Method, apparatus and system for volume holographic optical element fabrication

Abstract

The application provides a kind of body holographic optical element preparation method, device and system, it is related to optical element preparation technology.Therein, the method comprises: according to refractive index modulation degree level, the refractive index modulation degree distribution diagram corresponding to the target optical element to be prepared is divided into at least one subgraph, each subgraph has the same refractive index modulation degree level;Each subgraph is sequentially filled into exposure mask subgraph according to the opening time corresponding to the refractive index modulation degree level, to obtain the target exposure mask subgraph in an exposure period;According to target exposure mask subgraph, control spatial light modulator SLM modulates incident light in exposure period, to obtain target optical element.Through the present application, the accurate modulation of refractive index modulation degree can be realized.

Description

Technical Field

[0001] This application relates to optical element fabrication technology, and more particularly to a method, apparatus and system for fabricating a volume holographic optical element. Background Technology

[0002] A volume holographic optical element (VHOE) is an optical element fabricated using volume holographic photosensitive materials through laser interference. Its fabrication principle is to use laser interference technology and volume holographic photosensitive materials to construct a specific three-dimensional structure, which can be characterized by grating vector distribution and refractive index modulation.

[0003] Among known technologies, a phase-modulated wavefront printing method has been proposed to control the grating vector distribution by adjusting the exposure time and controlling the refractive index modulation. Specifically, a spatial light modulator (SLM) or a freeform surface is used to modulate the wavefront phase distribution of the recording light, thereby changing the intensity distribution of the interference light and controlling the grating vector distribution in the tangential and normal directions.

[0004] The above process has the drawback of not being able to achieve high-precision modulation, which will affect the performance of the obtained volume holographic optical element. Summary of the Invention

[0005] Based on this, this application provides a method, apparatus and system for fabricating volume holographic optical elements, wherein the method is used to achieve high-precision modulation of refractive index modulation in order to improve the performance of volume holographic optical elements.

[0006] In a first aspect, this application provides a method for fabricating a volume holographic optical element, comprising:

[0007] According to the refractive index modulation level, the refractive index modulation distribution map corresponding to the target optical element to be prepared is divided into at least one grade map, and each grade map has the same refractive index modulation level.

[0008] Each of the graded maps is sequentially filled into the exposure mask sub-map according to the on-time corresponding to the refractive index modulation level, to obtain the target exposure mask sub-map within one exposure cycle.

[0009] Based on the target exposure mask sub-map, the spatial light modulator (SLM) and filtering system are controlled to modulate the incident light during the exposure period to obtain the target optical element.

[0010] In one possible implementation, the control spatial light modulator (SLM) modulates the incident light during the exposure period to obtain the target optical element, comprising:

[0011] Based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element, the loading phase modulation diagram is determined; the preset carrier phase diagram satisfies preset conditions.

[0012] Based on the target exposure mask sub-map and the loaded phase modulation map, the exposure sub-map within the exposure cycle is determined;

[0013] During the exposure period, the phase-controlled SLM is used to load the exposure sub-map, and the incident light is modulated by the filtering system to obtain the target optical element.

[0014] In one possible implementation, the step of sequentially filling each of the graded maps into the exposure mask sub-map according to the on-time corresponding to the refractive index modulation level to obtain the target exposure mask sub-map within one exposure cycle includes:

[0015] Based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element, the loading phase modulation diagram is determined; the preset carrier phase diagram satisfies preset conditions.

[0016] Each of the hierarchical maps is logically ANDed with the loaded phase modulation map to obtain at least one target hierarchical map;

[0017] The target grading map is sequentially filled into the exposure mask sub-map according to the on-time corresponding to the refractive index modulation level to obtain the target exposure mask sub-map within one exposure cycle.

[0018] In one possible implementation, the control spatial light modulator (SLM) modulates the incident light during the exposure period to obtain the target optical element, comprising:

[0019] During the exposure cycle, the phase-controlled SLM loads the target exposure mask sub-map, and the filtering system modulates the incident light to obtain the target optical element.

[0020] In one possible implementation, the control spatial light modulator (SLM) modulates the incident light during the exposure period to obtain the target optical element, comprising:

[0021] Based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element, the loading phase modulation diagram is determined; the preset carrier phase diagram satisfies preset conditions.

[0022] During the exposure cycle, the amplitude-type SLM is controlled to load the target exposure mask sub-map, and the phase-type SLM is controlled to load the loading phase modulation map. Combined with the filtering system, the incident light is modulated to obtain the target optical element.

[0023] In one possible implementation, the preset conditions include: when the SLM inputs the loaded phase modulation map, the filtering system outputs a complete first positive image, and the first positive image has a complete phase modulation distribution.

[0024] In one possible implementation, the method further includes:

[0025] Obtain the required diffraction efficiency distribution map of the target optical element;

[0026] Based on the diffraction efficiency distribution map, the refractive index modulation distribution map corresponding to the target optical element is determined.

[0027] In one possible implementation, the method further includes:

[0028] A preset correlation between the pulse width modulation ratio and the refractive index modulation degree is obtained; the pulse width modulation ratio is the ratio of the on-time to the exposure period; the preset correlation is obtained by testing different optical elements under the same exposure conditions.

[0029] Based on the preset correlation, the activation time corresponding to the refractive index modulation level is determined.

[0030] Secondly, this application provides a volume holographic optical element fabrication apparatus, the apparatus comprising:

[0031] The partitioning module is used to divide the refractive index modulation distribution map corresponding to the target optical element to be prepared into at least one hierarchical map according to the refractive index modulation level, and each hierarchical map has the same refractive index modulation level.

[0032] The determination module is used to sequentially fill each of the graded images into the exposure mask sub-image according to the on-time corresponding to the refractive index modulation level, so as to obtain the target exposure mask sub-image within one exposure cycle.

[0033] The control module is used to control the spatial light modulator (SLM) and the filtering system to modulate the incident light during the exposure period according to the exposure mask sub-map, so as to obtain the target optical element.

[0034] Thirdly, this application provides an electronic device, including a processor and a memory communicatively connected to the processor;

[0035] The memory stores computer-executed instructions;

[0036] The processor executes computer execution instructions stored in the memory to implement the method as described in any of the first aspects.

[0037] Fourthly, this application provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, are used to implement the method as described in any of the first aspects.

[0038] Fifthly, this application provides a computer program product, including a computer program that, when executed by a processor, implements the method as described in any of the first aspects.

[0039] In a sixth aspect, this application provides a system for fabricating a volume holographic optical element. The system includes an electronic device as described in the third aspect, a spatial light modulator (SLM) and a filtering system that interact with the electronic device. The SLM is located upstream of the filtering system. The electronic device controls the SLM to load different phase images at different times and adjusts the allowed incident light angle indicated by the filtering system according to the phase images to achieve modulation of the incident light to obtain the target optical element.

[0040] In a seventh aspect, this application provides a volume holographic optical element, which is obtained by the method described in any one of the first aspects; the volume holographic optical element achieves modulation of incident light by forming a spatially varying refractive index distribution within the material.

