Method for improving display uniformity of volumetric holographic optical waveguide, and apparatus

Abstract

A method for improving display uniformity of a volumetric holographic optical waveguide, and an apparatus. The volumetric holographic optical waveguide includes a switchable grating structure, wherein some areas on the switchable grating structure can be directionally selected to serve as coupling areas, so that a light source can only be coupled out from the coupling areas on the basis of the maximum diffraction efficiency of the light source; and the coupling areas on the switchable grating structure are continuously switched, the process of covering all areas on the switchable grating structure by the continuously switched coupling areas is taken as a scan, and the time of the scan is not longer than the time for persistence of vision of human eyes. By using the switchable grating structure in the volumetric holographic optical waveguide, the coupling areas for the light source to perform a single emission are reduced, and the brightness and uniformity in a single light emission are improved; then, by means of controlling continuous switching of the coupling areas, an output field of view freely moves in different grating areas, and thus the brightness and uniformity are improved in a full-output field of view, thereby optimizing the overall display effect; furthermore, the construction time of the full-output field of view is not longer than the time of persistence of vision of human eyes, thereby improving the quality of an image observed by the human eyes.

Description

A method and apparatus for improving the uniformity of volume holographic waveguide displays Technical Field

[0001] This invention relates to the field of holographic projection display, and more specifically, to a method and apparatus for improving the uniformity of volume holographic waveguide displays. Background Technology

[0002] Augmented Reality (AR) technology is a technique that cleverly integrates virtual information with the real world. It simulates and applies computer-generated text, images, 3D models, music, and videos to the real world, thus "enhancing" it. Currently, in practical applications of AR technology, devices implementing AR display technology typically consist of display devices and optical components. Among these, optical waveguides are the mainstream technology, specifically including geometric waveguides and diffractive waveguides. Diffractive waveguides are implemented by "transferring" virtual images to the viewer's eyes and simultaneously replicating the exit pupil. Specifically, a diffractive waveguide consists of a planar waveguide and multiple diffraction gratings. Diffractive waveguides mainly include surface relief grating waveguides manufactured using photolithography and volume holographic grating waveguides manufactured using holographic interference technology.

[0003] AR display devices based on volume holographic grating waveguide technology typically employ grating structures such as coupling-in gratings, folded gratings, and coupling-out gratings. The beam projected by the projection engine is expanded and collimated before being coupled into the waveguide from the coupling-in grating region. The beam is then diffracted by the coupling grating, resulting in a totally internally reflected beam within the waveguide. This totally internally reflected beam propagates along the waveguide direction until it encounters the folded grating. The folded grating then deflects the beam at a certain angle, causing it to propagate along the waveguide in another direction. Finally, it encounters the coupling-out grating, where it is diffracted and coupled out of the waveguide, becoming an image received by the human eye. However, existing AR display devices generally suffer from poor uniformity. Uniformity is a crucial characteristic in AR display technology, typically encompassing both color and brightness uniformity. It plays a decisive role in the accurate reproduction of image colors within the eye box or field of view in AR displays. In particular, poor brightness uniformity significantly impacts image sharpness, three-dimensionality, and accuracy, affecting the visual experience. Specifically, due to the diffraction effect, and the fact that the projected image has a certain field of view, this field of view range causes the pupil imprint size within the waveguide to vary, resulting in striping and thus becoming a source of light field inhomogeneity. Secondly, due to the low diffraction efficiency of the grating, when the propagating beam within the waveguide encounters a folded grating or a coupling grating, the beam will propagate multiple times within these gratings and be diffracted multiple times, thereby causing pupil expansion to increase the eyebox range. However, with the energy loss of the beam during each propagation and diffraction, the light energy of each diffraction is different, leading to uneven light intensity distribution across the entire coupling region and a relatively low actual coupled brightness.

