Device and method for preparing volume holographic grating

Abstract

The embodiment of the invention discloses a preparation device and method of a volume holographic grating. The device comprises a coherent light source used for generating coherent light with the coherent length larger than the optical path difference of the grating recording device; the beam expanding and splitting device is used for expanding and splitting the coherent light into object light and reference light with the same polarization direction; the control unit is used for decomposing the volume holographic grating into a plurality of volume holographic sub-gratings related to the grating position; the light modulator unit is used for modulating complex amplitude distribution of an object light wave surface to obtain object light with certain complex amplitude distribution, and the object light with certain complex amplitude distribution and the reference light interfere to form stripes with light intensity distribution corresponding to the volume holographic sub-grating; a light transmission unit for transmitting the object light having a certain complex amplitude distribution and the reference light to a recording medium; and the spatial position adjusting unit is used for bearing the recording medium and adjusting the position of the recording medium according to the signal from the control unit, so that the recording medium records stripes corresponding to the position according to the position to obtain the volume holographic grating.

Description

Technical Field

[0001] The present invention relates to the field of optics. More specifically, it relates to a device and method for preparing a volume holographic grating. Background Art

[0002] Currently, in the preparation process of traditional volume holographic gratings, due to the fixation of optical elements, only simple components such as mirrors and lenses can be used, resulting in limitations on the refractive index distribution form of volume holographic gratings. It is difficult to achieve volume holographic gratings with arbitrary grating vector directions and diffraction efficiency distributions, and cannot meet the differentiated requirements of holographic waveguide devices in augmented reality display technology for the diffraction performance of volume holographic gratings.

[0003] Therefore, there is an urgent need to propose a device and method for preparing a volume holographic grating to solve problems such as the difficulty in arbitrarily controlling the grating vector and diffraction efficiency of volume holographic gratings during the preparation process of traditional volume holographic gratings, the relatively low equivalent spatial frequency and phase modulation resolution of optical modulators, the relatively low diffraction angle and fringe fineness of volume holographic gratings, the difficulty in realizing the splicing preparation of large-size gratings, and the relatively low functions and performance of volume holographic gratings. Summary of the Invention

[0004] The purpose of the present invention is to provide a device and method for preparing a volume holographic grating to solve at least one of the problems existing in the prior art.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The first aspect of the present invention provides a device for preparing a volume holographic grating, which includes

[0007] A coherent light source for generating coherent light with a coherence length greater than the optical path difference of the grating recording device;

[0008] An expanding and beam-splitting device for expanding and splitting the coherent light into object light and reference light with the same polarization direction;

[0009] A control unit for decomposing the volume holographic grating into multiple volume holographic sub-gratings related to the grating position;

[0010] An optical modulator unit for modulating the complex amplitude distribution of the object light wavefront to obtain object light with a certain complex amplitude distribution, and the object light with a certain complex amplitude distribution and the reference light can interfere to form fringes with an intensity distribution corresponding to the volume holographic sub-grating;

[0011] An optical transmission unit for transmitting the object light with a certain complex amplitude distribution and the reference light to the recording medium;

[0012] A spatial position adjustment unit for carrying the recording medium and adjusting the position of the recording medium according to a signal from a control unit, so that the recording medium records fringes corresponding to the position at the position to obtain a volume holographic grating.

[0013] Optionally, the positions of the volume holographic sub-gratings may overlap or not overlap.

[0014] Optionally, the beam expander and beam splitter includes a telescope group and a polarization beam splitter prism;

[0015] The optical modulator unit includes a first optical modulator and an optical modulator assembly;

[0016] The optical transmission unit includes a first beam splitter prism, a first lens, a second lens and a first mirror, and the focal length of the first lens is not equal to the focal length of the second lens; wherein

[0017] The light incident side of the telescope group is arranged on the light output side of the coherent light source;

[0018] The light incident side of the polarization beam splitter prism is arranged on the light output side of the telescope group;

[0019] The first mirror is arranged on the first light output side of the polarization beam splitter prism;

[0020] The light incident side of the optical modulator assembly is arranged on the second light output side of the polarization beam splitter prism;

[0021] The light incident side of the first beam splitter prism is arranged on the light output side of the optical modulator assembly;

[0022] The light incident side of the first optical modulator is arranged on the first light output side of the first beam splitter prism;

[0023] The light incident side of the first lens is arranged on the second light output side of the first beam splitter prism;

[0024] The light incident side of the second lens is arranged on the light output side of the first lens;

[0025] The second lens emits the object light with a specific complex amplitude distribution to the first side of the recording medium through its light output side;

[0026] The first mirror is used to reflect the reference light to the second side of the recording medium.

