Volume holographic grating, and grating vector distribution formulation method therefor, manufacturing method therefor, and manufacturing apparatus therefor

Abstract

Disclosed are a volume holographic grating, and a grating vector distribution formulation method therefor, a manufacturing method therefor, and a manufacturing apparatus therefor. A grating vector distribution is estimated by sampling the positions of eye box effective areas of a plurality of subfields of view and grating vectors at which light of the plurality of subfields of view satisfies a Bragg diffraction condition, and diffraction of ineffective light finally entering the area outside an eye box is not considered, so that most of effective light having different angles of incidence has high diffraction efficiency on a volume holographic grating, thereby ensuring the overall brightness uniformity of an output light beam, and expanding the range of a field of view. On this basis, the grating vector at which the light of each subfield of view accurately satisfies the Bragg diffraction condition is mounted at a coupling end of the eye box effective area of the subfield of view, so that the diffraction efficiency is maximized at the coupling end as far as possible, thereby being conducive to improving the brightness uniformity of the effective light, outputted from different positions of the volume holographic grating, of each subfield of view, and further improving the uniformity of the field of view and the eye box uniformity.

Description

Volume holographic grating and grating vector distribution planning, manufacturing method and manufacturing device thereof TECHNICAL FIELD

[0001] The present application belongs to the field of augmented reality waveguide display technology, and specifically relates to a volume holographic grating and a grating vector distribution planning, manufacturing method and manufacturing device thereof. BACKGROUND

[0002] Light waveguide display technology is a mainstream scheme for realizing high-transparency and lightweight augmented reality glasses, and has great potential in expanding the field of view and further improving the display effect. Light is transmitted in a transparent light waveguide in a total reflection manner, and a grating or other coupling elements are arranged in the light waveguide to control light input, output, turning, exit pupil expansion, energy distribution, etc., so as to guide the image light signal into the human eye. As a Bragg diffraction element, the volume holographic grating has most of the diffraction energy concentrated in the zeroth and first orders, and the proportion of the two can be adjusted by adjusting the grating parameters, so that the light waveguide with the volume holographic grating as the coupling element has special advantages in improving light efficiency and reducing light leakage.

[0003] The field of view and eye movement range of light waveguide display are important indicators for evaluating the performance of the light waveguide. In order to expand the field of view and eye movement range and improve the uniformity of the field of view and eye movement range, it is necessary to locally control and change the grating parameters in space. Compared with surface microstructure gratings, the structure of volume holographic gratings is relatively simple, and the variable parameters for control are thickness, refractive index modulation degree and grating vector.

[0004] In the augmented reality waveguide display, the eye movement range is the range in which the human eye can move to see the complete field of view image, and the human eye can only see part of the field of view image outside the eye movement range. Taking a two-dimensional pupil expanding waveguide as an example, the waveguide structure includes two layers of transparent glass substrates, and volume holographic gratings arranged between the two layers of substrates as in-coupling gratings, turning gratings and out-coupling gratings. For a specific input angle of light, the light is coupled into the waveguide through the in-coupling grating at the specific input angle from the micro-projection light machine, is transmitted by total reflection, is expanded in two directions by the turning grating, and is finally output from the waveguide at an angle corresponding to the input angle through the coupling of the out-coupling grating, wherein only a part of the light entering the eye movement range is finally received by the human eye to form an image, as shown in FIG. 1, the area covered by the part of the light entering the eye movement range on the volume holographic grating is defined as the eye movement range effective area of the specific input angle light on the volume holographic grating. Since the angles of light of different input angles entering the eye movement range from the waveguide through the out-coupling grating are different, the eye movement range effective areas of light of different input angles on the volume holographic grating are different. The eye movement range effective areas of light of multiple input angles on the volume holographic grating are shown in FIG. 2, and the eye movement range effective areas of light of different input angles on the volume holographic grating often overlap with each other, and the grating vectors of different positions on the volume holographic grating need to support the diffraction of light of many different input angles, so the grating vector distribution cannot be directly obtained. Single parameter regulation, such as only refractive index regulation or thickness regulation, is not conducive to high degree of freedom control of light transmission, so as to realize larger field of view range, field of view uniformity and eye movement range uniformity of the light waveguide display.

