磁光调制法双折射光纤拍长测试技术研究

研究了光纤拍长磁光调制法测试系统中,对于给定的磁隙宽度和磁场强度,起偏方式与检偏方式对拍长测试灵敏度的影响.通过理论分析与实验研究,发现有三种测试方式均能得到最大灵敏度:1) 入射线偏振光的偏振方向与光纤双折射主轴夹角θ为0°或90°,同时Wollaston棱镜的两个检偏主轴与保偏光纤的双折射主轴夹角γ为45°;2) 入射线偏振光θ= 45°,同时γ=0°或90°;3) 入射光为圆偏振光,同时γ=0°或90°.三种情况下的测试灵敏度基本相等,但是第三种实验方式不需要在入射端精确定位光纤的双折射主轴方向,简化了实验过程,并可避免角度调节所引入的测量误差.理论分析与实验数据基本一致.     

保偏光纤Bragg光栅传感特性的实验研究

设计了一种基于保偏光纤Bragg光栅(PMFBG)的横向负载传感方案,实验研究了PMFBG对横向负载、轴向应变和温度的传感特性。研究结果表明:PMFBG两谐振波长对温度和轴向应变的灵敏度近似相等,而对横向负载的灵敏度各不相同;PMFBG两谐振波长之差对横向负载的灵敏度取决于负载作用方向与保偏光纤快轴(或慢轴)之间的夹角,而不受温度和轴向应变的影响,实验得到的最高灵敏度为0.031nm/kg。基于PMFBG的横向负载传感测量系统在称重等领域具有广阔应用前景。     

熊猫光纤热双折射效应光纤偏振控制器研究

根据熊猫光纤热双折射效应原理.通过电热控制的方法实验研究其热双折射效应,提出并实验演示了基于熊猫光纤热双折射效应的光纤偏振控制器.研究了熊猫光纤热双折射效应的温度灵敏度和电热控的特点.将两段熊猫光纤按偏振轴相互偏离一定角度熔接后,两段熊猫光纤的电热控制将分别在邦加球上形成相交并互相成一定夹角的两个截交线圆,组合两段熊猫光纤的电热控制可实现偏振态在邦加球上的部分覆盖.根据熊猫光纤热双折射效应的特点,提出并实验演示了由三段熊猫光纤组成的电热控光纤偏振控制器,它可在实验上实现任意偏振态的扫描控制.     

夹角式强度反射型光纤声传感器

介绍了一种基于反射式强度型光纤传感原理的光纤声传感器,该传感器通过光纤模块将发射光纤和接收光纤的夹角固定为60°,同时采用基于微加工技术制作的反射振动膜片敏感声音信号并调制光信号强度.建立了该传感器的理论模型,并通过仿真和实验分析得到系统的最佳工作距离为8 μm,灵敏度为2.49 μW/μm.实验测试结果表明,该声传感器样机对声音的探测灵敏度为30 mV/Pa,同时给出了样机的频率响应及线性度测试结果.     

光纤干涉系统光学湍流测量原理及其偏振噪声问题的分析

光纤干涉仪具有测量精度高、探测灵敏度大等优点,可用于直接测量大气湍流折射率起伏.首先简要介绍了光纤Mach-Zehnder干涉仪的光学湍流测量原理,描述了低双折射单模光纤中光束偏振态变化诱导的偏振信号衰落现象,并通过偏振态的邦加球分析和详细的公式推导,得出了干涉仪可见度和相移噪声的关系式.结果表明:控制输入光偏振态与干涉仪本征向量之间的夹角在零度左右,可有效地抑制偏振噪声,最后给出了偏振控制器实现偏振控制的原理,为构建稳定的光学湍流测量光纤干涉系统提供了科学依据.     

光纤布拉格光栅压力增敏的实验研究

近年来光纤光栅作为压力、温度、应变等传感器已经成功地应用于光纤传感领域中。然而裸露的光纤光栅对于外界物理参量的变化灵敏度不高,因此有必要对光纤光栅进行增敏封装,以提高其对外界环境变化的灵敏度。采用两种聚合物材料均匀混合,将其对布拉格光纤光栅进行封装。在23℃情况下对封装后的光栅进行了压力实验,实验表明用两种聚合物封装后的光栅对压力有很高的灵敏性,在0～10MPa范围内压力灵敏度为-122×10-4MPa,是裸光栅压力灵敏度的62倍     

本征法布里-珀罗腔光纤压力传感器理论研究

建立了光子晶体光纤(PCF)型本征法布里-珀罗(F-P)腔光纤压力传感器压力响应理论模型,讨论了各参数对压力响应灵敏度的影响,给出了Matlab程序理论模拟结果。鉴于PCF焊接工艺的困难,提出了利用外径不同的单多模光纤熔接构成的改进型单多模光纤复合本征F-P腔光纤压力传感器结构,建立了压力响应理论模型,分析了提高压力响应灵敏度的关键参数,并模拟了光纤外径对压力响应灵敏度的影响。通过对两种本征F-P腔光纤压力传感器的比较分析看出,改进型结构无论在压力响应灵敏度还是制作难易度方面都颇具优势。     

