A technique for acquiring and tracking terminals in a free-space laser
communication system involves exchanging beacon laser beams between the
terminals to acquire and then track the terminals such that data laser
beams exchanged by the terminals for communication are steered based on
feedback from detection of the beacon laser beams. The beacon laser beams
used for acquisition have a greater beam divergence than those used for
tracking. Gimbals provide coarse steering of the data laser beams, and
steering mirrors provide fine steering. GPS position data exchanged via
an RF link can be used for initial pointing of the beacon laser beams for
acquisition. The beacon laser beams can be chopped such that all
terminals can use the same beacon wavelength and are distinguished by
using different chopping frequencies. By detecting a chopped signal, the
position sensor detector can be AC coupled to reduce sensitivity to solar
radiation and glint.