光纤光栅双折射效应的实验研究

本文对均匀光纤光栅和线性啁啾光纤光栅的双折射效应分别进行了实验研究. 利用压电陶瓷的压电效应实施对均匀光纤光栅和线性啁啾光纤光栅的侧向挤压, 使之产生双折射, 通过改变施加在压电陶瓷上的电压值, 可以实现对光纤光栅双折射大小的控制. 侧向挤压线性啁啾光纤光栅可以补偿光纤通信系统中的偏振模色散.     

声光调制原理及应用

声波通过固体媒质时,在媒质中产生的机械应力会引起媒质折射率的变化,从而在媒质中形成光栅状的折射率轮廓．该光栅结构导致入射光束的衍射,称为声光效应．利用声光效应可以实现光的调制。 图１给出声光调制器的示意图,它是一块透明的固体煤质（如石英）,煤质的两端分别与压电换能器和吸声器相连,当换能器上加以高频电压时,换能器的振动会在煤质中产生超声波．媒质的折射率ｎ＝,当超声波穿过团体媒质时,媒质分子电偶极矩发生变化（Χｅ发生变化）,从而使媒质的折射率发生周期性变化,形成折射率光栅（即超声光栅）．此时光栅常数…     

光纤投影双频自动轮廓测量术

提出一种双频光纤投影自动轮廓测量技术；用一分二单模光纤耦合器产生正弦光强分布的投影光栅场；将光纤一臂绕在压电陶瓷（ＰＺＴ）环上述旁瓣通过压电陶瓷环引入相移值；以改变出射端两光纤间的距离来发迹投影光栅场的空间频率，用双频光栅技术实现复杂表面自动轮廓测量。     

一种增益可调掺铒光纤放大器的研究

在所设计的增益可调掺铒光纤放大器中,采用可编程控制器PC机控制可变直流电压源引发压电陶瓷的电致伸缩效应,导致光纤布拉格光栅的Bragg波长发生漂移,实现被调制参数的变化.分析了双光纤光栅受到压电陶瓷电致伸缩效应时的反射谱变化规律和增益可调掺铒光纤放大器的放大特性.由该放大器的增益与输入信号功率的关系得出小的波长间隔,增益较小,但控制范围较大;大的波长间隔,增益较大,但控制范围较小的结论.在输入宽带光源时,得到两光纤布拉格光栅在不同中心波长之差时的掺铒光纤放大器的增益特性.     

纤维光学 光纤器件

TN253 2005031975 利用线性啁啾光纤光栅补偿PMD的实验研究=Experi- mental research on PMD compensation using linearly chirped fiber Bragg grating[刊,中]／张霞(北京邮电大学理 学院．北京(100876)),黄永清…∥半导体光电．-2004, 25(4)．-293-295 对利用线性啁啾光纤光栅补偿偏振模色散(PMD)进 行了实验研究。利用压电陶瓷的压电效应挤压线性啁啾 光纤光栅使之产生双折射,用于补偿光通信系统中的偏振 模色散。通过改变施加在压电陶瓷上的电压值,可实现对     

弛豫铁电单晶的研究进展—压电效应的起源研究

由于具有优异的压电性能,弛豫铁电单晶自上世纪90年代问世以来即成为了铁电压电领域研究的热点材料,并被认为是研发下一代高性能换能器、传感器等器件的重要压电材料。弛豫铁电单晶不但压电常数可达2500 pC/N,约为软性Pb(Zr,Ti)O3(PZT)陶瓷的5倍,而且其电致应变滞后也远小于软性PZT陶瓷。因此,弛豫铁电单晶高压电性能的产生机理一直是铁电压电领域的研究热点。本文主要介绍了弛豫铁电单晶材料在近些年的发展,从本征压电效应(晶格压电畸变)的角度归纳总结了弛豫铁电单晶高压电效应的产生机理,着重探讨了弛豫铁电单晶的重要特点—剪切压电效应。在本征效应的基础上,本文对弛豫铁电单晶压电效应与晶体组分、切向以及温度的关系进行了分析。需要指出的是,目前基于本征角度对弛豫铁电单晶高压电效应的分析仍处于定性的阶段,因而还不能完全排除一些可能导致弛豫铁电单晶高压电效应的非本征物理机制。     

压电陶瓷驱动的动态匹配光栅滤波解调法优化

提出并实验验证了一种动态匹配光栅滤波系统的优化解调方法.在压电陶瓷驱动的动态匹配(光纤)光栅滤波解调系统中,一方面采用上升高压锯齿波,以消除压电陶瓷滞回效应;另一方面将压电陶瓷电压与伸长量关系的反函数作为锯齿波上升电压,以校正压电陶瓷的非线性;进而,为实现解调系统的温度补偿,引入一根中心波长保持不变的参考(光纤)光栅.在锯齿波上升过程中,匹配光栅与参考光栅和传感(光纤)光栅在不同时刻匹配,匹配时间差仅与传感光栅有关,而与解调系统温度无关.实验结果表明,优化后系统的线性度可提高2%,灵敏度与理论值的相对误差小于0.6%;在10～60℃范围内,该解调系统温度变化引起的相对误差小于1%.     

