Large Piston Error Detection Method Based on the Multiwavelength Phase Shift Interference and Dynamic Adjustment Strategy

Abstract

As the loading space in rockets and mirror fabrication technology is limited, optical systems in space cannot have large optical apertures. However, the successful launch and excellent performance of the James Webb Telescope indicate that segmented mirrors can help realize large-aperture optical systems in space, owing to the fold–unfold mechanism in the telescope. However, all segments in the segmented mirror should be co-phased so that it is equivalent to a monolithic mirror. The co-phasing problem is significant in optical systems in space because of their low error tolerance. Owing to some accident factors, the piston error can be more than 1 mm after the unfolding process. Here, we introduced a multiwavelength interference method and dynamic adjusting strategy, aiming to solve the two problems of co-phasing: large detection range (~2 mm) and high detection precision (<1/20λ). Numerical simulations were performed, and a 400 mm aperture-segmented spherical mirror system was used to verify this method. The original piston error was set to 1 mm, after the coarse co-phasing, and the residual piston error to less than half the wavelength of the monochromatic light; for fine co-phasing, the achieved detection precision was approximately 1.2 nm.

Keywords

• segmented mirrors
• large aperture telescope
• interferometry
• active optics
• wave-front sensing