Optical design of an antenna that is insensitive to decenters for laser communication

In this paper, a laser communication antenna with two mirrors is designed. The decenters of the secondary mirror do not introduce field-linear coma, which reduces the antenna's sensitivity to misalignment, and we call it coma insensitive system. The conic coefficients of the primary and secondary mirrors of the coma insensitive system are different from those of the Cassegrain and Ritchey-Chretien systems. We derive the calculation formula of the coma insensitive system in detail based on the nodal aberration theory. Through a design example, the performance of the coma insensitive, Cassegrain and Ritchey-Chretien system in the nominal state and the secondary mirror decentered state is compared, and it is found that the aberration performance of the Cassegrain and Ritchey-Chretien system in the nominal state is much better than that of coma insensitive system. However, when the secondary mirror is decentered, the performance of Cassegrain and Ritchey-Chretien system is obviously inferior to coma insensitive system, and their rms spot diameter is about 2.8 times that of coma insensitive system.