[0004] To balance the light field distribution and reduce light emission non-uniformity in AR display devices based on volume holographic grating waveguide technology, common improvement schemes in existing technologies include: setting coupling gratings with altered diffraction efficiency, employing refractive index modification layers with semi-transparent and semi-reflective properties, and multiplexing or overlapping coupling gratings. When using coupling gratings with altered diffraction efficiency, a lower diffraction efficiency is typically observed at the end near the beam propagation direction, while a higher diffraction efficiency is observed at the other end to balance the energy of the coupled beam in all regions. Employing refractive index modification layers with semi-transparent and semi-reflective properties utilizes the pupil shift to improve the uniformity of the light field in the exit pupil region. Multiplexing or overlapping coupling gratings alter the combined properties of the gratings to shift the pupil and modulate the grating diffraction efficiency. However, holographic gratings with altered diffraction efficiency require modulation of the refractive index of the holographic film material. The main methods for changing the refractive index modulation of the holographic film material are to change the composition ratio of the holographic material in different regions or to change the grating exposure dose in different regions. Neither method can achieve a gradual change in diffraction efficiency in the grating propagation direction, and some inhomogeneity still exists. Moreover, these methods usually require special processing techniques and complex fabrication processes. Adding a refractive index modification layer with semi-transparent and semi-reflective properties or using multiplexed and overlapping gratings in the waveguide will greatly increase the overall waveguide fabrication difficulty and increase additional stray light effects. Technical issues

[0005] The present invention aims to overcome at least one of the defects of the prior art and provides a method and apparatus for improving the uniformity of volume holographic waveguide displays, thereby improving the brightness and uniformity of volume holographic grating waveguides. Technical solutions

[0006] The technical solution adopted by the present invention provides a method for improving the uniformity of volume holographic waveguide display, wherein the volume holographic waveguide includes a switchable grating structure, and a portion of the switchable grating structure can be oriented to be selected as its coupling region, so that the light source can only be coupled out from the coupling region with its maximum diffraction efficiency.

[0007] The process of continuously switching the coupling regions on the switchable grating structure and covering all regions of the switchable grating structure with the continuously switched coupling regions is called a scan, and the time of a scan is not greater than the visual persistence time of the human eye.

[0008] In this technical solution, a switchable grating structure is employed in the volume holographic waveguide. This switchable grating structure allows for the directional selection of specific regions as its coupling areas, ensuring that the light source can only emit from these coupling areas. This concentrates the light beam into a specific region of the switchable grating structure during each emission, reducing energy imbalance in the coupling area and improving the brightness and uniformity of each emission. Furthermore, the coupling area can be freely selected within the switchable grating structure, meaning that the same emission effect, brightness, and angular uniformity can be achieved across all regions. Moreover, by utilizing the continuous coupling areas on the switchable grating structure, the output field of view of the light source can be freely moved across different regions of the structure. Since the brightness and angular uniformity of the light beam passing through each coupling area are consistent, the brightness and uniformity of each emission are maintained throughout the entire output field of view, creating a more balanced light field distribution and improving the overall display effect. Furthermore, during a single light emission, the light source is coupled out at its maximum diffraction efficiency as it passes through the coupling region. This means the grating structure in the coupling region is modulated to its maximum diffraction efficiency, allowing most of the light energy to be coupled out in a single diffraction cycle as the light source passes through the coupling region, thereby further improving the brightness and uniformity of the single light emission. The maximum diffraction efficiency should be the maximum coupling efficiency achieving the best brightness visual effect achievable by the grating structure in existing or future technologies. Preferably, in existing technologies, this refers to an efficiency of not less than 60%, more preferably higher than 80%, and efficiencies higher than 95% are not excluded. Furthermore, the entire switchable grating structure is modulated to its maximum diffraction efficiency, thereby maximizing the utilization of the light beam in all regions and improving the overall brightness of the beam. Furthermore, since the entire switchable grating structure has the same diffraction efficiency, preferably its maximum diffraction efficiency, all gratings on the switchable grating can have the same optical characteristics. Therefore, the same manufacturing process can be used to ensure the consistency of all characteristics of the grating structure, thereby greatly reducing the complexity and difficulty of grating manufacturing. This not only improves production efficiency but also further enhances the performance of the grating structure. Furthermore, when a scan is defined as the continuous switching coupling region covering all areas of the switchable grating structure, one scan precisely couples the light source carrying the image from all areas of the switchable grating structure. Simultaneously, the time of one scan is kept no greater than the visual persistence time of the human eye; that is, what the human eye observes through the volume holographic waveguide display device is the entire image with improved brightness and uniformity, thus improving the image quality observed by the human eye while ensuring a good visual experience. Preferably, the image light source can be repeatedly scanned on the same switchable grating structure to better improve the visual communication effect.

