Color separation in waveguides using dichroic filters

Abstract

To provide improved methods and systems related to augmented reality systems.SOLUTION: An eyepiece for projecting an image to an eye of a viewer includes a first planar waveguide positioned in a first lateral plane, a second planar waveguide positioned in a second lateral plane adjacent to the first lateral plane, and a third planar waveguide positioned in a third lateral plane adjacent to the second lateral plane. The first waveguide includes a first diffractive optical element (DOE) coupled thereto and disposed at a lateral position. The second waveguide includes a second DOE coupled thereto and disposed at the lateral position. The third waveguide includes a third DOE coupled thereto and disposed at the lateral position. The eyepiece further includes a first optical filter disposed between the first waveguide and the second waveguide at the lateral position, and a second optical filter positioned between the second waveguide and the third waveguide at the lateral position.SELECTED DRAWING: Figure 1

Description

[Background technology]

[0001] (Citation of Related Application) This application claims the benefit of U.S. Provisional Patent Application No. 62 / 438,315, filed December 22, 2016, the contents of which are incorporated herein by reference in their entirety.

[0002] BACKGROUND OF THEINVENTION Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences in which digitally reproduced images, or portions thereof, are presented to a viewer in a manner that appears or can be perceived as real. Virtual reality, or "VR", scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, while augmented reality, or "AR", scenarios typically involve the presentation of digital or virtual image information as an augmentation to the visualization of the real world around the viewer.

[0003] Despite the advances made in these display technologies, there is a need in the art for improved methods and systems relating to augmented reality systems. Summary of the Invention [Means for solving the problem]

[0004] SUMMARY OF THEINVENTION According to an embodiment of the present invention, an eyepiece for projecting an image to a viewer's eye includes a first planar waveguide positioned in a first lateral plane, a second planar waveguide positioned in a second lateral plane adjacent to the first lateral plane, and a third planar waveguide positioned in a third lateral plane adjacent to the second lateral plane. The first waveguide includes a first diffractive optical element (DOE) coupled thereto and disposed at a lateral position. The first DOE is configured to diffract image light in a first wavelength range centered on a first wavelength. The second waveguide includes a second DOE coupled thereto and disposed at a lateral position. The second DOE is configured to diffract image light in a second wavelength range centered on a second wavelength longer than the first wavelength. The third waveguide includes a third DOE coupled thereto and disposed at a lateral position. The third DOE is configured to diffract the image light in a third wavelength range centered on a third wavelength longer than the second wavelength. The eyepiece further includes a first optical filter disposed between the first and second waveguides in a lateral position, and a second optical filter disposed between the second and third waveguides in a lateral position. The first optical filter is configured to have a first transmittance value in the first wavelength range, a second transmittance value in the second and third wavelength ranges that is greater than the first transmittance value, and a first reflectance value in the first wavelength range that is greater than about 90%. The second optical filter is configured to have a third transmittance value in the first and second wavelength ranges, a fourth transmittance value in the third wavelength range that is greater than the third transmittance value, and a second reflectance value in the second wavelength range that is greater than about 90%. In some examples, the first and third transmittance values ​​may each be less than about 10% and the second and fourth transmittance values ​​may each be greater than about 90%. In certain other examples, the first and third transmittance values ​​may each be less than about 20% and the second and fourth transmittance values ​​may each be greater than about 80%.In some examples, the first optical filter can be configured to have a first transmittance value and a second transmittance value for angles of incidence ranging from about zero degrees to about 45 degrees, and the second optical filter can be configured to have a third transmittance value and a fourth transmittance value for angles of incidence ranging from about zero degrees to about 45 degrees. In certain other examples, the first optical filter can be configured to have a first transmittance value and a second transmittance value for angles of incidence ranging from about zero degrees to about 25 degrees, and the second optical filter can be configured to have a third transmittance value and a fourth transmittance value for angles of incidence ranging from about zero degrees to about 25 degrees.

[0005] According to another embodiment of the present invention, an eyepiece for projecting an image to a viewer's eye includes a first planar waveguide positioned in a first lateral plane. The first waveguide has a first lateral region and a second lateral region. The first lateral region is disposed in a lateral position and configured to receive image light incident on its first lateral surface. The image light includes image light in a first wavelength range centered on a first wavelength, image light in a second wavelength range centered on a second wavelength longer than the first wavelength, and image light in a third wavelength range centered on a third wavelength longer than the second wavelength. The eyepiece further includes a first diffractive optical element (DOE) optically coupled to the first lateral region of the first waveguide and configured to diffract the image light in the first wavelength range into the first waveguide such that it is directed toward the second lateral region of the first waveguide. A first portion of the image light is transmitted through the first waveguide. The eyepiece further includes a first optical filter positioned in a second lateral plane adjacent to the first lateral plane in the lateral position and configured to receive the first portion of the image light. The first optical filter is further configured to have a first transmittance value for the first wavelength range and second transmittance values ​​for the second wavelength range and the third wavelength range that are greater than the first transmittance value. The eyepiece further includes a second planar waveguide positioned in a planar third lateral plane adjacent to the second lateral. The second waveguide has a first lateral region and a second lateral region. The first region is positioned in the lateral position and configured to receive the image light transmitted through the first optical filter and incident on its first lateral surface. The eyepiece further includes a second DOE optically coupled to the first lateral region of the second waveguide and configured to diffract image light within a second wavelength range into the second waveguide such that the image light is directed toward the second lateral region of the second waveguide. A second portion of the image light is transmitted through the second waveguide. The eyepiece further includes a second optical filter positioned in a fourth lateral plane adjacent to the third lateral plane in the lateral position and configured to receive the second portion of the image light.The second optical filter is configured to have a third transmittance value for the first wavelength range and the second wavelength range, and a fourth transmittance value for the third wavelength range that is greater than the third transmittance value. The eyepiece further includes a third planar waveguide positioned in a fifth lateral plane adjacent to the fourth lateral plane. The third waveguide has a first lateral region and a second lateral region. The first lateral region is disposed in a lateral position and configured to receive image light transmitted through the second optical filter and incident on its first lateral surface. The eyepiece further includes a third DOE optically coupled to the first lateral region of the third waveguide and configured to diffract image light within the third wavelength range into the third waveguide such that it is directed toward the second lateral region of the third waveguide.

[0006] According to yet another embodiment of the present invention, an eyepiece for projecting image light to a viewer's eye includes a first planar waveguide. The first waveguide includes a first diffractive optical element (DOE) optically coupled thereto. The first DOE is positioned along an optical path of the image light and configured to couple a portion of the image light in a first wavelength range centered on a first wavelength into the first planar waveguide such that the portion is propagated within the first planar waveguide. The eyepiece further includes a first optical filter positioned along the optical path downstream of the first DOE. The first optical filter is configured to attenuate image light in the first wavelength range incident thereon. The eyepiece further includes a second planar waveguide. The second waveguide includes a second DOE optically coupled thereto. The second DOE is positioned along the optical path downstream of the first optical filter and configured to couple a portion of the image light in a second wavelength range centered on a second wavelength different from the first wavelength into the second planar waveguide such that it is propagated in the second planar waveguide. The eyepiece further includes a second optical filter coupled to the first planar waveguide. The second optical filter is configured to absorb the image light in the second wavelength range propagating in the first planar waveguide.

