CN103472593A

CN103472593A - Polarization modulator without moving part

Info

Publication number: CN103472593A
Application number: CN2013104394192A
Authority: CN
Inventors: 赵佳; 周峰; 李欢; 赵海博; 钟晓明; 晋利兵
Original assignee: Beijing Research Institute of Mechanical and Electrical Technology
Current assignee: Beijing Research Institute of Mechanical and Electrical Technology
Priority date: 2013-09-24
Filing date: 2013-09-24
Publication date: 2013-12-25

Abstract

A polarization modulator without moving parts, including an achromatic 1/4 wave plate, an athermal multistage phase retarder, and a polarization beam splitter. The athermal multi-level phase retarder includes sapphire crystal and MgF ₂ crystal. The sapphire crystal is located on the side close to the achromatic 1/4 wave plate. The thickness ratio of sapphire crystal and MgF ₂ crystal is 1: (2~3), The fast axis direction of the sapphire crystal is perpendicular to the fast axis direction of the MgF ₂ crystal, and the included angles between the two fast axis directions and the horizontal direction are both 45°. The fast axis direction of the achromatic 1/4 wave plate is perpendicular to the horizontal direction, and the fast axis direction of the polarization beam splitter is parallel or perpendicular to the fast axis direction of the achromatic 1/4 wave plate. By using the polarization modulator of the present invention, a sinusoid whose amplitude varies with the degree of linear polarization and whose phase varies with the angle of linear polarization can be obtained on the detector. The modulator of the invention has the advantages of small volume, light weight, no moving parts, simple demodulation algorithm, high demodulation precision and the like.

Description

A Polarization Modulator with No Moving Parts

技术领域technical field

本发明属于航天光学遥感技术领域，涉及一种用于目标偏振信息获取的偏振调制器，特别适合于对行星大气中的云及气溶胶等粒子进行探测。The invention belongs to the technical field of aerospace optical remote sensing, and relates to a polarization modulator used for acquiring target polarization information, and is particularly suitable for detecting particles such as clouds and aerosols in planetary atmospheres.

背景技术Background technique

气象、大气环境监测、海洋、航空航天以及军事等部门的应用需求，推动了卫星大气遥感技术的进步。光学偏振遥感技术是光学遥感技术与偏振测量技术结合的产物。由于偏振测量的高精度特点，使得偏振遥感系统能够成为卫星大气遥感的新技术手段。The application requirements of meteorology, atmospheric environment monitoring, ocean, aerospace and military departments have promoted the progress of satellite atmospheric remote sensing technology. Optical polarization remote sensing technology is the product of the combination of optical remote sensing technology and polarization measurement technology. Due to the high-precision characteristics of polarization measurement, the polarization remote sensing system can become a new technology for satellite atmospheric remote sensing.

我国民用卫星已经形成了气象、资源与海洋三大卫星系列，和环境小卫星星座结合在一起，已经初步构成了我国民用卫星应用体系。对于这些资源、环境和海洋卫星的遥感需求，急需获得比较精确的大气参数，如气溶胶和云状况，用来进行精确的大气校正以大幅度提高其应用价值。而且气溶胶和云对辐射影响的不确定性是当前研究全球变化和气候变化的主要限制因素之一，气溶胶、云和地表反射率是影响地表能量辐射平衡的重要因素。此外，云相态是影响运载火箭飞行、导弹飞行及飞机飞行安全的重要因素。因此掌握全球大气气溶胶和云分布状况对航空、军事和空间科学研究工作是至关重要的。my country's civil satellites have formed three series of meteorological, resource and ocean satellites, combined with the constellation of environmental small satellites, and have initially formed the application system of my country's civil satellites. For the remote sensing needs of these resources, environment and ocean satellites, it is urgent to obtain more accurate atmospheric parameters, such as aerosol and cloud conditions, for precise atmospheric correction to greatly improve its application value. Moreover, the uncertainty of the influence of aerosols and clouds on radiation is one of the main limiting factors in the current research on global change and climate change. Aerosols, clouds and surface reflectance are important factors affecting the energy radiation balance of the surface. In addition, cloud phase is an important factor affecting the safety of launch vehicle flight, missile flight and aircraft flight. Therefore, mastering the global atmospheric aerosol and cloud distribution is very important for aviation, military and space science research.

探测大气中云及气溶胶最有效的手段就是偏振探测，目前已有POLDER、APS等多颗星载多角度偏振光谱仪研制成功。对这些载荷研究不难发现，其运用的偏振调制方式主要有两种，即时间调制和空间调制。The most effective way to detect clouds and aerosols in the atmosphere is polarization detection. At present, many spaceborne multi-angle polarization spectrometers such as POLDER and APS have been successfully developed. It is not difficult to find out from the research on these loads that there are mainly two polarization modulation methods used, namely time modulation and space modulation.

