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 light modulator unit is used for modulating complex amplitude distribution of the object light wave surface to obtain object light with certain complex amplitude distribution, and the object light with certain complex amplitude distribution interferes with the reference light to form stripes corresponding to light intensity distribution of the volume holographic grating; a light transmission unit for transmitting the object light having the certain complex amplitude distribution and the reference light to a recording medium; and the recording medium is used for recording the stripes to obtain the volume holographic grating. According to the embodiment of the invention, the equivalent spatial frequency and phase modulation resolution of the light modulator and the diffraction angle and stripe fineness of the volume holographic grating are effectively improved, and the function and performance of the volume holographic grating are improved.

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 low equivalent spatial frequency and phase modulation resolution of optical modulators, the low diffraction angle and fringe fineness of volume holographic gratings, and the 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] 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 the light intensity distribution corresponding to the volume holographic grating;

[0010] an optical transmission unit for transmitting the object light with a certain complex amplitude distribution and the reference light to the recording medium;

[0011] a recording medium for recording the fringes to obtain a volume holographic grating.

[0012] Optionally, the optical transmission unit is used to respectively transmit the object light with a specific complex amplitude distribution and the reference light to different sides of the recording medium.

[0013] Optionally, the beam expander and beam splitter includes a telescope group and a polarization beam splitter prism;

[0014] The optical modulator unit includes a first optical modulator and an optical modulator assembly;

[0015] The optical transmission unit includes a first beam splitter prism, a first lens, a second lens, and a first mirror; wherein

[0016] The incident light side of the telescope group is disposed on the outgoing light side of the coherent light source;

[0017] The incident light side of the polarization beam splitter prism is disposed on the outgoing light side of the telescope group;

[0018] The first mirror is disposed on the first outgoing light side of the polarization beam splitter prism;

[0019] The incident light side of the optical modulator assembly is disposed on the second outgoing light side of the polarization beam splitter prism;

[0020] The incident light side of the first beam splitter prism is disposed on the outgoing light side of the optical modulator assembly;

[0021] The incident light side of the first optical modulator is disposed on the first outgoing light side of the first beam splitter prism;

[0022] The incident light side of the first lens is disposed on the second outgoing light side of the first beam splitter prism;

[0023] The incident light side of the second lens is disposed on the outgoing light side of the first lens;

[0024] 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;

[0025] The first mirror is used to reflect the reference light to the second side of the recording medium.

[0026] Optionally, the optical modulator assembly includes a second mirror, a third mirror, and a second optical modulator; wherein

[0027] The second mirror is disposed on the second outgoing light side of the polarization beam splitter prism;

[0028] The incident light side of the second optical modulator is disposed in the reflection direction of the second mirror;

[0029] The third mirror is disposed on the outgoing light side of the second optical modulator;

[0030] The incident light side of the first beam splitter prism is disposed in the reflection direction of the third mirror.

[0031] Optionally, the device further includes a diaphragm; wherein

[0032] The light incident side of the diaphragm is arranged on the first light output side of the polarization beam splitter prism;

[0033] The first reflecting prism is arranged on the light output side of the diaphragm.

[0034] Optionally, the second light 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.

[0035] Optionally, the first light modulator is configured to perform phase modulation on the first object light to obtain an object light with a certain complex amplitude distribution and a light field distribution the same as the target light field distribution.

[0036] Optionally, the first light 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.

[0037] Optionally, the light 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 of the recording medium.

[0038] A second aspect of the present invention provides a method for preparing a volume holographic grating, the method comprising

[0039] Using a coherent light source to generate coherent light with a coherence length greater than the optical path difference of the grating recording device;

[0040] Using a beam expander and beam splitter to expand and split the coherent light into an object light and a reference light with the same polarization direction;

[0041] Using a light 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 the volume holographic grating;

[0042] Using a light transmission unit to transmit the object light with a certain complex amplitude distribution and the reference light to a recording medium;

[0043] Using the recording medium to record the fringes to obtain a volume holographic grating.

[0044] The beneficial effects of the present invention are as follows:

[0045] 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, and improves the diffraction angle and fringe fineness of the volume holographic grating, thereby enhancing the function and performance of the volume holographic grating. Description of the Drawings

[0046] The following further elaborates in detail on the specific embodiments of the present invention with reference to the drawings.

[0047] Figure 1 The structural schematic diagram of the preparation device for a volume holographic grating in the prior art is shown.

