An ar display module and control method based on lcd and polarization volume grating

Abstract

The application relates to an AR display module and a control method based on an LCD and a polarization volume grating, and belongs to the AR display field.The AR display module comprises a display module, a collimating lens group, a quarter-wave plate and a polarization volume grating.The display module comprises an LCD light machine unit provided with a polarizer and used for outputting a linearly polarized image light beam.The collimating lens group is arranged on the light output side of the display module.The quarter-wave plate is arranged on the light output path of the collimating lens group and is provided with adjacently arranged first and second polarization conversion zones and is used for performing polarization conversion on the linearly polarized image light beam.The first polarization conversion zone is configured to convert incident linearly polarized light into first circularly polarized light of a first rotation direction.The second polarization conversion zone is configured to convert incident linearly polarized light into second circularly polarized light of a second rotation direction opposite to the first rotation direction.Through cooperation of the quarter-wave plate and the polarization volume grating, efficient separation of left-eye and right-eye image light beams is realized.

Description

Technical Field

[0001] This application relates to the field of AR display technology, and in particular to an AR display module and control method based on LCD and polarization volume grating. Background Technology

[0002] With the rapid development of augmented reality (AR) technology, near-eye display devices have become an important human-computer interaction terminal in the era of spatial computing. In AR near-eye display optical systems, micro-display modules are usually used as image sources, and the light beam is projected into the human eye through coupling elements such as collimating lens groups and optical waveguides.

[0003] The prior art relates to a near-eye display device and an AR display device. The near-eye display device may include: a first waveguide lens and a second waveguide lens disposed on the same plane; a projection optical engine disposed at an intermediate position between the first waveguide lens and the second waveguide lens; a beam splitter disposed in the output optical path of the projection light source; the beam splitter is used to diffract the projection light output from the projection light source to output two paths of projection light rays that are coupled into the first waveguide lens and the second waveguide lens respectively; the first waveguide lens and the second waveguide lens are respectively used to conduct the coupled projection light rays through total internal reflection and couple them out from their corresponding coupling ends.

[0004] The beam splitting schemes in the above-mentioned and existing single-optical-mechanical systems adopt the amplitude division method, which inherently divides the incident light energy equally between the two paths. The highest theoretical light efficiency of a single path does not exceed 50%. Since the beam splitter is not selective for the polarization state of the incident light, it inevitably mixes the information of the two paths, resulting in binocular crosstalk. Summary of the Invention

[0005] This application provides an AR display module and control method based on LCD and polarization volume grating, which can solve the problem of difficulty in balancing system thinness and light efficiency and crosstalk separation of left and right eye images in single-optical-mechanical systems.

[0006] The technical solution of this application is as follows: An AR display module based on LCD and polarization volume grating, comprising: The display module includes an LCD optomechanical unit equipped with a polarizer for outputting linearly polarized image beams; A collimating lens group is disposed on the light-emitting side of the display module and is used to collimate the linearly polarized image beam. A quarter-wave plate is disposed on the light output path of the collimating lens group, and has a first polarization conversion region and a second polarization conversion region arranged adjacent to each other, for performing partitioned polarization conversion on the linearly polarized image beam; The first polarization conversion region is configured to convert incident linearly polarized light into first circularly polarized light with a first rotation direction, and the second polarization conversion region is configured to convert incident linearly polarized light into second circularly polarized light with the opposite rotation direction to the first rotation direction. A polarization volume grating is disposed on the light-emitting side of the quarter-wave plate, and has a first diffraction region and a second diffraction region corresponding to the positions of the first polarization conversion region and the second polarization conversion region, respectively. The first diffraction region is configured to diffract the first circularly polarized light and emit it as first diffracted light, and the second diffraction region is configured to diffract the second circularly polarized light and emit it as second diffracted light; and A coupling optical component is disposed on the diffraction path of the polarization volume grating to guide the first diffracted light and the second diffracted light to the user's left and right eyes, respectively.

[0007] By adopting the above scheme, since the first and second polarization conversion regions of the quarter-wave plate convert the same linearly polarized light into two circularly polarized lights with opposite rotation directions, and the polarization volume grating has the physical characteristic of selective diffraction of circularly polarized light with specific rotation directions, only a single display module is needed to achieve efficient separation of the left and right eye image beams in the polarization dimension, without the need for additional beam splitting prisms or semi-reflective elements, effectively reducing the number of optical components and the overall size of the system. At the same time, since the separation of the left and right eye beams is based on the orthogonal selectivity of polarization states rather than spatial or amplitude segmentation, optical crosstalk between binocular images can be effectively suppressed. In addition, this combined scheme achieves beam splitting in the polarization dimension, which is fundamentally different from the amplitude / spatial dimension beam splitting of existing technologies in terms of physical mechanism, reducing the light efficiency loss present in conventional beam splitting techniques.

[0008] In one embodiment of this application, the polarization volume grating includes a first polarization volume grating and a second polarization volume grating that are sequentially stacked along the light propagation direction, and the first polarization volume grating and the second polarization volume grating are each provided with adjacent first diffraction regions and second diffraction regions; The in-plane grating period and / or longitudinal spiral period of the second polarization volume grating are not equal to those of the first polarization volume grating. The second polarization volume grating is configured to diffract the zero-order light transmitted from the first polarization volume grating and direct the zero-order light into the coupling optical component.

[0009] By adopting the above scheme, the zero-order light transmitted by the first polarization volume grating that does not meet the Bragg condition is diffracted and recovered by setting a second polarization volume grating, which effectively broadens the angular bandwidth or spectral response range of the system, improves the overall diffraction utilization rate of the image beam, and helps to improve the uniformity of the display brightness of the image.

[0010] In one embodiment of this application, the quarter-wave plate comprises: Transparent substrate; At least three birefringence retardation layers are sequentially stacked on the transparent substrate; Each of the birefringent retardation layers is provided with an adjacent first polarization region and a second polarization region. At least three layers of the first polarization region are stacked to form the first polarization conversion region, and at least three layers of the second polarization region are stacked to form the second polarization conversion region.

[0011] By adopting the above scheme, since the phase delay of a single-layer birefringent material varies with the wavelength of the incident light and causes dispersion, it is difficult to simultaneously meet the quarter-wavelength delay requirement in the entire visible light band. By stacking and combining at least three birefringent delay layers, the phase delay cascade compensation effect between each layer can be utilized to maintain a delay close to one-quarter wavelength in the red, green, and blue bands, so that the beams in each band can obtain circularly polarized output with stable conversion rate, reducing stray light leakage and light energy loss caused by incomplete polarization conversion. In addition, when a quarter-wave plate is used in combination with a double-layer polarization volume grating, the quarter-wave plate provides high-purity circularly polarized input light across the entire visible light spectrum, enabling the double-layer polarization volume grating to operate at near its designed diffraction efficiency at all wavelengths, thus avoiding the diffraction efficiency reduction caused by impure input polarization states.

