High-efficiency holographic optical element preparation device and preparation method thereof

Abstract

The invention discloses a high-efficiency holographic optical element preparation device and a preparation method thereof, and belongs to the technical field of holography. The preparation device comprises a light source module, a beam combining module, a polarization beam splitter, a reflection module, an exposure control module and a placement rack, the light source module comprises a red laser, a green laser and a blue laser. The electronic shutters respectively located in front of the red laser, the green laser and the blue laser can be controlled to work through the precise electronic timer, the exposure time sequence and duration of red laser, green laser and blue laser can be accurately and independently controlled, and sequence exposure of red, green and blue primary colors and sub-channel time sequence control are achieved. And finally, three-channel high diffraction efficiency and uniformity are realized, and the problems of complex light path, non-uniform efficiency and poor stability in the existing panchromatic HOE preparation are solved, so that a reliable and optimizable technical guarantee is provided for preparing a panchromatic holographic optical element with high three-color diffraction efficiency and good uniformity on the premise of simple process and low cost.

Description

Technical Field

[0001] This invention relates to the field of holographic technology, and in particular to a high-efficiency holographic optical element fabrication apparatus and its fabrication method. Background Technology

[0002] Holographic optical elements (HOEs), as optical devices, have significant application value in fields such as augmented reality (AR) displays, laser projection, and optical communication. The diffraction efficiency η of a holographic optical element is a crucial parameter describing its ability to convert incident light into diffracted light. It characterizes the ability of incident light to be converted into diffracted light and directly affects the energy utilization and display effect of the entire optical system. Currently, the main technical means to improve the diffraction efficiency of HOEs fall into two categories: one is to optimize the interference angle of the recording beam, and the other is to develop photopolymer materials with high refractive index modulation.

[0003] Regarding angle control, as shown in Chinese patent CN1249457C, high diffraction efficiency can be achieved by minimizing the angle between the parallel recording light and the converging recording light inside the photorefractive crystal. However, this method requires precise design of the crystal shape to achieve small-angle interference, resulting in complex processes, high costs, and difficulty in applying it to the preparation of panchromatic HOEs.

[0004] Regarding materials, as described in Chinese patent CN116003693A, photopolymer materials containing specific olefin monomers can achieve diffraction efficiencies exceeding 80% in the green light band. However, such materials are typically optimized for a single wavelength (e.g., green light) and fail to accommodate the red and blue light bands. Therefore, they have significant limitations in full-color display applications and cannot achieve a balanced improvement in the diffraction efficiency of the three primary colors.

[0005] The existing high-efficiency holographic optical element fabrication methods involve designing crystal shapes to control the angle of the two beams used for holographic interference, or synthesizing new photopolymer materials to provide higher refractive indices. These methods are complex and difficult to transfer to the fabrication of full-color holographic optical elements. Therefore, developing a simple, low-cost HOE fabrication device and method that can achieve full-color high diffraction efficiency and uniform efficiency across the three channels is crucial for overcoming current technological bottlenecks and promoting the large-scale application of holographic technology in fields such as AR displays. Summary of the Invention

[0006] This invention provides a high-efficiency holographic optical element fabrication device and its fabrication method, which can solve the problem that the existing holographic optical element fabrication devices are complex in process and difficult to transfer to the fabrication of full-color holographic optical elements.

[0007] A high-efficiency holographic optical element fabrication apparatus includes a light source module, a beam combiner module, a polarization beam splitter, a reflection module, an exposure control module, and a placement frame. The light source module includes a red laser, a green laser, and a blue laser, each providing a highly coherent laser beam of the corresponding color. The beam combiner module is located at the output end of the light source module and combines the three highly coherent laser beams output by the light source module into a white laser beam. The polarization beam splitter is located at the output end of the beam combiner module and splits the white laser beam into two beams with the same polarization state, which are then used as the first... The system includes a first signal light and a second signal light; the reflection module is located at the output end of the polarization beam splitter and is used to reflect the first signal light and the second signal light onto the photopolymer placed on the mounting frame; the exposure control module includes three electronic shutters and a precision electronic timer. The three electronic shutters are respectively located in the output optical paths of the red laser, green laser, and blue laser. The precision electronic timer is electrically connected to the three electronic shutters and is used to control the opening and closing sequence of the three electronic shutters, thereby controlling the exposure time of the red, green, and blue light.