[0041] The volume holographic optical element fabrication method, apparatus, and system provided in this application are used to fabricate target optical elements. Specifically, the volume holographic optical element fabrication method of this application first divides the required refractive index modulation distribution map into at least one hierarchical map according to the refractive index modulation level. These at least one hierarchical map are then sequentially filled into the exposure mask sub-map according to the on-time corresponding to their refractive index modulation level, resulting in a target exposure mask sub-map used to control the SLM to modulate the incident light within the corresponding exposure cycle. This allows the method to achieve corresponding refractive indices in different regions of the fabrication medium, thereby achieving high-precision modulation of the refractive index modulation at the pixel-level on different regions of the fabrication medium, which is beneficial for ensuring the performance of the target optical element. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of a volume holographic optical element fabrication system provided in an embodiment of this application;

[0044] Figure 2A A schematic flowchart of the fabrication process of a volume holographic optical element provided in this application embodiment. Figure 1 ;

[0045] Figure 2B This is a schematic diagram of the exposure cycle provided in the embodiments of this application;

[0046] Figure 3 A schematic diagram illustrating the relationship between pulse width modulation ratio and refractive index modulation degree is provided for embodiments of this application;

[0047] Figure 4 A schematic flowchart (2) of a method for fabricating a volume holographic optical element provided for an embodiment of this application;

[0048] Figures 5A-5G An example diagram illustrating the fabrication of a volume holographic grating provided in this application embodiment;

[0049] Figures 6A-6D An example diagram illustrating the fabrication of a volume holographic lens provided in this application embodiment;

[0050] Figure 7A Schematic diagram of the exposure optical path provided for the embodiments of this application Figure 1 ;

[0051] Figure 7B Schematic diagram of the exposure optical path provided in the embodiments of this application (II);

[0052] Figure 8A An example diagram of a volume holographic optical element fabrication system provided in this application embodiment;

[0053] Figure 8B for Figure 8A Example of exposure optical path corresponding to the system shown. Figure 1 ;

[0054] Figure 8C for Figure 8A The system shown corresponds to an example of the exposure optical path, as illustrated in Figure 2.

[0055] Figure 9 A flowchart illustrating a method for fabricating a volume holographic optical element provided in this application embodiment. Figure 3 ;

[0056] Figure 10A An exposure optical path using an amplitude-type SLM as an amplitude-type modulation device is provided in an embodiment of this application;

[0057] Figure 10B An exposure optical path using an LCD structure as an amplitude modulation device is provided in an embodiment of this application;

[0058] Figure 11 This is a schematic diagram of the structure of a volume holographic optical element fabrication apparatus provided in an embodiment of this application;

[0059] Figure 12 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0060] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The described embodiments are some, but not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0062] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0063] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0064] The terms “first,” “second,” and “third” (if any) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0065] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or display that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or display.

[0066] A volume holographic optical element (VHOE) is an optical element fabricated using volume holographic photosensitive materials through laser interference. Unlike traditional diffractive optical elements, VHOEs form complex 3D micro / nano structures within the material, exhibiting characteristics such as high transmittance, high diffraction efficiency, strong wavelength selectivity, and the presence of only first-order diffracted light.

[0067] The fabrication principle of VHOEs utilizes laser interference technology and volume holographic photosensitive materials to construct specific 3D micro / nano structures. Specifically, it is based on the response of the dielectric constant of the fabrication medium to the light intensity distribution; this process is called the recording process. During the recording process, two coherent recording beams interfere in the three-dimensional space of the exposure material. The wavefront phase distribution of the two beams is converted into the intensity distribution of the coherent light, and the corresponding intensity distribution is recorded in the fabrication medium, transforming into the dielectric constant distribution of the material, thereby completing the three-dimensional structure construction of the volume holographic optical element.

[0068] The three-dimensional structure formed by the above process exhibits Bragg diffraction characteristics, resulting in first-order positive diffracted light with high diffraction efficiency. This three-dimensional structure can be characterized by the grating vector distribution and refractive index modulation. The tangential (xy) grating vector distribution determines the phase response to the input light, while the normal (z) grating vector and refractive index modulation distribution determine the intensity response to the input light. Furthermore, the refractive index modulation controls the response bandwidth of the volumetric holographic optical element to the input light.

[0069] Currently, known technologies propose using phase-modulated wavefront printing to fabricate VHOEs. Specifically, a phase-type spatial light modulator (SLM) or a freeform surface is used to modulate the wavefront phase distribution of the recording light, thereby changing the intensity distribution of the interference light and controlling the distribution of the grating vectors in the tangential and normal directions.

[0070] However, current phase-modulated wavefront printing technology can only manipulate the grating vector and lacks the ability to adjust the refractive index, making it difficult to precisely control the light response bandwidth. Therefore, known techniques propose controlling the refractive index modulation by adjusting the exposure time. However, the controllable range of refractive index modulation has a limited linear relationship with exposure time and is highly sensitive to exposure time, resulting in limited control accuracy and modulated range, and making it impossible to achieve different refractive index modulation at arbitrary positions. Furthermore, in the above methods, when the normal grating vector changes, the Bragg condition changes accordingly, causing a shift in the center wavelength. This may lead to problems such as dispersion, stray light, and ghosting in the resulting VHOE.

[0071] Furthermore, known techniques employ intensity-modulated laser direct writing (IMLDI) to fabricate VHOEs, specifically utilizing an intensity-modulated laser light lamp (SLM) to directly control the intensity distribution of the recorded light. However, IMLDI faces challenges such as unclear boundaries due to diffraction and low precision in intensity control. Simultaneously, it is difficult to integrate with phase modulation, thus limiting the simultaneous realization of phase and intensity modulation of light.

[0072] Another known technology provides a simultaneous modulation of intensity and phase SLM, which has a structure in which phase modulation pixels and intensity modulation pixels are arranged adjacently and alternately. This type of SLM suffers from problems such as slow response speed, high cost, and low complex amplitude modulation accuracy.

[0073] As can be seen from the above, the known methods and equipment used to prepare VHOEs have the drawback of being unable to achieve high-precision modulation of the refractive index of the preparation medium, thus failing to guarantee the performance of the final volume holographic optical element. Furthermore, in achieving phase modulation of the incident light, the known techniques cannot simultaneously achieve modulation of the refractive index of the preparation medium, resulting in an insufficiently comprehensive function of the final volume holographic optical element.

[0074] Therefore, this application provides a method, apparatus, and system for fabricating volume holographic optical elements to solve the aforementioned problems. Specifically, the method of this application is based on the fast response and timing control characteristics of SLM (Solid Liquid Crystal Display). Specifically, this application controls the refractive index modulation of the VHOE (Video Hoop Image) at different pixel positions through the exposure duty cycle. Based on this, combined with a filtered optical path, the exposure process is controlled by loading these frame images, thus constructing the intensity response characteristics of the device. The method of this application enables high-precision modulation of the refractive index, which is beneficial for ensuring the performance of the final device.

[0075] Building upon this, the method of this application is combined with known phase-modulated wavefront printing fabrication equipment to achieve simultaneous modulation of refractive index modulation and incident light phase under time-domain control. Specifically, the optical patterns required at different times are encoded into images, so that each frame image represents a specific optical distribution, and the refractive index modulation of VHOE at different pixel positions is controlled by the exposure duty cycle. Based on this, combined with a filtered optical path, the exposure process is controlled by loading these frame images to complete the construction of the device's intensity response characteristics. Therefore, it is possible to simultaneously achieve refractive index modulation and phase modulation, thereby ensuring the comprehensive functionality of the final volume holographic optical element.

