Holographic speckle diffusion plate manufacturing method based on 4f system spectrum regulation

Abstract

The application relates to a holographic speckle diffusion sheet manufacturing method based on 4F system spectrum regulation, and belongs to the optical technology field. The method is as follows: a holographic diffusion sheet single-beam exposure light path is established; a 4F system is established; the holographic diffusion sheet single-beam exposure light path is combined with the 4F system to regulate the spectrum of the holographic diffusion sheet; the 4F system is placed behind ground glass, a photoresist negative is placed behind the 4F system, and different mask plates are matched to realize regulation of different light spot shapes and angles. The application controls the spectrum control process of the holographic process, so that the holographic speckle diffusion sheet can easily realize control of various speckle patterns, has low processing difficulty, and can realize regulation of an arbitrary light spot pattern.

Description

Technical Field

[0001] This invention belongs to the field of optical technology and relates to a method for fabricating holographic speckle diffusers based on 4F system spectrum modulation. Background Technology

[0002] A holographic diffuser is an optical diffuser that records the spectral information of laser light passing through a randomly rough surface using a holographic medium. Due to its unique structure and fabrication method, it has wide applications in angle control and beam shaping. Holographic diffusers are typically fabricated by recording a holographic pattern on a photopolymer and then transferring the microstructure. The main recording methods include single-beam holographic recording and classical holographic recording. Classical holographic diffusers are formed by superimposing two beams of light, where the laser light passing through the speckle pattern on the frosted glass serves as the object beam, and the other beam serves as the reference beam. By precisely controlling the spectral distribution of the speckle, the holographic diffuser can strictly control the geometry of the scattered light, meeting various scattered light requirements. For the recording and reconstruction process of single-beam holography, the incident light is considered to be divided into multiple sub-beams, which serve as reference beams to each other, and the recorded and reconstructed patterns are essentially identical. Based on the holographic reproduction of the spectral record, spectral modulation becomes crucial in this technology.

[0003] The most common optical field manipulation device is the aperture, which is usually placed behind the diffuser to achieve scattered light of different shapes. However, this method greatly reduces energy efficiency. For holographic diffusers, a 4F system is a good solution for spectral modulation of the optical field, as it can directly control the scattered light field. By using two Fourier lenses to perform spatial-to-frequency and frequency-to-spatial transformations on the incident light field, and then performing corresponding filtering on the common focal plane (spectral plane) of the two Fourier lenses, spectral modulation of the incident light field can be achieved.

[0004] For the processing method of recording a single beam for holographic exposure, the current experimental results are good in eliminating zero order and reproducing diffusion morphology. However, this exposure method cannot achieve the effect of complex diffusion morphology and can usually only achieve circular and elliptical diffusion morphology. Most of the research on applying the 4F system to diffusers uses a dual-lens system for spectrum control. However, this control method will introduce too large optical error, so this control method is not suitable for the precision processing of micro and nano structures.

[0005] Holographic diffusers possess advantages such as controllable spatial distribution of scattering, controllable scattering angle, and high transmittance, making them widely used in display and lighting applications. However, due to limitations in their exposure methods, the scattering shapes are mostly confined to simple shapes like circles and ellipses. In practical experiments, single-shot spectral recording requires consideration not only of whether the incident light spectrum is completely recorded during exposure but also of avoiding zero-order problems caused by insufficient speckle density and exposure depth. Currently, the spatial distribution of scattering in existing diffusers is primarily circular, elliptical, and linear, lacking complex shapes such as circular patterns or lettering. Current research on diffuser spectrum modulation relies on simple combinations of Fourier lenses, neglecting the focusing at multiple angles on the spectral plane. This results in inaccurate speckle feature size analysis and spectral filtering, preventing the holographic reproduction of complex shapes and significantly limiting the spatial distribution of scattering. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method for fabricating holographic speckle diffuser based on 4F system spectrum modulation.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for fabricating holographic speckle diffuser sheets based on 4F system spectrum modulation, the method being as follows:

[0009] Establish a single-beam exposure optical path for a holographic diffuser;

[0010] The single-beam exposure optical path of the holographic diffuser includes an ultraviolet laser, an aspherical mirror, a pinhole, a lens, frosted glass, and a photoresist substrate. The ultraviolet laser emits a laser beam, which is focused by the aspherical mirror, collimated and expanded by the pinhole and lens to form a laser spot. The laser spot irradiates the surface of the frosted glass, causing the laser spot to scatter and form scattered laser light. The photoresist on the photoresist substrate records the laser scattering field of the scattered laser light, forming a microstructure of laser speckle on the surface of the photoresist, thus fabricating the holographic diffuser.

