基于布里渊散射的光纤双折射分布式测量方法研究

Fiber birefringence is one of the factors that limits the performance of optical communication and optical fiber sensing system. Due to the randomness of fiber birefringence both in time and spatial domain, currently it is difficult to distributed monitor fiber birerfringence in general single mode fibers. In this project, the technology of distributed fiber birefringence measurement is investigated based on Brillouin scattering in optical fibers. This tachnology can be further used to develop the methods for inhibitting effects of fiber birefringence in fiber communication and sensing systems. The technology is investigated from three aspects: from the aspect of theory, the mathmatical relations between fiber birefringence and Brillouin gain, peak frequency and linewidth are studied, then combined with the model of random fiber birefringence, the principles and procedures of the birefringence measurement methods using Brillouin gain, peak frequency and linewidth are developed seperately, also the measurment errors on different types of fibers are estimated based on theoretical simulations; from the aspect of experiment, the setup of distributed birefringence measurement system is designed and built in lab enviroment, and system performances are tested using several types of communication and sensing fibers; from the aspect of application, the methods of integrating the distributed birefringence measurement system into the existing fiber communication and sensing systems are studied.

光纤双折射导致的偏振相关问题是限制光纤通信及光纤传感系统性能指标提升的主要瓶颈之一。由于光纤中的双折射随时空随机变化，目前还没有理想的分布式监测方式。本项目旨在探索光纤双折射的分布式测量方法，力求为进一步研究光纤通信、光纤传感等领域的偏振相关问题并抑制其影响提供依据和手段。本项目从理论、实验及应用三个层面研究基于布里渊散射的光纤双折射分布式测量方法：首先研究布里渊散射谱增益、频移及线宽与光纤双折射的定量关系。结合光纤双折射的分布式数学模型，通过理论仿真提出应用布里渊散射谱各参数进行双折射分布式测量的原理及步骤，并估算其应用在不同种光纤时的测量误差；在实验室环境下设计并搭建基于上述测量原理的光纤双折射分布式测量系统，并利用各类通信及传感光纤测试系统性能；在上述研究基础上，研究将光纤双折射分布式测量方法整合到现有光纤通信系统及分布式传感系统的方法。

我们推导了受激布里渊散射的矢量模型，用于研究布里渊散射谱（主要是布里渊增益/损耗）与光纤双折射的关联性；通过模型的推导，我们熟悉了布里渊作用过程中的物理过程和简化原则；基于此矢量方程，我们能够在布里渊系统中，进行后续布里渊散射偏振相关的深入研究。首先，主要做了偏振态和双折射对布里渊增益信号影响的相关分析，给出了全面的最大平均增益对应的信号泵浦偏振态关系与光纤拍长的关系；研究了不同输入偏振态下信号的波动性，给出了一个波动范围。然后，我们研究了偏振相关增益矢量的统计性质；基于之前的矢量模型，推导了偏振相关增益矢量相关的新的理论模型；通过理论仿真和实验验证，我们得到了偏振相关增益矢量大小与光纤长度和拍长，以及泵浦功率的关系；相关的实验和理论相符合，验证了这一理论模型的正确性。最后，基于布里渊散射的偏振相关性，我们提出了一种基于增益统计的拍长测量方法；通过给出数值和实验结果，我们验证了这个新方法的合理性。

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