[0076] It is understood that the method of this application can be applied to any VHOE fabrication scenario and implemented by the volume holographic optical element fabrication system used in the corresponding scenario. Specifically, this application provides a volume holographic optical element fabrication system, including an electronic device, an SLM (Structured Lens), and a filtering system. The SLM is located upstream of the filtering system, and the electronic device is connected to the SLM and the filtering system. Based on the volume holographic optical element fabrication method of this application, it controls the SLM to load different phase images at different times and dynamically adjusts the allowable incident light angle indicated by the filtering system according to the phase images, thereby realizing the fabrication of the volume holographic optical element.

[0077] For example, Figure 1 This is a schematic diagram of a volume holographic optical element fabrication system provided in an embodiment of this application. Figure 1 As shown, in addition to the aforementioned electronic equipment, SLM, and filtering system, the volume holographic optical element fabrication system also includes: a laser, a beam expander, a beam splitter, a beam shrinker / expander, and a wavefront / image negative feedback detection system.

[0078] Specifically, the preparation medium is placed on a displacement fixture system. After the laser emits light, it passes through a beam expander and a beam splitter before entering the SLM. After being modulated by the SLM, it passes through a filter system and a beam shrinking / expanding system in sequence to expose the preparation medium on the displacement fixture system. The phase and intensity distribution of the exposed beam are detected by a wavefront / image detection system and fed back to the electronic equipment for real-time adjustment and compensation of the exposed plane.

[0079] The electronic device is based on the volume holographic optical element fabrication method of this application. According to the fabrication requirements, the SLM is controlled to load different phase images at different times, and the incident light is modulated in conjunction with the filtering system to achieve the required refractive index modulation in the fabrication medium, thereby obtaining the target optical element and completing the required volume holographic optical element.

[0080] It is understood that this application does not limit the number of SLMs; it can modulate only a single recording beam or multiple beams. For example... Figure 1As shown, two SLMs can be set to modulate two beams of light. Alternatively, multiple SLMs can be used to modulate a single recording beam; this embodiment does not limit this approach.

[0081] This application provides a method for fabricating a volume holographic optical element. The method will be described in detail below with reference to the accompanying drawings so that those skilled in the art can have a clearer and more detailed understanding of the contents of this application.

[0082] Figure 2A A schematic flowchart of the fabrication process of a volume holographic optical element provided in this application embodiment. Figure 1 ,like Figure 2A As shown, the method provided in this application embodiment includes:

[0083] S201, according to the refractive index modulation level, divide the refractive index modulation distribution map corresponding to the target optical element to be prepared into at least one grade map, and each grade map has the same refractive index modulation level.

[0084] It is understandable that the refractive index modulation profile is determined based on the fabrication requirements of the target optical element. Specifically, in this embodiment, the electronic device first obtains the diffraction efficiency profile required by the target optical element; based on the diffraction efficiency profile, it determines the refractive index modulation profile corresponding to the target optical element.

[0085] More specifically, the electronic device determines the refractive index modulation distribution of the target optical element based on the diffraction efficiency distribution map and diffraction theory. The diffraction theory can be rigorous coupled-wave analysis (RCWA) theory, or other theories such as scalar diffraction theory and finite-difference time-domain method; this embodiment does not limit the specific theory used.

[0086] In this embodiment, the electronic device is configured with a refractive index modulation level classification rule. It can be understood that the rule can indicate that a certain refractive index modulation level is a refractive index modulation level, or it can indicate that a certain range of refractive index modulation levels is a refractive index modulation level. It can be understood that the smaller the range, the more finely the target optical element can be divided, and correspondingly, higher precision refractive index modulation can be achieved.

[0087] In this embodiment, the electronic device uses a certain refractive index modulation range as a refractive index modulation level, and divides the obtained desired refractive index modulation distribution map according to this refractive index modulation level to obtain at least one classification map with the same refractive index modulation level.

[0088] S202, fill the exposure mask sub-map with the opening time corresponding to each grade map according to the refractive index modulation level, and obtain the target exposure mask sub-map within one exposure cycle.

[0089] S203, based on the target exposure mask sub-map, controls the spatial light modulator (SLM) and the filtering system to modulate the incident light during the exposure cycle to obtain the target optical element.

[0090] It is understandable that a recording process is divided into multiple exposure cycles, each with the same exposure sequence. For example, an exposure cycle can be 1 second. Within a single exposure cycle, there are on-time and off-time periods. Specifically... Figure 2B This is a schematic diagram of the exposure cycle provided for an embodiment of this application. For example... Figure 2B As shown, during the on-time, the object beam and reference beam undergo dual-beam exposure; during the off-time, the object beam is off and the reference beam is on, achieving single-beam exposure. Since SLM image loading uses discrete frame control, the statistical unit corresponding to the on-time and off-time is a frame.

[0091] In this embodiment, different optical elements obtained under the same exposure conditions are tested, and the test results are summarized to obtain the correlation between pulse width modulation ratio (PWM) and refractive index modulation. Here, PWM is the ratio of the aforementioned on-time to the exposure period.

[0092] Specifically, under the same exposure conditions, the maximum diffraction efficiency of the first positive stage of the optical element is measured by setting different pulse width modulation ratios. The relationship between the maximum diffraction efficiency of the first positive stage and the pulse width modulation ratio under the current exposure conditions is obtained, and then the correlation between the refractive index modulation degree and the pulse width modulation ratio is obtained.

[0093] It should be understood that diffraction efficiency refers to the ratio of the light intensity of a specific diffraction order to the incident light intensity, and the first positive order diffraction efficiency refers to the proportion of the light intensity in the first positive order direction to the incident light intensity. Therefore, in this embodiment, the light intensity of the first positive order can be measured by a photometer or power meter, and then compared with the incident light intensity to calculate the maximum diffraction efficiency of the first positive order. Furthermore, the refractive index modulation is calculated by combining the maximum diffraction efficiency of the first positive order, reflectivity, transmittance, and other optical properties, along with numerical simulations or theoretical models (such as RCWA).

[0094] As can be seen from the foregoing, the refractive index modulation can be controlled by changing the PWM. Specifically, the different PWM levels of the aforementioned refractive index modulation classification diagrams are made to correspond to different PWM levels. Each classification diagram is then filled into the exposure mask sub-diagram according to its corresponding turn-on time to obtain the target exposure mask sub-diagram within one exposure cycle.

[0095] It is understood that the activation time corresponding to the refractive index modulation level is determined through the correlation between the pulse width modulation ratio and the refractive index modulation level in the aforementioned process. Specifically, in this embodiment, the electronic device first obtains the correlation between the pulse width modulation ratio and the refractive index modulation level based on the current exposure conditions, and then determines the activation time corresponding to the refractive index modulation level based on the correlation.

[0096] Furthermore, it should be understood that within one exposure cycle, the smallest unit time within which the pulse width can be adjusted is the minimum adjustable pulse width modulation time, which determines the minimum duty cycle step of the PWM indication, specifically determined by the SLM refresh rate. For example, at an SLM refresh rate of 30Hz, the minimum pulse width modulation time is 33ms; at an SLM refresh rate of 60Hz, the minimum pulse width modulation time is 16.67ms; and at an SLM refresh rate of 2000Hz, the minimum pulse width modulation time is 0.5ms.