[0005] Moreover, the volume holographic grating with the parameters changing in space is difficult to prepare, especially the regulation of the grating vector, which must meet the requirement that the surface component of the grating vector remains constant according to the basic principle of the waveguide display, and the change range of the grating vector needs to support the light of all angles in the field of view range to match the Bragg diffraction condition as much as possible, so the requirements for the exposure device and the exposure process are very strict whether using double-beam exposure or mask exposure. TECHNICAL PROBLEM

[0006] The present scheme aims to overcome at least one of the defects in the prior art, and provides a method for formulating a grating vector distribution target, which can expand the angular bandwidth of the volume holographic grating, and is helpful to expand the field of view range of the light waveguide and improve the field of view uniformity and eye movement range uniformity. TECHNICAL SOLUTION

[0007] In order to solve the above technical problems, the following technical scheme is adopted:

[0008] In a first aspect, a method for determining a grating vector distribution is provided. The method comprises the following steps:

[0009] sampling a plurality of sub-fields of view;

[0010] recording positions of eye movement range effective areas of each sub-field of view, and calculating grating vectors of each sub-field of view that match a Bragg diffraction condition;

[0011] estimating a grating vector distribution of the volume holographic grating according to the positions of the eye movement range effective areas of the plurality of sub-fields of view and the grating vectors of the plurality of sub-fields of view that match the Bragg diffraction condition;

[0012] determining the grating vector distribution of the volume holographic grating according to the estimated grating vector distribution and a principle that grating vectors of coupling ends of the eye movement range effective areas of each sub-field of view exactly match the Bragg diffraction condition.

[0013] The present scheme estimates the grating vector distribution by sampling the positions of eye movement range effective areas of a plurality of sub-fields of view and grating vectors that match a Bragg diffraction condition, and does not consider diffraction of invalid light rays that finally enter outside the eye movement range, so that most of the effective light rays with different incident angles have high diffraction efficiency on the volume holographic grating, to ensure overall brightness uniformity of the output light beam and realize expansion of the field of view range. On this basis, the grating vector of each sub-field of view that exactly matches the Bragg diffraction condition is placed at the coupling end of the eye movement range effective area, so that the diffraction efficiency is maximized at the coupling end, which helps to improve the brightness uniformity of the effective light rays output from different positions of the volume holographic grating in each sub-field of view, thereby improving the field of view uniformity and eye movement range uniformity.

[0014] In a second aspect, a volume holographic grating is provided. The grating vector distribution of the volume holographic grating is estimated by sampling positions of eye movement range effective areas of a plurality of sub-fields of view and grating vectors that match a Bragg diffraction condition, and grating vectors of coupling ends of the eye movement range effective areas of each sub-field of view exactly match the Bragg diffraction condition. The grating vector distribution has at least one variation direction, and the at least one variation direction is the same as the direction of a surface component of the grating vector, and the surface components of grating vectors at different positions remain constant. The sub-field of view refers to a set of light rays with the same incident angle that finally enter the entire field of view range. The eye movement range effective area refers to an area covered by light rays that finally enter the eye movement range on the volume holographic grating.

[0015] The grating vector distribution of the scheme is obtained by sampling the positions of the eye movement range effective area of a plurality of sub-visual fields and estimating the grating vector matching the Bragg diffraction condition of the light rays, without considering the diffraction of invalid light rays finally entering the eye movement range, so that most of the effective light rays with different incident angles have high diffraction efficiency on the volume holographic grating, to ensure the overall brightness uniformity of the output light beam and realize the expansion of the visual field range. On this basis, the grating vector of each sub-visual field light ray accurately matching the Bragg diffraction condition is placed at the coupling end of the eye movement range effective area, so that the diffraction efficiency is maximized at the coupling end as much as possible, which helps to improve the brightness uniformity of the effective light rays output from different positions of the volume holographic grating in each sub-visual field, thereby improving the visual field uniformity and eye movement range uniformity.

[0016] The volume holographic grating can be a coupling-in grating, a coupling-out grating, a turning grating, or a combination of any two or three of the coupling-in grating, the turning grating, and the coupling-out grating, i.e., the volume holographic grating can include a coupling-in region, a turning region, and / or a coupling-out region. Preferably, the volume holographic grating includes a coupling-in region and a coupling-out region. More preferably, the volume holographic grating includes a coupling-in region, a turning region, and a coupling-out region.

