激光陀螺高反镜缺陷反演算法研究

Multilayer mirrors comprise the ring resonator of the ring laser gyro (RLG). The backscattering of these mirrors dominates the lock-in threshold of the RLG due to surface imperfections. Super-polishing process up-to-date has approached to solve the problem of substrate’s scattering, which implies that the loss of multilayer mirrors might come from the micro-structural defects formed during mirrors deposition process. However, effective reverse engineering algorithm does not exist to quantitatively or half-quantitatively evaluate those micro-structural defects of actual multilayer mirror such as the layer thickness errors and refractive index deviations. This project will try to establish a mathematical model suitable for the defects reverse engineering of RLG’s multilayer mirrors, with consideration of possible micro-structural defects based on the practical experience of countless runs of mirrors deposition. Based on optimization algorithms, fast and credible calculation algorithm will be explored for the defects reverse engineering of RLG’s multilayer mirrors. And new data processing method will be put forward to diminish the impact of mirrors spectral measurement errors on the accuracy of defects reverse engineering of RLG’s multilayer mirrors. The effectiveness and credibility of the above mathematical model, the reverse engineering algorithm and the data processing method will be experimentally tested by application to some unusual RLG’s multilayer mirrors with deliberately produced layer micro-structural defects. Through above research, the project can give quantitative or half-quantitative defects feedback for the daily deposition of RLG’s multilayer mirrors, can give directional guidance for optimizing the process control parameters of the coating deposition machine in order to further diminish the loss of RLG’s multilayer mirrors, and can give reference for the reverse engineering of other types of optical thin-film coatings.

高反镜是激光陀螺中形成环形谐振腔的关键元件，其背向散射损耗决定了陀螺的闭锁阈值。目前超抛工艺已基本解决基片的表面散射问题，高反镜损耗可能主要来源于多层膜镀膜中的微结构缺陷。但目前尚缺乏有效的反演算法，来定量或半定量评价实际高反镜中各层的厚度误差和光学参数偏差等微结构缺陷信息。项目采取数学建模、算法开发、数据处理、缺陷镀膜等方法，结合激光陀螺高反镜实际镀膜经验，考虑可能的膜层缺陷，建立适合陀螺高反镜反演的数学模型；基于最优化策略，开发适合陀螺高反镜反演的快速可靠计算算法；考虑实际的薄膜测量误差，提出新的数据处理方法，减小测量误差对陀螺高反镜反演精度的影响；通过人为引入缺陷的高反镜镀膜实验，对上述数学模型、反演算法和数据处理方法进行实验验证。通过以上研究，为激光陀螺高反镜的日常镀膜提供定量或半定量缺陷反馈，为优化镀膜机控制参数、减小高反镜损耗提供方向指导，为其他类型光学薄膜的反演提供参考。

为进一步降低批产激光陀螺腔镜损耗带来的锁区，项目围绕激光陀螺腔镜的膜层缺陷建模、反演算法设计和极低损耗镀膜工艺等内容进行研究，取得如下成果：（1）建立正、斜入射条件下，考虑吸收、色散、表面粗糙度和体折射率不均匀性等膜层缺陷时多层膜光谱特性分析的统一理论模型；（2）开发一套适合激光陀螺腔镜膜层缺陷反演的快速可靠计算算法；（3）研制一套稳定的批产极低损耗镀膜工艺。上述成果将《薄膜光学》学科中光学特性计算的理想薄膜模型推广至非理想薄膜模型，是基础理论上的突破与集成；基于上述成果批生产腔镜损耗已不大于10ppm，制成的二频机抖激光陀螺的闭锁阈值低达几度/小时，抖动过锁区导致的随机游走已接近量子噪声极限。上述研究为高精度激光陀螺大批量生产奠定坚实基础，将在基于激光陀螺的武器装备现代化建设中发挥重要作用。