[0097] It should be understood that the adjustable discrete data range of PWM is also determined by the SLM refresh rate. For example, when the SLM operating frequency is 60Hz, the adjustable discrete data of PWM includes 60 modulated discrete points such as 1 / 60, 2 / 60, 3 / 60...60 / 60, corresponding to a duty cycle range from 1 / 60 to 60 / 60 (i.e., 100%).

[0098] It should be understood that the adjustable discrete point range of the refractive index modulation is jointly determined by the properties of the preparation medium, the SLM refresh rate, and the correlation indicated by the aforementioned test results. For example, if the maximum achievable refractive index modulation of the preparation medium is 0.03 and the SLM refresh rate is 60Hz, then the adjustable discrete points of the refractive index modulation include 60 adjustable discrete points: 0, 0.0005, 0.001…0.028, 0.03, etc., ranging from 0 to 0.03, with the data distribution being nearly linear.

[0099] It should be understood that the minimum adjustable refractive index modulation spatial resolution is affected by the SLM pixel size, the applied phase spatial frequency, the scaling optical path, and the theoretical applicability range of local frequencies, with a typical value range greater than 100*100um. It should be noted that under some conditions that allow for tolerance of high noise, the spatial resolution can be further reduced, down to as low as 10um.

[0100] It should also be noted that the minimum adjustable refractive index modulation spatial resolution and the minimum adjustable refractive index resolution are different concepts. Since the refractive index varies spatially according to a sine or cosine function under the same refractive index modulation, the minimum adjustable refractive index distribution generally refers to the period of this sine or cosine function, which is a subwavelength dimension with a range greater than 200 nm.

[0101] It should be understood that the maximum adjustable refractive index modulation area in a single operation is limited by the SLM size, spot size, and scaling of the optical path. The typical value is 15.56mm*9.22mm, and the typical range is from 75mm*45mm to 100um*100um.

[0102] As an example, Figure 3 This diagram illustrates the relationship between pulse width modulation ratio and refractive index modulation, as provided in an embodiment of this application. Based on Figure 3 The diagram illustrating the correlation shows that, given the refractive index modulation degree, the corresponding pulse width modulation ratio can be determined. Based on this, and combined with the exposure period, the corresponding on-time can be determined.

[0103] Understandably, an exposure mask submap is a mask containing a specific pattern used to modulate the intensity, phase, or spectral characteristics of light during exposure. This pattern determines the distribution of light on the material, thus affecting the processing outcome of the fabricated medium.

[0104] In this embodiment, after the electronic device obtains the target exposure mask sub-map within an exposure cycle, it controls the SLM and filtering system to modulate the incident light within the exposure cycle according to the target exposure mask sub-map, ensuring that each graded map is exposed within the correct time period, so as to achieve the required refractive index modulation in the preparation medium and obtain the target optical element.

[0105] In the method provided in this embodiment, firstly, the refractive index modulation distribution map required by the target optical element is divided into at least one graded map according to the required refractive index modulation level. Secondly, these at least one graded map are sequentially filled into the exposure mask sub-map according to the on-time corresponding to their refractive index modulation level to obtain the target exposure mask sub-map. Finally, based on the target exposure mask sub-map, the SLM is controlled to load different phase images at different times, and the allowable incident light angle indicated by the filtering system is adjusted according to the phase image to achieve modulation of the incident light, thereby obtaining the required target optical element.

[0106] The method of this embodiment enables the realization of corresponding refractive indices in different regions of the preparation medium, thereby achieving high-precision modulation of the refractive index modulation in different regions of the preparation medium at the pixel-level, which helps to ensure the performance of the final target optical element.

[0107] It is understood that in this embodiment, the preparation system and the exposure optical path are not limited, as long as the preparation system includes the execution subject of the method of this embodiment (any electronic device), SLM, and filtering system, and can implement the method of this embodiment.

[0108] Furthermore, this embodiment does not limit the specific exposure time or exposure power. The goal is simply to coordinate the exposure time and power to ensure that the preparation medium is in a saturated exposure state even when only a single beam of light is used. For example, if the single beam exposure intensity is 1 mW / cm²... 2 If the saturation exposure dose is 30mJ, then the exposure time should be greater than 30s.

[0109] As an example, this application provides an embodiment of a method for fabricating a volume holographic optical element, implemented using a fabrication system comprising a phase-type SLM. Figure 4 A schematic flowchart of a method for fabricating a volume holographic optical element provided in this application is shown in Figure 2. Figure 4 As shown, the method in this embodiment includes:

[0110] S401, according to the refractive index modulation level, divide the refractive index modulation distribution map corresponding to the target optical element to be prepared into at least one grade map, and each grade map has the same refractive index modulation level.

[0111] S402, fill the exposure mask sub-map with the opening time corresponding to each grade map according to the refractive index modulation level, and obtain the target exposure mask sub-map within one exposure cycle.

[0112] For details regarding the refractive index modulation level, refractive index modulation distribution map, and target exposure mask sub-map, please refer to the aforementioned embodiments; they will not be repeated here.

[0113] S403, based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element, determine the loading phase modulation diagram.

[0114] The preset carrier phase diagram satisfies preset conditions. These preset conditions include: when the phase modulation diagram is loaded onto the SLM input, the filtering system outputs a complete first positive image, and the first positive image has a complete phase modulation distribution.

[0115] Understandably, an SLM can be controlled electronically, loading different phase images at different times to modulate the phase of the incident light. Some special phase patterns, such as blazed gratings and Fresnel lenses, can significantly alter the propagation direction of the SLM's first positive output light. Based on this, the system uses a filtering system to allow only exposure light at specific incident angles to exit, exposing the holographic recording material.

[0116] Therefore, in this embodiment, the aforementioned special phase pattern is used as the carrier phase map for switching. Within one exposure cycle, the preset carrier phase map is loaded during the object light on-time and not loaded during the object light off-time.

[0117] It is understandable that the phase modulation map is determined based on the fabrication requirements of the target optical element. Specifically, the phase modulation map of the exposure beam is obtained according to the spatial dielectric constant distribution of the designed holographic optical element.

[0118] S404, based on the target exposure mask sub-map and the loaded phase modulation map, determines the exposure sub-map within the exposure cycle.

[0119] Specifically, the target exposure mask sub-image and the loaded phase modulation image within the exposure cycle are superimposed to obtain the exposure sub-image.

[0120] S405 controls the phase-type SLM to load an exposure sub-map during the exposure cycle, and combines it with a filtering system to modulate the incident light to obtain the target optical element.

[0121] In this embodiment, the electronic device controls the phase-type SLM to load the exposure sub-pattern to achieve phase modulation of the incident light, while also enabling modulation of the refractive index of the preparation medium.

[0122] It is understandable that, such as Figure 4 As shown, in this embodiment, the processes from S401 to S402 can be executed in parallel with S403, or they can be executed sequentially. In this embodiment, the execution order of S401, S402 and S403 is not limited.

[0123] For example, obtaining the target optical element in this embodiment may specifically include the following process:

[0124] Step 1: Determine the loading phase modulation diagram based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element.

[0125] Step 2: Perform a logical AND operation between each hierarchical map and the loaded phase modulation map to obtain at least one target hierarchical map.

