光纤线双折射对光栅磁场传感器性能影响的理论分析

给出了基于偏振效应的光纤光栅磁场传感器的方法。为了降低传感器中线双折射对传感系统输出的影响, 提高测量系统的稳定性, 利用琼斯矩阵对线双折射及入射起偏角对系统输出特性的影响进行了理论推导及仿真, 研究了系统对线双折射变化的敏感度大小与起偏角的关系, 确定了最佳起偏角。以最佳起偏角入射, 可以将系统对线双折射变化的敏感度降到最低, 提高系统的稳定性和可靠性, 为光纤光栅磁场传感器的实用化设计提供了参考。     

基于斯托克斯参量的光纤光栅微压力传感方法研究

为了实现微压力的测量,提出了一种基于光纤光 栅Stokes参量的微压力传感新方法, 给出了理论分析和实验结果。在外界压力作用下,由于压力致双折射效应,光纤光栅两个线 偏振光的能量输出发生变化,仿真结果表明,第一归一化Stokes参量s₁峰值 与压力在一定 的测量范围内存在线性关系;另外为了减少波长抖动的影响并提高测量精度,文中提出了双 波长检测法。在外界压力为0~5N环境下,其压力灵敏度为0.075/N,实验结果与理论分析 结果吻合。     

低双折射均匀光纤布拉格光栅斯托克斯参量的研究

根据耦合模理论和琼斯矩阵与斯托克斯矢量的关系给出单模均匀光纤布拉格光栅(FBG)反射和透射斯托克斯参量公式,数值模拟出低双折射单模光纤均匀FBG在不同双折射值下反射和透射斯托克斯参量随波长变化的曲线。结果显示4个归一化斯托克斯参量中,s1关于中心波长λ0呈反对称分布,S0,s2和s3关于λ0呈对称分布;双折射值增大谱线不产生漂移,但谱线反射带宽变窄,反射信号与透射信号斯托克斯参量振幅均有不同程度的变化,表明双折射值对斯托克斯参量的影响非常显著。测出单模光纤均匀FBG反射和透射斯托克斯参量随波长变化曲线,理论分析与实验结果基本符合。     

新型三角形光栅斯托克斯参量磁场测量法

分析了均匀光栅反射光的第三归一化斯托克参量(S3)用于磁场测量的限制,提出了利用三角形光栅反射光的S3参量进行磁场测量的方法.并通过仿真,分析了三角形光栅反射光S3参量的性能曲线及其性能影响因素.     

基于保偏光纤的高精度光纤光栅传感解调方案

提出一种基于线偏振光干涉原理的无源波长解调系统.在普通光纤环镜中引入双折射效应.光纤环镜的反射(透射)光强足耦合器分光比K、温度t、保偏光纤长度L和两端偏振方向夹角的函数.在单调区间内反射(透射)光强与t存在对应关系.通过测定光强口可求得t.利用矩阵光学原理建立理论模型,研究了保偏光纤长度、耦合器耦合系数、偏振光入射夹角对光纤环镜(FLM)反射(透射)光强与入射光波长关系影响的特性,设计了基于保偏光纤环镜的分辨率可控的干涉型解调仪.用自制光纤光栅作为传感头监测温度变化,数据显示该系统对温度的测量平均精度可达0.03℃,准确度±0.1℃.     

基于FBG差分群时延的微压力传感方法研究

提出了一种基于光纤光栅差分群时延（Differential Group Delay,DGD）的微压力传感新方法,给出了理论分析和实验结果。在外界压力作用下,由于压力致双折射效应,光纤光栅两个线偏振光的群时延发生变化。仿真结果表明,DGD峰值与压力在一定的测量范围内存在线性关系。实验结果证明,在0～0.3 MPa的压力条件下,实验压力灵敏度为424.2 ps/MPa,实验结果与理论分析吻合较好,验证了该方法的可行性。     

布喇格光栅磁场传感器交叉敏感的研究

从光纤光栅传感的基本原理出发,分析了光纤光栅内外参量对于磁场测量的影响,对温度、应力、压力和光纤光栅内应力分别进行了讨论.仿真结果表明,基于PDL的磁场传感方案对于温度和应力不敏感,内应力和时变压力则会影响其性能,压力的影响尤为显著;测量精度要求高,内应力必须予以考虑.     

