Optical display system and augmented reality electronic device

Abstract

An optical display system and an augmented reality electronic device are disclosed. The optical display system includes: a waveguide; an input coupler disposed at an input end of the waveguide for coupling image light into the waveguide; and a two-dimensional grating disposed at an output end of the waveguide. The waveguide transmits the image light to the two-dimensional grating, which performs pupil expansion on the image light and performs out-coupling on the expanded image light. The two-dimensional grating has a diamond lattice. When viewed from a top view of the two-dimensional grating, the unit cells of the two-dimensional grating are asymmetric along respective axes parallel to the propagation direction of the image light incident on the two-dimensional grating. The unit cells are oriented in the propagation direction of the image light and each of the unit cells has at least two vertices at its end sides.

Description

Technical Field

[0001] The present disclosure relates to the technical field of optical display systems in augmented reality devices, and more particularly, to an optical display system and an augmented reality electronic device. Background Art

[0002] In an augmented reality (AR) waveguide system or an AR electronic device, light / image light emitted from a display is internally coupled into a waveguide through a grating that responds to the wavelength of the input image light, and the grating is an input coupler. For example, the display may include a laser beam scanner (LBS), a micro-LED display, or a liquid crystal on silicon (LCOS) display. The image light undergoes total internal reflection in the waveguide and is finally externally coupled into the air using an out-coupling grating.

[0003] In addition, the AR electronic device may be provided with an exit pupil expansion (EPE) component to expand the image light in the viewing area.

[0004] PCT Application Publication No. WO 2008 / 081070A1 discloses a device for two-dimensional exit pupil expansion, which is hereby incorporated by reference in its entirety.

[0005] U.S. Patent No. 10,038,840B2 discloses a diffractive optical element for pupil expansion using crossed gratings, which is hereby incorporated by reference in its entirety.

[0006] The article “Two-dimensional grating-based X-ray phase-contrast imaging using Fourier transform phase retrieval” (2011; 19(4): 3339. doi: 10.1364 / oe.19.003339) published by Itoh H, Nagai K, Sato G, etc. in Opt Express discloses a solution for two-dimensional grating-based imaging, which is hereby incorporated by reference in its entirety.

[0007] The article “Coherent optical generation and inspection of two-dimensional periodic structures” (24(4): 505-515. doi: 10.1080 / 713819570) published by Dammann H and Klotz E in Opt Acta (Lond) in 1977 discloses a solution for the coherent optical generation and inspection of two-dimensional periodic structures, which is hereby incorporated by reference in its entirety.

[0008] The article "Super-Resolution in Digital Holography by a Two-Dimensional Dynamic Phase Grating" by Paturzo M, Merola F, Grilli S, De Nicola S, Finizio A and Ferraro P, published in OptExpress (2008; 16(21): 17107. doi: 10.1364 / oe.16.017107), discloses a solution for a two-dimensional dynamic phase grating, which is hereby incorporated by reference in its entirety.

[0009] EP patent application No. 0618473A2 discloses a video device using a two-dimensional diffraction grating, which is hereby incorporated by reference in its entirety.

[0010] The article "Color filter based on a two-dimensional submicrometer metal grating" by Ye Y, Zhou Y and Chen L, published in Appl Opt. (2009; 48(27): 5035-5039. doi: 10.1364 / AO.48.005035), discloses a solution for a color filter based on a two-dimensional submicrometer metal grating, which is hereby incorporated by reference in its entirety.

[0011] The article "Two-dimensional grating coupler with a low polarization dependent loss of 025dB covering the C-band" by Zou J, Yu Y and Zhang X, published in Opt Lett. (2016; 41(18): 4206. doi: 10.1364 / ol.41.004206), discloses a solution for a two-dimensional grating coupler, which is hereby incorporated by reference in its entirety.

[0012] The article "Two dimensional silicon waveguide chirped grating couplers for vertical optical fibers" by Chen X, Li C and Tsang HK, published in Opt Commun. (2010; 283(10): 2146-2149. doi: 10.1016 / j.optcom.2010.01.059), discloses a solution for a two-dimensional silicon waveguide chirped grating coupler, which is hereby incorporated by reference in its entirety.