[0027] Optionally, the optical modulator assembly includes a second mirror, a third mirror and a second optical modulator; wherein

[0028] The second mirror is arranged on the second light output side of the polarization beam splitter prism;

[0029] The incident light side of the second optical modulator is arranged in the reflection direction of the second mirror;

[0030] The third mirror is arranged on the emergent light side of the second optical modulator;

[0031] The incident light side of the first beam splitting prism is arranged in the reflection direction of the third mirror.

[0032] Optionally, the device further includes a diaphragm; wherein

[0033] The incident light side of the diaphragm is arranged on the first emergent light side of the polarization beam splitting prism;

[0034] The first reflecting prism is arranged on the emergent light side of the diaphragm.

[0035] Optionally, the second optical modulator is configured to perform amplitude modulation on the object light to obtain a first object light with a light field distribution having the same light intensity as the target object light field.

[0036] Optionally, the first optical modulator is configured to perform phase modulation on the first object light to obtain an object light having a certain complex amplitude distribution with a light field distribution the same as the target light field distribution.

[0037] Optionally, the first optical modulator is further configured to generate a first adjustment amount with a first phase resolution for a first duration and a second adjustment amount with a second phase resolution for a second duration, and perform weighted summation on the first adjustment amount and the second adjustment amount to obtain a target value equivalent to the phase modulation.

[0038] Optionally, the optical transmission unit is further configured to respectively transmit the object light with a specific complex amplitude distribution and the reference light to the same side or different sides of the recording medium.

[0039] A second aspect of the present invention provides a method for preparing a volume holographic grating, the method including

[0040] Decomposing the volume holographic grating to be formed into a plurality of volume holographic sub-gratings related to the grating positions;

[0041] Generating coherent light with a coherence length greater than the optical path difference of the grating recording device by using a coherent light source;

[0042] Expanding and splitting the coherent light into object light and reference light with the same polarization direction;

[0043] Using an optical modulator unit to modulate the complex amplitude distribution of the object light wavefront to obtain an object light with a certain complex amplitude distribution, and the object light with a certain complex amplitude distribution and the reference light interfere to form fringes with a light intensity distribution corresponding to one of the plurality of volume holographic sub-gratings;

[0044] Using an optical transmission unit, the object light with a certain complex amplitude distribution and the reference light are transmitted to a recording medium;

[0045] Using a spatial position adjustment unit, the recording medium is adjusted to a position corresponding to one of the plurality of volume holographic sub-gratings, and the fringes are recorded;

[0046] Repeat the above operations to form each volume holographic sub-grating, and thereby obtain the volume holographic grating.

[0047] The beneficial effects of the present invention are as follows:

[0048] The present invention provides a preparation device for a volume holographic grating, which realizes the control of the grating vector and diffraction efficiency of the volume holographic grating, improves the equivalent spatial frequency and phase modulation resolution of the optical modulator, improves the diffraction angle and fringe fineness of the volume holographic grating, and realizes the splicing preparation of a large-size grating, thereby enhancing the functions and performance of the volume holographic grating. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0050] Figure 1 The structural schematic diagram of a preparation device for a volume holographic grating in the prior art is shown.

[0051] Figure 2 The structural schematic diagram of a preparation device for a volume holographic grating provided by an embodiment of the present invention is shown.

[0052] Figure 3 Another structural schematic diagram of a preparation device for a volume holographic grating provided by an embodiment of the present invention is shown.

[0053] Figure 4 The schematic diagram of time-division multiplexing of a preparation device for a volume holographic grating provided by an embodiment of the present invention is shown.

[0054] Figure 5 Another schematic diagram of time-division multiplexing of a preparation device for a volume holographic grating provided by an embodiment of the present invention is shown.