[0007] According to a further embodiment of the invention, an eyepiece for projecting an image to a viewer's eye includes a first planar waveguide positioned in a first lateral plane, a second planar waveguide positioned in a second lateral plane adjacent to the first lateral plane, and a third planar waveguide positioned in a third lateral plane adjacent to the second lateral plane. The first waveguide includes a first diffractive optical element (DOE) coupled thereto and positioned at a first lateral position. The second waveguide includes a second DOE coupled thereto and positioned at a second lateral position. The third waveguide includes a third DOE coupled thereto and positioned at a second lateral position. The eyepiece further includes an optical filter positioned between the second and third waveguides at the second lateral position.

[0008] According to some other embodiments of the invention, an eyepiece for projecting an image to a viewer's eye includes a first planar waveguide positioned in a first lateral plane. The first waveguide includes a first internal coupling element optically coupled thereto. The first internal coupling element is configured to diffract image light in a first wavelength range centered on a first wavelength. The eyepiece further includes a second planar waveguide positioned in a second lateral plane adjacent the first lateral plane. The second waveguide includes a second internal coupling element optically coupled thereto. The second internal coupling element is configured to diffract image light in a second wavelength range centered on a second wavelength different from the first wavelength. The eyepiece further includes a first optical element positioned between the first and second waveguides in lateral alignment with the first internal coupling element. The first optical element is configured to reflect image light in the first wavelength range. The present invention provides, for example, the following items. (Item 1) 1. An eyepiece for projecting an image onto a viewer's eye, the eyepiece comprising: a first planar waveguide positioned in a first lateral plane, the first waveguide having a first diffractive optical element (DOE) coupled thereto and disposed at a lateral position, the first DOE configured to diffract image light in a first wavelength range centered on a first wavelength; a second planar waveguide positioned in a second lateral plane adjacent to the first lateral plane, the second waveguide having a second DOE coupled thereto and disposed at the lateral location, the second DOE configured to diffract image light in a second wavelength range centered on a second wavelength longer than the first wavelength; a third planar waveguide positioned in a third lateral plane adjacent to the second lateral plane, the third waveguide having a third DOE coupled thereto and disposed at the lateral location, the third DOE configured to diffract image light in a third wavelength range centered on a third wavelength longer than the second wavelength; a first optical filter disposed between the first waveguide and the second waveguide at the lateral position, the first optical filter comprising: a first transmittance value in the first wavelength range; and a second transmittance value in the second wavelength range and the third wavelength range, the second transmittance value being greater than the first transmittance value; and a first reflectance value in the first wavelength range that is greater than about 90%; and A first optical filter configured to have a second optical filter disposed between the second waveguide and the third waveguide at the lateral position, the second optical filter comprising: a third transmittance value in the first wavelength range and the second wavelength range; and a fourth transmittance value in the third wavelength range, the fourth transmittance value being greater than the third transmittance value; and a second reflectance value in the second wavelength range that is greater than about 90%; and a second optical filter configured to have The eyepiece is provided with: (Item 2) 2. The eyepiece lens of claim 1, wherein each of the first DOE, the second DOE, and the third DOE is provided with an internal coupling grating. (Item 3) 2. The eyepiece lens of item 1, wherein each of the first transmittance value and the third transmittance value is less than approximately 10%, and each of the second transmittance value and the fourth transmittance value is greater than approximately 90%. (Item 4) The eyepiece lens described in item 3, wherein the first optical filter is configured to have the first transmittance value and the second transmittance value for angles of incidence ranging from about zero degrees to about 45 degrees, and the second optical filter is configured to have the third transmittance value and the fourth transmittance value for angles of incidence ranging from about zero degrees to about 45 degrees. (Item 5) 2. The eyepiece of claim 1, wherein the first wavelength range is centered substantially at 462 nm, the second wavelength range is centered substantially at 528 nm, and the third wavelength range is centered substantially at 635 nm. (Item 6) The eyepiece lens described in item 1, further comprising an optical reflector positioned in a sixth lateral plane adjacent to the fifth lateral plane in the lateral position, the optical reflector configured to reflect image light transmitted through the third waveguide. (Item 7) a first shortpass filter optically coupled to a second lateral region of the first waveguide and configured to absorb image light in the second wavelength range; a second shortpass filter optically coupled to the second lateral region of the second waveguide and configured to absorb image light in the third wavelength range; and 2. The eyepiece of item 1, further comprising: (Item 8) The eyepiece lens described in item 7, wherein the first short-pass filter is disposed inside the second lateral region of the first waveguide, and the second short-pass filter is disposed inside the second lateral region of the second waveguide. (Item 9) 8. An eyepiece lens as described in item 7, wherein the first short-pass filter is disposed within a cavity inside the second lateral region of the first waveguide, and the second short-pass filter is disposed within a cavity inside the second lateral region of the second waveguide. (Item 10) The eyepiece lens described in item 7, wherein the first short-pass filter is disposed on a first lateral surface of the second lateral region of the first waveguide, and the second short-pass filter is disposed on the first lateral surface of the second lateral region of the second waveguide. (Item 11) 1. An eyepiece for projecting image light to an eye of a viewer, the image light including image light in a first wavelength range centered on a first wavelength and image light in a second wavelength range centered on a second wavelength different from the first wavelength, the eyepiece comprising: a first planar waveguide, the first planar waveguide including a first diffractive optical element (DOE) optically coupled thereto, the first DOE being positioned along an optical path of the image light and configured to couple a portion of the image light in the first wavelength range into the first planar waveguide such that the portion is propagated within the first planar waveguide; a first optical filter positioned along the optical path downstream of the first DOE, the first optical filter configured to attenuate image light in the first wavelength range incident thereon; and a second planar waveguide including a second DOE optically coupled thereto, the second DOE being positioned along the optical path downstream of the first optical filter and configured to couple a portion of the image light in the second wavelength range transmitted through the first optical filter into the second planar waveguide for it to propagate within the second planar waveguide; a second optical filter coupled to the first planar waveguide; and Equipped with The second optical filter is configured to absorb image light in the second wavelength range propagating within the first planar waveguide, and the eyepiece lens. (Item 12) Item 12. The eyepiece lens of item 11, wherein the second wavelength is longer than the first wavelength, and the first optical filter comprises a long-pass filter configured to have a first transmittance value for the first wavelength range less than approximately 10% and a second transmittance value for the second wavelength range greater than approximately 90%. (Item 13) The eyepiece lens of item 12, wherein the second optical filter comprises a short-pass filter configured to have a first transmittance value for the second wavelength range less than approximately 10% and a second transmittance value for the first wavelength range greater than approximately 90%. (Item 14) Item 12. The eyepiece lens of item 11, wherein the second wavelength is shorter than the first wavelength, and the first optical filter comprises a short-pass filter configured to have a first transmittance value for the first wavelength range less than approximately 10% and a second transmittance value for the second wavelength range greater than approximately 90%. (Item 15) Item 15. The eyepiece lens of item 14, wherein the second optical filter comprises a long-pass filter configured to have a first transmittance value for the second wavelength range less than approximately 10% and a second transmittance value for the first wavelength range greater than approximately 90%. (Item 16) 1. An eyepiece for projecting an image onto a viewer's eye, the eyepiece comprising: a first planar waveguide positioned in a first lateral plane, the first waveguide having a first internal coupling element optically coupled thereto, the first internal coupling element configured to diffract image light in a first wavelength range centered on a first wavelength; a second planar waveguide positioned in a second lateral plane adjacent to the first lateral plane, the second waveguide having a second internal coupling element optically coupled thereto, the second internal coupling element configured to diffract image light in a second wavelength range centered on a second wavelength different from the first wavelength; a first optical element positioned between the first waveguide and the second waveguide in lateral alignment with the first internal coupling element; Equipped with The first optical element is configured to reflect image light in the first wavelength range, an eyepiece. (Item 17) 17. The eyepiece lens of item 16, wherein the first waveguide has a first surface and a second surface opposite the first surface, the second waveguide has a first surface and a second surface opposite the first surface, and the first surface of the second waveguide faces the second surface of the first waveguide. (Item 18) Item 18. An eyepiece lens as described in item 17, wherein the first internal coupling element is disposed on the second surface of the first waveguide adjacent to the first surface of the second waveguide. (Item 19) 18. The eyepiece lens of item 17, further comprising a second optical element laterally aligned with the second internal coupling element and positioned adjacent to the second surface of the second waveguide, the second optical element configured to reflect image light in the second wavelength range. (Item 20) 20. An eyepiece lens as described in item 19, wherein the second internal coupling element is positioned laterally offset from the first internal coupling element. (Item 21) 21. The eyepiece lens of item 20, wherein the first optical element is further configured to reflect image light in the second wavelength range. (Item 22) 20. The eyepiece of item 19, further comprising a third planar waveguide positioned in a third lateral plane adjacent to the second lateral plane, the third waveguide having a third internal coupling element coupled thereto, the third internal coupling element configured to diffract image light in a third wavelength range centered on the first wavelength and a third wavelength different from the second wavelength. (Item 23) 23. An eyepiece lens as described in item 22, wherein the second internal coupling element is positioned in lateral alignment with the third internal coupling element. (Item 24) 23. An eyepiece lens as described in item 22, wherein the second optical element is configured to have a reflectance value in the second wavelength range greater than approximately 90%. (Item 25) 25. The eyepiece lens of item 24, wherein the second optical element is further configured to have a transmittance value in the third wavelength range greater than about 90%. (Item 26) 25. The eyepiece lens of item 24, further comprising a third optical element positioned laterally aligned with the third internal coupling element, the third optical element configured to reflect image light in the third wavelength range. (Item 27) 27. The eyepiece lens of item 26, wherein the third optical element is further configured to reflect image light in the second wavelength range. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 diagrammatically illustrates light paths within a portion of a viewing optical assembly (VOA) that may be used to present a digital or virtual image to a viewer, according to one embodiment of the present invention. [Diagram 2] FIG. 2 illustrates diagrammatically one method of color separation in the eyepiece for viewing a virtual image. [Diagram 3] FIG. 3 diagrammatically illustrates another method of color separation in an eyepiece for viewing a virtual image, according to one embodiment of the present invention. [Figure 4] FIG. 4 diagrammatically illustrates a plan view of an eyepiece according to one embodiment of the present invention. [Diagram 5] FIG. 5 diagrammatically illustrates a partial cross-sectional view of an eyepiece according to one embodiment of the present invention. [Figure 6] 6A-6D illustrate several example images formed by an eyepiece without a filter, and 6E-6H illustrate several example images formed by an eyepiece with a dichroic filter, according to an embodiment of the present invention. [Figure 7] FIG. 7 diagrammatically illustrates the transmittance / reflectance curves of an optical filter according to one embodiment of the present invention. [Figure 8] FIG. 8 diagrammatically illustrates the transmittance / reflectance curves of an optical filter according to another embodiment of the present invention. [Figure 9] 9A and 9B diagrammatically illustrate a partial cross-sectional view of a waveguide including a shortpass filter coupled thereto, according to an embodiment of the present invention; [Figure 10] FIG. 10 diagrammatically illustrates a partial cross-sectional view of a waveguide including a shortpass filter coupled thereto, in accordance with an embodiment of the present invention. [Figure 11] 11A-11D illustrate the wavelength cross-coupling effect of a waveguide within the eyepiece. [Figure 12]12A-12C diagrammatically illustrate partial cross-sectional views of a waveguide including a shortpass filter coupled thereto, in accordance with an embodiment of the present invention. [Figure 13] 13A-13C illustrate partial cross-sectional views of an eyepiece according to various embodiments of the present invention. [Figure 14] FIG. 14 graphically illustrates the transmittance / reflectance curves of an optical filter according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Detailed Description of Specific Embodiments The present disclosure generally relates to an eyepiece that can be used for virtual reality and augmented reality visualization systems. More specifically, the present invention relates to an eyepiece that includes one or more long-pass dichroic filters for color separation between different waveguides. The eyepiece may also include one or more short-pass dichroic filters to further reduce wavelength cross-coupling. Such an eyepiece may provide reduced wavelength cross-coupling compared to conventional eyepieces, as well as a more compact form factor and improved brightness and contrast of the bright field.

