An apparatus and method for preparing a uniform holographic diffuser

Abstract

This invention belongs to the field of diffuser sheets for HUD display systems, and particularly relates to a fabrication apparatus and method for a uniform holographic diffuser sheet. The fabrication apparatus includes a 325nm He-Cd laser, a dual-beam superposition exposure optical path, a 4F spatial filtering system, and a photolithography receiving device. The dual-beam superposition exposure optical path includes a laser beam expander, a beam splitter, a reflector, and a source diffuser. The laser beam expander expands the ultraviolet laser beam, which is then split by the beam splitter to obtain two beams of equal energy. The reflector then illuminates the same position on the same surface of the source diffuser. The 4F spatial filtering system receives the scattered light emitted from the source diffuser and performs spectral filtering. The filtered scattered light is then illuminated by the photolithography receiving device. This invention can manufacture holographic diffusers with a uniformly distributed scattered light field, improving display quality and the energy utilization rate of the HUD system.

Description

Technical Field

[0001] This invention belongs to the field of diffuser sheets for HUD display systems, and particularly relates to a preparation apparatus and method for a uniform holographic diffuser sheet. Background Technology

[0002] Holographic diffusers are key light-diffusing devices in display systems such as 3D displays, head-up displays, and liquid crystal displays. They serve as both the receiving screen for digital image source projections and the object surface for the optical path of virtual image display. The light-scattering performance of holographic diffusers is crucial for ensuring the field of view, brightness uniformity, and maximum brightness of the display system.

[0003] A holographic diffuser is fabricated using a holographic medium to record the speckle pattern formed when laser light is irradiated onto a rough surface. This holographic medium then transmits over 90% of the visible light. The speckle structure formed by this holographic medium has an irregular three-dimensional profile, resulting in a more pronounced refractive effect and less sensitivity to the incident wavelength. Therefore, this holographic diffuser is suitable for beam shaping of various types of light sources. Due to the random distribution of the speckle and its characteristic size being on the micrometer scale, this holographic diffuser also provides a relatively fine display effect when used in a display screen, showing great promise for applications in the display field.

[0004] There are already many studies on manufacturing processes and holographic materials, as well as commercial products. However, existing holographic diffusers still have some defects, mainly in the following aspects: (1) The intensity of scattered light from a holographic diffuser gradually decreases with the increase of the scattering angle, exhibiting a Gaussian or near-Gaussian distribution. The illumination homogenization effect is limited. When used as an image receiving screen in a display system, in order to ensure a certain level of brightness uniformity, the scattering angle of the holographic diffuser is usually much larger than the display viewing angle, resulting in a large waste of energy outside the viewing angle range; (2) The scattered light spot can only be circular or elliptical, which cannot meet the needs of rectangular, ring, or even more complex illumination spot shapes that are frequently required in beam shaping applications. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides an apparatus and method for preparing a uniform holographic diffuser, thereby improving the controllability of the field of view and the uniformity of scattering of the holographic diffuser, while also controlling the shape of the illumination spot.

[0006] In a first aspect, the present invention provides an apparatus for fabricating a uniform holographic diffuser, comprising a 325nm He-Cd laser, a dual-beam superposition exposure optical path, a 4F spatial filtering system, and a photolithography receiving device, wherein:

[0007] A 325nm He-Cd laser is used to emit 325nm ultraviolet laser light from the exposure source into a dual-beam superposition exposure optical path;

[0008] The dual-beam superposition exposure optical path includes a laser beam expander system, a beam splitter, a reflector, and a source diffuser. The dual-beam superposition exposure optical path is used to expand the ultraviolet laser beam through the laser beam expander system. The expanded ultraviolet laser beam is split into two beams of equal energy by the beam splitter. The two beams of equal energy are then irradiated onto the same position on the same surface of the source diffuser by the reflector.

[0009] The 4F spatial filtering system is used to receive the scattered light emitted by the source diffuser and perform spectral filtering, and then irradiate the photolithography receiving device with the spectral filtered scattered light.

[0010] A photolithography receiver is used to record the spectral information of the scattered light after spectral filtering.

[0011] Furthermore, the laser beam expanding system includes an aspherical mirror, a pinhole aperture, a first cylindrical lens, and a second cylindrical lens arranged sequentially on the same axis.

[0012] Furthermore, the focal length of the first cylindrical lens is 20mm, and the focal length of the second cylindrical lens is 200mm.