POLDER采用了时间调制的方式，时间调制通过旋转波片和滤光片转轮来获取偏振信息和光谱信息。这种方式的优点是：调制原理简单。缺点是：波片只针对某一特定波长，因此探测多波长就要增加多路元件，系统的体积笨重；而且系统中有运动部件，抗振性、稳定性、可靠性较差；一次只能测量一个偏振态，需要转动波片多次测量才能获得所需要的偏振信息，所以不能实时测量。POLDER adopts the method of time modulation, and the time modulation obtains polarization information and spectral information by rotating the wave plate and filter wheel. The advantage of this method is that the modulation principle is simple. Disadvantages are: the wave plate is only for a specific wavelength, so multiple components need to be added to detect multiple wavelengths, and the system is bulky; and there are moving parts in the system, which have poor vibration resistance, stability, and reliability; To measure a polarization state, it is necessary to rotate the wave plate for multiple measurements to obtain the required polarization information, so it cannot be measured in real time.

APS采用了空间调制的方式，空间调制通过偏振分束器将入射光分为多束，每束光分别通过波片等偏振元件调制后获得所需的偏振态。空间调制的优点是：无机械转动可实时测量全Stocks参量I、Q、U、V。缺点是：光路调节非常困难，很难保证光束通过系统偏振态不改变；而且需要多个CCD（一般四个）同时测量，很难保证均一性和同步性；另外对多波长探测需滤光片（增加光路数或牺牲实时性），获得的数据精度并不够高，系统很笨重。APS adopts the method of spatial modulation, and the spatial modulation divides the incident light into multiple beams through a polarization beam splitter, and each beam of light is modulated by a polarization element such as a wave plate to obtain the required polarization state. The advantage of space modulation is that all Stocks parameters I, Q, U, V can be measured in real time without mechanical rotation. The disadvantages are: it is very difficult to adjust the optical path, and it is difficult to ensure that the polarization state of the beam passing through the system does not change; and it requires multiple CCDs (generally four) to measure at the same time, and it is difficult to ensure uniformity and synchronization; in addition, filters are required for multi-wavelength detection (Increase the number of optical paths or sacrifice real-time performance), the accuracy of the obtained data is not high enough, and the system is very bulky.

发明内容Contents of the invention

本发明的技术解决问题是：克服现有技术的不足，提供了一种体积小、重量轻、无运动部件、调制简单、解调精度高并且能够同时获得光谱信息和偏振信息的偏振调制器件。The technical solution of the present invention is to overcome the deficiencies of the prior art and provide a polarization modulation device with small volume, light weight, no moving parts, simple modulation, high demodulation accuracy and the ability to simultaneously obtain spectral information and polarization information.

本发明的技术解决方案是：一种无运动部件的偏振调制器，包括消色差的1/4波片、无热的多级相位延迟器、偏振分束器；所述的无热的多级相位延迟器包括蓝宝石晶体和MgF₂晶体，蓝宝石晶体位于靠近消色差的1/4波片的一侧，MgF₂晶体位于靠近偏振分束器的一侧，蓝宝石晶体和MgF₂晶体的厚度比为1:（2～3），蓝宝石晶体的快轴方向与MgF₂晶体的快轴方向垂直且两个快轴方向与水平方向的夹角均为45°；所述的消色差1/4波片的快轴方向与水平方向垂直，偏振分束器的快轴方向与消色差的1/4波片的快轴方向平行或者垂直。The technical solution of the present invention is: a polarization modulator without moving parts, including an achromatic 1/4 wave plate, an athermal multistage phase retarder, and a polarization beam splitter; the athermal multistage The phase retarder includes a sapphire crystal and a _MgF2 crystal, the sapphire crystal is located on the side close to the achromatic 1/4 wave plate, the _MgF2 crystal is located on the side close to the polarizing beam splitter, and the thickness ratio of the sapphire crystal and the _MgF2 crystal is 1: (2~3), the fast axis direction of the sapphire crystal is perpendicular to the fast axis direction of the MgF ₂ crystal, and the angles between the two fast axis directions and the horizontal direction are both 45°; the achromatic 1/4 wave plate The fast axis direction of the polarizing beam splitter is perpendicular to the horizontal direction, and the fast axis direction of the polarizing beam splitter is parallel or perpendicular to the fast axis direction of the achromatic 1/4 wave plate.