[0017] In a third aspect, a method for manufacturing the volume holographic grating is provided. The method includes the following steps:

[0018] Discretize the grating vector distribution into a plurality of grating units arranged at least along the grating vector surface component direction, and the grating vectors of different positions of the same grating unit remain constant;

[0019] Select or manufacture a mask grating with a surface period equal to the surface period of the volume holographic grating to be manufactured, so that the grating vector surface component of the volume holographic grating to be manufactured is parallel to the grating vector surface component of the mask grating;

[0020] According to the grating vector of the grating unit and the grating vector of the mask grating, calculate the incident angle of the collimated light beam corresponding to each grating unit;

[0021] Simultaneously switch to the exposure position and the incident angle of the collimated light beam corresponding to a certain grating unit, so that the zero-order light and the first-order light generated by the diffraction of the collimated light beam through the mask grating interfere on the volume holographic photosensitive material, and each grating unit is exposed in turn.

[0022] The scheme discretizes the volume holographic grating to be manufactured and grating vector distribution thereof into a plurality of grating units with specific grating vectors, which can avoid using high-precision exposure devices matched with customized beam shaping elements or customized mask grating, and reduce manufacturing difficulty and cost. Meanwhile, the diffraction of the collimated light beam by the mask grating generates zero-order light and first-order light for sequentially exposing each grating unit, and adjusting the incident angle of the collimated light beam can simultaneously adjust the incident angles of the zero-order light and the first-order light, which is lower in complexity and controllable in cost compared with other methods.

[0023] In a fourth aspect, a device for manufacturing the volume holographic grating is provided. The device includes a collimated light generating mechanism, a mask grating and a light-transmitting carrier arranged in sequence, and a first switching mechanism and a second switching mechanism acting simultaneously. The light-transmitting carrier is used to carry the volume holographic photosensitive material, the mask grating has the same surface period as the grating unit, and the grating vector surface components of the mask grating and the grating unit are parallel. The collimated light generating mechanism is used to generate a collimated light beam capable of being incident on the mask grating. The collimated light beam is diffracted by the mask grating into zero-order light and first-order light, and the zero-order light and the first-order light transmit through the light-transmitting carrier to interfere and expose on the volume holographic photosensitive material. The first switching mechanism is used to switch the exposure position, so that the zero-order light and the first-order light just cover the grating unit to be exposed. The second switching mechanism is used to switch the incident angle of the collimated light beam, so that the incident angle of the collimated light beam corresponds to the grating unit to be exposed.

[0024] The scheme generates zero-order light and first-order light for sequentially exposing each grating unit through the diffraction of the collimated light beam by the mask grating, and adjusting the incident angle of the collimated light beam can simultaneously adjust the incident angles of the zero-order light and the first-order light, which is lower in complexity and controllable in cost compared with other methods.

[0025] In a fifth aspect, an augmented reality waveguide structure using the volume holographic grating is provided. The augmented reality waveguide structure includes two transparent substrates, and the volume holographic grating provided between the two substrates. The volume holographic grating can be a coupling-in grating, a coupling-out grating, a turning grating, or a combination of any two or three of the coupling-in grating, the turning grating and the coupling-out grating, i.e., the volume holographic grating can include a coupling-in region, a turning region and / or a coupling-out region. Preferably, the volume holographic grating includes a coupling-in region and a coupling-out region. More preferably, the volume holographic grating includes a coupling-in region, a turning region and a coupling-out region.

[0026] The scheme uses the volume holographic grating proposed in the present case as a coupling-in grating and / or a coupling-out grating, which expands the field of view, and improves the uniformity of the field of view and the eye movement range. Advantages

[0027] Compared with the prior art, the present scheme has the following beneficial effects: the present scheme estimates the grating vector distribution by sampling the positions of the eye movement range effective area of multiple sub-visual fields and matching the grating vector of the Bragg diffraction condition, without considering the diffraction of the invalid light rays finally entering the eye movement range outside, so that most of the effective light rays with different incident angles have high diffraction efficiency on the volume holographic grating, to ensure the overall brightness uniformity of the output light beam and realize the expansion of the visual field range. On this basis, the grating vector of each sub-visual field light ray accurately matched with the Bragg diffraction condition is placed at the coupling end of the eye movement range effective area, so that the diffraction efficiency is maximized at the coupling end as much as possible, which helps to improve the brightness uniformity of the effective light rays output from different positions of the volume holographic grating in each sub-visual field, thereby improving the visual field uniformity and eye movement range uniformity. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings are only used for illustrative description and cannot be understood as a limitation on the present scheme; in order to better illustrate the present scheme, some components in the drawings are omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable for those skilled in the art that some known structures and their descriptions in the drawings can be omitted.

[0029] Fig. 1 is a schematic diagram of the transmission of light rays with an incident angle of a in a two-dimensional pupil expanding waveguide structure.

