极窄带宽的布拉格光纤光栅光谱特性研究

根据理想模展开下的耦合模方程，对光纤布拉格光栅的峰值反射率公式进行了数学推导，得到了布拉格光纤光栅的光谱反射率表达式。全面讨论了光栅周期、光纤栅长、光致折射率微扰最大值等参数与光纤光栅反射光谱的关系。仿真结果显示了固定参数下布拉格光栅的极限窄带宽，得到的反射率为1、带宽为0.02nm的窄带宽布拉格光栅，比现今分布式传感系统中使用的布拉格光栅的带宽窄1个数量级。这种布拉格光纤光栅用于分布式传感系统，可大大提高分布式传感系统中光源的带宽利用率，消除各信号间的相互串扰，提高传感光栅复用数目，降低解调系统成本。     

长周期光纤光栅折射率传感器的结构优化

为了提高长周期光纤光栅对环境介质折射率的传感灵敏度,提出一种长周期光纤光栅的周期和包层半径的结构优化.基于长周期光纤光栅的耦合模理论,分析了长周期光纤光栅的周期和包层半径的大小分别与环境介质折射率传感灵敏度的关系,讨论了长周期光纤光栅的周期和包层半径对折射率传感的影响以及控制光栅周期与包层半径对折射率传感的重要性.为使...     

光纤耦合模理论及其在光纤布拉格光栅上的应用

将正确的光纤中的正交关系应用于微扰耦合模理论得到了光纤中的微扰耦合模方程；并将其应用于光纤布拉格光栅，得到了一种新耦合模方程。该方程中作为标志性特性的耦合系数与其它理论中的耦合系数都不相同。讨论了方程的解，得到了峰值反射率与布拉格波长、光栅长度之间的简单关系式。用光纤布拉格光栅进行了实验，理论和实验结果符合得很好。     

CO2激光写入旋转折变型长周期光纤光栅的制作及理论分析

提出了一种光纤横截面折射率变化呈旋转非对称变化的长周期光纤光栅（R-LPFG） 结构,并利用多层圆波导理论和横截面折射率离散分析方法,结合模式耦合方程组和数值求解方法理论分析了这种光栅的模式耦合特征.理论分析表明R-LPFG纤芯基模主要与一阶非对称包层模发生耦合,当光栅旋转度逐渐变大时,R-LPFG基模会与一阶非对称包层模的奇模和偶模同时发生耦合,这就会使原来单一的谐振峰逐渐分裂成双峰,这是常规光栅类型所不具有的透射谱特征.由于R-LPFG的双峰来自同一对耦合模式,它们对温度的响应很相似,因此可利用双峰间 关键词： 光纤传感 光纤光栅 2激光')" href="#">CO₂激光 旋转折变     

长周期光纤光栅耦合模理论分析

长周期光纤光栅作为透射型光无源器件,以其在通信和传感领域具有广阔应用前景而引起人们的关注。要得到满足性能要求的光纤光栅,对其透射谱的分析是基础。通过耦合模方程确定了基模和一阶各次包层模之间的耦合常数。在设定的光纤光栅参数条件下,通过Matlab进行模拟得到了最终需要的长周期光纤光栅透射谱,并由此得出：长周期光纤光栅谐振波长出现的位置主要由光栅的周期决定,损耗大小可以通过调节光栅长度和折射率来实现。     

长周期光纤光栅和双锥形光纤问的倏逝波耦合作用

对长周期光纤光栅和双锥形光纤之间的倏逝波耦合作用进行了研究。理论分析和实验研究表明，由于锥形光纤和长周期光纤光栅物理边界外倏逝波之间的交叠，长周期光纤光栅产生的包层模，可以耦合到锥形光纤的包层模并从锥形光纤的纤芯输出。要获得高的耦合效率，应满足模式匹配的条件，同时要尽量减小两光纤之间的距离。耦合特性还与长周期光栅和双锥形光纤的相对位置有关，为获得高的耦合效率，耦合区应位于长周期光栅区的后面。这种倏逝波耦合作用，为监测实际应用系统中长周期光纤光栅的特性提供了一种新方法；为利用锥形光纤和长周期光纤光栅开发新型光纤器件，提供了一种可能的方案。     

基于光纤自适应耦合和自调谐的光纤光栅传感系统设计

针对光纤光栅传感系统应用中面临的应变能力和可靠性不稳定的问题,研究并设计了一种基于自适应耦合切换和自调谐光纤光栅传感系统。首先,基于长周期和短周期光纤光栅耦合特性建立了自适应耦合器件及其切换算法,然后再分析耦合特性的基础上设计了支持自调谐功能的光纤光栅传感器及其调谐算法,最后给出了支持耦合自适应切换和耦合特性自调谐功能的光纤光栅传感系统。实验表明,在检测精度、抗干涉能力和应变能力等方面,所提方案表现出了明显优势。     