边孔光纤光栅的传感特性

报道了一种新型边孔光纤及边孔光纤光栅的研究结果。采用有限元法分析了边孔光纤内部的应力分布和双折射数值,并通过波长扫描技术对其双折射进行了测量,理论计算和实验测量结果表明双折射数值达到4×10-5。根据边孔光纤光栅两反射峰偏振态相互正交的特性,提出了一种基于偏振检测的波长检测方案对边孔光纤光栅的传感特性进行了测量。结果表明两峰中心波长间隔随温度变化的灵敏度仅有0.05 pm/℃,是普通单模光纤光栅温度灵敏度的1/184。提出了一种基于横向荷载压力增敏的新型边孔光纤光栅封装装置,使边孔光纤光栅双峰间距的压力灵敏度从5.6 pm/MPa增加到119.14 pm/MPa,增敏21倍,实现了温度不敏感的高灵敏度压力传感。     

光纤非线性偏振不稳定性的研究

光纤中的交叉相位调制将导致非线性双折射,从而引起偏振不稳定性。研究了光纤中线偏振光的入射角度与非线性双折射拍长的关系, 得出了入射偏振光接近快轴时,非线性使双折射增强,拍长变短的结论。这一结果与文献［２］ 的理论相反     

基于偏振相关损耗测量磁场的高精度方法

为提高测量精度,提出了一种利用光纤光栅测量磁场的方法.依据磁场与光纤光栅偏振相关损耗成正比的理论,运用正交共轭反射镜来消除线性双折射,以Muller矩阵为基本方法,设计磁场测量原理图.数值仿真表明,通过正交共轭反射镜可以大幅度减少测量过程中的线性双折射,从而提高磁场的测量精度.     

光栅致双折射引起偏振相关损耗的理论分析

应用耦合模理论,给出均匀布拉格光纤光栅在考虑光栅致双折射时的透射与反射系数的解析式,按照测量偏振相关损耗(PDL)的确定性与非确定性两种方法,推导出了均匀布拉格光纤光栅中偏振相关损耗的解析公式。理论分析表明,该公式能够准确分析弱双折射光纤或者各向同性光纤上写入的均匀布拉格光纤光栅的偏振相关损耗特性,同时数值模拟高双折射光纤上写入的均匀布拉格光纤光栅偏振相关损耗特性,得到的结果也与已有实验曲线相近。     

Optical rotation sensing by the geometric effect of fiber-loop twisting

An optical technique for sensing a rotation angle is described and experimental results are presented. When a loop of an ideal fiber that exerts no linear birefringence is deformed into a nonplanar curve, the azimuth angle of linearly polarized light propagated in the fiber is rotated. The technique is based on this effect of geometric polarization rotation in an optical fiber. A twisted single-mode fiber is substituted for the ideal fiber. Experimental results include studies of polarization rotation and variations of light propagated in a loop of a twisted single-mode fiber under deformation.     

光纤光栅偏振模色散的研究

分析了光纤光栅 (FBG)偏振模色散 (PMD)产生的原因 :写入光栅用的光敏光纤对紫外光吸收是不均匀的 ,呈指数型吸收。建立了光栅偏振模色散的模型 ,利用建立的模型计算了不同折射率调制的偏振模色散 ,计算的结果与用偏振模色散分析仪测得的结果符合得很好。理论和实验说明了光栅色散对偏振模色散的影响 :光纤光栅的色散增大 ,光栅的偏振模色散也增大。     

光栅参数对线性啁啾光纤光栅偏振特性的影响

研究了单模线性啁啾光纤光栅的偏振相关损耗特性。运用耦合模理论和传输矩阵分析法推出了反射光的偏振相关损耗,并模拟了光栅的反射谱和偏振相关损耗随光栅参数和双折射量的变化曲线。模拟显示双折射值的变化对啁啾光栅偏振相关损耗的影响非常显著, 尤其是在带边比较陡峭时。啁啾光栅的偏振相关损耗也受光栅的啁啾系数和调制深度的影响。这表明线性啁啾光栅的偏振相关损耗不光依赖光栅双折射量,还依赖其啁啾系数等其他参数。实验结果与理论模拟基本吻合。     

