Multi-focal near-to-eye display holographic optical element and preparation method and device thereof

Abstract

The invention discloses a multi-focal near-to-eye display holographic optical element and a preparation method and device thereof. The element adopts a composite structure of a substrate, a multi-focal correction layer and a holographic recording layer, a holographic grating accurately matched with each optical partition of the correction layer is formed in the recording layer through a partition exposure technology, and multi-depth virtual image display and user refraction correction functions can be realized at the same time. The preparation device comprises a coherent light source, a beam splitter, a diffusion plate, a focal plane displacement system, a mask component and a master controller, and partition exposure is realized through cooperative control. The problem that traditional near-to-eye display cannot meet multi-focus display and refraction correction at the same time is solved, a user can clearly perceive fused multi-depth virtual information and a real environment without additionally wearing glasses, the visual comfort and experience are remarkably improved, and the method is suitable for AR / VR and other head-mounted display devices.

Description

Technical Field

[0001] The present invention belongs to the field of near-eye display and holographic optical technology, and specifically relates to a multi-focal near-eye display holographic optical element and a preparation method and device thereof, which is particularly suitable for user groups who need refractive correction (such as myopia and presbyopia). Background Art

[0002] As a vehicle for virtual reality (VR) and augmented reality (AR) technologies, near-eye displays (NEDs) hold broad application prospects in healthcare, communications, entertainment, education, manufacturing, and other fields. An ideal NED system must deliver high-quality, multifocal visual output in a compact design while also addressing the varying vision needs of users, particularly those with refractive errors such as myopia and presbyopia.

[0003] Holographic display technology is based on the principles of light interference and diffraction. It records specific wavefronts emitted by an object as interference fringes and, under certain conditions, reproduces them to create a three-dimensional image of the original object. Holographic displays retain the full amplitude and phase information of the object lightwave, allowing viewers to observe the holographic three-dimensional image with the exact same visual experience as the original object. Holographic displays encode and reproduce wavefronts by modulating light through diffractive optical elements, allowing for pixel-level focal plane control, aberration correction, and visual correction.

[0004] A holographic optical element (HOE) is a diffraction-based optical element that can be produced through analog holographic exposure or digital holographic printing and exhibits a certain degree of wavelength selectivity. Because HOEs can be recorded on a thin plate, they are often used as light combiners in AR near-eye displays to achieve a compact form factor. Currently, holographic near-eye display systems lack diopter adaptation or clip-on lens adaptation, posing a new challenge in achieving diopter adaptation for myopic and presbyopic individuals within a compact design.

[0005] Patent document CN111308877A discloses a processing device for holographic optical elements. The system uses a spatial light modulator array to provide incident light, realizing one-step processing of non-periodic holographic optical elements. Patent document CN114397720A proposes a multi-focal lens manufacturing method and near-eye display device based on angle-multiplexed grating technology. The core is to form a grating element (such as HOE / DOE) with multiple focal points (diopters) by exposing multiple groups of optical paths (each group containing object light and reference light) at different tilt angles on the same grating recording material. When the lens rotates, the change in tilt angle triggers different focal points, realizing dynamic adjustment of diopter. However, the holographic optical elements prepared by the above scheme are either only suitable for non-myopic and presbyopic people, and people with special diopters need to wear additional glasses or clips when using them, or they only ensure the clarity of the holographic display content, and cannot ensure that the virtual image and reality are clear at the same time, and it is inconvenient to wear multiple pairs of glasses at the same time.

[0006] Therefore, there is an urgent need for a holographic optical element preparation technology and device that can directly integrate multifocal correction functions, support multi-depth image display, and is suitable for people with refractive errors, so as to promote the popularization and application of near-eye display technology among a wider user group. Summary of the Invention

[0007] The present invention aims to provide a device and method for fabricating a multifocal near-eye display holographic optical element (HOE) combiner. This approach addresses the existing near-eye display technology's difficulty in displaying virtual images at multiple depths on a single optical element, and its inability to directly adapt to the visual needs of myopic / presbyopic users. By utilizing a zoned dynamic exposure technique, the present invention combines the optical properties of multifocal corrective lenses with the diffraction properties of a holographic element, enabling the recording of multiple holographic grating structures corresponding to different depths on a single HOE.

[0008] The technical solutions of the present invention are as follows:

[0009] In one aspect, the present invention provides a multi-focal near-eye display holographic optical element, which is characterized by comprising:

[0010] substrate;

[0011] a multifocal correction layer disposed on a surface of the substrate, the multifocal correction layer comprising at least two optical partitions with different refractive powers;

[0012] a holographic recording layer disposed on the other surface of the substrate, wherein a plurality of spatially partitioned holographic grating structures are recorded in the holographic recording layer, wherein each partitioned holographic grating structure corresponds one-to-one to a different optical partition of the multi-focus correction layer and is optically matched;

[0013] Each segmented holographic grating structure is configured to diffract and generate a virtual image display plane matching the refractive power of the corresponding optical segment when illuminated by the reproduced illumination light.

[0014] Furthermore, the multifocal correction layer is a progressive multifocal lens, a bifocal lens or a trifocal lens; and the material of the holographic recording layer is a photopolymer, a silver halide emulsion or a dichromate gelatin.

[0015] Furthermore, each partitioned holographic grating structure has a different spatial frequency and orientation to match the refractive properties of the corresponding optical partition.