[0013] The article "Incident light management in a thin silicon solar cell using a two-dimensional grating according a Gaussian distribution" (2019; 189(April): 457-463. doi: 10.1016 / j.solener.2019.07.099) published by Chen X, Li C and Heidarzadeh H in Sol Energy discloses a solution of a two-dimensional grating, which is hereby incorporated by reference in its entirety.

[0014] The article "Low-loss two-dimensional silicon photonic grating coupler with a backside metal mirror" (2018; 43(3): 474. doi: 10.1364 / ol.43.000474) published by Luo Y, Nong Z, Gao S et al. in Opt Lett. discloses a solution of a two-dimensional silicon photonic grating coupler, which is hereby incorporated by reference in its entirety.

[0015] The article "A compact two-dimensional grating coupler used as a polarization splitter" (2003; 15(9): 1249-1251. doi: 10.1109 / LPT.2003.816671) published by Taillaert D, Chong H, Borel PI, Frandsen LH, De La Rue RM and Baets R in IEEE Photonics Technol Lett. discloses a solution of a two-dimensional grating coupler, which is hereby incorporated by reference in its entirety.

[0016] Kroker S, The article "High efficiency two-dimensional grating reflectors with angularly tunable polarization efficiency" by T, Steiner S, Kley EB, and Tünnermann A in Appl Phys Lett. (2013; 102(16). doi:10.1063 / 1.4802883) is hereby incorporated by reference in its entirety.

[0017] The article "Excitation and direct imaging of surface plasmon polariton modes in a two-dimensional grating" by Tetz KA, Rokitski R, Nezhad M, and Fainman Y in Appl Phys Lett. (2005; 86(11):1 - 3. doi:10.1063 / 1.1883334) discloses a solution for a two-dimensional grating and is hereby incorporated by reference in its entirety.

[0018] The article "Laser action from two-dimensional distributed feedback in photonic crystals" by Meier M, Mekis A, Dodabalapur A, et al. in Appl Phys Lett. (1999; 74(1):7 - 9. doi:10.1063 / 1.123116) discloses laser action from two-dimensional distributed feedback in photonic crystals and is hereby incorporated by reference in its entirety.

[0019] The article "Polarization-independent high diffraction efficiency two-dimensional grating based on cylindrical hole nano arrays" by Zhou B, Jia W, Sun P, Wang J, Liu W, and Zhou C in Opt Express. (2020; 28(20):28810. doi:10.1364 / oe.402131). Discloses a two-dimensional grating and is hereby incorporated by reference in its entirety.

[0020] Danish Patent No. 3175280T3 and US Patent No. 10,359,635B2 disclose an exit pupil expanded diffractive optical waveguide device, which is hereby incorporated by reference in its entirety.

[0021] US Patent No. 10,895,685B2 and US Patent Application No. 2021 / 0191038A1 disclose planar optical waveguides based on two-dimensional optical gratings with a grating direction of 60°, which are hereby incorporated by reference in their entirety. Summary of the Invention

[0022] An object of the present disclosure is to provide a new technical solution for an optical display system.

[0023] According to a first aspect of the present disclosure, there is provided an optical display system, comprising: a waveguide; an input coupler disposed at an input end of the waveguide for coupling image light into the waveguide; and a two-dimensional grating disposed at an output end of the waveguide, wherein the waveguide transmits the image light coupled by the input coupler to the two-dimensional grating, and the two-dimensional grating performs exit pupil expansion on the image light and performs out-coupling on the expanded image light, wherein the two-dimensional grating has a rhombic lattice, wherein, when viewed from a top view of the two-dimensional grating, the unit cells of the two-dimensional grating are asymmetric along respective axes parallel to the propagation direction of the image light incident on the two-dimensional grating, and wherein the unit cells are oriented in the propagation direction of the image light, and each of the unit cells has at least two vertices at its end sides.

[0024] According to a second aspect of the present disclosure, there is provided an augmented reality electronic device, comprising: a display for generating image light; and an optical display system according to an embodiment for receiving the image light and guiding it to the eyes.