[0048] Figure 2 The structural schematic diagram of the preparation device for a volume holographic grating provided by an embodiment of the present invention is shown.

[0049] Figure 3 The schematic diagram of time-division multiplexing of the preparation device for a volume holographic grating provided by an embodiment of the present invention is shown.

[0050] Figure 4 Another schematic diagram of time-division multiplexing of the preparation device for a volume holographic grating provided by an embodiment of the present invention is shown. Detailed Description of the Invention

[0051] To more clearly illustrate the present invention, the following further describes the present invention with reference to embodiments and drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the specific content described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0052] Volume holographic gratings utilize the periodic distribution of refractive index in a medium to achieve the 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 continuously evolved, and their performance indicators have been continuously improved, gradually meeting the required field of view and eye movement range for AR displays, and having broad application prospects.

[0053] Currently, as Figure 1As shown, volume holographic gratings are generally prepared by the method of interference exposure. The specific process is to use two plane lasers to interfere to form bright and dark periodic fringes, and place the photosensitive material in the light field with the periodic distribution of light intensity for exposure, so as to obtain the 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 interfering light can also be changed, and a volume holographic grating related to the wavefront distribution of the interfering light wave can be obtained by exposure.

[0054] 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. It is difficult to realize volume holographic gratings with arbitrary grating vector directions and diffraction efficiency distributions, and cannot meet the differentiated requirements of the diffraction performance of volume holographic gratings for holographic waveguide devices in augmented reality display technology. Therefore, there is an urgent need to propose a preparation device and method for volume holographic gratings to solve problems such as the grating vector and diffraction efficiency of volume holographic gratings being difficult to control arbitrarily, the equivalent spatial frequency and phase modulation resolution of the optical modulator being relatively low, the diffraction angle and fringe fineness of volume holographic gratings being relatively low, and the functions and performance of volume holographic gratings being relatively low in the preparation process of traditional volume holographic gratings.

[0055] In view of this, an embodiment of the present invention provides a preparation device for 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; a beam expander and beam splitter for expanding and splitting the coherent light into object light and reference light with the same polarization direction; 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 the certain complex amplitude distribution and the reference light can interfere to form fringes with the light intensity distribution corresponding to the volume holographic grating; an optical transmission unit for transmitting the object light with the certain complex amplitude distribution and the reference light to the recording medium; and a recording medium for recording the fringes to obtain a volume holographic grating.

[0056] This embodiment aims at the problem that the grating vector and diffraction efficiency of volume holographic gratings are difficult to control arbitrarily in the preparation of traditional volume holographic gratings, and proposes a preparation device for volume holographic gratings, which realizes the control of the grating vector and diffraction efficiency of volume holographic gratings, improves the equivalent spatial frequency and phase modulation resolution of the optical modulator, improves the diffraction angle and fringe fineness of volume holographic gratings, and thus enhances the functions and performance of volume holographic gratings.

[0057] In a specific example, such as Figure 2As shown in the figure, the device includes a coherent light source, a beam expander and beam splitter, an optical modulator unit, an optical transmission unit, and a recording medium. Specifically, in the device for preparing the volume holographic grating, the coherent light beam emitted by the coherent light source forms two coherent light beams after passing through the beam expander and beam splitter. The reference light is reflected by the mirror group and then irradiates at the recording medium. The object light first irradiates on the optical modulator assembly, and after being adjusted by the optical modulator assembly, the complex amplitude distribution of the light field required for the interference pattern is formed. Subsequently, it irradiates at the photosensitive material through the optical transmitter. The modulated object light interferes with the reference light to form a specific light intensity distribution and is recorded by the photosensitive material to form a volume holographic grating.

[0058] In a specific example, the coherent light source is generally a laser light source, which is used to generate coherent light with a coherence length greater than the optical path difference of the grating recording device. Among them, the coherent light source can be monochromatic light or a combination of multi-color coherent light.

[0059] In a specific example, the beam expander and beam splitter is generally a combination of a telescope group and a polarization beam splitter prism, which is used to expand and split the coherent light emitted by the coherent light source into two beams of light with the same polarization direction. One beam is called the object light, and the other beam is called the reference light.

[0060] Specifically, the beam splitter can be equipped with a light intensity adjustment device, generally a half-wave plate, which is used to adjust the light intensity of the two beams of light after beam splitting.

[0061] 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.

