WO2024050973A1 - 一种反射式弯曲叉形面光栅的制备装置和方法 - Google Patents

一种反射式弯曲叉形面光栅的制备装置和方法 Download PDF

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WO2024050973A1
WO2024050973A1 PCT/CN2022/133141 CN2022133141W WO2024050973A1 WO 2024050973 A1 WO2024050973 A1 WO 2024050973A1 CN 2022133141 W CN2022133141 W CN 2022133141W WO 2024050973 A1 WO2024050973 A1 WO 2024050973A1
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light
slm
lens
grating
adjust
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晋云霞
吴昱博
孔钒宇
赵靖寅
张益彬
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中国科学院上海光学精密机械研究所
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1847—Manufacturing methods
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1861—Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

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  • the invention relates to the technical fields of reflective surface gratings and vortex beams, and in particular to a preparation device and method for reflective curved fork surface gratings.
  • Vortex light as the core research content of singularity optics, has received widespread attention.
  • a vortex beam is a beam with vortex characteristics.
  • the phase or wavefront of this light is spiral, and the complex amplitude contains a spiral phase term, which can be expressed as where l is the topological charge, is the angular coordinate.
  • Each photon in the vortex beam carries Orbital angular momentum (OAM), and this orbital angular momentum can be transferred to the radiated particles.
  • OFAM Orbital angular momentum
  • Vortex beams have orthogonality, that is, any two vortex beams of different orders are orthogonal to each other, and vortex beams of different orders can be separated from each other. Due to these unique properties, vortex beams have great potential value in many fields, such as optical communications, detection, optical tweezers and optical wrenches, optical processing, celestial body detection, quantum information processing and other fields.
  • vortex light with larger topological charges is often required.
  • the ring radius of traditional vortex light will increase as the topological charge increases.
  • larger topological charges and smaller spot sizes are needed to achieve good capture effects.
  • vortex lights with different topological charges need to be coaxially transmitted. Due to their different radii, it is difficult to couple them into fixed optical fibers.
  • the present invention proposes a device and method for preparing a reflective curved fork grating.
  • the method has a simple principle and a simple optical path.
  • the prepared grating has a high damage threshold and a simple structure. , can be mass-produced, and can produce high-power perfect vortex light.
  • a method for preparing a reflective curved fork grating which is characterized in that the method includes the following steps:
  • Step 1) Construct an optical path: set a laser, a beam expander, a linear polarizer and a depolarizing beam splitter coaxially; the depolarizing beam splitter divides the incident light into reflected light and transmitted light; along the reflected light
  • the optical path is sequentially provided with a reflector group, a microscopic objective lens with a pinhole, a first collimating lens and a rotating base for placing the grating sample to be exposed; an SLM is provided along the optical path of the transmitted light, and the SLM is controlled by the PC connected end to end;
  • Step 2) Adjust the optical path: start the laser, adjust the multiple of the beam expander so that the beam spot diameter after expansion is smaller than the short side length of the SLM screen, adjust the angle of the SLM without loading phase information, The light energy is returned along the original path and is incident on the depolarizing beam splitter and reflected to form a second reflected light;
  • Step 3) Construct an exposure optical path: set a Fourier lens, an adjustable aperture diaphragm, an attenuating plate, a third reflector and a second collimating mirror along the optical path of the second reflected light;
  • Step 4) Calculate the hologram loaded by SLM, that is, the phase increment ⁇ (x,y) provided by the incident fundamental mode Gaussian light.
  • the formula is as follows:
  • (x, y) is the position coordinate
  • l is the topological charge value of the perfect vortex light
  • atan2(y, x) is the four-quadrant arc tangent of the coordinate
  • ⁇ is the laser.