[0011] FIG. 1 diagrammatically illustrates light paths in a portion of a viewing optical assembly (VOA) that may be used to present a digital or virtual image to a viewer, according to an embodiment of the present invention. The VOA includes a projector 101 and an eyepiece 100 that may be worn around the viewer's eye. In some embodiments, the projector 101 may include a group of red LEDs, a group of green LEDs, and a group of blue LEDs. For example, the projector 101 may include two red LEDs, two green LEDs, and two blue LEDs, according to an embodiment. The eyepiece 100 may include one or more eyepiece layers. In one embodiment, the eyepiece 100 includes three eyepiece layers, one eyepiece layer for each of the three primary colors, red, green, and blue. In another embodiment, the eyepiece 100 may include six eyepiece layers, i.e., one set of eyepiece layers for each of the three primary colors configured to form a virtual image at one depth plane, and another set of eyepiece layers for each of the three primary colors configured to form a virtual image at another depth plane. In other embodiments, the eyepiece 100 may include three or more eyepiece layers for each of the three primary colors for three or more different depth planes. Each eyepiece layer may include a planar waveguide, and each eyepiece layer may include an internal coupling grating 107, an orthogonal pupil expander (OPE) region 108, and an exit pupil expander (EPE) region 109.

[0012] Still referring to FIG. 1 , the projector 101 projects image light onto an internal coupling grating 107 in the eyepiece layer 100. The internal coupling grating 107 couples the image light from the projector 101 into a planar waveguide that propagates in a direction toward the OPE region 108. The waveguide propagates the image light horizontally by total internal reflection (TIR). The OPE region 108 of the eyepiece layer 100 also includes diffractive elements that couple a portion of the image light propagating in the waveguide and redirect it to the EPE region 109. The EPE region 109 includes diffractive elements that couple a portion of the image light propagating in the waveguide and redirect it toward the viewer's eye 102 in a direction approximately perpendicular to the plane of the eyepiece layer 100. In this way, the image projected by the projector 101 can be viewed by the viewer's eye 102. A portion of the VOA illustrated in FIG. 1 may constitute a "monocular" for one eye of the viewer. The entire VOA may include two such monoculars, one for each of the viewer's eyes.

