用单一倾斜光纤光栅实现曲率和温度的同时测量

基于单个倾斜光纤光栅(TFBG)提出了一种实现双参量曲率和温度同时测量的方法.研究发现,当弯曲方向与光栅栅面成一定角度时,倾斜光纤光栅的纤芯模偕振波长对弯曲不敏感而随外界温度变化线性漂移;低阶包层模谐振峰透射功率随曲率的增加而线性减小且对温度变化不敏感.由此特性提出了用单个倾斜光纤光栅的纤芯模谐振波长和低阶包层模谐振峰透射功率,分别实现对两个参量温度和曲率进行同时独立测量的传感器设计方案,该方法有望解决光纤光栅在测量中存在的温度和弯曲之间的交叉敏感问题.     

基于纤芯失配多模干涉的光纤折射率传感器

基于多模干涉效应的单模-多模-单模(SMS)结构光纤折射率传感器通常需要进行包层腐蚀来提高灵敏度,而且易受环境温度影响。为克服SMS结构的这些不足,提出了一种新型的基于纤芯失配多模干涉的光纤折射率传感器,由单模光纤-色散补偿光纤-单模光纤(SMF-DCF-SMF)级联光纤布拉格光栅(FBG)构成,长度不超过100mm。对其灵敏度、线性范围和温度特性等进行了测试,实验结果显示在测量折射率为1.33～1.39的折射率液时,特征波长与折射率呈线性关系,灵敏度为232.8nm,级联的FBG具有良好的温度校准功能。     

LPFG折射率模式响应及其在传感建模中的应用

基于光纤光栅的模式耦合理论,采用严格的数学模型,给出了三层介质长周期光纤光栅(LPFG)的纤芯模和包层模的本征方程,分析了长周期光纤光栅中的纤芯模式和包层模式的有效折射率随外界环境折射率变化的情形,以及外界环境折射率变化对长周期光纤光栅谐振波长的影响.通过在长周期光纤光栅外涂覆折射率对外界环境变化敏感响应的特定薄膜可以显著提高其传感测量的灵敏度.研究结果可为长周期光纤光栅传感器结构参数的优化设计和实际应用提供理论支持.     

基于逐点法刻写的偏芯光纤布拉格光栅应变和温度传感研究

为解决当前光纤光栅制备灵活性较低,以及测量 中不利于实现分布式波分复用的问题,提出了一 种于基于逐点法刻写的偏芯光纤布拉格光栅传感器(eccentric fiber Bragg grating,EFBG)。采用飞秒激光(femtosecond laser,FSL)逐 点刻写技术,光栅刻写位置垂直偏离光纤中心3 μm,光栅长度为5 mm,光栅中心波长为1 633 nm。不 同于传统光纤光栅,偏芯结构的光栅可以激发出较宽的包层模共振范围,通过分析包层模共 振峰的波长 漂移量,表征施加的应变大小或温度高低。实验结果表明,应变测量范围在0—5 00 με时,包层模灵敏度为 0.98 pm/με,温度测量范围在30—80 ℃时, 包层模灵敏度为10.89 pm/℃,并且包层模灵敏度相比芯模灵敏 度数值相差较小,从而可以实现应变或温度的传感测量。     

基于马赫-曾德尔干涉的球形结构光纤温度传感器

提出一种基于马赫-曾德尔干涉的球形结构光纤 温度传感器。该传感器通过在单模光纤上熔接两个球 形结构形成球形-单模-球形结构的马赫-曾德尔干涉仪。外界温度的变化会引起光纤包层 模的有效折射率变化, 从而导致干涉光谱的变化,通过检测干涉谷的特征波长漂移量,实现对温度的测量。实验结 果表明,在温度 变化范围为18～78℃时,当中间单模光纤长度为1.8cm时,传感器 的灵敏度为0.129nm/℃ ,当中间单模 光纤长度为2.4cm时,传感器灵敏度为0.121 nm/℃,当中间单模光纤长度为4.0cm时,传感器灵敏度为 0.070nm/℃。根据0.01nm的波长分辨率,该传感器可以实现温度 的分辨率为0.077℃。该球形结构的 光纤温度传感器灵敏度高、结构紧凑、制作简单、成本低廉,在温度检测方面具有良好的应 用前景。     

一种双包层半径光纤布拉格光栅传感器

光纤布拉格光栅已经成为非常有前景的温度、应力及其它参数测量的传感元件,但其存在温度和应力的交叉敏感问题.提出了一种双包层半径光纤布拉格光栅传感器,将一个布拉格光纤光栅分成两半,各自具有不同的包层半径,其中一半保持不变,另一半包层半径从62.5m减小到40m.实验结果表明,两半光纤布拉格光栅的温度灵敏度均为10.4 pm/℃,而应力灵敏度分别为1.12 pm/ue 和3.89 pm/ue.初始的单个布拉格反射峰分裂成两个,分别对温度和应力敏感,而两个反射峰之间的波长差只受应力的影响,随着应力的增加其波长差逐渐增加.因此,通过这一个光纤布拉格光栅即可分辨出温度和应力所引起的布拉格波长漂移.该光纤光栅传感器结构简单、体积小巧、成本低廉、制作方便,可以广泛应用在各个领域实现温度和应力的同时测量.     