[0012] In one embodiment of this application, the optical retardation amount and fast axis reference angle of at least three birefringent retardation layers are all different to achieve achromatic delayed polarization conversion; In each of the birefringent retardation layers, the fast axis orientation angle of the first polarization region and the fast axis orientation angle of the second polarization region are mirror-symmetric about the boundary line between the two regions.

[0013] By adopting the above scheme, since the optical retardation amount and fast axis reference angle of each birefringent retardation layer are different, a cascaded retardation structure with complementary dispersion is formed between the multiple layers, which can achieve near achromatic polarization conversion in a wide spectral range, further improving the color reproduction under full-color display. At the same time, since the fast axis orientation angle of each layer in the first polarization region and the second polarization region is set to a mirror symmetry relationship, this symmetrical structure makes the two regions generate polarization state rotations with opposite directions but consistent amplitudes for incident linearly polarized light, thereby synchronously obtaining circularly polarized light output with opposite rotation directions on a single substrate, ensuring that the optical modulation characteristics distributed to the binoculars have good consistency and symmetry.

[0014] In one embodiment of this application, the fast axis orientation angle gradually increases or decreases radially from the center position to the edge within the first polarization conversion region and / or the second polarization conversion region, in order to further compensate for the incident angle deviation of the linearly polarized image beam emitted by the collimating lens group.

[0015] By adopting the above scheme, when the fast axis orientation angle is non-uniformly distributed in space, the phase modulation applied to the transmitted light wavefront also changes with the spatial position accordingly, which is equivalent to introducing a thin wavefront correction element based on geometric phase in the optical path. Its modulation effect on the transmitted light wavefront comes from the spatial gradient of the fast axis orientation, rather than the spatial change of physical surface shape or refractive index. By designing the rotational change rate of the fast axis orientation angle to gradually increase or decrease from the center to the edge, this equivalent surface shape can perform phase correction for aberrations such as field curvature and spherical aberration remaining in the collimating lens group, as well as phase deviation of oblique incident beams that deviate from the optical axis. This allows the device to improve the imaging quality of the edge field of view without adding additional optical components.

[0016] In one embodiment of this application, waveguide lenses are further included. Two waveguide lenses are provided, each corresponding to the first diffracted light and the second diffracted light respectively. The coupling optical component includes two coupling lenses, each corresponding to the first diffraction region and the second diffraction region respectively, so as to couple the first diffracted light and the second diffracted light into the corresponding waveguide lenses respectively. The display module, collimating lens group, quarter-wave plate and polarization volume grating are all disposed in the middle of the AR glasses frame, and the two waveguide lenses are respectively embedded on both sides of the AR glasses frame.

[0017] By adopting the above scheme, since the core optical components such as the display module, collimating lens group, quarter-wave plate and polarization volume grating are all concentrated in the nose bridge area of ​​the middle of the frame, the diffracted light from the left and right eyes after polarization and splitting is coupled into the corresponding waveguide lenses through the coupling lenses on both sides. This centrally symmetrical layout makes the center of gravity of the whole device located near the midline of the wearer's face, reducing the wearing tilt and pressure caused by weight offset in traditional single-sided optical mechanism schemes; at the same time, it reduces the possibility of inconsistencies in brightness, color and aberrations of binocular images.

[0018] In one embodiment of this application, a photoelectric sensor is further included. The photoelectric sensor is disposed in the middle of the AR glasses frame and located on the light-emitting side of the polarization volume grating. Its photosensitive surface intersects the output optical axis of the collimating lens group and is used to receive the zero-order transmitted light transmitted through the polarization volume grating. The LCD optical engine unit includes independently driven red, green, and blue light-emitting elements. The photoelectric sensor includes multiple photosensitive units corresponding to the red, green, and blue light channels, respectively. The multiple photosensitive units are used to receive the zero-order transmitted light of the corresponding color channel and output independent light intensity detection signals corresponding to each color channel.

[0019] By adopting the above scheme, the actual diffraction efficiency level of the current system can be indirectly calculated by placing the photoelectric sensor on the transmitted light side of the polarization volume grating to collect the zero-order leakage light; thus, there is no need to insert additional beam splitting or sampling elements in the effective diffraction optical path, reducing the loss of effective light energy and realizing non-destructive in-situ monitoring of changes in system light efficiency.

[0020] The second objective of this application is to provide an AR display control method based on LCD and polarization volume grating.

[0021] The technical solution is as follows: An AR display control method based on LCD and polarization volume grating, applied to an AR display module based on LCD and polarization volume grating, includes the following steps: S1: The light intensity of the zeroth order transmitted light is detected by the photoelectric sensor to obtain the light intensity detection value; S2: Compare the detected light intensity value with a preset reference value; S3: Adjust the backlight drive power of the LCD optical engine unit based on the comparison results: When the detected light intensity value is higher than the reference value, the backlight driving power of the LCD optomechanical unit is increased to compensate for the change in diffraction efficiency; When the detected light intensity value is lower than the reference value, the backlight driving power of the LCD optomechanical unit is reduced to compensate for the change in diffraction efficiency.

[0022] By adopting the above scheme, since the diffraction efficiency of the polarization volume grating fluctuates due to factors such as changes in ambient temperature and heat accumulation of the device itself, the zero-order leakage light intensity increases accordingly when the diffraction efficiency decreases. Therefore, the change in the zero-order leakage light intensity is used as a characterization signal for the real-time fluctuation of diffraction efficiency, so that the output power of the backlight unit can be dynamically and adaptively compensated with the change in diffraction efficiency.

[0023] In one embodiment of this application, the reference value is a pre-stored light intensity reference value, which corresponds to the light intensity of the zero-order transmitted light when the polarization volume grating is at a preset reference diffraction efficiency and the LCD optomechanical unit is at a reference output power.

[0024] By adopting the above scheme, since there are manufacturing process tolerances in different batches of polarization volume gratings, their initial diffraction efficiency and zero-order leakage ratio are not strictly consistent. By pre-calibrating the reference value of the zero-order leakage light intensity and writing it into the system storage, the interference of individual differences between devices on the feedback accuracy is reduced, and the consistency and reliability of the closed-loop adjustment strategy between different hardware products are improved.