[0030] Fig. 2 is a schematic diagram of the eye movement range effective area of light rays with different incident angles on a volume holographic grating.

[0031] Fig. 3 is a flow chart of a method for determining a grating vector distribution target.

[0032] Fig. 4 is a schematic diagram of the transmission of light rays in a volume holographic grating with spatially varying grating vectors.

[0033] Fig. 5 is a flow chart of a method for manufacturing a volume holographic grating.

[0034] Fig. 6 is a schematic diagram of a volume holographic grating composed of multiple grating units.

[0035] Fig. 7 is a schematic diagram of an apparatus for manufacturing a volume holographic grating.

[0036] Fig. 8 is a top view of the apparatus shown in Fig. 7.

[0037] Fig. 9 is a schematic diagram of a waveguide structure using the volume holographic grating shown in Fig. 4.

[0038] Fig. 10 is a curve of the diffraction efficiency of a mask grating varying with the angle.

[0039] Fig. 11 is a curve of the diffraction efficiency of a volume holographic grating with spatially varying grating vectors obtained by exposure using the mask grating shown in Fig. 10.

[0040] Explanation of reference signs: volume holographic grating 110, in-coupling grating 111, turning grating 112, out-coupling grating 113, substrate 120, mask 220, mask grating 221, light-transparent carrier 230, light ray L0 output by micro-projection light machine, light ray L111 coupled in by in-coupling grating, effective light ray L112a finally entering eyebox after expansion of turning grating, ineffective light ray L112b finally entering eyebox after expansion of turning grating, effective light ray L113a finally entering eyebox after coupling out of out-coupling grating, ineffective light ray L113b finally entering eyebox after coupling out of out-coupling grating, collimated light beam L210, zero-order light L2210, first-order light L2211, eyebox effective area A of light beam with incident angle α, eyebox effective area A1 of light beam with incident angle α1, eyebox effective area A1 of light beam with incident angle α2, eyebox effective area A3 of light beam with incident angle α3, eyebox effective area A4 of light beam with incident angle α4, grating unit u, grating vector surface component r xoy , coupling end e. Embodiments of the present application

[0041] In order for those skilled in the art to better understand the present application, the present application will be further described in detail below with specific examples.

[0042] FIG. 3 shows a method for formulating grating vector distribution targets. The method can be used to formulate grating vector distribution targets of volume holographic gratings (especially volume holographic gratings for augmented reality waveguide displays), so that the angular bandwidth of the obtained volume holographic gratings is expanded, which helps to expand the field of view range of the optical waveguide and improve the uniformity of the field of view and the eyebox. As shown in FIG. 3, the method can include the following steps:

[0043] S11: Sampling a plurality of sub-views.

[0044] In a display system, the field of view is the included angle between the edge of the display and the line connecting the display and the human eye, and the light rays with output angles in the entire field of view range can enter the human eye to form a complete field of view image. In other words, the complete field of view image is presented by light rays with different input angles entering the human eye together. For convenience of description, the present application defines the set of light rays with the same incident angle finally entering the entire field of view range as a sub-view. The incident angles of all light rays in the same sub-view are the same, and the angles after diffraction by the volume holographic grating are also the same. The number of sub-views sampled can be determined according to the size of the field of view designed for the display system. The sampling process can use random sampling methods such as simple random sampling, systematic sampling, grouped sampling, stratified sampling, or non-random sampling methods such as accidental sampling, judgment sampling, equal sampling, and snowball sampling.

[0045] S12: record the position of the eye movement range effective area of each sub field of view, and calculate the grating vector of each sub field of view that matches the light matching Bragg diffraction condition.

[0046] The light rays of the sub field of view diffracted by the volume holographic grating only part of which enters the eye movement range and is finally received by the human eye, which can be called effective light rays. For convenience of description, the area covered by the light rays finally entering the eye movement range on the volume holographic grating is defined as the eye movement range effective area, so the area covered by the light rays finally entering the eye movement range on the volume holographic grating in the sub field of view is the eye movement range effective area of the sub field of view, only the light rays in this area output can enter the eye movement range and contribute to the complete picture seen by the human eye, and the area other than this is invalid for the sub field of view. The grating vector is a vector with a magnitude of 2π / P perpendicular to the grating plane, where P is the interval of adjacent grating planes, i.e. the grating period. The grating vector matching the Bragg diffraction condition can be calculated according to the Bragg diffraction condition and the incident angle of the light rays.