[0008] Preferably, the beam combining module includes a first reflector, a dichroic mirror one, and a dichroic mirror two. The first reflector is disposed at the output end of the red laser, and the dichroic mirror one and the dichroic mirror two are disposed at the output ends of the green laser and the blue laser, respectively.

[0009] Preferably, the reflection module includes a second reflector and a third reflector, wherein the second reflector is used to reflect the first signal light onto the photopolymer, and the third reflector is used to reflect the second signal light onto the photopolymer.

[0010] Preferably, the three electronic shutters are a first electronic shutter, a second electronic shutter, and a third electronic shutter, wherein the first electronic shutter is located in the output optical path of the red laser, the second electronic shutter is located in the output optical path of the green laser, and the third electronic shutter is located in the output optical path of the blue laser.

[0011] Preferably, a first half-wave plate is disposed between the first electronic shutter and the beam combining module, a second half-wave plate is disposed between the second electronic shutter and the beam combining module, and a third half-wave plate is disposed between the third electronic shutter and the beam combining module.

[0012] Preferably, a first beam expander is provided on the first signal light output side of the polarization beam splitter, and a second beam expander is provided on the second signal light output side of the polarization beam splitter.

[0013] Preferably, the first beam expander includes a first lens and a second lens, the first lens being located between the polarization beam splitter and the second lens, and the second beam expander having the same structure as the first beam expander.

[0014] Preferably, a fourth half-wave plate is disposed between the polarization beam splitter and the first beam expander.

[0015] Preferably, a third lens is disposed between the second beam expander and the mounting frame.

[0016] A method for fabricating a high-efficiency holographic optical element, comprising: S1. Provide a photopolymer and fix it on a mounting rack; S2. Turn on the red laser, green laser and blue laser, and control the three electronic shutters to open alternately in a preset sequence through the exposure control module, so that the red high coherence laser beam, green high coherence laser beam and blue high coherence laser beam irradiate the photopolymer in a sequential exposure mode. S3. During the sequential exposure process, the exposure time of the green high coherence laser beam is used as a reference. The single exposure time of the red high coherence laser beam and the blue high coherence laser beam are adjusted according to the target diffraction efficiency. The optimal exposure time ratio of the red high coherence laser beam, the green high coherence laser beam, and the blue high coherence laser beam is determined through iterative optimization. S4. Based on the optimal exposure time ratio, control the precision electronic timer to execute multiple exposure cycles until the holographic recording of the photopolymer is completed. Each exposure cycle includes sequential exposure of a red high-coherence laser beam, a green high-coherence laser beam, and a blue high-coherence laser beam. S5. Post-process the exposed photopolymer to obtain a high-diffraction-efficiency holographic optical element.

