道威棱镜的偏振特性及偏振补偿研究

为了避免机载光电吊舱中共口径光学系统内部由于道威棱镜旋转引起的激光照射脉冲偏振态的变化,利用琼斯矩阵对道威棱镜的偏振特性与四分之一波片、半波片补偿道威棱镜旋转引起的激光脉冲偏振态变化进行了理论分析和实验验证。结果表明:线偏振的激光脉冲通过旋转一定角度的道威棱镜时,激光脉冲偏振态变为椭圆偏振,偏振态发生变化;而激光脉冲首先通过旋转一定角度的四分之一波片与半波片时,可使通过道威棱镜系统的激光脉冲偏振态保持不变,且两波片旋转角度与道威棱镜旋转角度之间存在一种非线性关系。采用偏振补偿方法可有效避免机载共口径光学系统中道威棱镜引起的激光脉冲偏振态变化,提高激光脉冲能量利用率,降低激光脉冲后向散射抑制难度。     

Modeling and simulation of polarization errors in Sagnac fiber optic current sensor

Sagnac fiber optic current sensor (S-FOCS) is a kind of optical interferometer based on Sagnac structure, optical polarization states of sensing light wave in Sagnac fiber optic current sensor are limited. However, several factors induce optical polarization error, and non-ideal polarized light waves cause the interference signal crosstalk in sensor, including polarizer, quarter-wave retarder, splice angular, birefringence and so on. With these errors, linearly polarized light wave in PM fiber and circularly polarized light wave in sensing fiber become elliptically polarized light wave, then, nonreciprocal phase shift induced by magnetic field of the current is interrupted by wrong polarization state. To clarify characteristics of optical polarization error in fiber optic current sensor, we analyze the evolution process of random optical polarization state, linear optical polarization state and circular optical polarization state in Sagnac fiber optic current sensor by using Poincare sphere, then, build optical polarization error models by using Jones matrix. Based on models of polarization state in Sagnac fiber optic current sensor, we investigate the influence of several main error factors on optical polarization error characteristics theoretically, including extinction ratio in polarizer, phase delay in quarter-wave retarder, splice angular between quarter-wave retarder and polarization maintaining fiber. Finally, we simulate and quantify nonreciprocal phase shift to be detected in fiber optic current sensor related with optical polarization errors. In the end, we demonstrate S-FOCS in test. The results show that transfer matrix errors are induced by inaccurate polarization properties during polarization state conversion, then, the stability and accuracy of the S-FOCS are affected, and it is important to control the polarization properties at each step of the polarization state conversion precisely.     

与人射线偏振光振动方向无关的低偏振度消偏器

消偏器是光纤传感器、光放大器等偏振敏感性光学系统中的关键器件,用于减小输入光的偏振度(DOP)。设计了一种与入射线偏振光振动方向无关的低偏振度消偏器,该器件中利用人为的偏振相关延迟代替了保偏光纤的双折射,并在偏振相关型消偏器前增加了一个1/4波片,从而对任意方向振动的线偏振光具有相同的消偏能力,结构紧凑。对消偏性能随波片阶数、入射光中心波长和振动方向的变化作了数值计算。实验中采用半峰全宽为0．13 nm的光源,入射线偏振光在任意方向振动时,输出光偏振度小于2．6%,消偏器的插入损耗为0．6 dB,损耗起伏小于0．11 dB。实验和数值计算结果表明,该消偏器具有低偏振度、低插入损耗和适合于宽光谱应用的优点。     

与入射线偏振光振动方向无关的低偏振度消偏器

消偏器是光纤传感器、光放大器等偏振敏感性光学系统中的关键器件,用于减小输入光的偏振度(DOP).设计了一种与入射线偏振光振动方向无关的低偏振度消偏器,该器件中利用人为的偏振相关延迟代替了保偏光纤的双折射,并在偏振相关型消偏器前增加了一个1/4波片,从而对任意方向振动的线偏振光具有相同的消偏能力,结构紧凑.对消偏性能随波片阶数、入射光中心波长和振动方向的变化作了数值计算.实验中采用半峰全宽为0.13 nm的光源,入射线偏振光在任意方向振动时,输出光偏振度小于2.6%,消偏器的插入损耗为0.6 dB,损耗起伏小于0.11 dB.实验和数值计算结果表明,该消偏器具有低偏振度、低插入损耗和适合于宽光谱应用的优点.     

Observation of two distinct phase states in a self-phase-locked type II phase-matched optical parametric oscillator

We demonstrate self-phase locking in a type II phase-matched optical parametric oscillator by mutual injection locking. An intracavity quarter-wave plate provides polarization mixing between the orthogonally polarized signal and idler that induces signal-idler self-phase locking when their frequency difference is within the capture range. We observed two distinct phase states that differ in their oscillator thresholds and their signal-idler phase differences, in good agreement with theory.     