[0016] Secondly, the present invention also provides a method for preparing the multi-focal near-eye display holographic optical element, which is characterized in that it includes the following steps:

[0017] providing a substrate;

[0018] forming a multifocal correction layer on the first surface of the substrate, wherein the multifocal correction layer comprises at least two optical partitions with different refractive powers;

[0019] forming a holographic recording layer on the second surface of the substrate;

[0020] Recording a plurality of spatially partitioned holographic grating structures in the holographic recording layer by a partitioned exposure method, so that each partitioned holographic grating structure is optically matched with a different optical partition of the multi-focus correction layer;

[0021] The partition exposure includes:

[0022] For each optical partition, adjusting the object focal plane position to match the refractive characteristics of the optical partition;

[0023] Selecting a mask pattern corresponding to the optical partition for blocking;

[0024] The exposure time is controlled to record the corresponding holographic grating structure in the partition.

[0025] Thirdly, the present invention also provides a device for preparing the multi-focal near-eye display holographic optical element, which is characterized by comprising:

[0026] Coherent light sources for generating laser light;

[0027] An electronic shutter and an attenuator are sequentially arranged on the outgoing light path of the coherent light source to control the on / off and power of the laser;

[0028] A beam expansion and collimation system, used for converting the coherent light output by the coherent light source into a wide beam of parallel light;

[0029] A beam splitter, used for splitting the parallel light into a reference beam and an object beam;

[0030] a diffuser plate, disposed in the optical path of the object beam and configured to convert the object beam into scattered light;

[0031] a focal plane displacement system, arranged in the object light path after the diffuser plate, for controlling the relative distance between the focal plane of the object light formed after the diffuser plate and the recording surface of the holographic dry plate;

[0032] a pair of mask components, respectively disposed in the reference light path and the object light path, for performing synchronous patterned shielding on the two light beams;

[0033] a multifocal corrective lens, composited with the holographic dry plate on a common substrate, and located in a reference optical path between the second mask unit and the holographic dry plate, so that a reference beam passing through different optical partitions thereof generates wavefronts carrying different refractive information;

[0034] a holographic dry plate, whose object light incident side and reference light incident side respectively receive the object light beam and the reference light beam after being patterned and shielded by the mask component, and are used to record the holographic grating structure formed by the interference of the two light beams;

[0035] A master controller is electrically connected to the electronic shutter, the focal plane shift system, and the mask component, and is used to control the timing of shutter opening and closing, focal plane shift, and mask pattern switching, so as to sequentially record holographic structures that match the multiple optical correction areas of the multifocal corrective lens on different spatial partitions of the holographic dry plate.

[0036] Furthermore, the mask component includes:

[0037] A mask template is a physical template having a light-transmitting pattern corresponding to the optical partitions of the multifocal corrective lens;

[0038] The rotary servo has an output shaft connected to the mask template and is used to drive the mask template to rotate to switch the shielding area.

[0039] Furthermore, the mask component is an electrically controlled mask plate, which adopts a transmissive spatial light modulator (SLM) or a digital micromirror device (DMD) and dynamically generates and switches the shielding pattern by receiving the electrical signal of the master controller.

[0040] Furthermore, the focal plane displacement system is a mechanical displacement system, comprising:

[0041] First lens;

[0042] A spatial displacement platform, used for carrying and driving the first lens to move along the optical axis;

[0043] a motor, mechanically connected to the spatial displacement platform;

[0044] a motor driver, electrically connected to the motor and receiving a control signal from the master controller;

[0045] Wherein, the spatial displacement platform is equipped with a built-in grating ruler or encoder for providing a position feedback signal to the master controller.

[0046] Furthermore, the focal plane displacement system is a zoom lens system, comprising:

[0047] Variable focus lenses, which are liquid lenses based on dielectric wetting, liquid crystal or pressure-adjustable technologies;

[0048] A driving module is mechanically or electrically connected to the zoom lens and is used to change the optical focal length thereof. The driving module is electrically connected to the master controller.

[0049] Furthermore, the multifocal corrective lens is a progressive lens, a bifocal lens or a trifocal lens.

[0050] Compared with the prior art, the present invention has the following obvious outstanding substantial features and significant advantages:

[0051] The device of the present invention adopts partitioned dynamic exposure technology and a dual-mode mask system to achieve accurate recording of multi-focal holographic structures. The core is to collaboratively control the electronic shutter, mask system and focal plane displacement system through the main controller to perform partitioned exposure on the holographic dry plate, and each partition strictly matches the different optical areas of the multifocal corrective lens (such as the hyperopia area or the myopia area). A rotating mask module can be optionally equipped to switch the physical light shielding plate by rotating the servo, or the electrically controlled mask plate uses a spatial light modulator to dynamically generate the mask pattern, which significantly improves the preparation efficiency. For example, the rotating mask solution ensures that the exposure process is focused on a specific refractive correction area by accurately blocking non-target areas; the electrically controlled mask supports millisecond-level pattern updates and is suitable for large-scale production.

[0052] The present invention uses a focal plane displacement system and multifocal corrective lenses to ensure the clear imaging of virtual images at multiple depth layers and seamless integration with the real environment. The focal plane displacement system is composed of a fourth lens, a spatial displacement platform, a motor and a motor driver, or a flexible optical zoom method of a zoom lens is used to accurately control the position of the focal plane of the object light beam from the holographic dry plate, while the multifocal corrective lens serves as the core component of the reference light path and penetrates its specific area (such as the presbyopia correction area of ​​a progressive lens) during exposure. The final HOE light combiner can be fitted with a multifocal corrective lens, and the near-eye virtual content and environmental background can be clearly observed at the same time without the need for additional glasses, effectively solving the visual conflict and wearing inconvenience problems of myopic aging people.

