Abstract

With the rapidly increasing interest in mobile communications and global satellite-based data networks, many designs for next-generation low-earth satellite systems include the use of onboard optical terminals providing a fast and interference-free inter-satellite data transfer. However, to make such systems competitive with the well-established RF technology, they must offer besides high data rates additional attractive features such as compactness, small size, low mass and low power consumption. In this respect, we initiated in 1998 a five-year feasibility study of a compact laser communications terminal consisting of all-optical modules linked to each other by optical fibers. Figure 1 shows the conceptual view of the envisaged terminal with its two main modules under current investigation, the optical antenna module and the modulator/demodulator (MOD/DEMOD) module. The antenna module comprises a small refractive telescope, liquid crystal (LC) optics for precise beam alignment and beam width control that are required in the acquisition process of a remote terminal, and fast beam steering optics to keep the link stabilized while tracking the remote terminal. The MOD/DEMOD module consists of an array of optical gates triggered by an optical clock. The transmission scheme takes advantage of time division multiplexed (TDM) short optical pulses. So far we have implemented prototypes with respect to both the LC optics [1] of the antenna module and the demodulator part of the MOD/DEMOD module [2]. The emphasis of the present paper is on the latter one.

© 2000 IEEE