Efficient and compact beam extender for vr / ar head mounted devices

Abstract

An apparatus of the subject technology includes a light source that generates a light beam, a first grating illuminated by the light beam, and a second grating optically coupled with the first grating. The first grating performs a first diffraction to expand the light beam in a first dimension to form a first beam. The second grating performs a second diffraction to expand the first beam in a second dimension to provide backlight for the display device.

Description

[0001] The present disclosure is related to U.S. Provisional Application No. 63 / 448,475, filed on February 27, 2023, entitled “EFFICIENT AND COMPACT BEAMEXPANDER FOR VR / AR HEADSETS,” and claims priority to that application under 35 U.S.C. §119(e). background Technical Field

[0002] The present disclosure relates to display devices for virtual reality (VR) and / or augmented reality (AR) headsets. More specifically, the present disclosure relates to efficient and compact devices that expand an illumination beam in two dimensions to illuminate a pixelated display device in a VR / AR headset.

[0003] Related technologies

[0004] Two-dimensional display devices (e.g., liquid crystal displays (LCDs)) are illuminated at the back end by collimated light sources (such as white light-emitting diodes (LEDs)) or coherent light sources (such as red-green-blue (RGB) lasers), which ideally illuminate the entire area behind the display device. These backlights may impose design limitations, such as those related to display size. In addition, multi-layer display devices used for VR / AR applications typically have low transmission efficiency, which exacerbates the power consumption of the display device and thus harms battery life, which is critical for head-mounted device applications. Summary of the Invention

[0005] According to a first aspect of the present invention, there is provided an apparatus comprising: a light source configured to generate a light beam; a first grating illuminated by the light beam; and a second grating optically coupled to the first grating, wherein the first grating is configured to perform a first diffraction to expand the light beam in a first dimension to form a first beam, and the second grating is configured to perform a second diffraction to expand the first beam in a second dimension to provide backlight for a display device.

[0006] Optionally, the first grating is illuminated by a collimated beam of a laser source.

[0007] Optionally, the first diffraction comprises a first single diffraction configured to expand the light beam in a first dimension of a first grating coupled to the second grating.

[0008] Optionally, the second diffraction comprises a second single diffraction configured to expand the expanded first beam in a second dimension to form a two-dimensional beam perpendicular to the plane of the second grating.

[0009] Optionally, the first grating includes a first volume Bragg grating (VBG), and the second grating includes a second VBG.

[0010] Optionally, the first VBG and the second VBG include single diffraction VBGs.

[0011] Optionally, at least one of the first VBG and the second VBG includes a multiplexed (MUX) VBG, the multiplexed VBG including a plurality of gratings with different pitches, the plurality of gratings being configured to increase a diffraction angle range.

[0012] Optionally, the display device includes an augmented reality (AR) display or a virtual reality (VR) display.

[0013] Optionally, the display device comprises a liquid crystal display (LCD) device.

[0014] Optionally, the display comprises a liquid crystal on silicon (LCOS) display device.

[0015] Optionally, the apparatus further comprises a polarization component located between the first grating and the second grating, wherein the polarization component comprises a half-wave plate configured to change a polarization state of the first beam.

[0016] Optionally, the apparatus further comprises a reflective plate configured to direct the light beam at various angles to increase a pupil size of the backlight.

[0017] Optionally, the light source comprises a grid of lasers, and wherein individual lasers of the grid are selectively controllable to be switched on or off to convert the backlight into a zonal backlight.

[0018] According to another aspect of the present invention, a beam expander system is provided, comprising: a laser configured to generate a first beam; a first Bragg grating illuminated by the first beam; a polarization component; and a second Bragg grating optically coupled to the first Bragg grating, wherein the first Bragg grating is configured to generate a first diffracted beam in a first dimension, the polarization component is configured to change a polarization state of the first diffracted beam, and the second Bragg grating is configured to generate a second diffracted beam to expand the first polarized diffracted beam in a second dimension to provide backlight for a display device.

[0019] Optionally, the first Bragg grating includes a first VBG, and the second Bragg grating includes a second VBG.

[0020] Optionally, the first diffracted beam comprises a first single diffracted beam expanded in a first dimension of the first Bragg grating, and wherein the second diffracted beam comprises a second single diffracted beam.

[0021] Optionally, the first diffracted beam comprises a first MUX diffracted beam expanded in a first dimension of the first Bragg grating, and wherein the second diffracted beam comprises a second MUX diffracted beam.

[0022] According to another aspect of the present invention, there is provided a beam expander system comprising: a first VBG illuminated by a first collimated beam and configured to form a first diffracted beam along a length of the first VBG; a polarization component configured to switch a polarization state of the first diffracted beam; and a second VBG configured to expand the first polarized diffracted beam to form a backlight for a display device.

[0023] Optionally, the first VBG comprises a first MUX VBG, wherein the second VBG comprises a second MUX VBG, and wherein the polarization component comprises a half-wave plate.

[0024] Optionally, the system further comprises a collimated light source for generating the first collimated beam, wherein the collimated light source comprises a grid of lasers, and wherein the grid of lasers is configurable to generate a zoned beam pattern, the zoned beam pattern causing the zoned backlight.