[0025] According to an embodiment of the present disclosure, the performance of the optical display system can be improved.

[0026] Other features and advantages of the present disclosure will become apparent from the following detailed description of exemplary embodiments of the present disclosure with reference to the accompanying drawings. Brief Description of the Drawings

[0027] The drawings incorporated in and constituting a part of this specification illustrate embodiments of the invention and, together with the description, are used to explain the principles of the invention.

[0028] Figure 1 A schematic diagram showing the structure of an electronic device including an optical display system according to an embodiment is shown.

[0029] Figure 2 A schematic top view of an optical display system according to an embodiment is shown.

[0030] Figure 3Shows a schematic top view of a two-dimensional grating according to an embodiment.

[0031] Figure 4 Shows a schematic top view of a two-dimensional grating according to another embodiment.

[0032] Figure 5 Shows a schematic top view of a two-dimensional grating according to yet another embodiment.

[0033] Figure 6 Shows an illustrative K-space of different diffractions.

[0034] Figure 7 Shows the reciprocal lattice of the wave vectors of a two-dimensional grating according to an embodiment.

[0035] Figure 8 Shows the diffraction of a two-dimensional grating according to an embodiment, where the p-polarized incident field varies with the emission angle.

[0036] Figure 9 Shows the diffraction of a two-dimensional grating according to an embodiment, where the s-polarized incident field varies with the emission angle.

[0037] Figure 10 Shows the diffraction of a two-dimensional grating according to an embodiment, where the p-polarized incident field varies with the wavelength.

[0038] Figure 11 Shows the diffraction of a two-dimensional grating according to an embodiment, where the s-polarized incident field varies with the wavelength.

[0039] Figure 12 Shows an example of an electronic device according to an embodiment. Detailed Description

[0040] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present invention.

[0041] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way a limitation on the present invention or its application or use.

[0042] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be regarded as part of the specification.

[0043] In all examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0044] It should be noted that like reference numerals and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0045] Figure 1 A schematic diagram showing the structure of an electronic device including an optical display system according to an embodiment is shown. The electronic device may be, for example, an augmented reality (AR) electronic device.

[0046] As Figure 1 shown, the electronic device includes a display D. The display D generates image light / rays R1. The display D may be a laser beam scanner (LBS), a micro-LED display, a liquid crystal on silicon (LCOS) display, etc.

[0047] The electronic device further includes an optical display system. The optical display system receives the image light from the display D and guides it to the viewer's eyes. The optical display system includes a waveguide W, an input coupler G1, and a two-dimensional grating G2.

[0048] The optical system is used to create an immersive scene and meet the requirements of good color / brightness uniformity within the field of view (FOV) of a single pupil.

[0049] As Figure 1 shown, the image light R1 is coupled into the waveguide W through the input coupler G1. The input coupler G1 is disposed at the input end of the waveguide W. The input coupler G1 may be an input coupler grating, such as a one-dimensional input coupler grating.

[0050] The two-dimensional grating G2 is disposed at the output end of the waveguide W. The waveguide W transmits the image light R2 coupled through the input coupler G1 to the two-dimensional grating G2. The internally coupled image light R2 travels in the waveguide W in a total internal reflection (TIR) manner. The two-dimensional grating G2 performs pupil expansion on the image light R2 and externally couples the expanded image light R3. The expanded image light R3 is directly or indirectly incident on the viewer's eyes E. For example, an optical unit may also be provided between the two-dimensional grating G2 and the eyes E.

[0051] Figure 2 A schematic top view of an optical display system according to an embodiment is shown. As Figure 2 shown, the input coupler G1 is, for example, a one-dimensional grating. The grating lines of the input coupler G1 are horizontal.

[0052] The two-dimensional grating G2 has a diamond lattice. For example, as Figure 2 shown, the diamond lattice is at ±30° with respect to the propagation direction.

