与偏振无关双向2×2和4×4自由空间光开关

利用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和反射镜构成的2×2光开关，该光开关所用器件少，具有结构简单紧凑、控制灵活方便、功能实现与信号光的偏振态无关以及可以双向交换等特点；在此基础上通过2×2光开关的串连，设计了一种与偏振无关的双向4×4光开关的实验模块，根据其路由选择与控制方法，得到了4×4光开关实现信号光全排列无阻塞输出与交换对应的路由状态表，并对该实验模块的功能实现进行了详细的分析与讨论。     

Polarization-independent bidirectional 4×4 optical switch in free space

Optical switches play an important role in all optical communication networks and multiprocessor computer systems. The 2×2 and 4×4 optical switches are the basic units of large-scale switch matrices. Using a conventional polarization control method, the optical switch system and structure is optimized, and a novel optical switch is proposed, which has the advantages of relatively low crosstalk and insertion loss, compact and simple construction, higher performance and cost effectiveness. First, a novel 2×2 optical switch is proposed using phase spatial light modulator (PSLM), polarizing beam splitter (PBS) and mirror. This configuration uses fewer optical components, is compact in structure, efficient in performance, and insensitive to polarization of the signal beam. Second, a new optical experimental module of 4×4 optical switch is presented by cascading a 2×2 optical switch. The routing method of polarization-independent bidirectional 4×4 optical switch is investigated. Finally, the operational characteristics of the polarization-independent bidirectional 2×2 and 4×2 optical switches are discussed in detail.     

Fiber Sagnac π-shifted interferometer for a polarization-independent PMNT high-speed electro-optic switch

We propose and analyze experimentally a high-speed polarization-independent lead magnesium niobate titanate (PMNT) electro-optic switch using a π-shifted fiber Sagnac interferometer (FSI). In the proposed switch, the PMNT high-speed electro-optic ceramic is used as a phase retarder for two counterpropagating waves, which can switch the energy between the reflection and transmission ports of the FSI. Because of an initial π shift introduced into the FSI by actively adjusting the polarization controller, the power response of the switch is independent of the polarization orientation of the incident light, which induces the polarization-independent characteristic of the switch. An optical switch with cross talk lower than -25 dB and a switching time of less than 200 ns is experimentally investigated. The insertion loss and electric hysteresis property are also demonstrated. Finally, a scheme to form the n × n switch matrix is proposed.     

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。     

4×4自由空间光开关结构及其矩阵分析

光开关是全光通信网络中的一种重要的光无源器件。提出了一种4×4自由空间光开关的结构设计方法,并进行了矩阵理论分析。该4×4光开关具有新颖的光模块化结构,该光开关结构仅由偏振分束组合棱镜,λ／4波片,λ／2波片,直角棱镜,全反镜和偏振光调制器组成,对光开关的控制与输入光束的偏振态无关。所有的输出端口可以和输入端口无阻塞地互连交换。这种新型的光开关结构具有光学元件少,结构紧凑,模块化,与偏振无关的特点。基于4×4光开关的矩阵分析得到了路由控制表,为4×4光开关从任意输人端口到任意输出端口的路由控制状态提供了理论分析手段,从而可以方便地实现无阻塞地光交换开关矩阵的路由控制功能。     

High-efficiency electrically tunable phase diffraction grating based on a transparent lead magnesium niobate-lead titanite electro-optic ceramic

An electrically tunable high-efficiency phase diffraction grating using the transparent lead magnesium niobate-lead titanite (PMNT) electro-optic ceramic is proposed. A photomask technique is used for fabricating the grating with the Ti/Pt/Au interdigital electrodes. With the variation of the equivalent phase face induced by the quadratic electro-optic effect of the PMNT ceramic, the diffraction patterns of the light beam will be changed in which the diffraction efficiency may be controlled by an applied DC voltage. When the applied voltages are 41, 80, and 139 V, the zero-order, first-order, or second-order diffraction lights will disappear in turn with about 100% diffraction efficiency. The proposed grating can be used as an electrically controlled switch in the laser beam modulation and scanning, especially for the application of the high-power laser systems.     

Optical characteristics of transparent PMNT ceramic and its application at high speed electro-optic switch

The optical characteristics of transparent lead magnesium niobate titanate (PMNT) electro-optic ceramic, including the electro-optic phase modulation, electric hysteresis property and thermo-optic coefficient, are investigated in detail. Based on this novel ceramic, a polarization independent electro-optic switch by using fiber Sagnac interferometer (FSI) structure is realized. An initial π-shift is introduced into the Sagnac loop to eliminate the effect of the polarization orientation of the incident light on the switch performance. Then an electrically controllable PMNT phase retarder is used to switch the optical signal between the reflection and transmission ports. Some theoretical analyses are given and the switch performances are also discussed, including the thermal characteristic and different switching frequency response.     