[0055] Figure 6 Another structural schematic diagram of a preparation device for a volume holographic grating provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] To more clearly illustrate the present invention, the following further describes the present invention with reference to the embodiments and the drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the following specific descriptions are illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0057] Volume holographic gratings utilize the periodic distribution of refractive index in a medium to achieve diffraction of incident light. Due to their high diffraction efficiency and simple preparation, they have been widely used. For example, in the field of augmented reality, holographic optical waveguides are a technical solution with important development prospects. Holographic optical waveguides utilize volume holographic gratings to achieve the coupling in and out of light in the optical waveguide. With the development of augmented reality (AR) display technology, holographic optical waveguides based on volume holographic gratings have been continuously developed, and their performance indicators have been continuously improved, gradually meeting the requirements of the field of view angle and eye movement range for AR displays, and having broad application prospects.

[0058] Currently, as Figure 1 shown, volume holographic gratings are generally prepared by the method of interference exposure. The specific process is to use two plane laser interferences to form bright and dark periodic fringes, place the photosensitive material in the light field with a periodic distribution of light intensity for exposure, so as to obtain a refractive index change consistent with the light intensity distribution and form a volume holographic grating. And by adding optical elements such as lenses in the interference optical path, the wavefront distribution of the interference light can also be changed, and a volume holographic grating related to the wavefront distribution of the interference light can be obtained by exposure.

[0059] However, in the preparation process of traditional volume holographic gratings, due to the fixation of optical elements, only simple components such as mirrors and lenses can be used, which results in the limitation of the refractive index distribution form of volume holographic gratings, making it difficult to achieve volume holographic gratings with arbitrary grating vector directions and diffraction efficiency distributions, and unable to meet the differentiated requirements of the diffraction performance of volume holographic gratings for holographic optical waveguide devices in augmented reality display technology. Therefore, it is urgent to propose a preparation device and method for volume holographic gratings to solve problems such as the difficulty in arbitrarily controlling the grating vector and diffraction efficiency of volume holographic gratings in the traditional preparation process, the low equivalent spatial frequency and phase modulation resolution of optical modulators, the low diffraction angle and fringe fineness of volume holographic gratings, the difficulty in realizing the splicing preparation of large-size gratings, and the low function and performance of volume holographic gratings.

[0060] In view of this, an embodiment of the present invention provides a device for preparing a volume holographic grating. The device includes a coherent light source for generating coherent light with a coherence length greater than the optical path difference of the grating recording device; an expanding and splitting device for expanding and splitting the coherent light into object light and reference light with the same polarization direction; a control unit for decomposing the volume holographic grating into a plurality of volume holographic sub-gratings related to the grating position; a light modulator unit for modulating the complex amplitude distribution of the object light wavefront to obtain object light with a certain complex amplitude distribution, and the object light with the certain complex amplitude distribution can interfere with the reference light to form fringes with a light intensity distribution corresponding to the volume holographic sub-grating; a light transmission unit for transmitting the object light with the certain complex amplitude distribution and the reference light to a recording medium; and a spatial position adjustment unit for carrying the recording medium and adjusting the position of the recording medium according to a signal from the control unit, so that the recording medium records the fringes corresponding to the position according to the position to obtain a volume holographic grating.

[0061] This embodiment realizes the control of the grating vector and diffraction efficiency of the volume holographic grating, improves the equivalent spatial frequency and phase modulation resolution of the light modulator, improves the diffraction angle and fringe fineness of the volume holographic grating, and realizes the splicing preparation of large-size gratings, thereby enhancing the functions and performance of the volume holographic grating.

[0062] In a specific example, as Figure 2 shown, the device includes a coherent light source, an expanding and splitting device, a light modulator unit, a light transmission unit, and a recording medium. Specifically, the coherent light beam emitted by the coherent light source in the device for preparing the volume holographic grating forms two coherent light beams after passing through the expanding and splitting device. The reference light is reflected by a mirror group and then irradiated on the recording medium. The object light first irradiates on the light modulator assembly, and after being adjusted by the light modulator assembly, it forms the complex amplitude distribution of the light field required for the interference pattern. Subsequently, it irradiates on the photosensitive material through the light transmitter. The modulated object light and the reference light interfere to form a specific light intensity distribution and are recorded by the photosensitive material to form a volume holographic grating.

[0063] In a specific example, the coherent light source is generally a laser light source for generating coherent light with a coherence length greater than the optical path difference of the grating recording device. The coherent light source can be monochromatic light or a combination of multi-color coherent light.