[0025] In one embodiment of this application, in step S1, the light intensity detection value of each color light channel is obtained by the plurality of photosensitive units respectively; In step S3, the driving power of the three-color light-emitting elements corresponding to each color light channel in the LCD optical engine unit is independently adjusted according to the light intensity detection value of each color light channel and the corresponding reference value.

[0026] By adopting the above scheme, since the diffraction efficiency temperature drift characteristics of red, green, and blue light are different, the attenuation of diffraction efficiency of the three color channels is not synchronous and unequal when the ambient temperature or device temperature changes. By setting independent photosensitive units for the corresponding red, green, and blue channels to detect each channel individually and independently adjusting the driving power of each color light emitting element, decoupling compensation can be performed on each channel, effectively suppressing the color shift and white balance shift problems caused by temperature drift in the display screen.

[0027] In summary, this application includes at least one of the following beneficial technical effects: by setting a quarter-wave plate with a first polarization conversion region and a second polarization conversion region, the linearly polarized image beam is split into two circularly polarized beams with opposite rotation directions in the polarization dimension, and the two circularly polarized beams are independently diffracted and output by a polarization volume grating based on its rotation-selective diffraction characteristics. Thus, efficient polarization beam splitting of binocular images is achieved under the condition of using only a single optical engine, without the need for additional beam splitting elements such as beam splitting prisms or half-reflective mirrors. While effectively suppressing binocular optical crosstalk, the number of optical elements and the overall size of the system are reduced.

[0028] By setting the fast axis orientation angle of the birefringent retardation layer in the quarter-wave plate to a non-uniformly continuous spatial distribution from the center to the edge within the polarization conversion region, the spatial gradient change of the fast axis orientation angle generates non-uniform geometric phase modulation on the transmitted light wavefront. This is equivalent to introducing a thin gradient phase compensation element based on geometric phase into the optical path. Thus, while realizing the polarization conversion function, it corrects the phase of aberrations such as field curvature and spherical aberration remaining in the collimated lens group, as well as the phase deviation of the obliquely incident beam, improving the imaging quality of the edge field of view without adding additional optical lens elements.

[0029] By placing a photoelectric sensor on the transmittance side of a polarization volume grating to collect the undiffracted zero-order leakage light, the complementary relationship between the zero-order leakage light intensity and diffraction efficiency is used to indirectly indicate the current actual diffraction efficiency of the system. This enables the system to dynamically and adaptively compensate for fluctuations in the diffraction efficiency of the polarization volume grating caused by factors such as temperature changes. At the same time, it can achieve in-situ monitoring of changes in system light efficiency and closed-loop brightness stability control without inserting beam splitting or sampling elements and without losing the effective light energy of the display. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of an AR display module based on LCD and polarization volume grating provided in the embodiments of this application; Figure 2 This is a schematic diagram of the optical path of an AR display module based on an LCD and a polarization volume grating provided in an embodiment of this application; Figure 3 This is a partial cross-sectional schematic diagram of a quarter-wave plate of an AR display module based on an LCD and a polarization volume grating provided in an embodiment of this application; Figure 4 This is a flowchart illustrating an AR display control method based on an LCD and a polarization volume grating provided in an embodiment of this application.

[0031] Explanation of reference numerals in the attached figures: 1. Display module; 11. LCD optical engine unit; 2. Collimating lens group; 3. Quarter-wave plate; 31. First polarization conversion region; 311. First polarization region; 32. Second polarization conversion region; 321. Second polarization region; 33. Transparent substrate; 34. Birefringent retardation layer; 4. Polarization volume grating; 41. First diffraction region; 42. Second diffraction region; 43. First polarization volume grating; 44. Second polarization volume grating; 5. Coupled optical component; 51. Coupled lens; 6. Waveguide lens; 7. Photoelectric sensor. Detailed Implementation

[0032] The following is in conjunction with the appendix Figures 1-4This application provides a more detailed description of an AR display module and control method based on an LCD and a polarization volume grating.

[0033] An AR display module based on an LCD and a polarization volume grating is provided in this application embodiment, including: a display module 1, a collimating lens group 2, a quarter-wave plate 3, a polarization volume grating 4, and a coupling optical component 5.

[0034] Display module 1 includes an LCD optomechanical unit 11 equipped with a polarizer for outputting a linearly polarized image beam; The collimating lens group 2 is disposed on the light-emitting side of the display module 1 and is used to collimate the linearly polarized image beam; A quarter-wave plate 3 is disposed on the light output path of the collimating lens group 2, and is provided with a first polarization conversion region 31 and a second polarization conversion region 32 arranged adjacently, for performing partitioned polarization conversion on the linearly polarized image beam; The first polarization conversion region 31 is configured to convert incident linearly polarized light into first circularly polarized light with a first rotation direction, and the second polarization conversion region 32 is configured to convert incident linearly polarized light into second circularly polarized light with the opposite rotation direction to the first rotation direction. A polarization volume grating 4 is disposed on the light-emitting side of the quarter-wave plate 3, and is provided with a first diffraction region 41 and a second diffraction region 42 corresponding to the positions of the first polarization conversion region 31 and the second polarization conversion region 32, respectively. The first diffraction region 41 is configured to diffract the first circularly polarized light and emit it as the first diffracted light, and the second diffraction region 42 is configured to diffract the second circularly polarized light and emit it as the second diffracted light. The coupling optical component 5 is disposed on the diffraction optical path of the polarization volume grating 4, and is used to guide the first diffracted light and the second diffracted light to the user's left eye and right eye, respectively.

[0035] It should be noted that the existing semi-reflective and semi-transparent beam splitting scheme requires at least two bulk optical elements, namely a beam splitting prism and a compensation prism, and the prism thickness is usually above 5mm. In contrast, this application replaces the above prism combination with a quarter-wave plate with a thickness of no more than 0.5mm and a polarization volume grating with a thickness of no more than 0.7mm, reducing the axial space occupied by the beam splitting region from more than 10mm to less than 1.5mm, thereby reducing the number of optical elements and reducing the volume.

[0036] In this embodiment, the LCD optical engine unit can be a Fast-LCD micro panel, with a diagonal size ranging from 0.2 inches to 0.6 inches, preferably 0.39 inches or 0.49 inches; the panel resolution is not less than 1280×720, preferably 1920×1080 or 2560×1440 (2K), and the pixel density is not less than 3000 PPI; the refresh rate of the LCD panel is not less than 120Hz, preferably 144Hz or higher, to support high frame rate dynamic image display and potential time-division multiplexing binocular stereoscopic display mode.