拉锥空心光纤的温度与应力传感特性研究

该文设计并制作了一款简易的拉锥空心光纤的高灵敏度传感器,通过实验测量了其温度与应力特性。首先利用光纤熔接机在两段标准单模光纤之间熔接一段空心光纤,再对准空心光纤中间位置进行放电,同时运用两个步进电机在单模光纤两端施加一定的拉力,这导致法布里-珀罗干涉仪转换为马赫-曾德尔干涉仪。实验结果表明,此拉锥过程使光纤传感器的温度灵敏度从理论值0.85 pm/℃提升到69.1 pm/℃,约提升了81.3倍,轴向应变灵敏度最高可达3.6 pm/με。该器件具有体积小、结构简单和灵敏度高等特点,在航空航天、医疗监测等领域具有广阔的应用前景。     

基于涂覆石墨烯量子点-聚乙烯醇的拉锥细芯光纤的温湿度传感器

提出了一种基于拉锥细芯光纤的温湿度传感器。先将细芯光纤熔接在两段多模光纤的中间，并在多模光纤两端熔接单模光纤，利用拉锥机对细芯光纤进行分步拉锥。实验测得细芯光纤拉锥前后的传感器的温度灵敏度分别为31 pm/℃和72.7 pm/℃。将少量石墨烯量子点-聚乙烯醇涂覆在传感器锥部得到温湿度传感器，实验测得其温度灵敏度最大为288.3 pm/℃，湿度灵敏度可达到131.7 pm/%。该传感器具有性能稳定、灵敏度高、制备简单、成本低的特点，在温度和湿度传感领域具有广阔的应用前景。     

基于两种光纤介质模型的长周期光纤光栅传感特性分析

仿真分析了单轴晶体光纤的两层介质模型与三层介质模型所得纤芯模有效折射率的差别,并基于该差别对长周期光纤光栅的外界环境折射率、温度和轴向应变传感灵敏度进行了仿真分析。结果表明,对两层、三层介质模型的纤芯模,尤其对薄包层光纤有效折射率有较大差别;用两层介质模型和/或材料的折变系数计算所得的长周期光纤光栅的外界环境折射率、温度和轴向应变灵敏度有较大的误差,需应用三层介质模型以及模式的有效折变系数进行准确计算。据此计算了上述3种传感灵敏度与光纤包层半径及包层模序数的关系。为长周期光纤光栅传感器的分析设计提供了指导。     

光纤消逝场传感器传感结构的分析与应用

对光纤消逝场理论进行了详细分析,阐述了影响光纤消逝场传感器灵敏度的一些关键因素,并对几种常见的光纤消逝场传感光纤的优缺点进行了比较,主要包括圆柱形、D形、U形、锥形以及光子晶体光纤等结构的传感光纤。通过分析各种传感结构的光纤消逝场传感器的应用实例,归纳总结了提高光纤消逝场传感器传感灵敏度的一般方法,包括在传感光纤表面镀薄敏感膜或者金属膜、优化传感光纤结构、进行荧光标记以及用纳米粒子修饰等一系列措施。     

Origins and control of polarization effects in single-mode fibers

The polarization state of light in single-mode fibers is very sensitive to any perturbation which is not symmetric about the fiber axis. While this is a source of noise, drift, or signal fading in some applications, it can also be exploited in novel guided-wave devices. The basic birefringences that couple the two modes and change the polarization state along the fiber are reviewed. The three cases of uniform, phase-matched, and random coupling are considered. Polarization preservation in both low- and high-birefringence fibers is achieved by reducing this coupling. In addition to polarization-state changes, bireftingent fibers can quickly reduce the polarization degree of nonmonochromatic light if both modes are excited, a characteristic that greatly simplifies evaluation of the degree of polarization preservation in these fibers. Current evaluations of the birefringence and the polarization-holding ability of state-of-the-art fibers are discussed, and it is concluded that fibers with good polarization-holding properties are becoming available.     

Investigation of the microbending sensitivity of fibers

The microbending sensitivity of fibers was calculated as a function of the MAC value, which is the quotient of mode field diameter and cut-off wavelength. Two different methods, the expandable drum test and the sieve test, were used to simulate the additional losses due to microbending in fiber-optic cables: The theoretical and experimental results generally show an increase of the microbending sensitivity with increasing MAC value. In addition, the microbending loss of fibers strongly depends on the material and structure of the coating. Measurements of fibers in “real” cables confirmed the predicted correlation between attenuation and MAC value     

/spl gamma/-rays and pulsed X-ray radiation responses of germanosilicate single-mode optical fibers: influence of cladding codopants

