Exposure method and device for liquid crystal computer generated hologram
阅读说明：本技术 一种液晶计算全息图的曝光方法和装置 (Exposure method and device for liquid crystal computer generated hologram ) 是由 胡摇 王臻 王劭溥 张万隆 郝群 于 2019-11-22 设计创作，主要内容包括：一种液晶计算全息图的曝光方法及装置,其能够避免目前制作液晶计算全息图采取的掩膜版曝光法的问题,简化制作流程,降低制作成本,缩减掩膜版与待曝光基板间的距离,减少对基板表面光敏材料的破坏。方法包括：(1)构建液晶计算全息图曝光装置,不加入平面镜与空间光调制器；(2)放入涂覆有光敏材料的待曝光基板并进行参数调整；(3)进行第一次曝光；(4)在曝光装置中加入平面镜与空间光调制器,并对两者及待曝光基板进行参数调整,调整空间光调制器的输入参数,使其能够将入射的平面光波调制为预期波前的光波；(5)进行第二次曝光。(An exposure method and device for liquid crystal calculation hologram can avoid the problem of mask exposure method adopted by the prior liquid crystal calculation hologram manufacture, simplify the manufacture process, reduce the manufacture cost, reduce the distance between the mask and the substrate to be exposed and reduce the damage to the photosensitive material on the surface of the substrate. The method comprises the following steps: (1) constructing a liquid crystal calculation hologram exposure device without adding a plane mirror and a spatial light modulator; (2) putting the substrate to be exposed coated with the photosensitive material and adjusting parameters; (3) carrying out first exposure; (4) adding a plane mirror and a spatial light modulator into an exposure device, adjusting parameters of the plane mirror and the spatial light modulator and a substrate to be exposed, and adjusting input parameters of the spatial light modulator to enable the spatial light modulator to modulate incident planar light waves into light waves with expected wave fronts; (5) a second exposure is performed.)
1. An exposure method of a liquid crystal computer generated hologram, characterized in that: which comprises the following steps:
(1) constructing a liquid crystal calculation hologram exposure device without adding a plane mirror and a spatial light modulator;
(2) putting a substrate to be exposed coated with a photosensitive material and adjusting parameters, wherein the parameters comprise a space position and a pitching angle, so that light emitted by a light source vertically enters the substrate;
(3) carrying out first exposure;
(4) adding a plane mirror and a spatial light modulator into an exposure device, adjusting parameters of the plane mirror and the spatial light modulator and a substrate to be exposed, wherein the parameters comprise respective spatial position, pitch angle and angle between the substrate and the plane mirror, and adjusting input parameters of the spatial light modulator to enable the spatial light modulator to modulate incident plane light waves into light waves with expected wave fronts;
(5) a second exposure is performed.
2. The exposure method for liquid crystal computer generated hologram according to claim 1, characterized in that: in the step (3), the laser output beam vertically enters the substrate to be exposed, and the exposure time is determined according to the exposure dose required by the photosensitive material and the output power of the laser.
3. The exposure method for liquid crystal computer generated hologram according to claim 2, characterized in that: in the step (4), the plane mirror and the substrate to be exposed are orthogonally contacted to form a Rockwell mirror structure, and when the output light beam of the laser reaches the Rockwell mirror structure, the included angle between the central line of the output light beam and the plane mirror and the included angle between the output light beam and the substrate to be exposed are determined according to the pattern to be exposed; and adjusting the input electric signal of the spatial light modulator, wherein the input electric signal is not loaded in the area corresponding to the half of the light beam incident to the substrate, and the input electric signal loaded in the area corresponding to the half of the light beam incident to the plane mirror is determined according to the pattern to be exposed.
4. The exposure method for liquid crystal computer generated hologram according to claim 3, characterized in that: in the step (5), the exposure time is determined according to the required exposure dose of the photosensitive material and the output power of the laser.
5. An exposure apparatus for a liquid crystal computer generated hologram, characterized in that: it includes: the device comprises a laser (1), a beam expander (2), a collimating mirror (3), a linear polarizer (4), a spatial light modulator (5), a Rockwell mirror (6) and a substrate to be exposed (7); the laser emits small-caliber parallel laser beams, and the small-caliber parallel laser beams are expanded into wide-caliber parallel laser beams after passing through the beam expander and the collimating mirror to become planar light waves; the expanded light is changed into linearly polarized light through a linear polarizer and then vertically enters the spatial light modulator; taking the middle line of the cross section of the light beam as a boundary, half of the plane light wave is subjected to wavefront modulation by the spatial light modulator and converted into light wave with expected wavefront, and the other half is not modulated and still emits out as the plane light wave; the plane mirror is orthogonally contacted with the substrate to be exposed to form a Rockwell mirror structure; the central line of the light beam passes through the intersection line of the light beam and the light beam, the unmodulated half of the light wave directly enters the surface of the substrate, and the modulated half of the light wave enters the plane mirror and is reflected to the surface of the substrate; the two parts of light are completely overlapped in the irradiation range of the substrate surface, and interfere with each other to generate expected interference fringes so as to realize the exposure of the photosensitive material.