[0062] Specifically, the optical modulator can be a spatial light modulator (SLM), a digital micromirror device (DMD), a liquid crystal on silicon (LCoS) device, 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.

[0063] In a specific example, the optical transmission component is used to transmit the light field modulated by the optical modulator to the photosensitive material.

[0064] Specifically, the photosensitive material can be silver salt, dichromate gelatin, photopolymer, or other photosensitive materials, which are used to record the interference fringes with the above specific distribution to form a volume holographic grating. Among them, the photosensitive material can be planar, spherical, or have other shaped surfaces.

[0065] 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; 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.

[0066] 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.

[0067] In a specific example, a reflective volume holographic grating preparation device using a 532nm laser as a coherent light source is taken as an example to illustrate this example.

[0068] Specifically, a 532nm solid-state laser is used as the light source, and its emitted beam forms a collimated coherent beam with a diameter of about 20mm after passing through the beam expander assembly. Through the polarization beam splitter prism, it is decomposed into two coherent light beams, namely the object light and the reference light.

[0069] Further, 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.

[0070] 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.

[0071] In a specific example, the recording medium uses a photopolymer, which has the advantages of high photosensitivity, high diffraction efficiency and long lifespan.

[0072] In a possible implementation, the optical modulator assembly includes a second reflector, a third reflector, and a second optical modulator; wherein the second reflector 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 reflector; the third reflector 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 reflector.

[0073] In this embodiment, the interference light wavefront is controlled by using an optical modulator, so as to generate a specific interference light field, and then a volume holographic grating with an arbitrarily distributed grating vector and a controllable grating diffraction efficiency can be fabricated.

[0074] In a specific example, as Figure 2 shown, the optical modulator assembly of this embodiment includes a light intensity modulation assembly, and the light intensity modulation assembly can be a device such as a DMD or an LCoS, etc., for realizing the adjustment of the diffraction efficiencies of different parts of the volume holographic grating.

[0075] Specifically, the object light first forms a light field distribution A(x, y) with the same light intensity as the target light field after being modulated by the light intensity modulation assembly, 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. is the light field phase, and (x, y) is the spatial coordinate of the pixel in the light field.

[0076] Further, subsequently, the object light is phase-modulated by the optical modulator, so that the light field distribution is the same as the target light field distribution, which is

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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 a light field distribution having the same light intensity as the target object light field.

[0081] 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.

[0082] In a specific example, such as Figure 2 shown, the optical modulator assembly of this embodiment includes an intensity modulation assembly, and the intensity modulation assembly can be a device such as DMD or LCoS, etc., which is used to adjust the diffraction efficiency of different parts of the volume holographic grating.

[0083] Specifically, the object light first passes through the intensity modulation assembly 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.

[0084] Further, 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 During the exposure process of the photosensitive material, keeping the intensity of the reference light unchanged, controlling the light intensity ratio of the object light and the reference light at different positions of the interference light field 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.

[0085] In a possible implementation manner, the first optical modulator is used 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.

[0086] This embodiment improves the resolution of the phase modulation of the optical modulator for the interference light field, further improves the preparation accuracy of the volume holographic grating, and effectively improves the performance of the volume holographic grating.

[0087] In a possible implementation manner, the first optical modulator is further used 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.

[0088] This embodiment realizes time-division multiplexing through the optical modulator, improves the resolution of the phase modulation of the optical modulator for the interference light field, can also further improve the preparation accuracy of the volume holographic grating, and effectively improves the performance of the volume holographic grating.

[0089] In a specific example, such as Figure 3 shown, the first optical modulator is further used to realize time-division multiplexing optical modulation, thereby improving the phase adjustment accuracy of the optical modulator for the object light when generating interference fringes.

[0090] Specifically, the phase adjustment level L (i.e., phase L) required for the target pixel lies 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.

[0091] Furthermore, during the exposure process of the volume holographic grating, the target pixel of the light modulator is controlled to alternately generate phase modulation amounts of L n and L n+1 , and the time ratio of the two satisfies a:b. Specifically, 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.

[0092] This embodiment can produce a phase modulation result higher than the phase resolution of the light modulator, further improving the fineness of the fringes required for interference exposure.

[0093] 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 under the current light power is T, the above 4 frames of images are sequentially displayed within T / 4 of time, thus completing the holographic interference exposure process of 1024 phase gray levels, and further improving the gray level of the volume holographic grating phase modulation.

