectance of the input light coupler 20 versus wavelength includes a first band edge 43a for the first incident angle bl and a second band edge 43c for the second incident angle b2.

[0113] For example, for the substantially collimated light 40, 41 incident from within the optical core 10, and for the first polarization state, the curve 802p of the reflectance of the input light coupler 20 versus wavelength includes the first band edge 43a for the first incident angle bl of about 0 degree and the curve 806p of the reflectance of the input light coupler 20 versus wavelength includes the second band edge 43c for the second incident angle b2 of about 65 degrees.

[0114] Further, in the illustrated embodiment of FIG. 7A, for the substantially collimated light 41 incident from within the optical core 10, and for the first polarization state, the curve 804p of the reflectance of the input light coupler 20 versus wavelength includes a second band edge 43b for the second incident angle b2 of about 35 degrees.

[0115] In some embodiments, along each of the first and second band edges 43a, 43b, 43c, the reflectance of the input light coupler 20 decreases with increasing wavelength, such that along each of the first and second band edges 43a, 43b, 43c, the reflectance decreases by at least 50 percentage points when the wavelength increases by no more than about 50 nm.

[0116] In some embodiments, along each of the first and second band edges 43a, 43b, 43c, the reflectance of the input light coupler 20 decreases with increasing wavelength, such that along each of the first and second band edges 43a, 43b, 43c, the reflectance decreases by at least 55, at least 60, at least 65, at least 70, at least 75, at least 80, at least 85, at least 90, or at least 95 percentage points when the wavelength increases by no more than about 45 nm, no more than about 40 nm, no more than about 35 nm, no more than about 30 nm, no more than about 25 nm, or no more than about 20 nm.

[0117] As is apparent from the curves 802p, 804p, 806p, along each of the first and second band edges 43a, 43b, 43c, the reflectance of the input light coupler 20 decreases by about 90 percentage points when the wavelength increases by about 50 nm.

[0118] FIG. 8A shows a graph 900 depicting optical reflectance verses incident angle of the optical film 20 for the first polarization state, according to an embodiment of the present disclosure. FIG. 8B shows a graph 910 depicting optical reflectance verses incident angle of the optical film 20 for the second polarization state, according to an embodiment of the present disclosure.

[0119] In the graphs 900, 910, the incident angles are expressed in degrees in the abscissa and the optical reflectance is expressed in percentage (%) in the ordinate.

[0120] The graph 900 includes a curve 902p depicting the optical reflectance verses incident angle of the input light coupler 20 for the first polarization state and for the blue wavelength range 42b (shown in FIG. 7A).

[0121] The graph 900 further includes a curve 904p depicting the optical reflectance verses incident angle of the input light coupler 20 for the first polarization state and for the green wavelength range 42g (shown in FIG. 7A).

[0122] Further, the graph 900 includes a curve 906p depicting the optical reflectance verses incident angle of the input light coupler 20 for the first polarization state and for the red wavelength range 42r (shown in FIG. 7A).

[0123] The graph 910 includes a curve 902s depicting the optical reflectance verses incident angle of the input light coupler 20 for the second polarization state and for the blue wavelength range 42b (shown in FIG. 7A).

[0124] The graph 910 further includes a curve 904s depicting the optical reflectance verses incident angle of the input light coupler 20 for the second polarization state and for the green wavelength range 42g (shown in FIG. 7A).

[0125] Further, the graph 910 includes a curve 906s depicting the optical reflectance verses incident angle of the input light coupler 20 for the second polarization state and for the red wavelength range 42r (shown in FIG. 7A).

[0126] Referring to FIGS. 8A-8B, a non-overlapping continuous first range of larger angles 50b, 51b and a continuous second range of smaller angles 50a, 51a is also shown. Each of the first and second ranges of angles 50b, 51b, 50a, 51a is at least 10 degrees wide.

[0127] In some embodiments, each of the first and second ranges of angles 50b, 51b, 50a, 51a is at least 15 degrees, at least 20 degrees, at least 25 degrees, at least 30 degrees, at least 35 degrees, or at least 40 degrees wide.

[0128] As shown in the graph 900, the non-overlapping continuous first range of larger angles 50b is from about 62 degrees to about 84 degrees. Therefore, the first range of larger angles 50b is about 42 degrees wide. In some embodiments, the continuous second range of smaller angles 50a is from about 0 degree to about 41 degrees. Therefore, the second range of smaller angles 50a is about 41 degrees wide.

