Piston sensing for a segmented mirror system via a digital dispersed fringe generated by wavelength tuning.

A dispersed fringe sensor (DFS) is a promising approach for sensing the large-scale piston error for segmented mirror systems. In this Letter, a novel method, to the best of our knowledge, for piston sensing based on a digital dispersed fringe (DDF), which is generated by wavelength tuning, is introduced. By continuously changing the wavelength of light passing through the sensor, a collection of far-field spot arrays can be acquired, which are used to construct the DDF with steps of accumulation and stacking in sequence for each inter-segment region. A correlation-based method is applied to extract the encoded piston information from the DDF. The method greatly eases the demanding hardware requirement in traditional DFS and shows high efficiency for the reason that it could simultaneously measure all of the relative piston settings; in addition, it exhibits strong robustness to noise.