[0017] The beneficial effects of this invention are: (1) In this invention, the electronic shutters located in front of the red, green and blue lasers can be controlled by a precision electronic timer. This allows for precise and independent control of the exposure sequence and duration of the red, green and blue lasers, enabling sequential exposure and channel-specific timing control of the three primary colors. This avoids the problems of excessively fast monomer polymerization and insufficient refractive index modulation caused by simultaneous exposure. Furthermore, it allows for flexible adjustment of the single-wavelength exposure time based on the photosensitivity differences of photopolymers to different wavelengths, ultimately achieving high diffraction efficiency and uniformity in the three channels. This solves the problems of complex optical paths, uneven efficiency, and poor stability in the preparation of existing full-color HOEs. Thus, under the premise of simple process and low cost, it provides a reliable and optimizable technical guarantee for the preparation of full-color holographic optical elements with high diffraction efficiency and good uniformity. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a high-efficiency holographic optical element fabrication apparatus according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a high-efficiency holographic optical element fabrication apparatus according to another embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. Light source module; 2. Beam combiner module; 3. Polarizing beam splitter; 4. Reflection module; 5. Exposure control module; 6. Placement frame; 7. First half-wave plate; 8. Second half-wave plate; 9. Third half-wave plate; 10. First beam expander assembly; 11. Second beam expander assembly; 12. Fourth half-wave plate; 13. Third lens; 14. Photopolymer; 101. Red laser; 102. Green laser; 103. Blue laser; 201. First reflector; 202. Dichroic mirror one; 203. Dichroic mirror two; 41. Second reflector; 42. Third reflector; 51. Precision electronic timer; 52. First electronic shutter; 53. Second electronic shutter; 54. Third electronic shutter; 1001. First lens; 1002. Second lens. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0021] Example 1: like Figure 1 As shown in the figure, an embodiment of the present invention provides a high-efficiency holographic optical element fabrication device, including a light source module 1, a beam combiner module 2, a polarization beam splitter 3, a reflection module 4, an exposure control module 5, and a placement frame 6. The light source module 1 includes a red laser 101, a green laser 102, and a blue laser 103, which are used to provide highly coherent laser beams of corresponding colors, respectively. The beam combiner module 2 is located at the output end of the light source module 1 and is used to combine the three highly coherent laser beams output by the light source module 1 into a white laser. The polarization beam splitter 3 is located at the output end of the beam combiner module 2 and is used to split the white laser into two paths with the same polarization state. The light beams are used as the first signal light and the second signal light, respectively. The reflection module 4 is set at the output end of the polarization beam splitter 3 to reflect the first signal light and the second signal light onto the photopolymer 14 placed on the placement frame 6. The exposure control module 5 includes three electronic shutters and a precision electronic timer 51. The three electronic shutters are respectively set in the output light paths of the red laser 101, the green laser 102 and the blue laser 103. The precision electronic timer 51 is electrically connected to the three electronic shutters to control the opening and closing sequence of the three electronic shutters, thereby controlling the exposure time of the red light, green light and blue light.

[0022] In the technical solution of this invention, the light source module 1 uses a red laser 101, a green laser 102, and a blue laser 103 to provide a precise wavelength and stable light intensity foundation for panchromatic holographic interference, avoiding light intensity loss and wavelength deviation caused by the splitting of a single white light source. The beam combining module 2 merges the three laser beams into a white laser, realizing multi-wavelength optical path integration, simplifying the complex structure of traditional panchromatic preparation which requires multiple sets of interference optical paths, while ensuring the overlap of the three primary color spots to improve panchromatic consistency. The polarization beam splitter 3 splits the white light into two signal lights with the same polarization state by amplitude splitting, which not only satisfies the polarization conditions of interference but also precisely controls the intensity ratio of the two light lights, ensuring the contrast of interference fringes and recording quality. The reflection module 4 guides the interference light through a precise optical path to control the incident angle of the interference light to match the requirements of holographic recording, while shortening the optical path length to reduce light intensity attenuation and vibration interference. To mitigate interference and improve device stability, a precision electronic timer 51 controls the operation of electronic shutters located in front of the red laser 101, green laser 102, and blue laser 103, respectively. This allows for precise and independent control of the exposure sequence and duration of the red, green, and blue lasers, enabling sequential exposure and channel-specific timing control of the three primary colors. This avoids the problems of excessively rapid monomer polymerization and insufficient refractive index modulation caused by simultaneous exposure, while also allowing for flexible adjustment of the single-wavelength exposure time based on the differences in photosensitivity of photopolymers to different wavelengths. Ultimately, this achieves high diffraction efficiency and uniformity across the three channels, solving the problems of complex optical paths, uneven efficiency, and poor stability in existing full-color HOE fabrication. Thus, it provides a reliable and optimizable technical guarantee for fabricating full-color holographic optical elements with high diffraction efficiency and good uniformity under the premise of simple process and low cost.

[0023] Specifically, there are currently two technical routes for preparing full-color HOEs: simultaneous exposure and sequential exposure. Simultaneous exposure involves irradiating the holographic material with RGB lasers simultaneously within the same time interval, where the exposure dose for a single wavelength is controlled by the exposure time and laser intensity. However, simultaneous exposure has a high power density, which can lead to accelerated monomer polymerization and rapid termination of the polymerization reaction, failing to achieve the highest refractive index modulation and thus affecting the peak diffraction efficiency of the full-color HOE. Furthermore, simultaneous exposure cannot individually adjust the exposure time of a single-color channel, and the power of a single-mode laser is generally not adjustable. This results in different peak powers for different colors, leading to uneven diffraction efficiency across the three channels of the full-color HOE, which cannot be adjusted. Therefore, sequential exposure is used for recording. Sequential exposure irradiates the photopolymer 14 with only one wavelength of light within a single time interval. This ensures an appropriate monomer polymerization rate and allows for separate control of the exposure time ratio for each color, providing room for optimization of the uniformity of diffraction efficiency across the RGB three channels.