  • the wavelength of For the period number on, take g y 0, so that the diffraction spots at all levels are distributed laterally;
  • D is the diameter of the aperture (8)
  • r POV is the radius of the POV on the focal plane:
  • L 2 is the distance between the second-order diffracted light and the 0-order light:
  • f is the focal length of the lens
  • m is the diffraction order
  • H is the actual x-direction length of the SLM display screen
  • phase increment ⁇ (x, y) is mapped to the gray value range of (0, 255) using the following formula
  • the gray value distribution map is loaded on the SLM display screen, the object light is modulated by the SLM, and the light field of the first-order diffracted light is the Bessel Gaussian light field;
  • Step 5 Adjust the angle ⁇ between the object light and the reference light: temporarily remove the vortex light phase loaded by the SLM, leaving only the blazed grating phase; temporarily replace the sample to be exposed with a mirror; adjust the angle of the rotating base to make the object light path Return to the original path; turn the rotating base at an angle of ⁇ /2, adjust the position and angle of the reflector group so that the reference light path coincides with the object light path, then the angle between the object light path and the reference light path is ⁇ , and the grating period is:
  • Step 6 Adjust the position and angle of the Fourier lens so that the front focal plane coincides with the SLM screen and the center is perpendicular to the first-order diffracted light. Adjust the position of the aperture so that it is aligned with the back focus of the lens. The surfaces are coplanar, and the aperture size is adjusted to allow only the first-order diffracted light to pass through the aperture;
  • Step 7) Rotate the polarizing plate to select the polarization direction with the strongest first-order diffracted light intensity.
  • the diffracted light is reflected by the reflecting mirror.
  • Adjust the position of the collimating lens so that the front focal plane of the lens is in line with the polarization direction.
  • the planes where the diaphragm is located coincide with each other, and the angle of the collimating lens is adjusted so that the first-order diffracted light passes vertically through the center of the lens; at this time, the light field on the back focal plane of the collimating lens is an amplification of the light field on the front focal plane of the lens.
  • the magnification is the ratio of the focal lengths of the two lenses.
  • Step 8) The light field interferes with the reference light to form an interference light field.
  • the intensity distribution of the interference light field is a curved fork-shaped stripe distribution.
  • the grating sample to be exposed in the interference area is plated with metal after exposure and development. film to prepare a reflective curved fork grating.
  • the depolarizing beam splitter divides incident light into reflected light and transmitted light without changing the polarization state of the incident beam, and the splitting ratio is 1:1.
  • the phase image loaded by the SLM is a grayscale image, with a grayscale value ranging from 0 to 255, corresponding to a phase increment of 0 to 2 ⁇ .
  • the PC control terminal is connected to the SLM and controls the phase diagram loaded by the SLM.
  • the grating sample to be exposed includes a substrate and a photosensitive material on the substrate, and the photosensitive material evenly covers the substrate.
  • the substrate is a film or substrate made of fused quartz, silicon carbide, silicon or metal.
  • the metal material is gold or silver (Au/Ag), and the thickness of the metal film is 100 to 220 nanometers.
  • the photosensitive material is photoresist. After the photoresist is exposed to light of a specific wavelength, chemical decomposition or polymerization reaction will occur.
  • the optical path of the present invention has high conversion efficiency, low cost, high damage threshold, wide spectrum, small size, etc.
  • High-power perfect vortex light can be obtained, which has important application prospects in optical communications, optical manipulation and other fields.
  • Figure 1 Schematic diagram of the optical path of the preparation of the reflective curved fork grating of the present invention.
  • Figure 2 In the embodiment of the present invention, the pattern loaded on the reflective pure phase liquid crystal spatial light modulator, g x is 37.5, g y is 0, the corresponding blazed grating period is 32 microns, and the topological charge l is 3 , the refractive index n of the cone lens is set to 1.5, and the base angle parameter ⁇ of the cone lens is 0.8°.
  • Figure 3 The overall distribution diagram of the diffraction light field of the curved fork grating simulated according to the embodiment of the present invention.
  • Figure 4 Diffraction light field + 1st order distribution diagram of the curved fork grating simulated according to the embodiment of the present invention.
  • Figure 5 The light intensity distribution at the plane where the aperture is located experimentally obtained according to the embodiment of the present invention, and a series of POV rings appear.
  • Figure 6 Diffraction light field + 1st order distribution diagram of the curved fork grating experimentally obtained according to the embodiment of the present invention.
  • Figure 1 is a schematic diagram of the preparation device of the reflective curved fork grating of the present invention.
  • the preparation device of the reflective curved fork grating of the present invention includes: 1. Laser; 2. Beam expander; 3. Linear polarizing plate; 4. Depolarizing beam splitter; 5. Reflective pure phase liquid crystal Spatial light modulator (SLM); 6. PC control terminal; 7. Fourier lens; 8. Adjustable aperture diaphragm; 9. Attenuator; 10. Third reflector; 11. Second collimating mirror; 12 , first reflecting mirror; 13. second reflecting mirror; 14. microscope objective with pinhole; 15. first collimating mirror; 16. grating sample to be exposed; 17. rotating base.