[0064] In a specific example, the expanding and splitting device is generally a combination of a telescope group and a polarization beam splitter prism for expanding and splitting the coherent light emitted by the coherent light source into two beams of light with the same polarization direction, one beam is called object light, and the other beam is called reference light.

[0065] Furthermore, the beam splitter can be provided with a light intensity adjustment device, generally a half-wave plate, for adjusting the light intensities of the two beams of light after splitting.

[0066] In a specific example, the optical modulator unit is used to modulate the complex amplitude distribution of the object light wavefront, so that the object light changes from a plane light wave to a light wave with a specific complex amplitude distribution. The modulated object light interferes with the reference light to form fringes with a specific light intensity distribution.

[0067] Furthermore, the optical modulator can be a Spatial Light Modulator (SLM), a Digital Micromirror Device (DMD), a Liquid Crystal on Silicon (LCoS), or other optical modulators, or a combination of several of the above devices, or a combination of the above devices and other optical elements, such as concave lenses, convex lenses, and binary optical elements.

[0068] In a specific example, the optical transmission component is used to transmit the optical field modulated by the optical modulator to the photosensitive material.

[0069] Furthermore, the photosensitive material can be silver salt, dichromate gelatin, photopolymer, or other photosensitive materials, and is used to record the interference fringes with the above specific distribution to form a volume holographic grating. The photosensitive material can be planar, spherical, or have other shaped surfaces.

[0070] In a specific example, as Figure 3 and 6 shown, the apparatus for preparing the volume holographic grating further includes an imaging device and a spatial position adjustment structure, which are used to achieve spatial division multiplexing optical modulation and thereby improve the distribution fineness of the grating fringes.

[0071] Specifically, the imaging device is arranged between the optical modulator and the photosensitive material, and is used to scale and image the optical field modulated by the optical modulator at the photosensitive material, so as to reduce the equivalent pixel size of the optical modulator at the photosensitive material and further improve the adjustment fineness of the interference exposure pattern. The imaging device can be a 4F system with different focal lengths or other lens devices.

[0072] In a specific example, a 4F system is placed behind the beam splitter prism 1, where the focal length ratio of lens 1 to lens 2 is 4:1, so as to reduce the cross-section of the object light to 1 / 4 of the original cross-section. The optical modulator and the recording medium are respectively located at the focal points of the lenses on both sides of the 4F system. The size of the optical field modulated by the optical modulator is reduced to 3.89 mm × 2.305 mm, and the equivalent pixel size is reduced to 0.935 μm.

[0073] Specifically, the spatial position adjustment mechanism is used to adjust the position of the photosensitive material. After the recording process of a volume holographic grating at one location on the photosensitive material is completed, the unexposed part is moved into the interference light field, so as to record multiple gratings and achieve the splicing of the gratings. In addition, during the grating splicing process, the gratings can be separated by a certain distance, so as to weaken the crosstalk at the edges of adjacent gratings, or the gratings can overlap or coincide with each other, so as to form a composite grating in the recording medium.

[0074] In a specific example, the required grating is decomposed into M×N sub-gratings of 3.89 mm×2.305 mm, and their positions on the recording medium are determined. According to this position, the distribution of the interference exposure light field is calculated. The recording medium is placed on the spatial position adjustment structure, and the first interference pattern is exposed at the target position. After completion, the recording medium is moved so that the interference light field is located at the position of the second sub-grating and exposed. This process is repeated until the entire grating exposure recording process is completed. Thus, a combined grating larger than the size of the interference light field is formed.

[0075] In this embodiment, spatial division multiplexing is realized through a light modulator, which reduces the equivalent pixel size of the light modulator, increases the spatial frequency of the interference light field, thereby improving the preparation accuracy of the volume holographic grating, expanding the diffraction angle of the prepared grating, increasing the resolution of the grating, and at the same time enabling the preparation of large-size gratings.

[0076] In a possible implementation manner, the positions of the volume holographic sub-gratings may overlap or not overlap.

[0077] This embodiment can effectively realize the splicing of gratings. In addition, during the grating splicing process, the gratings can be separated by a certain distance, so as to weaken the crosstalk at the edges of adjacent gratings, or the gratings can overlap or coincide with each other, so as to form a composite grating in the recording medium, effectively improving the diffraction angle and fringe fineness of the volume holographic grating and realizing the splicing preparation of large-size gratings, thereby enhancing the functions and performance of the volume holographic grating.