[0053] For example, the two-dimensional grating G2 is a surface relief grating. In the prior art, two-dimensional gratings have long been used for spatial filters, wavelength filters, fiber chip coupling of photonic integrated circuits, light reflection, polarization beam splitters, far-field imaging, and laser resonators. Here, the two-dimensional grating is used to perform pupil expansion and out-coupling. The two-dimensional grating can be used to implement the grating vector and wave vector addition / subtraction principle, and it can also provide a lattice and a unit cell to provide various energy distributions by adding different symmetries and duty cycles (DC) more freely in two dimensions. These degrees of freedom in physical parameters provide greater flexibility for the TDG used as a pupil expansion grating and an output coupler grating (OCG).

[0054] Figures 3 to 5 A top view of a two-dimensional grating according to various embodiments is shown.

[0055] In Figures 3 to 5 it can be seen from the top view of the two-dimensional grating that the unit cells 31, 41, 51 of the two-dimensional grating are asymmetric along the respective axes parallel to the propagation direction of the image light incident on the two-dimensional grating. In Figures 3 to 5 the propagation direction is from left to right. The asymmetric structure of the unit cell can provide a higher pupil expansion efficiency. For example, the asymmetric structure can reduce the intensity difference of light / rays with different polarizations, which provides better uniformity for the image light. In addition, by using such an asymmetric unit cell, the diffraction efficiencies of different polarizations (p and s polarizations) can compensate for each other, thereby providing a uniform color output.

[0056] The unit cells 31, 41, 51 are oriented in the propagation direction of the image light, and each unit cell has at least two vertices (34, 35), (44, 45), (54, 55) at its end sides. These vertices can improve the diffraction efficiency and uniformity, so that the grating can be made thinner. It is easier to manufacture a thinner grating, thereby improving the manufacturing yield.

[0057] Considering the eye position change or movement in a viewing electronic device such as a head-up display (HUD), the requirements for uniformity and color balance are addressed here in the expanded pupil or eye box (EB), such that when the viewer's eye position changes or the eye moves, the brightness and RGB balance still remain within the perceptible range of the human eye. For example, in a HUD, the image resolution seen by the viewer as the modulation transfer function (MTF) of the system is directly related to the contrast ratio (CR) of the rendered image. For example, the constant ambient light in the electronic device serves as the background, so the brightness of the RGB colors determines the MTF of the rendered image.

[0058] Here, the two-dimensional grating can achieve efficient energy distribution to ensure the RGB luminance magnitude and uniformity within a viewing device such as an eye box (EB). This embodiment can also achieve an exit pupil expansion (EPE) with a thinner device profile that must be achieved.

[0059] Figure 3 The lattice 32 of the two-dimensional grating is shown. The lattice 32 is formed by four unit cells 31. In Figure 4 it, the lattice 42 is formed by four unit cells 41. In Figure 5 it, the lattice 52 is formed by four unit cells 51.

[0060] The refractive index of the two-dimensional grating can be equal to or greater than 1.7, or equal to or greater than 1.8. In this embodiment, a higher refractive index material for the two-dimensional grating can be used such that an image with a wider field of view can be coupled in the system and transmitted to the viewer's eyes. Additionally, due to the asymmetric pattern of the unit cells, the expansion difference of different polarizations is reduced. Compared with other two-dimensional gratings, the relatively high refractive index does not cause significant image disorder. Therefore, this embodiment can provide a wider field of view by using a two-dimensional grating of a relatively high refractive index material while maintaining acceptable display performance.

[0061] The thickness of the two-dimensional grating is equal to or less than 200 nm or 100 nm. In this embodiment, the two-dimensional grating can achieve high diffraction efficiency, so its thickness can be made thinner than others. The thinner thickness makes it easier to manufacture, thus improving the product yield.

[0062] As Figures 3 to 5 shown, the unit cells 31, 41, and 51 are oriented in the propagation direction of the image light, and the apex angle of the unit cell starting from the oriented position is greater than 45 degrees and less than 60 degrees. Compared with the unit cell with an apex angle of 60 degrees, the smaller apex angle in this embodiment can make the lateral refractive index change of the two-dimensional grating tend to be faster, which will improve the diffraction efficiency of the exit pupil expansion. This also improves the color uniformity and / or brightness. This angle should be above 45 degrees to maintain relatively reasonable diffraction performance.