[0037] The polarizer can be a linear absorption polarizer, integrated and pasted on the light-emitting side of the LCD panel. Its transmission axis direction is predetermined according to the polarization matching requirements of the subsequent quarter-wave plate 3 and polarization volume grating 4, and can be set to the horizontal or vertical direction.

[0038] The LCD optical engine unit also includes a backlight unit, which uses a white LED array or an RGB three-color independent LED array as the light-emitting element. When using white LEDs, the LED color temperature should be selected within the range of 5500K to 7000K, with 6500K being preferred. When using an RGB three-color LED array, the center wavelength of the red LED is 625±5nm, the center wavelength of the green LED is 525±5nm, and the center wavelength of the blue LED is 455±5nm. Each color LED can be driven and its brightness can be adjusted independently. The nominal output brightness of the backlight unit is no less than 5000 nits to ensure that after subsequent beam splitting and waveguide transmission losses, the brightness at eye level can still reach an AR display usable level of no less than 500 nits.

[0039] A diffuser and a brightness enhancement film may also be provided between the backlight unit and the LCD panel to improve backlight uniformity and light output efficiency in the normal direction. On the output side of the linearly polarized image beam, the polarization extinction ratio (PER) is not less than 500:1 to ensure that the incident beam provided to the subsequent quarter-wave plate 3 has a high-purity linear polarization state.

[0040] The collimating lens group 2 consists of at least two optical lenses, preferably a combination of three aspherical lenses. The optical lenses can be made of optical plastic or optical glass, with optical plastic being preferred to reduce the weight of the module.

[0041] The effective focal length of the collimating lens group 2 is selected from 8mm to 20mm, preferably from 12mm to 15mm, and its numerical aperture is not less than 0.15.

[0042] The divergence angle of the collimated beam is no greater than 2° and the wavefront error is no greater than λ / 4 (based on the green light wavelength of 525nm), to ensure that the subsequent quarter-wave plate 3 and polarization volume grating 4 receive a near-parallel beam of good quality.

[0043] The optical axis of the collimating lens group 2 is set to coincide with the normal direction of the light-emitting surface of the LCD panel. Each lens is coaxially positioned through a precision lens barrel or an integrated injection-molded lens mount. The lens mount material can be aluminum alloy or engineering plastic. The cross-sectional shape of the emitted beam of the collimating lens group 2 matches the shape of the effective display area of ​​the LCD panel, which is usually rectangular with a cross-sectional size of no more than 10mm × 6mm.

[0044] The overall dimensions of the quarter-wave plate 3 are adapted to the output beam cross-section of the collimating lens group 2, with typical dimensions ranging from 10mm × 8mm to 15mm × 12mm and a thickness not exceeding 0.5mm. The first polarization conversion region 31 and the second polarization conversion region 32 are arranged adjacent to each other along the width direction of the quarter-wave plate 3, with an area ratio of 1:1. Each region covers the left and right halves of the collimated beam cross-section, respectively.

[0045] Here, the first rotation direction is defined as left-handed, so the first circularly polarized light is left-handed circularly polarized light and the second circularly polarized light is right-handed circularly polarized light; Conversely, the first rotation direction can be defined as right-handed, and the rotation directions of the two regions can be interchanged, as long as they match the rotation selectivity of the subsequent polarization volume grating 4.

[0046] It should be noted that the polarization volume grating 4 is a volume holographic optical element prepared by photo-controlled orientation and ultraviolet polymerization based on chiral liquid crystal or reactive liquid crystal mesocrystalline monomer.

[0047] The liquid crystal molecules inside the PVG are oriented in a three-dimensional helical periodic structure. This helical structure has a grating period Λ_x in the plane and a helical half-period Λ_z in the thickness direction. Together, they determine the Bragg diffraction conditions of the bulk grating.

[0048] PVG exhibits axial selectivity for incident circularly polarized light: when the axial direction of the incident circularly polarized light matches the chirality of the liquid crystal spiral structure inside the PVG, the Bragg matching condition is satisfied, and the incident light is diffracted to a preset angle direction; when the axial direction of the incident circularly polarized light is opposite to the helical chirality, the beam is almost completely transmitted, and the diffraction efficiency is close to zero. This axial selectivity is the physical basis for PVG to achieve polarization beam splitting.

[0049] Based on the above, the PVG in the first diffraction region 41 adopts a right-handed spiral liquid crystal structure, which matches the rotation direction of the first circularly polarized light output from the first polarization conversion region 31. The PVG in the second diffraction region 42 adopts a left-handed spiral liquid crystal structure, which matches the rotation direction of the second circularly polarized light output from the second polarization conversion region 32.

[0050] The first diffraction region 41 and the second diffraction region 42 are prepared on the same glass substrate, and the boundary line between the two regions is aligned with the boundary line between the first polarization conversion region 31 and the second polarization conversion region 32 on the quarter-wave plate 3 in the optical axis direction.

[0051] The PVG film thickness is selected from 2μm to 10μm, preferably 3μm to 5μm, and the glass substrate thickness is 0.3mm to 0.7mm, preferably 0.5mm. The substrate is coated with antireflective coatings on both sides, and the single-sided reflectivity is not greater than 0.5%. The diffraction angles of the first diffraction region 41 and the second diffraction region 42 are symmetrically arranged about the incident optical axis, and the absolute value of the diffraction angle is selected from 30° to 60°, preferably 40° to 50°.

[0052] The in-plane grating period Λ_x of the PVG satisfies the following relationship with the operating wavelength λ and the diffraction angle θ: Λ_x = λ / (n_eff × sinθ); Where n_eff is the effective refractive index of the PVG liquid crystal film.

[0053] The polarization volume grating 4 includes a first polarization volume grating 43 and a second polarization volume grating 44 stacked sequentially along the light propagation direction. The first polarization volume grating 43 and the second polarization volume grating 44 are each provided with adjacent first diffraction regions 41 and second diffraction regions 42. The in-plane grating period and / or longitudinal spiral period of the second polarization volume grating 44 are not equal to those of the first polarization volume grating 43. The second polarization volume grating 44 is configured to diffract the zero-order light transmitted from the first polarization volume grating 43 and direct the zero-order light into the coupling optical component 5.

[0054] In this embodiment, the first polarization volume grating 43 and the second polarization volume grating 44 can be fabricated on their respective independent glass substrates and then assembled by bonding with optical adhesive. The thickness of the adhesive layer between the two substrates is no more than 20 μm, and the refractive index of the adhesive layer matches the refractive index of the glass substrate to reduce interlayer interface reflection. Alternatively, the first polarization volume grating 43 and the second polarization volume grating 44 can also be fabricated on the front and back sides of the same glass substrate, thereby eliminating one substrate layer and further reducing the overall thickness of the module.