[0025] One aspect of the subject technology relates to an apparatus comprising a light source that generates a light beam, a first grating illuminated by the light beam, and a second grating optically coupled to the first grating. The first grating performs a first diffraction to expand the light beam in a first dimension to form a first beam. The second grating performs a second diffraction to expand the first beam in a second dimension to provide backlighting for a display device.

[0026] Another aspect of the present disclosure relates to a beam expander system that includes a laser that generates a first beam, a first Bragg grating illuminated by the first beam, a polarization component, and a second Bragg grating optically coupled to the first Bragg grating. The first Bragg grating generates a first diffracted beam in a first dimension, and the polarization component changes the polarization state of the first diffracted beam. The second Bragg grating generates a second diffracted beam to expand the first polarized diffracted beam in a second dimension to provide backlight for a display device.

[0027] Yet another aspect of the present disclosure relates to a beam expander system, comprising a first volume Bragg grating (VBG) illuminated by a first collimated beam to form a first diffracted beam along a length of the first VBG; and a polarization component configured to switch a polarization state of the first diffracted beam. The beam expander system also includes a second VBG for expanding the first polarized diffracted beam to form a backlight for a display device. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To easily identify the discussion of any particular element or act, the most significant digit(s) in a reference number refers to the figure number in which the element is first introduced.

[0029] Figure 1A and Figure 1B is a schematic diagram illustrating an example of a compact beam expander in accordance with certain aspects of the subject technology.

[0030] Figure 1C and Figure 1D is a schematic diagram showing a conventional LCD with a laser backlight.

[0031] Figure 2A and Figure 2B is a schematic diagram illustrating an example of an LCD with improved throughput and a corresponding display device with fill-factor limitation according to certain aspects of the subject technology.

[0032] Figure 2C 、 Figure 2D 、 Figure 2E and Figure 2F is a schematic diagram illustrating an example of an image of a beam expander and corresponding beams with improved throughput, in accordance with certain aspects of the subject technology.

[0033] Figure 3A and Figure 3B is a schematic diagram illustrating an example of a compact liquid crystal on silicon (LCOS) display device and a corresponding display with an improved fill factor according to certain aspects of the subject technology.

[0034] Figure 3C is a schematic diagram showing an example of a conventional LCOS display system.

[0035] Figure 4 is a schematic diagram illustrating an example of a monolithic dual VBG illuminator with a wave plate in accordance with certain aspects of the subject technology.

[0036] Figure 5 is a diagram illustrating certain aspects of the subject technology Figure 4Schematic diagram of an example monolithic dual-VBG illuminator with optional prisms.

[0037] Figure 6A and Figure 6B is a schematic diagram illustrating an example of a monolithic dual VBG illuminator with a have-wave film and a cross-sectional view of the have-wave film in accordance with certain aspects of the subject technology.

[0038] Figure 7A is a schematic diagram illustrating an example of a monolithic dual VBG illuminator with polarization components in accordance with certain aspects of the subject technology.

[0039] Figure 7B is a schematic diagram illustrating an example of a monolithic dual VBG illuminator having an angled surface VBG1 in accordance with certain aspects of the subject technology.

[0040] Figure 8A and Figure 8B is a schematic diagram illustrating an example of a backlight system with a collimated beam and a corresponding image including artifacts.

[0041] Figure 9A and Figure 9B is a schematic diagram illustrating an example of a compact beam expander with illumination steering and a corresponding backlight system in accordance with certain aspects of the subject technology.

[0042] Figure 10A and Figure 10B is a schematic diagram illustrating an example of a compact beam expander and multiplexer (MUX) pitch VBG in accordance with certain aspects of the subject technology.

[0043] Figure 10C is a diagram illustrating an example of steps for forming a MUX gap VBG according to certain aspects of the subject technology.

[0044] Figure 11A 、 Figure 11B and Figure 11C is a schematic diagram illustrating an example of a compact beam expander with zoned illumination and corresponding images of beamlets and an expanded beam, in accordance with certain aspects of the subject technology.

[0045] In the drawings, elements with the same or similar reference numerals relate to the same or similar properties, unless explicitly stated otherwise. DETAILED DESCRIPTION

[0046] In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that embodiments of the present disclosure may be practiced without some of these specific details. In other instances, well-known structures and techniques are not shown in detail to avoid obscuring the present disclosure. The embodiments disclosed herein will be described with reference to the accompanying drawings.

[0047] An example architecture of the subject technology relates to an apparatus comprising a light source that generates a light beam, a first grating illuminated by the light beam, and a second grating optically coupled to the first grating. The first grating is configured to perform a first diffraction that expands the light beam in a first dimension and forms a first beam. The second grating is configured to perform a second diffraction that expands the first beam in a second dimension and provides backlighting for a display device (e.g., an LCD or LCOS).

[0048] In some implementations, the first grating is illuminated by a collimated beam of light from a laser source.

[0049] In one or more implementations, the first diffraction is a first single diffraction that generates a first single diffraction beam that can expand the beam in a first dimension of a first grating coupled to a second grating.

[0050] In some implementations, the second diffraction is a second single diffraction that generates a second single diffraction beam that expands the expanded first beam in a second dimension to form a two-dimensional beam perpendicular to the plane of the second grating.

[0051] In one or more implementations, the first grating is a first Bragg grating, such as a first VBG, and the second grating is a second Bragg grating, such as a second VBG.