6. The exposure apparatus for liquid crystal computer generated hologram according to claim 5, wherein: the laser is a single-wavelength laser with ultraviolet or blue light wave band, and the specific wavelength is determined according to the absorption characteristic of the photosensitive material.
7. The exposure apparatus for liquid crystal computer generated hologram according to claim 6, wherein: the working spectral ranges of the beam expander and the collimating lens are adjusted along with the laser.
8. The exposure apparatus for liquid crystal computer generated hologram according to claim 7, wherein: the linear polarizer has an extinction ratio of not less than 500: 1.
9. The exposure apparatus for liquid crystal computation holograms of claim 8, characterized in that: the spatial light modulator is a transmission type and phase type spatial light modulator, and the size of an image surface of the spatial light modulator is not smaller than the aperture of a beam after beam expansion; the plane mirror is a rectangular plane mirror, and the size of the plane mirror is selected by integrating the size of the substrate to be exposed and the aperture of the beam after beam expansion.
10. The exposure apparatus for liquid crystal computation holograms of claim 9, characterized in that: the surface of the substrate to be exposed is coated with a photosensitive material capable of performing photo-alignment on liquid crystal.
Technical Field
The invention relates to the technical field of optical precision manufacturing, in particular to an exposure method of a liquid crystal computer hologram and an exposure device of the liquid crystal computer hologram.
Background
The computer holographic method is one kind of aspheric surface detecting method and belongs to the field of zero compensating interference method. The computer generated hologram is a diffraction element, and theoretically, the interconversion between the spherical wave and any aspheric wave can be realized through the diffraction principle. The liquid crystal calculation hologram is a novel calculation hologram, and the calculation hologram is manufactured by a liquid crystal photo-alignment technology based on the birefringence characteristic of liquid crystal.
The liquid crystal computer hologram has more manufacturing steps, wherein the key step is photoalignment. The liquid crystal photoalignment technology has the basic principle that certain photosensitive materials can perform physical or chemical reaction under the irradiation of ultraviolet linear polarized light, so that anisotropic surface acting force can be generated, and then liquid crystal molecules are induced to be aligned.
At present, the exposure method of the liquid crystal computer hologram is a mask exposure method, and the thought is as follows: coating photosensitive materials with uniform thickness on the surface of a substrate to be exposed, using an ultraviolet lamp or a blue lamp as a light source, modulating light emitted by the light source into linearly polarized light through a polarizing film, and carrying out primary exposure on the surface of the whole substrate to be exposed; and then adjusting the direction of the linearly polarized light to be vertical to the previous polarization direction, covering the mask plate with the pattern to be exposed on the surface of the substrate, and carrying out second exposure. After exposure, liquid crystal solution is coated on the surface of the substrate, and the photosensitive material can induce liquid crystal molecules to be directionally arranged, so that the liquid crystal photoalignment is completed.
The mask exposure method has some inherent limitations, for example, a 1:1 mask with the same calculation hologram pattern needs to be manufactured before the liquid crystal calculation hologram is manufactured, so the manufacturing time is long, and the manufacturing cost is high. And the mask plate is provided with a fixing device, such as a vacuum adsorption device, for reducing the gap between the mask plate and the substrate. Otherwise, if the gap between the mask and the substrate surface is too large, light path deviation can be generated due to diffraction and other reasons after the light passes through the mask, and the photosensitive material which is not exposed under the opaque region of the mask can be exposed, so that the liquid crystal computer hologram with the expected pattern can not be obtained. In addition, in the reticle exposure method, a large area of the substrate surface is required to be in contact with the reticle, and damage may be caused to the photosensitive material layer coated on the substrate surface.
Spatial light modulators are devices that modulate the spatial distribution of light waves, either under the control of a time-varying electrical drive signal or under the influence of another spatial light intensity distribution, to change the phase, polarization, amplitude (or intensity) of the incident light, or to effect the conversion of incoherent light into coherent light.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides an exposure method of a liquid crystal calculation hologram, which can avoid the problem of a mask exposure method adopted by the conventional liquid crystal calculation hologram manufacturing, simplify the manufacturing process, reduce the manufacturing cost, reduce the distance between the mask and a substrate to be exposed and reduce the damage to a photosensitive material on the surface of the substrate.