[0055] It should be noted that the purpose of setting up two PVG layers is to broaden the angular bandwidth or wavelength bandwidth to improve the uniformity of diffraction efficiency. The principle is as follows: the Bragg diffraction conditions of a single-layer PVG have a certain selective window for both the incident angle and wavelength. When the angle of the incident light deviates from the Bragg angle or the wavelength deviates from the design center wavelength, the diffraction efficiency will decrease. This part of the light passes through the first PVG as zero-order transmitted light and is not utilized.

[0056] The Bragg condition of the second polarization volume grating 44 (determined by its grating period Λ_x and longitudinal period Λ_z) differs from that of the first polarization volume grating 43. Specifically, the in-plane grating period Λ_x' and / or longitudinal period Λ_z' of the second polarization volume grating 44 have a certain offset ΔΛ relative to the first polarization volume grating 43. The offset is selected from 2% to 15% of the corresponding parameters of the first polarization volume grating 43, preferably from 5% to 10%. Through this differentiated design, the angle / wavelength range of efficient diffraction of the first polarization volume grating 43 and the angle / wavelength range of efficient diffraction of the second polarization volume grating 44 complement each other, and the equivalent angular bandwidth after the two layers are superimposed can be extended to 1.5 to 2 times that of a single-layer PVG.

[0057] Calculations show that the first polarization volume grating 43 is designed to have a first-order diffraction efficiency of no less than 85%. The zero-order light intensity transmitted through the first polarization volume grating 43 accounts for approximately 5% to 15% of the total intensity of the incident matched polarized light. This portion of the zero-order light enters the second polarization volume grating 44 and is diffracted a second time by the second polarization volume grating 44 with an efficiency of no less than 80%. The diffraction output direction of the second polarization volume grating 44 is designed to be basically consistent with the diffraction output direction of the first polarization volume grating 43 (angle deviation no greater than 1°), so that the diffraction output beams of the two PVG layers can be collected by the same coupling lens 51 and coupled into the waveguide lens 6. The composite diffraction efficiency of the two PVG layers is no less than 90% within the designed field of view, and the decrease in diffraction efficiency at the edge field of view is no greater than 15% relative to the center field of view.

[0058] In this process, the first diffraction region 41 and the second diffraction region 42 on the first polarization volume grating 43 and the second polarization volume grating 44 are aligned in the same position, that is, the boundary line of the partition of the two PVG layers is aligned in the optical axis direction, and the alignment accuracy is no greater than ±50μm.

[0059] The quarter-wave plate 3 includes a transparent substrate 33 and a birefringent retardation layer 34.

[0060] The birefringence retardation layer 34 is provided with at least three layers, and the at least three layers of the birefringence retardation layer 34 are stacked sequentially on the transparent substrate 33. Each layer of the birefringence retardation layer 34 is provided with an adjacent first polarization region 311 and a second polarization region 321. The at least three layers of the first polarization region 311 are stacked to form the first polarization conversion region 31, and the at least three layers of the second polarization region 321 are stacked to form the second polarization conversion region 32.

[0061] In this embodiment, the transparent substrate 33 is made of optical-grade glass with a thickness of 0.3 mm to 0.7 mm, preferably 0.5 mm. The substrate has a transmittance of not less than 92% in the visible light band, a surface flatness of not more than λ / 4, and a surface roughness Ra of not more than 1 nm.

[0062] The material of the birefringent retardation layer 34 is a reactive liquid crystal mesocrystalline monomer.

[0063] It should be noted that the film thickness of each birefringent retardation layer 34 is determined based on the required optical retardation Γ_i and the inherent birefringence Δn of the material, with the relationship being film thickness d_i = Γ_i / Δn. The use of a multilayer structure in this embodiment does not require each layer to achieve λ / 4 retardation on its own, but rather to achieve broadband λ / 4 polarization conversion through the cascaded combination of multiple layers. Therefore, the optical retardation of each layer can be a value different from λ / 4.

[0064] The thickness of each birefringent retardation layer 34 is selected from 0.3 μm to 3.0 μm, the total thickness of at least three birefringent retardation layers 34 is from 1.5 μm to 9.0 μm, and the overall thickness of the quarter-wave plate 3, including the transparent substrate 33, is no more than 0.8 mm.

[0065] When preparing a multilayer structure, after the previous RM layer is polymerized and cured, a new PAL layer is spin-coated on its surface and a new orientation pattern is exposed. Then, a new RM solution is spin-coated and the annealing-polymerization process is repeated, and so on, layer by layer.

[0066] The exposure patterns of each PAL layer, i.e. the spatial distribution of the fast axis orientation direction, can be different, so that each birefringent retardation layer 34 has different fast axis reference angles and spatial variation rules.

[0067] It should be noted that the partitioning patterns of the first polarization region 311 and the second polarization region 321 are defined by a single exposure of a photomask within the same layer. The width of the transition band between the two regions is no more than 100 μm, preferably no more than 50 μm, in order to reduce the impact of incomplete polarization conversion at the boundary between the two regions on the imaging quality.

[0068] The optical retardation and fast axis reference angle of at least three birefringent retardation layers 34 are all different to achieve achromatic delayed polarization conversion. In each birefringent retardation layer 34, the fast axis orientation angle of the first polarization region 311 and the fast axis orientation angle of the second polarization region 321 are mirror-symmetric about the boundary line between the two regions.

[0069] In this embodiment, the implementation principle and design parameters of chromatic polarization conversion are explained as follows: There is a dispersion relationship between the optical retardation Γ of the single-layer birefringent retardation layer 34 and the incident light wavelength λ: Γ(λ) = (2π / λ) × Δn(λ) × d; Where Δn(λ) is the dispersive birefringence of the birefringent material, and d is the film thickness.

[0070] Since Δn(λ) usually decreases with increasing wavelength, and with the effect of the 1 / λ factor, the delayed phase of short wavelengths (such as blue light) is greater than that of long wavelengths (such as red light).

[0071] Therefore, if a single-layer λ / 4 delayer is designed with green light wavelength, the delay will be too large in the blue light band and too small in the red light band, resulting in a decrease in polarization conversion efficiency in the red and blue bands, and the ellipticity of the converted "circularly polarized light" will deviate from the ideal value.

[0072] By superimposing multiple (at least three) birefringent retardation layers 34 with their own different optical retardation amounts Γ_i and fast axis reference angles φ_i, the cascaded product effect of the Jones matrix can be used to achieve achromatic quarter-wavelength delay.