[0013] Furthermore, the 4F spatial filtering system includes lens L1, lens L2, and a grayscale mask; lens L1 and lens L2 are placed coaxially, and the grayscale mask is placed on the confocal surface of lens L1 and lens L2.

[0014] Furthermore, the photolithography receiving device includes a photoresist receiving screen, a clamping device, and a two-dimensional moving stage.

[0015] Furthermore, the photoresist receiving screen is made of a quartz substrate spin-coated with AZ4562 photoresist with a thickness of 10μm.

[0016] Furthermore, the photoresist receiving screen records the spectral information of the scattered light after spectral filtering; after developing and transferring the spectral information of the scattered light recorded on the photoresist receiving screen with spectral filtering, it is then transferred a second time onto a 2mm thick K9 glass substrate using a photosensitive adhesive with a refractive index n=1.56, thus creating a holographic diffuser sheet with high transmittance, structurally resistant to deformation, and a wide temperature adaptability range.

[0017] In a second aspect, based on the fabrication apparatus proposed in the first aspect, the present invention also provides a method for fabricating a uniform holographic diffuser, comprising the following steps:

[0018] A 1.325nm He-Cd laser emits 325nm laser light, which is then directed to a laser beam expander system to form a rectangular uniform beam.

[0019] S2. A rectangular uniform beam is split into two beams of equal energy by a beam splitter. The two beams of equal energy are then directed by a mirror to the source diffuser at the same incident angle to form scattered light.

[0020] S3. The scattered light is processed by the 4F spatial filtering system for spectral filtering, and the spectrally filtered scattered light illuminates the photoresist receiving screen.

[0021] S4. The photoresist receiving screen records the spectral information of the scattered light after spectral filtering. After developing and transferring the photoresist receiving screen to PDMS, it is transferred to the K9 glass substrate a second time through photosensitive adhesive to obtain a uniform holographic diffuser.

[0022] Furthermore, step S3 involves filtering the scattered light using a 4F spatial filter system.

[0023] S31. The scattered light enters lens L1 and undergoes Fourier transform to obtain the scattered light spectrum;

[0024] S32. Focus the scattered light spectrum onto a grayscale mask for spatial spectrum filtering;

[0025] S33. The spatial spectrum filtering result is scattered to the photoresist receiving screen after inverse Fourier transform by lens L2.

[0026] The beneficial effects of this invention are:

[0027] To address the problem of uneven display brightness caused by the Gaussian distribution of scattered light intensity from holographic diffusers when viewed from different angles, as well as the energy waste and heat generation issues of the display system caused by the actual diffusion angle of the holographic diffuser being much larger than the designed diffusion angle, this invention designs a dual-beam superposition exposure optical path based on spectrum splicing technology. This path can produce holographic diffusers with a uniformly distributed scattered light field, thereby improving display quality and the energy utilization rate of the HUD system.

[0028] To address the problem that the scattered light spot shape of holographic diffusers can only be circular or elliptical and cannot meet the needs of complex lighting, this invention designs a 4F spatial filtering system based on spectrum modulation technology. This system can achieve precise control over the shape of the scattered light spot, manufacture holographic diffusers with precise control over the scattering angle and flexible control over the shape of the scattered light spot, and improve the applicability of holographic diffusers. Attached Figure Description

[0029] Figure 1 This is a structural diagram of the apparatus for preparing the uniform holographic diffusion sheet of the present invention;

[0030] Figure 2 This is a diagram of the optical path structure for dual-beam superposition exposure according to the present invention;

[0031] Figure 3 This is a schematic diagram of the spectral synthesis principle of the dual-beam superposition exposure optical path of the present invention;

[0032] Figure 4This is a schematic diagram illustrating the principle of holographic diffuser fabrication based on speckle field spectrum modulation to achieve controllable scattering intensity and light spot shape. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Currently, all types of holographic diffusers on the market suffer from a problem where the intensity of scattered light gradually decreases as the scattering angle increases. To address this, two design improvements are proposed. The first is to make the scattering angle of the holographic diffuser equal to the display viewing angle. However, since the holographic diffuser is used as an image receiving screen, this approach results in a phenomenon where the center is bright and the surrounding area is dark when viewed from different angles, reducing image display quality. The second approach is to make the scattering angle of the holographic diffuser much larger than the display viewing angle. However, this leads to significant energy waste outside the viewing angle range and low energy utilization of the light source.