[0047] S13: estimate the grating vector distribution of the volume holographic grating according to the positions of the eye movement range effective areas of the plurality of sub fields of view and the grating vectors of the plurality of sub fields of view matching the Bragg diffraction condition.

[0048] The grating vector distribution refers to the change of the grating vector in space, which describes how the grating vector changes with the change of position. Among them, the surface component of the grating vector refers to the component of the grating vector projected on the entire volume holographic grating plane, which must be constant for the entire volume holographic grating for light waveguide display, i.e. the surface component of the grating vector at different positions remains constant, which can ensure the one-to-one correspondence of the input angle and the output angle of the light waveguide for different light rays, i.e. the accuracy of the waveguide imaging.

[0049] The grating vector distribution has at least one change direction, which can be one-dimensional distribution or two-dimensional distribution. One-dimensional distribution has one change direction, and two-dimensional distribution has two perpendicular change directions. Generally, at least one change direction of the grating vector distribution should be along the direction of the surface component of the grating vector. If the grating vector distribution is one-dimensional distribution, its change direction is the same as the direction of the surface component of the grating vector; if the grating vector distribution is two-dimensional distribution, one of its two change directions is the same as the direction of the surface component of the grating vector.

[0050] The grating vector distribution of the volume holographic grating is estimated by the positions of the eyebox effective area of the multiple sub-visual fields and the grating vectors matching the Bragg diffraction condition of the light rays, without considering the diffraction of the invalid light rays finally entering the eyebox outside, so that most of the effective light rays with different incident angles have high diffraction efficiency on the volume holographic grating, to ensure the overall brightness uniformity of the output light beam and realize the expansion of the visual field range.

[0051] S14: The grating vector distribution of the volume holographic grating is determined according to the estimated grating vector distribution and the principle that the grating vector of the coupling end of the eyebox effective area of each sub-visual field precisely matches the Bragg diffraction condition.

[0052] On the basis of the estimated grating vector distribution, for each sub-visual field, the grating vector precisely matching the Bragg diffraction condition is placed at the coupling end of the eyebox effective area, so that the diffraction efficiency is maximized at the coupling end as much as possible, which helps to improve the brightness uniformity of the effective light rays output from different positions of the volume holographic grating for each sub-visual field, thereby improving the visual field uniformity and eyebox uniformity.

[0053] FIG. 4 shows a volume holographic grating with spatially varying grating vectors (which can be referred to as a first volume holographic grating). The volume holographic grating can be used in optical waveguide display technology, and specifically can be used as a coupling-in grating, a turning grating, or a coupling-out grating in an augmented reality waveguide structure.

[0054] As shown in FIG. 4, the grating vector distribution of the volume holographic grating is estimated by sampling the positions of the eyebox effective area of the multiple sub-visual fields and the grating vectors matching the Bragg diffraction condition of the light rays, and the grating vector of the coupling end of the eyebox effective area of each sub-visual field precisely matches the Bragg diffraction condition. The grating vector distribution has at least one variation direction, and the at least one variation direction is the same as the direction of the surface component of the grating vector, and the surface components of the grating vectors at different positions remain constant. The sub-visual field refers to a set of light rays with the same incident angle finally entering the entire visual field range. The eyebox effective area refers to the area covered by the light rays finally entering the eyebox on the volume holographic grating.

[0055] The grating vector distribution of the volume holographic grating is estimated by sampling the positions of the eye movement range effective area of a plurality of sub-visual fields and matching the grating vectors of the positions with the Bragg diffraction condition, without considering the diffraction of invalid light rays finally entering the eye movement range, so that most of the effective light rays with different incident angles have high diffraction efficiency on the volume holographic grating, to ensure the overall brightness uniformity of the output light beam and realize the expansion of the visual field range. On this basis, the grating vector of each sub-visual field light ray accurately matched with the Bragg diffraction condition is placed at the coupling end of the eye movement range effective area, so that the diffraction efficiency is maximized at the coupling end, which helps to improve the brightness uniformity of the effective light rays output from different positions of the volume holographic grating in each sub-visual field, thereby improving the visual field uniformity and eye movement range uniformity. The grating vector of the volume holographic grating changes in space, but the surface component of the grating vector at different positions remains constant, ensuring one-to-one correspondence of the input angle and the output angle of different light rays, i.e., ensuring the accuracy of imaging.

[0056] According to the number of grating vector change directions, the grating vector distribution can be one-dimensional or two-dimensional. The one-dimensional distribution has one change direction, and the two-dimensional distribution has two perpendicular change directions. If the grating vector distribution is one-dimensional, the change direction is the same as the direction of the grating vector surface component; if the grating vector distribution is two-dimensional, one of the two change directions is the same as the direction of the grating vector surface component.