[0052] In some implementations, the first VBG and the second VBG are single diffraction VBGs.

[0053] In one or more implementations, at least one of the first VBG and the second VBG is a multiplexed (MUX) VBG including a plurality of gratings having different pitches for generating MUX diffraction beams to increase the diffraction angle range.

[0054] In one or more implementations, the display device includes an LCD display device or an LCOS display device.

[0055] In some implementations, the apparatus of the subject technology further includes a polarization component positioned between the first grating and the second grating.

[0056] In one or more implementations, the polarization component includes a half-wave plate for changing a polarization state of the first beam.

[0057] In some implementations, the apparatus of the subject technology further includes a reflective plate for directing the light beam at various angles to increase the pupil size of the backlight.

[0058] In one or more implementations, the light source is a grid of lasers, and the individual lasers of the grid are selectively controllable to turn on or off to form a zoned beam pattern that can convert the backlight into a zoned backlight having a zoned pattern.

[0059] Display devices of the subject technology can be advantageously used in a variety of applications, including AR and VR devices, to make these devices more compact. Furthermore, application of the subject technology can improve image uniformity and diffraction efficiency and mitigate some artifact issues, such as those caused by particles in the light of the illumination beam and scratches in the optical device. Some implementations of the subject technology can allow for zoned illumination, thereby saving power and improving contrast, as further described herein.

[0060] Turning now to the description of the drawings, Figure 1A and Figure 1B is a schematic diagram illustrating examples of compact beam expander systems 100A and 100B according to certain aspects of the subject technology. The compact beam expander system 100A provides a wide illumination beam for a pixelated display device (such as an LCD or LCOS) in an AR headset and / or a VR headset. The compact beam expander system 100A includes a light source 102, a first VBG 104, and a second VBG 106. The light source 102 provides input backlighting for the display device. In one or more implementations, the light source 102 can include a laser (e.g., a laser diode) of one or more visible colors (e.g., RGB), or a broadened source such as a light emitting diode (LED) and / or other light source. In some implementations, a collimating element can be used to form the input illumination into a collimated beam directed toward the first VBG 104. The first VBG 104 receives the collimated beam input having a first polarization and provides a first expanded beam along a first direction to the second VBG 106 using single diffraction. The second VBG 106 receives the first expanded beam in the first direction and uses another single diffraction to provide a second expanded beam 108 having a second polarization in a second direction to a display device, such as an AR headset and / or a VR headset. In some implementations, the second polarization is the same as the first polarization.

[0061] The compact beam expander system 100B includes a light source 110 (e.g., an RGB laser), a beam shaper 112, a VBG beam expander 114, a phase mask 116, and a display device 118. The beam shaper 112 can be a collimating element that receives a collimated Gaussian beam at a first surface, such as a collimated Gaussian beam provided by a gradient index (GRIN) lens placed in front of an LED or laser diode. The output surface of the collimating element is shaped to provide a collimated beam with a uniform intensity distribution (e.g., a flat-top distribution) in cross-section. Such a collimated beam can produce uniform intensity in a display screen of a VR / AR head-mounted device as desired.

[0062] Phase mask 116 is a phase-shifting mask that is an optical element that can encode the entire spectral response (including the Bragg wavelength and spectral response type) of VBG beam expander 114. Display device 118 can be an LCD display or an LCD-thin film transistor (TFT) display. TFTs are active elements (e.g., transistors) made of semiconductors (e.g., silicon) that act as switches for each pixel of an LCD display, turning them on or off. The addition of TFTs to LCD displays has greatly improved the use of LCDs in various display applications.

[0063] Figure 1C and Figure 1D is a schematic diagram illustrating a conventional LCD structure 100C and a phase plate structure 100D. The LCD structure 100C is composed of multiple layers, including 110, a grating light guide or waveguide 120, a phase plate 122 (or a microlens array), a first polarizer 124, a TFT 126, an LC 128, a color filter 130, and a second polarizer 132. When illuminated by a light source 110 (which may be an RGB laser source), the LCD structure 100C generates an RGB light beam 134. Each layer of the LCD 100C has a specific throughput, resulting in an overall throughput of approximately 70%.

[0064] This overall throughput is less than approximately 95% of the throughput of the compact beam expander system 100B of the subject technology. Furthermore, in addition to being more compact than the existing LCD structure 100C and being a monolithic structure capable of achieving higher throughput, the compact beam expander system 100B also offers other advantages. For example, the compact beam expander system of the subject technology can reduce fringe speckle, improve the angular spread of compact LCOS solutions, and enable zoned illumination using compact VBG illumination, thereby saving power.

[0065] Phase plate structure 100D shows a more detailed structure of the phase plate 122 of LCD structure 100C and includes a waveguide 140 , a microlens array 142 , and an LC plate with TFTs 144 .

[0066] Figure 2A and Figure 2B 2 is a schematic diagram illustrating an example of an LCD 200A with improved throughput and a corresponding display 200B with fill factor limitations according to certain aspects of the subject technology. The LCD 200A of the subject technology includes a light source 202, a beam shaper 204, a VBG compact beam expander 206 (hereinafter referred to as beam expander 206), a phase mask 208, and a display panel 210. The light source 202 can be an RGB laser or other light source. The beam shaper 204 can be a collimator, as described above with respect to Figure 1B The VBG compact beam expander 206 is similar to the beam shaper 112 described above. Figure 1A A VBG beam expander is formed by the first VBG and the second VBG, as described above.