[0129] As shown in the graph 910, the non-overlapping continuous first range of larger angles 5 lb is from about 49 degrees to about 70 degrees. Therefore, the first range of larger angles 5 lb is about 21 degrees wide. In some embodiments, the continuous second range of smaller angles 51a is from about 0 degree to about 45 degrees. Therefore, the second range of smaller angles 51a is about 45 degrees wide.

[0130] For the at least the first polarization state, and for each of the blue wavelength range 42b, the green wavelength range 42g, and the red wavelength range 42r, for each first angle in thecontinuous first range of larger angles 50b, 51b, the optical film 20 reflects less than about 20% of the incident light ray 3 lb, 3 Ir.

[0131] In some embodiments, for the at least the first polarization state, and for each of the blue wavelength range 42b, the green wavelength range 42g, and the red wavelength range 42r, for each first angle in the continuous first range of larger angles 50b, 5 lb, the optical film 20 reflects less than about 15%, less than about 10%, or less than about 5% of the incident light ray 31b, 31r.

[0132] For the at least the first polarization state, and for each of the blue wavelength range 42b, the green wavelength range 42g, and the red wavelength range 42r, for each second angle in the continuous second range of smaller angles 50a, 51a, the optical film 20 reflects at least 70% of the incident light ray 3 lb, 3 Ir.

[0133] In some embodiments, for the at least the first polarization state, and for each of the blue wavelength range 42b, the green wavelength range 42g, and the red wavelength range 42r, for each second angle in the continuous second range of smaller angles 50a, 51a, the optical film 20 reflects at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the incident light ray 31b, 31r.

[0134] In some embodiments, for the incident light ray 31b, 3 Ir, for the at least the first polarization state, and for the at least one of the blue, green, and red wavelength ranges 42b, 42g, 42r, a plot (e.g., the curves 902p, 904p, 904s, 906s) of the average reflectance of the optical film 20 versus angle of incidence has a global minimum in the continuous first range of larger angles 50b, 5 lb.

[0135] For the substantially collimated light 40, 41 incident from within the optical core 10, for at least the first polarization state, and for the at least one continuous wavelength range that is at least 10 nm wide and lies in the visible wavelength range 42v, a plot of the average reflectance of the input light coupler 20 versus angle of incidence has a band edge where the average reflectance of the input light coupler 20 decreases with increasing incident angle, such that along the band edge, the average reflectance decreases by at least 30 percentage points when the incident angle increases by no more than about 10 degrees.

[0136] In some embodiments, for the substantially collimated light 40, 41 incident from within the optical core 10, for at least the first polarization state, and for the at least one continuous wavelength range that is at least 10 nm wide and lies in the visible wavelength range 42v, the plot of the average reflectance of the input light coupler 20 versus angle of incidence has the band edge where the average reflectance of the input light coupler 20 decreases with increasing incident angle, such that along the band edge, the average reflectance decreases by at least 35 percentage points, by at least 40 percentage points, by at least 45 percentage points, by at least 50 percentage points, by at least 55 percentage points, or by at least 60 percentage points when the incident angle increases by no more than about 8 degrees, no more than about 6 degrees, no more than about 5 degrees, no more than about 4 degrees, no more than about 3.5 degrees, or no more than about 3 degrees.

[0137] In the illustrated embodiment of FIG. 8 A, for the substantially collimated light 40, 41 incident from within the optical core 10, for at least the first polarization state, and for the bluewavelength range 42b, the curve 902p of the average reflectance of the input light coupler 20 versus angle of incidence has a band edge 52b where the average reflectance of the input light coupler 20 decreases with increasing incident angle, such that along the band edge 52b, the average reflectance decreases by about 60 percentage points when the incident angle increases about 3 degrees.

[0138] Further, for the substantially collimated light 40, 41 incident from within the optical core 10, for at least the first polarization state, and for the green wavelength range 42g, the curve 904p of the average reflectance of the input light coupler 20 versus angle of incidence has a band edge 52g where the average reflectance of the input light coupler 20 decreases with increasing incident angle, such that along the band edge 52g, the average reflectance decreases by about 60 percentage points when the incident angle increases about 4.5 degrees.

[0139] Furthermore, for the substantially collimated light 40, 41 incident from within the optical core 10, for at least the first polarization state, and for the red wavelength range 42r, the curve 906p of the average reflectance of the input light coupler 20 versus angle of incidence has a band edge 52r where the average reflectance of the input light coupler 20 decreases with increasing incident angle, such that along the band edge 52r, the average reflectance decreases by about 60 percentage points when the incident angle increases about 3.5 degrees.