[0053] This invention introduces closed-loop control logic and a dynamic mask programming mechanism to enhance system stability and manufacturing flexibility. Closed-loop control utilizes feedback devices such as accelerometers or Hall sensors integrated into the master controller to monitor the motion of the displacement platform in real time, ensuring the system is completely still before exposure and avoiding image distortion caused by motion blur. Dynamic mask programming utilizes an electrically controlled mask (such as a transmissive spatial light modulator) to generate programmable patterns in real time, supporting millisecond-level regional mask switching and custom parameter configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic structural diagram of a device for preparing a holographic optical element light combiner for multi-focal near-eye display self-interference based on a mask rotation module provided in Example 1 of the present invention.

[0055] Figure 2 Schematic diagram of a mask pattern produced according to the partitioning of a multifocal corrective lens in a device for preparing a holographic optical element light combiner for multifocal near-eye display self-interference based on a mask rotation module provided in Example 1 of the present invention.

[0056] Figure 3 Schematic diagram of the multifocal correction lens partitioning of the device for preparing a holographic optical element light combiner for multifocal near-eye display self-interference based on a mask rotation module provided in Example 1 of the present invention.

[0057] Figure 4 This is a schematic structural diagram of a device for preparing a holographic optical element light combiner for multi-focal near-eye display self-interference based on an electrically controlled mask module provided in Example 2 of the present invention.

[0058] Figure 5 This is a schematic structural diagram of a device for preparing a holographic optical element light combiner for multi-focal near-eye display self-interference based on a zoom lens provided in Example 3 of the present invention.

[0059] Figure 6 This is a working timing diagram of a device for preparing a holographic optical element light combiner for multi-focal near-eye display self-interference based on a mask rotation module provided in Example 1 of the present invention.

[0060] Figure 7 This is a working timing diagram of a device for preparing a holographic optical element light combiner for multi-focal near-eye display self-interference based on an electrically controlled mask module provided in Example 2 of the present invention.

[0061] Figure 8 This is a working timing diagram of a device for preparing a holographic optical element light combiner for multi-focal near-eye display self-interference based on a zoom lens provided in Example 3 of the present invention.

[0062] Figure 9 This is a flowchart of a manufacturing apparatus for a holographic optical element light combiner for multi-focal near-eye display self-interference based on a mask module provided in Examples 1, 2 and 3 of the present invention.

[0063] In the figure: 140-coherent light source, 150-electronic shutter, 160-attenuator,

[0064] 170- beam expansion and collimation system: 171- second lens, 172- pinhole filter, 173- third lens;

[0065] 190-beam splitter,

[0066] 180-first reflector, 200-second reflector, 210-third reflector;

[0067] 220-mask template,

[0068] 230-rotary servo,

[0069] 240 - first focal plane displacement system: 241 - first lens, 242 - spatial moving platform, 243 - motor, 244 - motor driver;

[0070] 250-multifocal corrective lenses, 260-holographic dry plates;

[0071] 270- master controller;

[0072] 280-diffuser plate;

[0073] 290 - Second focal plane displacement system: 291 - Driving module, 292 - Zoom lens, 300 - Electronically controlled mask. DETAILED DESCRIPTION

[0074] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0075] The above solution is further described below with reference to specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0076] Example 1

[0077] This embodiment provides an embodiment of a device for preparing a holographic optical element for multi-focal near-eye display, such as Figure 1 As shown, it includes: a coherent light source 140, followed by an electronic shutter 150 controlled by a main controller 270, an attenuator 160, a beam expander and collimator system 170 composed of a second lens 171, a pinhole filter 172 and a third lens 173, a first reflector 180, a beam splitter 190, a second reflector 200, a third reflector 210, a mask template 220, a rotary servo 230, a diffuser 280, a first focal plane displacement system 240, a multifocal corrective lens 250, a holographic dry plate 260 and a main controller 270.

[0078] The coherent light source 140 is a visible light laser, used to generate pure, spectrally stable laser light. The laser can be a semiconductor laser, a gas laser, or a solid-state laser. The laser wavelength should be tailored to the specific needs. For color holography, lasers with different wavelengths corresponding to RGB should be used.

[0079] The electronic shutter 150 is connected to the master controller 270 and controls the opening and closing of the optical path. The master controller 270 controls the operating state of the electronic shutter 150 based on the operating status of the mask rotation servo 230 and the space mobile platform 242. When the rotation servo 230 and the space mobile platform 242 are operating, the master controller 280 controls the electronic shutter 150 to stop operating. When the rotation servo 230 and the space mobile platform 242 are stopped, the master controller 280 controls the electronic shutter 150 to operate. The electronic shutter 150 can also be a mechanical shutter or a mechatronic system with similar functions.

[0080] The attenuator 160 is a laser power attenuator used to control the power of the laser in the optical path. The attenuator 160 can be an absorption-type laser power attenuator, a dielectric reflection-type laser power attenuator, or a modulation-type laser power attenuator.

[0081] The beam expansion and collimation system 170 is located behind the output end of the coherent light source, and is used to collimate, expand and filter the coherent light output by the coherent light source 140 to obtain a wide beam of parallel light. The beam expansion and collimation system 170 is generally composed of a second lens 171, a pinhole filter 172 and a third lens 173. After the laser generated by the coherent light source passes through the second lens 171 and converges to the pinhole filter 172, the pinhole will filter out the stray light and generate a nearly ideal spherical wave, which is then collimated by the third lens 173 to form a wide beam of parallel light. The second lens can be a microscope objective lens. The third lens 173 can be a single lens, a doublet lens or a collimating lens group composed of multiple lenses.