[0067] In some implementations, the phase mask 208 can be a microlens array (MLA), which can encode the spectral response of the beam expander 206, as described above. In one or more implementations, the display panel 210 can be made of an LCD or a TFT LCD, as described above.

[0068] Display 200B is composed of a plurality of pixels 212, of which pixel representations 214 illustrate shaded areas used by electrodes and conductors for the circuitry on the LCD pixel. This can limit the fill factor of the LCD. Furthermore, LCDs typically have a larger area than LCOS display devices.

[0069] Figure 2C 、 Figure 2D 、 Figure 2E and Figure 2F 2 is a diagram illustrating an example of a beam expander 200C with improved throughput and images 200D, 200E, and 200F of corresponding beams according to certain aspects of the subject technology. Figure 2A Detailed structure of the beam expander 206. The beam expander 200C includes a light source 220, which can be a small (e.g., approximately 2 mm) laser; a first VBG 222; and a second VBG 224. The first VBG 222 is a VBG layer that diffracts incident light from the light source 220 along the length of the VBG layer into the second VBG 224 to form an expanded beam (e.g., 2 cm in size).

[0070] Figure 2D and Figure 2E Images 200D and 200E of the respective beams along the first VBG 222 and the second VBG 224 are shown in two dimensions. Figure 2F An image 200F shows a three-dimensional view of the expanded beam formed by the second VBG 224. The shape of the three-dimensional view follows Figure 2A The shape of the laser beam formed by the beam shaper 204 is not limited to Figure 2F Circular is shown, and Gaussian, rectangular, or other shapes may be used.

[0071] Figure 3A and Figure 3B is a schematic diagram illustrating an example of a compact LCOS display system 300A and a corresponding display 300B with an improved fill factor according to certain aspects of the subject technology. The compact LCOS display system 300A includes a compact LCOS beam expander 302, a projection lens 314, and a waveguide 316 for AR display. The compact LCOS beam expander 302 includes a light source 304 (e.g., an RGB laser), a beam shaper 306, a compact VBG beam expander 308 (hereinafter referred to as beam expander 308), an LCOS 310, and an aluminum (Al) layer 312. The beam shaper 306 can be a collimator that can collimate the input light from the light source 304 and shape it into a beam profile that can be circular or other shapes. The collimated beam and / or the shaped beam from the beam shaper 306 is received by the beam expander 308, which expands the received beam into the LCOS display device. The Al layer 312 is a reflector that reflects the expanded beam toward a projection lens 314 and a waveguide 316 , which may be a waveguide for an AR device or a VR device. The circuitry and wiring of the LCOS 310 are embedded behind the Al layer 312 .

[0072] Figure 3B The corresponding display 300B of the compact LCOS display system 300A is shown. Figure 2B The fill factor of the compact LCOS display system 300A shows a significant improvement compared to the display 200B.

[0073] Figure 3C 3 is a schematic diagram illustrating an example of a conventional LCOS display system 300C, which includes a light source 322 (eg, RGB lasers), a condenser lens 324 , a lens array 326 , a pre-polarization layer 328 , a polarization beam splitter 330 , and an LCOS display device 332 . Figure 3CAlso shown are projection lens 334 and viewer eye 336. Polarization beam splitter 330 is a beam splitting cube that increases the volume of the existing LCOS display system 300C. Figure 3A The subject technology is shown replacing polarization beam splitter 330 with beam expander 308, which improves the compactness of the overall system.

[0074] Figure 4 4 is a schematic diagram illustrating an example of a monolithic dual VBG illuminator 400 with a wave plate 414 according to certain aspects of the subject technology. The monolithic dual VBG illuminator 400 (hereinafter referred to as VBG illuminator 400) includes a first VBG 410, a second VBG 412, and a wave plate 414. The first VBG 410 and the second VBG 412 are similar to those described above. Figure 1A The first VBG 104 and the second VBG 106 in the embodiment of the present invention are shown in FIG. 4. A wave plate 414 (e.g., a polarization switching layer is a half-wave plate (HWP) embedded between the first VBG 410 and the second VBG 412) transmits the light beam generated by the first VBG 410 and modifies its polarization state without attenuating, deflecting, or shifting the beam. The wave plate 414 can convert the first polarization of the light beam to a second polarization. In some implementations, the wave plate 414 converts the Z-polarization of the light beam to X-polarization, which expands into a two-dimensional beam depicted by ray 416. For illustration purposes, for Z-polarization, the electric field (E) is parallel to Figure 4 The Z axis of the XYZ coordinate system shown, while for X-polarization, the electric field is parallel to the X axis. Therefore, a collimated input beam with Z-polarization in the XY plane and a diameter of approximately 2 mm is converted into a collimated output beam with a diameter of approximately 20 mm, propagating in the Z direction and having X-polarization.

[0075] Because the Z-polarization is aligned along the grooves of the first VBG 410 (S-polarization), the input collimated beam is diffracted from the first VBG 410 in the Y direction with maximum efficiency. After passing through the wave plate 414, the diffracted beam switches to X-polarization and is aligned along the grooves of the second VBG 412 (S-polarization). The light is then diffracted from the second VBG 412 in the Z direction with high diffraction efficiency (e.g., >95%). Therefore, by including the wave plate 414, the VBG illuminator 400 utilizes the maximum diffraction efficiency of both the first VBG 410 and the second VBG 412.