The radiation-induced attenuation (RIA) in germanosilicate single-mode optical fibers was measured at 1.55 and 1.31 mm after a pulsed X-ray irradiation and at 1.55 mm during and after a steady-state g-ray irradiation. The influence of codoping the fiber cladding with germanium (Ge), phosphorus (P), and fluorine (F) on the sensitivity of Ge-doped core fibers was characterized. P-codoping makes it possible to decrease the RIA for short times (10/sup *6/ s*10/sup *3/ s) post- pulse. However, P-codoped fibers exhibit larger values of permanent RIA than P-free fibers after transient exposure and are inadequate for a steady-state environment. The impact of F-codoping depends on the other codopants incorporated in the fiber cladding, but its addition seems to be deleterious for the radiation hardening of the germanosilicate fiber at the two tested wavelengths. Ge-codoping increases the sensitivity of P-, F-codoped fibers under X-rays and steady-state g-ray irradiation, whereas it decreases the RIA in F-doped ones. Some hypotheses on the creation mechanisms and properties of the color centers related to these three codopants are proposed.     

Experimental investigation of the factors influencing temperature dependence of radiation-induced attenuation in optical fiber

The effects of transmission wavelength, total dose and light source power on temperature dependence of radiation-induced attenuation (RIA) in Ge–P co-doped fibers were investigated. Three fibers irradiated up to total dose of 100 Gy and 10,000 Gy were used as test samples. A test system for temperature dependence of RIA was built up. The influence of transmission wavelength, total dose and light power on temperature sensitivity and linearity of RIA in three irradiated fibers were researched. The test results show that temperature sensitivity and linearity of RIA in optical fibers could be improved by adjusting total dose and selecting transmission wavelength. The light source power does not have obvious influence on temperature sensitivity and linearity. The Ge–P co-doped fiber at 850 nm transmission wavelength with higher total dose is a very promising candidate for fiber-optic temperature sensor.     

Phase sensitivity of polarization-maintaining optical fiber used as temperature sensor

A method is given to calculate the thermal stress distributions in coated polarization-maintaining fibers. From the stresses, the phase sensitivities of these fibers are calculated. It is found that polarization-maintaining fibers do not offer any significant increase in phase sensitivity over conventional fiber. Coating with Silicone resin tends to reduce the sensitivity while the glass substrate (start tube) with higher thermal expansion coefficient than that of the cladding increases the sensitivity.     

Role of the fusion splice in the concatenation problem

Near-field measurements used to derive an empirical model of a fusion splice have indicated that fusion splices generate very little mode coupling between multimode graded-index fibers of identical parameters. Results of dispersion measurements confirm this. In particular it is found that the bandwidth of a concatenated link of identical fibers (respliced fibers from the same preform) is determined by longitudinal profile variations and not splice characteristics. Fusion splices between nonidentical fibers can generate a larger degree of mode coupling. This unequal parameter-induced mode coupling has a measurable effect on file dispersion properties of concatenated fiber links.     

Degree of Polarization in Anisotropic Single-Mode Optical Fibers: Theory

The degree of polarization for propagation waves in anisotropic single-mode fibers is formulated in terms of light source spectrum, incident polarization condition, and fiber parameters. The polarization degree deterioration is based on the incident wave split into two eigenpolarization modes inherent in the fiber. Since the two eigenpolarization modes have different group velocities from each other, the degree of polarization is degraded when both of the modes are excited. Polarization degree is preserved when only one of the eigenpolarization modes is excited. The degradation is determined by the mutual correlation function gamma, between the two modes, which depends on the light source spectra, fiber polarization dispersion, and fiber length.     

Analytical approximations for the propagation characteristics of dual-mode fibers

In this paper we present accurate analytical approximations for the modal fields of dual-mode optical fibers with power law profiles based on a scalar variational analysis. We propose single parameter and two parameter trial functions and use these to study the dispersion characteristics and estimate the value of the normalized frequency corresponding to zero intermodal dispersion, which defines the operating point for such fibers. Our results show that the relatively simple single parameter field for the LP11mode gives a good fit to the field inside the core and estimates the propagation constant fairly well, but is inadequate to calculate the dispersion characteristics. On the other hand, the two parameter field estimates all these characteristics with a high degree of accuracy and enables one to accurately compute the normalized frequency for zero intermodal dispersion as well as dispersion tolerance around this value.     

双光纤双参量布里渊光时域分析传感技术的研究

对于布里渊分布式光纤传感器(DOFS),温度或应变的变化都会引起布里渊频移谱改变,因此存在交叉敏感问题。在以往对布里渊光时域反射(BOTDR)计的双参量传感研究中,采用单根光纤,通过同时检测布里渊频移和功率变化,实现双参量传感。但对于布里渊光时域分析(BOTDA),由于受激布里渊散射的偏振相关性,不能实现对受激散射光功率的准确检测,因此难以实现单光纤的双参量传感。针对这一问题采用温度和应变系数不同的双光纤进行双参量传感。先测量了几种常用光纤的温度和应变布里渊频移系数,然后选择G652和G652成缆两种光纤,通过构建系数矩阵,由两根光纤的布里渊频移计算得出温度和应力,从而实现了温度分辨率25℃左右,应变分辨率约为200με的双参量传感。