所述的消色差的1/4波片为菲涅耳菱体。所述的偏振分束器为Wollaston棱镜。所述的蓝宝石晶体和MgF₂晶体的厚度比是1:2.4。The achromatic 1/4 wave plate is a Fresnel rhombus. The polarizing beam splitter is a Wollaston prism. The thickness ratio of the sapphire crystal and the MgF ₂ crystal is 1:2.4.

本发明与现有技术相比的优点在于：The advantage of the present invention compared with prior art is:

（1）本发明的偏振调制器对入射光进行光谱调制后，在探测器上能够得到振幅随着线偏振度变化而相位随着线偏振角变化的正弦曲线，经过解调之后能够直接得到目标的光谱信息和偏振信息；(1) After the polarization modulator of the present invention performs spectral modulation on the incident light, a sinusoid whose amplitude varies with the degree of linear polarization and whose phase varies with the angle of linear polarization can be obtained on the detector, and the target can be directly obtained after demodulation. The spectral information and polarization information of

（2）本发明的偏振调制器与现有的基于分光路及分振幅方式的空间调制偏振测量方式相比，具有体积小、重量轻的优点；(2) The polarization modulator of the present invention has the advantages of small size and light weight compared with the existing spatial modulation polarization measurement method based on split light path and split amplitude method;

（3）本发明的偏振调制器与现有的基于旋转偏振片以及电光调制的时间调制偏振测量方式相比，具有实时性好、无运动部件、稳定性好等优点；(3) Compared with the existing time-modulated polarization measurement methods based on rotating polarizers and electro-optic modulation, the polarization modulator of the present invention has the advantages of good real-time performance, no moving parts, and good stability;

（4）本发明的偏振调制方式由于经算法解调可直接得到所需的线偏振度和线偏振角，而不是像空间调制偏振测量那样测得Stocks四个参量I、Q、U、V后再计算偏振度以及偏振角，所以光谱调制的解调方法简单、解调精度高、运算速度快；(4) The polarization modulation method of the present invention can directly obtain the required degree of linear polarization and linear polarization angle through algorithm demodulation, instead of measuring the four Stocks parameters I, Q, U, and V like the spatial modulation polarization measurement. Then calculate the polarization degree and polarization angle, so the demodulation method of spectral modulation is simple, the demodulation accuracy is high, and the calculation speed is fast;

（5）本发明的偏振调制器通过光谱调制把随着波长变化的偏振信息编码在了光谱维，降低了时间（例如用旋转滤光片及偏振片获得不同偏振角信息时，不同时间测量时目标的偏振信息可能会发生改变）或空间（如分振幅的空间调制，不同光路的光学元件透过率不一致，影响结果的精度）的不一致性对测量结果的影响。(5) The polarization modulator of the present invention encodes the polarization information that changes with the wavelength in the spectral dimension through spectral modulation, which reduces the time (for example, when using rotating filters and polarizers to obtain different polarization angle information, when measuring at different times The polarization information of the target may change) or the inconsistency of the space (such as the spatial modulation of the sub-amplitude, the transmittance of the optical elements of different optical paths is inconsistent, which affects the accuracy of the results) affects the measurement results.

附图说明Description of drawings

图1为本发明偏振调制器的组成原理框图；Fig. 1 is the composition principle block diagram of polarization modulator of the present invention;

图2为本发明偏振调制器的组成元件快轴方向示意图；Fig. 2 is a schematic diagram of the fast axis direction of the constituent elements of the polarization modulator of the present invention;

图3为采用本发明光谱调制后得到的归一化的s、p分量的强度图；Fig. 3 is the intensity diagram of the normalized s and p components obtained after spectral modulation of the present invention;

图4为采用本发明光谱调制后得到的模拟偏振信号的真实偏振度和偏振角图像。Fig. 4 is an image of the real degree of polarization and polarization angle of the simulated polarization signal obtained after spectral modulation of the present invention.

具体实施方式Detailed ways

如图1所示，本发明用于光谱调制的调制器主要由消色差的1/4波片、无热的多级相位延迟器以及偏振分束器组成。As shown in FIG. 1 , the modulator used for spectral modulation of the present invention is mainly composed of an achromatic 1/4 wave plate, an athermal multi-level phase retarder and a polarization beam splitter.