[0078] In a possible implementation, the beam expander and beam splitter includes a telescope group and a polarization beam splitter prism; the optical modulator unit includes a first optical modulator and an optical modulator assembly; the optical transmission unit includes a first beam splitter prism, a first lens, a second lens and a first mirror, and the focal length of the first lens is not equal to the focal length of the second lens; wherein the incident light side of the telescope group is arranged on the outgoing light side of the coherent light source; the incident light side of the polarization beam splitter prism is arranged on the outgoing light side of the telescope group; the first mirror is arranged on the first outgoing light side of the polarization beam splitter prism; the incident light side of the optical modulator assembly is arranged on the second outgoing light side of the polarization beam splitter prism; the incident light side of the first beam splitter prism is arranged on the outgoing light side of the optical modulator assembly; the incident light side of the first optical modulator is arranged on the first outgoing light side of the first beam splitter prism; the incident light side of the first lens is arranged on the second outgoing light side of the first beam splitter prism; the incident light side of the second lens is arranged on the outgoing light side of the first lens; the second lens emits the object light with a specific complex amplitude distribution to the first side of the recording medium through its outgoing light side; the first mirror is used to reflect the reference light to the second side of the recording medium.

[0079] This embodiment realizes the control of the grating vector and diffraction efficiency of the volume holographic grating, improves the equivalent spatial frequency and phase modulation resolution of the optical modulator, improves the diffraction angle and fringe fineness of the volume holographic grating, thereby enhancing the function and performance of the volume holographic grating.

[0080] In a specific example, a reflective volume holographic grating preparation device using a 532 nm laser as a coherent light source is taken as an example to illustrate this example.

[0081] Specifically, a 532 nm solid-state laser is used as the light source, and its emitted beam forms a collimated coherent beam with a diameter of about 20 mm after passing through the beam expander assembly. Through the polarization beam splitter prism, it is decomposed into two coherent light beams, namely object light and reference light.

[0082] Furthermore, the reference light is reflected by Mirror 1 and then irradiated onto the recording medium, and its incident angle relative to the recording medium is θ1.

[0083] In a specific example, the beam expander and beam splitter assembly is adjusted so that the light intensity ratio of the object light to the reference light is (1 / 4):cos(θ1), so that the light intensity ratio irradiated onto the recording medium is 1:1.

[0084] In a specific example, the recording medium uses a photopolymer, which has the advantages of high photosensitivity, high diffraction efficiency and long lifespan.

[0085] In a possible implementation, the optical modulator component includes a second mirror, a third mirror, and a second optical modulator; wherein the second mirror is disposed on the second light output side of the polarization beam splitter prism; the light input side of the second optical modulator is disposed in the reflection direction of the second mirror; the third mirror is disposed on the light output side of the second optical modulator; the light input side of the first beam splitter prism is disposed in the reflection direction of the third mirror.

[0086] In this embodiment, the interference light wavefront is controlled by using an optical modulator to generate a specific interference light field, and thus a volume holographic grating with an arbitrary distribution of grating vectors and a controllable grating diffraction efficiency can be fabricated.

[0087] In a specific example, as Figure 2 and Figure 6 shown, the optical modulator component of this embodiment includes a light intensity modulation component, and the light intensity modulation component can be a device such as a DMD or an LCoS, etc., for realizing the adjustment of the diffraction efficiency of different parts of the volume holographic grating.

[0088] Specifically, the object light first passes through the light intensity modulation component for modulation to form a light field distribution A(x, y) with the same light intensity as the target light field where A is the light field amplitude, is the light field phase, and (x, y) is the spatial coordinate of the pixel in the light field.

[0089] Furthermore, subsequently, the object light passes through the optical modulator for phase modulation, so that the light field distribution is the same as the target light field distribution as

[0090] In this embodiment, during the exposure process of the photosensitive material, the intensity of the reference light is kept unchanged, and the light intensity ratio of the object light and the reference light at different positions of the interference light field is controlled to change with the required diffraction efficiency at this position, so that the diffraction efficiency of the volume holographic grating formed by exposure at this position can be controlled.

