Volume holographic diffraction grading and creation of grating vector distribution thereof, production method and production device

Abstract

To disclose a volume holographic diffraction grating and creation of grating vector distribution thereof, production method and production device.SOLUTION: A grading vector distribution is estimated by sampling positions of effective areas of an eye movement range of a plurality of subfields and grating vectors whose rays match Bragg diffraction condition, and most of the effective rays with different incident angles all exhibit relatively high diffraction efficiency in the volume holographic diffraction grating, without taking into consideration of diffraction of ineffective rays that ultimately enter outside the eye movement range so that the overall brightness uniformity of the output beam is maintained, thereby achieving an expansion of the field of view. Furthermore, the diffraction efficiency is maximized as much as possible at a joining end by placing a grating vector whose each subfield ray precisely matches the Bragg diffraction condition at the joining end of the effective area of the eye movement range. This helps to improve the brightness uniformity of the effective light rays output by each sub-field from different positions on the volume holographic diffraction grating, thereby improving the field uniformity and eye movement range uniformity.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present application relates to the technical field of augmented reality waveguide display, and more particularly to a volume hologram diffraction grating and its grating vector distribution fabrication method and fabrication device. [Background technology]

[0002] Optical waveguide display technology is a mainstream solution for augmented reality glasses, achieving high transparency and light weight, while also offering great potential for expanding the field of view and further improving display effects. Light propagates through a transparent optical waveguide via total internal reflection. Coupling elements such as gratings are placed in the optical waveguide to control the input, output, redirection, exit pupil expansion, and energy allocation of the light rays, thereby directing the image light signal to the human eye. As a Bragg diffraction element, a volume hologram diffraction grating concentrates most of the diffracted energy in the zeroth and first diffraction orders, and the ratio between the two can be adjusted by controlling the grating parameters. Therefore, optical waveguides using volume hologram diffraction gratings as coupling elements have special advantages in terms of improving optical efficiency and reducing light leakage.

[0003] The field of view and eye movement range of an optical waveguide display are important indicators for evaluating the performance of the optical waveguide. To extend the field of view and eye movement range and improve the field of view uniformity and eye movement range uniformity, it is necessary to locally control the spatially variable grating parameters. Compared with surface microstructure gratings, volume hologram diffraction gratings have a relatively simple structure, and the controllable variable parameters include thickness, refractive index modulation degree, and grating vector.

[0004] In an augmented reality waveguide display, the eye movement range is the range within which a person's eyes can move to see a full-field-of-view image. Outside the eye movement range, the human eye can only see a partial field-of-view image. Taking a two-dimensional pupil-expanding waveguide as an example, the waveguide structure includes two transparent glass substrates and a volume hologram diffraction grating, which includes an in-coupling grating, a folded grating, and an out-coupling grating, disposed between the two substrates. A light ray with a specific input angle from a microprojector passes through the in-coupling grating at this specific input angle, enters the waveguide, undergoes total internal reflection, expands in two directions through the folded grating, and finally exits the waveguide at an angle corresponding to the input angle through the folded grating. Only a portion of the light enters the eye movement range and is ultimately received by the human eye to form an image. As shown in Figure 1, the area covered by the volume hologram diffraction grating for the light ray entering the eye movement range is defined as the effective eye movement range area on the volume hologram diffraction grating. Because the angles at which light rays with different input angles enter the eye movement area from the waveguide through the coupling grating are also different, the effective eye movement area of ​​the volume hologram diffraction grating for light rays with different input angles differs. The effective eye movement area of ​​the volume hologram diffraction grating for light rays with multiple input angles often overlaps with the effective eye movement area of ​​the volume hologram diffraction grating for light rays with different input angles, as shown in Figure 2. In addition to the fact that light rays with different input angles have different grating vectors that match the Bragg diffraction condition, grating vectors at different positions on the volume hologram diffraction grating must support the diffraction of many light rays with different input angles, making it impossible to directly determine the grating vector distribution. However, controlling only a single parameter, such as the refractive index modulation depth or thickness, is disadvantageous in controlling light transmission with a high degree of freedom, making it impossible for optical waveguide displays to achieve a relatively large field of view, field of view uniformity, and eye movement area uniformity.

[0005] Furthermore, the manufacturing of volume hologram diffraction gratings with spatially varying parameters is relatively difficult. In particular, the control of the grating vector must satisfy the requirement that the surface component of the grating vector be kept constant, based on the basic principle of waveguide display. At the same time, the range of variation of the grating vector must support light rays of all angles within the field of view to match the Bragg diffraction conditions as much as possible. Therefore, whether double-beam exposure or reticle exposure is used, the requirements for the exposure equipment and exposure process are both strict. Summary of the Invention [Problem to be solved by the invention]

[0006] The present application aims to overcome at least one deficiency in the prior art and provide a method for creating a grating vector distribution target, which can help expand the angular bandwidth of a volume hologram diffraction grating, expand the field of view range of an optical waveguide, and improve field of view uniformity and eye movement range uniformity. [Means for solving the problem]

[0007] In order to solve the above technical problems, the following technical proposals are adopted.