[0035] Meanwhile, the holographic diffusers sold on the market only have a few specific scattering angles, and their scattered light spot patterns can only be circular or elliptical, which cannot meet the requirements of accurate scattering angle matching in specific applications, as well as the requirements of rectangular, ring, or even more complex illumination spot shapes often needed in beam shaping applications.

[0036] To address the above problems, the present invention provides an apparatus for preparing a uniform holographic diffuser, such as... Figure 1 As shown, it includes a 325nm He-Cd laser, a dual-beam superposition exposure optical path, a 4F spatial filtering system, and a photolithography receiving device, wherein:

[0037] A 325nm He-Cd laser is used to emit 325nm ultraviolet laser light from the exposure source into a dual-beam superposition exposure optical path;

[0038] The dual-beam superposition exposure optical path includes a laser beam expander system, a beam splitter, a reflector, and a source diffuser (frosted glass). The dual-beam superposition exposure optical path is used to expand the ultraviolet laser beam through the laser beam expander system. The expanded ultraviolet laser beam is split into two beams of equal energy by the beam splitter. The two beams of equal energy are then irradiated onto the same position on the same surface of the source diffuser by the reflector.

[0039] The 4F spatial filtering system is used to receive the scattered light emitted by the source diffuser and perform spectral filtering, and then irradiate the photolithography receiving device with the spectral filtered scattered light.

[0040] The photolithography receiving device is used to record the spectral information of the scattered light after spectral filtering. The result obtained by the photolithography receiving device is an undeveloped photoresist master, which is then processed through development and transfer processes to produce the finished holographic diffusion film.

[0041] Specifically, such as Figure 1 As shown, the 4F spatial filtering system includes lens L1, lens L2 and grayscale mask; lens L1 and lens L2 are placed coaxially, and the back focal plane of lens L1 overlaps with the front focal plane of lens L2 to form a confocal plane, and a grayscale mask is placed on the confocal plane of lens L1 and lens L2.

[0042] Specifically, the photolithography receiving device includes a photoresist receiving screen, a clamping device, and a two-dimensional moving stage; wherein, the two-dimensional moving stage can rotate 360° and translate bidirectionally in the horizontal plane, thereby recording and analyzing speckle patterns at different positions and angles in space.

[0043] Specifically, the source diffuser is placed at the front focal plane of lens L1, and the photoresist receiving screen is placed at the rear focal plane of lens L2.

[0044] Specifically, the photoresist receiving screen is made of a quartz substrate spin-coated with AZ4562 photoresist with a thickness of 10μm.

[0045] Specifically, such as Figure 2 As shown, the dual-beam superposition exposure optical path includes a laser beam expander system, a beam splitter, two mirrors, and a source diffuser. The laser beam expander system includes an aspherical mirror, a pinhole aperture, a first cylindrical lens, and a second cylindrical lens arranged sequentially on the same axis. The aspherical mirror and the pinhole aperture form a filtering system to improve the uniformity of the incident light. The first cylindrical lens and the second cylindrical lens have different orientations; the first cylindrical lens is placed horizontally, and the second cylindrical lens is placed vertically, forming an orthogonal arrangement. The distance between the first cylindrical lens and the second cylindrical lens can be flexibly adjusted according to the aspect ratio of the incident beam.

[0046] Specifically, the first cylindrical lens has a focal length of 20mm and the second cylindrical lens has a focal length of 200mm. Both are used to control the shape of the beam and collimate it, forming incident light spots of different sizes and controlling the illumination area.

[0047] Specifically, the laser beam expander system is placed coaxially with the beam splitter, which is located at the back focal plane of the second cylindrical lens. A reflector is placed on both the front and back of the beam splitter. The rectangular uniform beam output by the laser beam expander system is divided into two beams of equal energy by the beam splitter. The two beams of equal energy are emitted from the front and back of the beam splitter and enter the corresponding reflectors. The reflectors are adjusted so that the reflected light of the two beams enters the same position on the same surface of the source diffuser with symmetrical incident angles and the same incident angle value. The incident angle value is usually between 10° and 25°.