[0011] Establish a 4F system;

[0012] The 4F system includes a first aperture stop, a first plano-concave lens, a first meniscus lens, a first biconvex lens, a parallel plate, a second biconvex lens, a second meniscus lens, a second plano-concave lens, and a second aperture stop; the incident parallel beam is focused onto the surface of the parallel plate; the numerical aperture of the 4F system is NA = n*sinθ, where n is the refractive index of air and θ is the half-angle value of the incident light.

[0013] The laser scattered light is set at the entrance pupil of the 4F system and spectrum is modulated. Utilizing the Fourier transform property of the lens, the photoresist substrate is placed on the rear focal plane of the lens. The light fields on the front focal plane and the rear focal plane of the lens are related by Fourier transform, and the light field on the front focal plane of the lens is the spectrum of the speckle field.

[0014] A mask is placed at a designated parallel plate to modulate the spectrum of the speckle field. The spectrum of the speckle field after modulation by the 4F system is as follows:

[0015] E(u,v)=F{E(x0,y0)}×T(u,v)

[0016] Where E(x0,y0) is the incident light field, and T(u,v) is the modulation function of the mask;

[0017] The holographic diffuser single-beam exposure optical path is combined with the 4F system to regulate the spectrum of the holographic diffuser;

[0018] The 4F system is placed behind the frosted glass, and the photoresist substrate is placed behind the 4F system. Different photomasks are used to control the shape and angle of the photomask.

[0019] Furthermore, the lens is a cylindrical lens.

[0020] Furthermore, the cylindrical lens includes a first cylindrical lens and a second cylindrical lens, which are placed perpendicular to each other to achieve angular expansion in two directions.

[0021] Furthermore, all devices in the 4F system are fused silica.

[0022] Furthermore, the first and second apertures are square holes with a side length of b, and the incident angle range is ±20°.

[0023] The parallel plate and the mask have the same thickness.

[0024] Furthermore, in the 4F system, the incident scattered light is equivalent to parallel beams with different deflection angles, and the field of view angles are set to 0°, 5°, 10°, 15° and 20° respectively. Different field of view angles correspond to different height values ​​of the mask, with values ​​ranging from 0mm to 80mm.

[0025] Furthermore, the 4F system is placed at a distance b behind the frosted glass, and the photoresist substrate is placed at a distance b behind the 4F system.

[0026] The beneficial effects of this invention are as follows: Through the spectral control process of the holographic process, this invention enables the holographic speckle diffuser to easily control a variety of speckle patterns, with low processing difficulty, and can achieve the adjustment of arbitrary light spot patterns.

[0027] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0029] Figure 1 This is a single-beam exposure optical path diagram;

[0030] Figure 2 This is the optical path diagram for the 4F system;

[0031] Figure 3 This is a schematic diagram of a grayscale mask.

[0032] Figure 4 This is a schematic diagram of the system wavefront;

[0033] Figure 5 This is a schematic diagram of the system's exposure optical path. Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0035] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0036] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0037] Holographic diffuser single-beam exposure optical path as follows Figure 1 As shown, the single-beam exposure optical path of the holographic diffuser includes an ultraviolet laser, an aspherical mirror, a pinhole, a cylindrical lens, a frosted glass, and a photoresist substrate;

[0038] An ultraviolet laser emits a laser beam, which is focused by an aspherical mirror, then collimated and expanded by a pinhole and cylindrical lens to form a laser spot. The laser spot irradiates the surface of a frosted glass, causing the laser spot to scatter. The laser scattering field is recorded by photoresist on a photoresist substrate, forming a microstructure of laser speckle on the photoresist surface, thus realizing the fabrication of a holographic diffuser.

[0039] Among them, ultraviolet lasers have the following characteristics:

[0040] Short wavelength: Ultraviolet lasers typically have wavelengths in the range of 200-400nm, enabling them to produce higher energy densities than visible and infrared light, especially at the microscopic level.

[0041] High energy density: Because ultraviolet lasers can generate high-energy beams, they are widely used in industrial processing and scientific research.

[0042] Excellent monochromaticity: Ultraviolet lasers can only produce light of a single wavelength, which makes them very monochromatic, thus having a wide range of applications in precision optical detection and spectral analysis.