电流变液态光栅实验研究

利用电流变液在电场作用下可以形成周期性链状结构的性质，在实验上制作了电流变液态光栅。搭建了产生均匀、细小激光光束的光路装置，调制了均匀、浓度适当的电流变液，并以此为材料在电场作用下形成了电流变液态光栅。利用电流变液态光栅，观察到了标准的光栅衍射现象。测量了电流变液态光栅的光栅常数、衍射条纹间距等实验数据，分析处理，总结了数据。为了验证流体光栅的物理性质，进一步做了液态光栅和传统固态光栅的对比实验，发现两者的对比度十分良好。     

基于压电陶瓷的激光频率调谐技术

在充分研究各种激光调谐方法优缺点的基础上,针对其调谐范围、调谐速率、调谐线性等方面存在的不足,提出一种基于压电陶瓷的激光频率调谐技术。该方法将压电陶瓷与光纤光栅激光器的布拉格光栅进行粘结,通过调整压电陶瓷的驱动电压来带动布拉格光栅的伸缩,实现波长（即频率）的调谐。同时,利用虚拟仪器中的计算机软件拟合技术,校正压电陶瓷输入电压与输出位移之间的非线性,使系统呈线性频率调谐,以提高测量精度。实验结果表明,当压电陶瓷的驱动电压变化126 V时,可实现0.8 nm（即100 GHz）的调谐范围。     

用光纤光栅传感器研究压电陶瓷的特性

提出了一种利用光纤光栅传感器研究压电陶瓷特性的新方法.该方法采用非平衡Michelson扫描干涉仪对光纤光栅传感信号进行相位解调,通过观测波长漂移引起的相移,从而获得压电陶瓷的位移量与所加电压间的关系.实验分析了迟滞特性和蠕变现象,得到了压电陶瓷的电压-位移特性曲线以及蠕变特性曲线.实验表明,光源功率的波动对压电陶瓷迟...     

单轴晶体包层啁啾光纤光栅中电光效应和弹光效应的理论研究

提出了以单轴晶体材料为包层,光轴平行于光栅主轴(z轴)的新型啁啾光纤光栅模型,应用耦合模理论和传输矩阵方法在理论上分析了该类光纤光栅中的电光效应和弹光效应,理论研究发现在包层施加沿光栅轴向的电场和应变场可以改变布拉格波长和反射谱。得到了3种不同单轴晶体为包层时布拉格波长λB和反射光谱随外加电场和应变场变化的曲线。研究结果表明当轴向外加电场从1×107V/m变化到8×107V/m时λB减小0.12nm,当外加应变场从0变化到0.04时,λB减小0.45nm。     

波长尺寸表面浮雕光栅的严格理论计算和分析

本文采用麦克斯韦(Maxwell)方程微分积分方程对波长尺寸的梯形反射光栅在TE模式(横向电场)偏振状态入射下,进行严格理论的计算和分析.表面电场计算表明,光栅刻槽斜边边界对于金属材料金和铝光栅表面电场分布具有明显效应,对于入射波长为λ=1.0μm附近的红外区域,金材料具有强烈的金属特性,此时表面电场的斜边边界效应更加明显.表面电场及其远场衍射效率伴随刻槽深度变化,而振荡特性进一步阐明了此效应对近,远场的作用.该方程适用于任意形状光栅或单一散射体对任意入射方向,任意偏振态的衍射和散射问题.     

多层介质膜脉冲压缩光栅近场光学特性分析

利用傅里叶模式理论分析了TE波自准直角入射的使用条件下，多层介质膜光栅的光栅区和多层膜区电场分布的特点.分别讨论了HfO₂和SiO₂为顶层光栅材料时，光栅结构参数对光栅脊峰值电场的影响，结果表明，对于不同膜厚的顶层材料，存在一个最佳膜厚度，使光栅脊峰值电场最小，并且当膜厚增大时，设计大高宽比的光栅可以降低该电场峰值.最后，在大角度条件下使用多层膜光栅也可以降低光栅脊处的峰值电场. 关键词： 衍射光学 多层介质膜光栅 模式理论 损伤阈值     

Stabilization of Drift Instabilities of an Inhomogeneous Plasma by Means of an RF Electric Field