[0073] Experiments show that within the visible light band of 400nm to 700nm, the deviation of the equivalent quarter-wavelength delay is no greater than ±5nm, and the polarization conversion efficiency η(λ) is no less than 97% across the entire band, and no less than 99% at the three LED center wavelengths of red light (625nm), green light (525nm), and blue light (455nm). In comparison, when a single-layer quarter-wave plate 3 is designed with 525nm as the wavelength, the polarization conversion efficiency at 455nm blue light is usually only about 90% to 93%, and at 625nm red light it is about 89% to 92%.

[0074] Additionally, it should be noted that the geometric meaning of the aforementioned mirror symmetry relationship is as follows: If the boundary line between the first polarization region 311 and the second polarization region 321 on the plane where the quarter-wave plate 3 is located is taken as the axis of symmetry, then the fast axis orientation angle φ of the same birefringent retardation layer 34 at a certain position in the first polarization region 311 and its fast axis orientation angle φ' at its mirror position about the axis of symmetry in the second polarization region 321 satisfy φ' = −φ.

[0075] This symmetry holds true for each of the three layers, such that when the first polarization conversion region 31 after multi-layer stacking outputs, for example, left-handed circularly polarized light, the second polarization conversion region 32 will necessarily output right-handed circularly polarized light, and the ellipticity and polarization purity of the two circularly polarized lights are consistent.

[0076] The fast axis orientation angle gradually increases or decreases radially from the center position to the edge within the first polarization conversion region 31 and / or the second polarization conversion region 32, in order to further compensate for the incident angle deviation of the linearly polarized image beam emitted by the collimating lens group 2.

[0077] In this embodiment, the implementation principle and design method of the spatial rotational change of the fast axis orientation angle are explained as follows: When the fast axis orientation angle of the birefringent retardation layer 34 is spatially non-uniformly distributed, the transmitted light will obtain geometric phase modulation related to the spatial distribution of the fast axis orientation angle.

[0078] Specifically, when incident circularly polarized light passes through a half-wave delay layer with a fast axis orientation angle of α(x,y), the additional geometric phase acquired by the transmitted light is Φ_PB(x,y) = ±2α(x,y), where the sign depends on the rotation direction of the incident circularly polarized light.

[0079] Although each layer in this embodiment is not a strictly half-wave delay layer and the incident light is linearly polarized, when the equivalent effect of the multi-layer stacked structure on a specific polarization component includes the contribution of fast axis rotation, a spatially varying phase modulation effect can still be introduced. The equivalent effect of the multi-layer cascaded structure on a specific polarization component can be calculated by multiplying the Jones matrix layer by layer. When the fast axis orientation angle of each layer includes a spatial variation component, an equivalent phase modulation term related to the fast axis rotation angle is generated in the cascaded product. The spatial distribution of this modulation term can be designed by optimizing the fast axis spatial variation function of each layer to match the spatial distribution of the aberration to be compensated.

[0080] The rotational change of the fast axis orientation angle is achieved by superimposing a position-dependent additional rotation amount δα_i(x,y) on the aforementioned achromatic fast axis reference angle φ_i. That is, the actual fast axis angle of the i-th layer at position (x,y) is α_i(x,y) = φ_i + δα_i(x,y). The spatial distribution of the additional rotation amount δα_i(x,y) can be designed as a function that varies radially with respect to the center of the region, for example: δα_i(r) = a_i × r² + b_i × r 4 ; Where r is the radial distance from the center of the polarization conversion region, and a_i and b_i are the design coefficients of the i-th layer.

[0081] The quadratic coefficient a_i is mainly used to compensate for field curvature (focal plane curvature) and defocus deviation of collimating lens group 2, while the quartic coefficient b_i is mainly used to compensate for spherical aberration and higher-order aberrations. The coefficients a_i and b_i of each layer can be the same or different, and the specific values ​​are determined by joint optimization using optical design software in conjunction with the residual aberration data of collimating lens group 2.

[0082] Let's illustrate this with a specific design example: When collimating lens group 2 has a field curvature of 0.5 wavelengths and a spherical aberration of 0.3 wavelengths in the peripheral field of view, the quadratic coefficient of δα is set to a = 0.012 rad / mm² and the quartic coefficient to b = 0.003 rad / mm². 4 Spatial rotation variations can reduce the residual aberrations to no more than 0.1 wavelengths (based on 525nm), with wavefront corrections of approximately 0.4 to 0.7 wavelengths.

[0083] In the implementation of "increasing from the center to the edge", the fast axis orientation angle at the center of the polarization conversion region is used as the reference value. As the radial distance increases, the additional rotation amount δα of the fast axis orientation angle gradually increases. For example, δα=0° at the center, δα=+2.8° at a distance of 2mm from the center, and δα=+11.2°+0.8°=+12.0° at a distance of 4mm from the center.

[0084] In the "decreasing from center to edge" implementation, the additional rotation amount δα gradually decreases, depending on the concave-convex direction of the wavefront correction to be applied.

[0085] The aforementioned spatially varying fast axis orientation pattern is fabricated by pixel-by-pixel exposure or multi-step mask exposure of the light orientation layer. Pixel-by-pixel exposure can be performed using a direct-write lithography system, in which the designed fast axis angle spatial distribution α_i(x,y) is written pixel by pixel into the PAL layer in the form of rotating the polarization direction of polarized ultraviolet light. The pixel size is no larger than 5μm, preferably no larger than 2μm.

[0086] Multi-step mask exposure discretizes the continuously changing spatial distribution of fast axis angles into several angular step regions. Each step corresponds to a mask and an exposure in a specific polarization direction. The number of steps is no less than 8 to ensure that the phase step error introduced by angle discretization is no greater than λ / 10.

[0087] It also includes waveguide lenses 6, of which two are provided and correspond to the first diffracted light and the second diffracted light respectively. The coupling optical component 5 includes two coupling lenses 51, which are respectively provided to correspond to the first diffraction region 41 and the second diffraction region 42, so as to couple the first diffracted light and the second diffracted light into the corresponding waveguide lenses 6 respectively. The display module 1, collimating lens group 2, quarter-wave plate 3 and polarization volume grating 4 are all provided in the middle of the AR glasses frame, and the two waveguide lenses 6 are respectively embedded on both sides of the AR glasses frame.

[0088] In this embodiment, the waveguide lens 6 is a diffractive waveguide, made of high-refractive-index optical glass or high-refractive-index optical resin, with a waveguide substrate thickness of 0.3mm to 1.0mm, preferably 0.5mm to 0.7mm, and an outline that matches the shape of a conventional eyeglass lens, with a lateral dimension of approximately 40mm × 25mm to 50mm × 30mm.