[0076] It is important to note that the VBG behaves as a series of reflectors. When constructive interference occurs under Bragg conditions, a high diffraction efficiency results. This diffraction efficiency is a function of the polarization of the light. Similar to a general reflector, the diffraction efficiency of S-polarization reflection is higher than that of P-polarization. In particular, at the Brewster angle, the diffraction efficiency of S-reflection can reach approximately 100%, while the diffraction efficiency of P-reflection can be approximately 0%. Double diffraction in compact illuminators occurs in orthogonal planes, so the optimal polarization diffracted from the first diffraction is orthogonal to the optimal polarization of the second diffraction. To connect the two diffractions to the optimal polarization, a wave plate 414 is located in the optical path between the two diffractions.

[0077] Figure 5 is a diagram illustrating certain aspects of the subject technology Figure 4 Schematic diagram of an example monolithic dual-VBG illuminator with optional prisms. Figure 5 The embodiment 500 shown in FIG includes a first VBG 510, a second VBG 512, and a wave plate 514. The first VBG 510, the second VBG 512, and the wave plate 514 are connected to Figure 4 The first VBG 410, the second VBG 412 and the wave plate 414 are similar. The first VBG 410 and the second VBG 412 are similar to Figure 1A The embodiment 500 further includes a prism 516 having a wedge-shaped surface, which is an optical component. The prism 516 is placed at the illumination source (e.g., Figure 3A A shallow prism (e.g., having a thickness of about a few microns) is positioned near the beam expander 304, and the illumination source can abut the wedge-shaped surface of the prism 516. This configuration provides a compact coupling between the illumination source and the beam expander, which prevents misalignment of the different components. In some implementations, the prism 516 can be replaced with a mirror. In some implementations, the dimensions of the first VBG 510 are approximately 22 x 2.6 mm, and the dimensions of the second VBG 512 are approximately 22 x 20 mm. In some implementations, the first VBG 510 and the second VBG 512 are fabricated on a substrate having dimensions of approximately 22 x 22 x 2.6 mm. These exemplary dimensions, and implementations of embodiment 500, are not limited to these dimensions.

[0078] Figure 6A and Figure 6Bis a schematic diagram illustrating an example of a monolithic dual VBG illuminator 600A with a half-wave film 640, and a cross-sectional view 600B of the half-wave film, according to certain aspects of the subject technology. Monolithic dual VBG illuminator 600A includes a first VBG 610 and a second VBG 620. In one or more implementations, the input surface of first VBG 610 can have an angle q relative to the Z axis of the XYZ coordinates shown adjacent to second VBG 620. In certain aspects, angle q can be optional or can have a small value (e.g., a few degrees).

[0079] The bonding between the substrates of the first VBG 610 and the second VBG 620 is optional. Such bonding at the half-wave film 640 can reduce the reflection loss of the film / air and substrate / air. Bonding the first VBG 610 and the second VBG 620 together can make it easier to manufacture in terms of alignment of the entire system. Figure 6A As can be seen in FIG, the iso-refractive index lines in the first VBG 610 can be along the vertical direction (Z-axis), and the iso-refractive index lines of the second VBG 620 can be along the horizontal direction (X-axis).

[0080] Figure 6B The cross-sectional view 600B of the half-wave film shown depicts a fast axis at approximately 45 degrees relative to the horizontal (X-axis). Light polarized along the fast axis travels faster than light polarized along the slow axis.

[0081] Figure 7A FIG2 is a schematic diagram illustrating an example of a monolithic dual-VBG illuminator 700A having a polarization component according to certain aspects of the subject technology. The monolithic dual-VBG illuminator 700A includes a first VBG 710, a second VBG 720, and a polarization component 730 (e.g., a half-wave plate) placed in the space between the first VBG 710 and the second VBG 720. Figure 7A The polarization propagating between the first VBG 710 and the second VBG 720 is depicted. In some implementations, the polarization component 730 can be a half-wave plate coupled between the first VBG 710 and the second VBG 720 or a half-wave film formed on the first VBG 710.

[0082] VBGs typically have higher diffraction efficiency for S-polarized (perpendicular to the plane) light. To ensure high diffraction efficiency for both VBGs (first VBG 710 and second VBG 720), a polarization manipulation component (such as polarization component 730) is placed between the VBGs to rotate the light polarization to S-polarization in the plane of the second VBG 720.

[0083] Figure 7Bis a schematic diagram illustrating an example of a monolithic dual VBG illuminator 700B having an angled surface first VBG 710 according to certain aspects of the subject technology. The monolithic dual VBG illuminator 700B is similar to Figure 7A The monolithic dual VBG illuminator 700A, except that the first surface of the first VBG 710 is opposite to Figure 7B The Z axis of the XYZ coordinate system is shown with an angle 712. In some implementations, the angle 712 can be approximately 5.7 degrees, but is not limited to this value and can be less than or greater than 5.7 degrees. Figure 7B As can be seen from the figure, the propagation direction of the illumination beam is downward.

