Alignment for center distance of optical telescope in satellite optical communication terminal

The optical telescope of satellite optical communication terminal is composed of an objective and an eyepiece, and the axial center distance of the two lenses has an important influence on emitting and receiving performance of the system. The digital single-wavelength interferometer is an effective device to measure and adjust the axial center distance, however, it is usually difficult to be determined precisely when there is a wavelength difference between the interferometer and the optical telescope, because the focal length difference of the objective and the eyepiece varies with the wavelength. In this paper, the relation between the variations of center distance and the corresponding interference fringe counts was deduced on the basis of eikonal equation, then an efficient alignment method was given according to the relation. Several proof schemes including experiments and numerical simulation were suggested, and the second scheme was chosen to verify the alignment method presented in this paper. Numerical results show that the alignment error of center distance in a Cassegrain reflective optical telescope is less than 15%, and that in a refractive optical telescope is only about 3%. These results show that the proposed method can meet the alignment requirement of the satellite optical communication terminal.