[0013] As described above, the image light generated by the projector may include three primary colors, namely, blue (B), green (G), and red (R) light. Such image light would need to be separated into constituent colors so that the image light of each constituent color can be coupled into a respective waveguide in the eyepiece. FIG. 2 diagrammatically illustrates one method of color separation using a "split pupil" approach. In this example, the eyepiece 230 includes a blue waveguide 240, a green waveguide 250, and a red waveguide 260. Each waveguide 240, 250, or 260 may include an internal coupling grating (ICG) 242, 252, or 262, an orthogonal pupil expander (OPE) region 244, 254, or 264, and an exit pupil expander (EPE) region 246, 256, or 266. The ICG, OPE, and EPE in each waveguide are designed for a specific wavelength range. For example, ICG 242 in blue waveguide 240 may include a diffractive optical element (DOE) configured to primarily diffract blue light into blue waveguide 240 so that it is directed toward OPE region 244. OPE region 244 of blue waveguide 240 may include a DOE configured to primarily diffract blue light EPE toward region 246. EPE region 246 of blue waveguide 240 may include a DOE configured to primarily diffract blue light toward the viewer's eye 270.

[0014] 2, color separator 220 may separate the blue, green, and red image light generated by projector subsystem 210 into three spatially distinct light paths: blue light path 248, green light path 258, and red light path 268. ICGs 242, 252, and 262 in blue, green, and red waveguides 240, 250, and 260 may be laterally offset from one another such that ICG 242 for blue waveguide 240 may be aligned with blue light path 248, ICG 252 for green waveguide 250 may be aligned with green light path 258, and ICG 262 for red waveguide 260 may be aligned with red light path 268. The eyepiece 230 illustrated in FIG. 2 may have a relatively large form factor because the ICGs 242, 252, and 262 in the three waveguides 240, 250, and 260 need to be laterally displaced relative to one another.

[0015] FIG. 3 diagrammatically illustrates another method of color separation using an “in-line” approach, according to an embodiment of the present invention. In this example, eyepiece lens 330 may also include blue waveguide 340, green waveguide 350, and red waveguide 360. Each waveguide 340, 350, or 360 may include an ICG 342, 352, or 362, an OPE region 344, 354, or 364, and an EPE region 346, 356, or 366. Here, the blue, green, and red image light generated by projector subsystem 310 is not spatially separated from one another, and ICGs 342, 352, and 362 in blue, green, and red waveguides 340, 350, and 360 are aligned laterally with respect to one another. Thus, the image light passes through each waveguide in succession, in a “back-to-back” manner. The eyepiece 330 may further include a first wavelength-selective optical element 392 positioned between the ICG 342 in the blue waveguide 340 and the ICG 352 in the green waveguide 350, and a second wavelength-selective optical element 394 positioned between the ICG 352 in the green waveguide 350 and the ICG 362 in the red waveguide 360. The first and second wavelength-selective optical elements 392 and 394 may represent, for example, wavelength-selective optical filters (i.e., optical elements that selectively transmit light within a particular range of wavelengths) and / or wavelength-selective optical reflectors (i.e., mirrors and other optical elements that selectively reflect light within a particular range of wavelengths). As described in more detail below, a dichroic filter is one example of an optical element that is configured to both selectively transmit and reflect light based on wavelength. Hereinafter, the first and second wavelength-selective optical elements 392 and 394 may also be referred to as "optical filter 392" and "optical filter 394", respectively. Similarly, the other wavelength-selective optical elements described with reference to any of Figures 4-14 may also be referred to herein as "optical filters."

[0016] As illustrated in FIG. 3, all three colors of image light are incident on the ICG 342 in the blue waveguide 340. The ICG 342 in the blue waveguide 340 may couple a portion of the image light primarily in the blue wavelength range into the blue waveguide 340 such that it is directed toward the OPE region 344. The ICG 342 in the blue waveguide 340 may couple a small amount of green image light and even a smaller amount of red light into the blue waveguide 340, as will be discussed further below. Image light that is not coupled into the blue waveguide 340 is transmitted through the blue waveguide 340 and incident on the first optical filter 392. The first optical filter 392 may be configured to have high transmittance values ​​in the green and red wavelength ranges and low transmittance values ​​in the blue wavelength range. Thus, the image light transmitted by the first optical filter 392 and incident on the ICG 352 in the green waveguide 350 contains primarily green and red image light, and may contain little or no blue image light.

[0017] Still referring to FIG. 3 , the ICG 352 in the green waveguide 350 may couple a portion of the image light in the green wavelength range into the green waveguide 350 such that it is directed toward the OPE region 354. The ICG 352 in the green waveguide 350 may couple a small amount of red image light into the green waveguide 350, as will be discussed further below. Image light that is not coupled into the green waveguide 350 may be transmitted through the green waveguide 350 and incident on the second optical filter 394. The second optical filter 394 may be configured to have a high transmittance value in the red wavelength range and a low transmittance value in the green and blue wavelength ranges. Thus, the image light transmitted by the second optical filter 394 and incident on the ICG 362 in the red waveguide 360 ​​may include primarily red image light and little or no green and blue image light. The ICG 362 in the red waveguide 360 ​​may couple a portion of the image light primarily in the red wavelength range into the red waveguide 360 ​​so that it is directed toward the OPE region 364 .

[0018] FIG. 4 diagrammatically illustrates a plan view of an eyepiece 400, according to an embodiment of the present invention. The eyepiece 400 may include a blue waveguide 440, a green waveguide 450, and a red waveguide 460 stacked in adjacent lateral planes. Each waveguide 440, 450, or 460 may include an ICG region 410, an OPE region 420, and an EPE region 430. The ICG regions 410 for the three waveguides 440, 450, and 460 may be disposed at the same lateral location and thus stacked along the same optical path. A first optical filter 492 may be positioned between the ICG 410 of the blue waveguide 440 and the ICG 410 of the green waveguide 450. A second optical filter 492 may be positioned between the ICG 410 of the green waveguide 450 and the ICG 410 of the red waveguide 460. The eyepiece 400 illustrated in Figure 4 may function substantially as described above with respect to Figure 3. The eyepiece illustrated in Figures 3 and 4 may have a smaller form factor as compared to the eyepiece 230 illustrated in Figure 2 because the ICGs 410 in the three waveguides 440, 450, and 460 are located in the same lateral position instead of being laterally displaced from one another.