[0009] Furthermore, the switchable grating structure is a grating array formed by the directional arrangement of several sub-gratings. The directional selection of the coupling region of the grating array is achieved by controlling the opening or closing of some sub-gratings within the grating array. The scanning method is either sequential scanning or random scanning, and at least one sub-grating is opened each time during either sequential or random scanning. By setting the switchable grating structure to a grating array formed by the directional arrangement of several sub-gratings, the selection of the coupling region can be controlled by the sub-grating dimension. That is, by controlling the opening of some sub-gratings in the grating array while closing other sub-gratings, the directional selection of the coupling region on the switchable grating structure can be conveniently and quickly achieved. Preferably, at least one sub-grating is opened each time a scan is performed. By controlling and selecting the coupling region of the sub-grating, the accuracy and convenience of coupling region selection and control are improved, and the scanning methods on the switchable grating structure are broadened to adapt to different application scenarios and build different visual effects experiences. Specifically, when performing full-field scanning by continuously switching the coupling region, it is possible to form a regional sequential scan by sequentially selecting and opening the sub-grating, or to form a regional random scan by randomly selecting and opening the sub-grating.

[0010] Another object of the present invention is to provide a volume holographic waveguide display device, characterized in that the volume holographic waveguide display device adopts the method provided in this technical solution to improve its display uniformity;

[0011] The volume holographic waveguide display device includes an optomechanical system, a waveguide system, and a control system; the optomechanical system is used to emit a collimated light source; the waveguide system includes a waveguide substrate and a grating structure disposed within the waveguide substrate; the grating structure includes at least an input grating and an output grating, the collimated light source enters the waveguide substrate through the input grating and propagates toward the output grating, and is then expanded by the output grating and coupled out of the waveguide substrate;

[0012] The output grating adopts a switchable grating structure; the control system modulates the switchable grating structure accordingly to realize the directional selection and continuous switching of the coupling region on the switchable grating structure.

[0013] In this technical solution, by setting a control system corresponding to the modulated switchable grating structure in the volumetric holographic waveguide display device, the orientation selection and continuous switching of the switchable grating structure can be realized through electronic control and other means, thereby providing a faster, more accurate and stable scanning process. In a specific implementation, the grating structure employs an input grating and an output grating. The optomechanical system expands and collimates the image pixel point light source and couples it into the waveguide substrate. The light beam entering the waveguide substrate is diffracted by the input grating to generate a first-order diffracted wave, which can propagate in the waveguide with total internal reflection. The input grating is set to the highest diffraction efficiency so that most of the light entering the waveguide is diffracted into first-order diffracted light and propagates in the waveguide. The diffracted wave propagates in the waveguide substrate towards the output grating with total internal reflection until it encounters the output grating and undergoes a second diffraction. This diffraction diffracts the light beam that originally propagated with total internal reflection in the waveguide into light that propagates towards the waveguide surface and finally exits the waveguide substrate to enter the human eye for imaging. At the same time, the output grating also causes the light beam to produce a pupil expansion effect, thereby expanding the exit pupil diameter and field of view of the volume holographic waveguide display device. Furthermore, the coupling grating employs a switchable grating structure. By controlling the system to orient and switch the coupling region on the coupling grating, the area from which the beam is coupled out in a single operation is reduced. Simultaneously, the beam is ensured to exit only from the coupling region with maximum diffraction efficiency, improving both diffraction efficiency and brightness. Furthermore, by continuously and rapidly switching the coupling region on the coupling grating to cover the entire coupling grating array, the exit pupil diameter and field of view designed for the original coupling grating array are achieved. Moreover, the volume holographic waveguide display device eliminates the need for additional optical components and avoids introducing stray light, exhibiting both excellent static and dynamic characteristics.

[0014] Furthermore, the grating structure further includes a folded grating. The collimated light source enters the waveguide substrate through the coupling grating and propagates toward the folded grating; then, after being pupil-expanded once by the folded grating, it propagates toward the coupling grating, and after being pupil-expanded a second time by the coupling grating, it is coupled out and coupled out of the waveguide substrate. Preferably, the folded grating employs a switchable grating structure.