[0140] FIG. 9 A shows an exemplary graph 1000 depicting layer thickness verses layer number for the first and second polymeric layers 21, 22 (shown in FIG. 6) of the input light coupler 20 (shown in FIG. 6). FIG. 9B shows a magnified graph 1010 depicting the layer thickness verses layer number for the first and second polymeric layers 21, 22 (shown in FIG. 6) of the input light coupler 20 (shown in FIG. 6).

[0141] In the graphs 1000, 1010, the layer numbers are expressed in the abscissa and the layer thickness is expressed in nanometers (nm) in the ordinate.

[0142] The graphs 1000, 1010 include a curve OF11 depicting the layer thickness verses layer number for the first polymeric layers 21 of the input light coupler 20.

[0143] The graphs 1000, 1010 further include a curve OF12 depicting the layer thickness verses layer number for the second polymeric layers 22 of the input light coupler 20.

[0144] Referring to FIGS. 6, 9A, and 9B, in some embodiments, the optical film 20 includes the plurality of polymeric layers 21, 22 numbering about 650 in total.

[0145] In some embodiments, the first polymeric layers 21 include polyethylene naphthalate (PEN) material. In some embodiments, the second polymeric layers 22 include glycol-modified polyethylene terephthalate (PETG) material.

[0146] FIG. 10 shows an exemplary graph 1100 depicting index verses wavelength for the first and second polymeric layers 21, 22 (shown in FIG. 6) of the optical film 20 (shown in FIG. 6).

[0147] In the graph 1100, the wavelength is expressed in the abscissa in nanometers (nm) and the index is expressed in the ordinate.

[0148] In some embodiments, the first and second polymeric layers 21, 22 have respective refractive indices nxl and nx2 along a same in -plane first direction (i.e., substantially along the x’-axis), respective refractive indices nyl and ny2 along a same in-plane second direction (i.e., substantially along the y’-axis) orthogonal to the first direction, and respective refractive indices nzl and nz2 along a same out-of-plane direction (i.e., substantially along the z’-axis) of the first and second polymeric layers 21, 22 orthogonal to the first and second directions.

[0149] In some embodiments, for at least one wavelength in the visible wavelength range 42v (shown in FIG. 7B), the refractive index nxl is about 1.741, the refractive index nyl is about 1.739, and the refractive index nzl is about 1.537. Further, for the at least one wavelength in the visible wavelength range 42v, each of the refractive indices nx2, ny2, and nz2 is about 1.577. Further, in some embodiments, the at least one wavelength in the visible wavelength range 42v is about 550 nm.

[0150] Referring to FIGS. 1 A to 10, typically, correct or intended light rays (i.e., the incident light ray 31b, 31r) are incident on the input light coupler 20 at smaller angles (i.e., the first incident angle bl) and the stray light rays (which may be caused due to the dual reflections on the input light coupler 20) are incident on the input light coupler 20 at larger angles (i.e., the second incident angle b2). As R1 / R2 is greater than about 1.5, the input light coupler 20 has a lower average reflectance for light incident at the greater angles (i.e., the stray light rays).

[0151] Since the input light coupler 20 has the lower average reflectance for the stray light rays, the stray light rays may substantially transmit through the input light coupler 20 and therefore may not propagate along the in-plane length-direction of the optical core 10. Thus, the undesired stray light may be eliminated and may not reach the viewer 90.

[0152] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0153] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

CLAIMS1. An optical waveguide comprising an optical core and an input light coupler embedded in the optical core between substantially parallel opposing first and second major surfaces of the optical core, the input light coupler making an oblique angle of between about 10 to about 60 degrees with the first and second major surfaces and configured to reflect at least a portion of an incident light ray that enters the optical core through one of the first and second major surfaces of the optical core so that a reflected light ray propagates along an in-plane length-direction of the optical core by undergoing total internal reflections at each of the first and second major surfaces of the optical core,such that for a substantially collimated light incident from within the optical core, a first incident angle of less than about 10 degrees and a second incident angle of greater than about 30 degrees, for at least one continuous wavelength range that is at least 10 nm wide and lies in a visible wavelength range extending from about 420 nm to about 680 nm, and for at least one of mutually orthogonal first and second polarization states, the input light coupler has a first average reflectance R1 for the first incident angle and a second average reflectance R2 for the second incident angle, R1 / R2 greater than about 1.5.