[0008] In a first aspect, a method for creating a grating vector distribution target is provided, the method includes the steps of: sampling multiple sub-fields of view, recording the position of the effective area of ​​the eye movement range of each sub-field of view, and calculating the grating vector that the light beam of each sub-field of view matches the Bragg diffraction condition; estimating the grating vector distribution of a volume hologram diffraction grating based on the positions of the effective area of ​​the eye movement range of each sub-field of view and the grating vector that the light beam of each sub-field of view matches the Bragg diffraction condition; and determining the grating vector distribution of the volume hologram diffraction grating based on the estimated grating vector distribution and the principle that the grating vector at the connecting end of the effective area of ​​the eye movement range of each sub-field of view accurately matches the Bragg diffraction condition.

[0009] The present application estimates the lattice vector distribution by sampling the positions of the effective areas of the eye movement ranges of multiple sub-fields and the lattice vectors whose rays match the Bragg diffraction condition, and ensures that most of the effective rays with different incident angles all have relatively high diffraction efficiency on the volume hologram diffraction grating, regardless of the diffraction of ineffective rays that ultimately fall outside the eye movement range, thereby ensuring the overall brightness uniformity of the output beam and realizing an expanded field of view. Furthermore, by arranging the lattice vectors whose rays of each sub-field accurately match the Bragg diffraction condition at the junction end of the effective area of ​​its eye movement range, the diffraction efficiency at the junction end is maximized as much as possible, which helps to improve the brightness uniformity of the effective rays output from different positions of the volume hologram diffraction grating for each sub-field, thereby improving the field of view uniformity and the uniformity of the eye movement range.

[0010] In a second aspect, a volume hologram diffraction grating is provided. The grating vector distribution of the volume hologram diffraction grating is estimated by sampling the positions of the effective areas of the eye movement ranges of multiple sub-fields and the grating vectors whose light rays match the Bragg diffraction condition, and the grating vectors at the connecting ends of the effective areas of the eye movement ranges of each sub-field accurately match the Bragg diffraction condition. The grating vector distribution has at least one change direction, and at least one change direction is the same as the direction of the grating vector surface component, and the surface component of the grating vector at different positions is kept constant. The sub-fields are sets of light rays with the same incident angle that ultimately enter the entire field range, and the effective area of ​​the eye movement range is the area covered by the volume hologram diffraction grating for the light rays that ultimately enter the eye movement range.

[0011] The lattice vector distribution in the present application is estimated by sampling the positions of the effective areas of the eye movement ranges of multiple sub-fields and the lattice vectors whose light rays match the Bragg diffraction condition, and most of the effective light rays with different incident angles are made to have relatively high diffraction efficiency on the volume hologram diffraction grating, regardless of the diffraction of ineffective light rays that ultimately fall outside the eye movement range, thereby ensuring the overall brightness uniformity of the output beam and realizing an expanded field of view. Furthermore, by arranging the lattice vectors whose light rays of each sub-field accurately match the Bragg diffraction condition at the junction end of the effective area of ​​its eye movement range, the diffraction efficiency at the junction end is maximized as much as possible, which helps to improve the brightness uniformity of the effective light rays output from different positions on the volume hologram diffraction grating for each sub-field, thereby improving the field of view uniformity and the uniformity of the eye movement range.

[0012] The volume hologram diffraction grating may be a coupling-in grating, a coupling-out grating, a folded grating, or a combination of any two or three of the coupling-in grating, folded grating, and coupling-out grating, i.e., the volume hologram diffraction grating may include a coupling-in region, a folded region, and / or a coupling-out region. Preferably, the volume hologram diffraction grating includes a coupling-in region and a coupling-out region. More preferably, the volume hologram diffraction grating includes a coupling-in region, a folded region, and a coupling-out region.

[0013] In a third aspect, we provide a method for fabricating the volume hologram diffraction grating described above. This method includes the steps of: discretizing a grating vector distribution into a plurality of grating units arranged along at least the direction of the grating vector surface component, so that the grating vectors at different positions of the same grating unit are kept constant; selecting or fabricating a reticle grating whose surface period is equal to the surface period of the volume hologram diffraction grating to be fabricated so that the surface component of the grating vector of the volume hologram diffraction grating to be fabricated is parallel to the surface component of the grating vector of the reticle grating; calculating a collimated beam incident angle corresponding to each grating unit based on the grating vectors of the grating units and the grating vector of the reticle grating; and simultaneously switching the exposure position and the collimated beam incident angle corresponding to a certain grating unit so that the zeroth-order light and first-order light generated by the reticle grating diffraction interfere with each other in the volume hologram diffraction photosensitive material, thereby sequentially exposing each grating unit.