CO2激光写入旋转折变型长周期光纤光栅的制作及理论分析

提出了一种光纤横截面折射率变化呈旋转非对称变化的长周期光纤光栅(R-LPFG) 结构,并利用多层圆波导理论和横截面折射率离散分析方法,结合模式耦合方程组和数值求解方法理论分析了这种光栅的模式耦合特征.理论分析表明R-LPFG纤芯基模主要与一阶非对称包层模发生耦合,当光栅旋转度逐渐变大时,R-LPFG基模会与一阶非对称包层模的奇模和偶模同时发生耦合,这就会使原来单一的谐振峰逐渐分裂成双峰,这是常规光栅类型所不具有的透射谱特征.由于R-LPFG的双峰来自同一对耦合模式,它们对温度的响应很相似,因此可利用双峰间距来进行无需温度补偿的扭曲、应变等物理量的测量.最后利用高频CO2激光脉冲写入法制作了这种光栅,并实验研究了这类光栅的传输谱演变特征,实验结果和理论分析一致.可以预见,这类光栅在光纤传感或通信中将具有较大的潜在应用价值.     

Bragg光纤光栅傅里叶模式耦合理论

建立了Bragg光纤光栅傅里叶模式耦合理论.在分析光纤光栅的耦合模时,发现了耦合模式的振幅系数间存在傅里叶变换关系.推导了将傅里叶变换和模式耦合融合在一起的Bragg光纤光栅反射谱和透射谱的通用表达式.该理论是用傅里叶变换得到Bragg光纤光栅折射率微扰的空域谱,再对该空域谱进行模式耦合分析计算,从而得到Bragg光纤光栅的光谱特性.根据该理论,仿真分析了Bragg光纤光栅的谱特性,与耦合模理论、直接傅里叶变换法进行了对比分析.结果表明,傅里叶模式耦合理论与传统的耦合模理论及实际Bragg光纤光栅的光谱特性一致,具有简单、清晰、直接、精确和分析效率高的特点,可分析任意轴向折射率微扰分布的Bragg光纤光栅结构.     

线性啁啾莫尔光纤光栅的理论研究

以经典耦合模理论为基础,结合线性啁啾莫尔光纤光栅的结构特性,给出了线性啁啾莫尔光纤光栅的耦合系数和耦合模方程,并用龙格库塔迭代法数值求解耦合模方程.对多种线性啁啾莫尔光纤光栅的光谱特性和时延特性进行了理论模拟.分析结果表明,线性啁啾莫尔光纤光栅的相移特性和切趾特性,使得该类型光栅在波分复用全光网中有着很好的应用前景.     

平行双转镜傅里叶变换光谱仪

在时间调制傅里叶变换光谱仪中,直线运动型动镜很难精确驱动,容易引起倾斜和剪切的问题。旋转型动镜可以解决该类问题。介绍了一种转镜式傅里叶变换光谱仪方案,并对其进行了原理分析和光程差公式推导,提出了工程设计约束条件。该光谱仪由一个分束器,两个固定平面镜,两面平行固定在一个转轴上旋转的平面反射镜,前置镜,后置镜及探测器组成。通过原理介绍得出,该光谱仪结构简单,两条分光光线经同一平面镜反射后干涉,使仪器更容易装调;通过光程差推算得出,该光谱仪容易实现大光程差,光谱分辨率高;通过工程设计约束及仿真分析得出,该光谱仪需要在高速旋转的条件下实现高分辨率采样,容易实现精确运动控制,稳定性好,测量速度快。     

CPT-Frames for Non-Hermitian Hamiltonians

Based on the PT-symmetric quantum theory, the concepts of PT-frame, PT-symmetric operator and CPT-frame on a Hilbert space K and for an operator on K are proposed. It is proved that the spectrum and point spectrum of a PT-symmetric linear operator are both symmetric with respect to the real axis and the eigenvalues of an unbroken PT-symmetric operator are real. For a linear operator H on C^d, it is proved that H has unbroken PT- symmetry if and only if it has d different eigenvalues and the corresponding eigenstates are eigenstates of PT. Given a CPT-frame on K, a new positive inner product on K is induced and called CPT-inner product. Te relationship between the CPT-adjoint and the Dirac adjoint of a densely defined linear operator is derived, and it is proved that an operator which has a bounded CPT-frame is CPT-Hermitian if and only if it is T-symmetric, in that case, it is similar to a Hermitian operator. The existence of an operator C consisting of a CPT-frame is discussed. These concepts and results will serve a mathematical discussion about PT-symmetric quantum mechanics.     

On a well-balanced high-order finite volume scheme for shallow water equations with topography and dry areas

We present a finite volume scheme for solving shallow water equations with source term due to the bottom topography. The scheme has the following properties: it is high-order accurate in smooth wet regions, it correctly solves situations where dry areas are present, and it is well-balanced. The scheme is developed within a general nonconservative framework, and it is based on hyperbolic reconstructions of states. The treatment of wet/dry fronts is carried out by solving specific nonlinear Riemann problems at the corresponding intercells.     