Three-Dimensional Large Screen Display Using Polymer-Dispersed Liquid-Crystal Light Valves and a Schlieren Optical System: Proposal and Basic Experiments

A novel three-dimensional (3-D) projection display used with polarized eyeglasses is proposed. It consists of polymer-dispersed liquid crystal-light valves that modulate the illuminated light based on light scattering, a polarization beam splitter, and a Schlieren projection system. The features of the proposed display include a 3-D image display with a single projector, half size and half power consumption compared with a conventional 3-D projector with polarized glasses. Measured electro-optic characteristics of a polymer-dispersed liquid-crystal cell inserted between crossed polarizers suggests that the proposed display achieves small cross talk and high-extinction ratio.     

Beam steering of external cavity diode laser by an intracavity electro-optic ceramic deflector

A novel beam-steering external cavity diode laser using an intracavity lead lanthanum zirconate titanate(PLZT) electro-optic ceramic deflector is proposed and demonstrated experimentally.The laser consists of a semiconductor laser with single mode fiber coupled output,polarization controller,PLZT electro-optic ceramic deflector,and output concave mirror.By applying proper driven electrical signals on the PLZT electro-optic deflector,the beam deflection angle achieves 5.8 mrad at 1 000 V.A high-speed beam-steering property with less than 120-ns switching time is also observed.Moreover,a good beam quality with Gaussian spatial profile and a linear polarization state are obtained.     

Laser ranging based on electro-optic switch

Based on electro-optic switch effect in crystal, a novel laser ranging method is proposed. CW-laser emitted by laser transmitter propagates forward to the measured target, after being reflected by the target, and then goes back to the transmitter. Close to the transmitter, a special mono-block LiNbO₃ crystal is added into the round-trip light beams. High-voltage pulses with the sharp enough changes in rising edges are loaded on the crystal. Based on electro-optic effect, double refraction and internal double reflection effect in crystal, the crystal cuts off the round-trip light beams, and reflects a light pulse cut out by the crystal to a detector aside from the original beam path. The pulse width T is the period that laser propagates forward and back between the crystal and the target. The feasibility of the new idea is proved by our experiments and a brand-new way for the laser ranging is provided.     

法拉第镜旋转角的偏振分束测量法

提出了基于偏振分束法的法拉第镜偏振旋转角的测量方法.利用非偏振分束器改变法拉第镜出射光的方向,偏振分束器将该出射光分为p光和s光,分别测量其光强,应用后续"差除和"信号处理方案消除光源波动的影响,推导出法拉第镜偏振旋转角的理论表达式.分析了起偏器的消光比非0及起偏角误差对输出结果的影响,分别是0.057 29°和-0.100 0°.实验验证了该方法的可行性,重复测量结果为89.68°,均方值为0.014 93.     

Ultrasonic diffraction of Bessel light beams in uniaxial gyrotropic crystals

Specific features of the acousto-optic diffraction of Bessel light beams propagating in the vicinity of the optical axis of a uniaxial gyrotropic crystal have been investigated. The dependences of the diffraction efficiency on the acousto-optic interaction length, ultrasound power, and polarization state of the incident Bessel light beam have been analyzed using the coupled-wave equations and the overlap-integral method. It is shown that polarization-independent diffraction of Bessel light beams is observed in paratellurite crystals, when the Bragg diffraction efficiency is independent of the polarization state of the incident beam. The physical reason for this diffraction has been established (both theoretically and experimentally) to be simultaneous implementation of two processes of anisotropic scattering, at which the Bragg synchronism conditions are satisfied for orthogonal polarized Bessel beams with elliptical polarization.     