[0014] The present application discretizes the volume hologram diffraction grating to be fabricated and its grating vector distribution into multiple grating units with specific grating vectors, thereby avoiding the need for a customized beam shaping element or customized reticle grating in a high-precision exposure device, thereby reducing the difficulty and cost of fabrication. At the same time, the reticle grating diffracts the collimated beam to generate zeroth-order and first-order beams for sequentially exposing each grating unit. By adjusting the incident angle of the collimated beam, the incident angles of the zeroth-order and first-order beams can be simultaneously adjusted, which is less complex and more cost-controllable than other methods.

[0015] In a fourth aspect, we provide an apparatus for fabricating the volume hologram diffraction grating. The apparatus includes a collimated light generating mechanism, a reticle grating, and a light-transmitting carrier, which are sequentially arranged, and further includes a first switching mechanism and a second switching mechanism that operate simultaneously. The light-transmitting carrier is used to carry a volume hologram diffraction photosensitive material, and the reticle grating has the same surface period as the grating units and is parallel to the grating vector surface component of the grating units. The collimated light generating mechanism is used to generate a collimated beam that can be incident on the reticle grating. The collimated beam is diffracted by the reticle grating into zeroth-order light and first-order light, and the zeroth-order light and first-order light pass through the light-transmitting carrier and are exposed to interference in the volume hologram diffraction photosensitive material. The first switching mechanism is used to switch the exposure position so that the zeroth-order light and the first-order light just cover the grating unit to be exposed, and the second switching mechanism is used to switch the incident angle of the collimated beam so that the incident angle of the collimated beam corresponds to the grating unit to be exposed.

[0016] This application generates zeroth-order and first-order light for sequentially exposing each grating unit by diffracting the reticle grating into a collimated beam, and by adjusting the incident angle of the collimated beam, the incident angles of the zeroth-order and first-order light can be adjusted simultaneously, which is less complex and more cost-controllable than other methods.

[0017] In a fifth aspect, an augmented reality waveguide structure employing the volume hologram diffraction grating is provided. The augmented reality waveguide structure includes two transparent substrates and the volume hologram diffraction grating disposed between the two substrates. The volume hologram diffraction grating may be an in-coupling grating, an out-coupling grating, a folded grating, or a combination of any two or three of the in-coupling grating, the folded grating, and the out-coupling grating. That is, the volume hologram diffraction grating may include an in-coupling region, a folded region, and / or an out-coupling region. Preferably, the volume hologram diffraction grating includes an in-coupling region and an out-coupling region. More preferably, the volume hologram diffraction grating includes an in-coupling region, a folded region, and an out-coupling region.

[0018] In this application, by employing the volume hologram diffraction grating proposed in this invention as a coupling-in grating and / or a coupling-out grating, the field of view range is expanded and the uniformity of the field of view and the eye movement range is improved. [Effects of the Invention]

[0019] Compared with the prior art, the present application has the following advantageous effects: The present application estimates the lattice vector distribution by sampling the positions of the effective areas of the eye movement ranges of multiple sub-fields and the lattice vectors whose light rays match the Bragg diffraction condition, and ensures that most of the effective light rays with different incident angles all have relatively high diffraction efficiency on the volume hologram diffraction grating, regardless of the diffraction of ineffective light rays that ultimately fall outside the eye movement range. This ensures the overall brightness uniformity of the output beam and realizes an expanded field of view. Furthermore, by arranging the lattice vectors whose light rays of each sub-field accurately match the Bragg diffraction condition at the junction end of its effective area of ​​the eye movement range, the diffraction efficiency at the junction end is maximized as much as possible, which helps improve the brightness uniformity of the effective light rays output from different positions on the volume hologram diffraction grating for each sub-field, thereby improving the field of view uniformity and the uniformity of the eye movement range. [Brief explanation of the drawings]