[0082] The beam splitter 190 is a block-shaped or flat beam splitter that splits the incident light beam into two beams. The coating parameters can be adjusted to control the ratio of reflected and transmitted light energy. It collimates the beam expansion and collimation system 170, splitting the parallel light reflected by the first reflector 180 into two beams. One beam of parallel light is reflected by the second reflector 200 and the third reflector 210, then passes off-axis through the mask 220 and is blocked accordingly. It then passes through the multifocal corrective lens 250 and is transmitted to the holographic dry plate 260, serving as the reference beam. The other beam of parallel light passes through the diffuser 280 and the first lens 241, is blocked by the mask 220, and then illuminates the holographic dry plate 140, serving as the object beam. The appropriate splitting ratio of the beam splitter 190 must be selected based on system requirements. The beam splitter 190 can also be a polarizing beam splitter, which can be combined with a polarizer and a half-wave plate to create an arbitrary light intensity proportioner. The beam splitter 190 can be placed before the beam expansion and collimation system 170 or after the beam expansion and collimation system 170 , and the specific placement position needs to be determined according to actual needs.

[0083] The mask template 220 is a diaphragm with a specific pattern on its surface that can selectively block or transmit light. Figure 2 As shown, mask 220 is fabricated based on the three focal length zones of a multifocal corrective lens 250. White areas represent light-transmitting portions, while black areas represent light-blocking portions. Mask 220 is positioned on either side of the holographic plate 250, and the rotation of servos 230 ensures precise alignment of the light-transmitting areas on either side. This, combined with the electronic shutter 150 and first focal plane shift system 240, allows for corresponding exposure of the three focal length zones.

[0084] The diffuser 280 is an optical device that randomly scatters incident light, uniformly transmitting light to create a wide-viewing diffuse light pattern, essentially forming and serving as the projection imaging surface. Located on the reflective optical path of the beam splitter 190, the diffuser 280 converts the collimated plane wave of the object beam into a scattered wave. The diffuser 280 can be made of frosted glass, frosted plastic, or a transparent plate containing scattering particles or having a microstructured surface.

[0085] The first focal plane displacement system 240 consists of a first lens 241, a spatial displacement platform 242, a motor 243, and a motor driver 244. It is used to control the position of the focal plane formed by the signal light passing through the diffuser 280 relative to the holographic dry plate 260. The first lens 241 can be a single lens, a doublet, or a lens assembly consisting of multiple lenses. The position of the spatial displacement platform 242 is not fixed but is adjustable based on the focal plane position required for exposure. The range of motion should be less than or equal to one focal length of the first lens 241. The position of the spatial displacement platform 242 is controlled by the motor 243 and the motor driver 244. The motor 243 is typically a stepper motor or a servo motor. The motor driver 244 is connected to the main controller 280 via USB, serial port, or general I / O. The transmission between the motor 243 and the spatial displacement platform 242 can be a belt drive, gear drive, rack and pinion drive, worm gear drive, or a combination of these. The motor driver 244 should match the selected motor.

[0086] The multifocal corrective lens 250 is a multifocal prescription lens used to meet the daily wearing needs of myopic people and the elderly. It can correct vision problems such as myopia and presbyopia, and support clear viewing of near and far objects. The multifocal corrective lens 250 is compounded with the holographic dry plate 260 on the same substrate to form a stacked optical structure, and the multifocal corrective lens 250 should be placed on one side of the parallel reference light path. If the curvature of the multifocal corrective lens 250 is too large, it is necessary to consider designing and placing a coupling prism to ensure that the reference beam is correctly coupled in. Figure 3As shown, the multifocal corrective lens 250 is a trifocal lens, but it can also be a progressive lens or a bifocal lens. The selection of the multifocal corrective lens 250 should be tailored to actual visual needs. If a balance between reading and farsightedness is required, a progressive lens should be selected to reduce image jumps. Alternatively, lens parameters can be customized based on eye examination results and personal lifestyle habits to ensure comfort and visual accuracy.

[0087] The holographic plate 260 is a holographic recording material used to record the amplitude and phase of light. Signal light and reference light are directed toward the holographic plate 260 from both sides along coaxial and off-axis optical paths, respectively, completely covering its surface. The centers of the two light spots must coincide with each other, facing the geometric center of the holographic plate 260. Commonly used holographic recording media include silver halide emulsion, dichromated gelatin, photoresist, photopolymers, and photothermal plastics. Silver halide emulsion offers high photosensitivity, a wide spectral response range, strong versatility, and good environmental stability. However, silver halide materials also have disadvantages such as low diffraction efficiency, high image noise after bleaching, and complex material preparation and post-processing steps. Dichromated gelatin almost possesses the ideal properties of phase holograms, but it has low sensitivity, poor stability, and is easily erased in high-temperature and high-humidity environments. Photoresist is an important photosensitive polymer holographic recording material. Using positive photoresist can produce high-quality relief holograms. Photopolymers are non-silver-salt photosensitive polymer holographic recording materials that primarily use photochemical methods to generate free radicals or ions to initiate monomer polymerization. They offer advantages such as high sensitivity and diffraction efficiency, ease of processing, and real-time dry development. Photothermal plastics are relief-type phase recording materials, constructed by coating a substrate with a layer of transparent conductor, a layer of transparent photoconductor, and finally a layer of thermoplastic. The advantages of photothermal plastics as holographic recording materials include visible light sensitivity, dry development, high diffraction efficiency, and reusability. However, their disadvantages include low resolution and difficulty in producing high-quality films.

