磁光玻璃光纤的偏振特性及其在全光纤电流传感器中的应用

在磁光玻璃裸光纤偏振特性研究的基础上，研制磁光玻璃光纤，偏振特性及其在全光纤电流传感器中的应用。将采用模管法拉制成的磁光玻璃光纤置于亥姆霍兹线圈产生的磁场中，当线偏振光通过该光纤时，其偏振面旋转一定角度，把该角度转换成光信号的强度，然后再用仪器进行检测。通过对线偏振光偏振面在磁场中的偏振特性的测试与实验，提出用磁光玻璃光纤构成的全光纤电流传感器，可用于电流和磁场测试。     

混合型大电流光纤传感器的研究

本文叙述了混合合型大电流光纤传感器的工作原理及制作方法.以LED作光源、PIN作接收、火石玻璃为磁感应材料、多模光纤作导光波导的混合型大电流光纤传感器,用于监视高压电网系统中的电流.适用范围10~2～10~4A,精度±0.5%.     

Brillouin fiber optic current sensor

A novel reciprocal Brillouin fiber optic current sensor has been developed and tested. The sensor is based on two counter-propagating Brillouin lasers circulating in a fiber ring cavity. It shows a sensitivity of 126 Hz/A that is very close to the maximum sensitivity obtained by using fibers without linear birefringence. The limitations due to the Kerr effect and optical feedbacks in the system are also investigated.     

单模光纤的磁光效应

本文利用琼斯(Janes)矩阵叙述了单模光纤磁光效应的理论,导出了既具有双折射又具有法拉第效应的琼斯矩阵形式,并利用Mueller矩阵导出电流传感器系统输出光强与法拉第旋转角之间的关系.     

光交换节点中的全光再生技术研究

比较了光交换节点中几种全光再生技术方案的优缺点,重点描述光纤参量振荡器的时钟提取实验和基于磁光四波混频的光门整形技术。实验揭示了光纤参量振荡器闲频光反馈控制方法的工作原理,并提取出稳定的高质量时钟信号。仿真比较了4种四波混频光门再生方案的功率转移特性,开展了磁光四波混频再生实验。研究表明:通过对高非线性光纤加载180 Gs直流磁场,可使光接收机灵敏度进一步提升2 dB。最后指出了全光再生技术的多信道、集成化发展趋势。     

基于光纤反射腔的高灵敏电流传感器方案

提出了一种基于平面Y分支波导与法拉第旋镜的高灵敏度光纤电流传感器结构方案。利用两个法拉第旋镜与平面Y分支波导构成一个光纤反射腔,通过光在腔中的多次反射来增加待测电流导致的传感光纤中的法拉第相移,从而实现对微弱电流的测量。该结构方案中首次采用了平面Y分支光波导,从而可降低光路系统损耗,增加灵敏度,为微弱电流测量的工程化提供了一种可行的方法。     

用于电力系统的光学电流互感器技术进展

介绍了光学电流测量技术的发展情况，描述了目前几种主要的互感器结构及其基本原理，并对各自存在的问题及解决途径进行了讨论。从研究现状来看，块状玻璃型传感器技术相对成熟，已经有商业产品问世；混合型传感器测量精度较高，但传感头有源电路的供电技术复杂，还没有圆满的解决方案；全光纤型是光学电流互感器发展的最终目标，目前存在的主要问题是光纤的固有线性双折射难以处理，有赖于新型光纤材料及集成光学元件的进一步发展。最后综合评述了光学电流互感器技术的发展趋势及产业化前景。     

Further Theoretical Investigations for Laser Relative Intensity Noise with Fiber Nonlinearities and Higher Order Dispersion

In this article, we theoretically investigate relative intensity noise (RIN) in optical communication systems with fiber nonlinearities due to optical Kerr effects and higher order dispersion. The impact of modulation frequencies, launch power, and laser bias current on RIN has been illustrated. We show that RIN increases with modulating frequencies up to the resonance frequency and launch power, and decreases in the laser bias current. We also show that higher order dispersion terms have no impact on the RIN, but with first order dispersion compensation the higher order dispersion terms have significant impact at high modulating frequencies. The RIN with and without fiber nonlinearities is further investigated. It has been shown that the RIN with fiber nonlinearity is more than the RIN without nonlinearity and the effect of nonlinearity appears at higher modulation frequencies only.     