[0057] The grating vector distribution of the volume holographic grating described above can be formulated by the method shown in FIG. 3.

[0058] FIG. 5 illustrates a method for manufacturing a volume holographic grating, which can be used to manufacture the volume holographic grating shown in FIG. 4. As shown in FIG. 5, the method can include the following steps:

[0059] S21. Discretize the grating vector distribution into a plurality of grating units arranged at least along the direction of the grating vector surface component, and the grating vectors of different positions of the same grating unit remain constant.

[0060] Fabrication of volume holographic gratings with continuously varying grating vector distribution requires high-precision exposure devices with customized beam shaping elements or customized mask gratings, which is difficult and costly. Discretization of the grating vector distribution into multiple grating units, i.e. discretization of the volume holographic grating to be fabricated into multiple grating units, can reduce the fabrication difficulty to some extent, as the grating vector at different positions of the same grating unit remains constant. The grating vector distribution can be discretized into one-dimensional grating units (as shown in FIG. 6) or two-dimensional grating units. In general, at least one of the arrangement directions should be along the surface component direction of the grating vector. For optical waveguide display, one-dimensional grating units are generally sufficient to meet the field of view requirement. The grating units need to be selected with appropriate length or width, and a larger grating unit length or width is selected by evaluating the overall grating angular bandwidth formed by the grating vector distribution, so as to facilitate fabrication. The lengths or widths of different grating units can be the same or different. A small amount of overlap is allowed at the boundary between adjacent grating units.

[0061] S22. Select or fabricate a mask grating with a surface period equal to that of the volume holographic grating to be fabricated, so that the surface component of the grating vector of the volume holographic grating to be fabricated is parallel to the surface component of the grating vector of the mask grating.

[0062] According to the diffraction principle, the collimated beam is diffracted when incident on the mask grating, and the zero-order light and first-order light of the diffraction overlap and interfere on the volume holographic photosensitive material to be exposed, generating a volume holographic grating with a grating vector surface component amplitude equal to that of the mask grating. Therefore, the amplitudes of the grating vector surface components of the mask grating and the volume holographic grating to be fabricated should be set to be equal, i.e. the surface periods of the two should be equal.

[0063] The mask grating can be an amplitude grating or a phase grating fabricated by photolithography, nanoimprint or other micro-nano processing technology, or a volume holographic grating previously fabricated by double-beam exposure. Using a volume holographic grating fabricated by double-beam exposure as a mask grating can greatly reduce the production cost of the mask, but due to the Bragg diffraction characteristics of the volume holographic grating, its angular bandwidth is small, and the diffraction efficiency is very low at incident angles far from the Bragg diffraction condition, which is not conducive to the fabrication of optical waveguide volume holographic gratings with a large grating vector spatial variation range. Using a volume holographic grating with a relatively small thickness as a mask grating can expand the angular bandwidth, thereby expanding the grating vector spatial variation range of the optical waveguide. Specifically, the thickness of the volume holographic grating used as the mask grating is preferably 1-5 μm.

[0064] The pre-holographic photosensitive material should be placed in the correct orientation on the exposure device before exposure, so that the grating vector surface component of the volume holographic grating to be fabricated is parallel to the grating vector surface component of the mask grating, as shown in FIG. 8.

[0065] S23. Calculate the incident angle of the collimated light beam corresponding to each grating unit according to the grating vector of the grating unit and the grating vector of the mask grating.

[0066] When the incident angle of the incident collimated light beam is changed, the amplitude of the surface component of the grating vector of the generated volume holographic grating remains unchanged, but the normal component of the grating vector changes, and the synthesized grating vector also changes. This method can be used to manufacture a volume holographic grating with a spatially-varying grating vector. To facilitate subsequent rapid exposure, the incident angle of the collimated light beam corresponding to each grating unit can be calculated in advance according to the grating vector of the grating unit and the grating vector of the mask grating.

[0067] S24. Simultaneously switch to the exposure position corresponding to a grating unit and the incident angle of the collimated light beam, so that the zero-order light and the first-order light generated by the diffraction of the collimated light beam through the mask grating interfere on the volume holographic photosensitive material, and each grating unit is exposed in turn.

[0068] The area corresponding to each grating unit with a specific grating vector can be exposed in turn. When each grating unit is switched, the incident angle of the collimated light beam needs to be adjusted to the pre-calculated angle according to the corresponding grating vector, so as to expose and generate the corresponding grating vector at the corresponding grating unit.