  • SLM Spatial light modulator
  • a method for preparing a reflective all-dielectric curved fork grating includes the following steps:
  • the laser wavelength is 413 nanometers
  • the Gaussian spot radius after beam expansion is 3 mm
  • the SLM screen size is 8.64 mm * 15.36 mm;
  • D is the diameter of the aperture, which is 1 mm
  • r POV is the radius of the POV on the focal plane
  • L 2 is the distance between the second-order diffracted light and the 0-order light:
  • f is the focal length of lens 7, which is 30 millimeters
  • m is the diffraction order
  • H is the actual x-direction length of the SLM display screen, which is 15.36 millimeters.
  • the value of ⁇ is 0.8 within the value range of ⁇ .
  • Adjust the angle ⁇ between the object light and the reference light In the example, the value is 33.6°, corresponding to the grating linear density 1400: temporarily remove the vortex light phase loaded by the SLM and only retain the blazed grating phase; temporarily replace it with a reflector Sample to be exposed; adjust the angle of the rotating base so that the object light path returns to its original path; rotate the rotating base 16.8° and adjust the position and angle of the reflector so that the reference light path coincides with the object light path.

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)

Abstract

一种反射式弯曲叉形面光栅的制备方法，方法制备出的光栅为纯相位光栅，可用于产生完美涡旋光(POV)。通过一束高阶贝塞尔高斯光束与高斯光干涉曝光，其中高阶贝塞尔高斯光束由反射式纯相位液晶空间光调制器(SLM)（5）产生，将干涉条纹记录在基底上的光敏材料中，经显影、镀金属膜后，即可制备出反射式弯曲叉形面光栅。使用基模高斯光照射，可在1级衍射方向的远场或透镜焦平面上获得 POV。这种利用反射式弯曲叉形面光栅获得POV的方法，相对于使用空间光调制器的传统方法，优势在于具有更高的损伤阈值、更宽的工作波长范围、以及更高的转换效率，且结构简单、成本低、可大批量生产，在产生高功率POV方面具有重要的前景，可用于光学操控、光学加工等领域。

Description

一种反射式弯曲叉形面光栅的制备装置和方法 技术领域
本发明涉及反射式面光栅和涡旋光束技术领域，特别是一种反射式弯曲叉形面光栅的制备装置和方法。
背景技术