Further Theoretical Investigations for Laser Relative Intensity Noise with Fiber Nonlinearities and Higher Order Dispersion

In this article, we theoretically investigate relative intensity noise (RIN) in optical communication systems with fiber nonlinearities due to optical Kerr effects and higher order dispersion. The impact of modulation frequencies, launch power, and laser bias current on RIN has been illustrated. We show that RIN increases with modulating frequencies up to the resonance frequency and launch power, and decreases in the laser bias current. We also show that higher order dispersion terms have no impact on the RIN, but with first order dispersion compensation the higher order dispersion terms have significant impact at high modulating frequencies. The RIN with and without fiber nonlinearities is further investigated. It has been shown that the RIN with fiber nonlinearity is more than the RIN without nonlinearity and the effect of nonlinearity appears at higher modulation frequencies only.     

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.     

光纤偏振态自动补偿的光纤电流互感器

提出了一种对状结构光纤电流互感器中的输入光纤偏振态进行自动补偿的新结构,并给出了理论分析和实验结果。这种结构使光纤电流互感器的稳定性和检测精度有显著提高。     

磁光非线性光纤中光参量增益的研究

将光纤中磁光效应和非线性效应作为微扰,推导了磁光四波混频的耦合模方程.通过解析解研究了各向同性磁光非线性光纤的参量过程,并指出利用磁光耦合系数的色散特性可以实现四波混频的相位匹配.同时,采用龙格-库塔法分析了在线双折射磁光非线性光纤中,忽略费尔德常量的波长依赖性时,左旋圆偏振光参量增益的磁控特性,指出了实验中采用较高费尔德常量的非线性光纤的必要性.研究表明:1)对于低线双折射磁光非线性光纤,优化双折射大小可以获得最大的参量增益;2)根据参量增益对磁光耦合系数的单调依赖特性,适当选择光纤长度、泵浦功率以及输入导波光的偏振态,可使参量增益的磁可调范围大大提高.     

基于变截面梁的光纤光栅线性无啁啾调谐

从理论上分析了利用变截面（等强度）弹性梁实现光纤光栅波长线性、无啁啾调谐的基本原理,给出了实现无啁啾波长调谐的弹性梁截面满足条件及其设计方案,并讨论了矩形等截面和变截面悬臂梁调谐方案的特点.理论分析与实验结果均表明,通过对变截面梁侧向施加载荷,可以实现光纤光栅中心波长的线性无啁啾调谐,且系统结构简单、易于设计.     

一种新型Sagnac式光纤电流传感器

为了消除震动对Sagnac式电流传感器测量结果的影响,提出一种光路改进方法来消除传感器对震动的敏感性,其基本原理是抵消Sagnac效应而不影响法拉第磁光效应。利用琼斯矩阵对改进后的光路结构进行了偏振态分析,理论分析和实验结果吻合,表明改进后的传感器其输出与震动无关。耦合半波片后Sagnac式光纤电流传感器的震动敏感性被消除了,为Sagnac式光纤电流传感器的工程化实现提供了一种可行的方法。     

Temporal Talbot effect applied to determine dispersion parameters

The space–time duality theory and the temporal selfimaging phenomenon (or Talbot effect) are used to propose a method for determining dispersion parameters associated with an optic fiber link. From the space–time analogy, the actions of free-space propagation and phase curvatures taking place in the general spatial Talbot effect are implemented for time-varying wavefields. Using the temporal selfimaging conditions, a relationship is derived for determining the second-order dispersion coefficient of a given dispersive medium under test. As a particular application, we analyze the feasibility of the measuring approach using a linearly chirped fiber grating as the dispersive component under test. Some simulations are carried out in order to study the sensitivity and accuracy of the developed method.     