[0126] Step 3: Fill the exposure mask sub-map with the target grading map according to the on-time corresponding to the refractive index modulation level, and obtain the target exposure mask sub-map within one exposure cycle.

[0127] Step 4: During the exposure period, control the phase-type SLM to load the target exposure mask sub-map, and combine it with the filtering system to modulate the incident light to obtain the target optical element.

[0128] In the above process, after the electronic device obtains the loaded phase modulation map, it first performs a logical AND operation between each grade map and the loaded phase modulation map, and then fills at least one target grade map into the exposure mask sub-map to obtain the target exposure mask sub-map for the current exposure cycle.

[0129] In the method provided in this embodiment, by preparing exposure mask sub-maps with different PWM, each pixel / region on the loaded phase modulation map has a different PWM exposure timing, thereby enabling precise phase modulation of the incident light and precise modulation of the refractive index modulation in different regions of the preparation medium. This is beneficial to ensuring the performance and functional comprehensiveness of the target optical element.

[0130] The method provided in this embodiment can simultaneously change the grating vector distribution and refractive index modulation distribution of a volume holographic optical element, improving the design flexibility of the volume holographic optical element. Therefore, the method of this embodiment can be used to design and fabricate a wider variety of volume holographic optical elements suitable for near-eye display systems, expanding the application scenarios of volume holographic optical elements.

[0131] For example, the method of this embodiment can optimize the results at the design end and expose an output holographic grating with a specific distribution of diffraction efficiency, thereby improving the uniformity of the exit pupil of the volume holographic waveguide display system.

[0132] The method described in this embodiment can suppress or improve the diffraction efficiency of certain regions of a volume holographic optical element by modulating the refractive index, effectively solving the problem of intensity response distribution issues such as diffraction uniformity of the volume holographic optical element. For example, by improving the diffraction efficiency uniformity of a reflective volume holographic lens, the imaging brightness uniformity of a near-infrared eye-tracking system for near-eye display systems can be improved, thereby enhancing the accuracy of the eye-tracking system.

[0133] Based on the above, it should be clear that the method of this embodiment can achieve pixel-level modulation of refractive index modulation at different positions of a volume holographic optical element and can be combined with phase modulation methods in known technologies. Specifically, the process can be described as follows: by preparing exposure mask sub-images with different PWMs, each pixel / region on the loaded phase modulation map has a different PWM exposure timing. More specifically, this process is mainly divided into a refractive index modulation part and a phase modulation part. The refractive index modulation part outputs the mask sub-image corresponding to the exposure timing, and the phase modulation part outputs the loaded phase modulation map required for exposure. Finally, a logical AND operation is performed between each exposure mask sub-image and the loaded phase modulation map to obtain all the exposure sub-images loaded onto the SLM within one exposure cycle. The following is a detailed description of these two parts:

[0134] Refractive index modulation (RIM) section: In the RIM section, based on the diffraction efficiency distribution required for the designed holographic optical element, and in conjunction with RCWA or other diffraction theories, a refractive index modulation distribution map of the device needs to be obtained. The RIM is then divided into different RI levels, breaking down a single map into multiple graded maps with the same RI level. Different graded maps correspond to different PWM (Pulse Width Modulation). These different graded maps are then sequentially loaded into the exposure mask sub-map according to their RIM results and timing. Specifically, different graded maps are loaded into the exposure mask sub-map according to their level and timing. This timing control ensures that each graded map is exposed within the correct time period, thereby achieving precise control over the entire image.

[0135] Phase modulation section: First, the phase modulation map of the exposure beam needs to be obtained based on the spatial dielectric constant distribution of the designed holographic optical element. Then, a carrier phase map suitable for the filter system needs to be selected, and the carrier phase map and the phase modulation map are added together to obtain the loaded phase modulation map. The selected carrier phase map must satisfy the following condition: when the SLM input is the loaded phase modulation map, the filter system can completely output the first positive image, which has a complete phase modulation distribution and is free from aliasing or other effects.

[0136] It is understood that the method of this embodiment can be used in the fabrication process of any volume holographic optical element, in conjunction with a volume holographic optical element fabrication system that includes an SLM and a filtering system.

[0137] As an example, the method of this embodiment can be used in the fabrication process of volume holographic gratings. It is understood that volume holographic gratings are used in near-eye display systems such as AR / MR as input and output coupling devices. Because volume holographic gratings fabricated in known technologies suffer from the problem of difficulty in precisely controlling the refractive index modulation distribution, the design freedom of AR / MR display systems is reduced. The method of this embodiment for fabricating volume holographic gratings can effectively solve this problem.

[0138] As an explanation, Figures 5A-5G This is an example diagram illustrating the fabrication of a volume holographic grating, provided as an embodiment of this application. Figure 5A As shown, this example fabricates a volume holographic grating with a center wavelength of 532 nm, a Bragg incident angle of 0°, and a first positive diffraction angle of 45°. The refractive index modulation of this volume holographic grating has a checkerboard distribution, increasing sequentially from the upper left corner to the lower right corner, to demonstrate the modulation function of the refractive index modulation that this scheme can achieve.

[0139] like Figure 5BAs shown, the exposure optical path in this example has the following characteristics: a 532nm light source is used, and the filter system is a 4f system consisting of two lenses. The SLM is located at the object-side focal length of the first lens, and the filter stop is located at the image-side focal length of the first lens, which is also the object-side focal length of the second lens. The preparation medium is located at the image-side focal length of the second lens. The reference light and object light are exposed on opposite sides, and the angle between the reference light and the normal of the preparation medium is 45°.

[0140] In addition, this example uses, for example Figure 5C The carrier phase map shown is specifically a lateral blazed grating with a grating period of 8 pixels. Because a tilted exposure has been used, the phase modulation map in this example is blank.

[0141] In this example, the SLM is set to 4000*2464 pixels and a refresh rate of 60Hz. The exposure cycle is 60 frames, or 1 second. The exposure time is 25 seconds. The object light power density is 1.9mw / cm^2, the ratio of the object light to the projected reference light power density is 1:1, and the polarization is P-beam.

[0142] In the example, the refractive index modulation is divided into 18 levels, and the refractive index modulation distribution map is divided based on these 18 levels as follows: Figure 5D The diagram shows 18 hierarchical figures.

[0143] Based on this, the exposure sub-image of a single frame in a single exposure cycle of the electronic device input SLM in this example is as follows: Figure 5E As shown, the exposure sub-images of all frames within one exposure cycle are as follows: Figure 5F As shown.

[0144] Furthermore, the volume holographic grating finally fabricated in this example, after being reconstructed with reference light, can achieve the following: Figure 5G The intensity distribution of the first positive order diffracted light shown is consistent with... Figure 5A The design goals are shown. It should be understood that because a 4f filter system is used in this example, ... Figure 5G The effect presented has been reversed.

[0145] As another example, the method of this embodiment can also be used in the fabrication process of volume holographic lenses. Specifically, Figures 6A-6D This is an example diagram illustrating the fabrication of a volume holographic lens, provided in an embodiment of this application.