[0048] Because the beam enters the source diffuser at a certain incident angle, the spectral distribution of the scattered light generated after a single beam passes through the source diffuser is not symmetrical about the frequency f=0; instead, a spectral shift occurs. Therefore, this embodiment proposes a dual-beam superposition exposure optical path. The spectral synthesis principle of the dual-beam superposition exposure optical path is as follows: Figure 3 As shown, when two beams enter the source diffuser at symmetrical incident angles, the resulting scattered light has opposite spectral offsets but equal offsets, thus forming two symmetrically distributed Gaussian spectra. Based on the continuous nature of the spectrum, a uniform spectrum can be synthesized by splicing the spectra. Spectral distribution and light intensity distribution have a strong similarity. When superimposed into a uniform spectrum, the scattered light intensity of the holographic diffuser is uniform within a certain range during use. In a display system, when viewed from multiple angles, the brightness of the displayed image is uniform, avoiding the situation of a Gaussian spectrum (i.e., a Gaussian light intensity distribution) where the center is bright and the surrounding area is dark.

[0049] This invention also provides a method for preparing a uniform holographic diffuser, comprising the following steps:

[0050] A 1.325nm He-Cd laser emits 325nm laser light, which is then directed to a laser beam expander system to form a rectangular uniform beam.

[0051] S2. A rectangular uniform beam is split into two beams of equal energy by a beam splitter. The two beams of equal energy are then directed by a mirror to the source diffuser at the same incident angle to form scattered light.

[0052] S3. The scattered light is processed by the 4F spatial filtering system for spectral filtering, and the spectrally filtered scattered light illuminates the photoresist receiving screen.

[0053] S4. The photoresist receiving screen records the spectral information of the scattered light after spectral filtering. After the photoresist receiving screen is transferred by PDMS, it is transferred a second time to the K9 glass substrate by photosensitive adhesive to obtain a uniform holographic diffuser.

[0054] Specifically, step S3 involves filtering the scattered light using a 4F spatial filter system.

[0055] S31. The scattered light enters the lens L1. The complex amplitude of the light field of the scattered light is transformed by the Fourier transform of the lens L1 to obtain the spectrum of the scattered light, thus completing the conversion from the spatial domain to the frequency domain.

[0056] S32. Focus the scattered light spectrum onto a grayscale mask for spatial spectrum filtering;

[0057] S33. The spatial spectrum filtering result is subjected to inverse Fourier transform through lens L2, and after completing the conversion from the frequency domain to the spatial domain, it is scattered onto the photoresist receiving screen.

[0058] Specifically, such as Figure 4 As shown, by selecting the focal length f1 of lens L1 and the focal length f2 of lens L2, the range of the speckle field spectrum (spectral information of the scattered light after spectral filtering) of the holographic recording can be controlled. That is, by controlling the maximum diffusion angle of the filtered scattered light received by the photoresist receiving screen, the size of the scattered light spot can be controlled (for example, if the scattered light spots are all circular, then the size of the circular scattered light spot can be controlled here). Taking the change in one-dimensional spatial spectrum distribution as an example, let u be the maximum spatial frequency of the spectrum of the scattered light at the rear surface of the frosted glass (source diffuser). Then, the maximum spatial frequency u' of the spectrum at the receiving surface of the photoresist receiving screen is:

[0059]

[0060] An intensity adjustment function for the grayscale mask is designed to implement the spectral filtering function of the 4F spatial filtering system. Simultaneously, it allows selection of the speckle field spectrum of the holographic recording, controlling the scattering angle to obtain scattered light spot patterns of different shapes. The speckle field spectral distribution is as follows:

[0061] E(u,v)=F{T(x0,y0)}×M(u,v)

[0062] Where E(u,v) represents the speckle field spectrum, T(x0,y0) represents the transmittance function of the source diffuser, M(u,v) represents the intensity modulation function of the grayscale mask, and F represents the Fourier transform.

[0063] Specifically, such as Figure 4 As shown, the white part is the high transmittance part of the grayscale mask, and the black part is the low transmittance part. In the 4F spatial filtering system, the spectral information of the white part is selectively passed through and then recorded by the photoresist receiving screen.

[0064] Preferably, the photoresist receiving screen records the spectral information of the scattered light after spectral filtering; after developing and transferring the photoresist receiving screen containing the filtered speckle field spectral information to PDMS, it is then transferred a second time to a 2mm thick K9 glass substrate using a photosensitive adhesive with a refractive index n=1.56, thus producing a holographic diffuser sheet with high transmittance, structurally resistant to deformation, and with a wide temperature adaptability range.