[0094] Furthermore, during the exposure process of the sub-hologram, the light intensity distribution of the object light field of each sub-hologram is adjusted by controlling 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.

[0095] 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 grating diffraction efficiency and diffraction angle in holographic optical waveguide devices such as AR displays, and improve the design freedom of the holographic optical waveguide.

[0096] In a specific example, such asFigure 4 As shown, the time-division multiplexing method can repeat the gray-scale combination of L n and L n+1 many times during the exposure process.

[0097] In order to further improve the modulation accuracy of the spatial light modulator, the process of alternating L n and L n+1 during the exposure process can be repeated many times, as long as the time ratio of the adjustment amounts of the total L n and L n+1 is equal to a:b, and the total exposure time is equal to the total time of the volume holographic grating exposure process.

[0098] In a possible implementation, 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 of the recording medium.

[0099] In a possible implementation, the optical transmission unit is configured to respectively transmit the object light with a specific complex amplitude distribution and the reference light to different sides of the recording medium.

[0100] In this embodiment, 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.

[0101] In the interference exposure preparation process of the traditional grating in this embodiment, its grating vector is restricted by optical elements, and generally only planar or curved gratings can be realized. The diffraction efficiency of the grating cannot be controlled either, which limits its application in holographic optical waveguide devices in the AR display field. 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 be precisely controlled, which can greatly improve the performance and function of the volume holographic grating; in addition, time-division multiplexing is realized through the light modulator, thereby solving 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, and can greatly improve the performance index of the volume holographic grating.

[0102] Another embodiment of the present invention provides a method for preparing a volume holographic grating, which includes 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 by using a beam expander and a beam splitter; modulating the complex amplitude distribution of the object light wavefront by using an optical modulator unit to obtain object light with a specific complex amplitude distribution, and the object light with the specific complex amplitude distribution and the reference light interfere in the device to form fringes with a specific light intensity distribution; transmitting the object light with the specific complex amplitude distribution and the reference light to a recording medium by using an optical transmission unit; and recording the fringes by using the recording medium to obtain a volume holographic grating.

[0103] In the interference exposure preparation process of traditional gratings, the grating vector is restricted by optical elements. Generally, only planar or curved gratings can be realized, and the diffraction efficiency of the gratings cannot be controlled, which limits their application in holographic optical waveguide devices in the field of AR displays. By introducing an optical 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 be precisely controlled, which can greatly improve the performance and function of the volume holographic grating; in addition, time-division multiplexing is realized through the optical modulator, thereby solving the problems of insufficient spatial bandwidth product, large pixel size and insufficient phase modulation resolution of the optical modulation device in the grating preparation process, and can greatly improve the performance index of the volume holographic grating.

[0104] 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, and 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, and therefore should not be construed as a limitation of the present invention. Unless otherwise clearly specified and defined, the terms "mounted", "connected" and "connected" 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.

[0105] 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 "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0106] 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 variations can be made based on the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or variations 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; 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 the light intensity distribution corresponding to the volume holographic grating; an optical transmission unit for transmitting the object light with a certain complex amplitude distribution and the reference light to the recording medium; a recording medium for recording the fringes to obtain a volume holographic grating.

2. The device for preparing a volume holographic grating according to claim 1, wherein the optical transmission unit is used to respectively transmit the object light with a specific complex amplitude distribution and the reference light to different sides of the recording medium.

3. The device 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; 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.

4. The device 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 outgoing 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 outgoing 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, characterized in that, The device further includes a diaphragm; wherein the incident light side of the diaphragm is arranged on the first outgoing light side of the polarization beam splitter prism; the first reflecting prism is arranged on the outgoing light side of the diaphragm.

6. The device for preparing a volume holographic grating according to claim 5, wherein the second optical modulator is used to perform amplitude modulation on the object light to obtain first object light with a light field distribution the same as the light intensity of the target object light field.

7. The preparation apparatus of the volume holographic grating according to claim 6, wherein 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 optical field distribution is the same as the target optical field distribution.

8. The preparation apparatus of the volume holographic grating according to claim 7, wherein 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, wherein 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 of the recording medium.

10. A method for preparing a volume holographic grating, characterized in that, The method includes using a coherent light source to generate coherent light with a coherence length greater than the optical path difference of the grating recording apparatus; using a beam expander and splitter to expand and split 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 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 the light intensity distribution corresponding to the volume holographic grating; 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 recording medium to record the fringes to obtain a volume holographic grating.

Images