[0024] Among them, the red laser 101, the green laser 102 and the blue laser 103 are all single-longitudinal-mode lasers with center wavelengths of 639nm, 532nm and 473nm, respectively. The photopolymer 14 is used to receive the first signal light and the second signal light after beam expansion and modulation, and to record interference fringes to form a holographic optical element.

[0025] The three electronic shutters are the first electronic shutter 52, the second electronic shutter 53, and the third electronic shutter 54. The first electronic shutter 52 is located in the output optical path of the red laser 101, the second electronic shutter 53 is located in the output optical path of the green laser 102, and the third electronic shutter 54 is located in the output optical path of the blue laser 103.

[0026] like Figure 1 As shown, the beam combining module 2 includes a first reflector 201, a dichroic mirror 1 202, and a dichroic mirror 203. The first reflector 201 is disposed at the output end of the red laser 101, and the dichroic mirror 1 202 and the dichroic mirror 203 are disposed at the output ends of the green laser 102 and the blue laser 103, respectively.

[0027] Specifically, the beam combining module 2 adopts a combination structure of first reflector 201 + dichroic mirror 1 202 + dichroic mirror 2 203, which has the advantages of precise, efficient and low loss three-laser beam combining. Among them, the first reflector 201 can precisely change the propagation direction of the laser output by the red laser 101, so that it is adapted to the optical path of the green and blue light, laying the directional foundation for the subsequent fusion of the three beams. Dichroic mirror 1 202 and dichroic mirror 2 203 correspond to the output ends of green laser 102 and blue laser 103, respectively. With the characteristics of high transmission at specific wavelengths and high reflection at other wavelengths, dichroic mirrors can achieve precise sequential fusion of green, blue and red light without the introduction of additional filters. This ensures that the three laser beams of red, green and blue completely overlap after beam combining, avoiding the color splicing marks caused by beam offset. It also maximizes the preservation of the light intensity of each wavelength. Compared with complex prism beam combining or fiber beam combining schemes, this structure does not require high-precision prism grinding or fiber coupling calibration. This not only reduces the processing and debugging difficulty of the beam combining module, but also improves the optical path stability during long-term use, ensuring that the subsequent polarization beam splitting and interference recording stages can obtain white laser with sufficient light intensity, pure wavelength and uniform beam.

[0028] like Figure 1 As shown, the reflection module 4 includes a second reflector 41 and a third reflector 42. The second reflector 41 is used to reflect the first signal light onto one side of the photopolymer 14, and the third reflector 42 is used to reflect the second signal light onto the other side of the photopolymer 14, so that the light spots of the two beams of light overlap at the same position of the HOE, which can produce a high diffraction efficiency holographic optical element.

[0029] Specifically, the reflection module 4 employs a second reflector 41 and a third reflector 42 to guide the two signal beams to the two sides of the photopolymer 14, providing key optical path support for the fabrication of high diffraction efficiency holographic optical elements. This design allows the first and second signal beams to be incident from both sides of the photopolymer, forming layered phase interference fringes that are roughly parallel to the surface inside the material. This fringe structure can significantly reduce light scattering loss, directly laying the structural foundation for high diffraction efficiency. At the same time, the incident method from both sides can flexibly control the interference angle of the two beams inside the material by adjusting the angle of the reflectors. This can match the photosensitive characteristics of the photopolymer to form high-contrast fringes, while avoiding the problems that may occur when incident from one side, ensuring the integrity and clarity of the holographic record.

[0030] like Figure 1 As shown, a first half-wave plate 7 is disposed between the first electronic shutter 52 and the beam combining module 2, a second half-wave plate 8 is disposed between the second electronic shutter 53 and the beam combining module 2, and a third half-wave plate 9 is disposed between the third electronic shutter 54 and the beam combining module 2.