[0043] Semiconductor materials: The light source of ultraviolet lasers is usually made of semiconductor materials. These materials have good electrical properties and stability, which enables ultraviolet lasers to operate at high frequencies and high power.

[0044] Small size and low power consumption: Due to the use of semiconductor materials, ultraviolet lasers are typically small in size and have low power consumption.

[0045] High focusing capability: The beam of an ultraviolet laser can be focused very precisely, which is very important in micro and nanofabrication.

[0046] "Cold treatment": When processing materials, ultraviolet lasers usually do not cause overall damage to the material, but only process specific areas on the surface. This avoids thermal damage and protects the integrity of the material.

[0047] Wide range of applications: Ultraviolet lasers not only have important applications in the fields of microelectronics and microfabrication, but also play a role in many other fields such as medical diagnosis, biomaterial processing, fluorescence analysis, and microscopic imaging.

[0048] Durable marking: Marks made by ultraviolet lasers will not disappear due to environmental factors, which is one of the differences between it and other marking technologies.

[0049] Non-contact: Ultraviolet lasers can perform non-contact processing, which avoids damage to the workpiece from mechanical extrusion or stress and ensures the original precision of the workpiece.

[0050] During the exposure process, all components in the single-beam exposure optical path of the holographic diffuser remain coaxial, two beam expanders are placed vertically to achieve angular expansion in two directions, scattering is achieved through frosted glass, and recording is performed using a photoresist substrate.

[0051] like Figure 2 The diagram shows the optical path of a 4F system, which is a symmetrical image-side telecentric optical path. The 4F system includes a first aperture stop, a first plano-concave lens, a first meniscus lens, a first double-convex lens, a parallel plate, a second double-convex lens, a second meniscus lens, a second plano-concave lens, and a second aperture stop.

[0052] The 4F system is suitable for ultraviolet lasers, enabling precise focusing of a parallel beam incident at ±20° onto the surface of a parallel plate, thus achieving accurate spectral control. Its numerical aperture is:

[0053] NA = n*sinθ

[0054] In the formula, n is the refractive index of air and θ is the half-angle value of the incident light.

[0055] The scattered light from the frosted glass is adjusted to the entrance pupil set by the 4F system for spectrum modulation. The speckle field spectrum can be modulated using the Fourier transform property of the lens. The receiving screen is placed on the rear focal plane of the lens. Since the light fields on the front and rear focal planes of the lens have a Fourier transform relationship, the light field on the front focal plane of the lens represents the spectrum of the speckle field. A mask is placed at the designated parallel plate to further modulate the speckle field spectrum. The spectrum of the speckle field after modulation using the 4F system is as follows:

[0056] E(u,v)=F{E(x0,y0)}×T(u,v)

[0057] In the formula, E(x0,y0) is the incident light field, and T(u,v) is the modulation function of the mask.

[0058] Based on holographic spectral recording and reproduction, the spatial distribution of the scattered light field can be controlled by spectral modulation of the speckle, enabling the manipulation of various complex light spots and diffusion angles.

[0059] The materials used in the 4F system are all fused silica, which ensures the exposure conditions of the ultraviolet beam and is also a relatively common material that is suitable for processing.

[0060] The first and second apertures are rectangular holes with a diameter of 8mm*8mm, and the incident angle range is ±20°. The overall system length and focal length are also limited. The overall system length is 330mm, and the focal length is 119.05mm. The optical power is evenly distributed to reduce tolerance sensitivity and simplify subsequent machining.

[0061] The parallel plate has a thickness of 2mm, similar to the thickness of the grayscale mask. Different grayscale masks are used instead of the parallel plate during spectrum modulation to achieve the desired effect. Grayscale masks come in various styles, such as... Figure 3 As shown, this also allows for the diversity of spectrum modulation.

[0062] In the 4F system, the incident scattered light is equivalent to parallel beams with different deflection angles. The field of view angles are set to 0°, 5°, 10°, 15°, and 20°, respectively. Different field of view angles correspond to different height values ​​of the mask: 0mm to 80mm, which also allows the system to directly control the angle.

[0063] In the 4F system, the thickness, shape, and other parameters of each lens element are detailed in Table 1, which includes detailed parameters and position information for each lens element. Wavefront analysis at the parallel plate is also provided. Figure 4 As shown.