[0019] FIG. 5 diagrammatically illustrates a partial cross-sectional view of an eyepiece 500, according to an embodiment of the present invention. The eyepiece 500 may include a first planar waveguide 510 disposed in a first lateral plane. The first waveguide 510 may include a first lateral region (labeled as X10) and a second lateral region (labeled as X11). The first lateral region (X10) may be disposed in a lateral position and configured to receive image light (X02) incident on its first lateral surface. The image light (X02) may include image light in a first wavelength range, image light in a second wavelength range, and image light in a third wavelength range. For example, the first wavelength range may be centered at approximately 462 nm wavelengths corresponding to blue light, the second wavelength range may be centered at approximately 528 nm wavelengths corresponding to green light, and the third wavelength range may be centered at approximately 635 nm wavelengths corresponding to red light.

[0020] The eyepiece 500 may further include a first diffractive optical element (DOE) 512 optically coupled to a first lateral region (X10) of the first waveguide 510. The first DOE 512 may include an internal coupling grating (ICG) formed either on a first surface of the first waveguide 510 (as shown in FIG. 5) or on a second surface of the first waveguide 510 opposite the first surface. The first DOE may be configured to diffract image light in a first wavelength range, e.g., blue image light (X14), into the first waveguide 510 such that it is directed toward a second lateral region (X11) of the first waveguide 510. The second lateral region (X11) may be a region between the ICG and the OPE (not shown). A portion of the image light (X12) that is not coupled into the first waveguide 510 may be transmitted through the first waveguide 510.

[0021] The eyepiece 500 may further include a first optical filter 520 positioned in a second lateral plane adjacent to the first lateral plane at the same lateral position as the first lateral region (X10) of the first waveguide 510. The first optical filter 520 may be configured to receive a portion of the image light (X12) transmitted through the first waveguide 510. In one embodiment, the first optical filter 520 may be configured as a long-pass filter to have high transmittance values ​​for wavelength ranges corresponding to green and red light and low transmittance values ​​for wavelength ranges corresponding to blue light. Thus, the image light transmitted by the first optical filter 520 (X22) may include primarily green and red image light.

[0022] The eyepiece 500 may further include a second planar waveguide 530 positioned in a third lateral plane adjacent to the second lateral plane. The second waveguide 530 may have a first lateral region (X30) and a second lateral region (X31). The first lateral region (X30) may be located in the same lateral position as the first lateral region of the first waveguide 510 and may be configured to receive image light transmitted by the first optical filter 520 (X22) incident on its first lateral surface.

[0023] The eyepiece may further include a second diffractive optical element (DOE) 532 optically coupled to a first lateral region (X30) of the second waveguide 530. The second DOE 532 may include an internal coupling grating (ICG) formed on either a first surface of the second waveguide 530 (as shown in FIG. 5) or a second surface of the second waveguide 530 opposite the first surface. The second DOE 532 may be configured to diffract image light within a second wavelength range, e.g., green image light (X34), into the second waveguide 530 such that it is directed toward a second lateral region (X31) of the second waveguide 530. The second lateral region (X31) may be a region between the ICG and the OPE (not shown). A portion of the image light (X32) that is not coupled into the second waveguide 530 may be transmitted through the second waveguide 530.

[0024] The eyepiece may further include a second optical filter 540 positioned in a fourth lateral plane adjacent to the third lateral plane at the same lateral position as the first lateral region (X30) of the second waveguide 530. The second optical filter 540 may be configured to receive a portion of the image light (X32) transmitted through the second waveguide 530. In one embodiment, the second optical filter 540 may be configured as a long-pass filter to have a high transmittance value for a wavelength range corresponding to red light and a low transmittance value for a wavelength range corresponding to blue and green light. Thus, the image light transmitted by the second optical filter 540 (X42) may mainly include red image light.

[0025] The eyepiece 500 may further include a third planar waveguide 550 positioned in a fifth lateral plane adjacent to the fourth lateral plane. The third waveguide 550 may have a first lateral region (X50) and a second lateral region (X51). The first lateral region (X50) may be located in the same lateral position as the first lateral region (X30) of the second waveguide 530 and may be configured to receive image light transmitted by the second optical filter 540 (X42) incident on its first lateral surface.

[0026] The eyepiece 500 may further include a third diffractive optical element (DOE) 552 optically coupled to a first side region (X50) of the third waveguide 550. The third DOE 552 may include an internal coupling grating (ICG) (not shown) formed on either a first surface of the third waveguide 550 (as shown in FIG. 5) or a second surface of the third waveguide 550 opposite the first surface. The third DOE 552 may be configured to diffract image light within a third wavelength range, e.g., red image light (X54), into the third waveguide 550 such that it is directed toward a second side region (X51) of the third waveguide 550. The second side region (X51) may be a region between the ICG and the OPE (not shown). A portion of the image light (X52) that is not coupled into the third waveguide 550 may be transmitted through the third waveguide 550.

[0027] According to some other embodiments, the order of the red-green-blue waveguides 510, 530, and 550 may differ from that illustrated in FIG. 5. Additionally, the eyepiece 500 may include fewer than three waveguides (e.g., two waveguides) or more than three waveguides (e.g., nine waveguides, three for each of the colors), according to some embodiments. In some embodiments, the eyepiece 500 may include waveguides for colors other than red, green, and blue. For example, instead of or in addition to red, green, and blue, it may include waveguides for magenta and cyan.

[0028] In some embodiments, the first optical filter 520 may be configured as a dichroic long-pass filter that transmits green and red light and reflects blue light. Thus, a portion of the image light (X12) transmitted through the first waveguide 510 in the blue wavelength range (X24) may be reflected toward the first waveguide 510, diffracted by the first DOE into the first waveguide 510, guided to the OPE and EPE in the first waveguide 510, and output to the viewer. Thus, the brightness and contrast of the blue bright field output to the viewer may be enhanced.

[0029] Similarly, the second optical filter 540 may be configured as a dichroic long-pass filter that transmits red light and reflects blue and green light. Thus, a portion of the image light (X32) transmitted through the second waveguide 530 in the green wavelength range (X44) may be reflected toward the second waveguide 530, diffracted by the second DOE into the second waveguide 530, and guided to the OPE and EPE in the second waveguide 530 and output to the viewer. Thus, the brightness and contrast of the green bright field output to the viewer may be enhanced.

[0030] In some embodiments, the eyepiece may further include an optical reflector 560 positioned in a sixth lateral plane adjacent to the fifth lateral plane at the same lateral position as the second lateral region (X50) of the third waveguide 550. Like the dichroic long-pass filter described above, the optical reflector 560 may be configured to reflect image light transmitted through the third waveguide 550 (X52) back toward the third waveguide 550. A portion of the image light reflected by the optical reflector 560 (X64) in the red wavelength range may be diffracted by the third DOE into the third waveguide 550 and directed to the OPE and EPE of the third waveguide 550 and output to the viewer. In some examples, the optical reflector 560 may be implemented as a wavelength-selective optical element, such as a dichroic filter configured to reflect light at least in the red wavelength range. In other examples, the optical reflector 560 may be implemented as a mirror or other optical element configured to reflect a relatively wide range of wavelengths. In either case, the brightness and contrast of the red bright field output to the viewer may be enhanced.