[0088] This embodiment can be used to prepare a light combiner that is compatible with multifocal corrective lenses. The coherent light source 140 emits a laser with pure quality and stable spectrum. The laser generates a wide beam of parallel light through the beam expansion and collimation system 170. The parallel light is divided into two beams through the beam splitter 190. One beam of parallel light (reference light) passes through the third reflector 200. After being reflected by the fourth reflector 210, it is off-axis irradiated to the mask template 220, and then irradiated to the holographic dry plate 260 after being blocked by the fourth reflector. The other beam of parallel light (object light) is scattered by the diffuser 280, and is irradiated to the mask template 220 through the first focal plane displacement system 240. After being blocked by the fourth reflector, it is irradiated to the holographic dry plate 260. Among them, the focal plane position formed by the object light beam passing through the diffuser 280 is determined by the first focal plane displacement system 240. The main controller 270 controls the electronic shutter 150, the rotary servo 230, and the first focal plane displacement system 240 according to the following. Figure 6The determined working sequence shown works to realize the preparation of holographic optical elements for multi-focal near-eye display.

[0089] Example 2

[0090] An embodiment of the preparation of a holographic optical element for multi-focal near-eye display according to the present invention is as follows: Figure 4 As shown, the system includes a coherent light source 140, an electronic shutter 150, an attenuator 160, a beam expander and collimator system 170, a first reflector 180, a beam splitter 190, a second reflector 200, a third reflector 210, a diffuser 280, a first focal plane displacement system 240, a multifocal corrective lens 250, a holographic dry plate 260, a master controller 270, and an electrically controlled mask plate 300.

[0091] The coherent light source 140 is a laser in the visible light band, which is used to generate laser light with pure quality and stable spectrum.

[0092] The electronic shutter 150 is connected to the main controller 270 to control the opening and closing of the optical path. The main controller 270 controls the operating state of the electronic shutter 150 based on the operating status of the electronically controlled mask 300 and the spatial mobile platform 242. When the electronically controlled mask 300 and the spatial mobile platform 242 are operating, the main controller 280 controls the electronic shutter 150 to stop operating. When the electronically controlled mask 300 and the spatial mobile platform 242 are stopped, the main controller 270 controls the electronic shutter 150 to operate. The electronic shutter 150 can also be a mechanical shutter or a mechatronic system with similar functions.

[0093] The attenuator 160 is a laser power attenuator, which is used to control the power of the laser in the optical path.

[0094] The beam expansion and collimation system 170 is located after the coherent light source output end and is used to collimate, expand and filter the coherent light output by the coherent light source 140 to obtain a wide beam of parallel light. The beam expansion and collimation system 170 is generally composed of a second lens 171, a pinhole filter 172 and a third lens 173.

[0095] The beam splitter 190 is a block-shaped or flat beam splitter that splits the incident light beam into two beams. It splits the parallel light, collimated by the beam expansion and collimation system 170 and reflected by the first reflector 180, into two beams. One beam is reflected by the second reflector 200 and the third reflector 210, passes off-axis through the mask 220 and is blocked accordingly. It then passes through the multifocal corrective lens 250 and is transmitted to the holographic dry plate 260, serving as the reference beam. The other beam is transmitted through the first lens 241, blocked by the electronically controlled mask 300, and then illuminates the holographic dry plate 140, serving as the object beam. The beam splitter 190 must select an appropriate splitting ratio based on system requirements.

[0096] The diffuser 280 is an optical device that randomly scatters incident light, uniformly transmitting light to create a wide-viewing diffuse light pattern, essentially forming and serving as the projection imaging surface. Located on the reflective optical path of the beam splitter 190, the diffuser 280 converts the collimated plane wave of the object beam into a scattered wave. The diffuser 280 can be made of frosted glass, frosted plastic, or a transparent plate containing scattering particles or having a microstructured surface.

[0097] The first focal plane displacement system 240, consisting of a first lens 241, a spatial displacement platform 242, a motor 243, and a motor driver 244, is used to control the position of the focal plane formed by the signal light passing through the diffuser 280 relative to the holographic dry plate 260. The position of the spatial displacement platform 242 is not fixed but rather changes according to the focal plane position required for exposure. Its range of motion should be less than or equal to one focal length of the first lens 241.

[0098] The multifocal corrective lens 250 is a multifocal prescription lens designed to meet the daily wear needs of myopic individuals and the elderly. It corrects vision problems such as myopia and presbyopia, and enables clear viewing of both near and far objects. The multifocal corrective lens 250 is composited with the holographic dry plate 260 on a common substrate, forming a laminated optical structure. The multifocal corrective lens 250 should be placed on the side parallel to the reference beam path. If the curvature of the multifocal corrective lens 250 is excessive, the design and placement of a coupling prism should be considered to ensure proper coupling of the reference beam.

[0099] The holographic dry plate 260 is a holographic recording material used to record the amplitude and phase of light. Commonly used holographic recording media include silver halide emulsion, dichromate gelatin, photoresist, photopolymer, photothermal plastic, etc.