[0020] It should be understood that the accompanying drawings are merely illustrative and should not be understood as limitations on the present application. In order to better explain the present application, some parts of the accompanying drawings may be omitted, enlarged or reduced in size, and may not represent the size of actual products. It should be understood that some structures and descriptions thereof that are well known to those skilled in the art may be omitted in the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram of the transmission of a light ray with an incident angle α in a two-dimensional pupil-expanding waveguide structure. [Figure 2] 1 is a schematic diagram of the effective area of ​​the eye movement range in a volume hologram diffraction grating for light rays of different incident angles. [Figure 3] 1 is a flowchart of a method for creating a lattice vector distribution target. [Figure 4] FIG. 1 is a schematic diagram of the ray transmission of a volume hologram diffraction grating whose grating vector varies spatially. [Figure 5] 1 is a flowchart of a method for fabricating a volume hologram diffraction grating. [Figure 6] FIG. 1 is a schematic diagram of a volume hologram diffraction grating made up of multiple grating units. [Figure 7] FIG. 1 is a schematic diagram of an apparatus for producing a volume hologram diffraction grating. [Figure 8] FIG. 8 is a plan view of the device shown in FIG. 7. [Figure 9] 5 is a schematic diagram of a waveguide structure using the volume hologram diffraction grating shown in FIG. 4. [Figure 10] The diffraction efficiency curve of a reticle grating varies with angle. [Figure 11] 11 is a diffraction efficiency curve of a volume hologram diffraction grating of a grating vector space variation obtained by exposure using the reticle grating shown in FIG. 10. DETAILED DESCRIPTION OF THE INVENTION

[0021] In order to enable those skilled in the art to better understand the present application, the present application will be described in more detail below in conjunction with specific examples.

[0022] FIG. 3 shows a method for creating a grating vector distribution target. This method may be used to create a grating vector distribution target for a volume hologram diffraction grating (especially a volume hologram diffraction grating for an augmented reality waveguide display), thereby expanding the angular bandwidth of the resulting volume hologram diffraction grating, which helps to expand the field of view of the optical waveguide and improve the field of view uniformity and eye movement range uniformity. As shown in FIG. 3, this method may include the following steps:

[0023] S11 samples multiple sub-fields of view.

[0024] In a display system, the field of view is the angle formed by the line connecting the display edge and the human eye. Light rays with output angles within the full field of view range can enter the human eye and form a full field of view image. In other words, the full field of view image is represented by the joint representation of light rays with different input angles entering the human eye. For convenience of description, this proposal defines a sub-field of view as a set of light rays with the same incident angle that ultimately enters the full field of view range. All light rays in the same sub-field of view have the same incident angle and are also diffracted by the volume hologram diffraction grating at the same angle. The number of sub-fields to be sampled may be determined according to the size of the field of view designed for the display system. The sampling process may employ random sampling methods such as simple random sampling, systematic sampling, group sampling, and hierarchical sampling, or non-random sampling methods such as chance sampling, judgment sampling, equal-amount sampling, and snowball sampling.

[0025] S12 records the position of the effective area of ​​the eye movement range for each sub-field and calculates the grating vector at which the light rays of each sub-field match the Bragg diffraction condition.

[0026] After being diffracted by the volume hologram diffraction grating, only a portion of the light beams in a sub-field of view enter the eye movement range and are ultimately received by the human eye. This portion of the light beams may be referred to as effective light beams. For convenience of description, the present invention defines the area covered by the volume hologram diffraction grating for the light beams that ultimately enter the eye movement range as the effective area of ​​the eye movement range. Therefore, the area covered by the volume hologram diffraction grating for the light beams that ultimately enter the eye movement range in a sub-field of view is the effective area of ​​the eye movement range of this sub-field of view. Only the light beams within this area enter the eye movement range and contribute to the complete image seen by the human eye when output. The remaining area is ineffective for this sub-field of view. The grating vector is a vector perpendicular to the grating plane and has an amplitude of 2π / P, where P is the spacing between adjacent grating planes, i.e., the grating period. The grating vector that matches the Bragg diffraction condition may be calculated based on the Bragg diffraction condition and the incident angle of the light beam.

[0027] In step S13, a grating vector distribution of the volume hologram diffraction grating is estimated based on the positions of the effective areas of the eye movement ranges of the multiple sub-fields and the grating vectors at which the light rays of the multiple sub-fields match the Bragg diffraction condition.

[0028] The grating vector distribution is the spatial variation of the grating vector, which describes how the grating vector changes with position. The surface component of the grating vector is the component of the grating vector projected onto the entire plane of the volume hologram diffraction grating. For optical waveguide display, this surface component must be constant over the entire volume hologram diffraction grating. That is, only by keeping the surface component of the grating vector constant at different positions can the one-to-one correspondence between the input and output angles of the optical waveguide for different light rays be ensured, which in turn ensures the accuracy of the waveguide imaging.

[0029] The lattice vector distribution has at least one direction of change, and specifically, it may be a one-dimensional distribution or a two-dimensional distribution. A one-dimensional distribution has one direction of change, and a two-dimensional distribution has two mutually perpendicular directions of change. Generally, at least one direction of change in the lattice vector distribution should be along the direction of the surface component of the lattice vector. When the lattice vector distribution is a one-dimensional distribution, its direction of change is the same as the direction of the surface component of the lattice vector. When the lattice vector distribution is a two-dimensional distribution, one of the two directions of change is the same as the direction of the surface component of the lattice vector.