涡旋光作为奇点光学的核心研究内容，得到了广泛的关注。涡旋光束是具有涡旋特性的光束，这种光的相位或波前呈螺旋形，复振幅含有螺旋相位项，可以表示为
Figure PCTCN2022133141-appb-000001
其中l是拓扑荷，
Figure PCTCN2022133141-appb-000002
是角向坐标。涡旋光束中的每一个光子都携带
Figure PCTCN2022133141-appb-000003
的轨道角动量(OAM)，并且这种轨道角动量可以传递到被辐射的微粒上。涡旋光束具有正交性，即任意两束不同阶次的涡旋光相互正交，不同阶次的涡旋光束可以相互分离。由于具有这些独特的性质，涡旋光束在许多领域具有很大的潜在价值，比如光通信领域，探测领域，光镊和光学扳手，光学加工，天体探测，量子信息处理等领域。
在上述的领域中，为了追求更好的性能，往往需要具有较大拓扑荷的涡旋光。但是传统的涡旋光的环半径会随着拓扑荷的增大而增大。在光操控领域，需要较大的拓扑荷和较小的光斑尺寸，来实现好的捕获效果。在光通信领域，需要同轴传输不同拓扑荷值的涡旋光，由于它们的半径不同，很难将它们耦合到固定的光纤中。
2013年，Ostrovsky等人首次提出完美涡旋光这一概念，它们的环径与拓扑荷值无关【Opt Lett 38,534-536(2013)】。他们使用空间光调制器得到了完美涡旋光，但是存在多个次级的亮环，信噪比很低。同年，chen等人用锥透镜配合反射式空间相位调制器(以下简称为SLM)产生了涡旋光，得到了质量更好的完美涡旋光，并观察到它可以用来束缚粒子【Opt Lett 38,4919-4922(2013)】。2015年，Pravin Vaity等人将锥透镜的透过率函数和相位掩模板叠加在SLM上，通过改变锥角，实现了对完美涡旋光束尺寸的控制【Opt Lett 40,597-600(2015)】。2016年，Chaitanya将螺旋相位板和锥透镜级联，产生了高能高阶的完美涡旋光【Opt Lett 41,1348-1351(2016)】，但光路非常复杂，光学 中心也难以对准。在实际运用中，目前最普遍方式是用SLM产生完美涡旋光(POV)，但是成本高，设备体积较大，其液晶结构使损伤阈值难以提高，无法产生高功率的完美涡旋光。
发明内容
本发明针对目前制备高功率的完美涡旋光较为困难的问题，提出一种反射式弯曲叉形面光栅的制备装置和方法，该方法原理简单，光路简洁，制备出的光栅损伤阈值高，结构简单，可大批量生产，可以实现产生高功率的完美涡旋光。
本发明的技术解决方案如下：
一种反射式弯曲叉形面光栅的制备方法，其特点在于，该方法包括如下步骤：
步骤1)构建光路：同轴设置激光器、扩束器、线偏振片和消偏振分束器；所述的消偏振分束器将入射光分为反射光和透射光；沿所述的反射光的光路依次设置反射镜组、带针孔的显微物镜、第一准直镜和供待曝光的光栅样品放置的旋转基座；沿所述的透射光的光路设置SLM，该SLM与PC控制端相连；
步骤2)调节光路：启动所述的激光器，调整所述的扩束器的倍数，使扩束后的光斑直径小于SLM的屏幕短边长，在不加载相位信息的情况下调整SLM的角度，使光能沿原路返回，入射至所述的消偏振分束器反射形成第二反射光；
步骤3)构建曝光光路：沿所述的第二反射光的光路设置傅里叶透镜、可调孔径光阑、衰减片第三反射镜和第二准直镜；
步骤4)计算SLM加载的全息图，即入射基模高斯光提供的相位增量Ф(x,y)，公式如下：
Figure PCTCN2022133141-appb-000004
式中，(x,y)为位置坐标，l为完美涡旋光的拓扑荷值，atan2(y，x)为坐标的四 象限反正切，k＝2π/λ为曝光光束的波数，λ为激光器的波长，γ与n为锥透镜相位参数，其中，γ等效为锥透镜底角，n等效为锥透镜折射率，g x和g y分别为屏幕范围内的闪耀光栅在x和y方向上的周期数，取g y＝0，使各级衍射光斑在横向分布；
γ、n和g x之间满足以下关系：
2r POV＜D＜L 2-2r POV
式中，D为光阑(8)的直径，r POV为焦平面上的POV的半径：
r POV＝tan(arcsin(n·sin(γ))-γ)·f
L 2是二级衍射光与0级光的间距：
L m＝f·tanθ m
Figure PCTCN2022133141-appb-000005