[0089] Each waveguide lens 6 has at least three functional regions: a coupling grating region, a pupil expansion region, and an output grating region. The coupling grating is located on the edge region of the waveguide lens 6 near the nose bridge side. It is used to receive the diffracted beam from the corresponding coupling lens 51 and couple it into the waveguide substrate at an angle greater than the critical angle of total internal reflection for total internal reflection propagation. The pupil expansion region and the coupling grating region are located in the central region of the waveguide lens 6 facing the human eye pupil. They are used to sequentially couple out the image light propagating in the waveguide to form the expanded eye box. The coupling grating, pupil expansion grating, and coupling out grating can be implemented using surface relief gratings (SRG) or polarization volume gratings (PVG), with the grating period determined based on the operating wavelength and the designed diffraction angle.

[0090] The waveguide lens 6 has an ambient light transmittance of not less than 70% in the visible light band, preferably not less than 80%. The exit pupil size is not less than 8mm × 6mm, preferably not less than 10mm × 8mm, to allow for the natural range of motion of the wearer's pupil.

[0091] It also includes a photoelectric sensor 7, which is disposed in the middle of the AR glasses frame and located on the light-emitting side of the polarization volume grating 4. Its photosensitive surface intersects with the output optical axis of the collimating lens group 2 and is used to receive the zero-order transmitted light transmitted through the polarization volume grating 4. The LCD optical engine unit 11 includes independently driven red, green and blue light-emitting elements. The photoelectric sensor 7 includes multiple photosensitive units corresponding to the red, green and blue light channels respectively. The multiple photosensitive units are used to receive the zero-order transmitted light of the corresponding color light channel and output independent light intensity detection signals corresponding to each color light channel.

[0092] In this embodiment, when it is necessary to detect red, green and blue light in separate channels, the photoelectric sensor 7 can be a multi-channel photoelectric sensor chip with integrated RGB three-color filters.

[0093] The second objective of this application is to provide an AR display control method based on LCD and polarization volume grating.

[0094] The technical solution is as follows: An AR display control method based on LCD and polarization volume grating, applied to an AR display module based on LCD and polarization volume grating, includes the following steps: S1: The light intensity of the zeroth order transmitted light is detected by the photoelectric sensor 7 to obtain the light intensity detection value; S2: Compare the detected light intensity value with a preset reference value; S3: Adjust the backlight driving power of LCD optical engine unit 11 according to the comparison result: When the light intensity detection value is higher than the reference value, the backlight driving power of the LCD optomechanical unit 11 is increased to compensate for the change in diffraction efficiency; When the light intensity detection value is lower than the reference value, the backlight driving power of the LCD optomechanical unit 11 is reduced to compensate for the change in diffraction efficiency.

[0095] In this embodiment, the control method is executed by the main controller in the AR display module 1, and the control cycle is no more than 100ms, preferably 10ms to 50ms, so as to ensure that the response speed to the change in diffraction efficiency is faster than the human eye's perception time constant for changes in brightness.

[0096] In step S1, the main controller reads the ADC output value of the photoelectric sensor 7 via the I²C or SPI interface as the light intensity detection value V_det. This value can be a single reading or the average of multiple samples within a control cycle to reduce the impact of sensor noise. The sampling rate is not less than 100 Sa / s.

[0097] In step S2, the light intensity detection value V_det is compared with the preset reference value V_ref stored in non-volatile memory. A tolerance band ΔV can be introduced during the comparison. That is, when |V_det − V_ref| ≤ ΔV, the diffraction efficiency is considered to be within the normal range, and backlight power adjustment is not triggered. This avoids frequent adjustments to the backlight power due to small fluctuations in diffraction efficiency, which could cause screen brightness flicker. The tolerance band ΔV is set to correspond to a light intensity change of no more than 1% to 2% in diffraction efficiency.

[0098] In step S3, the backlight power is adjusted as follows: the main controller adjusts the output current of the LED backlight driver chip through a PWM signal or I²C command, thereby changing the backlight brightness. The PWM frequency is not less than 10kHz, and the duty cycle adjustment resolution is not less than 10 bits.

[0099] Specific adjustment strategies can employ proportional control or proportional-integral control: When the adjustment strategy is proportional control: the formula for adjusting the backlight drive power is: ΔP = K_p × (V_det − V_ref) / V_ref; Where K_p is the proportional gain coefficient, typically ranging from 0.5 to 2.0. This strategy is simple to implement, but may have steady-state errors.

[0100] When the adjustment strategy is proportional-integral control: the formula for adjusting the backlight drive power is: ΔP = K_p × e(t) + K_i × ∫e(t)dt; Where e(t) = (V_det − V_ref) / V_ref is the normalization error, and K_i is the integral gain coefficient, typically ranging from 0.01 to 0.1. The integral term can eliminate steady-state error, enabling the backlight power to converge precisely to the level that restores the brightness at eye level to the target value.

[0101] The adjustable range of the backlight drive power is 50% to 150% of the nominal power, meaning it can be adjusted down to 50% or up to 150% of the nominal value. When changes in ambient temperature cause a decrease in PVG diffraction efficiency of no more than 10%, it can be compensated for by increasing the backlight power by approximately 10% to 12%. The step size for adjusting the drive power is no greater than 0.5% of the nominal power to achieve a smooth and imperceptible brightness adjustment process.

[0102] In step S3, the physical meaning of the adjustment logic needs to be specifically explained: When the light intensity detection value V_det is higher than the reference value V_ref, it indicates that the zero-order transmission leakage of the PVG increases, that is, the diffraction efficiency decreases. At this time, the effective light energy diffracted to the waveguide and entering the human eye is reduced. In order to maintain the brightness entering the eye, the backlight power should be increased to compensate for the decrease in diffraction efficiency. Conversely, when V_det is lower than V_ref, it indicates that the diffraction efficiency has increased, and the original backlight power will lead to higher brightness in the eye. In this case, the backlight power should be reduced.

[0103] The reference value is a pre-stored light intensity reference value, which corresponds to the light intensity of the zero-order transmitted light when the polarization volume grating 4 is at a preset reference diffraction efficiency and the LCD optomechanical unit 11 is at a reference output power.

[0104] In step S1, the light intensity detection value of each color light channel is obtained by the plurality of photosensitive units respectively; In step S3, the driving power of the three-color light-emitting elements corresponding to each color light channel in the LCD optical engine unit 11 is independently adjusted according to the light intensity detection value of each color light channel and the corresponding reference value.

[0105] In this embodiment, the multi-channel photoelectric sensor 7 may be a photoelectric sensor chip with an integrated RGB color sensing channel or a similar multi-channel integrated optical sensor chip.