[0015] In one implementation, the grating structure in the waveguide system is configured as an input grating, a folded grating, and an output grating. The optomechanical system expands and collimates the image pixel point light source and couples it into the waveguide substrate. The light beam entering the waveguide substrate is diffracted by the input grating to generate a first-order diffracted wave, which can propagate in the waveguide substrate with total internal reflection. The input grating is set to the highest diffraction efficiency so that most of the light entering the waveguide is diffracted into first-order diffracted light and propagates in the waveguide. The diffracted wave propagates in the waveguide towards the folded grating with total internal reflection until it encounters the folded grating and interacts with it to cause secondary diffraction, causing the light beam to turn at a certain angle. Through the action of the folded grating, the incident light beam generates a pupil expansion in the initial propagation direction. After secondary diffraction, the beam continues to propagate within the waveguide plane via total internal reflection towards the coupling grating until it encounters the coupling grating and undergoes a third diffraction. This diffraction diffracts the beam, which originally propagated through total internal reflection within the waveguide, into a beam that propagates towards the waveguide surface and ultimately couples off from the waveguide substrate to enter the human eye for imaging. Simultaneously, the coupling grating causes secondary pupil expansion, thus enlarging the exit pupil diameter and field of view of the volume holographic waveguide display device through a two-dimensional pupil expansion scheme. The coupling grating is a switchable grating structure, and a control system controls the switching of coupling regions on the grating to achieve rapid scanning, improving the overall brightness and uniformity of the beam emitted from the coupling grating, thereby enhancing image quality and market performance. Preferably, the folded grating can also be configured as a switchable grating structure, controlled by the control system along with the coupling grating, thus realizing a two-dimensional scanning mode in the waveguide system. This achieves the original grating structure's designed exit pupil diameter while improving the diffraction efficiency and brightness of the beam propagating within the waveguide plane, enhancing light uniformity and field of view.

[0016] Furthermore, the switchable grating structure is a grating array formed by oriented arrangement of several sub-gratings, and the switchable grating structure is a switchable Bragg grating made of holographic polymer dispersed liquid crystal.

[0017] In this technical solution, the switchable grating structure is configured as a grating array formed by the directional arrangement of several sub-gratings, so that the adjustment dimension of the switchable grating structure is minimized to a single sub-grating. When the switchable grating structure adopts a switchable Bragg grating composed of holographic polymer-dispersed liquid crystal, the holographic polymer-dispersed liquid crystal is formed by polymerization-induced phase separation under coherent laser light, resulting in a grating composed of periodically arranged polymer-rich and liquid crystal-rich phases. This allows for convenient and economical modification of the grating structure with the required parameters by changing the spatial energy distribution of the exposure light field of the holographic polymer-dispersed liquid crystal, thereby easily modulating the diffraction efficiency of the switchable grating structure. Secondly, since liquid crystal molecules themselves possess the characteristic of deflecting the optical axis under the action of an electric field, the liquid crystal molecules can change their orientation and thus change the refractive index of the liquid crystal under the action of an electric field. Therefore, this characteristic can be used to modulate the refractive index modulation of the holographic polymer-dispersed liquid crystal grating or for switching the grating; this is also called a switchable Bragg grating (SBG). In this technical solution, the switchable grating structure is a switchable Bragg grating made of holographic polymer-dispersed liquid crystal material. This allows the switchable grating structure to generate optical axis deflection through an applied electric field, thereby conveniently and quickly defining and realizing the opening and closing of the grating structure. Furthermore, when the switchable grating structure is a switchable Bragg grating made of holographic polymer-dispersed liquid crystal, since each sub-grating is configured with the highest diffraction efficiency, all gratings have the same optical characteristics. The same fabrication process can be used to mass-produce the gratings, greatly reducing the complexity and difficulty of grating fabrication. It also makes it easier to ensure the consistency of all characteristics of the grating structure, improving not only production efficiency but also the performance of the grating structure.

[0018] Furthermore, the control system includes a plurality of control electrodes, each of which modulates a sub-grating separately and is parallel to and corresponds to the sub-grating, and the coverage area of ​​the control electrode is not less than the area of ​​the grating array.

[0019] In this technical solution, the sub-grating is a switchable Bragg grating, so the optical state of the sub-grating can be modulated by applying an electric field of a certain magnitude to both sides of it through the control electrodes. Furthermore, through the corresponding connection and individual modulation between the sub-grating and the control electrodes, the coupling region selection based on a single sub-grating dimension can be accurately and conveniently achieved, and the diffraction efficiency of each sub-grating can be modulated individually. Therefore, the control electrodes form an electrode array parallel to the grating array it modulates. The area of ​​the electrode array should be greater than or equal to the area of ​​the grating region to be modulated, for achieving stable modulation of the grating array. Simultaneously, by setting the size of the sub-grating along the arrangement direction of the grating array to be no greater than the size of a pupil, the area of ​​the grating selected and opened by the control system at a time is equal to or slightly larger than the size of the pupil, while keeping other gratings in a closed state. This results in a more concentrated beam with higher diffraction efficiency during actual operation, thereby improving the brightness and uniformity of the single-emission light.

