异面环形激光谐振腔中本征模式偏振及背向散射特性的表征与调控

Nonplanar ring resonators have advantages in increasing the beam quality, decreasing the line-width and eliminating the spatial hole burning effect. The ring laser gyros with this structure also have unique features, such as non mechanical noise, low random walk coefficient, short signal delay and so on. Therefore the nonplanar ring resonators are becoming a new research direction in the fields of inertial navigation and geophysics recently. In this project, we analyze the polarization and backscattering properties of the eigenmodes in the nonplanar ring resonator, and propose a solution to increase the uniformity and measure the polarization of the eigenmodes correspondingly. Providing the guideline to optimize the structure of nonplanar ring resonators, and improve the performance of nonplanar ring laser gyros. The main contents of this project are as followed: ① A system is explored to measure the backscattering coupling parameters and backscattering phase shift in a nonplanar ring resonator, and the only real way to eliminate the lock-in effect of the laser gyros is bring out by modulating the phase of the backscattering. ② The quantitative physical model is established to characterize the propagation proterties of the high-order transverse modes. A method is proposed to improve the uniformity of the laser field and reduce the mode pulling effect by controlling the phase of the high-order transverse modes. ③ The formation mechanism of the eigenmodes’ polarization is revealed and the experimental facility to measure this polarization is also explored. The relationship between the polarization of the eigenmodes and the gyros’ precision is disclosed. The deviation range of the gyros’ precision can be estimated and a method to eliminate or compensate the ellipticity of the eigenmodes is finally put forward correspondingly.

异面谐振腔具有提高光束质量、降低谱线宽度以及消除空间烧孔效应的优点，且相应结构激光陀螺在消除机械干扰、降低随机游走系数以及缩短信号延迟等方面表现出的优越性，使得该结构成为惯性导航及地球物理学领域的研究热点。本项目旨在研究异面谐振腔中本征模式的偏振和背向散射特性，提出改善光场均匀性及测量本征模式偏振态的方案，为优化谐振腔结构并提高相应结构激光陀螺测量精度提供必要的理论和技术支持。具体包括：①开发异面环形谐振腔中背向散射光耦合参数和相移的测量系统，探索一种通过调控背向散射光来消除锁区的方法；②建立异面环形谐振腔中高阶横模传输的物理模型，通过对高阶横模进行调控来提供光场均匀性并降低模式牵引效应；③揭示异面谐振腔输出光偏振态的形成机理并提出测量该偏振态的实验设计方案，掌握异面腔结构激光陀螺精度对腔内本征模式偏振态的依赖规律并预估激光陀螺输出精度的偏差范围，提出一种消除或补偿本征模式椭圆度的新方法。

作为激光陀螺的核心部件，非共面环形谐振腔内，同时维持着偏振态相互正交的左、右旋相向行波模式的振荡，而腔内本征模式的演化规律会对激光陀螺的测量精度产生明显的影响。因此，研究异面谐振腔内本征模式偏振态的变化及谐振腔输出频差对本征模式偏振态的依赖关系对于提高激光陀螺的测量精度显得极为重要。本项目主要针对异面环形谐振腔中本征模式的背向散射及偏振特性展开研究，所开展的研究工作及取得主要进展如下：.① 以光传输矩阵理论为基础，建立了谐振腔输出频差对腔内本征模式偏振态的依赖关系。在此基础之上，分析了在不同入射角和旋转轴情况下，谐振腔内本征模式偏振态变化对Sagnac输出频差的影响。.② 结合自再现条件和菲涅耳-基尔霍夫衍射积分，在同时考虑本征模式偏振特性和光场分布的基础上，给出了异面谐振腔内不同阶次振荡模式的频谱特性，并以TEMq00、TEMq10和TEMq01模为例，给出了本征模式偏振态、异面谐振腔结构参数对不同模式频率间隔的影响。.③ 结合背向散射光与谐振腔本征模式的耦合特性，推导了激光陀螺中背向散射光所引起的锁区阈值具体表达式，提出通过调节异面腔折叠角来减小并消除闭锁效应的新方法。.④ 以琼斯矩阵理论和自再现条件为基础，分析了存在轻微非共面效应高斯光束远场发散角情况下，全反射棱镜式（TRP: Total Reflection Prism）谐振腔中的应力双折射效应对本征模式偏振态和输出频差的影响。.⑤ 当TRP谐振腔中径向和角向误差同时存在时，推导得到了所有扰动源同时存在时棱镜折射面的扩展光线矩阵。结合本征模式自再现条件，进一步分析了腔内本征模式的光轴扰动特性（用光轴扰动灵敏度因子描述），得到了扰动源处于不同类型的棱镜时光轴扰动灵敏度因子的位置。.⑥ 利用飞秒激光在载氢和非载氢的多模光纤中成功写入FBG，并在高温条件下实现了对温度和应变的同时传感。