In the Fizeau imaging interferometer testbed we recently built, the optical path difference (OPD; i.e., piston error) among three sub-telescopes should be corrected for phased imaging to enhance the spatial resolution. This study presents the detection of the OPD via a dispersed fringe sensor (DFS) method and its closed-loop control. The retrieval of the OPD from a dispersed fringe map is a fast-Fourier-transform-based DFS method, which indicates in theory that the OPD has a linear relationship with the displacement of the secondary peaks in the Fourier spectrum of the dispersed fringe map. Then the design and alignment of the OPD detection module are presented, as well as the OPD compensation module with a two-level motion stage. A unique benefit of the fast-Fourier-transform-based DFS is high time efficiency for closed-loop control; for a window of 32 x 128 pixels, a 932 Hz computation rate was achieved by dedicated electrical hardware, which is significant for the distributed satellite formation-flying platform. The experiments validated (1) that the detection range of the DFS is more than +/- 160 mu m, (2) that the OPD has a fine-line relationship with the secondary peak displacement, (3) the feasibility of the DFS method used for closed-loop control, and (4) that an OPD control precision of 0.0593 mu m RMS is achieved. (C) 2020 Optical Society of America
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机译：在我们最近建造的FIZEA成像干涉仪测试平面上，应纠正三个子望远镜中的光路径（OPD;即活塞误差），以便分阶段成像来提高空间分辨率。本研究通过分散的条纹传感器（DFS）方法及其闭环控制来介绍OPD的检测。从分散的边缘图检索OPD是一种基于快速傅里叶变换的DFS方法，其理论上表明OPD与分散的条纹图的傅立叶光谱中的次级峰值的位移具有线性关系。然后，呈现OPD检测模块的设计和对准，以及具有双级运动级的OPD补偿模块。基于快速傅立叶变换的DFS的独特优势是闭环控制的高时间效率;对于32 x 128像素的窗口，通过专用电气硬件实现了932 Hz计算速率，这对于分布式卫星形成飞行平台具有重要意义。实验验证（1）DFS的检测范围大于+/- 160 mu m，（2），OPD具有与二级峰位移的细线关系，（3）DFS方法的可行性用于闭环控制，实现了0.0593 mu M rms的OPD控制精度。 （c）2020美国光学学会
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