Research On The Design Theory Of Large-aperture Diffractive Telescope Optical System

Membrane diffraction imaging has been the key technology for constructing large-aperture space-based optical telescopes in the future.Membrane diffraction device greatly reduces the weight and surface accuracy requirements of the telescope primary mirror,and therefore provides a new solution for the construction of large-aperture telescope.In order to build more efficient large aperture diffractive telescope,several key technical issues are discussed in this thesis,mainly include design of Fresnel Corrector with large feature size,design of photon sieve telescope imaging system working in the visible light range,and central obscuration analysis and spectrum modified design in large aperture diffractive telescopes.The specific work is as follows:1.Two large feature size Fresnel Correctors are proposed to reduce the processing difficulty of the Fresnel Corrector,one is a mixed modulation diffractive lens,and the other is a harmonic diffractive lens.Simulation results show that both mixed modulation diffractive lens and harmonic diffractive lens can be used as a Corrector to eliminate the chromatic aberration introduced by the diffractive primary lens.However,the two diffractive lens have different optical and processing characteristics.Mixed modulation diffractive lens is easier to process than harmonic diffractive lens due to their larger feature size and feature angle,but the diffraction efficiency of a diffractive system based on a mixed modulation diffractive lens(-10%)is lower than that based on a harmonic diffractive lens(>90%).2.Two RGB three-channel photon sieve telescope designs are proposed to cover the spectral width of the telescope to the visible range,one is a RGB three-channel telescope based on a radial partitioned multi-wavelength photon sieve,and the other is a RGB three-channel telescope based on a random partitioned multi-wavelength photon sieve.Simulation results show that the random partitioned design can better eliminate the chromatic aberration of R,G,B channels,and has better optical focusing characteristics,but the spectrums of the three channels are limited by the harmonic wavelengths of the harmonic diffractive lens,and therefore cannot be arbitrarily chosen.In contrast,the spectrums of the radial partitioned design have higher design freedom,but this design has a lower imaging quality because of the higher side lobes of the outer channel and the difference in imaging resolution among different channels.3.A membrane support mechanism based on a flexible symmetric steel ring is proposed to support the membrane photon sieve,and a membrane support mechanism supporting a 100 mm photon sieve is fabricated.This support mechanism has the advantages of light weight,simple structure,easy folding and unfolding,and self-stability,therefore,it has great research value for the support and deployment of the diffractive membranes in the future.4.The central obscuration problem in large-aperture diffractive telescopes is analyzed,and then a spectral translation design method is proposed based on the analysis results,which can effectively reduce the spectral obscuration in large-aperture diffractive telescopes.Furthermore,a one-meter diffractive telescope on the geostationary orbit is designed to evaluate the effectiveness of our method to reduce the spectrum obscuration.Simulation results show that our design not only avoids the obscuration of the designed spectrum,but also improves the MTF curve of the telescope.