[0106] The chip integrates independent analog-to-digital converters for each channel, and outputs the digital light intensity detection values ​​of each channel through the I²C interface.

[0107] Alternatively, the multi-channel photoelectric sensor 7 can also be implemented by discretely assembling three independent silicon photodiodes with red, green, and blue narrowband filters respectively. This solution is slightly more expensive, but the spectral response characteristics and sensitivity of each channel can be optimized independently.

[0108] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An AR display module based on LCD and polarization volume grating, characterized in that, include: The display module (1) includes an LCD optomechanical unit (11) equipped with a polarizer for outputting a linearly polarized image beam; A collimating lens group (2) is disposed on the light-emitting side of the display module (1) and is used to collimate the linearly polarized image beam; A quarter-wave plate (3) is disposed on the light output path of the collimating lens group (2) and is provided with a first polarization conversion region (31) and a second polarization conversion region (32) arranged adjacently, for performing partitioned polarization conversion on the linearly polarized image beam; The first polarization conversion region (31) is configured to convert incident linearly polarized light into first circularly polarized light with a first rotation direction, and the second polarization conversion region (32) is configured to convert incident linearly polarized light into second circularly polarized light with the opposite rotation direction to the first rotation direction. A polarization volume grating (4) is disposed on the light-emitting side of the quarter-wave plate (3), and is provided with a first diffraction region (41) and a second diffraction region (42) respectively corresponding to the positions of the first polarization conversion region (31) and the second polarization conversion region (32). The first diffraction region (41) is configured to diffract the first circularly polarized light and emit it as the first diffracted light, and the second diffraction region (42) is configured to diffract the second circularly polarized light and emit it as the second diffracted light. as well as A coupling optical component (5) is disposed on the diffraction path of the polarization volume grating (4) to guide the first diffracted light and the second diffracted light to the user's left eye and right eye, respectively.

2. An AR display module based on LCD and polarization volume grating according to claim 1, characterized in that: The polarization volume grating (4) includes a first polarization volume grating (43) and a second polarization volume grating (44) stacked sequentially along the light propagation direction. The first polarization volume grating (43) and the second polarization volume grating (44) are each provided with adjacent first diffraction regions (41) and second diffraction regions (42). The in-plane grating period and / or longitudinal spiral period of the second polarization volume grating (44) are not equal to those of the first polarization volume grating (43). The second polarization volume grating (44) is configured to diffract the zero-order light transmitted from the first polarization volume grating (43) and direct the zero-order light into the coupling optical component (5).

3. An AR display module based on LCD and polarization volume grating according to claim 1, characterized in that, The quarter-wave plate (3) includes: Transparent substrate (33); At least three birefringent retardation layers (34) are stacked sequentially on the transparent substrate (33); Each of the birefringent retardation layers (34) is provided with an adjacent arrangement of a first polarization region (311) and a second polarization region (321). At least three layers of the first polarization region (311) are stacked to form the first polarization conversion region (31), and at least three layers of the second polarization region (321) are stacked to form the second polarization conversion region (32).

4. An AR display module based on LCD and polarization volume grating according to claim 3, characterized in that: The optical retardation and fast axis reference angle of at least three birefringent retardation layers (34) are all different to achieve achromatic delayed polarization conversion; In each of the birefringent retardation layers (34), the fast axis orientation angle of the first polarization region (311) and the fast axis orientation angle of the second polarization region (321) are mirror-symmetric about the boundary line between the two regions.

5. An AR display module based on LCD and polarization volume grating according to claim 4, characterized in that: The fast axis orientation angle gradually increases or decreases radially from the center position to the edge within the first polarization conversion region (31) and / or the second polarization conversion region (32) to further compensate for the incident angle deviation of the linearly polarized image beam emitted by the collimating lens group (2).

6. An AR display module based on LCD and polarization volume grating according to claim 1, characterized in that: It also includes waveguide lenses (6), two of which are provided and correspond to the first diffracted light and the second diffracted light respectively. The coupling optical component (5) includes two coupling lenses (51), which are respectively provided to the first diffraction region (41) and the second diffraction region (42) to couple the first diffracted light and the second diffracted light into the corresponding waveguide lenses (6). The display module (1), collimating lens group (2), quarter-wave plate (3) and polarization volume grating (4) are all provided in the middle of the AR glasses frame. The two waveguide lenses (6) are respectively embedded on both sides of the AR glasses frame.

7. An AR display module based on LCD and polarization volume grating according to claim 1, characterized in that: It also includes a photoelectric sensor (7), which is disposed in the middle of the AR glasses frame and located on the light-transmitting side of the polarization volume grating (4). Its photosensitive surface intersects with the output optical axis of the collimating lens group (2) and is used to receive the zero-order transmitted light transmitted through the polarization volume grating (4). The LCD optical engine unit (11) includes independently driven red, green and blue light-emitting elements. The photoelectric sensor (7) includes multiple photosensitive units corresponding to the red, green and blue light channels respectively. The multiple photosensitive units are used to receive the zero-order transmitted light of the corresponding color light channel and output independent light intensity detection signals corresponding to each color light channel.

8. An AR display control method based on LCD and polarization volume grating, applied to an AR display module based on LCD and polarization volume grating as described in claim 7, characterized in that, Includes the following steps: S1: The light intensity of the zero-order transmitted light is detected by the photoelectric sensor (7) to obtain the light intensity detection value; S2: Compare the detected light intensity value with a preset reference value; S3: Adjust the backlight driving power of the LCD optical engine unit (11) according to the comparison result: When the light intensity detection value is higher than the reference value, the backlight driving power of the LCD optomechanical unit (11) is increased to compensate for the change in diffraction efficiency; When the light intensity detection value is lower than the reference value, the backlight driving power of the LCD optomechanical unit (11) is reduced to compensate for the change in diffraction efficiency.

9. The AR display control method based on LCD and polarization volume grating according to claim 8, characterized in that: The reference value is a pre-stored light intensity reference value, which corresponds to the light intensity of the zero-order transmitted light when the polarization volume grating (4) is at a preset reference diffraction efficiency and the LCD optomechanical unit (11) is at a reference output power.

10. The AR display control method based on LCD and polarization volume grating according to claim 8, characterized in that: In step S1, the light intensity detection value of each color light channel is obtained by the plurality of photosensitive units respectively; In step S3, the driving power of the three-color light-emitting elements in the LCD optical engine unit (11) corresponding to each color light channel is independently adjusted according to the light intensity detection value of each color light channel and the corresponding reference value.

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