基于单侧几何形变结构的全光纤Michelson干涉高温传感器

利用CO2激光脉冲对标准单模光纤(SMF)单向形成较小的几何形变,把部分基模能量耦合到光纤包层,制作了一种新型的在线型Michelson干涉传感器。理论分析了这种几何微扰激发的包层模特性,并利用芯模-包层模较大的热光系数差,把这种传感器应用于高温测量。实验结果表明,这种干涉传感器的温度灵敏度为0.093 7nm/℃,并且在800℃温度范围内具有良好的线性和重复性。这种制作简单、结构稳定、体积小和灵敏度高的全光纤在线型Michelson温度传感器将具有较大的潜在应用价值。     

基于单一倾斜光纤光栅的温度应变同时测量

利用光纤光栅分析软件OptiGrating对倾斜光纤光 栅温度与应变传感进行系统的理论仿真,研究发 现,温度、应变的变化都可以引起倾斜光纤光栅的纤芯模和包层模谐振峰的漂移,而且温度 和应变对纤芯 模与包层模的影响是各不相同的。利用倾斜光纤光栅这一特性,提出了一种基于单一倾斜光 纤光栅的温度 与应变同时测量的传感系统,并通过实验进行了验证。在实验中,光电探测器可以将倾斜光纤 光栅的波长的 漂移转换成电压的变化,由此得到了倾斜光纤光栅只受温度变化时,随着温度的变化,示波 器测到其纤芯 模与包层模的电压(峰—峰值)的变化呈线性变化,其斜率分别为0.063mV/℃和0.001mV/ ℃;其只受 应变变化时,随着应变的变化,示波器测到其纤芯模与包层模的电压(峰—峰值)的变化也 呈线性变化, 其斜率分别为0.009mV/με, 0.001mV/με。研究结果将对倾斜光纤光栅的传感应用具 有一定的指导意义。     

基于腰椎扩径熔接马赫-曾德尔干涉仪的温度光纤传感器

实现了一种基于腰椎扩径熔接马赫-曾德尔(M-Z )干涉仪的温度光纤传感器。通过腰椎扩径熔接技术,分别对4.5cm 长的单模光纤(SMF)两端进行扩径,构成球形-单模-球形结构的M-Z干涉仪。该干涉仪具 有温 度敏感特性,因外界环境温度的变化会引起光纤包层模的有效折射率发生变化,从而导致干 涉光谱的变化。 通过检测同一级次干涉谷的特征波长漂移,实现对温度的测量。实验结果表明,在温度变化 范围为15～60℃ 时,干涉谱发生了明显的红移现象,传感器相应的温度灵敏度为0.068nm/℃。本文温度光纤传感器结构简单、成本低和灵敏度高,在温度检测方面具有良好的 应用前景。     

倾斜长周期光纤光栅薄膜传感器特性研究

为设计高灵敏光纤光栅薄膜传感器,基于耦合模理论研究了表面镀制高折射率敏感薄膜的倾斜长周期光纤光栅（TLPFG）耦合特性和薄膜折射率传感特性。TLPFG能激发高阶（角向序数l1）包层模耦合,高阶包层模耦合系数随倾角增大而增大,80时,高阶包层模耦合系数远小于1阶包层模耦合系数。研究表明,光栅倾角变化不影响包层模耦合谐振波长,但影响光谱透过率。进一步研究了TLPFG在80时1阶5次包层模耦合的光谱透过率对薄膜折射率变化的响应,分析了光栅结构参数（L、、）和薄膜参数（h3,n3）对薄膜折射率响应灵敏度的影响,结果表明,响应灵敏度相比于非倾斜LPFG可提高一个数量级,对薄膜折射率的分辨率可达10-9。     

Pure Bending Characteristic of Tilted Fiber Bragg Grating

a novel structure of the pure macro- bending sensor based on the tilted fiber Bragg grating （TFBG） is proposed. The TFBG located in the half circle with the different diameters is bent at a constant angle with respect to the tilted grating planes. With the variations of the curvature, the core-mode resonance is unchanged and the transmission power of cladding modes detected by the photodiodes varies linearly with curvature, while the ghost mode changes by the form of two-order polynomial. So we can use the transmission power of ghost mode or other cladding modes to detect bending curvature as shape sensor. From a practical point of view, the sensor proposed here is simple, low cost and easy to implement. Moreover, it is possible to make a temperature-insensitive shape sensor due to the same temperature characteristic between the core mode and the cladding modes.     