[0020] Optionally, the control electrodes are arranged in pairs on the outer plane of the waveguide substrate and are parallel to and correspond to the sub-grating they modulate; and / or, the control electrodes are arranged in pairs in the waveguide substrate and are parallel to and correspond to the sub-grating they modulate; the control electrodes are transparent electrodes.

[0021] In this technical solution, control electrodes are arranged in pairs and parallel on both sides of the pupil of the desired modulation sub-grating. These electrodes are used to create an electric field in the sub-grating, thereby accurately controlling the pupil's direction and opening or closing the sub-grating. Preferably, the positions of the control electrodes overlap with the beam passage positions near the sub-grating, and the control electrodes are made of highly transparent electrodes to facilitate beam coupling in and out. More preferably, the control electrodes are made of ITO conductive glass to improve the transparency of the coupling out region.

[0022] Optionally, in order to improve the diffraction efficiency of the grating structure and increase the field of view, the switchable grating structure can be a one-dimensional grating array or a two-dimensional grating array composed of sub-gratings.

[0023] Optionally, in order to improve the uniformity and angular uniformity of the local grating, the switchable grating structure can also use multiplexed gratings, overlapping gratings as sub-gratings, or a smaller grating array. Beneficial effects

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. A method for improving the uniformity of volume holographic waveguide displays is provided. By employing a switchable grating structure, the light source can only be coupled and emitted from a selected area on the grating at a time. This concentrates the light beam in a specific area of ​​the switchable grating structure during a single emission, thereby reducing the energy imbalance of the beam in the coupling area and improving the brightness and uniformity of the single emission. Secondly, the coupling area on the switchable grating structure can be freely selected and continuously switched, allowing the output field of view of the light source through the switchable grating structure to move freely in different areas. Furthermore, since the brightness and angle uniformity of the beam passing through each coupling area of ​​the switchable grating structure are consistent, a more balanced light field distribution is constructed in the entire output field of view, improving the overall display effect.

[0026] Furthermore, during a single light emission, the light source is coupled out with its maximum diffraction efficiency when passing through the coupling region. This allows the light source to couple out most of the light energy in a single diffraction when passing through the coupling region, further improving the brightness and uniformity of the single light emission. By rapidly switching the coupling region, the utilization rate of the beam is maximized in all regions, thus improving the overall brightness of the beam.

[0027] 2. When a scan is defined as the continuous switching of coupling regions covering all regions of the switchable grating structure, one scan precisely couples out all regions of the switchable grating structure from which the light source carrying the image is located. At the same time, the time of one scan is not greater than the visual persistence time of the human eye. That is, what the human eye observes through the volume holographic waveguide display device is the entire image after the improvement of brightness and uniformity, which improves the image quality observed by the human eye while ensuring the visual experience.

[0028] 3. A high-brightness, high-uniformity volume holographic waveguide display device is provided. By adding a control system and adjusting the coupling grating or folded grating in the waveguide system to a switchable grating structure, the coupling area on the coupling grating or folded grating can be continuously and quickly switched to cover the switchable grating structure. This not only realizes the one-dimensional or two-dimensional pupil expansion scheme of the original grating structure design, preserving its exit pupil diameter and field of view, but also improves the overall brightness and uniformity of the light source emission through one-dimensional or two-dimensional scanning light output, thus enhancing luminous efficiency and display quality. Furthermore, the volume holographic waveguide display device does not require the introduction of additional optical components and does not introduce extra stray light, exhibiting both excellent static and dynamic characteristics. Attached Figure Description

[0029] Figure 1 is a cross-sectional schematic diagram of a switchable Bragg grating composed of holographic polymer-dispersed liquid crystal.

[0030] Figure 2 is a planar schematic diagram of a waveguide system using a one-dimensional grating array for the coupling grating.

[0031] Figure 3 is a planar schematic diagram of a waveguide system using a two-dimensional grating array for the coupling grating.

[0032] Figure 4 is a cross-sectional schematic diagram of a waveguide system with control electrodes disposed on both sides of the waveguide substrate surface.

[0033] Figure 5 is a cross-sectional schematic diagram of a waveguide system in which the control electrodes are located inside the waveguide substrate and on both sides of the grating structure.

[0034] Figure 6 is a planar schematic diagram of a waveguide system using multiplexed gratings for a coupled grating array.

[0035] Figure 7 is a planar schematic diagram of a waveguide system using overlapping gratings for a coupled grating array.