The technical scheme of the invention is as follows: the exposure method of the liquid crystal computer hologram comprises the following steps:
(1) constructing a liquid crystal calculation hologram exposure device without adding a plane mirror and a spatial light modulator;
(2) putting a substrate to be exposed coated with a photosensitive material and adjusting parameters, wherein the parameters comprise a space position and a pitching angle, so that light emitted by a light source vertically enters the substrate;
(3) carrying out first exposure;
(4) adding a plane mirror and a spatial light modulator into an exposure device, adjusting parameters of the plane mirror and the spatial light modulator and a substrate to be exposed, wherein the parameters comprise respective spatial position, pitch angle and angle between the substrate and the plane mirror, and adjusting input parameters of the spatial light modulator to enable the spatial light modulator to modulate incident plane light waves into light waves with expected wave fronts;
(5) a second exposure is performed.
According to the invention, by utilizing the interference principle of the Luoene lens structure and the modulation function of the spatial light modulator on the light wave phase, the defect of a mask exposure method adopted by the conventional liquid crystal calculation hologram manufacturing process can be overcome, a mask with the same calculation hologram pattern does not need to be manufactured in advance, the manufacturing process is simplified, and the manufacturing cost is reduced; compared with an exposure device of a mask exposure method, the device simplifies a fixing device at the mask, and does not need a vacuum adsorption device to reduce the distance between the mask and a substrate to be exposed; the contact area between the substrate and the plane mirror is small, so that large-area damage to the photosensitive material on the surface of the substrate is avoided.
There is also provided an exposure apparatus for a liquid crystal computer generated hologram, comprising: the device comprises a laser (1), a beam expander (2), a collimating mirror (3), a linear polarizer (4), a spatial light modulator (5), a Rockwell mirror (6) and a substrate to be exposed (7); the laser emits small-caliber parallel laser beams, and the small-caliber parallel laser beams are expanded into wide-caliber parallel laser beams after passing through the beam expander and the collimating mirror to become planar light waves; the expanded light is changed into linearly polarized light through a linear polarizer and then vertically enters the spatial light modulator; taking the middle line of the cross section of the light beam as a boundary, half of the plane light wave is subjected to wavefront modulation by the spatial light modulator and converted into light wave with expected wavefront, and the other half is not modulated and still emits out as the plane light wave; the plane mirror is orthogonally contacted with the substrate to be exposed to form a Rockwell mirror structure; the central line of the light beam passes through the intersection line of the light beam and the light beam, the unmodulated half of the light wave directly enters the surface of the substrate, and the modulated half of the light wave enters the plane mirror and is reflected to the surface of the substrate; the two parts of light are completely overlapped in the irradiation range of the substrate surface, and interfere with each other to generate expected interference fringes so as to realize the exposure of the photosensitive material.
Drawings
Fig. 1 is a flowchart of an exposure method of a liquid crystal computation hologram according to the present invention.
Fig. 2 is a schematic configuration diagram of an exposure apparatus for liquid crystal computer holograms according to the present invention.
The device comprises a laser 1, a beam expander 2, a
Detailed Description
As shown in fig. 1, the exposure method of the liquid crystal computer hologram comprises the following steps:
(1) constructing a liquid crystal calculation hologram exposure device without adding a plane mirror and a spatial light modulator;
(2) putting a substrate to be exposed coated with a photosensitive material and adjusting parameters, wherein the parameters comprise a space position and a pitching angle, so that light emitted by a light source vertically enters the substrate;
(3) carrying out first exposure;
(4) adding a plane mirror and a spatial light modulator into an exposure device, adjusting parameters of the plane mirror and the spatial light modulator and a substrate to be exposed, wherein the parameters comprise respective spatial position, pitch angle and angle between the substrate and the plane mirror, and adjusting input parameters of the spatial light modulator to enable the spatial light modulator to modulate incident plane light waves into light waves with expected wave fronts;
(5) a second exposure is performed.
According to the invention, by utilizing the interference principle of the Luoene lens structure and the modulation function of the spatial light modulator on the light wave phase, the defect of a mask exposure method adopted by the conventional liquid crystal calculation hologram manufacturing process can be overcome, a mask with the same calculation hologram pattern does not need to be manufactured in advance, the manufacturing process is simplified, and the manufacturing cost is reduced; compared with an exposure device of a mask exposure method, the device simplifies a fixing device at the mask, and does not need a vacuum adsorption device to reduce the distance between the mask and a substrate to be exposed; the contact area between the substrate and the plane mirror is small, so that large-area damage to the photosensitive material on the surface of the substrate is avoided.
Preferably, in the step (3), the laser output beam is perpendicularly incident on the substrate to be exposed, and the exposure time is determined according to the required exposure dose of the photosensitive material and the output power of the laser.
