An Image-based alignment errors correction method for segmented Fresnel primary mirror

Licheng Zhu,Lujia Zhao,Ping Yang,Bing Xu,Chunlin Guan,Lianghua Wen

doi:10.1109/jphot.2020.2968566

Licheng Zhu, Lujia Zhao + Show 4 more

Open Access

https://doi.org/10.1109/jphot.2020.2968566

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Abstract

The alignment errors correction of segmented Fresnel primary mirror in multiple imaging scenes is simulated. Based on the linear relationship between five kinds of alignment errors and modulation transfer function metric or image frequency domain metric, an iterative correction method is introduced to compensate the alignment errors of segmented Fresnel lens at five degrees of freedom. The correction capability under point target imaging and the effect of alignment error correction under extended target imaging are studied. The simulation results show that the proposed correction scheme can effectively correct the alignment error when the rms value of segmented Fresnel primary mirror is less than 0.7λ. This method does not need to add any additional devices to the telescope, but optimizes directly based on the images, and is independent of the spatial structure of the imaging target. It may be suitable for fine phasing correction of segmented membrane diffractive optical telescope in orbit.

Highlights

The membrane diffractive optical telescope replaces the traditional optical elements with lightweight binary optical elements, which significantly reduces the weight of the imaging system, and because of the transmission configuration of elements, the requirement of surface tolerance of primary mirror is more relaxed
J(k) = J(k) (u + u) − J(k) (u − u) where u are the correction values for each alignment errors in k iteration. u is the random perturbations with fixed amplitude, whose amplitude is determined by the sensitivity of the modulation transfer function (MTF) metric to five kinds of alignment errors. i is the number of alignment error types
In order to simulate the fixed alignment errors introduced in the assembly process, A group of alignment errors are randomly applied to SFL1∼SFL4 within the linear range between alignment errors and Jp

Summary

Introduction

The membrane diffractive optical telescope replaces the traditional optical elements with lightweight binary optical elements, which significantly reduces the weight of the imaging system, and because of the transmission configuration of elements, the requirement of surface tolerance of primary mirror is more relaxed. It has become a research hotspot of lightweight, large aperture and high-resolution space imaging system. It is the key problem to detect and correct the alignment error if we want to maintain high-performance imaging of segmented membrane diffractive optical telescope

Methods

Results

Conclusion