[0036] Figure 8 is a planar schematic diagram of a two-dimensional pupil-expanding waveguide system. Embodiments of the present invention

[0037] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] The present invention will now be further illustrated with specific examples. The following embodiments are only for explaining the present invention and do not constitute a limitation thereof. The test samples and test procedures used in the following embodiments include the following (if the specific experimental conditions are not specified in the embodiments, they are usually performed according to conventional conditions or the conditions recommended by the reagent company; the reagents, consumables, etc. used in the following embodiments can be obtained commercially unless otherwise specified). Example

[0040] This embodiment provides a method for improving the uniformity of volume holographic waveguide displays. The volume holographic waveguide includes a switchable grating structure. A portion of the switchable grating structure can be oriented to serve as its coupling region, allowing the light source to couple out only from this region at its maximum diffraction efficiency. By employing the switchable grating structure, the light source can only couple out from this oriented region at a time, concentrating the light beam in a specific area of ​​the switchable grating structure during a single emission. This reduces the energy imbalance of the beam in the coupling region during a single emission, improving the brightness and uniformity of the single emission. Furthermore, the light source couples out at its maximum diffraction efficiency each time it passes through the coupling region, allowing most of the light energy to be coupled out in a single diffraction cycle, further enhancing the brightness and uniformity of the single emission.

[0041] Secondly, by freely selecting and continuously switching the coupling regions on the switchable grating structure, the output field of view of the light source through the switchable grating structure can move freely in different regions of the structure, thus restoring the entire field of view of the switchable grating structure. Simultaneously, since the brightness and angle uniformity of the light beam passing through each coupling region on the switchable grating structure are consistent, the utilization rate of the light beam is maximized in all regions, improving the overall brightness of the beam. This results in a more balanced light field distribution in the full output field of view and improves the overall display effect. When the process of continuously switching coupling regions covering all regions of the switchable grating structure is considered a single scan, one scan precisely couples the light source carrying the image through all regions of the switchable grating structure, and the time of one scan is no greater than the visual persistence of the human eye, thus improving the image quality observed by the human eye while ensuring a good visual experience. Preferably, the image light source can be repeatedly scanned on the same switchable grating structure to further improve the visual communication effect.

[0042] Furthermore, the switchable grating structure is configured as a grating array formed by the directional arrangement of several sub-gratings. By controlling the opening of some sub-gratings and the closing of others in the grating array, the directional selection of coupling regions on the switchable grating structure can be conveniently and quickly achieved. This allows the selection of coupling regions to be controlled by the sub-grating dimension, improving the accuracy and convenience of coupling region selection and control. Preferably, by controlling the selection and switching of coupling regions through the sub-gratings, the scanning methods on the switchable grating structure are also broadened to adapt to different application scenarios and construct different visual effects experiences. Specifically, sequential scanning or random scanning can be used, and at least one sub-grating is opened each time during sequential or random scanning.

[0043] Furthermore, the size of the sub-grating along the grating array arrangement direction is no larger than the size of one pupil. This ensures that the area of ​​the grating selected and opened by the control system in a single operation is equal to or slightly larger than the size of the pupil. In actual operation, the beam coupled out in a single operation is more concentrated and has higher diffraction efficiency, thereby improving the brightness and uniformity of the single-output light. The control system includes several control electrodes, each corresponding to a single sub-grating for modulation. This accurately and conveniently achieves the selection of coupling regions based on the dimension of a single sub-grating and allows for the individual modulation of the diffraction efficiency of each sub-grating. The coverage area of ​​the control electrodes is no smaller than the area of ​​the grating array, enabling stable modulation of the grating array. Example

[0044] This embodiment provides a volume holographic waveguide display device, including an optomechanical system, a waveguide system, and a control system. The optomechanical system emits a collimated light source into the waveguide system. The waveguide system includes a waveguide substrate and a grating structure disposed within the waveguide substrate. The grating structure guides the collimated light source into the waveguide substrate for propagation and modulates the collimated light source, and couples out the modulated light source. Specifically, as shown in Figure 2, the waveguide substrate 101 is composed of a single layer or multiple layers of transparent glass, constructing a space for light source modulation. The grating structure includes at least an input grating 102 and an output grating 103. The collimated light source enters the waveguide substrate 101 through the input grating 102 and propagates along 201 within the waveguide substrate 101. The output grating 103 is a switchable grating structure. The control system is used to directionally select and continuously switch the coupling region on the output grating.