The possibility of stabilizing effects that an rf electric field imposes on drift instabilities in an inhomogeneous plasma is investigated. A two-species, nonisothermal plasma, situated in an externally applied static magnetic field is considered with the rf electric field applied in the same direction as the dc magnetic field. The plasma is "mildly" inhomogeneous in density, with a density gradient perpendicular to the confining magnetic field. Using a hydrodynamic model for the plasma it is found that under certain conditions an increase in the frequency of the drift oscillations is obtained as the result of the application of the rf electric field. The increase in the frequency of the drift oscillations results in an increase in the magnitude of the stabilizing term associated with Landau damping which in turn yields a smaller growth rate for the drift instability. Discussions of the state of the plasma for different values of the frequency of the applied electric field are presented and the feasible ranges of values of the above quantity required for stabilization are determined. It is concluded that the resulting stabilization is significant only in a very narrow rf band. Therefore, the application of this technique appears to be a difficult experimental undertaking.     

Percolation-enhanced nonlinear scattering from metal-dielectric composites

It is shown that large percolation-enhanced nonlinear scattering occurs in metal-dielectric random composites near the percolation threshold. The enhancement is due to giant local electric field fluctuations that are extremely inhomogeneous and consist of spatially separated sharp peaks, "hot" spots, where the local field is greater by many orders of magnitude than the applied field.     

全内反射式衍射光栅近场光学特性

 利用傅里叶模式理论分析了具有高衍射效率的全内反射式衍射光栅在TE 和TM偏振态下的近场光分布特点，讨论了光栅结构参数以及入射角度对光栅内电场增强的影响。结果表明：全内反射光栅内部电场分布对偏振态较敏感，光栅槽深和占宽比对电场增强影响较小，光栅内的峰值电场随光栅周期增大而增大，并且峰值电场随着入射角度的增大而减小。在应用于高功率激光时，降低光栅内部的电场增强可以有效降低损伤风险。     

Near-field optical properties of wide bandwidth metal multi-layer dielectric gratings for pulse compressor

Metal multi-layer dielectric gratings (MMDG) for pulse compressors in high-energy laser systems should provide broad bandwidth as well as high laser-induced damage thresholds. The non-uniform optical near-field distribution of MMDG is an important factor that limits damage resistant capabilities. MMDG for pulse compressors operating at 800 nm with a corrugated SiO₂ layer are designed by using a genetic algorithm and the Fourier mode method. The diffraction efficiency, bandwidth, and near-field distribution of the MMDG are theoretically investigated. For the single dielectric match layer grating, the bandwidth is 140 nm, if the thickness and refractive index of the match layer are changed, the maximum electric field in the grating ridge, match layer, and metal layer of the grating increases with the decrease in grating diffraction efficiency. For the multi-dielectric match layer grating, the bandwidth and the maximum electric field in the metal layer decrease with the increase in high- and low-index material pairs, and the maximum electric field in the grating ridge and match layer initially decreases and then increases. Over a wide wavelength range, the maximum electric field in the grating ridge, match layer, and metal layer is minimal near the central wavelength. Moreover, MMDG should be used at larger incident angles while keeping enough bandwidth to reduce the electric field in the grating.     

Theoretical Study of Electro-Optic Effect and Elasto-Optic Effect in Chirped Fiber Grating with Uniaxial Crystal Materials Cladding

A chirped fiber grating with cladding made of uniaxial crystal material whose optical axis is parallel to the axis of grating, i.e., z-axis is proposed. Electro-optic effect and elasto-optic effect in this kind of fiber gratings are theoretically analyzed for the first time. The influences of the electric field and the strain applied to the fiber grating cladding along z-axis on Bragg wavelength λ _B and the reflectivity spectra of this kind of chirped grating are theoretically examined using coupled-mode theory and transfer matrix method. The curves of Bragg wavelength λ _B as a function of an external electric field or the strain are theoretically obtained respectively for three kinds of uniaxial crystal materials as the grating claddings. The calculated results indicate that when the axial electric field applied to the grating cladding varies from 1 × 10⁷ to 8 × 10⁷ V/m, λ _B has the decreases of 0.12 nm, and when the applied strain varies from 0 to 0.04, λ _B has the decreases of 0.45 nm.     

Magnetoelectric control of domain walls in a ferrite garnet film

A displacement of magnetic domain walls under the effect of an electric field is observed in epitaxial ferrite garnet films (on substrates with the (210) orientation). The displacement of the domain walls changes to the opposite when the electric field changes sign, and it is independent of the direction of magnetization in the domains. The mechanism proposed for explaining the observed phenomenon is based on the inhomogeneous magnetoelectric effect.     

Induction of superconductivity by strong electric field

It is shown that strong electric field perpendicular to the surface of a solid with free charges creates the surface inhomogeneous superconducting state with critical parameters depending on the surface electrical potential only.The critical temperature and magnetic field of the surface inhomogeneous state can be high in the strong electric field.