[0084] Figure 8A and Figure 8B 8 is a schematic diagram illustrating an example of a backlight system 800A with a collimated beam and a corresponding image 800B including artifacts. The conventional backlight system 800A (e.g., LCOS) includes a backlight source 802 (illuminator) and an imaging lens 804 that focuses incident light from the backlight source 802 through a pupil 806 into a lens 808 of a viewer's eye, where the incident light forms an image on the viewer's retina 810.

[0085] Figure 8B The image 800B formed on the retina 810 is depicted. When the collimated beam passes through the backlight system 800A, artifacts 807 appear in the image due to the narrow beam and pupil 806. The source of these artifacts can be tiny dust particles on the narrow beam light and / or tiny obstructions or scratches on the imaging lens 804, which can cause severe image non-uniformity (brightness variations). Such artifacts can also be observed by the human eye when observing a bright, uniform sky, i.e., floaters appear in the eye. The subject technology reduces these artifacts, as shown below: Figure 9B shown and discussed.

[0086] Figure 9A and Figure 9B FIG2 is a schematic diagram illustrating an example of a compact beam expander 900A and a corresponding backlight system 900B with illumination steering according to certain aspects of the subject technology. The compact beam expander 900A (LCD or LCOS, hereinafter referred to as beam expander 900A) includes a collimated light source 912, a first VBG 910, a second VBG 920, and a beam scanner 930. The beam scanner 930 can be a microelectromechanical system (MEMS) reflector that can change the angle of incidence of the incident collimated beam on the first VBG 910 of the beam expander 900A. The movable reflector scans the desired angular spread of the input pupil.

[0087] The backlight system 900A of the subject technology is Figure 8A Backlight system 900B is a modified version of backlight system 800A, meaning that the illumination angle (θ) is greater than zero (e.g., less than or equal to about 5 degrees). Similar to backlight system 800A, backlight system 900B includes an illuminator 902 (LCD or LCOS) with an illumination angle 903 (θ) and an imaging lens 904 that creates a focal region on the lens 808 through pupil 806 (the pupil of the eye). The illumination angle θ can be determined by Figure 9A The LC illuminator's illumination angle θ increases the pupil size, as shown in FIG900B . This increased pupil size is effectively the result of the focal point being shifted to a focal region to avoid artifacts caused by issues such as dust or scattering at the eye position, thereby improving the uniformity of the displayed image. By increasing the input aperture in the imaging lens 904, each light source point in the LCOS display (e.g., pixel) is allowed to have a larger angle of incidence. The incident light on the viewer's retina 810, 940 is smeared (e.g., blurred), thereby eliminating artifacts.

[0088] Figure 10A and Figure 10B is a schematic diagram illustrating an example of a compact beam expander 1000A and a multiplexed (MUX) VBG according to certain aspects of the subject technology. The compact beam expander 1000A includes a light source 1012 (e.g., a collimated laser) that generates a beam directed toward a first VBG 1010, which diffracts the beam into a second VBG 1020. At least one of the first VBG 1010 and the second VBG 1020 includes a MUX grating, such as Figure 10B The MUX grating 1040 is shown. Figure 10B Also shown is a diagram 1000B of an exposure pattern 1030 comprising multiple (eg, 20) sinusoidal exposures via an optical interference technique, the exposure pattern being used to write the grooves of a grating into a substrate.

[0089] Figure 10C 1000C is a schematic diagram illustrating an example of steps for forming a MUX pitch VBG according to certain aspects of the subject technology. By exposing the substrate multiple times at different diffraction angles, various grooves with different pitch values ​​(e.g., 1050, 1060, and 1070) can be produced on the same substrate to form a MUX grating. Each set of grooves can diffract an incident light beam into different directions (1052, 1062, and 1072) at different angles corresponding to the different pitch values. Each step shown in 1000C will produce a set of grooves with a specific pitch. The result of these steps is Figure 10B The MUX gratings 1040 are generated on a substrate to produce a MUX pitch VBG.

[0090] The Compact Beam Expander 1000A with MUX VBG is another way to achieve the required angular spread of the input pupil, such as Figure 9A The beam scanner 930 is used to perform the above operations. In other words, the compact beam expander 1000A does not use any beam scanner because the function of the beam scanner is replaced by using the MUX VBG.

[0091] Figure 11A 、 Figure 11B and Figure 11C is a schematic diagram illustrating an example of a compact beam expander 1100A with zoned illumination and corresponding images 1100B and 1100C of a beamlet and an expanded beam, respectively, according to certain aspects of the subject technology. Figure 4 The VBG illuminator 400 is similar to the VBG illuminator 400 and uses an array (grid) of lasers (e.g., 2x2 mm) instead of a single illumination source to generate the incident beam. The incident beam is located at Figure 11A The Z direction of the XYZ coordinates shown is diffracted by the compact beam expander 1100A to produce a zoned illumination with a larger size (e.g., 20x20 mm). This feature is a power-saving feature that allows turning on only the specific lasers needed in the array and keeping the rest of the lasers in the array off to save power. For example, in a 3x3 laser array 1100B including 9 lasers, only the ninth laser is turned on and the rest of the lasers are turned off. This illumination produces 9 zone beams (in the Z direction), as shown Figure 11C , where only zone 9 is turned on and the remaining zones are turned off. In other words, the compact beam expander 1100A allows for the generation of a partitioned illumination pattern with selectively turned on and off zones in the field of view. For example, in AR applications, the partitioning feature of the subject technology allows for the formation of a partitioned display in which a portion of the LCOS display can be desirably turned off to allow direct transmission of light through the eyepiece of the smart glasses. Thus, a portion (e.g., a corner of at least one eyepiece) can be left to display computer-generated images, readable text or symbols, etc. In addition, the zones that are turned on in the display can be changed dynamically so that the AR application changes accordingly. Note that each zone in the LCOS display can include multiple pixels and therefore can display quite complex images (e.g., with high resolution, contrast, color gamut, etc.).