基于倾斜光纤Bragg光栅的横向压力传感器研究

设计了一种基于4°倾斜光纤Bragg光栅(TFBG)和弹 性 材料的横向压力传感器。利用TFBG光谱对周围介质折射率响应的特性,实现了 对较低压力范围(0~7N)的线性测量。采 用快速傅里叶变换(FFT)方法对光谱进行解调,测量灵敏度可达1920 a.u./(N/mm),线性拟 合度为0.998。研究了不同弹性材料对测量灵敏度的影响,实现对测 量范围和测量灵 敏度的调谐。本文传感器工作在反射光谱方式,易于集成(光栅区长度仅5mm),可以植入弹 性材料内部用于协调接触压力的测量。     

利用线性啁啾光纤光栅补偿偏振模色散方案的研究

本文提出一种基于线性啁啾光纤光栅补偿偏振模色散的新方案 ,对光纤光栅由于挤压而产生的群时延差进行了理论计算 ,并实验测量了一被挤压的线性啁啾光纤光栅的两偏振方向的群时延曲线 ,测量的结果证明这种方案切实可行 .     

Optical arbitrary waveform generation based on an array of tunable apodized waveguide Bragg gratings

A structure of optical arbitrary waveform generation (OAWG) based on an array of tunable apodized waveguide Bragg gratings (WBGs) is proposed. The WBGs array on lithium niobate (LN) consists of several apodized gratings, waveguides and electrodes deposited on both sides of gratings and waveguides. The properties of OAWG are analyzed using transfer matrix method. Due to the electro-optic effect of LN, the amplitude and phase of incident light source are controlled via adjusting the voltages on electrodes. Consequently, the optical pulses with different waveforms are obtained and the amplitude is linearly tuned. In addition, voltages compensating amplitude and phase distortion are demonstrated.     

Birefringence effect of optical fiber laser with intracore fiberBragg grating

The spectra of Nd³⁺- and Pr³⁺-doped fibre lasers utilizing an intracore Bragg grating reflector written at 1.08-μm Bragg wavelength and a dichroic mirror for cavity feedback have been investigated under 0.6-GHz resolution. Two oscillating frequencies corresponding to two orthogonal linear polarization states of laser emission were observed. The frequencies and orientations of the two linearly polarized emissions could be changed by varying the fiber birefringence with an inline polarization controller. A phenomenological model is proposed to explain the experimental results     

Multi-parameter harsh environment sensing using asymmetric Bragg gratings inscribed by IR femtosecond irradiation

In this paper, we review our recent work on multi-parameter harsh environment sensing using asymmetric Bragg gratings inscribed by IR femtosecond irradiation, which includes the investigations of fiber Bragg gratings inscribed by graded-index silica multimode fibers and polarization maintaining (PM) single mode fibers. The unique features of this type of grating are: (1) formed by multi-photon ionization, this kind of grating can withstand temperature as high as 1000 °C, which makes it suitable for harsh environment sensing; (2) bending (or pressure, strain) and ambient temperature fluctuations affect the shapes of multiple transmission dips in different ways, which enables multi-parameter sensing capability. The principle of multi-parameter sensing of the multimode fiber gratings is based on the fact that multimode fiber gratings have multiple resonant dips in spectrum and the change of spectral shape is different for different types of perturbations (e.g., temperature and pressure). The main challenge of sensing using multimode fiber is that the shape of spectrum also depends on the excitation condition, which makes the analysis of the sensing data complicated. On the other hand, the PM single mode fiber supports only two linearly polarized modes, which results in two resonant dips in the transmission spectrum. Since measured parameters such as the temperature and bending affect the transmission spectrum of two dips in different ways, one can implement multi-parameter sensing in harsh environment using PM fiber. Note that it is much easier to analyze the data of two dips (in the case of PM fibers) instead of multiple dips (in the case of multimode fibers). Finally, we also investigate the ultra thin multimode and PM single mode harsh environment fiber gratings for multi-parameter sensing applications. After etching the most part of the cladding, both multimode and PM single mode fiber grating spectra become sensitive to ambient refractive index changes, and their sensitivity to bending and strain is also enhanced. This enables the application for multi-parameter chemical/bio and pressure sensing.