基于时分复用的多点式环形腔光纤电流传感器

为实现输电线路上的多点电流监测,利用通信用普通单模光纤,设计基于时分复用的多点式光纤环形腔结构电流传感器.多路传感系统共用一套光源、检测设备和数字信号处理系统,在节约成本的同时,提高了利用率.实验中选用双路全光纤电流传感器结构,在两个不同的点同时测量电流,其中一测量点对0~600A范围内的电流进行测量,另一测量点对0~1 500A范围内的电流进行测量.对实验数据进行线性拟合,结果表明:循环次数取8比较合适,此时系统具有比取2时高约3~4倍的灵敏度;两个测量点光信号的偏振态与电流之间有良好的线性关系,两个传感单元的灵敏度不同,而且相互之间没有串扰是各自独立的传感系统.     

Microwave photonic filter design and optimization based on stimulated Brillouin scattering using a directly modulated pump

We propose a general guideline on the design of a stimulated Brillouin scattering(SBS)-based microwave photonic filter(MPF) using a directly modulated pump. Filter gain profiles and passband ripples with waveform repetition periods of the driving current ranging from 2 to 100 ns are measured after the transmission of different fiber lengths. The results show that the filter performance has nothing to do with the fiber length, and the digitalto-analog converter bandwidth requirement for the driving current is no more than 500 MHz. Therefore, the low cost, flexible reconfiguration, and miniaturization characteristics make an SBS filter using a directly modulated pump a promising choice as an MPF.     

Application of multimode fiber optical sensor in optical tomography technology

In this paper, an attempt to use a multimode optical fiber sensor in tomography is made. Two types of lens, one sphere and one cylinderical, are designed for two terminals of the fiber. It solves the problem of insufficient power collection of natural light beam using current fiber with polished terminals. A theoretical analysis of the relationships among the sphere lens radius, the cylinderical lens radius, the refractive index of the fiber is carried out. The relationship between the scanning angles and the number of the optical fibers is experimentally investigated in the air medium.     

Low-threshold performance of fiber Bragg grating external-cavity semiconductor lasers using genetic algorithms

The lowest threshold current of the external-cavity semiconductor laser with fiber Bragg grating using genetic algorithms is investigated. Effects of the external cavity length, coupling efficiency and anti-reflection coating reflectivity on static characteristics, such as L-I curves and side mode suppression ratios (SMSR) are investigated by using multi-mode rate equation. It is found that the reflectivity of the anti-reflection coating for low-threshold performance needs to be increased at the cost of the stability of the fiber grating external-cavity semiconductor laser. The optimal external cavity length obtained by genetic algorithms can be used to obtain the lowest threshold current for sacrificing a little SMSR. However, with the decrease of AR-coating reflectivity, output powers and SMSRs are slightly dependent on the external cavity length.     

Miniature optical fiber current sensor based on a graphene membrane

The unique electronic and mechanical properties, of graphene make it an ideal material for nanoelectromechanical system (NEMS) applications. Here, a miniature optical fiber current sensor based on a quasistatic graphene NEMS with a graphene membrane covering the hole on a pre‐etched fiber tip and two gold electrodes on opposite sides of the tip has been demonstrated. The sensor overcomes the shortcomings of conventional optical fiber current sensors based on thermal effects, such as relatively low sensitivity, long response time, and huge device size; it has simultaneously a high sensitivity of 2.2 × 10⁵ nm/A², a short response time of ∼0.25 s and a compact device size of ∼15 μm, and has found practical application. Using a smaller graphene membrane with better quality can reduce the response time to submillisecond levels with a more precise measurement system. The sensor presented in this paper may pave the way for the practical usage of optical fiber current sensors based on thermal effects.