Optical Design for Thermal and Radiation Effects in Space Optical Communication Systems

Free-space optical communication systems operate with very limited field of view and in narrow spectral regions, leading to relatively simple optical designs. Operation in the space environment, however, imposes severe environmental requirements. Typically mounted on the exterior of a spacecraft, the optical components of a free-space optical system must withstand extreme thermal and radiation environments. Traditionally, this is accomplished using multiple materials to athermalize the design and the use of specialty radiation-tolerant glasses. Recent studies ([1], [2]) investigating the effects of radiation on non rad-hard glasses have shown that specific standard glasses exhibit little radiation darkening at optical communication wavelengths. As little chromatic correction is required in free-space optical systems, glasses can then be chosen to match thermo-optical coefficients of structural materials. Alternately, thermo-optical coefficients of achromatic pairs of glasses can be evaluated and used to select appropriate glass pairs and structural materials to provide athermal achromatic designs. Compact fiber collimators, key components in space optical communication systems, were designed for athermal operation over the C-band using glasses exhibiting low radiation darkening at 1550 nm.