[0092] In addition to saving power, the compact beam expander 1100A has the additional advantage that it also improves image contrast because only the region of interest receives light.

[0093] The compact beam expanders of the subject technology, including the compact beam expander 1100A, may be used in various optical devices, such as AR / VR headsets.

[0094] As used herein, the phrase "at least one of" following a series of items, and the terms "and" or "or" used to separate any of those items, modifies the entire list, rather than each element of the list (i.e., each item). The phrase "at least one of" does not require selection of at least one item; rather, the phrase allows for meanings that include at least one of any of a plurality of items, and / or at least one of any combination of a plurality of items, and / or at least one of each of a plurality of items. For example, the phrases "at least one of A, B, and C" or "at least one of A, B, or C" refer to only A, only B, or only C; any combination of A, B, and C; and / or at least one of each of A, B, and C.

[0095] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or superior to other embodiments. Phrases such as aspect, the aspect, another aspect, some aspects, one or more aspects, implementation, the implementation, another implementation, some implementations, one or more implementations, embodiment, the embodiment, another embodiment, some embodiments, one or more embodiments, configuration, the configuration, another configuration, some configurations, one or more configurations, subject technology, disclosure, the present disclosure, and other variations thereof are for convenience and do not imply that the disclosure associated with such phrases is essential to the subject technology or that the disclosure applies to all configurations of the subject technology. The disclosure associated with such phrases may apply to all configurations, or one or more configurations. The disclosure associated with such phrases may provide one or more embodiments. Phrases such as one aspect or some aspects may refer to one or more aspects, and vice versa, and the same applies to the other aforementioned phrases.

[0096] Unless otherwise specified, references to elements in the singular are not intended to mean "one and only one", but rather "one or more". Positive pronouns (e.g., his) include the negative and neuter genders (e.g., her and its), and vice versa. The term "some" refers to one or more. Titles and subtitles with underlines and / or italics are used for convenience only, do not limit the subject technology, and are not mentioned in association with the description of the subject technology. Relevant terms (such as first and second, etc.) can be used to distinguish one entity or action from another entity or action without requiring or implying any actual such relationship or order between such entities or actions. It is known or will be known to those of ordinary skill in the art that all structural and functional equivalents of the elements of the various configurations described throughout this disclosure are expressly incorporated herein by reference and are intended to be covered by the subject technology. In addition, regardless of whether such disclosure is expressly recorded in the above description, anything disclosed herein is not intended to be dedicated to the public. No claim element shall be construed under the terms of 35 USC §112, sixth paragraph, unless the element is expressly recited using the phrase "means for" or, in the case of a method claim, the element is recited using the phrase "step for."

[0097] Although this specification contains many details, these details should not be interpreted as limitations on the scope of what may be described, but rather as descriptions of specific implementations of the subject matter. Certain features described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually in multiple embodiments or in any suitable subcombination. Furthermore, although features may be described above as functioning in certain combinations, and even initially described as such, in some cases, one or more features from the described combination may also be removed from the combination, and the described combination may involve variations of subcombinations or subcombinations.

[0098] The subject matter of this specification has been described with respect to specific aspects, but other aspects may also be implemented and are within the scope of the appended claims. For example, although operations are described in a particular order in the accompanying drawings, this should not be understood as requiring that these operations be performed in the particular order shown or in sequential order, or requiring that all shown operations be performed to obtain the desired result. The actions recited in the claims can be performed in a different order and still achieve the desired result. As an example, the processes described in the accompanying drawings do not necessarily require the particular order shown or sequential order to achieve the desired result. In some cases, multi-tasking parallel processing may be advantageous. Moreover, the separation of various system components in the various aspects described above should not be understood as requiring such separation in all aspects, and it should be understood that the described program components and systems can generally be integrated into a single software product or packaged into multiple software products.

[0099] The invention title, background technology, figure description, abstract and drawings are incorporated into this disclosure and are provided as illustrative examples of the present disclosure, not as limiting descriptions. It should be understood that they will not be used to limit the scope or meaning of the claims. In addition, in the detailed description, it can be seen that in order to make the present disclosure smooth, the description provides illustrative examples and various features are grouped together in various embodiments. This method of disclosure should not be interpreted as reflecting an intention that the described subject matter requires more features than those expressly recited in each claim. Rather, as reflected in the claims, the subject matter of the present invention lies in less than all the features of a single disclosed configuration or operation. The claims are incorporated into the detailed description, with each claim independently serving as the subject matter of a separate description.

[0100] Various aspects of the subject matter described in this disclosure can be implemented to achieve one or more of the following potential advantages. The described techniques can be implemented to support a range of benefits and significant advantages of the disclosed eye tracking system. Notably, the subject technology enables the production of an all-solid-state device for depth sensing that is compact, low-power, and low-cost.