[0100] The electrically controlled mask 300 is a programmable optical element based on a transmissive spatial light modulator (SLM) or digital micromirror device (DMD). It dynamically changes the transmittance or reflectance of liquid crystals at different locations through electrical control, thereby generating and switching specific optical patterns in real time, achieving a digital aperture effect without replacing a physical template. The electrically controlled mask 300 is located in the optical paths on either side of the holographic plate 250. By receiving electrical signals, it precisely changes its transmittance at different locations, ensuring strict alignment of the light-transmitting areas on either side. In conjunction with the electronic shutter 150 and the first focal plane displacement system 240, it dynamically forms the desired blocking mask pattern, achieving corresponding exposure of focal length zones. The electrically controlled mask 300 is a transmissive spatial light modulator, primarily including liquid crystal (LCD) and liquid crystal on silicon (LCoS) types. LCD spatial light modulators are typically based on transmissive liquid crystal panels. Their primary advantages are relatively mature technology, relatively low device cost, and the ability to achieve a larger clear aperture and higher spatial resolution. However, LCD-type spatial light modulators also have some limitations, including limited light utilization efficiency or overall transmittance, the diffraction effect of pixel spacing on light that may produce undesirable stray light, the relatively slow response speed of liquid crystal molecules affecting the pattern switching speed, and thermal stability issues under high-energy light. The advantage of silicon-based liquid crystal (LCoS) spatial light modulators is that they can achieve very high spatial resolution and pixel fill factor, thereby reducing the diffraction effect of pixel spacing and improving image quality; at the same time, they usually have higher light modulation efficiency (transmittance or reflectivity) and faster response speed. However, their disadvantages are that the process is more complex and sophisticated, resulting in a significantly higher device cost than the LCD type. The optical path design may be more complex due to polarization characteristics, and there are usually specific requirements for the polarization state of the incident light. The biggest advantage of micromirror array-type digital micromirror devices is that the mechanical switching speed of the micromirrors is extremely fast (microseconds), they are insensitive to the polarization of light, have good stability, and have high photothermal tolerance. Its main disadvantage is that it is essentially a binary modulation (on / off, and it is difficult to achieve multi-level grayscale transmittance), and it requires a specific angle splitting design in the optical system to be used as a transmission mask. The diffraction noise pattern is also different from that of liquid crystal spatial light modulators.

[0101] This embodiment can be used to prepare a light combiner that is compatible with multifocal corrective lenses. The coherent light source 140 emits pure quality laser light with a stable spectrum. The laser light passes through the beam expansion and collimation system 170 to generate a wide beam of parallel light. The parallel light passes through the beam splitter 190 and is divided into two beams. One beam of parallel light (reference light) passes through the third reflector 200. After being reflected by the fourth reflector 210, it is off-axis irradiated onto the electrically controlled mask plate 300. After being blocked by the fourth reflector, it is irradiated onto the holographic dry plate 260. The other beam of parallel light (object light) is scattered by the diffuser 280, passes through the first focal plane displacement system 240, and irradiates the electrically controlled mask 300. After being blocked by the fourth reflector, it is irradiated onto the holographic dry plate 260. Among them, the focal plane position formed by the object light beam passing through the diffuser 280 is determined by the first focal plane displacement system 240. The main controller 280 controls the electronic shutter 150, the first focal plane displacement system 240, and the electrically controlled mask plate 300 according to the following steps: Figure 7 The determined working sequence shown works to realize the preparation of holographic optical elements for multi-focal near-eye display.

[0102] Example 3

[0103] This embodiment provides an embodiment of a device for preparing a holographic optical element for multi-focal near-eye display, which is used to prepare Figure 5 As shown, the system includes a coherent light source 140, an electronic shutter 150, an attenuator 160, a beam expander and collimator system 170, a first reflector 180, a beam splitter 190, a second reflector 200, a third reflector 210, a mask template 220, a rotary servo 230, a diffuser 280, a second focal plane displacement system 290, a multifocal corrective lens 250, a holographic dry plate 260, and a main controller 270.

[0104] The coherent light source 140 is a laser in the visible light band, which is used to generate laser light with pure quality and stable spectrum.

[0105] The electronic shutter 150 is connected to the master controller 270 to control the opening and closing of the optical path. The master controller 270 controls the operating state of the electronic shutter 150 in conjunction with the operating states of the mask rotation servo 230 and the drive module 291. The electronic shutter 150 can also be a mechanical shutter or a mechatronic system with similar functions.

[0106] The attenuator 160 is a laser power attenuator, which is used to control the power of the laser in the optical path.

[0107] The beam expansion and collimation system 170 is located after the coherent light source output end and is used to collimate, expand and filter the coherent light output by the coherent light source 140 to obtain a wide beam of parallel light. The beam expansion and collimation system 170 is generally composed of a second lens 171, a pinhole filter 172 and a third lens 173.

[0108] The beam splitter 190 is a block-shaped or flat beam splitter that splits the incident light beam into two beams. The coating parameters can be adjusted to control the energy ratio of the reflected and transmitted light. It collimates the beam expansion and collimation system 170 and splits the parallel light reflected by the first reflector 180 into two beams. One beam of parallel light is reflected by the second reflector 200 and the third reflector 210, then passes off-axis through the mask 220 and is blocked accordingly. It then passes through the multifocal corrective lens 250 and is transmitted to the holographic dry plate 260, serving as the reference beam. The other beam of parallel light passes through the diffuser 280 and the first lens 241, is blocked by the mask 220, and then strikes the holographic dry plate 140, serving as the object beam. The appropriate splitting ratio of the beam splitter 190 must be selected based on system requirements.