[0030] The lattice vector distribution of the volume hologram diffraction grating is estimated based on the position of the effective area within the eye movement range of multiple sub-fields and the lattice vector at which the light rays match the Bragg diffraction condition. The diffraction of ineffective rays that ultimately fall outside the eye movement range is not taken into account, and most effective rays with different incident angles all have relatively high diffraction efficiency in the volume hologram diffraction grating, thereby ensuring the overall brightness uniformity of the output beam and realizing an expansion of the field of view range.

[0031] S14 determines the grating vector distribution of the volume hologram diffraction grating based on the estimated grating vector distribution and the principle that the grating vectors at the combined ends of the effective area of ​​the eye movement range of each sub-field of view exactly match the Bragg diffraction condition.

[0032] Based on the estimated lattice vector distribution, for each sub-field of view, a lattice vector that accurately matches the Bragg diffraction condition is placed at the joint end of the effective area of ​​its eye movement range, thereby maximizing the diffraction efficiency at the joint end as much as possible and helping to improve the brightness uniformity of the effective light beams output by each sub-field of view from different positions of the volume hologram diffraction grating, thereby improving field of view uniformity and eye movement range uniformity.

[0033] Figure 4 shows a volume hologram diffraction grating (which may be called the first volume hologram diffraction grating) whose grating vector changes spatially. This volume hologram diffraction grating can be used in optical waveguide display technology, specifically as a coupling-in grating, a folding grating, or a coupling-out grating in an augmented reality waveguide structure.

[0034] As shown in Figure 4, the grating vector distribution of this volume hologram diffraction grating is estimated by sampling the positions of the effective areas of the eye movement range of multiple sub-fields and the grating vectors whose light rays match the Bragg diffraction condition, and the grating vectors at the connecting ends of the effective areas of the eye movement range of each sub-field accurately match the Bragg diffraction condition. The grating vector distribution has at least one change direction, and at least one change direction is the same as the direction of the grating vector surface component, and the surface component of the grating vector at different positions is kept constant. The sub-fields are sets of light rays with the same incident angle that ultimately enter the entire field of view, and the effective area of ​​the eye movement range is the area covered by the volume hologram diffraction grating for the light rays that ultimately enter the eye movement range.

[0035] The grating vector distribution of this volume hologram diffraction grating is estimated by sampling the positions of the effective areas of the eye movement range of multiple sub-fields and the grating vectors whose rays match the Bragg diffraction condition. This ensures that most effective rays with different incident angles have relatively high diffraction efficiency on the volume hologram diffraction grating, regardless of the diffraction of ineffective rays that ultimately fall outside the eye movement range. This ensures overall brightness uniformity of the output beam and expands the field of view. Furthermore, by locating the grating vectors whose rays of each sub-field accurately match the Bragg diffraction condition at the junction end of the effective area of ​​its eye movement range, the diffraction efficiency at the junction end is maximized, helping to improve the brightness uniformity of the effective rays output from each sub-field from different positions on the volume hologram diffraction grating, thereby improving field of view uniformity and eye movement range uniformity. Although the grating vectors of the volume hologram diffraction grating vary in space, the surface components of the grating vectors at different positions remain constant, ensuring a one-to-one correspondence between the input and output angles of different rays, thereby ensuring accurate imaging.

[0036] Depending on the number of lattice vector variation directions, the lattice vector distribution may be one-dimensional or two-dimensional. A one-dimensional distribution has one variation direction, while a two-dimensional distribution has two mutually perpendicular variation directions. When the lattice vector distribution is one-dimensional, its variation direction is the same as the direction of the lattice vector surface component. When the lattice vector distribution is two-dimensional, one of the two variation directions is the same as the direction of the lattice vector surface component.

[0037] The grating vector distribution of the volume hologram diffraction grating may be created by the method shown in FIG.

[0038] Figure 5 shows a method for fabricating a volume hologram diffraction grating, which may be used to fabricate the volume hologram diffraction grating shown in Figure 4. As shown in Figure 5, the method may include the following steps:

[0039] S21 discretizes the lattice vector distribution into a plurality of lattice units arranged along at least the direction of the lattice vector surface component, and the lattice vectors at different positions of the same lattice unit are kept constant.