[0045] The optomechanical system expands and collimates the image pixel point light source before coupling it into the waveguide substrate. The light beam entering the waveguide substrate is diffracted by the coupling grating to generate a first-order diffracted wave, which can propagate within the waveguide with total internal reflection. The coupling grating is set to its maximum diffraction efficiency so that most of the light entering the waveguide is diffracted into first-order diffracted light and propagates within the waveguide. The diffracted wave propagates along the direction towards the output grating in the waveguide with total internal reflection until it encounters the output grating and undergoes a second diffraction. This diffraction expands the pupil of the light beam that originally propagated with total internal reflection within the waveguide and finally couples it out of the waveguide substrate to enter the human eye for imaging. At the same time, the coupling region can be continuously and rapidly switched by the control system to cover all areas of the output grating, and the light is superimposed by scanning to ensure that the final light effect restores the exit pupil diameter and field of view of the original output grating array design.

[0046] Furthermore, the coupling grating adopts a switchable Bragg grating composed of holographic polymer-dispersed liquid crystal. Since the holographic polymer-dispersed liquid crystal is formed by polymerization-induced phase separation under coherent laser, and the grating is formed by periodically arranging polymer-rich phase and liquid crystal-rich phase, the required grating structure can be formed conveniently and economically by changing the spatial energy distribution of the exposure light field of the holographic polymer-dispersed liquid crystal. Simultaneously, due to the inherent characteristic of liquid crystals to deflect their optical axis under the influence of an electric field, as shown in Figure 1, the optical axis direction of the liquid crystal material molecules 302 can change with the voltage applied by the paired control electrodes 301. When there is no voltage, the optical axis of the liquid crystal material molecules 302 is perpendicular to the polymer material 303, and at this time, the liquid crystal material molecules 302 have the maximum refractive index in the horizontal direction. When a certain voltage is applied by the control electrodes 301, the optical axis of the liquid crystal material molecules 302 turns, becoming parallel to the polymer material 303. At this time, the refractive index of the liquid crystal material molecules 302 is the lowest in the horizontal direction and is close to that of the polymer material 303. Furthermore, the magnitude of the applied voltage can adjust the refractive index difference between the liquid crystal material molecules 302 and the polymer material 303, thereby adjusting the diffraction efficiency of the grating. The switchable Bragg grating composed of holographic polymer-dispersed liquid crystals can achieve pupil redirection by applying an external electric field to both sides of its pupil, thereby modulating the transmittance of the beam relative to the grating, realizing the opening or closing of the grating, and achieving directional selection of the beam coupling region.

[0047] Therefore, the control system can include several control electrodes 301. By switching the opening or closing of the sub-gratings in the coupling grating array through the control electrodes, the coupling area on the coupling grating array can be selected in a directional manner, thereby reducing the coupling area of ​​a single beam and improving the diffraction efficiency and brightness of the beam. The control electrodes 301 are connected to the sub-gratings and modulated by them individually. Each sub-grating can be physically divided or physically undivided but defined by the area of ​​the control electrode 301. Each sub-grating can be individually modulated to any diffraction efficiency between the maximum diffraction efficiency and zero diffraction efficiency.

[0048] Since the sub-gratings in the grating structure are parallel to and correspond to the control electrode 301 and are individually modulated by the control electrode 301, each control electrode 301 can be individually connected to the control system, specifically, a voltage controller, and individually modulate the diffraction efficiency of each sub-grating. Therefore, the control electrode 301 forms an electrode array corresponding to the grating array it modulates. The area of ​​the electrode array should be greater than or equal to the area of ​​the grating region to be modulated, in order to achieve stable modulation of the grating array. Specifically, in order to facilitate the corresponding modulation between the control electrode 301 and the sub-gratings, and to maximize the realization of the electronic control function while avoiding interference with the function of the waveguide system itself, the control electrodes 301 should be arranged in pairs on the waveguide substrate 101 and parallel to and correspond to the sub-gratings they modulate.

[0049] Optionally, in order to improve the diffraction efficiency of the grating structure and increase the field of view, as shown in Figure 2, the coupling grating can be a one-dimensional grating array composed of sub-gratings, or, as shown in Figure 3, a two-dimensional grating array.

[0050] Optionally, to facilitate the corresponding modulation between the control electrode 301 and the sub-grating, and to maximize the electronic control function while avoiding interference with the waveguide system's own function, as shown in Figure 4, the control electrode 301 is disposed on both sides of the waveguide region corresponding to the coupling grating 103, and the control electrodes 301 are arranged in pairs and parallel to the grating structure they modulate; or, as shown in Figure 5, the control electrode 301 is disposed inside the waveguide substrate 101 and on both sides of the coupling grating 103; furthermore, the control electrode 301 may or may not be in contact with the modulated grating structure. Preferably, the control electrode 301 is a transparent electrode made of ITO transparent conductive glass.