[0069] Figs. 7-8 illustrate a device for manufacturing a volume holographic grating, which can be used to manufacture the volume holographic grating shown in Fig. 4 by the method shown in Fig. 5. As shown in Figs. 7-8, the device includes a collimated light generating mechanism (not shown in the drawings), a mask grating, and a light-transmitting carrier arranged in sequence, and further includes a first switching mechanism (not shown in the drawings) and a second switching mechanism (not shown in the drawings). The light-transmitting carrier is used to carry the volume holographic photosensitive material, the surface period of the mask grating is the same as that of the volume holographic grating to be manufactured, and the surface component of the grating vector of the mask grating is parallel to the surface component of the grating vector of the volume holographic grating to be manufactured. The collimated light generating mechanism is used to generate a collimated light beam that can be incident on the mask grating. The collimated light beam is diffracted by the mask grating into zero-order light and first-order light, and the zero-order light and the first-order light transmit through the light-transmitting carrier to interfere and expose on the volume holographic photosensitive material. It should be noted that if the manufactured volume holographic grating is used for an augmented reality waveguide structure, the light-transmitting carrier can directly carry the augmented reality waveguide structure to be manufactured, i.e., carry two layers of transparent substrates and the volume holographic photosensitive material arranged between the two layers of substrates. After interference exposure, the volume holographic photosensitive material forms a volume holographic grating arranged between the two layers of substrates.

[0070] The first switching mechanism is used to switch the exposure position so that the zero-order light and the first-order light just cover the grating unit to be exposed; the second switching mechanism is used to switch the incident angle of the collimated light beam so that the incident angle of the collimated light beam corresponds to the grating unit to be exposed. Since the incident light beam angle for exposing each grating unit is one-to-one corresponding to the grating vector, the incident angle of the collimated light beam is switched at the same time when the exposure position is switched, that is, the first switching mechanism and the second switching mechanism must act together. If the first switching mechanism and the second switching mechanism are both automatic mechanisms, they can act at the same time, which helps to quickly expose multiple grating units in turn.

[0071] The mask grating can be an amplitude grating or a phase grating made by photolithography, nanoimprint or other micro-nano processing technology, or can be a volume holographic grating (which can be referred to as a second volume holographic grating) made in advance by double-beam exposure. Using a volume holographic grating made by double-beam exposure as a mask grating can greatly reduce the production cost of the mask, but due to the Bragg diffraction characteristics of the volume holographic grating, its angle bandwidth is small, and the diffraction efficiency is very low at the incident angle far from the Bragg diffraction condition, which is not conducive to the production of a light waveguide volume holographic grating with a large grating vector spatial variation range. Using a volume holographic grating with a relatively small thickness as a mask grating can expand the angle bandwidth, thereby expanding the grating vector spatial variation range of the light waveguide. Specifically, the thickness of the volume holographic grating used as the mask grating is preferably 1-5 μm.

[0072] Figure 9 illustrates an augmented reality waveguide structure. The waveguide structure includes two layers of transparent substrates, and a coupling-in grating, a turning grating and a coupling-out grating arranged between the two layers of substrates. The coupling-in grating, the turning grating and the coupling-out grating all adopt the above-mentioned volume holographic grating with spatially varying grating vectors. It can be understood that the waveguide structure can also be a one-dimensional pupil expanding waveguide that does not include a turning grating, and the coupling-in grating, the turning grating and the coupling-out grating can also select one or two of them to adopt the above-mentioned volume holographic grating with spatially varying grating vectors.

[0073] The above-mentioned scheme can expand the angle bandwidth of the volume holographic grating, and in fact provides different effective Bragg matching angles at different positions of the volume holographic grating, thereby helping to expand the field of view range, improve the uniformity of the field of view and the eye movement range. Moreover, the manufacturing method and device provided by the above-mentioned scheme have low complexity and controllable cost compared with other ways. For example, Figure 10 shows a possible curve of the diffraction efficiency of the mask grating varying with the angle, and the collimated light beams with incident angles of about -6 degrees, 2.5 degrees and 10 degrees are selected to expose three different grating units in turn, to obtain a coupling-out grating composed of grating units with three different grating vectors, and the curve of the diffraction efficiency of the coupling-out grating varying with the angle is shown in Figure 11, and the combined angle bandwidth is expanded.