[0063] The unit cells 31, 41, and 51 have waists 36, 46, and 56 along the propagation direction. As Figures 3 to 5 shown, along the propagation direction, the part of the unit cell 31, 41, or 51 before the waist 36, 46, or 56 is longer than the part after the waist. Thus, the refractive index change at the part after the waist tends to become larger, so that the diffraction efficiency and uniformity will be improved.

[0064] Figure 3 It shows that four unit cells 31 form a rhombus-shaped lattice 32. The unit cells 31 are separated from each other by the gaps therebetween. As Figure 3As shown, the two-dimensional grating uses a diamond lattice or a rhombus-shaped lattice. The unit cell 31 is asymmetric along the optical propagation axis, i.e., the x-axis. Figure 3 The duty cycle DC of the two-dimensional grating in Figure 3 can range from 0.3 to 0.7, and the refractive index n of the two-dimensional grating is 1.7.

[0065] There are gaps on both the horizontal and vertical axes. Such gaps add new degrees of freedom for modifying the diffraction efficiency of different polarizations and for increasing the total diffraction efficiency of the two-dimensional grating. In Figure 3 the apex angle ranges from 55 degrees to 60 degrees. The shape of the unit cell 31 is oriented along the length direction of the optical propagation axis. The unit cell 31 can have different thicknesses or gap coefficients along the waist 36. In Figure 3 the waist 36 is narrower than other parts. A coating material can be applied to the two-dimensional grating to improve the reflection efficiency. The thickness of the two-dimensional grating ranges from 50 nm to 200 nm.

[0066] Figure 4 Four unit cells 41 are shown forming a lattice 42. The lattice 42 is connected into a closed shape. This connection structure makes it easier to fabricate the two-dimensional grating.

[0067] In addition, as Figure 4 shown, the portion 47 surrounded by the unit cells 41 of the two-dimensional grating forms a low-refractive-index unit cell. The portion 47 has a refractive index lower than that of the unit cells 41. As Figure 4 shown, the portion 47 is also asymmetric along each axis parallel to the propagation direction and has at least two apex angles at its end sides. Although only one portion 47 is shown in Figure 4 it should be understood that the same portion 47 can also be formed by other unit cells 41 in the two-dimensional grating.

[0068] For example, the portion 47 can be hollow (a hole), so the refractive index difference between the portion 47 and the unit cells 41 will be greater. This will improve the performance of the two-dimensional grating. In addition, the hollow portion or hole 47 within the two-dimensional grating has the ability to adjust the polarization ratio between the pupil expansion and the external coupling of the two-dimensional grating. Figure 4 The duty cycle DC of the two-dimensional grating in Figure 4 can range from 0.5 to 1.

[0069] In Figure 5 the thickness coefficient of the unit cell 51 along the waist 56 is larger than that of other parts. Figure 5 The two-dimensional grating in Figure 5 has narrow gaps between different unit cells 51, and Figure 5 the duty cycle DC of the two-dimensional grating in Figure 5 can range from 0.5 to 0.95.

[0070] In Figures 3 to 5Among them, the cells 31, 41, and 51 have a diamond-like bowtie shape. The duty cycle of the two-dimensional grating ranges from 0.5 to 0.95.

[0071] As described above, the two-dimensional grating has the potential to control the polarization efficiency by adjusting the cell gap, cell structure, etc., which makes the two-dimensional grating more advantageous than the one-dimensional surface relief grating.

[0072] As Figure 1 and Figure 2 shown, the waveguide W is a single-layer waveguide, and the input coupler G1 and the two-dimensional grating G2 are formed on or in the single-layer waveguide W to provide a compact optical display system.

[0073] Accordingly, the embodiments can use the grating vector addition / subtraction principle and can be optimized by a self-written optimization algorithm using thickness, gap, duty cycle, lattice type, and apex angle as variables. The Rigorous Coupled-Wave Analysis (RCWA) algorithm can be applied to this embodiment.