光互连网络中四功能交换开关研究

由节点开关单元按照一定的连接规则所构成的光互连网络,在全光通信和光信息处理中具有重要的应用。基于节点开关一般实现光信号的直通和交换功能的特点,利用成熟的偏振光控制技术,通过位相型空间光调制器对信号光偏振态的控制,完成信号的路由和开关动作,从而设计出具有直通、交换、上播和下播功能的节点交换开关。与传统设计思想相比,该方法不仅能够充分利用信号光的能量,有效的减少光能量的损耗,而且还具有与偏振无关等特点。该四功能交换开关,对于优化和拓展光互连网络的结构和功能具有一定的意义。     

畴反转结构片状集成4×4电光开关的设计与仿真

基于铁电体畴反转结构的电光偏转特性,设计了一种片状集成的4×4电光开关,其由四个结构相同的半抛物和四个抛物形微小偏转器集成构成.通过优化抛物形偏转器结构,给出了电光开关的设计参量,电光开关性能通过光束传播法进行仿真模拟,仿真结果表明该开关切实可行.实际应用中,系统误差可以通过电场调节补偿,使光路准确交换.该片状电光开关的整体尺寸为48 mm×2.2 mm×0.5 mm(长×宽×高),最大使用电场约13.73 V/μm,适用于高速交换的光互连系统.     

偏振无关的波长间隔可调的全光纤双折射滤波器

 设计了一种新的便于调谐且波长间隔可调的全光纤双折射滤波器。该滤波器由一个偏振分束器（PBS）、2段保偏光纤（PMFs）和4个二分之一波片（HWPs）连接而成。计算并分析了它的理论结果,发现在合理调节环中4个二分之一波片的情况下,该滤波器除了可以获得有很好的滤波光谱输出之外,还具有波长间隔可调的作用。这种滤波器在设计可灵活改变波长间隔的多波长光纤激光器及光纤系统等方面具有巨大的应用前景。     

Tunable multi-function broadband splitter with optical bistability based on surface plasmon

A tunable multi-function broadband splitter consisted of a silver film, Kerr medium and a silver grating sandwiched between linear dielectrics waveguides is proposed and numerically investigated. This splitter can realize the functions of the beam splitter, the polarization splitter and wavelength beam splitter. This surface plasmon based device provides a unique approach for polarization sensitive manipulation of light in an integrated circuit and will be essential for future classical and quantum information processes.     

Polarization beam splitter using a binary blazed grating coupler

A novel polarization beam splitter using a two-layer grating coupler is proposed and demonstrated. It can directly couple the normally incident light from fiber into two separate waveguides according to their polarization states while splitting them. It realizes high coupling efficiency and a good extinction ratio by using binary blazed grating couplers. The coupling length is less than 14 microm. The extinction ratio is better than 20 dB for both polarizations over a 40 nm wavelength range, and the coupling efficiencies for the two layers are 58% and 50%.     

Polarization Insensitive Wavelength Conversions by a LiNbO3 Waveguide Using a Multi-Ring Configuration

A novel configuration is proposed for polarization insensitive wavelength conversions using a LiNbO₃ waveguide with a periodically domain inverted structure. The proposed configuration consists of multiple rings, which are connected by a polarization sensitive wavelength converter such as the LiNbO₃ waveguide described. One ring containing a pump light source is used to pump the wavelength converter bidirectionally, while the other rings containing a polarization beam splitter and a 90° polarization rotator are used to couple in the input signal and extract the converted light. The proposed method is proven experimentally by the wavelength conversion based on sum frequency generation.     

Modal analysis of deep-etched low-contrast two-port beam splitter grating

Modal analysis of a deep-etched low-contrast two-port beam splitter grating under Littrow mounting is presented. The guideline for the design of a subwavelength transmission fused-silica phase grating as high-efficiency grating, polarizing beam splitter (PBS), and two-port beam splitter, is summarized. As an example, a polarization-independent two-port beam splitter grating is designed at wavelength of 1064 nm. We firstly analyzed the physical essence of the grating by the simplified modal method. The guideline for the grating design and the approximate grating parameters are obtained. Then using the rigorous coupled-wave analysis (RCWA) with parameters varying around the approximate ones, optimum grating parameters can be determined. With the design guideline, the time for the rigorous calculation of the grating profile parameters can be reduced significantly.     

Generation of arbitrary vector beams based on a single spatial light modulator and a thin-film polarization splitting cubic

A setup for the generation of arbitrary vector beams is proposed. The setup mainly consists of a spatial light modulator(SLM), an angle-adjustable polarization beam splitter modulator, and a spatial filtering imaging system. Compared with the system using a birefringent beam splitter with a non-adjustable splitting angle,the polarization splitting angle of the improved setup can be adjusted by slightly rotating the related mirrors,which will bring more convenience when different wavelengths and different pixel sizes of SLMs are involved.The experimental results also demonstrate that the setup possesses a good polarization-selective imaging ability, which reveals that the setup may also be useful in polarization-selective spatial filtering imaging and polarization-encoded encryption.