消色差的1/4波片选用了菲涅耳菱体，基于全内反射原理的菲涅耳菱体其相位延迟量仅与折射率有关，其快轴方向与水平方向垂直。除此之外，消色差的1/4波片还可以选用菲涅耳菱体、穆尼菱体、AD-1型消色差相位延迟器、AD-2型消色差相位延迟器、菱体相位延迟器、长方体型相位延迟器、梯形相位延迟器等。具体可参考李国良，宋连科，范开敏.高精度菱体型消色差延迟器的优化设计[J].激光技术,2011,35(2)或者李国良.高性能消色差延迟器的优化设计[D].2007。The achromatic 1/4 wave plate uses a Fresnel rhombic body. The phase delay of the Fresnel rhombic body based on the principle of total internal reflection is only related to the refractive index, and its fast axis direction is perpendicular to the horizontal direction. In addition, the achromatic 1/4 wave plate can also choose Fresnel rhombic, Mooney rhomboid, AD-1 type achromatic phase retarder, AD-2 type achromatic phase retarder, rhombic phase Retarder, cuboid phase retarder, trapezoidal phase retarder, etc. For details, please refer to Li Guoliang, Song Lianke, Fan Kaimin. Optimal design of high-precision diamond-shaped achromatic retarder [J]. Laser Technology, 2011, 35 (2) or Li Guoliang. Optimal design of high-performance achromatic retarder [D]. 2007 .

无热的多级相位延迟器由蓝宝石和MgF₂晶体组成，两块晶体的快轴方向与1/4波片的快轴方向分别成±45°排列。1/4波片的快轴方向与偏振片的透光轴方向平行，可以为0°或90°。由于波片的相位延迟量受温度的影响很大，尤其是多级波片，所以两种晶体要选择合适的厚度比以消除总的相位延迟量对温度的依赖性。这里所述的蓝宝石和MgF₂的厚度比是1:（2～3）。The athermal multilevel phase retarder is composed of sapphire and MgF ₂ crystals, and the fast axes of the two crystals are aligned at ±45° to the fast axes of the 1/4 wave plate. The direction of the fast axis of the 1/4 wave plate is parallel to the direction of the transmission axis of the polarizer, which can be 0° or 90°. Since the phase retardation of the wave plate is greatly affected by temperature, especially the multi-level wave plate, the appropriate thickness ratio of the two crystals should be selected to eliminate the dependence of the total phase retardation on temperature. The thickness ratio of sapphire and MgF ₂ described here is 1:(2-3).

为了设计无热化的多级相位延迟器，需要找到两种热光常数不同的材料，使对于某一确定厚度比率结合后的延迟量的残余温度依赖性在所要求的可见光波长范围内最小。两个波片j=1、2，厚度d_j，双折射率n_e,j-n_o,j，组合的光程差可由下式给出：In order to design an athermalized multilevel phase retarder, it is necessary to find two materials with different thermo-optic constants to minimize the residual temperature dependence of the combined retardation for a certain thickness ratio in the required visible wavelength range. Two wave plates j=1, 2, thickness d _j , birefringence n _e,j -n _o,j , the combined optical path difference can be given by the following formula:

δ(λ,T)=δ₁(λ,T)±δ₂(λ,T)=|n_e,1(λ,T)-n_o,1(λ,T)|d₁±|n_e,2(λ,T)-n_o,2(λ,T)|d₂ δ(λ,T)=δ ₁ (λ,T)±δ ₂ (λ,T)=|n _e,1 (λ,T)-n _o,1 (λ,T)|d ₁ ±|n _{e ,2} (λ,T)-n _o,2 (λ,T)|d ₂

“±”：表示组合晶体数目的增加或减少，式中取了双折射率的绝对值是为了描述波片的快轴之间的对应角度而不是光轴。所要求的无热性质可由下式给出："±": Indicates the increase or decrease of the number of combined crystals. The absolute value of birefringence is taken in the formula to describe the corresponding angle between the fast axes of the wave plate instead of the optical axis. The required athermal properties are given by:

γ₁·δ₁(λ₀)±γ₂·δ₂(λ₀)=0γ ₁ ·δ ₁ (λ ₀ )±γ ₂ ·δ ₂ (λ ₀ )=0

γ_j是晶体的热光常数，其中：γ _j is the thermo-optic constant of the crystal, where:

${γ γ}_{j j} = = \frac{11}{{δ δ}_{j j} (({λ λ}_{00}))} \cdot &Center Dot; \frac{d d {δ δ}_{j j} (({λ λ}_{00}))}{dT dT} = = \frac{11}{{d d}_{j j}} \cdot \cdot \frac{{dd dd}_{j j}}{dT dT} + + \frac{11}{{n no}_{e e,, j j} (({λ λ}_{00})) - - {n no}_{o o,, j j} (({λ λ}_{00}))} \cdot \cdot \frac{d d (({n no}_{e e,, j j} (({λ λ}_{00})) - - {n no}_{o o,, j j} (({λ λ}_{00}))))}{dT dT}$

用上述公式计算：能够得到厚度比1:2～1:3。Calculated with the above formula: the thickness ratio can be obtained as 1:2 to 1:3.