[0091] In a possible implementation, the device further includes a diaphragm; wherein the light input side of the diaphragm is disposed on the first light output side of the polarization beam splitter prism; the first reflecting prism is disposed on the light output side of the diaphragm.

[0092] In this embodiment, the irradiation area of the reference light on the recording medium is made equal to the irradiation area of the object light on the recording medium by adjusting the diaphragm size.

[0093] In a possible implementation, the second optical modulator is used to perform amplitude modulation on the object light to obtain a first object light with the same light intensity as the target object light field.

[0094] This embodiment reduces the equivalent pixel size of the optical modulator, increases the spatial frequency of the interference light field, thereby improving the preparation accuracy of the volume holographic grating, expanding the diffraction angle of the prepared grating, improving the resolution of the grating, and at the same time, this embodiment can realize the preparation of large-size gratings.

[0095] In a possible implementation manner, the first optical modulator is configured to perform phase modulation on the first object light to obtain object light with a certain complex amplitude distribution whose light field distribution is the same as the target light field distribution.

[0096] This embodiment improves the resolution of the phase modulation of the interference light field by the optical modulator, further improves the preparation accuracy of the volume holographic grating, and effectively improves the performance of the volume holographic grating.

[0097] In a possible implementation manner, the first optical modulator is further configured to generate a first adjustment amount with a first phase resolution for a first duration and a second adjustment amount with a second phase resolution for a second duration, and perform weighted summation on the first adjustment amount and the second adjustment amount to obtain a target value equivalent to the phase modulation.

[0098] This embodiment realizes time-division multiplexing through the optical modulator, improves the resolution of the phase modulation of the interference light field by the optical modulator, can also further improve the preparation accuracy of the volume holographic grating, and effectively improves the performance of the volume holographic grating.

[0099] In a specific example, as Figure 4 shown, the first optical modulator is further configured to implement time-division multiplexing optical modulation to further improve the phase adjustment accuracy of the object light by the optical modulator when generating interference fringes.

[0100] Specifically, the phase adjustment level L (i.e., phase L) required for the target pixel is located between two gray levels L n (i.e., the first phase resolution) and L n+1 (i.e., the first phase resolution), satisfying (L n < L < L n+1 ), and can be expressed as L = aL n + bL n+1 , where a and b are values between 0 and 1.

[0101] Furthermore, during the exposure process of the volume holographic grating, the target pixel of the optical modulator is controlled to alternately generate phase modulation amounts of L n and L n+1 , and the time ratio between the two satisfies a:b. Particularly, the phase gray levels L n and L n+1 can be alternately generated multiple times, as long as the total exposure time is equal to the target exposure time.

[0102] This embodiment can generate a phase modulation result higher than the phase resolution of the optical modulator, further improving the fineness of the fringes required for interference exposure.

[0103] In a specific example, a method of combining 4 frames into 1 frame is used to combine 256 gray levels into 1024 gray levels. The phase distribution of the target light field of the spatial light modulator from 0 to 2π calculated is quantized into 1024 gray levels, and 4 frames I1(x,y), I2(x,y), I3(x,y) and I4(x,y) when the target light field at 1024 gray levels is mapped to 256 gray levels are calculated. Assuming that the exposure time required for the recording medium at the current optical power is T, the above 4 frames of images are sequentially displayed within a time of T / 4, thereby completing the holographic interference exposure process of 1024 phase gray levels, and further improving the gray level of the volume holographic grating phase modulation.

[0104] Furthermore, during the exposure of the sub-hologram, the light intensity distribution of the object light field of each sub-hologram is adjusted by the DMD, so that the diffraction efficiency at each location of the sub-hologram can be controlled. An interference exposure volume hologram with an equivalent pixel size of 3.89mm X 2.305mm and 1024 phase modulation levels can be prepared.

[0105] This embodiment can quickly prepare a volume holographic grating with large size, high diffraction efficiency and arbitrarily adjustable grating vector and diffraction efficiency through the light intensity adjustment of the DMD and the phase adjustment of the SLM, which can meet the diverse requirements of the holographic optical waveguide device in AR display for the grating diffraction efficiency and diffraction angle, and improve the design freedom of the holographic optical waveguide.

[0106] In a specific example, as Figure 5 shown, the time-division multiplexing method can repeat the gray combination of L n and L n+1 many times during the exposure process.