2. The optical waveguide of claim 1 further comprising an optical cladding disposed on, and covering substantially an entirety of, at least one of the opposing first and second major surfaces of the optical core and having an index of refraction less than an index of refraction of the optical core for at least one same wavelength in the visible wavelength range.

3. The optical waveguide of claim 1, wherein the first and second major surfaces of the optical core are substantially parallel to each other.

4. The optical waveguide of claim 1, wherein at least one of the first and second major surfaces of the optical core is an outermost major surface of the optical core.

5. The optical waveguide of claim 1, wherein the input light coupler is substantially planar.

6. The optical waveguide of claim 1, wherein the input light coupler comprises an optical film comprising a plurality of polymeric layers numbering at least 5 in total, each of the polymeric layers having an average thickness of less than about 1000 nm and greater than about 10 nm.

7. The optical waveguide of claim 6, wherein the optical core has an average thickness tl, the optical film has an average thickness t2, and t2 / tl is less than about 0.5.

8. The optical waveguide of claim 1, wherein the incident light ray enters the optical core through a region of the one of the first and second major surfaces, such that in a plan top view in a thickness direction of the optical waveguide, the region corresponds to the input light coupler.

9. The optical waveguide of claim 1, wherein the input light coupler extends across at least 70% of an entire thickness of the optical core.

10. The optical waveguide of claim 1, wherein the at least one continuous wavelength range comprises at least a green wavelength range extending from about 520 nm to about 540 nm and a red wavelength range extending from about 615 nm to about 635 nm.

11. The optical waveguide of claim 10, wherein the at least one continuous wavelength range comprises at least a blue wavelength range extending from about 455 nm to about 475 nm, and wherein R1 / R2 is greater than about 5.

12. The optical waveguide of claim 1, wherein for a substantially collimated light incident from within the optical core, and for the at least one of the mutually orthogonal first and second polarization states, a plot of a reflectance of the input light coupler versus wavelength comprises a first band edge for the first incident angle and a second band edge for the second incident angle, where along each of the first and second band edges, the reflectance of the input light coupler decreases with increasing wavelength, such that along each of the first and second band edges, the reflectance decreases by at least 50 percentage points when the wavelength increases by no more than about 50 nm.

13. An optical waveguide comprising an optical film disposed between opposing first and second major surfaces of the optical waveguide, the optical film positioned relative to a thickness direction of the optical waveguide so that for a light ray that enters the optical waveguide and is incident on the optical film, for non-overlapping continuous first range of larger angles and continuous second range of smaller angles, each of the first and second ranges of angles being at least 10 degrees wide, for at least a first polarization state, and for each of a blue wavelength range extending from about 455 nm to about 475 nm, a green wavelength range extending from about 520 nm to about 540 nm, and a red wavelength range extending from about 615 nm to about 635 nm:for each first angle in the continuous first range of larger angles, the optical film reflects less than about 20% of the incident light ray; andfor each second angle in the continuous second range of smaller angles, the optical film reflects at least 70% of the incident light ray, the reflected light ray propagating along a length-direction of the optical waveguide by undergoing a plurality of total internal reflections.

14. The optical waveguide of claim 13, wherein for the incident light ray, for the at least the first polarization state, and for at least one of the blue, green, and red wavelength ranges, a plot of an average reflectance of the optical film versus angle of incidence has a global minimum in the continuous first range of larger angles.

15. An optical system comprising:a display configured to form and emit an image comprising an emitted image light; and an optical waveguide comprising an optical core, an input light coupler, and an output light coupler, the input light coupler embedded in the optical core between opposing first and second major surfaces of the optical core,the input light coupler configured to receive at least a portion of the emitted image light that enters the optical core, the received image light propagating toward the output light coupler by undergoing multiple reflections at each of the first and second major surfaces of the optical core, the output light coupler configured to extract at least a portion of the propagating image light out of the optical core for viewing by a viewer;such that for a substantially collimated light incident from within the optical core, for at least a first polarization state, and for at least one continuous wavelength range that is at least 10 nm wide and lies in a visible wavelength range that extends from about 420 nm to about 680 nm, a plot of an average reflectance of the input light coupler versus angle of incidence has a band edge where the average reflectance of the input light coupler decreases with increasing incident angle, such that along the band edge, the average reflectance decreases by at least 30 percentage points when the incident angle increases by no more than about 10 degrees.

Images