[0074] The two-dimensional grating in the embodiments can follow the design principle of grating vector addition / subtraction. The two-dimensional grating can perform exit pupil expansion and out-coupling. It exhibits higher efficiency. In addition, the two-dimensional grating in the embodiments can have a better balance between two polarizations, making it suitable for some non-polarized displays such as micro-LEDs.

[0075] The two-dimensional grating according to the embodiments can provide more design freedoms to improve the diffraction efficiency.

[0076] Moreover, the two-dimensional grating according to the embodiments can improve the imbalance between different polarizations.

[0077] In addition, the two-dimensional grating according to the embodiments can exhibit equally excellent or more advanced capabilities to handle the incident light within the FOV.

[0078] In addition, the two-dimensional grating according to the embodiments can provide the compactness of the optical display system and balance the cell complexity with greater design freedoms.

[0079] Figure 6 Shows the resulting K-space where the incident image ray principal beam passes through the optical display system. As Figure 6 (a) shows, the incident principal beam 61 is located in the middle of the figure. For example, the horizontal FOV θ = 30°, the image ratio is 16 / 9, and the refractive index n of the waveguide and the grating is 1.7. The principal beam 61 passes through the optical display system and is output as a beam 62. The beam 62 is dispersed as Figure 6 (a) shows. For example, the red, green, and blue components of the beam 62 are dispersed.

[0080] InFigure 6 In (b), the optical display system has an exit pupil expansion in the +z direction. As Figure 6 shown in (b), an additional light beam 63 is formed in the +z direction through the optical display system.

[0081] In Figure 6 (b), the optical display system has an exit pupil expansion in the -z direction. As Figure 6 (b) shows, an additional light beam 64 is formed in the -z direction through the optical display system.

[0082] It can be seen from Figure 6 that after passing through the optical display system, the light beams 62, 63, and 64 are within an acceptable range.

[0083] Figure 7 The reciprocal lattice of the wave vectors of a two-dimensional grating according to an embodiment is shown.

[0084] Figure 8 The diffraction of a two-dimensional grating according to an embodiment is shown, where the p-polarized incident field varies with the emission angle. Figure 9 The diffraction of a two-dimensional grating according to an embodiment is shown, where the s-polarized incident field varies with the emission angle. In Figure 8 and Figure 9 , the ray has a wavelength λ = 532 nm. (-1,0)R is the order of the diffraction of the main light beam without pupil expansion. (-1,1)R is the order of the light beam with pupil expansion on the TDG.

[0085] It can be seen from Figure 8 and Figure 9 that at the total internal reflection (TIR) angle of the WG refractive index, the polar angle of the ray in the central view is approximately θ = 52°. Both p-polarized and s-polarized rays show a relatively high diffraction efficiency (DE).

[0086] Table 1 shows a comparison of the performance of the embodiments of the present disclosure with a lattice angle less than 60 degrees and the performance of a two-dimensional grating TDG with a lattice angle of 60 degrees.

[0087] Table 1

[0088]

[0089] It can be seen from Table 1 that by using a two-dimensional grating with a lattice angle less than 60 degrees, the imbalance between the diffraction efficiencies DE of different polarizations can be reduced.

[0090] Figure 10 The diffraction of a two-dimensional grating according to an embodiment is shown, where the p-polarized incident field varies with the wavelength. Figure 11 The diffraction of a two-dimensional grating according to an embodiment is shown, where the s-polarized incident field varies with the wavelength. That is,Figure 10 and Figure 11 shows the diffraction wavelength response of a two-dimensional grating according to an embodiment. In Figure 10 and Figure 11 , the incident angle of the ray is θ = 52°. (-1,0)R is the order of the diffraction of the main beam without pupil expansion. (-1,1)R is the order of the beam with pupil expansion on the two-dimensional grating.