Preferably, in the step (4), the plane mirror is orthogonally contacted with the substrate to be exposed to form a lorentzian mirror structure, and when the laser output beam reaches the lorentzian mirror structure, an included angle between a central line of the laser output beam and the plane mirror and an included angle between the central line of the laser output beam and the substrate to be exposed are determined according to the pattern to be exposed; and adjusting the input electric signal of the spatial light modulator, wherein the input electric signal is not loaded in the area corresponding to the half of the light beam incident to the substrate, and the input electric signal loaded in the area corresponding to the half of the light beam incident to the plane mirror is determined according to the pattern to be exposed.
Preferably, in the step (5), the exposure time is determined according to the required exposure dose of the photosensitive material and the output power of the laser.
As shown in fig. 2, there is also provided an exposure apparatus for a liquid crystal computer hologram, comprising: the device comprises a laser 1, a beam expander 2, a
Preferably, the laser is a single-wavelength laser in ultraviolet or blue light band, and the specific wavelength is determined according to the absorption characteristic of the photosensitive material.
Preferably, the working spectral ranges of the beam expander and the collimating mirror are adjusted with the laser.
Preferably, the linear polarizer has an extinction ratio of not less than 500: 1.
Preferably, the spatial light modulator is a transmission type and phase type spatial light modulator, and the image plane size of the spatial light modulator is not smaller than the aperture of the expanded beam; the plane mirror is a rectangular plane mirror, and the size of the plane mirror is selected by integrating the size of the substrate to be exposed and the aperture of the beam after beam expansion.
Preferably, the substrate to be exposed has a surface coated with a photosensitive material capable of photoaligning liquid crystals.
One embodiment of the present invention is described in detail below.
The liquid crystal computer hologram pattern to be exposed in this embodiment is an equidistant straight stripe with a period of 405.130 mm. In the exposure process, the laser 1 is a blue light band laser with the central wavelength of 405.130nm, the output power is 44mW, and the diameter of a light spot after passing through the beam expander 2 and the
Calculating a hologram pattern and equipment according to the liquid crystal to be exposed, and determining an exposure scheme: the laser output beam vertically enters the substrate to be exposed during the first exposure, and the exposure time is five minutes; when the output beam of the laser reaches the Rockwell mirror structure, the included angle between the central line and the plane mirror is 30 degrees, and the included angle between the central line and the substrate to be exposed is 60 degrees. In an image plane of the spatial light modulator, an input electric signal does not need to be loaded in an area corresponding to a half of light beam incident to the plane mirror and an area corresponding to a half of light beam incident to the substrate. The exposure time was ten minutes.
The exposure steps are as follows:
the method comprises the following steps: the liquid crystal calculation hologram exposure device is constructed without adding a plane mirror and a spatial light modulator.
Step two: and putting the substrate to be exposed coated with the photosensitive material, and adjusting parameters, wherein the parameters comprise a space position and a pitching angle, so that light emitted by the light source vertically enters the region to be exposed on the substrate.
Step three: the first exposure was carried out for five minutes.
Step four: the plane mirror and the spatial light modulator are added into the exposure device, parameters of the plane mirror and the spatial light modulator and a substrate to be exposed are adjusted, wherein the parameters comprise respective spatial position, pitch angle and angle between the substrate and the plane mirror, so that an included angle between the substrate and the plane mirror is 90 degrees, an intersection line of the substrate and the plane mirror is perpendicular to a light beam central line, an included angle between the light beam central line and the plane mirror is 30 degrees, and an included angle between the light beam central line and the plane mirror is 60 degrees. The input electrical signal of the spatial light modulator is zeroed.
Step five: a second exposure was performed for ten minutes.
The invention has the following beneficial effects:
(1) the method of the invention firstly provides a liquid crystal calculation hologram exposure method based on a Luoyer mirror and a spatial light modulator, which is characterized in that the method utilizes the interference principle of the structure of the Luoyer mirror and the modulation function of the spatial light modulator on the light wave phase, can overcome the defects of the mask exposure method adopted by the prior liquid crystal calculation hologram manufacture, does not need to manufacture a mask with the same calculation hologram pattern in advance, simplifies the manufacturing process and reduces the manufacturing cost.
(2) Compared with an exposure device of a mask exposure method, the device simplifies a fixing device at the mask, and does not need a vacuum adsorption device to reduce the distance between the mask and a substrate to be exposed.
(3) The device of the invention has small contact area between the substrate and the plane mirror, and avoids large-area damage to the photosensitive material on the surface of the substrate.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications, equivalent variations and modifications made to the above embodiment according to the technical spirit of the present invention still belong to the protection scope of the technical solution of the present invention.
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