式中，f为透镜的焦距，m为衍射级次，H为SLM显示屏实际的x方向长度；
所述的PC控制端控制下，将所述的相位增量Ф(x,y)，利用下式映射到(0，255)的灰度值范围
Figure PCTCN2022133141-appb-000006
将该灰度值分布图加载在所述的SLM显示屏上，物光经由SLM调制，1级衍射光的光场即为所述的贝塞尔高斯光场；
步骤5)调节物光与参考光之间夹角φ：暂时移除SLM加载的涡旋光相位，只保留闪耀光栅相位；暂时以一反射镜替代待曝光样品；调节旋转基座角度，使物光路以原路返回；转动旋转基座φ/2角度，调节反射镜组位置与角度，使参考光路与物光光路重合，则物光光路与参考光光路夹角为φ，光栅周期为：
Figure PCTCN2022133141-appb-000007
步骤6)调节所述的傅里叶透镜的位置与角度，使前焦面与SLM屏幕重合，并中心垂直于1级衍射光，调节所述的光阑的位置，使其与透镜的后焦面共面，调节孔径大小，仅使1级衍射光经过光阑；
步骤7)旋转所述的偏振片，选择1级衍射光强相对最强的偏振方向，衍射光被所述的反射镜反射，调节所述的准直透镜的位置，使透镜的前焦面与光阑所在平面重合，调节所述的准直透镜的角度，使1级衍射光垂直经过透镜中心；此时在准直透镜的后焦面上的光场为透镜前焦面上光场的放大，放大倍数为两透镜的焦距之比。
步骤8)所述光场与参考光干涉形成干涉光场，该干涉光场强度分布呈弯曲叉形条纹分布，在干涉区域内所述的待曝光的光栅样品，经曝光、显影后，镀金属膜，制备出反射式弯曲叉形面光栅。
所述的消偏振分束器将入射光分为反射光和透射光，不改变入射光束的偏振态，分光比为1:1。
所述的SLM加载的相位图为灰度图，灰度值范围0～255，对应相位增量0～2π。
所述的PC控制端与所述的SLM相连，并控制SLM加载的相位图。
所述的待曝光的光栅样品包括基底以及基底上的光敏材料，且光敏材料均匀地覆盖在基底上。
所述衬底为熔石英、碳化硅、硅或金属材质的薄膜或基板。
所述金属材料为金或银(Au/Ag)，金属膜厚度为100～220纳米。
所述光敏材料为光刻胶，该光刻胶被特定波长的光曝光后，会发生化学分解或聚合反应。
本发明的有益技术效果：
首次提出基于反射式弯曲叉形面光栅产生完美涡旋光的方法和系统，同使用SLM产生POV的技术相比，本发明光路具有转换效率高，成本低，损伤阈值高，宽光谱，体积小等优点，可获得高功率的完美涡旋光，在光通信、光操纵等领域中具有重要的应用前景。
附图说明
图1：本发明反射式弯曲叉形面光栅的制备的光路示意图。
其中，1、激光器；2、扩束器；3、线偏振片；4、消偏振分束器；5、反射式纯相位液晶空间光调制器(SLM)；6、PC控制端；7、傅里叶透镜；8、可调孔径光阑；9、衰减片；10、第三反射镜；11、第二准直镜；12、第一反 射镜；13、第二反射镜；14、带针孔的显微物镜；15、第一准直镜；16、待曝光的光栅样品；17、旋转基座。
图2：本发明实施例中，在反射式纯相位液晶空间光调制器上加载的图案，g x取37.5，g y取0，对应闪耀光栅周期为32微米，拓扑荷值l取值为3，锥透镜折射率n设为1.5，锥透镜底角参数γ为0.8°。
图3：本发明实施例仿真得到的弯曲叉形光栅的衍射光场整体分布图。
图4：本发明实施例仿真得到的弯曲叉形光栅的衍射光场+1级分布图。
图5：本发明实施例实验得到的光阑所在平面处的光强分布，出现一系列POV圆环。
图6：本发明实施例实验得到的弯曲叉形光栅的衍射光场+1级分布图。
具体实施方式
现结合实施例、附图对本发明作进一步描述。以下实例仅是为了解释本发明，并不对其内容进行限定。如果实施例中未注明的实验具体条件，通常按照常规条件，或按照销售公司所推荐的条件。
请参阅图1，图1是本发明反射式弯曲叉形面光栅的制备装置示意图。由图可见，本发明反射式弯曲叉形面光栅的制备装置，包括：1、激光器；2、扩束器；3、线偏振片；4、消偏振分束器；5、反射式纯相位液晶空间光调制器(SLM)；6、PC控制端；7、傅里叶透镜；8、可调孔径光阑；9、衰减片；10、第三反射镜；11、第二准直镜；12、第一反射镜；13、第二反射镜；14、带针孔的显微物镜；15、第一准直镜；16、待曝光的光栅样品；17、旋转基座。
