Compact Optical Terminal System for Two-Way Time and Frequency Transfer

SummaryThe economical, reciprocal, low-loss, and compact optical terminals are essential for establishing high-precision optical time and frequency transfer networks in a turbulent free-space atmosphere. In this paper, we propose an optical terminal designed for long-distance time and frequency transfer, which includes a coarse tracking module and an angle-of-arrival compensation control module. The coarse tracking module consists of a telescope with repeatability and theoretical step resolution each less than 10 arcseconds, a visible guidance laser, and a visible camera. The angle-of-arrival compensation control module is composed of beam splitter, a position-sensitive quadrant photodetector (QPD), a fast steering mirror (FSM), a beam expander, and a PID control circuit. Additionally, the system minimizes insertion loss to maximize the power margin of the signal light. The terminal is capable of optimizing the aperture to reduce the fluctuation of the angle-of-arrival in different turbulence conditions. The proposed optical terminal design will show a potential in optical clock network spanning ground-to-satellite and inter-satellite distances.