[0031] Specifically, a first half-wave plate 7, a second half-wave plate 8, and a third half-wave plate 9 are correspondingly set between each electronic shutter and beam combining module. This has the significant advantages of precisely controlling the polarization state and light intensity of a single wavelength and ensuring the quality of panchromatic interference. The half-wave plate can change the polarization direction of the corresponding wavelength laser (red light, green light, and blue light) by rotating its angle. On the one hand, it can work with the subsequent polarization beam splitter 3 to precisely adjust the beam splitting ratio of each wavelength, ensuring that the power density of the two signal lights illuminating the photopolymer 14 is consistent, thereby achieving the strongest interference effect (avoiding interference caused by uneven power of a single wavelength). (Decreased fringe contrast); On the other hand, to address the potential differences in the initial polarization states of the red, green, and blue lasers, the corresponding half-wave plates can be independently adjusted to ensure that the polarization states of the three primary colors are uniform before beam combining, reducing the interference of chaotic polarization states on the interference recording after beam combining. Combined with the exposure control module 5's control over the exposure time, this further provides dual protection for the high diffraction efficiency and uniformity of the panchromatic HOE three-channel system at the polarization and intensity levels. Moreover, the feature of independent adjustment of a single wavelength allows the device to adapt to lasers with different polarization characteristics, improving the flexibility and compatibility of the optical path.

[0032] like Figure 1 As shown, a first beam expander 10 is provided on the first signal light output side of the polarization beam splitter 3, and a second beam expander 11 is provided on the second signal light output side of the polarization beam splitter 3. The first beam expander 10 includes a first lens 1001 and a second lens 1002. The first lens 1001 is located between the polarization beam splitter 3 and the second lens 1002. The second beam expander 11 has the same structure as the first beam expander 10.

[0033] Specifically, a first beam expander 10 and a second beam expander 11 with identical structures, each containing a first lens 1001 and a second lens 1002, are respectively set on the two signal light output sides of the polarization beam splitter 3. This has significant advantages in ensuring the uniformity of the interference spot and improving the effective aperture and fabrication consistency of the holographic element. On the one hand, by combining the first lens 1001 and the second lens 1002, the two signal beams split by the polarization beam splitter can be synchronously and uniformly expanded, effectively increasing the laser spot size and thus improving the effective aperture of the final holographic optical element. This meets the application requirements of large-aperture HOEs in AR displays, laser projections, and other scenarios, while avoiding the spot edge distortion problem that is easily caused by single-lens beam expansion. This ensures that the beam power density is uniform after beam expansion, laying the foundation for the formation of clear and uniform interference fringes on the surface of the photopolymer 14. On the other hand, the two beam expansion components adopt the same structural design, which can ensure that the beam expansion factor, spot shape, and light intensity distribution of the two signal beams are highly consistent. This avoids the problem of asymmetrical interference fringes and decreased local diffraction efficiency caused by the difference in beam expansion between the two beams, further improving the uniformity and repeatability of the three-channel diffraction efficiency of the panchromatic HOE. Moreover, the component has a simple structure and is easy to debug. It can achieve a stable beam expansion effect without complex optical calibration, taking into account both performance and process practicality.

[0034] like Figure 1 As shown, a fourth half-wave plate 12 is disposed between the polarization beam splitter 3 and the first beam expander 10, and a third lens 13 is disposed between the second beam expander 11 and the mounting frame 6.

[0035] Specifically, a fourth half-wave plate 12 is disposed between the polarization beam splitter 3 and the first beam expander 10, while a third lens 13 is disposed between the second beam expander 11 and the mounting frame 6. These two elements work together to provide a dual guarantee of precise polarization state matching and beam shape optimization for holographic recording. The fourth half-wave plate 12 can finely adjust the polarization state of the first signal light split by the polarization beam splitter 3, ensuring that it is completely consistent with the polarization state of the second signal light, thus completely eliminating the problem of reduced interference efficiency caused by slight differences in polarization state after beam splitting, and providing key polarization conditions for forming high-contrast interference fringes. The third lens 13 can separate the second signal light after it has been expanded by the second beam expander 11. The signal light is precisely modulated into a spherical wave, which forms an interference field with the first signal light on the surface of the photopolymer 14 that meets the requirements of holographic recording. This effectively improves the recording quality of the holographic fringes and the accuracy of the subsequent diffraction direction. At the same time, the lens can further optimize the beam focusing effect and avoid the problem of local underexposure caused by the energy dispersion at the beam edge after beam expansion. The combination of the two not only solves the problem of consistency of interference polarization conditions, but also realizes the targeted control of beam shape, providing important support for the realization of high diffraction efficiency and stable optical performance of panchromatic HOE. Moreover, the structure is simple and easy to integrate, and the function can be achieved without additional complex optical paths, taking into account both practicality and performance advantages.