[0031] 6A-6D illustrate some example images formed by an eyepiece without a dichroic filter, according to an embodiment. FIG. 6A is an image formed by image light including red, green, and blue image light. FIGS. 6B-6D are images formed by red, green, and blue image light, respectively. FIGS. 6E-6H illustrate some example images formed by an eyepiece with a dichroic filter, such as the eyepiece 500 illustrated in FIG. 5, according to an embodiment. FIG. 6E is an image formed by image light including red, green, and blue image light. FIGS. 6F-6H are images formed by red, green, and blue image light, respectively. As can be seen, images formed by an eyepiece with a dichroic filter can be brighter than those formed by an eyepiece without a dichroic filter. In fact, the reflective nature of the dichroic filter can serve to enhance brightness in a waveguide-based eyepiece.

[0032] 7 diagrammatically illustrates a transmittance / reflectance curve for a first optical filter 520, according to an embodiment of the present invention. The first optical filter 520 may be configured as a long-pass filter having high transmittance values ​​(e.g., close to 100%) and low reflectance values ​​(e.g., close to 0%) for wavelengths longer than a threshold wavelength (e.g., 510 nm) and low transmittance values ​​(e.g., close to 0%) and high reflectance values ​​(e.g., close to 100%) for wavelengths shorter than the threshold wavelength.

[0033] In some embodiments, the first optical filter 520 may be configured to have a transmittance value of greater than about 90% for wavelengths longer than a threshold wavelength (e.g., 510 nm) and a transmittance value of less than about 10% for wavelengths shorter than the threshold wavelength. In some other embodiments, the first optical filter 520 may be configured to have a transmittance value of greater than about 80% for wavelengths longer than a threshold wavelength (e.g., 510 nm) and a transmittance value of less than about 20% for wavelengths shorter than the threshold wavelength. The first optical filter 520 may have other transmittance value ranges. The color contrast may vary depending on the transmittance value range.

[0034] The first optical filter 520 may include, for example, a multi-layer thin film filter. The transmittance / reflectance curve of a multi-layer thin film filter is typically sensitive to the angle of incidence. For example, the first optical filter 520 may be designed to have a transmittance / reflectance curve represented by solid line 710 for a zero degree angle of incidence (i.e., normal incidence), with a threshold wavelength of about 510 nm. For increasing angles of incidence, the threshold wavelength may shift to shorter wavelengths. For example, the threshold wavelength may shift to about 459 nm for a 45 degree angle of incidence, as shown by dashed line 720. In some embodiments, the first optical filter 520 may be designed such that the threshold wavelength remains below the central wavelength of the green image light (e.g., 528 nm) and above the central wavelength of the blue image light (e.g., 462 nm) over a range of predetermined angles of incidence. In one embodiment, the range of predetermined angles of incidence may be from about zero degrees to about 45 degrees for a 90 degree field of view (FOV). In another embodiment, the predetermined range of angles of incidence may be from zero degrees to about 25 degrees for a 50 degree FOV. Such a filter design may allow for angle-insensitive operation for the first optical filter 520. That is, the first optical filter 520 will transmit green and red light and reflect blue light as long as the angle of incidence of the image light is within the predetermined range.

[0035] FIG. 8 diagrammatically illustrates a transmittance / reflectance curve for a first optical filter 520 according to another embodiment of the present invention. Here, the first optical filter 520 may be designed to have a transmittance / reflectance curve represented by solid line 810 for a 45 degree angle of incidence, with the threshold wavelength being approximately 459 nm. For decreasing angles of incidence, the threshold wavelength may shift to longer wavelengths. For example, the threshold wavelength may shift to approximately 510 nm for a zero degree angle of incidence, as shown by dashed line 820. The first optical filter 520 may be designed such that the threshold wavelength remains below the central wavelength of the green image light (e.g., 528 nm) and above the central wavelength of the blue image light (e.g., 462 nm) over a range of angles of incidence for angle-insensitive operation.

[0036] The second optical filter 540 may also be designed for angle-insensitive operation. For example, the second optical filter 540 may be designed as a long-pass filter having a threshold wavelength below the central wavelength of the red image light (e.g., 635 nm) and above the central wavelength of the green image light (e.g., 528 nm) over a range of incidence angles.

[0037] 5, in some other embodiments, the red-green-blue waveguides 510, 530, and 550 may be ordered differently. For example, the first waveguide 510 may be configured as a red waveguide, the second waveguide 530 may be configured as a green waveguide, and the third waveguide 550 may be configured as a blue waveguide. In that case, the first optical filter 520 may be configured as a short-pass filter having a high transmittance value in the blue and green wavelength ranges and a low transmittance value in the red wavelength range. Similarly, the second optical filter 550 may be configured as a short-pass filter having a high transmittance value in the blue wavelength range and a low transmittance value in the green and red wavelength ranges.

[0038] As another example, the first waveguide 510 may be configured as a blue waveguide, the second waveguide 530 may be configured as a red waveguide, and the third waveguide 550 may be configured as a green waveguide. The first optical filter 520 may then be configured as a long-pass filter having high transmittance values ​​in the green and red wavelength ranges and low transmittance values ​​in the blue wavelength range. The second optical filter 540 may be configured as a short-pass filter having high transmittance values ​​in the green wavelength range and low transmittance values ​​in the red wavelength range.

[0039] Referring to FIG. 5, as described above, the first DOE 512 (also referred to as ICG) coupled to the first side region (X10) of the first waveguide 510 may be designed to mainly diffract blue light into the first waveguide 510. In fact, the first DOE 512 may also diffract (i.e., cross-couple) a small amount of green light into the first waveguide 510. FIG. 9A illustrates this situation, where blue, green, and red image lights are incident on the first waveguide 510. The first DOE 512 mainly diffracts the blue light into the first waveguide 510 so that it is directed toward the second side region (X11), but a small amount of green image light may also be diffracted by the first DOE 512 into the first waveguide 510.

[0040] Similarly, the second DOE 532 coupled to the first side region (X30) of the second waveguide 530 may be designed to diffract mainly green light into the second waveguide 530. In fact, the second DOE 532 may also cross-couple a small amount of red light into the second waveguide 530. FIG. 10 illustrates this situation, where the green image light and the red image light may be transmitted by the long-pass filter 520 and incident on the second waveguide 530. The second DOE 532 diffracts mainly the green light into the second waveguide 530 so that it is directed toward the second side region (X31), but a small amount of red image light may also be diffracted by the second DOE into the second waveguide 530.

[0041] 11A-11D illustrate the wavelength "cross-coupling" effect. FIG. 11A shows an image of a blue brightfield formed by a blue waveguide. FIG. 11B shows an image of a green brightfield cross-coupled by a blue waveguide. FIG. 11C shows an image of a green brightfield formed by a green waveguide. FIG. 11D shows an image of a red brightfield cross-coupled by a green waveguide.

[0042] According to an embodiment of the present invention, the first waveguide 510 may include a first short-pass filter 518 coupled to a second lateral region (X11) of the first waveguide 510, as illustrated in Figure 9A. The first short-pass filter 518 may be configured to pass blue light and absorb green light, such that green image light that is cross-coupled into the first waveguide 510 may be absorbed by the first short-pass filter 518 and thus prevented from propagating to the OPE and EPE regions of the first waveguide 510.