绝大多数常见晶体的γ_j值都是负的，因此必须选择“-”晶体组合来构造无热的多级相位延迟器。The γ _j values of most common crystals are negative, so the "-" crystal combination must be selected to construct an athermal multi-level phase retarder.

组合波片的FOV性能取决于n_e,1-n_o,1及n_e,2-n_o,2的符号。假设第一个波片的双折射率是正值（石英或MgF₂）。通过查阅相关材料的γ_j值，找到了在350nm-800nm波长范围内能够产生无热化的晶体组合波片。选择了蓝宝石和MgF₂作为无热的晶体组合，其最优厚度比是1:2.4。The FOV performance of the combined waveplate depends on the sign of ne _,1 -n _o,1 and ne _,2 -n _o,2 . Assume that the birefringence of the first wave plate is positive (quartz or MgF ₂ ). By consulting the γ _j values of related materials, a crystal combination wave plate capable of producing athermalization in the wavelength range of 350nm-800nm was found. Sapphire and _MgF2 were chosen as an athermal crystal combination with an optimal thickness ratio of 1:2.4.

由可知，蓝宝石Al₂O₃在0.22-5.0um波长范围内，其o光和e光的折射率可由下式得出：It can be seen that the refractive index of sapphire Al ₂ O ₃ in the wavelength range of 0.22-5.0um, its o light and e light can be obtained by the following formula:

${n no}_{o o}^{22} = = 11 + + \frac{{1.43134936 1.43134936 λ λ}^{22}}{[[{λ λ}^{22} - - {((0.0726631 0.0726631))}^{22}]]} + + \frac{0.65054713 0.65054713 {λ λ}^{22}}{[[{λ λ}^{22} - - {((0.1193242 0.1193242))}^{22}]]} + + \frac{{5.3414021 5.3414021 λ λ}^{22}}{[[{λ λ}^{22} - - {((18.028251 18.028251))}^{22}]]}$

${n no}_{e e}^{22} = = 11 + + \frac{{1.5039759 1.5039759 λ λ}^{22}}{[[{λ λ}^{22} - - {((0.0740288 0.0740288))}^{22}]]} + + \frac{{0.55069141 0.55069141 λ λ}^{22}}{[[{λ λ}^{22} - - {((0.1216529 0.1216529))}^{22}]]} + + \frac{{6.59273791 6.59273791 λ λ}^{22}}{[[{λ λ}^{22} - - {((20.072248 20.072248))}^{22}]]}$

MgF₂在0.4-3.1um波长波长范围内，其o光和e光的折射率可由下式得出：In the wavelength range of 0.4-3.1um wavelength of MgF ₂ , the refractive index of its o light and e light can be obtained by the following formula:

${n no}_{o o}^{22} = = 11 + + \frac{{0.48755108 0.48755108 λ λ}^{22}}{[[{λ λ}^{22} - - {((0.04338408 0.04338408))}^{22}]]} + + \frac{0.39875031 0.39875031 {λ λ}^{22}}{[[{λ λ}^{22} - - {((0.09461442 0.09461442))}^{22}]]} + + \frac{{2.3120353 2.3120353 λ λ}^{22}}{[[{λ λ}^{22} - - {((23.793604 23.793604))}^{22}]]}$

${n no}_{e e}^{22} = = 11 + + \frac{{0.41344023 0.41344023 λ λ}^{22}}{[[{λ λ}^{22} - - {((0.03684262 0.03684262))}^{22}]]} + + \frac{{0.50497499 0.50497499 λ λ}^{22}}{[[{λ λ}^{22} - - {((0.09076162 0.09076162))}^{22}]]} + + \frac{{2.4904862 2.4904862 λ λ}^{22}}{[[{λ λ}^{22} - - {((12.771995 12.771995))}^{22}]]}$

由上述公式可以得到光谱调制的δ，即光程差。The δ of the spectral modulation can be obtained from the above formula, that is, the optical path difference.

以上内容具体可参见S.Guimond,and D.Elmore,’Designing effective crystalwaveplates requires understanding the engineering tradeoffs’,OE magazine May(2004)。For the above content, please refer to S. Guimond, and D. Elmore, 'Designing effective crystal waveplates requires understanding the engineering tradeoffs', OE magazine May (2004).