[0146] In this embodiment, the lens focal length is 1m, the object light is modulated by SLM, and a Fresnel lens phase modulation pattern is applied. The corresponding phase modulation pattern is as follows: Figure 6A As shown. The carrier phase map used in this embodiment is a lateral blazed grating with a blazed grating period of 8 pixels. The loading phase map used in this embodiment is as follows. Figure 6B As shown.

[0147] In this embodiment, the first positive order diffraction intensity distribution of the reconstructed light satisfying the Bragg condition at a wavelength of 532 nm by the volume holographic optical element is the same as in the previous example, such as... Figure 5B As shown. The exposure sub-image of this embodiment constructed by the method proposed in this case is as follows. Figure 6C and 6D As shown. By loading this exposure sub-image onto an SLM, a volume holographic lens with a specific refractive index modulation distribution can be created.

[0148] Furthermore, as described above, this embodiment does not limit the exposure optical path; it is sufficient to cooperate with electronic devices and SLM to implement the above-described method embodiment.

[0149] Specifically, as an example, Figure 7A Schematic diagram of the exposure optical path provided for the embodiments of this application Figure 1 ,like Figure 7A As shown, the exposure optical path used in this example is different from... Figure 5B The exposure optical path shown has been augmented with a scaling system, which can improve the SLM modulation phase range.

[0150] Specifically, the scaling principle is that when the size of a unit SLM modulated pixel is reduced by a factor of n, the maximum modulated angle that can be adjusted satisfies:

[0151]

[0152] Where d is the pixel size and λ is the exposure wavelength.

[0153] Understandably, adding a scaling system reduces the exposure area, shrinking the area scale by a factor of n. Therefore, a displacement stage is needed to complete the stitching exposure.

[0154] Understandable, Figure 7A The intermediate filter stop 1 is used for filtering, limiting the diffraction light of other orders of the SLM, and only allowing the projected image of the effective exposure frame to pass through. The filter stop 2 is used to filter out other stray light.

[0155] The method of this embodiment, applied to this optical path, can be described as follows: based on the refractive index modulation distribution and phase distribution of the designed holographic optical element to be exposed, the phase map to be loaded onto the SLM is encoded, and the PWM timing control method proposed in this embodiment controls the SLM to load different phase maps at different times, thereby achieving simultaneous modulation of the grating vector distribution and refractive index modulation distribution of the device to be exposed.

[0156] As yet another example, Figure 7B The second schematic diagram of the exposure optical path provided in the embodiment of this application is as follows: Figure 7BAs shown, the optical path presented in this embodiment is a dual-arm SLM-modulated immersion exposure optical path, which can realize the modulation of two beams by the SLM. The use of an immersion objective lens increases the numerical aperture and further expands the exposure angle.

[0157] The method of this embodiment, applied to this optical path, can be described as follows: based on the refractive index modulation distribution and phase distribution of the designed holographic optical element to be exposed, the phase map to be loaded on the dual-arm SLM is encoded, and the PWM timing control method proposed in this embodiment controls the dual-arm SLM to load different phase maps at different times, so as to achieve simultaneous modulation of the grating vector distribution and refractive index modulation distribution of the device to be exposed.

[0158] It is understood that in practical applications, the method of this embodiment can also be implemented by other optical element fabrication systems, and this embodiment does not limit this.

[0159] Specifically, as an example, Figure 8A This is an example diagram of a volume holographic optical element fabrication system provided in an embodiment of this application. For Figure 8A The volume holographic optical element fabrication system shown in this embodiment utilizes a combination of SLM and freeform surfaces to simultaneously modulate the phase and refractive index of the volume holographic optical element.

[0160] It is understandable that the phase modulation of the above system can be achieved by a freeform surface, or by a combination of a freeform surface and an SLM. The refractive index modulation of this system is achieved by the SLM. A freeform surface can achieve a wide range of phase distributions, but cannot achieve abrupt phase changes. An SLM can achieve modulation patterns with abrupt phase changes, but achieving a wide range of phase distributions is difficult. Therefore, an SLM and a freeform surface can be applied simultaneously to the exposure beam to achieve complementary modulation advantages. The technique proposed in this case can also be applied to an SLM to achieve simultaneous phase and refractive index modulation.

[0161] Figure 8B for Figure 8A Example of exposure optical path corresponding to the system shown. Figure 1 , specifically Figure 8B The specific optical path of the above system is shown, in which the transmission freeform surface needs to be located on the object-side focal plane of the last lens of the filtering system, and also on the image-side focal plane of the first lens of the scaling system.

[0162] It is understood that the specific optical paths described above for applying the method of this embodiment are all for the exposure of reflective volume holographic optical elements. The method of this embodiment can also be used for the exposure of transmissive volume holographic optical elements. Figure 8C for Figure 8A The system shown in Figure 2 is an example of the exposure optical path. Figure 8CAs shown, it demonstrates a transmissive dual-arm SLM modulation immersion exposure optical path. SLM1 and SLM2 modulate two recording beams respectively, and electronic equipment controls the exposure sequence of SLM1 and SLM2 to achieve simultaneous modulation of the refractive index modulation and phase distribution of the transmissive volume holographic optical element.

[0163] As can be seen from the above, the exposure method proposed in this embodiment is easy to use, can be closely integrated with design software, and is simple to implement, low in cost, and does not require modification of the existing pure phase-type volume holographic exposure optical path. It only requires timing control of the SLM-loaded image. Specifically, the exposure mask sub-image can be directly output based on the diffraction efficiency distribution diagram of the volume holographic optical element required for the design, and the refractive index modulation distribution of the device can be controlled.

[0164] Furthermore, when the method of this embodiment is applied to an existing pure phase-type volume holographic exposure optical path, if the optical path adopts a 4F system to transmit the SLM phase modulation surface, there is no diffraction problem caused by the free space transmission process. Therefore, there are no problems such as unclear exposure boundaries faced by the current intensity-modulated laser direct writing technology.

[0165] It is understandable that in the aforementioned embodiments, the timing control of the opening and closing of the exposure beam amplitude on the exposure plane is achieved through the cooperation of the carrier phase map and the filtering system. However, this process is limited by the loading phase image response speed of the phase-type SLM with the carrier phase map, and can only achieve a limited number of refractive index modulation sampling levels with a large sampling interval.

[0166] Therefore, as another design, this application also provides an embodiment of a method for fabricating a volume holographic optical element, proposing to introduce a new amplitude-type modulation device to perform time-sequential binary amplitude distribution modulation on the beam of the input phase-type SLM, thereby completing the time-sequential control of the opening and closing of the exposure beam amplitude on the exposure plane. The amplitude-type modulation device used is characterized by high spatial resolution and high refresh rate.

[0167] It should be noted that the method in this embodiment is achieved through... Figure 1 The volume holographic optical element fabrication system shown is realized, which includes phase-type SLM and amplitude-type SLM. Figure 9 A flowchart illustrating a method for fabricating a volume holographic optical element provided in this application embodiment. Figure 3 ,like Figure 9 As shown, the method in this embodiment includes:

[0168] S901, according to the refractive index modulation level, divide the refractive index modulation distribution map corresponding to the target optical element to be prepared into at least one grade map, and each grade map has the same refractive index modulation level.

[0169] S902, fill the exposure mask sub-map with the opening time corresponding to each grade map according to the refractive index modulation level, and obtain the target exposure mask sub-map within one exposure cycle.