[0107] To further improve the modulation accuracy of the spatial light modulator, the process of alternating L n and L n+1 can be repeated many times during the exposure process, as long as the time ratio of the adjustment amounts of the total L n and L n+1 produced is equal to a:b, and the total exposure time is equal to the total time of the volume holographic grating exposure process.

[0108] In a possible implementation manner, the optical transmission unit is further configured to respectively transmit the object light with a specific complex amplitude distribution and the reference light to the same side or different sides of the recording medium.

[0109] In a specific example, during the interference process of the object light and the reference light, a transmissive volume holographic grating can be formed by incident light on the same side of the photosensitive material, or a reflective volume holographic grating can be formed by incident light on both sides of the photosensitive material respectively.

[0110] In this embodiment, during the interference exposure preparation process of the traditional grating, its grating vector is restricted by optical elements, generally only planar or curved gratings can be realized, and the diffraction efficiency of the grating cannot be controlled, which limits its application in holographic optical waveguide devices in the field of AR display. By introducing a light modulator, the amplitude and phase of the interference light can be arbitrarily controlled to generate an interference light field with a specific distribution form, so that a volume holographic grating with an arbitrarily complex grating vector can be prepared; at the same time, the diffraction efficiency can also be precisely controlled, which can greatly improve the performance and function of the volume holographic grating; in addition, by realizing time-division multiplexing through the light modulator, the problems of insufficient spatial bandwidth product, large pixel size, and insufficient phase modulation resolution of the light modulation device during the grating preparation process can be solved, and the performance index of the volume holographic grating can be greatly improved.

[0111] Another embodiment of the present invention provides a method for preparing a volume holographic grating, the method includes decomposing the volume holographic grating to be formed into a plurality of volume holographic sub-gratings related to the grating position; generating coherent light with a coherence length greater than the optical path difference of the grating recording device by using a coherent light source; expanding and splitting the coherent light into object light and reference light with the same polarization direction; using a light modulator unit to modulate the complex amplitude distribution of the object light wavefront to obtain object light with a certain complex amplitude distribution, and the object light with a certain complex amplitude distribution and the reference light interfere to form fringes corresponding to the light intensity distribution of one of the plurality of volume holographic sub-gratings; using an optical transmission unit to transmit the object light with a certain complex amplitude distribution and the reference light to a recording medium; using a spatial position adjustment unit to adjust the recording medium to a position corresponding to one of the plurality of volume holographic sub-gratings, and record the fringes; repeating the above operations to form each volume holographic sub-grating, and thus obtain the volume holographic grating.

[0112] In this embodiment, during the interference exposure preparation process of the traditional grating, its grating vector is restricted by optical elements, generally only planar or curved gratings can be realized, and the diffraction efficiency of the grating cannot be controlled, which limits its application in holographic optical waveguide devices in the field of AR display. By introducing a light modulator, the amplitude and phase of the interference light can be arbitrarily controlled to generate an interference light field with a specific distribution form, so that a volume holographic grating with an arbitrarily complex grating vector can be prepared; at the same time, the diffraction efficiency can also be precisely controlled, which can greatly improve the performance and function of the volume holographic grating; in addition, by realizing spatial-division multiplexing and time-division multiplexing through the light modulator, the problems of insufficient spatial bandwidth product, large pixel size, and insufficient phase modulation resolution of the light modulation device during the grating preparation process can be solved, and the performance index of the volume holographic grating can be greatly improved.

[0113] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "upper" and "lower" is based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. Unless otherwise clearly specified and defined, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0114] It should also be noted that in the description of the present invention, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the existence of another identical element in the process, method, article or device comprising the said element.

[0115] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A preparation device for a volume holographic grating, characterized in that The device includes a coherent light source for generating coherent light with a coherence length greater than the optical path difference of the grating recording device; a beam expander and beam splitter for expanding and splitting the coherent light into object light and reference light with the same polarization direction; a control unit for decomposing the volume holographic grating into a plurality of volume holographic sub-gratings related to the grating position; an optical modulator unit for modulating the complex amplitude distribution of the object light wavefront to obtain object light with a certain complex amplitude distribution, and the interference between the object light with a certain complex amplitude distribution and the reference light can form fringes with an intensity distribution corresponding to the volume holographic sub-grating; an optical transmission unit for transmitting the object light with a certain complex amplitude distribution and the reference light to a recording medium; a spatial position adjustment unit for carrying the recording medium and adjusting the position of the recording medium according to a signal from the control unit, so that the recording medium records the fringes corresponding to the position at the position to obtain a volume holographic grating.