CPT-Frames for Non-Hermitian Hamiltonians

Based on the P T-symmetric quantum theory,the concepts of P T-frame,P T-symmetric operator and CPT-frame on a Hilbert space K and for an operator on K are proposed.It is proved that the spectrum and point spectrum of a P T-symmetric linear operator are both symmetric with respect to the real axis and the eigenvalues of an unbroken P T-symmetric operator are real.For a linear operator H on Cd,it is proved that H has unbroken P Tsymmetry if and only if it has d diferent eigenvalues and the corresponding eigenstates are eigenstates of P T.Given a C P T-frame on K,a new positive inner product on K is induced and called C P T-inner product.Te relationship between the CP T-adjoint and the Dirac adjoint of a densely defined linear operator is derived,and it is proved that an operator which has a bounded CP T-frame is CP T-Hermitian if and only if it is T-symmetric,in that case,it is similar to a Hermitian operator.The existence of an operator C consisting of a CP T-frame is discussed.These concepts and results will serve a mathematical discussion about P T-symmetric quantum mechanics.     

A new approach for describing amplified spontaneous emission in a KrF excimer laser using z-dependency of gain-coefficient

Based on our recent realization concerning the geometrically dependent gain coefficient in self-terminating gas lasers, where it is shown that in one-dimensional approach it is z-dependent, we applied the gain formulation to explain, both numerically and analytically, the behavior of the amplified spontaneous emission (ASE) output energy vs. excitation length of the active medium. As an example, we used experimental measurements reported for a KrF excimer laser. In the approach it was realized that it is needed to present a gain-profile slightly lower than the gain-profile deduced from different reports appeared in the literature, where it is also indicating that the contribution of the ASE on the laser output is significant and it is the active medium length dependent. The present analytical presentation of the ASE output energy behavior, also, introduces a generalized formulation compared to that appeared in the literature. With this approach it is possible to remove most of the present ambiguities existing on understanding of the ASE behavior.     

对5通路3/2环绕声系统缺陷的分析

本文利用环绕声重发的声像定位理论，对一种受到重视、很可能将被国际上广泛应用的通用环绕声系统—5通路3／2系统的声像特性进行了分析，并对系统进行了声像定位实验．理论和实验结果表明，按目前的信号馈给方式，系统可在倾听者前方产生稳定而明晰的声像；但在侧向和后方只能产生模糊和不稳定的声像（扬声器方向除外）；将别是在侧向，存在着一个声像的死区，并且对侧向和后方声像来说，听音区域片不宽阔，因而作为一种通用的系统，虽然将其用作伴随图像的重发时，可获得较好的效果；但用作不伴随图像的重发时，系统并不能很好地再观原声场的空间感。由于系统存在这种不容忽视的缺陷，文中着重强调应设法在这方面对系统加以改进     

混沌伪随机序列复杂度分析的符号动力学方法

通过将混沌伪随机序列看成一个符号序列，提出了用符号动力学的 方法来分析混沌伪随机序列的复杂度.以Logistic映射和耦合映射格子系统产生的混沌伪随 机序列为例，说明了该方法的应用，并将计算结果与近似熵ApEn法的计算结果作了比较.结 果表明，该方法可以有效地判断出不同的混沌伪随机序列的复杂程度，而且比近似熵法更为 优越. 关键词： 混沌 伪随机序列 符号动力学 熵     

Connected Lie groups having faithful locally bounded (not necessarily continuous) finite-dimensional representations

In the paper, it is proved that a connected Lie group admits a (possibly discontinuous) faithful finite-dimensional representation if and only if it admits a continuous faithful finite-dimensional representation, i.e., if and only if it is a linear Lie group.     

小间隙异面电极结构的光导开关

介绍了应用于介质壁加速器的小间隙异面电极结构的光导开关。所用光导开关为异面结构的砷化镓（GaAs）光导开关,电极间隙5 mm,偏置电压为15~22 kV脉冲高压,工作在非线性（高增益）模式,由半导体激光器产生的脉冲激光触发。脉冲激光的中心波长为905 nm,脉冲宽度（FWHM）约20 ns,前沿约3.1 ns,抖动小于200 ps,峰值功率约90 W。实验结果表明:光导开关的偏置电压较低时,开关寿命较长,导通性能较差;偏置电压较高、驱动脉冲激光功率较大时,开关导通性能较好,寿命较短。     

Holographic particle image velocimetry (HPIV)

There are several well-known difficulties in forming and analysing holographic particle data in the micrometre and sub-micrometre size range. This paper suggests that these problems can be overcome by using a combination of research techniques. Firstly, it has been found that it is possible to record images of sub-micrometre particles using conventional photographic materials. Essentially, a diffraction limited optical component has been used to provide aberration free particle images. Secondly, the sensitivity of the holographic material has been increased with the use of specialized holographic processing chemicals. Thirdly, it has been found that it is possible to encode holoraphically double, slightly displaced, particle images using a pulse laser. Thus, Young's fringes can be obtained directly from the stored holographic data and the particle velocity can be measured directly from the hologram. Fourthly, the holographic particle data can be automatically analysed using a software programme. Finally, since the data is stored holographically, it is possible to obtain instantaneous three-dimensional particle velocity. This paper demonstrates that it is possible to perform holographic particle image velocimetry automatically, with only a small amount of pre-processing.