【作者】 李海峰；

【导师】 张以谟； 周革；

【作者基本信息】 天津大学 ， 光学工程， 2004， 博士

【摘要】 在本论文中,系统分析了白光干涉法检测保偏光纤内部偏振耦合的原理,设计并实现了整个保偏光纤偏振耦合测试系统。利用该测试系统可以有效的检测出光纤陀螺传感器中的重要部件-保偏光纤绕组内部由于扭曲、压力等原因造成的偏振寄生耦合现象,能够有效的控制光纤绕组的质量,对于光纤陀螺的生产与研制具有重要实践意义。保偏光纤内部的高双折射,使得其内部传播的偏振主模和耦合模之间存在着一定大小的光程差。在本文中,利用干涉仪内部的高精度扫描平面镜实现对光程差的补偿,不仅可以实现线偏振主模间的干涉,而且能够实现线偏振主模和偏振耦合模间的干涉。通过检测两个白光干涉主极大值间的距离,就可以确定偏振耦合点在整个保偏光纤上分布的具体位置。整个测试系统中,包含两个主要结构:偏振调整机构和迈克尔逊干涉仪。在偏振调整机构中,使用可旋转半波片、偏振棱镜、光电检测模块实现了对入射线偏振光的偏振态调整;在迈克尔逊干涉仪中通过高精度线性平移平台和高精度步进电机实现对光程差的补偿,利用光电检测模块实现对干涉光信号的采集,通过PCI 采集卡将采集数据输入至计算机。测试系统利用计算机对采集到的干涉数据进行处理和计算,得到最终的测试结果。利用该测试系统可以检测出1000m 长保偏光纤内部的耦合强度为-33dB 的偏振耦合,测试的空间分辨率为57.2mm。论文的主要创新之处: 1、利用白光光源相干长度短的特性提高了检测偏振耦合点的空间分辨率,实现了白光干涉系统,分析了白光干涉法检测保偏光纤内部偏振耦合的原理,根据检测系统的具体结构,建立了测试系统的理论计算模型。2、通过扫描平面反射镜300mm 的直线平移实现了光程差的补偿,有效的检测出1000m 长度的被测保偏光纤上的偏振耦合现象,空间分辨率达到57.2mm。使测试系统具有以短距离的干涉扫描尺寸(300mm)反映长距离被扫描空间(1000m)的技术特点。3、利用可旋转半波片和偏振棱镜实现了线偏振光偏振态的调整,通过控制两相干线偏振光的偏振态取得了偏振光的最佳相干效果,提高了干涉的对比度和测试的灵敏度,实现了线偏振光的干涉。同时解决了保偏光纤的对准问题。4、在机械结构设计中,采用精密滚珠丝杠结构减小直线移动装置中各相对运动零件之间的摩擦,扫描平面镜及其微调装置采用小尺寸结构,减轻了移动平台的负载载荷,克服了“爬行”现象,保证了微移动的精度,利用高精度步进电更多还原

【Abstract】 The principle of detecting polarization coupling in Polarization-Maintaining fiber based on white light interferometry is systematically analyzed in this dissertation. The whole testing system of polarization coupling in PM fiber had been designed and achieved. The PM fiber coil is an important part of fiber gyro. The polarization coupling caused by stress and twist in coil of fiber gyro can be found effectively by using this system. So the quality of fiber gyro could be controlled. The test system using white light interferometry has great signification for the research and production of fiber gyro. The main polarization mode and coupling mode in PM fiber has some optical path difference because of internal birefringence. The optical path difference between the main polarization mode and coupling mode could be compensated through the scanning mirror in Michelson interferometer. The interference between the main polarization mode and coupling polarization mode could be realized. By checking the distance between two zero grade interferential fringe, the position of polarization coupling along the detected PM fiber could be computing. There are two main structures in the test system: polarization state adjustment and Michelson interferometer. In the structure of polarization state adjustment, the polarization state of input linear polarization light can be adjusted by the rolling half-wave plate, polarization prism and optical-electronic detecting module. In the Michelson interferometer, the compensation of optical path difference can be achieved by high precise linear motion rail and high precise step-motor. The interferential signal is captured by an optical-electronic detecting module. Then, the acquisition data is transferred to a computer by PCI data acquisition card. The final test result is gained after the data processing. The system could test a 1000m long PM fiber and the coupling coefficient that could be detected is -33dB. The spatial resolution of testing system is 57.2mm. The following are innovations of this dissertation. 1. The system spatial resolution had been improved by using broadband white light source. White light interferometer had been realized in this dissertation. The principle of testing polarization coupling based on white light interferometry had been analyzed. The theory computing model of testing system had been founded according to the test system structure. 2. By using white light source with low coherence length, the white light interferometry had been realized. The optical path difference was compensated by moving scanned mirror 300mm. The coupling along 1000m PM fiber could be detected, and the spatial resolution of system is 57.2mm. 3. The polarization state of linear polarization light is adjusted by the rotational half-wave plate and polarization prism. The best results of linear polarization light interference had been implemented by adjusting the polarization state. The contrast ratio and the test sensitivity had been improved. The problem of PM fiber alignment of PM fiber was resolved. 4. In the mechanical design, the high accuracy ball screw has been used to reduce the friction between the motive parts. The load of motion block had been decreased through using less size scanning mirror and adjustment mechanism. The high level micro motion has been achieved by linear motion rail and step motor. In the full scanning range of 300mm, the 0.2μm motion precision was implemented to scan the compensated optical path difference. 5. The interferential data was processed, and the noise level had been reduced by filter. Because of system characteristic, the maximum points of interferential curve are dense. The wavelet transform had been applied in the process of interferential data to check the maximum points because wavelet transform has the advantage of zooming in data details.更多还原