[0170] S903, based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element, determines the loading phase modulation diagram.

[0171] Among them, the preset carrier phase diagram meets the preset conditions.

[0172] For details regarding the refractive index modulation level, refractive index modulation distribution map, and target exposure mask sub-map, please refer to the aforementioned embodiments; they will not be repeated here.

[0173] S904, during the exposure cycle, controls the amplitude-type SLM to load the target exposure mask sub-map and controls the phase-type SLM to load the phase modulation map, and combines the filtering system to achieve modulation of the incident light to obtain the target optical element.

[0174] In this embodiment, the electronic device specifically controls an amplitude-type SLM to load a target exposure mask sub-pattern, used to modulate the refractive index of the preparation medium. The electronic device also controls a phase-type SLM to load a phase modulation pattern, used to modulate the phase of the incident light.

[0175] It is understood that in this embodiment, the fabrication system and exposure optical path of the volumetric holographic optical element are not limited, as long as the electronic device can cooperate with the amplitude-type SLM and the phase-type SLM to implement the method of this embodiment.

[0176] As an example, this embodiment uses an amplitude-type SLM and its filtering system to achieve amplitude timing control of the input beam. The amplitude-type SLM can be a Liquid Crystal On Silicon (LCOS-SLM) or a Digital Micromirror Device (DMD).

[0177] Specifically, Figure 10A This application provides an exposure optical path that uses an amplitude-type SLM as the amplitude modulation device. For example... Figure 10AAs shown, the input beam passes through a beam splitter and enters filter system 1, which employs a 4F structure. After passing through filter system 1, the beam is incident on a reflection amplitude-type SLM. The amplitude-type SLM can modulate the binary incident light amplitude distribution for each pixel, replacing the original timing control of the phase-type SLM, and serving as a dynamic mask to control the mask sub-image of each exposure sub-image. The modulated beam then passes through filter system 1 again, through a beam splitter, and is incident on the phase-type SLM. The phase-type SLM is located at the fourth focal length position of the 4F structure. The 4F structure shifts the amplitude distribution of the beam modulated by the amplitude-type SLM to the position of the phase-type SLM.

[0178] Compared to the methods in the aforementioned embodiments, this approach requires a more complex exposure optical path, such as pixel-level alignment of the amplitude-type SLM and the phase-type SLM. However, because this approach uses an amplitude-type SLM, it can increase the system timing control frequency, reduce the single-frame exposure time, and increase the adjustable refractive index modulation resolution. For example, using a typical DMD as the amplitude-type SLM can increase the maximum timing control frequency from 60Hz in the original approach to 1kHz.

[0179] As another example, an LCD structure can also be used in this embodiment to achieve amplitude and timing control of the input beam. This structure includes two polarizers with perpendicular polarization directions and an LCD liquid crystal layer.

[0180] Specifically, Figure 10B An exposure optical path using an LCD structure as an amplitude modulation device is provided in an embodiment of this application, such as... Figure 10B As shown, the exposure optical path in this embodiment is as follows: Figure 10B As shown. The input beam is reflected by a P-beam beam splitter and then incident on the beam splitter, before being reflected onto an S-beam polarizer. Electronic equipment controls the LCD liquid crystal layer, loading an exposure mask sub-pattern. When a voltage is applied to a specific pixel in the LCD liquid crystal layer, the twisted nematic liquid crystal straightens. At that pixel location, the polarization state of the incident light does not change and cannot pass through the subsequent P-beam polarizer; therefore, the incident light at that pixel location cannot illuminate the phase-type SLM. When no voltage is applied to a specific pixel in the LCD liquid crystal layer, the nematic liquid crystal remains twisted. At that pixel location, the polarization state of the incident light changes from S-beam to P-beam, passing through the P-beam polarizer. Therefore, the incident light at that pixel location illuminates the phase-type SLM, and the SLM achieves phase modulation of that region. Therefore, by applying voltage to different pixel locations in the LCD liquid crystal layer, the beam incident on the corresponding position of the phase-type SLM can be controlled to turn off, thereby controlling the opening and closing of the beam at different positions on the exposure plane.

[0181] The above embodiments describe a method for fabricating a volume holographic optical element from the perspective of process flow. The following embodiments describe a device for fabricating a volume holographic optical element from the perspective of virtual module or virtual unit. For details, please refer to the following embodiments.

[0182] This application provides an apparatus for fabricating volume holographic optical elements. Specifically... Figure 11 This is a schematic diagram of a volume holographic optical element fabrication apparatus provided in an embodiment of this application. Figure 11 As shown, the device includes:

[0183] The partitioning module 111 is used to divide the refractive index modulation distribution map corresponding to the target optical element to be prepared into at least one hierarchical map according to the refractive index modulation level, and each hierarchical map has the same refractive index modulation level.

[0184] The module 112 is used to fill the exposure mask sub-map with the opening time corresponding to each grade map according to the refractive index modulation level, so as to obtain the target exposure mask sub-map within one exposure cycle.

[0185] The control module 113 is used to control the spatial light modulator (SLM) and the filtering system to modulate the incident light during the exposure cycle according to the exposure mask sub-map in order to obtain the target optical element.

[0186] In one possible implementation, the control module 113 is specifically used for:

[0187] The loading phase modulation diagram is determined based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element; the preset carrier phase diagram satisfies the preset conditions;

[0188] Based on the target exposure mask sub-map and the loaded phase modulation map, the exposure sub-map within the exposure cycle is determined;

[0189] During the exposure cycle, the phase-controlled SLM is used to load the exposure sub-map, and the incident light is modulated by a filtering system to obtain the target optical element.

[0190] In one possible implementation, the determining module 112 is specifically used for:

[0191] The loading phase modulation diagram is determined based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element; the preset carrier phase diagram satisfies the preset conditions;

[0192] Each hierarchical map is logically ANDed with the loaded phase modulation map to obtain at least one target hierarchical map.

[0193] The target grading map is filled into the exposure mask sub-map according to the on-time corresponding to the refractive index modulation level, so as to obtain the target exposure mask sub-map within one exposure cycle.

[0194] In one possible implementation, the control module 113 is specifically used for:

[0195] During the exposure cycle, the phase-controlled SLM loads the target exposure mask sub-map, and the incident light is modulated by the filtering system to obtain the target optical element.

[0196] In one possible implementation, the control module 113 is specifically used for:

[0197] The loading phase modulation diagram is determined based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element; the preset carrier phase diagram satisfies the preset conditions;

[0198] During the exposure cycle, the amplitude-controlled SLM loads the target exposure mask sub-map, and the phase-controlled SLM loads the phase modulation map. Combined with the filtering system, the incident light is modulated to obtain the target optical element.

[0199] In one possible implementation, the preset conditions include: when the phase modulation map is loaded at the SLM input, the filtering system outputs a complete first positive image, and the first positive image has a complete phase modulation distribution.

[0200] In one possible implementation, the partitioning module 111 is also used for:

[0201] Obtain the diffraction efficiency distribution map required by the target optical element;

[0202] Based on the diffraction efficiency distribution map, the refractive index modulation distribution map corresponding to the target optical element is determined.