[0091] From Figure 10 and Figure 11 's wavelength response, it can be seen that although the wavelength response is not very uniform for one type of polarization (p-polarization or s-polarization), the other type of polarization (s-polarization or p-polarization) will show a compensating effect on the wavelength response. For example, in Figure 10 , blue light and green light (about 435 nm and 546 nm) both have relatively high diffraction efficiencies DE compared to the red light (about 700 nm) of p-polarization, while in Figure 11 , green light and red light both have relatively high diffraction efficiencies DE. Since the human eye perceives light intensity rather than its polarization, this compensating phenomenon of the optical display system according to the embodiments of the present disclosure can be used to provide uniform light output. Therefore, this phenomenon can be beneficial for reducing color non-uniformity of the entire system.

[0092] Table 2 and Table 3 show a comparison between the embodiments in the present disclosure with a lattice angle less than 60 degrees and the two-dimensional grating TDG with a lattice angle of 60 degrees.

[0093] Table 2 shows a comparison of the output coupling efficiency in the case of pupil expansion.

[0094] Table 2

[0095]

[0096] Table 3 shows a comparison of the output coupling efficiency in the case of direct output.

[0097] Table 3

[0098]

[0099] Table 2 and Table 3 show that the two-dimensional grating with a lattice angle less than 60 degrees according to the embodiments here exhibits a relatively high diffraction efficiency in both the cases of direct output and pupil expansion. In addition, the two-dimensional grating with a lattice angle less than 60 degrees also shows an improved intensity balance between different polarizations.

[0100] Figure 12 shows an example of an electronic device according to an embodiment. The electronic device 71 can be AR glasses. The electronic device 71 can include a display 73 and the optical display system 72 as described above.

[0101] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustrating the present invention and not for limiting the scope of the present invention.

Claims

1. An optical display system, comprising: a waveguide, an input coupler disposed at an input end of the waveguide and coupling image light into the waveguide; and a two-dimensional grating disposed at an output end of the waveguide, wherein the waveguide transmits the image light coupled by the input coupler to the two-dimensional grating, and the two-dimensional grating performs pupil expansion on the image light and performs out-coupling on the expanded image light, wherein the two-dimensional grating has a diamond lattice, wherein, when viewed from a top view of the two-dimensional grating, cells of the two-dimensional grating are asymmetric along respective axes parallel to a propagation direction of the image light incident on the two-dimensional grating, and wherein the cells are oriented in the propagation direction of the image light, and each of the cells has at least two vertices at an end side thereof along the propagation direction, the cell has a waist along the propagation direction, and the waist is narrower than other parts.

2. The optical display system according to claim 1, wherein, The refractive index of the two-dimensional grating is equal to or greater than 1.7 or 1.

8.

3. The optical display system according to claim 1, wherein, The thickness of the two-dimensional grating is equal to or less than 200 nm or 100 nm.

4. The optical display system according to claim 1, wherein The cells are oriented in the propagation direction of the image light, and a vertex angle of the cell from a self-orienting position is greater than 45 degrees and less than 60 degrees.

5. The optical display system according to claim 1, wherein, Along the propagation direction, a part of the cell before the waist is longer than a part of the cell after the waist.

6. The optical display system according to claim 1, wherein A thickness coefficient of the cell along the waist is larger than a thickness coefficient of other parts.

7. The optical display system according to claim 1, wherein The cells are connected into a closed shape.

8. The optical display system according to claim 6, wherein, A part of the two-dimensional grating surrounded by the cells has a lower refractive index and forms a low-refractive-index cell, the low-refractive-index cell is asymmetric along respective axes parallel to the propagation direction, and each of the low-refractive-index cells has at least two vertices at its end side.

9. The optical display system according to claim 1, wherein, The waveguide is a single-layer waveguide, and the input coupler and the two-dimensional grating are formed on or in the single-layer waveguide.

10. The optical display system according to claim 1, wherein, The cell has a diamond-shaped bow-tie shape.

11. The optical display system according to claim 1, wherein, The diamond lattice is at ±30 degrees with respect to the propagation direction.

12. The optical display system according to claim 1, wherein, The duty cycle of the two-dimensional grating is in a range from 0.5 to 0.

95.

13. The optical display system according to claim 1, wherein, The two-dimensional grating is a surface relief grating.

14. An augmented reality electronic device, comprising: a display that generates image light; and the optical display system according to claim 1, which receives the image light and guides it to an eye.

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