[0051] Alternatively, in order to improve the uniformity and angular uniformity of the local grating, as shown in Figures 6 and 7, multiplexed gratings, overlapping gratings, or smaller grating arrays can also be used. Example

[0052] This embodiment also provides a volume holographic waveguide display device. The difference from embodiment 2 is that the grating structure further includes a folded grating 104, as shown in Figure 8. The grating structure includes an input grating 102, a folded grating 104, and an output grating 103. Preferably, in this waveguide system, both the folded grating 104 and the output grating 103 have an array structure, and both the folded grating 104 and the output grating 103 are switchable grating structures, thereby providing a two-dimensional pupil-expanding waveguide system. The folded grating 104 and the output grating 103 can be either a one-dimensional array or a two-dimensional array. Consistent with the aforementioned embodiments, the folded grating 104 and the output grating 103 can also have the aforementioned various grating structure configurations and control system configurations, so that the folded grating 104 and the output grating 103 can be directionally selected and continuously switched by the control system to jointly constitute a two-dimensional scanning mode, thereby reflecting the dynamic characteristics of the waveguide display.

[0053] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for improving the uniformity of volume holographic waveguide displays, characterized in that, The bulk holographic waveguide includes a switchable grating structure, on which a portion of the switchable grating structure can be oriented to serve as its coupling region, so that the light source can only be coupled out from the coupling region with its maximum diffraction efficiency. The process of continuously switching the coupling regions on the switchable grating structure and covering all regions of the switchable grating structure with the continuously switched coupling regions is called a scan, and the time of a scan is not greater than the visual persistence time of the human eye.

2. The method according to claim 1, characterized in that, The switchable grating structure is a grating array formed by oriented arrangement of several sub-gratings. The directional selection of the coupling region of the grating array is achieved by controlling the opening or closing of some sub-gratings in the grating array. The scanning method is either sequential scanning or random scanning, and at least one of the sub-gratings is opened each time during the sequential or random scanning process.

3. A volume holographic optical waveguide display device, characterized in that, The volume holographic waveguide display device employs the method described in any one of claims 1-2 to improve its display uniformity; The volume holographic waveguide display device includes an optomechanical system, a waveguide system, and a control system; the optomechanical system is used to emit a collimated light source; the waveguide system includes a waveguide substrate and a grating structure disposed within the waveguide substrate; the grating structure includes at least an input grating and an output grating, the collimated light source enters the waveguide substrate through the input grating and propagates toward the output grating, and is then expanded by the output grating and coupled out of the waveguide substrate; The output grating adopts a switchable grating structure; the control system modulates the switchable grating structure accordingly to realize the directional selection and continuous switching of the coupling region on the switchable grating structure.

4. The apparatus according to claim 3, characterized in that, The grating structure further includes a folded grating. The collimated light source enters the waveguide substrate through the coupling grating and propagates toward the folded grating. Then, it is pupil-expanded once by the folded grating and propagates toward the coupling grating. After pupil-expanding a second time by the coupling grating, it is coupled out and coupled out of the waveguide substrate.

5. The apparatus according to claim 4, characterized in that, The folded grating adopts a switchable grating structure.

6. The apparatus according to any one of claims 3-5, characterized in that, The switchable grating structure is a grating array formed by oriented arrangement of several sub-gratings, and the switchable grating structure is a switchable Bragg grating made of holographic polymer dispersed liquid crystal.

7. The apparatus according to claim 6, characterized in that, The control system includes a plurality of control electrodes, each of which modulates a sub-grating separately and is parallel to and corresponds to the sub-grating. The coverage area of ​​the control electrode is not less than the area of ​​the grating array.

8. The apparatus according to claim 7, characterized in that, The control electrodes are arranged in pairs on the outer plane of the waveguide substrate and are parallel to and correspond to the sub-grating they modulate; and / or, the control electrodes are arranged in pairs in the waveguide substrate and are parallel to and correspond to the sub-grating they modulate; the control electrodes are transparent electrodes.

9. The apparatus according to claim 7, characterized in that, The grating array is a one-dimensional array or a two-dimensional array.

10. The apparatus according to claim 7, characterized in that, The sub-grating is one or more of an overlapping grating or a multiplexed grating.

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