Coarse co-phasing method based on slope of visibility-enhanced dispersed fringe pattern for segmented telescope

Abstract

Dispersed fringe sensing (DFS) is a promising strategy to bring segmented primary mirror into in-phase for large-aperture segmented telescope. Conventional intensity-based piston extraction methods show operational complexity due to the spectral calibration and poor sensing accuracy for large piston error because of the terrible visibility resulting from the dense fringe modulation. In order to overcome these disadvantages, a visibility improvement technique based on side-lobe enhancement and a slope-based piston extraction algorithm are developed. By scaling up the side lobes in 2-D spectrum of dispersed fringe pattern (DFP), the visibility of DFP could be greatly improved. At the same time, by theoretical analysis, the slope of dispersed fringe is not sensitive to the spectral non-uniformity of the broadband source, thus, the introduced piston extraction algorithm avoids the procedure of spectral calibration. Numerical experiment is conducted to demonstrate its feasibility and accuracy. It provides an efficient, alternative solution to large-scale piston sensing via dispersed fringe sensor.