[0109] The mask 220 is a stop with a specific pattern on its surface that selectively blocks or transmits light. Positioned in the optical paths on either side of the holographic plate 250, the mask 220 rotates the servo 230 to ensure precise alignment of the light-transmitting areas on either side. This, combined with the electronic shutter 150 and focal plane shift system 240, allows for corresponding exposure of three focal length zones. Similarly, the mask 220 can be replaced with an electronically controlled reticle 300 as needed.

[0110] The diffuser 280 is an optical device that randomly scatters incident light, uniformly transmitting light to create a wide-viewing diffuse light pattern, essentially forming and serving as a projection imaging surface. The diffuser 280 is located on the reflected light path side of the beam splitter 190 and converts the collimated plane wave of the object beam into a scattered wave.

[0111] The second focal plane displacement system 290, consisting of a drive module 291 and a zoom lens 292, is used to control the distance between the focal plane formed by the signal light passing through the diffuser plate 280 and the holographic dry plate 260. The drive module 291 is a mechano-deformation drive module driven by a motor, hydraulic drive, or an electro-deformation drive module driven by an electromagnetic drive. The drive module 291 is connected to the master controller 270 and applies a driving force to the zoom lens 292. The zoom lens 292 is an optical system that achieves continuous focal length adjustment by changing the curvature and refractive index of the liquid interface within the lens film. This allows for fast and flexible optical zoom without mechanical movement or lens replacement, while maintaining a stable imaging surface. The zoom lens 292 is located behind the diffuser plate 280 in a fixed position, and its focal length is adjusted according to the position of the focal plane to be exposed. Specifically, the maximum focal length can be infinite, but the minimum focal length should not be less than the spatial distance between the zoom lens 292 and the diffuser plate 280. The zoom lens 292 is mainly a liquid lens, and its types include various solutions driven by technologies such as liquid crystal materials, electrochemical activation, dielectrophoresis, dielectric wetting, electrostatic force, electromagnetic force, pressure regulation, and environmental response.

[0112] The multifocal corrective lens 250 is a multifocal prescription lens designed to meet the daily wear needs of myopic individuals and the elderly. It corrects vision problems such as myopia and presbyopia, and enables clear viewing of both near and far objects. The multifocal corrective lens 250 is composited with the holographic dry plate 260 on a common substrate, forming a laminated optical structure. The multifocal corrective lens 250 should be placed on the side parallel to the reference beam path. If the curvature of the multifocal corrective lens 250 is excessive, the design and placement of a coupling prism should be considered to ensure proper coupling of the reference beam.

[0113] The holographic dry plate 260 is a holographic recording material used to record the amplitude and phase of light. Commonly used holographic recording media include silver halide emulsion, dichromate gelatin, photoresist, photopolymer, photothermal plastic, etc.

[0114] This embodiment can be used to prepare a light combiner that is compatible with multifocal corrective lenses. The coherent light source 140 emits a laser with pure quality and stable spectrum. The laser generates a wide beam of parallel light through the beam expansion and collimation system 170. The parallel light is divided into two beams through the beam splitter 190. One beam of parallel light (reference light) passes through the third reflector 200. After being reflected by the fourth reflector 210, it is off-axis irradiated to the mask template 220, and then irradiated to the holographic dry plate 260 after being blocked by the fourth reflector. The other beam of parallel light (object light) is scattered by the diffuser 280, and is irradiated to the mask template 220 through the second focal plane displacement system 290. After being blocked by the fourth reflector, it is irradiated to the holographic dry plate 260. Among them, the focal plane position formed by the object light beam passing through the diffuser 280 is determined by the second focal plane displacement system 290. The main controller 270 controls the electronic shutter 150, the rotary servo 230, and the second focal plane displacement system 290 according to the following procedures. Figure 8 The determined working sequence shown works to realize the preparation of holographic optical elements for multi-focal near-eye display.

[0115] Example 4

[0116] Embodiments 1, 2 and 3 of the present invention provide a method for preparing a multi-focal near-eye display holographic optical element light combiner, the specific process is as follows: Figure 9 .

[0117] The method is as follows:

[0118] Step 1: Build the holographic interference exposure optical path, install the corresponding focal plane displacement system, determine the position of the focal plane to be passed, and set the mask template as needed;

[0119] Step 2: Plan the running path and specify the exposure time T required for each focal plane position i (i is the focal plane position of the i-th exposure);

[0120] Step 3: The preparation device moves along the planned path or zooms the zoom lens until it reaches the first focal plane to be exposed. The preparation device stops, changes the mask to the specified position, and remains stationary for time t. The main controller receives feedback from the preparation device and determines whether the preparation device has stabilized within t time.

[0121] Step 4: After the preparation device is judged to be stable and the waiting time t is over, the electronic shutter is immediately opened to connect the light path and the electronic shutter is kept open for a period of time T according to the calculated exposure time. i ;

[0122] Step 5: Repeat steps 3 and 4 until all focal plane positions are exposed;

[0123] Step 6: Obtain a multi-focal holographic optical element light combiner for near-eye display that is friendly to myopia and presbyopia people.

[0124] In the third step, to ensure that the multifocal near-eye display corresponds to the different depth zones of the multifocal corrective lens, different masks must be aligned with the position of the object focal plane from the holographic plate. The motion time is calculated based on the focal plane position and the device's operating speed, taking into account the rotation duration of the rotary servo. It can also be self-adjusted using feedback control. Possible feedback methods include contact switches, accelerometers, or Hall sensors.