[0036] A method for fabricating a high-efficiency holographic optical element, comprising: S1. Provide photopolymer 14 and fix it on the placement rack 6; S2. Turn on the red laser 101, green laser 102 and blue laser 103, and control the three electronic shutters to open alternately in a preset sequence through the exposure control module 5, so that the red high coherence laser beam, the green high coherence laser beam and the blue high coherence laser beam irradiate the photopolymer 14 in a sequential exposure manner. S3. During the sequential exposure process, the exposure time of the green and red high coherence laser beams is used as a reference. The single exposure time of the red and blue high coherence laser beams is adjusted according to the target diffraction efficiency. The optimal exposure time ratio of the red, green, and blue high coherence laser beams is determined through iterative optimization. S4. Based on the optimal exposure time ratio, control the precision electronic timer 51 to execute multiple exposure cycles until the holographic recording of the photopolymer 14 is completed. Each exposure cycle includes the sequential exposure of a red high-coherence laser beam, a green high-coherence laser beam, and a blue high-coherence laser beam. S5. Post-process the exposed photopolymer 14 to obtain a high-diffraction-efficiency holographic optical element.

[0037] In this embodiment, the high-efficiency holographic optical element fabrication method, through a process design of precise fixation, sequential exposure, iterative optimization, cyclic execution, and post-processing, possesses significant advantages in achieving high diffraction efficiency and uniformity across all colors, simplifying operations, and ensuring fabrication stability. First, the photopolymer 14 is fixed on the placement frame 6 to ensure material stability during exposure, avoiding holographic fringe distortion due to displacement. Second, sequential exposure with alternating three-color lasers avoids the problems of excessively rapid monomer polymerization and insufficient refractive index modulation caused by power superposition during simultaneous exposure, laying the foundation for high diffraction efficiency. Crucially, the single exposure time of red and blue light is iteratively optimized based on the green light exposure time, enabling targeted optimization. By adapting to the varying photosensitivity of photopolymers to different wavelengths (e.g., low sensitivity to red light), the optimal exposure ratio is precisely determined, effectively solving the problem of uneven efficiency across the three channels of panchromatic HOE. This ultimately achieves a balanced effect with red, green, and blue diffraction efficiencies of 84.4%, 69.2%, and 66.5%, respectively. Simultaneously, multiple exposure cycles are executed using a precision electronic timer 51, ensuring that exposure parameters can be repeatedly called, thus improving the consistency of different batches of products. Finally, combined with post-processing, the holographic recording quality is further consolidated. The overall method does not require complex crystal processing or the synthesis of novel materials; high-performance panchromatic HOE fabrication can be achieved solely through timing and parameter optimization, balancing process simplicity, cost control, and potential for large-scale application.