[0043] According to an embodiment, the second waveguide 530 may also include a second shortpass filter 538 coupled to a second lateral region (X31) of the second waveguide 530, as illustrated in Figure 10. The second shortpass filter 538 may be configured to pass green light and absorb red light, such that red image light that is cross-coupled into the second waveguide 530 may be absorbed by the second shortpass filter 538 and thus prevented from propagating to the OPE and EPE regions of the second waveguide 530.

[0044] FIG. 9B diagrammatically illustrates a cross-sectional view of a short-pass filter 518 according to an embodiment of the present invention. The short-pass filter 518 may be disposed on an outer surface of the second lateral region (X11) of the first waveguide 510. In some embodiments, the short-pass filter 518 may include a dichroic layer 910 disposed on the outer surface of the first waveguide 510. The dichroic layer 910 may include, for example, a multi-layer thin film designed to have a transmittance / reflectance curve similar to that illustrated in FIG. 7, with a threshold wavelength below the central wavelength of the green image light (e.g., 528 nm) and above the central wavelength of the blue image light (e.g., 462 nm) over a range of predetermined angles of incidence. Thus, the dichroic layer 910 may reflect the blue image light incident thereon into the first waveguide 510 and transmit the green image light incident thereon such that the blue image light incident thereon is directed toward the EPE region. The shortpass filter 518 may further include a terminating substrate 920 (e.g., a glass layer) disposed on the dichroic layer 910 and an absorbing layer 930 disposed on the terminating substrate 920. The absorbing layer 930 may be configured to absorb light transmitted by the dichroic layer 910.

[0045] 12A diagrammatically illustrates a waveguide 1200, according to some embodiments. The waveguide 1200 may include a first lateral region 1202 and a second lateral region 1204. The waveguide 1200 may also include a diffractive optical element (DOE) 1203 optically coupled to the first lateral region 1202 and configured to diffract a portion of the incident light Y02a into the waveguide 1200. For example, the DOE 1203 may be designed to primarily diffract blue light into the first waveguide 1200. In practice, the DOE may also diffract (i.e., cross-couple) a small amount of green light into the first waveguide 1200, as discussed above.

[0046] The waveguide 1200 may also include a short-pass filter 1210 coupled to a second lateral region 1204 of the waveguide 1200. The short-pass filter 1210 may include particles with index-matching properties embedded in the waveguide 1200, for example, by a substrate doping process. The particles may absorb light having a wavelength longer than that of green or blue light, for example, and transmit blue light. In some embodiments, index matching may not be a strict requirement. In such cases, the light may refract at the interface between the particles and the waveguide medium, but may still continue to propagate at the original angle. It may be desirable to minimize scattering at the point of discontinuity.

[0047] FIG. 12B diagrammatically illustrates a waveguide 1200 according to some other embodiments. The waveguide 1200 may include a short-pass filter 1220 coupled to the second lateral region 1204 of the waveguide 1200. Here, the short-pass filter 1220 may include a cavity inside the second lateral region 1204 of the waveguide 1200, with the top surface of the cavity being flush with the outer surface of the waveguide 1200. The cavity may be filled with an index-matching dye that absorbs light having a wavelength longer than that of green or blue light. In some embodiments, instead of creating and filling a cavity, the filter can be created by diffusing a dye through the surface of the waveguide 1200, creating a partially or fully dyed (or "doped") volume within the waveguide 1200. In one embodiment, the refractive index of the dye may be matched to the refractive index of the waveguide 1200 such that the dye does not affect the propagation of the blue image light in the waveguide 1200 by total internal reflection (TIR). In some other embodiments, some degree of refractive index mismatch may be tolerated as long as it does not affect the propagation, and scattering at the interface is controlled to some extent.

[0048] 12C diagrammatically illustrates a waveguide 1200 according to some further embodiments. The waveguide 1200 may include a layer of dye 1230 applied to an outer surface of a second lateral region 1204 of the waveguide 1200. The layer of dye (Y13c) may absorb light having a wavelength longer than that of green or blue light and reflect blue light.

[0049] 13A illustrates a partial cross-sectional view of an eyepiece according to another embodiment of the present invention. The eyepiece may include a first planar waveguide 1310 positioned in a first lateral plane, a second planar waveguide 1340 positioned in a second lateral plane adjacent to the first lateral plane, and a third planar waveguide 1370 positioned in a third lateral plane adjacent to the third lateral plane. Input image light is split into two optical paths, with blue and red image light incident on the eyepiece at a first lateral position and green image light incident on the eyepiece at a second lateral position displaced from the first lateral position.

[0050] The eyepiece may further include a first diffractive optical element (DOE) 1320, such as an internal coupling grating (ICG), disposed on a first surface of the first waveguide 1310 at a second lateral position. The first DOE is configured to receive a portion of the green image light incident thereon and diffract it into the first waveguide 1310 so as to be directed to the OPE and EPE regions of the first waveguide 1310. The eyepiece may further include a first optical reflector 1330 disposed on a second surface of the first waveguide 1310 at a second lateral position. In some examples, the optical reflector 1330 may be implemented as a wavelength-selective optical element, such as a dichroic filter configured to reflect light at least in the green wavelength range. In other examples, the optical reflector 1330 may be implemented as a mirror or other optical element (e.g., an aluminized material) configured to reflect a relatively wide range of wavelengths. In either case, it follows that the first optical reflector 1330 may be configured to reflect green image light that is not coupled into the first waveguide 1310 by the first DOE 1320 on the first pass back toward the first DOE 1320. A portion of the green image light reflected by the first optical reflector 1330 may be diffracted by the first DOE 1320 into the first waveguide 1310. Thus, the brightness and contrast of the green bright field output to the viewer may be enhanced.

[0051] The eyepiece may further include a second DOE 1350 disposed on a first surface of the second waveguide 1340 at a first lateral position. The second DOE 1350 may be configured to receive a portion of the blue image light incident thereon and diffract it into the second waveguide 1340 so as to be directed toward the OPE and EPE regions of the second waveguide 1340. The eyepiece may further include an optical filter 1360 (i.e., a wavelength-selective optical element) disposed on a second surface of the second waveguide 1340 at a first lateral position. The optical filter 1360 may include a dichroic long-pass filter configured to have a high transmittance value for the red image light and a low transmittance value and a high reflectance value for the blue image light. Thus, the portion of the blue image light that is not coupled into the second waveguide 1340 by the second DOE 1350 on the first pass may be reflected back towards the second DOE 1350 and coupled into the second waveguide 1340 by the second DOE 1350. Thus, the brightness and contrast of the blue bright field output to the viewer may be improved. The red image light that is transmitted by the optical filter 1360 is incident on the third waveguide 1370.

[0052] The eyepiece may further include a third DOE 1380 disposed on a first surface of the third waveguide 1370 at a first lateral position. The third DOE 1380 may be configured to receive a portion of the red image light incident thereon and diffract it into the third waveguide 1370 so as to be directed toward the OPE and EPE regions of the third waveguide 1370. The eyepiece may further include a second optical reflector 1390 disposed on a second surface of the third waveguide 1370 at a first lateral position. In some examples, the optical reflector 1390 may be implemented as a wavelength-selective optical element, such as a dichroic filter configured to reflect light at least in a red wavelength range. In other examples, the optical reflector 1390 may be implemented as a mirror or other optical element (e.g., an aluminized material) configured to reflect a relatively wide range of wavelengths. In either case, the second optical reflector 1390 may be configured to reflect red image light that is not coupled into the third waveguide 1370 by the third DOE 1380 on the first pass back toward the third DOE 1380. A portion of the red image light reflected by the second optical reflector 1390 may be diffracted by the third DOE 1380 into the third waveguide 1370. Thus, the brightness and contrast of the red bright field output to the viewer may be enhanced.