[0040] Fabricating a volume hologram diffraction grating with a continuously varying grating vector distribution requires a high-precision exposure device combined with a customized beam shaping element or customized reticle grating, which makes fabrication difficult and costly. However, fabrication difficulty can be somewhat reduced by discretizing the grating vector distribution into multiple grating units, i.e., by discretizing the target volume hologram diffraction grating into multiple grating units and maintaining constant grating vectors at different positions on the same grating unit. The grating vector distribution can be discretized into a one-dimensional array of grating units (Figure 6) or a two-dimensional array of grating units. Generally, at least one array direction must be aligned with the surface component direction of the grating vector. For optical waveguide displays, a one-dimensional array of grating units is generally sufficient to meet the viewing requirements. The grating units must have an appropriate length or width. To facilitate fabrication, a relatively large grating unit length or width is selected to achieve the overall grating angle bandwidth formed by evaluating the grating vector distribution. The lengths or widths of different grating units can be the same or different. A small amount of overlap is allowed at the edges between adjacent lattice units.

[0041] In step S22, a reticle grating is selected or fabricated whose surface period is equal to that of the volume hologram diffraction grating to be fabricated so that the surface component of the grating vector of the volume hologram diffraction grating to be fabricated is parallel to that of the reticle grating.

[0042] Based on the principle of diffraction, a collimated beam is incident on a reticle grating and diffracted, and the diffracted zeroth-order and first-order beams overlap and interfere on the exposed volume hologram diffraction photosensitive material. The amplitude of the generated volume hologram diffraction grating is equal to the amplitude of the surface component of the grating vector of the reticle grating. Therefore, the amplitudes of the surface components of the grating vector of the reticle grating and the volume hologram diffraction grating to be fabricated should be set to be equal, i.e., the surface periods of both should be equal.

[0043] The reticle grating may be an amplitude grating or phase grating fabricated using lithography, nanoimprinting, or other micro-nanomachining techniques, or it may be a volume hologram diffraction grating fabricated in advance by double-beam exposure. Using a volume hologram diffraction grating fabricated by double-beam exposure as the reticle grating can significantly reduce reticle production costs, but due to the Bragg diffraction characteristics of the volume hologram diffraction grating, its angular bandwidth is relatively narrow and its diffraction efficiency is very low at incident angles far from the Bragg diffraction condition, making it unsuitable for fabricating optical waveguide volume hologram diffraction gratings with a relatively large grating vector spatial variation range. Using a relatively thin volume hologram diffraction grating as the reticle grating can expand the angular bandwidth and therefore the grating vector spatial variation range of the optical waveguide. Specifically, the thickness of the volume hologram diffraction grating used as the reticle grating is preferably 1 to 5 μm.

[0044] Before exposure, the volume hologram diffraction photosensitive material must be placed in the exposure device in the correct orientation so that the surface component of the grating vector of the volume hologram diffraction grating to be fabricated is parallel to the surface component of the grating vector of the reticle grating, as shown in Figure 8.

[0045] S23 calculates the collimated beam incident angle corresponding to each grating unit based on the grating vector of the grating unit and the grating vector of the reticle grating.

[0046] When the incident angle of the collimated beam is changed, the amplitude of the surface component of the grating vector of the generated volume hologram diffraction grating remains unchanged, but the normal component of the grating vector changes, and the synthesized grating vector also changes. In this way, the grating vector can be used to create a spatially varying volume hologram diffraction grating. To facilitate subsequent rapid exposure, the incident angle of the collimated beam corresponding to each grating unit can be calculated in advance based on the grating vector of the grating unit and the grating vector of the reticle grating.

[0047] S24 simultaneously switches the exposure position and the collimated beam incident angle corresponding to a certain grating unit, so that the zeroth-order light and the first-order light generated by the collimated beam through the reticle grating diffraction interfere with each other in the volume hologram diffraction photosensitive material, thereby sequentially exposing each grating unit.

[0048] The area corresponding to each grating unit with a particular grating vector may be exposed sequentially, and each time a grating unit is switched, the angle of incidence of the collimated beam needs to be readjusted to a pre-calculated angle based on the corresponding grating vector, thereby exposing the corresponding grating unit to produce the corresponding grating vector.

[0049] 7 and 8 show an apparatus for fabricating a volume hologram diffraction grating. This apparatus can fabricate the volume hologram diffraction grating shown in FIG. 4 using the method shown in FIG. 5. As shown in FIGS. 7 and 8, this apparatus includes a collimated light generating mechanism (not shown in the accompanying drawings), a reticle grating, and a light-transmitting carrier, which are sequentially arranged. It also includes a first switching mechanism (not shown in the accompanying drawings) and a second switching mechanism (not shown in the accompanying drawings). The light-transmitting carrier is used to mount a volume hologram diffraction photosensitive material. The surface period of the reticle grating is the same as the surface period of the volume hologram diffraction grating to be fabricated, and its grating vector surface component is parallel to the grating vector surface component of the volume hologram diffraction grating to be fabricated. The collimated light generating mechanism is used to generate a collimated beam that can be incident on the reticle grating. The collimated beam is diffracted by the reticle grating into zeroth-order and first-order beams. The zeroth-order and first-order beams pass through the light-transmitting carrier and are exposed to interference by the volume hologram diffraction photosensitive material. Furthermore, when the fabricated volume hologram diffraction grating is used in an augmented reality waveguide structure, the target augmented reality waveguide structure is directly mounted on the transparent carrier, i.e., two transparent substrates and a volume hologram diffraction photosensitive material placed between the two substrates are mounted. After interference exposure, the volume hologram diffraction photosensitive material can form a volume hologram diffraction grating placed between the two substrates.