[0074] Obviously, the above embodiments of the present application are merely exemplary but not intended to limit the embodiments of the present application. Based on the above description, any other variations or modifications of the embodiments can be made by those skilled in the art without departing from the spirit and principles of the present application. It is to be understood that the present application is not limited to the above-described embodiments but covers any modifications or variations thereof within the spirit and principles of the present application.

Claims

1. A method for formulating a grating vector distribution target, characterized in that: The steps include: Sampling multiple sub-fields of view; Record the position of the effective area of ​​the eye movement range of each sub-field of view, and calculate the grating vector of the light matching the Bragg diffraction condition of each sub-field of view; estimating the grating vector distribution of the volume holographic grating according to the positions of the effective areas of the eye movement range of the multiple sub-fields of view and the grating vectors of the multiple sub-fields of view that match the Bragg diffraction conditions; The grating vector distribution of the volume holographic grating is determined based on the estimated grating vector distribution and the principle that the grating vector at the coupling end of the effective area of ​​the eye movement range of each sub-field of view accurately matches the Bragg diffraction condition; The sub-field of view refers to a collection of light rays with the same incident angle that eventually enter the entire field of view; the effective area of ​​the eye movement range refers to the area covered by the light rays that eventually enter the eye movement range on the volume holographic grating; the grating vector distribution has at least one changing direction, and at least one changing direction is the same as the direction of the surface component of the grating vector, and the surface components of the grating vectors at different positions remain constant.

2. The method according to claim 1, characterized in that The grating vector distribution is a one-dimensional distribution or a two-dimensional distribution.

3. A volume holographic grating, characterized in that: The grating vector distribution of the volume holographic grating is estimated by sampling the positions of the effective areas of the eye movement range of multiple sub-fields of view and the grating vectors of their rays matching the Bragg diffraction conditions, and the grating vectors of the coupling ends of the effective areas of the eye movement range of each sub-field of view accurately match the Bragg diffraction conditions; In which, 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 components of the grating vectors at different positions remain constant; the sub-field of view refers to the set of light rays with the same incident angle that eventually enter the entire field of view range; the effective area of ​​the eye movement range refers to the area covered by the light rays that eventually enter the eye movement range on the volume holographic grating.

4. The volume holographic grating according to claim 3, characterized in that The grating vector distribution is formulated using the method described in any one of claims 1 to 2.

5. The volume holographic grating according to claim 4, characterized in that The volume holographic grating includes an incoupling region, a turning region and / or an outcoupling region.

6. A method for manufacturing a volume holographic grating according to any one of claims 3 to 5, characterized in that: The steps include: Discretizing the grating vector distribution into a plurality of grating units arranged at least along the direction of the grating vector surface component thereof, wherein the grating vectors at different positions of the same grating unit remain constant; Select or produce a mask grating with a surface period equal to the surface period of the volume holographic grating to be produced, so that the surface component of the grating vector of the volume holographic grating to be produced is parallel to the surface component of the grating vector of the mask grating; Calculating the incident angle of the collimated light beam corresponding to each grating unit according to the grating vector of the grating unit and the grating vector of the mask grating; At the same time, the exposure position and incident angle of the collimated light beam corresponding to a certain grating unit are switched to make the zero-order light and the first-order light generated by the diffraction of the collimated light beam through the mask grating interfere with each other on the volume holographic photosensitive material, and expose each grating unit in turn.

7. The method according to claim 6, characterized in that The mask grating is an amplitude grating, a phase grating or a volume holographic grating.

8. The method according to claim 6, characterized in that The mask grating is a volume holographic grating with a thickness of 1 to 5 μm.

9. The method according to claim 6, characterized in that The grating vector distribution is discretized into a plurality of grating units arranged in one dimension or two dimensions.

10. A device for producing a volume holographic grating using the method according to any one of claims 6 to 9, characterized in that: The device comprises a collimated light generating mechanism, a mask grating, and a light-transmitting carrier arranged in sequence, wherein the light-transmitting carrier is used to carry a volume holographic photosensitive material, the mask grating has the same surface period as the grating unit, and the grating vector surface components of the mask grating and the grating unit are parallel, the collimated light generating mechanism is used to generate a collimated light beam that can be incident on the mask grating, the collimated light beam is diffracted by the mask 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 to generate interference exposure on the volume holographic photosensitive material; The device also includes a first switching mechanism and a second switching mechanism that operate simultaneously. The first switching mechanism is 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. The second switching mechanism is used to switch the incident angle of the collimated light beam so that the incident angle of the collimated light beam corresponds to the grating unit to be exposed.

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