Claims

1. A multi-focal near-eye display holographic optical element, characterized in that: include: substrate; a multifocal correction layer disposed on a surface of the substrate, the multifocal correction layer comprising at least two optical partitions with different refractive powers; a holographic recording layer disposed on the other surface of the substrate, wherein a plurality of spatially partitioned holographic grating structures are recorded in the holographic recording layer, wherein each partitioned holographic grating structure corresponds one-to-one to a different optical partition of the multi-focus correction layer and is optically matched; Each segmented holographic grating structure is configured to diffract and generate a virtual image display plane matching the refractive power of the corresponding optical segment when illuminated by the reproduced illumination light.

2. The multi-focal near-eye display holographic optical element according to claim 1, characterized in that: The multifocal correction layer is a progressive multifocal lens, a bifocal lens or a trifocal lens; the material of the holographic recording layer is a photopolymer, a silver halide emulsion or a dichromate gelatin.

3. The multi-focal near-eye display holographic optical element according to claim 1, characterized in that: Each partitioned holographic grating structure has a different spatial frequency and orientation to match the refractive properties of the corresponding optical partition.

4. A method for preparing a multi-focal near-eye display holographic optical element according to any one of claims 1 to 3, characterized in that: The steps are as follows: providing a substrate; forming a multifocal correction layer on the first surface of the substrate, wherein the multifocal correction layer comprises at least two optical partitions with different refractive powers; forming a holographic recording layer on the second surface of the substrate; Recording a plurality of spatially partitioned holographic grating structures in the holographic recording layer by a partitioned exposure method, so that each partitioned holographic grating structure is optically matched with a different optical partition of the multi-focus correction layer; The partition exposure includes: For each optical partition, adjusting the object focal plane position to match the refractive characteristics of the optical partition; Selecting a mask pattern corresponding to the optical partition for blocking; The exposure time is controlled to record the corresponding holographic grating structure in the optical partition.

5. A device for preparing a multi-focal near-eye display holographic optical element according to any one of claims 1 to 3, characterized in that: include: a coherent light source (140) for generating laser light; An electronic shutter (150) and an attenuator (160) are sequentially arranged on the outgoing light path of the coherent light source (140) and are used to control the on / off and power of the laser; A beam expansion and collimation system (170) is used to convert the coherent light output by the coherent light source (140) into a wide beam of parallel light; A beam splitter (190) for splitting the parallel light into a reference beam and an object beam; a diffuser plate (280), arranged in the optical path of the object light beam, for converting the object light beam into scattered light; a focal plane displacement system, arranged in the object light path after the diffusion plate (280), for controlling the relative distance between the focal plane of the object light formed after the diffusion plate (280) and the recording surface of the holographic dry plate (260); a pair of mask components, respectively disposed in the reference light path and the object light path, for performing synchronous patterned shielding on the two light beams; A multifocal correction lens (250) is composited with a holographic dry plate (260) on a common substrate and is located in a reference optical path between the second mask unit and the holographic dry plate (260), so that a reference light beam generates wavefronts carrying different refractive information after transmitting through different optical partitions thereof; A holographic dry plate (260), whose object light incident side and reference light incident side respectively receive the object light beam and the reference light beam after being patterned and shielded by the mask component, and are used to record the holographic grating structure formed by the interference of the two light beams; A master controller (270) is electrically connected to the electronic shutter (150), the focal plane displacement system, and the mask component, and is used to control the timing of shutter opening and closing, focal plane displacement, and mask pattern switching, so as to sequentially record holographic structures that match the multiple optical correction areas of the multifocal correction lens (250) on different spatial partitions of the holographic dry plate (260).

6. The device for preparing a multi-focal near-eye display holographic optical element according to claim 5, characterized in that: The mask component includes: A mask template (220) is a physical template having a light-transmitting pattern corresponding to the optical partitions of the multifocal corrective lens (250); A rotary steering engine (230), the output shaft of which is connected to the mask template (220), is used to drive the mask template to rotate so as to switch the shielding area.

7. The device for preparing a multi-focal near-eye display holographic optical element according to claim 5, characterized in that: The mask component is an electrically controlled mask plate (300), which adopts a transmissive spatial light modulator (SLM) or a digital micromirror device (DMD) and dynamically generates and switches a shielding pattern by receiving an electrical signal from the master controller (270).

8. The device for preparing a multi-focal near-eye display holographic optical element according to claim 5, characterized in that: The focal plane displacement system is a mechanical displacement system, comprising: a first lens (241); A spatial displacement platform (242) for carrying and driving the first lens (241) to move along the optical axis; a motor (243) mechanically connected to the spatial displacement platform (242); a motor driver (244), electrically connected to the motor (243) and receiving a control signal from the master controller (270); The spatial displacement platform (242) is equipped with a built-in grating ruler or encoder for providing a position feedback signal to the master controller (270).

9. The device for preparing a multi-focal near-eye display holographic optical element according to claim 5, characterized in that: The focal plane displacement system is a zoom lens system, comprising: A variable focus lens (292) is a liquid lens based on dielectric wetting, liquid crystal or pressure adjustment technology; A driving module (291) is mechanically or electrically connected to the zoom lens (292) for changing its optical focal length. The driving module (291) is electrically connected to the master controller (270).

10. The device for preparing a multi-focal near-eye display holographic optical element according to any one of claims 5 to 9, characterized in that: The multifocal corrective lens (250) is a progressive lens, a bifocal lens or a trifocal lens.

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