Linear edge and temperature characteristic of tilted fiber Bragg gratings cladding-mode envelope

In this paper, a system of linear edge filter demodulation based on weakly tilted fiber Bragg gratings in fiber sensor was proposed. The linear edge of the cladding-mode envelope and temperature characteristic between cladding modes and core mode of tilted fiber Bragg grating (TFBG) were experimentally investigated. The results show that falling edge (1505–1535 nm) and rising edge (1545–1565 nm) of the cladding-mode envelope is approximately linear and can be used as an edge filter. Moreover, the temperature characteristics of the core mode and cladding modes are similar to FBG’s. It can dynamically compensate the temperature induced wavelength shift of the FBG and the effect of temperature on the demodulated sensing signals is minimized. The advantages of this simple system are an all-fiber design, quasi static and dynamic operation, high stability and lower cost.     

Temperature and strain sensing characteristics of the tilted fiber Bragg grating

Theoretical and experimental studies on the tilted fiber Bragg grating (TFBG) temperature and strain sensing characteristics are conducted. The TFBG is stuck to the surface of the beam along the axis direction. When the free end of the beam is forced, both the strain and temperature will induce wavelength shifts. The temperature characteristic of TFBG cladding modes is similar to that of the core mode while the strain characteristics of TFBG core mode and cladding modes are different. A novel method to discriminate the temperature and strain simultaneously is put forward based on TFBG sensing characteristics.     

基于倾斜光纤光栅的相对湿度传感器

提出了一种基于倾斜光纤光栅(TFBG)的包层上覆盖着聚乙烯醇(PVA)的空气相对湿度传感器,成功实现了对相对湿度在20～98%RH范围内的监测。研究发现,TFBG的透射功率在20～74%RH和74～98%RH2个相对湿度区域内分别呈现不同的线性变化,敏感度分别为2.52 dBm/%RH和14.95 dBm/%RH,并且在高湿度区有更高的敏感性。     

Bragg gratings in multimode and few-mode optical fibers

Bragg gratings in optical fibers in multimode propagation are investigated experimentally and theoretically. Bragg gratings formed in optical fibers in multimode propagation show multiple reflection peaks or multiple transmission dips in the reflection or transmission spectra, respectively. For standard graded-index multimode fiber, the number of reflection peaks of a Bragg grating depends on excitation condition of propagating modes. The number of reflection peaks of a Bragg grating at around 1.55 μm is 19 for highly multimode excitation and 3-4 for lower order mode excitation. We analyze the phase-matching conditions of the propagating modes and identify half of the reflection peaks as the reflection to the same mode and the rest as the reflection to the neighboring modes. In dispersion-shifted fiber, a Bragg grating at around 0.8 μm in three-mode propagation shows three reflection peaks in the reflection spectrum. The temperature dependence of each reflection peak is similar to that of a conventional Bragg grating in single-mode fiber. Polarization dependence measured on a Bragg grating in multimode graded-index fiber is negligible. An advantage of Bragg gratings in multimode fiber (MMF) and the applications are discussed     

Simultaneous measurement of strain and temperature using single tilted fibre Bragg grating

Tilted fibre Bragg grating (TFBG) with grating planes tilted at an angle of 3deg corresponding to the fibre axis shows core mode and a large number of cladding-mode resonances in its transmission. Discriminating temperature and strain simultaneously using a single tilted fibre Bragg grating is proposed and demonstrated experimentally. The wavelength shifts of the TFBG in response to temperature and strain are investigated. The results show that the cladding modes and core mode have different strain sensitivities while the temperature sensitivities are equal. So, it is possible to monitor the core-mode resonance and the cladding-mode resonances of the TFBG spectrum, allowing the separation of the temperature and strain induced wavelength shifts.     

基于乙醇灌注边孔光纤的Sagnac干涉型温度传感器

提出并研究了一种基于乙醇灌注边孔光纤(SHF)的Sagnac干涉型温度传感器。边孔光纤是一种高双折射光纤,其包层中纤芯两侧具有两个空气孔。将乙醇填充进边孔光纤的空气孔中,利用乙醇的折射率随温度的变化,改变边孔光纤的双折射系数,使Sagnac干涉仪的输出谱发生波长漂移,从而实现了温度传感。实验获得该传感器在20℃～80℃的温度变化范围内灵敏度为86.8pm/℃,为普通光纤布拉格光栅(FBG)传感器的8倍。     

High-sensitivity pressure sensor based on tilt fibre Bragg grating radial load effect

In this paper, a simple and novel optical fibre pressure sensor with tilt fibre Bragg grating is put forward. The radial compression and rebound on tilt fibre Bragg grating (TFBG) cause grating angle and length change, meanwhile, its cladding mode spectra decrease sharply. Some transmission spectrum characteristics, such as amplitude, extinction ratio value, wavelengths of cladding and Bragg modes, are extracted and analyzed. It shows that they are nearly linear with the radial pressure on surface of bare TFBG. Among them, the extinction ratio value with high sensitivity of 0.7 dB/N can keep consistent with pressure. The max amplitudes of some cladding mode resonance are good linear with radial press with sensitivity of 0.18 dB/N. The relation between each mode resonance wavelength shift and radial press on TFBG keeps good linearity with 0.8-pm/N sensitivity. By means of choosing tygon elastic pad material imposed on bare TFBG, the pressure sensitivity with amplitude of 0.21 dB/N and extinction ratio of 0.25 dB/N is obtained in order to use in practical engineering.