[0038] Specifically, to obtain a panchromatic HOE with high diffraction efficiency and uniformity, further optimization of the RGB three-color exposure recording process is needed. The overall optimization approach is to find an initial reference point, and then iteratively optimize the exposure time by changing the exposure time based on this reference point. Considering the photosensitivity of the holographic material, the exposure doses for red, green, and blue are 150 mJ / cm². 2 30mJ / cm 2 and 30mJ / cm 2 Holographic materials exhibit similar photosensitivity to blue and green light, while their sensitivity to red light is approximately one-fifth that of blue and green light. Therefore, to ensure photosensitivity to red light, the relative power density of red light needs to be increased. This principle must be considered when selecting a single-mode laser for exposure. The power densities of the three colors can be fine-tuned by using attenuators. The power densities for red, green, and blue exposures are set to 4.1 mW / cm². 2 0.9mW / cm 2 and 0.5mW / cm 2 Next, the initial single exposure time is set. The number of exposures for each type of light is consistent in the sequential exposure. Based on the exposure dose value, the total exposure time for each type of light is determined, from which the relative proportions of red, green, and blue exposure times can be calculated. Since the human eye is most sensitive to green light, and the wavelength of green light lies between the red and blue wavelengths, the exposure time of green light is selected as the benchmark. Based on experience in exposure experiments, the initial single exposure time for green light is set to 600 ms. The exposure time for each of red, green, and blue light is recorded as one cycle, thus determining that a total of 55 exposure cycles are required. The initial single exposure times for red and blue light are set to 600 ms and 750 ms, respectively. The above time-series exposure process is implemented using three shutters (Daheng Optoelectronics GCI-7101M) and a precision electronic timer 51 (Daheng Optoelectronics GCI-73M). The shutter response time is within 1 ms and can be ignored. The total exposure time for the panchromatic holographic lens is approximately 2.5 minutes. Including laser stabilization and post-processing, the recording time for one panchromatic HOE is approximately 20 minutes. We obtained the diffraction peaks and diffraction efficiencies of panchromatic HOEs at different exposure times, as shown in Table 1.

[0039] Table 1. Peak diffraction efficiency of panchromatic HOE at different exposure times.

[0040] In Experiment 1, the peak diffraction efficiency of blue light was close to 100%, while that of red light was almost zero. In Experiment 2, increasing the exposure time of red light improved its peak diffraction efficiency; however, the peak diffraction efficiency of blue light did not change significantly. Therefore, in Experiment 3, the exposure time of blue light was reduced. In Experiment 3, the peak diffraction efficiency of red light was close to 100%, while that of blue light was almost zero, and the peak diffraction efficiency of green light remained relatively stable at 30% to 40%. In Experiment 4, we reduced the exposure time of red light and increased the exposure time of blue light, obtaining satisfactory diffraction efficiency values. The diffraction efficiencies of red, green, and blue light for a single panchromatic HOE were 84.4%, 69.2%, and 66.5%, respectively, with an average peak diffraction efficiency of 73.4% and a standard deviation of 7.9%.

[0041] Compared with existing technologies, the preparation method proposed in this patent achieves the preparation of high diffraction efficiency full-color holographic optical elements by optimizing the exposure time of each of the three colors (RGB) through multiple experimental iterations. The average peak diffraction efficiency of RGB reaches 73.4%. This method can be achieved through electronic shutter control, which is low in cost and simple and stable in process.

[0042] Example 2: like Figure 2 As shown, the reflection module 4 includes a second reflector 41 and a third reflector 42. The second reflector 41 is used to reflect the first signal light onto one side of the photopolymer 14, and the third reflector 42 is used to reflect the second signal light onto the same side of the photopolymer 14, which can produce a transmissive holographic optical element.

[0043] Specifically, the reflection module 4 uses a second reflector 41 and a third reflector 42 to guide the two signal beams to the same surface of the photopolymer 14, providing an efficient and flexible optical path solution for the fabrication of transmissive holographic optical elements. This allows the two signal beams to be incident from the same side and form layered phase interference fringes that are approximately perpendicular to the surface inside the material. This structure allows the incident light and the diffracted light to be located on opposite sides of the material, which meets the core requirement of light transmission and propagation in transmissive optical elements and is suitable for scenarios such as optical communication and laser projection that require direct light transmission. At the same time, the same-surface incident method can precisely control the interference angle of the two beams by adjusting the angle of the reflector. This can avoid the material thickness limitation problem that may be caused by incident from both sides and flexibly adjust the fringe spacing to match the diffraction requirements of different wavelengths, which is especially suitable for panchromatic applications that require wide-band transmission.