[0064] Table 1

[0065] 0 unlimited 1.00E+10 1 unlimited 1.00E+01 2 1.49E+03 1.25E+01 F_SILICA 3 4.60E+01 4.40E+01 4 2.50E+02 2.50E+01 F_SILICA 5 5.51E+01 2.71E+01 6 2.16E+02 2.50E+01 F_SILICA 7 2.21E+02 1.88E+02 8 unlimited 2.30E+00 F_SILICA 9 unlimited 1.85E+02 10 2.21E+02 2.50E+01 F_SILICA 11 2.16E+02 2.71E+01 12 5.51E+01 2.50E+01 F_SILICA 13 2.50E+02 4.40E+01 14 4.60E+01 1.25E+01 F_SILICA 15 1.49E+03 1.00E+01 16 unlimited 0.00E+00

[0066] like Figure 5 As shown, the spectrum of the holographic diffuser is controlled by combining the single-beam exposure optical path with the 4F system. The 4F system is placed 8mm behind the frosted glass, and the photoresist film is placed 8mm behind the 4F system. Different spot shapes and angles are controlled by using different masks.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for fabricating holographic speckle diffuser sheets based on 4F system spectrum modulation, characterized in that: The method is as follows: Establish a single-beam exposure optical path for a holographic diffuser; The single-beam exposure optical path of the holographic diffuser includes an ultraviolet laser, an aspherical mirror, a pinhole, a lens, frosted glass, and a photoresist substrate. The ultraviolet laser emits a laser beam, which is focused by the aspherical mirror, collimated and expanded by the pinhole and lens to form a laser spot. The laser spot irradiates the surface of the frosted glass, causing the laser spot to scatter and form scattered laser light. The photoresist on the photoresist substrate records the laser scattering field of the scattered laser light, forming a microstructure of laser speckle on the surface of the photoresist, thus fabricating the holographic diffuser. Establish a 4F system; The 4F system includes a first aperture stop, a first plano-concave lens, a first meniscus lens, a first biconvex lens, a parallel plate, a second biconvex lens, a second meniscus lens, a second plano-concave lens, and a second aperture stop; the incident parallel beam is focused onto the surface of the parallel plate; the numerical aperture of the 4F system is NA = n sin ,in n The refractive index of air, The angle value is the half-angle value of the incident light. The laser scattered light is set at the entrance pupil of the 4F system and spectrum is modulated. Utilizing the Fourier transform property of the lens, the photoresist substrate is placed on the rear focal plane of the lens. The light fields on the front focal plane and the rear focal plane of the lens are related by Fourier transform, and the light field on the front focal plane of the lens is the spectrum of the speckle field. A mask is placed at a designated parallel plate to modulate the spectrum of the speckle field. The spectrum of the speckle field after modulation by the 4F system is as follows: E(u,v)=F{ E(x0,y0)}×T(u,v) Where E(x0,y0) is the incident light field, T(u,v) is the modulation function of the mask; u and v are the spectral information in different directions; F is the Fourier transform; The holographic diffuser single-beam exposure optical path is combined with the 4F system to regulate the spectrum of the holographic diffuser; The 4F system is placed behind the frosted glass, and the photoresist substrate is placed behind the 4F system. Different photomasks are used to control the shape and angle of the photomask.

2. The method for fabricating a holographic speckle diffuser based on 4F system spectrum modulation according to claim 1, characterized in that: The lens is a cylindrical lens.

3. The method for fabricating a holographic speckle diffuser based on 4F system spectrum modulation according to claim 2, characterized in that: The cylindrical lens includes a first cylindrical lens and a second cylindrical lens, which are placed perpendicular to each other to achieve angular expansion in two directions.

4. The method for fabricating a holographic speckle diffuser based on 4F system spectrum modulation according to claim 1, characterized in that: All devices in the 4F system are fused silica.

5. The method for fabricating a holographic speckle diffuser based on 4F system spectrum modulation according to claim 1, characterized in that: The apertures of the first and second apertures have side lengths of b A square aperture with an incident angle range of ±20°; The parallel plate and the mask have the same thickness.

6. The method for fabricating a holographic speckle diffuser based on 4F system spectrum modulation according to claim 5, characterized in that: In the 4F system, the incident scattered light is equivalent to parallel beams with different deflection angles. The field of view angles are set to 0°, 5°, 10°, 15°, and 20°, respectively. Different field of view angles correspond to different height values ​​of the mask, with values ​​ranging from 0mm to 80mm.

7. The method for fabricating a holographic speckle diffuser based on 4F system spectrum modulation according to claim 5, characterized in that: The 4F system is placed behind the frosted glass at a distance of [missing information]. b The photoresist substrate is placed at a distance of [missing information] after being placed in the 4F system. b The location.

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