[0101] An important aspect of the disclosed technology is that it provides a solid-state (eg, silicon) photonic interferometer system that is capable of depth sensing corneal shape to determine gaze direction.

[0102] As used herein, the phrase "at least one of" following a list of items, and the terms "and" or "or" used to separate any of those items, modifies the entire list and does not modify each element (ie, each item) of the list.

[0103] To the extent that the terms "including," "having," and the like are used in this specification or the claims, such terms are intended to be inclusive in a manner similar to the term "comprising" as interpreted when used as a transitional word in a claim.

[0104] Unless otherwise specified, references to elements in the singular are not intended to mean "one and only one," but rather "one or more." All structural and functional equivalents to the elements of the various configurations described throughout this disclosure that are known or later become known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the subject technology. Furthermore, nothing disclosed herein is intended to be dedicated to the public, regardless of whether such disclosure is explicitly cited in the above description.

[0105] Although this specification contains many details, these details should not be interpreted as limitations on the scope of what may be claimed, but rather as descriptions of specific implementations of the subject matter. Certain features described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually in multiple embodiments or in any suitable subcombination. Furthermore, although features may be described above as functioning in certain combinations, and even initially claimed as such, in some cases one or more features from a described combination may also be removed from that combination, and a claimed combination may involve a subcombination or a variant of a subcombination.

Claims

1. A device, comprising: a light source configured to generate a light beam; a first grating, the first grating being illuminated by the light beam; as well as a second grating, the second grating being optically coupled to the first grating, wherein the first grating is configured to perform a first diffraction to expand the light beam in a first dimension to form a first beam, and The second grating is configured to perform a second diffraction to expand the first beam in a second dimension to provide backlighting for a display device.

2. The device according to claim 1, wherein The first grating is illuminated by a collimated beam of a laser source.

3. The device according to claim 1 or 2, wherein: The first diffraction comprises a first single diffraction configured to expand the light beam in the first dimension of the first grating coupled to the second grating.

4. The device according to any one of claims 1 to 3, wherein The second diffraction includes a second single diffraction configured to expand the expanded first beam in the second dimension to form a two-dimensional beam perpendicular to the plane of the second grating.

5. An apparatus according to any preceding claim, wherein The first grating comprises a first volume Bragg grating (VBG), and the second grating comprises a second VBG, in which case optionally any one of the following is present: a) wherein the first VBG and the second VBG comprise single diffraction VBGs; or b) wherein at least one of the first VBG and the second VBG comprises a multiplexed (MUX) VBG, the multiplexed VBG comprising a plurality of gratings having different pitches, the plurality of gratings being configured to increase a diffraction angle range.

6. An apparatus according to any preceding claim, wherein one or more of the following are present: a) wherein the display device comprises an augmented reality (AR) display or a virtual reality (VR) display; or b) Among them, The display device comprises a liquid crystal display (LCD) device; or c) Among them, The display includes a liquid crystal on silicon (LCOS) display device.

7. A device according to any preceding claim, further comprising a polarisation component located between the first grating and the second grating, wherein The polarization component includes a half-wave plate configured to change a polarization state of the first beam.

8. An apparatus according to any preceding claim, further comprising a reflective plate configured to direct the light beam at various angles to increase the pupil size of the backlight.

9. An apparatus according to any preceding claim, wherein The light source comprises a grid of lasers, and wherein individual lasers of the grid are selectively controllable to be switched on or off to convert the backlight into a zoned backlight.

10. A beam expander system, comprising: a laser configured to generate a first beam; a first Bragg grating, the first Bragg grating being illuminated by the first beam; Polarization components; as well as a second Bragg grating, the second Bragg grating being optically coupled to the first Bragg grating, wherein the first Bragg grating is configured to generate a first diffracted beam in a first dimension, The polarization component is configured to change the polarization state of the first diffracted beam, and The second Bragg grating is configured to generate a second diffracted beam to expand the first polarized diffracted beam in a second dimension to provide backlighting for a display device.

11. The system according to claim 10, wherein: The first Bragg grating includes a first VBG, and the second Bragg grating includes a second VBG.

12. The system according to claim 10 or 11, wherein: The first diffracted beam comprises a first single diffracted beam expanded in the first dimension of the first Bragg grating, and wherein the second diffracted beam comprises a second single diffracted beam.

13. The system according to any one of claims 10 to 12, wherein: The first diffracted beam comprises a first MUX diffracted beam expanded in the first dimension of the first Bragg grating, and wherein the second diffracted beam comprises a second MUX diffracted beam.

14. A beam expander system, the system comprising: a first VBG illuminated by a first collimated beam and configured to form a first diffracted beam along a length of the first VBG; a polarization component configured to switch a polarization state of the first diffracted beam; as well as a second VBG configured to expand the first polarized diffracted beam to form a backlight for a display device.

15. The system according to claim 14, wherein: The first VBG comprises a first MUX VBG, wherein the second VBG comprises a second MUX VBG, and wherein the polarization component comprises a half-wave plate, in which case the system optionally further comprises a collimated light source for generating the first collimated beam, wherein the collimated light source comprises a grid of lasers, and wherein the grid of lasers is configurable to generate a partitioned beam pattern, the partitioned beam pattern causing a partitioned backlight.

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