[0044] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A high-efficiency holographic optical element fabrication apparatus, characterized in that, It includes a light source module (1), a beam combiner module (2), a polarization beam splitter (3), a reflection module (4), an exposure control module (5), and a mounting frame (6); The light source module (1) includes a red laser (101), a green laser (102) and a blue laser (103), which are used to provide highly coherent laser beams of the corresponding colors. The beam combining module (2) is located at the output end of the light source module (1) and is used to combine the three highly coherent laser beams output by the light source module (1) into a white laser. The polarization beam splitter (3) is located at the output end of the beam combining module (2) and is used to split the white laser into two beams with the same polarization state, which are used as the first signal light and the second signal light, respectively. The reflection module (4) is disposed at the output end of the polarization beam splitter (3) and is used to reflect the first signal light and the second signal light onto the photopolymer (14) placed on the placement frame (6), respectively. The exposure control module (5) includes three electronic shutters and a precision electronic timer (51). The three electronic shutters are respectively set in the output optical paths of the red laser (101), the green laser (102) and the blue laser (103). The precision electronic timer (51) is electrically connected to the three electronic shutters and is used to control the opening and closing sequence of the three electronic shutters, thereby controlling the exposure time of red light, green light and blue light.

2. The high-efficiency holographic optical element producing apparatus according to claim 1, wherein The beam combining module (2) includes a first reflector (201), a dichroic mirror one (202) and a dichroic mirror two (203). The first reflector (201) is disposed at the output end of the red laser (101), and the dichroic mirror one (202) and the dichroic mirror two (203) are disposed at the output ends of the green laser (102) and the blue laser (103).

3. The high efficiency holographic optical element producing apparatus according to claim 1, wherein The reflection module (4) includes a second reflector (41) and a third reflector (42). The second reflector (41) is used to reflect the first signal light onto the photopolymer (14), and the third reflector (42) is used to reflect the second signal light onto the photopolymer (14).

4. The high efficiency holographic optical element producing apparatus according to claim 1, wherein The three electronic shutters are a first electronic shutter (52), a second electronic shutter (53), and a third electronic shutter (54). The first electronic shutter (52) is located in the output optical path of the red laser (101), the second electronic shutter (53) is located in the output optical path of the green laser (102), and the third electronic shutter (54) is located in the output optical path of the blue laser (103).

5. The high efficiency holographic optical element producing apparatus according to claim 4, wherein A first half-wave plate (7) is provided between the first electronic shutter (52) and the beam combining module (2), a second half-wave plate (8) is provided between the second electronic shutter (53) and the beam combining module (2), and a third half-wave plate (9) is provided between the third electronic shutter (54) and the beam combining module (2).

6. The high efficiency holographic optical element producing apparatus according to claim 1, wherein The polarization beam splitter (3) has a first beam expander (10) on the first signal light output side and a second beam expander (11) on the second signal light output side.

7. The high-efficiency holographic optical element producing apparatus according to claim 6, wherein The first beam expander (10) includes a first lens (1001) and a second lens (1002). The first lens (1001) is located between the polarization beam splitter (3) and the second lens (1002). The second beam expander (11) has the same structure as the first beam expander (10).

8. The high efficiency holographic optical element producing apparatus according to claim 6, wherein A fourth half-wave plate (12) is provided between the polarization beam splitter (3) and the first beam expander (10).

9. The high-efficiency holographic optical element fabrication apparatus as described in claim 6, characterized in that, A third lens (13) is provided between the second beam expander (11) and the placement frame (6).

10. A method for fabricating a high-efficiency holographic optical element, using the high-efficiency holographic optical element fabrication apparatus as described in any one of claims 1-9, characterized in that, include: S1. Provide a photopolymer (14) and fix it on the mounting bracket (6); S2. Turn on the red laser (101), green laser (102) and blue laser (103), and control the three electronic shutters to open alternately in a preset sequence through the exposure control module (5), so that the red high coherence laser beam, the green high coherence laser beam and the blue high coherence laser beam irradiate the photopolymer (14) in a sequential exposure manner. S3. During the sequential exposure process, the exposure time of the green high coherence laser beam is used as a reference. The single exposure time of the red high coherence laser beam and the blue high coherence laser beam are adjusted according to the target diffraction efficiency. The optimal exposure time ratio of the red high coherence laser beam, the green high coherence laser beam, and the blue high coherence laser beam is determined through iterative optimization. S4. Based on the optimal exposure time ratio, control the precision electronic timer (51) to execute multiple exposure cycles until the holographic recording of the photopolymer (14) is completed, wherein each exposure cycle includes the sequential exposure of a red high coherence laser beam, a green high coherence laser beam, and a blue high coherence laser beam. S5. Post-process the exposed photopolymer (14) to obtain a high-diffraction-efficiency holographic optical element.

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