2. The apparatus for preparing a volume holographic grating according to claim 1, wherein the positions of the volume holographic sub-gratings may overlap or not overlap.

3. The apparatus for preparing a volume holographic grating according to claim 2, wherein the beam expander and beam splitter includes a telescope group and a polarization beam splitter prism; the optical modulator unit includes a first optical modulator and an optical modulator assembly; the optical transmission unit includes a first beam splitter prism, a first lens, a second lens and a first mirror, and the focal length of the first lens is not equal to the focal length of the second lens; wherein the incident light side of the telescope group is arranged on the output light side of the coherent light source; the incident light side of the polarization beam splitter prism is arranged on the output light side of the telescope group; the first mirror is arranged on the first output light side of the polarization beam splitter prism; the incident light side of the optical modulator assembly is arranged on the second output light side of the polarization beam splitter prism; the incident light side of the first beam splitter prism is arranged on the output light side of the optical modulator assembly; the incident light side of the first optical modulator is arranged on the first output light side of the first beam splitter prism; the incident light side of the first lens is arranged on the second output light side of the first beam splitter prism; the incident light side of the second lens is arranged on the output light side of the first lens; the second lens emits the object light with a specific complex amplitude distribution to the first side of the recording medium through its output light side; the first mirror is used to reflect the reference light to the second side of the recording medium.

4. The apparatus for preparing a volume holographic grating according to claim 3, wherein the optical modulator assembly includes a second mirror, a third mirror and a second optical modulator; wherein the second mirror is arranged on the second output light side of the polarization beam splitter prism; the incident light side of the second optical modulator is arranged in the reflection direction of the second mirror; the third mirror is arranged on the output light side of the second optical modulator; the incident light side of the first beam splitter prism is arranged in the reflection direction of the third mirror.

5. The preparation apparatus of the volume holographic grating according to claim 4, wherein The device further includes a diaphragm; wherein the incident light side of the diaphragm is arranged on the first output light side of the polarization beam splitter prism; the first reflecting prism is arranged on the output light side of the diaphragm.

6. The preparation apparatus of the volume holographic grating according to claim 5, characterized in that the second optical modulator is configured to perform amplitude modulation on the object light to obtain a first object light with a light field distribution having the same light intensity as the target object light field.

7. The preparation apparatus of the volume holographic grating according to claim 6, characterized in that the first optical modulator is configured to perform phase modulation on the first object light to obtain an object light with a certain complex amplitude distribution having the same light field distribution as the target light field.

8. The preparation apparatus of the volume holographic grating according to claim 7, characterized in that the first optical modulator is further configured to generate a first adjustment amount with a first phase resolution for a first duration and a second adjustment amount with a second phase resolution for a second duration, and perform weighted summation on the first adjustment amount and the second adjustment amount to obtain a target value equivalent to the phase modulation.

9. The preparation apparatus of the volume holographic grating according to claim 1, characterized in that the optical transmission unit is further configured to respectively transmit the object light with a specific complex amplitude distribution and the reference light to the same side or different sides of the recording medium.

10. A method for preparing a volume holographic grating, characterized in that, The method includes decomposing the volume holographic grating to be formed into a plurality of volume holographic sub-gratings related to the grating position; generating coherent light with a coherence length greater than the optical path difference of the grating recording device by using a coherent light source; expanding and splitting the coherent light into object light and reference light with the same polarization direction; using an optical modulator unit to modulate the complex amplitude distribution of the object light wavefront to obtain an object light with a certain complex amplitude distribution, and the interference between the object light with a certain complex amplitude distribution and the reference light can form fringes with a light intensity distribution corresponding to one of the plurality of volume holographic sub-gratings; using an optical transmission unit to transmit the object light with a certain complex amplitude distribution and the reference light to a recording medium; using a spatial position adjustment unit to adjust the recording medium to a position corresponding to one of the plurality of volume holographic sub-gratings, and record the fringes; repeating the above operations to form each volume holographic sub-grating, and thereby obtaining the volume holographic grating.

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