Simulations Study of Segmented Mirror Coarse Phasing Using Two-Dimensional Dispersion Fringe Sensing Technology

Two-Dimensional Dispersion Fringe Sensing (TDDFS) is an efficient method for coarse phasing of segmented mirrors. Modeling and simulations based on double-aperture diffraction are used to study dispersion fringe in two directions. In the dispersion direction, the nonlinear least squares fitting method is used to extract the piston error. The theoretical capture range is +/- 96 mu m which is verified compared with the simulation results, and the detection accuracy can be reached to lambda/10. However, the nonlinear least squares fitting method cannot effectively detect piston errors within one wavelength. In the diffraction direction, the principal maximum extraction method is used to measure the piston error, which is suitable for the piston error detection with a small range within one wavelength. In order to reduce the influence of the extraction error of the center line, we propose a corrective method. The results show that the accuracy of the modified principal maximum extraction method can reach 30nm. The two methods can effectively meet the requirements of the piston detection of the large-aperture segmented mirror telescopes.