制备反射式全介质弯曲叉形面光栅的方法，包括如下步骤：
1)启动激光器1，调整扩束器2的倍数，使扩束后的光斑直径略小于SLM(5的屏幕短边长，在不加载相位信息的情况下调整SLM5的角度，使光能沿原路返回，实施例中激光器波长为413纳米，扩束后高斯光斑半径3毫米，SLM屏幕尺寸8.64毫米*15.36毫米；
2)计算SLM5需要加载的计算全息图。计算全息图为入射基模高斯光提供的相位增量为：
Figure PCTCN2022133141-appb-000008
其中，l为完美涡旋光的拓扑荷值，设为3，atan2(y，x)为坐标的四象限反正切，k＝2π/λ为曝光光束的波数，λ为激光器1的波长，为413纳米，γ与n为锥透镜相位参数，γ等效为锥透镜底角，n等效为锥透镜折射率，设为1.5，g x和g y分别为屏幕范围内的闪耀光栅在x和y方向上的周期数，取g x为37.5，g y为0，对应闪耀光栅周期为32微米，各级衍射光斑横向分布，焦平面处强度分布图如附图5所示。
由γ、n和g x之间的关系：
2r POV＜D＜L 2-2r POV
其中D为光阑的直径，为1毫米，r POV为焦平面上的POV的半径：
r POV＝tan(arcsin(n·sin(γ))-γ)·f
L 2是二级衍射光与0级光的间距：
L m＝f·tanθ m
Figure PCTCN2022133141-appb-000009
f为透镜7的焦距，为30毫米，m为衍射级次，H为SLM显示屏实际的x方向长度，为15.36毫米，本实施例在γ的取值范围内取值0.8。
3)将相位增量Ф(x,y)，利用下式映射到(0，255)的灰度值范围
Figure PCTCN2022133141-appb-000010
将该灰度值分布图加载在所述的SLM显示屏上，1级衍射光的光场即为所述的贝塞尔高斯光场；
4)调节物光与参考光之间夹角φ，实施例中取值33.6°，对应光栅线密度1400：暂时移除SLM加载的涡旋光相位，只保留闪耀光栅相位；暂时以一反射镜替代待曝光样品；调节旋转基座角度，使物光路以原路返回；转动旋转基座16.8°，调节反射镜位置与角度，使参考光路与物光光路重合。
5)调节傅里叶透镜7的位置与角度，使前焦面与SLM屏幕重合，并中心垂直于1级衍射光，调节所述的光阑的位置，使其与透镜7的后焦面共面，调节孔径大小到1毫米，仅使1级衍射光经过光阑。
6)旋转偏振片3，选择1级衍射光强相对最强的偏振方向。衍射光被反射镜反射，调节准直透镜11的位置，使物光路中两透镜焦面重合于光阑处，调节准直透镜11的角度，使光路垂直经过中心。此时在准直透镜的后焦面上的光场即为前一透镜前焦面上光场的放大，放大倍数为两透镜的焦距之比。实施例中透镜7焦距为30毫米，透镜11焦距为500毫米，放大倍数为16.67倍。
7)采用1.5毫米熔石英材料基板为衬底。在衬底上涂覆约200纳米厚的光刻胶。
8)在干涉区域内设置待曝光的光栅样品16，经曝光、显影后，在光刻胶光栅层上镀200纳米厚金属膜，材料为金(Au)，金薄膜和光刻胶光栅层紧密贴合，制备出反射式弯曲叉形面光栅。

Claims (8)

  1. 一种反射式弯曲叉形面光栅的制备方法，其特征在于，该方法包括如下步骤：
    步骤1)构建光路：同轴设置激光器(1)、扩束器(2)、线偏振片(3)和消偏振分束器(4)；所述的消偏振分束器(4)将入射光分为反射光和透射光；沿所述的反射光的光路依次设置反射镜组、带针孔的显微物镜(14)、第一准直镜(15)和供待曝光的光栅样品(16)放置的旋转基座(17)；沿所述的透射光的光路设置SLM(5)，该SLM(5)与PC控制端(6)相连；
    步骤2)调节光路：启动所述的激光器(1)，调整所述的扩束器(2)的倍数，使扩束后的光斑直径小于SLM(5)的屏幕短边长，在不加载相位信息的情况下调整SLM(5)的角度，使光能沿原路返回，入射至所述的消偏振分束器(4)反射形成第二反射光；
    步骤3)构建曝光光路：沿所述的第二反射光的光路设置傅里叶透镜(7)、可调孔径光阑(8)、衰减片(9)、第三反射镜(10)和第二准直镜(11)；
    步骤4)计算SLM(5)加载的全息图，即入射基模高斯光提供的相位增量Ф(x,y)，公式如下：