[0203] In one possible implementation, the determining module 112 is further configured to:

[0204] Obtain the preset correlation between pulse width modulation ratio and refractive index modulation degree; pulse width modulation ratio is the ratio of on-time to exposure period; preset correlation is obtained by testing different optical elements under the same exposure conditions;

[0205] Based on the preset correlation, determine the activation time corresponding to the refractive index modulation level.

[0206] The volume holographic optical element fabrication apparatus provided in this application is applicable to the above-described method embodiments, and will not be described again here.

[0207] This application provides an electronic device. Figure 12 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application, such as... Figure 12As shown, the electronic device includes a processor 121 and a memory 122. The processor 121 and the memory 122 are connected, for example, via a bus 123. Optionally, the electronic device may also include a transceiver 124. It should be noted that in practical applications, the transceiver 124 is not limited to one, and the structure of this electronic device does not constitute a limitation on the embodiments of this application.

[0208] Processor 121 may be a central processing unit (CPU), a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. It may implement or execute the various exemplary logic blocks, modules, and circuits described in conjunction with the disclosure of this application. Processor 121 may also be a combination that implements computational functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc.

[0209] Bus 123 may include a pathway for transmitting information between the aforementioned components. Bus 123 may be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. Bus 123 may be divided into address bus, data bus, control bus, etc. For ease of representation, Figure 12 The symbol is represented by a single thick line, but this does not mean that there is only one bus 123 or one type of bus 123.

[0210] The memory 122 may be a read-only memory (ROM) or other type of static storage device capable of storing static information and instructions, random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited thereto.

[0211] The memory 122 is used to store application code that executes the solution of this application, and its execution is controlled by the processor 121. The processor 121 is used to execute the application code stored in the memory 122 to implement the content shown in the foregoing method embodiments.

[0212] This application also provides a computer-readable storage medium, which may include various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk. Specifically, the computer-readable storage medium stores program instructions, which are used to implement the methods in the above embodiments.

[0213] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the technical solution of the above method embodiments. Its implementation principle and technical effects are similar, and will not be repeated here.

[0214] This application also provides a volume holographic optical element, which is obtained by the method described in the foregoing method embodiments; the volume holographic optical element modulates incident light by forming a spatially varying refractive index distribution within the material.

[0215] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the claims.

[0216] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method of producing a volume holographic optical element, characterized by, The method includes: According to the refractive index modulation level, the refractive index modulation distribution map corresponding to the target optical element to be prepared is divided into at least one grade map, and each grade map has the same refractive index modulation level. Each of the graded maps is sequentially filled into the exposure mask sub-map according to the on-time corresponding to the refractive index modulation level, to obtain the target exposure mask sub-map within one exposure cycle. Based on the target exposure mask sub-map, the spatial light modulator (SLM) and filtering system are controlled to modulate the incident light during the exposure period to obtain the target optical element.

2. The method of claim 1, wherein, The control spatial light modulator (SLM) modulates the incident light during the exposure period to obtain the target optical element, comprising: Based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element, the loading phase modulation diagram is determined; the preset carrier phase diagram satisfies preset conditions. Based on the target exposure mask sub-map and the loaded phase modulation map, the exposure sub-map within the exposure cycle is determined; During the exposure period, the phase-controlled SLM is used to load the exposure sub-map, and the incident light is modulated by the filtering system to obtain the target optical element.

3. The method of claim 1, wherein, The step of sequentially filling each of the graded maps into the exposure mask sub-map according to the on-time corresponding to the refractive index modulation level to obtain the target exposure mask sub-map within one exposure cycle includes: Based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element, the loading phase modulation diagram is determined; the preset carrier phase diagram satisfies preset conditions. Each of the hierarchical maps is logically ANDed with the loaded phase modulation map to obtain at least one target hierarchical map; The target grading map is sequentially filled into the exposure mask sub-map according to the on-time corresponding to the refractive index modulation level to obtain the target exposure mask sub-map within one exposure cycle.

4. The method of claim 3, wherein, The control spatial light modulator (SLM) modulates the incident light during the exposure period to obtain the target optical element, comprising: During the exposure cycle, the phase-controlled SLM loads the target exposure mask sub-map, and the filtering system modulates the incident light to obtain the target optical element.

5. The method according to claim 1, characterized in that, The control spatial light modulator (SLM) modulates the incident light during the exposure period to obtain the target optical element, comprising: Based on the preset carrier phase diagram and the phase modulation diagram corresponding to the target optical element, the loading phase modulation diagram is determined; the preset carrier phase diagram satisfies preset conditions. During the exposure cycle, the amplitude-type SLM is controlled to load the target exposure mask sub-map, and the phase-type SLM is controlled to load the loading phase modulation map. Combined with the filtering system, the incident light is modulated to obtain the target optical element.

6. The method according to any one of claims 2-5, characterized in that, The preset conditions include: when the SLM inputs the loaded phase modulation map, the filtering system outputs a complete first positive image, and the first positive image has a complete phase modulation distribution.

7. The method according to any one of claims 1-5, characterized in that, The method further includes: Obtain the required diffraction efficiency distribution map of the target optical element; Based on the diffraction efficiency distribution map, the refractive index modulation distribution map corresponding to the target optical element is determined.

8. The method according to any one of claims 1-5, characterized in that, The method further includes: A preset correlation between the pulse width modulation ratio and the refractive index modulation degree is obtained; the pulse width modulation ratio is the ratio of the on-time to the exposure period; the preset correlation is obtained by testing different optical elements under the same exposure conditions. Based on the preset correlation, the activation time corresponding to the refractive index modulation level is determined.

9. A device for fabricating volume holographic optical elements, characterized in that, The device includes: The partitioning module is used to divide the refractive index modulation distribution map corresponding to the target optical element to be prepared into at least one hierarchical map according to the refractive index modulation level, and each hierarchical map has the same refractive index modulation level. The determination module is used to sequentially fill each of the graded images into the exposure mask sub-image according to the on-time corresponding to the refractive index modulation level, so as to obtain the target exposure mask sub-image within one exposure cycle. The control module is used to control the spatial light modulator (SLM) to modulate the incident light during the exposure period according to the exposure mask sub-map, so as to obtain the target optical element.

10. An electronic device, characterized in that, Includes a processor and a memory communicatively connected to the processor; The memory stores computer-executed instructions; The processor executes computer execution instructions stored in the memory to implement the method as described in any one of claims 1-8.

11. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions, which, when executed by a processor, are used to implement the method as described in any one of claims 1-8.

12. A computer program product, characterized in that, Includes a computer program that, when executed by a processor, implements the method as described in any one of claims 1-8.

13. A system for fabricating volume holographic optical elements, characterized in that, The system includes the electronic device as described in claim 10, and a spatial light modulator (SLM) and a filtering system that interact with the electronic device, wherein the SLM is located upstream of the filtering system; the electronic device controls the SLM to load different phase images at different times, and adjusts the incident light angle indicated by the filtering system according to the phase images to achieve modulation of the incident light to obtain the target optical element.

14. The system according to claim 13, characterized in that, The spatial light modulator includes at least one phase-type SLM.

15. The system according to claim 13, characterized in that, The spatial light modulator includes at least one phase-type SLM and at least one amplitude-type SLM.

16. A volume holographic optical element, characterized in that, The volume holographic optical element is obtained by the method described in any one of claims 1-8; the volume holographic optical element modulates the incident light by forming a spatially varying refractive index distribution within the material.

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