[0050] The first switching mechanism is used to switch the exposure position so that the zeroth-order and first-order beams cover only the grating unit to be exposed, and the second switching mechanism is used to switch the incident angle of the collimated beam so that the incident angle of the collimated beam corresponds to the grating unit to be exposed. Because the incident beam angle exposing each grating unit has a one-to-one correspondence with the grating vector, the incident angle of the collimated beam must be switched simultaneously with the exposure position switching; that is, the first and second switching mechanisms must operate together. If both the first and second switching mechanisms are automated, they can operate simultaneously, helping to quickly expose multiple grating units sequentially.

[0051] Specifically, the reticle grating may be an amplitude grating or phase grating fabricated using lithography, nanoimprinting, or other micro-nanomachining techniques, or it may be a volume hologram diffraction grating fabricated in advance by double-beam exposure (also referred to as a second volume hologram diffraction grating). Using a volume hologram diffraction grating fabricated by double-beam exposure as the reticle grating significantly reduces reticle production costs, but due to the Bragg diffraction characteristics of the volume hologram diffraction grating, its angular bandwidth is relatively narrow and its diffraction efficiency is very low at incident angles far from the Bragg diffraction condition. This makes it unsuitable for fabricating optical waveguide volume hologram diffraction gratings with a relatively large grating vector spatial variation range. Using a relatively thin volume hologram diffraction grating as the reticle grating allows for a wider angular bandwidth and therefore a wider grating vector spatial variation range for the optical waveguide. Specifically, the thickness of the volume hologram diffraction grating used as the reticle grating is preferably 1 to 5 μm.

[0052] FIG. 9 shows an augmented reality waveguide structure. This waveguide structure includes two transparent substrates and a coupling-in grating, a folded grating, and a coupling-out grating disposed between the two substrates. The coupling-in grating, the folded grating, and the coupling-out grating all employ volume holographic diffraction gratings whose grating vectors vary spatially. It can be understood that this waveguide structure may be a one-dimensional pupil-widening waveguide without a folded grating, or one or two of the coupling-in grating, the folded grating, and the coupling-out grating may employ volume holographic diffraction gratings whose grating vectors vary spatially.

[0053] The above expands the angular bandwidth of the volume hologram diffraction grating, and in fact, by providing different effective Bragg matching angles at different positions on the volume hologram diffraction grating, it can help expand the field of view and improve the uniformity of the field of view and the uniformity of the eye movement range. Furthermore, the fabrication method and apparatus provided in the above application are less complex and more cost-controllable than other methods. For example, Figure 10 shows the diffraction efficiency curves of possible reticle gratings as a function of angle. By selecting collimated beams with three incident angles of approximately -6 degrees, 2.5 degrees, and 10 degrees, three different grating units are sequentially exposed to obtain a combined grating consisting of grating units with three different grating vectors. The resulting diffraction efficiency curves as shown in Figure 11 show that the combined angular bandwidth is expanded.

[0054] Obviously, the above examples of the present application are merely examples for clarifying the present application, and do not limit the embodiments of the present application. In addition to the above description, those skilled in the art may make other different types of changes or variations. It is not necessary or possible to cover all embodiments here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application are all included in the protection scope of the claims of the present application. [Explanation of symbols]

[0055] 110 Volume hologram diffraction grating 111 bonded lattice 112 Folded lattice 113 Coupling output lattice 120 boards 220 reticle 221 Reticle Grid 230 Translucent Carrier L0 Light beam emitted from the microprojector L111 coupled ray from coupled grating L112a Effective rays that finally enter the eye movement range after the expansion of the folded grating L112b Ineffective rays that ultimately fall outside the eye movement range after the extension of the folded grating L113a Effective rays that finally enter the eye movement range after coupling out of the coupling grating L113b Ineffective rays that ultimately enter outside the eye movement range after coupling of the coupling grating L210 Collimated Beam L2210 0th order light L2211 Primary light A: Effective area of ​​the eye movement range for a beam with an incident angle of α A1 is the effective area of ​​the eye movement range of the beam with an incident angle of α1 A2 Effective area of ​​the eye movement range for a beam with an incident angle of α2 A3: Effective area of ​​the eye movement range for a beam with an incident angle of α3 A4: Effective area of ​​the eye movement range for a beam with an incident angle of α4 u lattice unit r xoy Lattice vector surface component e bonded end