[0065] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "rotation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An apparatus for preparing a uniform holographic diffuser sheet, characterized in that, It includes a 325nm He-Cd laser, a dual-beam superposition exposure optical path, a 4F spatial filtering system, and a photolithography receiving device, wherein: A 325nm He-Cd laser is used to emit 325nm ultraviolet laser light from the exposure source into a dual-beam superposition exposure optical path; The dual-beam superposition exposure optical path includes a laser beam expander system, a beam splitter, a reflector, and a source diffuser. The dual-beam superposition exposure optical path is used to expand the ultraviolet laser beam through the laser beam expander system. The expanded ultraviolet laser beam is then split by the beam splitter into two beams of equal energy. The reflector is configured to allow the two beams of equal energy to be incident symmetrically at the same position on the same surface of the source diffuser with the same incident angle value, so as to generate two symmetrically distributed scattered light fields that, after being spliced ​​together, form a uniform spectrum. The 4F spatial filtering system includes lens L1, lens L2, and a grayscale mask; lens L1 and lens L2 are placed coaxially, and a grayscale mask is placed on the confocal surface of lens L1 and lens L2; ​​the 4F spatial filtering system is used to receive the scattered light field of the uniform spectrum emitted by the source diffuser, and to use the grayscale mask to perform spatial spectrum filtering on the scattered light field of the uniform spectrum corresponding to the preset spot shape, and to illuminate the photolithography receiving device with the spectrum filtered scattered light; A photolithography receiver is used to record the spectral information of the scattered light after spectral filtering.

2. The apparatus for preparing a uniform holographic diffuser according to claim 1, characterized in that, The laser beam expander system includes an aspherical mirror, a pinhole aperture, a first cylindrical lens, and a second cylindrical lens arranged sequentially on the same axis.

3. The apparatus for preparing a uniform holographic diffuser according to claim 2, characterized in that, The focal length of the first cylindrical lens is 20mm, and the focal length of the second cylindrical lens is 200mm.

4. The apparatus for preparing a uniform holographic diffuser according to claim 1, characterized in that, The photolithography receiving device includes a photoresist receiving screen, a clamping device, and a two-dimensional moving stage.

5. The apparatus for preparing a uniform holographic diffuser according to claim 4, characterized in that, The photoresist receiving screen is made of a quartz substrate spin-coated with AZ4562 photoresist with a thickness of 10μm.

6. The apparatus for preparing a uniform holographic diffuser according to any one of claims 4 or 5, characterized in that, A photoresist receiving screen records the spectral information of the scattered light after spectral filtering. After developing and transferring the spectral information of the scattered light recorded on the photoresist receiving screen with spectral filtering, it is then transferred a second time onto a 2mm thick K9 glass substrate using a photosensitive adhesive with a refractive index of n=1.56, thus creating a holographic diffuser sheet with high transmittance, structurally resistant to deformation, and a wide temperature adaptability range.

7. A method for preparing a uniform holographic diffuser, using the apparatus for preparing a uniform holographic diffuser as described in any one of claims 1-6, characterized in that, Includes the following steps: A 1.325nm He-Cd laser emits 325nm laser light, which is then directed to a laser beam expander system to form a rectangular uniform beam. S2. A rectangular uniform beam is split into two beams of equal energy by a beam splitter. The two beams of equal energy are then directed by a mirror to the source diffuser at the same incident angle to form scattered light. S3. The scattered light is processed by the 4F spatial filtering system for spectral filtering, and the spectrally filtered scattered light illuminates the photoresist receiving screen. S4. The photoresist receiving screen records the spectral information of the scattered light after spectral filtering. The photoresist receiving screen is then developed, transferred by PDMS, and then transferred a second time onto the K9 glass substrate through photosensitive adhesive to obtain a uniform holographic diffuser.

8. The method for preparing a uniform holographic diffuser according to claim 7, characterized in that, Step S3: The process of filtering the scattered light through the 4F spatial filter system. S31. The scattered light enters lens L1 and undergoes Fourier transform to obtain the scattered light spectrum; S32. Focus the scattered light spectrum onto a grayscale mask for spatial spectrum filtering; S33. The spatial spectrum filtering result is scattered to the photoresist receiving screen after inverse Fourier transform by lens L2.

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