Coupling starlight into single-mode fiber optics

Abstract

We have calculated the efficiency with which starlight can be coupled into a single-mode fiber optic that is placed in the focal plane of a telescope. The calculations are performed for a wide range of seeing conditions, with and without rapid image stabilization, and for a wide range of wavelengths. The dependence of coupling efficiency on the f-ratio of the incident beam is explored. Also, we calculate the coupling efficiency as a function of displacement for a perfect Airy pattern. We have also used a computer program which simulates atmospheric wavefronts to determine the variance of instantaneous coupling efficiency as a function of seeing. In perfect conditions, the maximum efficiency at the LP11 mode cutoff is 78% due to the mismatch of the Airy pattern and the nearly Gaussian mode of the fiber. Maximum total coupled power is attained at d/r0 = 4 with rapid image stabilization.