Optical design of compact unobscured ground-based diffractive telescope

Abstract

To realize unobscured, compact structure and maintain loose tolerance, a novel method based on flat-field relay mirror for designing the ground-based diffractive telescope is proposed. Based on this mthod, we perform two different studies devised to design and reduce the manufacturing difficulty of compact unobscured ground-based diffractive telescope. Firstly, the formula of flat-field relay mirror structure based on aberration theory is deduced. Combining the Schupmann achromatic theory, a compact unobscured diffractive telescope with loose tolerance is designed. The designed focal length is 400 mm, F number is 5, the working waveband is 612.8-652.8 nm. After optimization by optical design software ZEMAX, the size of system is 720 mm × 435 mm, the total track distance is only 1/12 of transmissive diffractive telescope. The modulation transfer function (MTF) is greater than 0.73 at 50 lp/mm within 0.30°×0.07° field of view (FOV), and the imaging quality is approached the diffraction limit. Secondly, to further reduce the difficulty, the fabricating parameters of diffractive optical elements (DOE) and the alignment tolerance of system are designed and fully analyzed. The analysis results show that the DOE can be fabricated by existing binary lithography, the designed system meet the requirement of alignment. The designed system provides a good solution for ground-based diffractive telescope.