偏振分束器选用Wollaston棱镜，因为偏振分束器不仅要有大的消光比还要有大的波长范围，Wollaston棱镜能够很好的满足要求。除此之外，偏振分束器还可以选用：尼科耳棱镜、格兰棱镜、savart板等偏振分束器。具体可参考《物理光学》梁铨廷电子工业出版社2008.4或者《干涉成像光谱技术》张淳民科学出版社2010.1。A Wollaston prism is selected as the polarizing beam splitter, because the polarizing beam splitter not only has a large extinction ratio but also has a large wavelength range, and the Wollaston prism can well meet the requirements. In addition, polarizing beam splitters can also be selected: Nicol prisms, Glan prisms, savart plates and other polarizing beam splitters. For details, please refer to "Physical Optics" Liang Quanting Electronic Industry Press 2008.4 or "Interference Imaging Spectrum Technology" Zhang Chunmin Science Press 2010.1.

如图2所示，目标的偏振光由左侧进入本发明偏振调制器，假设入射光的Stokes为：As shown in Figure 2, the polarized light of the target enters the polarization modulator of the present invention from the left, assuming that the Stokes of the incident light is:

S_in＝(S₀(σ) S₁(σ) S₂(σ) S₃(σ))^T S _in ＝(S ₀ (σ) S ₁ (σ) S ₂ (σ) S ₃ (σ)) ^T

菲涅耳棱体的穆勒矩阵为：The Muller matrix of the Fresnel prism is:

${M m}_{Fresnel Fresnel} = = (\begin{matrix} 11 & 00 & 00 & 00 \\ 00 & 11 & 00 & 00 \\ 00 & 00 & 00 & - - 11 \\ 00 & 00 & 11 & 00 \end{matrix})$

相位延迟器的相位延迟为φ(σ)，快轴方向角度θ，σ为波数，穆勒矩阵为：The phase delay of the phase retarder is φ(σ), the fast axis direction angle θ, σ is the wave number, and the Mueller matrix is:

$M m = = (\begin{matrix} 11 & 00 & 00 & 00 \\ 00 & {cos cos}^{22} 22 θ θ + + {sin sin}^{22} 22 θ θ cos cos φ φ ((σ σ)) & sin sin 22 θ θ cos cos 22 θ θ ((11 - - cos cos φ φ ((σ σ)))) & - - sin sin 22 θ θ sin sin φ φ ((σ σ)) \\ 00 & sin sin 22 θ θ cos cos 22 θ θ ((11 - - cos cos φ φ ((σ σ)))) & {sin sin}^{22} 22 θ θ + + {cos cos}^{22} 22 θ θ cos cos φ φ ((σ σ)) & cos cos 22 θ θ sin sin φ φ ((σ σ)) \\ 00 & sin sin 22 θ θ sin sin φ φ ((σ σ)) & - - cos cos 22 θ θ sin sin φ φ ((σ σ)) & cos cos φ φ ((σ σ)) \end{matrix})$

因此，蓝宝石的快轴角度为45°，相位延迟为φ₁(σ)，MgF₂的快轴角度为-45°，相位延迟为φ₂(σ)，其穆勒矩阵分别为：Therefore, the fast axis angle of sapphire is 45°, the phase delay is φ ₁ (σ), the fast axis angle of MgF ₂ is -45°, and the phase delay is φ ₂ (σ), and their Mueller matrices are:

${M m}_{sapphire sapphire} = = (\begin{matrix} 11 & 00 & 00 & 00 \\ 00 & cos cos {φ φ}_{11} ((σ σ)) & 00 & - - sin sin {φ φ}_{11} ((σ σ)) \\ 00 & 00 & 11 & 00 \\ 00 & sin sin {φ φ}_{11} ((σ σ)) & 00 & cos cos {φ φ}_{11} ((σ σ)) \end{matrix}),, {M m}_{Mg Mg {F f}_{22}} = = (\begin{matrix} 11 & 00 & 00 & 00 \\ 00 & cos cos {φ φ}_{22} ((σ σ)) & 00 & sin sin {φ φ}_{22} ((σ σ)) \\ 00 & 00 & 11 & 00 \\ 00 & - - sin sin {φ φ}_{22} ((σ σ)) & 00 & cos cos {φ φ}_{22} ((σ σ)) \end{matrix})$

Wollaston棱镜的穆勒矩阵为：The Muller matrix of the Wollaston prism is:

${M m}_{wollaston wollaston} = = \frac{11}{22} (\begin{matrix} 11 & - - 11 & 00 & 00 \\ - - 11 & 11 & 00 & 00 \\ 00 & 00 & 00 & 00 \\ 00 & 00 & 00 & 00 \end{matrix})$

则出射光的Stokes为：Then the Stokes of the outgoing light is:

${S S}_{out out} = = {M m}_{wollaston wollaston} {M m}_{sapphire sapphire} {M m}_{Mg Mg {F f}_{22}} {M m}_{fresnel fresnel} {S S}_{in in}$

$(\begin{matrix} {S S}_{00}^{' '} ((σ σ)) \\ {S S}_{11}^{' '} ((σ σ)) \\ {S S}_{22}^{' '} ((σ σ)) \\ {S S}_{33}^{' '} ((σ σ)) \end{matrix}) = = \frac{11}{22} (\begin{matrix} 11 & - - 11 & 00 & 00 \\ - - 11 & 11 & 00 & 00 \\ 00 & 00 & 00 & 00 \\ 00 & 00 & 00 & 00 \end{matrix}) (\begin{matrix} 11 & 00 & 00 & 00 \\ 00 & {cos cos φ φ}_{22} ((σ σ)) & 00 & {sin sin φ φ}_{22} ((σ σ)) \\ 00 & 00 & 11 & 00 \\ 00 & - - sin sin {φ φ}_{22} ((σ σ)) & 00 & cos cos {φ φ}_{22} ((σ σ)) \end{matrix}) (\begin{matrix} 11 & 00 & 00 & 00 \\ 00 & {cos cos φ φ}_{11} ((σ σ)) & 00 & - - sin sin {φ φ}_{11} ((σ σ)) \\ 00 & 00 & 11 & 00 \\ 00 & {sin sin φ φ}_{11} ((σ σ)) & 00 & cos cos {φ φ}_{11} ((σ σ)) \end{matrix}) (\begin{matrix} 11 & 00 & 00 & 00 \\ 00 & 11 & 00 & 00 \\ 00 & 00 & 00 & - - 11 \\ 00 & 00 & 11 & 00 \end{matrix}) (\begin{matrix} {S S}_{00} ((σ σ)) \\ {S S}_{11} ((σ σ)) \\ {S S}_{22} ((σ σ)) \\ {S S}_{33} ((σ σ)) \end{matrix})$

等号左边为光谱调制出射光的Stokes矢量元素谱矩阵，等号右边从左至右分别为Wollaston棱镜、MgF₂晶体、蓝宝石（Sapphire）晶体、菲涅耳菱体的穆勒矩阵和入射光的Stokes矢量元素谱矩阵。用P(σ)表示S′₀(σ)，即出射光的输出功率谱：The left side of the equal sign is the Stokes vector element spectrum matrix of the spectrally modulated outgoing light, and the right side of the equal sign from left to right is the Mueller matrix of the Wollaston prism, MgF ₂ crystal, sapphire crystal, Fresnel rhomboid and the incident light Stokes vector element-wise spectral matrix. Use P(σ) to represent S′ ₀ (σ), that is, the output power spectrum of the outgoing light:

$P P ((σ σ)) = = \frac{11}{22} {{{S S}_{00} ((σ σ)) - - {S S}_{11} ((σ σ)) [[cos cos {φ φ}_{22} ((σ σ)) cos cos {φ φ}_{11} ((σ σ)) + + {sin sin φ φ}_{22} ((σ σ)) sin sin {φ φ}_{11} ((σ σ))]] + + {S S}_{22} ((σ σ)) [[cos cos {φ φ}_{22} ((σ σ)) sin sin {φ φ}_{11} ((σ σ)) - - {sin sin φ φ}_{22} ((σ σ)) cos cos {φ φ}_{11} ((σ σ))]]}}$

由于 $P_{L} = \frac{\sqrt{S_{1}^{2} + S_{2}^{2}}}{S_{0}}, φ_{L} = \frac{1}{2} \arctan \frac{S_{3}}{S_{2}},$ 其中P_L和φ_L分别表示线偏振度以及线偏振角，代入输出功率谱并对其变换可得到：because $P_{L} = \frac{\sqrt{S_{1}^{2} + S_{2}^{2}}}{S_{0}}, φ_{L} = \frac{1}{2} \arctan \frac{S_{3}}{S_{2}},$ Among them, P _L and φ _L represent the degree of linear polarization and the angle of linear polarization, respectively, which can be obtained by substituting the output power spectrum and transforming it:

$P P ((σ σ)) = = {S S}_{00}^{' '} ((λ λ)) = = \frac{11}{22} {S S}_{00} ((λ λ)) {{11 - - {P P}_{L L} ((λ λ)) cos cos [[\frac{22 π π}{λ λ} δ δ ((λ λ,, T T)) + + 22 {φ φ}_{L L} ((λ λ))]]}}$

以上公式中，σ表示波数，λ表示波长，δ表示光谱调制产生的光程差，S₀(λ)表示目标的偏振光的光强，S′₀(λ)表示经光谱调制后得到偏振光光强。In the above formula, σ represents the wave number, λ represents the wavelength, δ represents the optical path difference caused by spectral modulation, S ₀ (λ) represents the light intensity of the polarized light of the target, and S′ ₀ (λ) represents the polarized light obtained after spectral modulation light intensity.

通过解调算法对上式解调即可得到目标不同波长的线偏振度以及线偏振角。由于偏振信息直接储存在了光谱维中，即得到的偏振信息是随波长连续变化的，在得到偏振信息的同时也得到了高光谱信息。By demodulating the above formula through a demodulation algorithm, the degree of linear polarization and linear polarization angle of different wavelengths of the target can be obtained. Since the polarization information is directly stored in the spectral dimension, that is, the obtained polarization information changes continuously with the wavelength, and hyperspectral information is also obtained while obtaining the polarization information.

图3是用本发明原理经仿真光谱调制Wollaston棱镜分光后得到的归一化的s、p分量的强度图。入射的线偏振光经过光谱调制模块的Wollaston棱镜后，被调制成为两束呈正弦曲线变化的异相的振动方向互相垂直的S波和P波。因为两束偏振光异相，所以一束偏振光处于波峰时，另外一束偏振光处于波谷。两调制偏振光束的强度和等于入射偏振光的总光强。Fig. 3 is an intensity diagram of the normalized s and p components obtained after the Wollaston prism is modulated by the simulation spectrum using the principle of the present invention. After the incident linearly polarized light passes through the Wollaston prism of the spectral modulation module, it is modulated into two S-waves and P-waves with out-of-phase vibration directions that change sinusoidally and are perpendicular to each other. Because the two polarized lights are out of phase, when one polarized light is at the peak, the other polarized light is at the trough. The sum of the intensities of the two modulated polarized light beams is equal to the total light intensity of the incident polarized light.

图4是用本发明的原理经仿真反演得到的模拟偏振信号的偏振度和偏振角图像。根据本发明提出的光谱调制的原理进行仿真分析，对模拟目标的线偏振度及线偏振角进行了解调。其中图4（a），图4（b）分别为对目标信息解调得到的线偏振度及线偏振角。经仿真可知，得到的偏振信息曲线与所输入的参数一致相符。Fig. 4 is an image of degree of polarization and polarization angle of an analog polarization signal obtained through simulation inversion by using the principle of the present invention. Simulation analysis is carried out according to the principle of spectrum modulation proposed by the invention, and the linear polarization degree and linear polarization angle of the simulated target are demodulated. Among them, Figure 4(a) and Figure 4(b) respectively show the degree of linear polarization and angle of linear polarization obtained by demodulating the target information. It can be seen from the simulation that the obtained polarization information curve is consistent with the input parameters.

本发明说明书中未作详细描述的内容属本领域技术人员的公知技术。The content that is not described in detail in the description of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A polarization modulator without moving parts, characterized in that: comprise achromatic 1/4 wave plate, athermal multistage phase retarder, polarization beam splitter; described athermal multistage phase retardation The filter includes a sapphire crystal and a _MgF2 crystal, the sapphire crystal is located on the side close to the achromatic 1/4 wave plate, the _MgF2 crystal is located on the side close to the polarizing beam splitter, and the thickness ratio of the sapphire crystal and the _MgF2 crystal is 1: (2-3), the fast axis direction of the sapphire crystal is perpendicular to the fast axis direction of the MgF ₂ crystal and the angle between the two fast axis directions and the horizontal direction is 45°; the fast axis of the achromatic 1/4 wave plate The axis direction is perpendicular to the horizontal direction, and the fast axis direction of the polarization beam splitter is parallel or perpendicular to the fast axis direction of the achromatic 1/4 wave plate.

2 . The polarization modulator without moving parts according to claim 1 , wherein the achromatic 1/4 wave plate is a Fresnel rhomboid.

3. The polarization modulator without moving parts according to claim 1, characterized in that: said polarization beam splitter is a Wollaston prism.

4. A polarization modulator without moving parts according to claim 1, characterized in that: the thickness ratio of the sapphire crystal to the MgF ₂ crystal is 1:2.4.