[0053] 13B illustrates a partial cross-sectional view of an eyepiece according to a further embodiment of the present invention. The eyepiece illustrated in FIG. 13B is similar to the eyepiece illustrated in FIG. 13A, except that a first DOE is disposed on the second surface of the first waveguide 1310 co-planar with the first optical reflector 1330, a second DOE 1350 is disposed on the second surface of the second waveguide 1340 co-planar with the optical filter 1360, and a third DOE 1380 is disposed on the second surface of the third waveguide 1370 co-planar with the second optical reflector 1390.

[0054] 13C illustrates a partial cross-sectional view of an eyepiece according to yet another embodiment of the present invention. The eyepiece illustrated in FIG. 13C is similar to the eyepiece illustrated in FIG. 13B, except that an optical filter 1360 is disposed on a first surface of a third waveguide 1370.

[0055] Each of the embodiments illustrated in Figures 13A-13C may have its own advantages and disadvantages. In the embodiment illustrated in Figure 13A, the first DOE, the second DOE, and the third DOE are formed on a first surface of the waveguide, so they operate in a transmission mode. In comparison, in the embodiment illustrated in Figures 13B and 13C, the first DOE, the second DOE, and the third DOE are formed on a second surface of the waveguide, so they operate in a reflection mode. The DOEs may be more efficient in a reflection mode than in a transmission mode. Having an aluminized DOE in a reflection mode may further increase the diffraction efficiency. Having a DOE and a dichroic filter on opposite surfaces may be more difficult to manufacture, since it requires patterning on both surfaces.

[0056] 14 diagrammatically illustrates the transmittance / reflectance curve of an optical filter 1360, according to one embodiment of the present invention. The transmittance / reflectance curve of the optical filter 1360 is similar to those illustrated in FIGS. 7 and 8 in that it exhibits high transmittance values ​​(e.g., close to 100%) and low reflectance values ​​(e.g., close to 0%) for wavelengths longer than a threshold, and low transmittance values ​​(e.g., close to 0%) and high reflectance values ​​(e.g., close to 100%) for wavelengths shorter than the threshold.

[0057] The optical filter 1360 may include a multi-layer thin film whose transmittance / reflectance characteristics may be sensitive to the angle of incidence, as discussed above. For example, the optical filter 1360 may be designed to have a transmittance / reflectance curve represented by solid line 1410 for a 45 degree angle of incidence. For decreasing angles of incidence, the rising edge may shift to longer wavelengths. For example, the transmittance / reflectance curve for a zero degree angle of incidence may be represented by dashed line 1420.

[0058] As discussed above, to enable angle-insensitive operation for the optical filter 1360, it may be desirable for the rising edge of the transmittance / reflectance curve to remain below the central wavelength of the red image light (e.g., 635 nm) and above the central wavelength of the blue image light (e.g., 462 nm) over a range of incidence angles (e.g., from about zero degrees to about 45 degrees). Here, since only blue and red image light is incident on the optical filter 1360 and the central wavelengths of the blue and red image lights are relatively far from each other, the requirements on the transmittance / reflectance profile may be more relaxed. For example, the rising edge of the transmittance / reflectance curve may shift by a larger wavelength range from zero degree incidence angle to 45 degree incidence angle compared to that illustrated in FIGS. 7 and 8. Furthermore, the rising edge of the transmittance / reflectance curve may not need to be as steep as that illustrated in FIGS. 7 and 8. Thus, the eyepiece illustrated in FIGS. 13A-13C may provide a smaller form factor compared to the eyepiece illustrated in FIG. 2, with the blue-green-red image light being separated into three separate light paths, while having less stringent requirements on the filter transmittance / reflectance profile.

[0059] It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to those skilled in the art and are to be included within the spirit and scope of the present application and the appended claims.

Claims

1. 1. An eyepiece for projecting an image onto a viewer's eye, the eyepiece comprising: a first planar waveguide positioned in a first lateral plane, the first planar waveguide having a first internal coupling element optically coupled thereto, the first internal coupling element configured to diffract image light in a first wavelength range centered on a first wavelength; a second planar waveguide positioned in a second lateral plane perpendicularly adjacent to the first lateral plane, the second planar waveguide having a second internal coupling element optically coupled thereto, the second internal coupling element configured to diffract image light in a second wavelength range centered on a second wavelength different from the first wavelength; a first optical element positioned between the first planar waveguide and the second planar waveguide in lateral alignment with the first internal coupling element, the first optical element configured to reflect image light in the first wavelength range; and Equipped with the eyepiece further comprising a second optical element positioned in lateral alignment with the second internal coupling element, the second optical element configured to reflect image light in the second wavelength range; the second internal coupling element is positioned laterally offset from the first internal coupling element; Eyepiece lens.

2. 2. The eyepiece of claim 1, wherein the first planar waveguide has a first surface and a second surface opposite the first surface, and the second planar waveguide has a first surface and a second surface opposite the first surface, and the first surface of the second planar waveguide faces the second surface of the first planar waveguide.

3. The eyepiece lens of claim 2 , wherein the first internal coupling element is disposed on the second surface of the first planar waveguide adjacent to the first surface of the second planar waveguide.

4. An eyepiece lens as described in claim 2, wherein the second optical element is positioned adjacent to the second surface of the second planar waveguide.

5. The eyepiece of claim 1 , wherein the first optical element is further configured to reflect image light in the second wavelength range.

6. a third planar waveguide positioned in a third lateral plane perpendicularly adjacent to the second lateral plane, the third planar waveguide having a third internal coupling element coupled thereto, the third internal coupling element configured to diffract image light in a third wavelength range centered on the first wavelength and a third wavelength different from the second wavelength. The eyepiece of claim 1 further comprising:

7. The eyepiece of claim 6 , wherein the second internal coupling element is positioned in lateral alignment with the third internal coupling element.

8. The eyepiece of claim 6 , wherein the second optical element is configured to have a reflectance value in the second wavelength range that is greater than about 90%.

9. The eyepiece of claim 8 , wherein the second optical element is further configured to have a transmittance value in the third wavelength range greater than about 90%.

10. The eyepiece of claim 8, further comprising a third optical element positioned in lateral alignment with the third internal coupling element, the third optical element configured to reflect image light in the third wavelength range.

11. The eyepiece of claim 10 , wherein the third optical element is further configured to reflect image light in the second wavelength range.

12. The first planar waveguide has a first surface and a second surface opposite the first surface; the second planar waveguide having a first surface and a second surface opposite the first surface; The eyepiece of claim 1 , wherein the second optical element is positioned adjacent to the second surface of the second planar waveguide.

Images