Li Duan, Savransky Dmitry
J Opt Soc Am A Opt Image Sci Vis. 2023 Jul 1;40(7):1327-1336. doi: 10.1364/JOSAA.483283.
Automated alignment can significantly increase optical system precision and flexibility, and reduce time and labor costs in system setup and maintenance. We present an automated alignment technique on a double off-axis parabolic mirror system, which poses challenging alignment problems due to the mirrors' high sensitivity to aberrations, rotational asymmetry, and non-orthogonality in stage adjustments. In our methodology, we use focal plane wavefront sensing to eliminate the non-common path error, increase optical throughput, and reduce cost and system complexity. We incorporate model-based optimal estimation and control to better handle the nonlinearity, model uncertainty, and noise. Using either an iterated extended Kalman filter or a square-root unscented Kalman filter as the optimal nonlinear misalignment state estimator, we are able to consistently reduce the linear misalignment from around 1 mm to <5µ and the angular misalignment from around 500 to <6 in simulation, achieving a final wavefront error of <5∗10 waves in the field of view when tested at wavelength 635 nm. We discover a multi-state coupling effect, which implies that different misalignment states have compensating effects on system measurements, thus interfering with the estimator's observation of misalignment state changes. We further investigate the coupling's effects on alignment quality through observability analysis.
自动对准可显著提高光学系统的精度和灵活性，并降低系统设置和维护中的时间和人工成本。我们提出了一种用于双离轴抛物面镜系统的自动对准技术，由于这些镜子对像差、旋转不对称以及平台调整中的非正交性高度敏感，该系统存在具有挑战性的对准问题。在我们的方法中，我们使用焦平面波前传感来消除非共路误差、提高光通量，并降低成本和系统复杂性。我们纳入基于模型的最优估计和控制，以更好地处理非线性、模型不确定性和噪声。使用迭代扩展卡尔曼滤波器或平方根无迹卡尔曼滤波器作为最优非线性对准状态估计器，在模拟中，我们能够将线性对准误差从约1毫米持续降低至<5微米，将角度对准误差从约500持续降低至<6 ，在波长635纳米下进行测试时，在视场中实现最终波前误差<5×10 波。我们发现了一种多状态耦合效应，这意味着不同的对准状态对系统测量具有补偿作用，从而干扰估计器对对准状态变化的观测。我们通过可观测性分析进一步研究了这种耦合对对准质量的影响。