Claims

1. 1. A method for creating a lattice vector distribution target, comprising: sampling a plurality of sub-fields of view; recording the position of the effective area of ​​the eye movement range for each sub-field of view and calculating the grating vector at which the light beam for each sub-field of view matches the Bragg diffraction condition; Estimating a grating vector distribution of the volume hologram diffraction grating based on the positions of effective areas of the eye movement range of the plurality of sub-fields and grating vectors at which the light rays of the plurality of sub-fields match the Bragg diffraction condition; and determining a grating vector distribution of a volume hologram diffraction grating based on the estimated grating vector distribution and the grating vector at the combined end of the effective area of ​​the eye movement range of each sub-field of view exactly matching the Bragg diffraction condition; The method is characterized in that the sub-field of view is a set of light rays with the same incident angle that finally enter the entire field of view range, the effective area of ​​the eye movement range is the area covered by the volume hologram diffraction grating for the light rays that finally enter the eye movement range, the grating vector distribution has at least one change direction that is the same as the direction of the grating vector surface component, and the surface component of the grating vector at different positions is kept constant.

2. The lattice vector distribution is a one-dimensional distribution or a two-dimensional distribution. The method of claim 1.

3. The grating vector distribution of the volume hologram diffraction grating is estimated by sampling the positions of the effective areas of the eye movement ranges of multiple sub-fields and the grating vectors whose light rays match the Bragg diffraction condition, and the grating vectors at the connecting ends of the effective areas of the eye movement ranges of each sub-field accurately match the Bragg diffraction condition; the grating vector distribution has at least one change direction, and the at least one change direction is the same as the direction of the grating vector surface component, and the surface component of the grating vector at different positions is kept constant; the sub-field of view is a set of light rays that finally enter the entire field of view range at the same incident angle; and the effective area of ​​the eye movement range is an area that the light rays finally enter the eye movement range are covered by the volume hologram diffraction grating. Volume hologram diffraction grating.

4. The lattice vector distribution is created by the method according to any one of claims 1 to 2.

4. The volume hologram diffraction grating according to claim 3.

5. The volume hologram diffraction grating includes a coupling in area, a folding area, and / or a coupling out area.

5. The volume hologram diffraction grating according to claim 4.

6. discretizing the lattice vector distribution into a plurality of lattice units arranged along at least the direction of the lattice vector surface component, so that the lattice vectors at different positions of the same lattice unit are kept constant; selecting or preparing a reticle grating having a surface period equal to that of the volume hologram diffraction grating to be prepared, so that a surface component of a grating vector of the volume hologram diffraction grating to be prepared is parallel to a surface component of a grating vector of the reticle grating; calculating a collimated beam incident angle corresponding to each grating unit based on the grating vector of the grating unit and the grating vector of the reticle grating; and simultaneously switching the exposure position corresponding to a certain grating unit and the incident angle of the collimated beam, so that the zeroth order light and the first order light generated by the collimated beam through the reticle grating diffraction interfere with each other in the volume hologram diffraction photosensitive material, thereby sequentially exposing each grating unit. A method for producing the volume hologram diffraction grating according to claim 3.

7. The reticle grating is an amplitude grating, a phase grating, or a volume hologram diffraction grating. The method of claim 6.

8. The reticle grating is a volume hologram diffraction grating having a thickness of 1 to 5 μm. The method of claim 6.

9. the lattice vector distribution is discretized into a plurality of lattice units in a one-dimensional array or a two-dimensional array. The method of claim 6.

10. the collimated light generating mechanism includes a collimated light generating mechanism, the reticle grating, and a light-transmitting carrier, which are sequentially arranged, and the light-transmitting carrier is used to carry a volume hologram diffraction photosensitive material, and the reticle grating has the same surface period as the grating unit, and the reticle grating is parallel to the grating vector surface component of the grating unit; the collimated light generating mechanism is used to generate a collimated beam that can be incident on the reticle grating, and the collimated beam is diffracted by the reticle grating into zero-order light and first-order light, and the zero-order light and the first-order light pass through the light-transmitting carrier and are exposed to interference by the volume hologram diffraction photosensitive material; the apparatus further includes a first switching mechanism and a second switching mechanism that operate simultaneously, the first switching mechanism being used to switch the exposure position so that the zero-order light and the first-order light just cover only the grating unit to be exposed, and the second switching mechanism being used to switch the incident angle of the collimated beam so that the incident angle of the collimated beam corresponds to the grating unit to be exposed. An apparatus for fabricating a volume hologram diffraction grating using the method of claim 6.

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