Switching between the Functions of Half-Wave Plate and Quarter-Wave Plate Simply by Using a Vanadium Dioxide Film in a Terahertz Metamaterial

We propose a switchable THz metamaterial that can be switched between two functions of half-wave plate and quarter-wave plate.The two switchable functions can be simply achieved by inserting a VO_2 film in the metamaterial design.Finite-difference time-domain(FDTD) simulation results show that the proposed metamaterial can convert x-polarized incident wave to y-polarized reflected wave when VO_2 is at metal phase,and convert x-polarized wave to circularly polarized wave when VO_2 is at insulator phase.The metamaterial performs well in the two functions,i.e.,the same broad working frequency band and near perfect polarization conversion.The switching effect originates from the switchable Fabry-Perot cavity length induced by the phase change of VO_2.We believe that our findings provide a reference in designing switchable metamaterials.     

Realization of Arbitrary Inverse Unitary Transformation of Single Mode Fibre by Using Three Wave Plates

We report a method to realize the arbitrary inverse unitary transformation imposed by a single-mode fibre on photon＇s polarization by the succession of two quarter-wave plates and a half-wave plate. The process of realization is analysed on a Poincar6 sphere due to the fact that unitary transformation does not change the angle formed by polarization state vector. The method is meaningful in quantum communication experiment such as quantum teleportation, in which an unknown arbitrary quantum state should be kept to be unchanged in the case of using a single-mode fibre for time delay.[第一段]     

激光遥感偏振成像系统光学元件调整及误差分析

改进了利用双旋转波片方法进行偏振成像的实验装置,提出了通过一次测量获得目标偏振度和强度编码图像的方法.运用光强法对激光遥感偏振成像装置的光学元件进行调整,通过斯托克斯和穆勒矩阵在偏振光学元件中的应用,给出了相应光学元件的调整原理、方法及过程.分析了激光器中心波长变动、偏振片的角度误差和波片的相位延迟及角度误差对整个系统的影响.结果表明,由偏振片角度和波片角度误差造成的出射光斯托克斯误差较小,不超过0.001,可以忽略;由波片相位延迟不精确造成的误差在0.02左右,所以应采用延迟精度较高的波片;激光器中心波长变化的影响最大,不能忽略,必须加滤光片使接收光的中心波长控制在808nm;镀有铝膜望远镜对接收到的散射光偏振度影响较小,适于激光遥感偏振成像系统的应用.     

Polarization eigenmodes of a QHQ retarder — some new features

A detailed analysis of the polarization eigenmodes of a QHQ retarder (a half-wave plate sandwiched between two identical quarter-wave plates) is presented. These are shown to be discontinuous as a function of the orientation of the half-wave plate, as a function of the wavelength of incident light and as a function of the retardation of the middle waveplate.     

Multi-Wavelength Mueller Matrix Polarimeter

The retardation of two quarter-wave plates designed for a particular wavelength decreases or increases in accordance with the wavelength of input light beam. Compensating the shifted retardation at each measurement wavelength allows us to get Mueller matrices of samples at different wavelengths without exchanging the plates. Initial orientation errors of two plates and an analyzer, which remain constant through all wavelengths, are also taken into consideration. The availability and accuracy of this polarimeter is assessed by measurement of a quarter-wave plate designed for 632.8 nm wavelength. The results show that this system is very attractive to measure optical properties and dispersion in samples.     

Method for measuring retardation of a quarter-wave plate based on normalized secondary harmonic component

A method for measuring retardation of a quarter-wave plate based on normalized secondary harmonic component is proposed, and the measuring principle is analyzed. The optical measuring system is composed of a laser, a polarizer, a phase modulator, the quarter-wave plate to be measured, an analyzer and a detector. The azimuths of the transmission axes of the polarizer and the analyzer with respect to the modulating axis of the phase modulator are +45°, 0°, respectively. The retardation of the quarter-wave plate is calculated precisely using the normalized secondary harmonic components prior to and after 22.5° rotation of the quarter-wave plate. In this method, the major axis position of the quarter-wave plate is not required to be known in advance, and the measured retardation is independent of the intensity fluctuation of the light source. The feasibility of the method is verified by the experiments.     

Achromatic half-wave combination of birefringent plates

Half-wave retarders are primarily used in rotating the plane of polarization of polarized light. These retarders usually exhibit strong wavelength dependence. In this paper, the design and characteristics of an achromatic half-wave plate, formed by a cascaded system of birefringent plates, have been studied. Pancharatnam proposed a combination of three retarders in series and discussed the possibility of fabricating reasonably good achromatic quarter-wave plate with a suitable combination of their retardance. The system studied here is similar in construction to Pancharatnam configuration and behaves as an achromatic half-wave plate over a wide spectral range. The proposed configuration exhibits a maximum variation of only about ±1.4 degree over the entire wavelength range of 500–750 nm. In our analysis we have used Jones matrix formalism for the derivation of the general expression for the equivalent retardation and the azimuth of the combination.     