    Figure PCTCN2022133141-appb-100001
    式中，(x,y)为位置坐标，l为完美涡旋光的拓扑荷值，atan2(y，x)为坐标的四象限反正切，k＝2π/λ为曝光光束的波数，λ为激光器(1)的波长，γ与n为锥透镜相位参数，其中，γ等效为锥透镜底角，n等效为锥透镜折射率，g x和g y分别为屏幕范围内的闪耀光栅在x和y方向上的周期数，取g y＝0，使各级衍射光斑在横向分布；
    γ、n和g x之间满足以下关系：
    2r POV＜D＜L 2-2r POV
    式中，D为光阑(8)的直径，r POV为焦平面上的POV的半径：
    r POV＝tan(arcsin(n·sin(γ))-γ)·f
    L 2是二级衍射光与0级光的间距：
    L m＝f·tanθ m
    Figure PCTCN2022133141-appb-100002
    式中，f为透镜(7)的焦距，m为衍射级次，H为SLM显示屏实际的x方向长度；
    所述的PC控制端(6)控制下，将所述的相位增量Ф(x,y)，利用下式映射到(0，255)的灰度值范围
    Figure PCTCN2022133141-appb-100003
    将该灰度值分布图加载在所述的SLM(5)显示屏上，物光经由SLM(5)调制，1级衍射光的光场即为所述的贝塞尔高斯光场；
    步骤5)调节物光与参考光之间夹角φ：暂时移除SLM加载的涡旋光相位，只保留闪耀光栅相位；暂时以一反射镜替代待曝光样品；调节旋转基座(17)角度，使物光路以原路返回；转动旋转基座(17)φ/2角度，调节反射镜组(12，13)位置与角度，使参考光路与物光光路重合，则物光光路与参考光光路夹角为φ，光栅周期为：
    Figure PCTCN2022133141-appb-100004
    步骤6)调节所述的傅里叶透镜(7)的位置与角度，使前焦面与SLM屏幕重合，并中心垂直于1级衍射光，调节所述的光阑(8)的位置，使其与透镜(7)的后焦面共面，调节孔径大小，仅使1级衍射光经过光阑；
    步骤7)旋转所述的偏振片(3)，选择1级衍射光强相对最强的偏振方向，衍射光被所述的反射镜(10)反射，调节所述的准直透镜(11)的位置，使透镜(11)的前焦面与光阑(8)所在平面重合，调节所述的准直透镜(11)的角度，使1级衍射光垂直经过透镜(11)中心；此时在准直透镜(11)的后焦面上的光场为透镜(7)前焦面上光场的放大，放大倍数为两透镜的焦距之比。
    步骤8)所述光场与参考光干涉形成干涉光场，该干涉光场强度分布呈弯 曲叉形条纹分布，在干涉区域内所述的待曝光的光栅样品(16)，经曝光、显影后，镀金属膜，制备出反射式弯曲叉形面光栅。
  2. 根据权利要求1所述的反射式弯曲叉形面光栅的制备方法，其特征在于，所述的消偏振分束器(4)将入射光分为反射光和透射光，不改变入射光束的偏振态，分光比为1:1。
  3. 根据权利要求1所述的反射式弯曲叉形面光栅的制备方法，其特征在于，所述的SLM(5)加载的相位图为灰度图，灰度值范围0～255，对应相位增量0～2π。
  4. 根据权利要求1所述的反射式弯曲叉形面光栅的制备方法，其特征在于，所述的PC控制端(6)与所述的SLM(5)相连，并控制SLM(5)加载的相位图。
  5. 根据权利要求1所述的反射式弯曲叉形面光栅的制备方法，其特征在于，所述的待曝光的光栅样品(16)包括基底以及基底上的光敏材料，且光敏材料均匀地覆盖在基底上。
  6. 根据权利要求5所述的反射式弯曲叉形面光栅的制备方法，其特征在于，所述衬底为熔石英、碳化硅、硅或金属材质的薄膜或基板。
  7. 根据权利要求6所述的反射式弯曲叉形面光栅的制备方法，其特征在于，所述金属材料为金或银(Au/Ag)，金属膜厚度为100～220纳米。
  8. 根据权利要求5所述的反射式弯曲叉形面光栅的制备方法，其特征在于，所述光敏材料为光刻胶，该光刻胶被特定波长的光曝光后，会发生化学分解或聚合反应。
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