Anisotropic antireflection coatings: use as a laser intracavity polarization-direction selector

A double-layer anisotropic antireflection coating is designed and fabricated using the technique of serial bideposition. Both layers in the coating are biaxial with nanostructural columns directed normal to the substrate. Incident light with the p polarization encounters a pair of quarter-wave layers with refractive indices that satisfy the standard relationship for zero reflectance at the design wavelength. Light with the s polarization meets non-quarter-wave layers and different indices and hence is partially reflected. As an example to illustrate potential applications of the coating, we have used a thin glass plate with anisotropic antireflection coatings on both sides as an intracavity element to select the direction of polarization of an open-cavity HeNe laser.     

Measurement of the linear electrooptic effect in poled polymer thin films with coplanar electrodes

The linear electrooptic (EO) effect of poled polymer thin film is measured in the coplanar-electrode structure. The optical geometry of the coplanar-electrode thin-film setup is analysed theoretically to find a relationship between the linear optical parameters and the EO modulation intensity. EO modulated intensity is measured as a function of the direction of incident light polarization relative to the macroscopic optic axis, also as a function of optical bias determined by quarter-wave plate. Comparison of experimental measurements with the theoretical analysis shows good agreement.     

Error analysis and Stokes parameter measurement of rotating quarter-wave plate polarimeter

In this paper, we present a simple Stokes parameter measurement method for a rotating quarter-wave plate polarimeter.This method is used to construct a model to describe the principle of how the magnitudes of errors influence the deviation of the output light Stokes parameter, on the basis of accuracy analysis of the retardance error of the quarter-wave plate,the misalignment of the analyzing polarizer, and the phase shift of the measured signals, which will help us to determine the magnitudes of these errors and then to acquire the correct results of Stokes parameters. The method is validated by the experiments on left-handed circularly polarized and linear horizontal polarization beams. With the improved method, the maximum measurement deviations of Stokes parameters for these two different polarized states are reduced from 2.72%to 2.68%, and from 3.83% to 1.06% respectively. Our results demonstrate that the proposed method can be used as a promising approach to Stokes parameter measurement for a rotating quarter-wave plate polarimeter.     

两种亚波长金属波片的透射特性对比

综合等效介质理论和表面等离子激元(SPP)Bloch模型,对比分析了两种新的亚波长光栅结构:二维矩形金属光栅和二维椭圆柱金属光栅。利用时域有限差分(FDTD)算法,对比分析了两种结构的透射率及其相位延迟与入射光波长及偏振角变化的关系,尤其两种结构实现λ/4波片功能所对应的透射特性。仿真结果表明,当入射光偏振角为75°时,两种结构均可实现λ/4波片功能,此时二维矩形和椭圆柱金属光栅的透射率分别为0.77和0.67,表明二维矩形金属光栅比椭圆柱光栅具有更好的透射效果。对应550～800nm的入射波长,两种光栅在各自允许的入射偏振角范围内均表现了较为平坦的宽带透射特性。     

Ultraviolet wave plates based on monolithic integration of two fully filled and planarized nanograting layers

We successfully fabricated a high-performance half-wave plate for the 405 nm wavelength based on monolithic integration of two nanograting layers. Each of the nanograting layers functions as a quarter-wave plate. Both of the nanograting layers were fully filled and planarized to achieve the monolithic integration. UV-nanoimprint lithography, along with thin-film deposition, high-aspect-ratio reactive ion etching, and trench-filling technologies, was used in fabrication and integration of the individual nanograting layers. High-aspect-ratio nanogratings with sub-50 nm linewidths and 100 nm spacing were fabricated to achieve good optical performance at the near-UV wavelength. The ability to integrate multiple nanostructure-based optical layers opens a path for integrated multifunction devices, as well as a new strategy for driving both miniaturization and cost.     

Common-path double-pass optical interferometry using a wire-grid polarizer as a reference mirror

A novel common-path double-pass optical interferometer that employs a wire-grid polarizer (WGP) as a reference mirror is presented. When a laser beam polarized at 45° relative to the wire grid is incident on the WGP, the polarization component parallel to the grid direction (s-polarized beam) is reflected and is used as a reference beam. The perpendicular component (p-polarized beam) passes through the WGP coupled with a quarter-wave plate and serves as a probe beam, with its polarization transformed as p, right-circular, s, left-circular, and p, to irradiate the sample surface twice in order to double the phase change due to displacement of the sample. This beam is then retransmitted through the WGP, where it recombines and interferes with the reference beam. Preliminary experiments demonstrate that the WGP performs successfully as a reference mirror, and that the interferometer has a potential displacement sensitivity as low as 0.1 nm.     

与偏振无关的双向3×3光开关结构设计

利用传统成熟的偏振控制技术,设计了一种由偏振光分束器、相位型空间光调制器、反射镜和四分之一波片构成的3×3光开关。该光开关具有结构紧凑规整、功能的实现与信号光的偏振态无关以及可以完成双向交换等特点。根据其路由控制表对该3×3光开关交换模块功能的实现进行了分析,结果表明,通过对各相位型空间光调制器状态的调整,控制通过其信号光的偏振态,完成信号光的路由,该交换模块可以完成输入信号光的全排列无阻塞输出与交换。同时,该交换模块具有一定的扩容和重构能力,对于构建大规模的交换矩阵具有一定的作用。