Large-aperture double-focus laser collimator for PAT performance testing of inter-satellite laser communication terminal

A laser collimator is necessary for testing and verification of the pointing, acquisition and tracking (PAT) performance of inter-satellite laser communication terminals on the ground. The laser collimator must have a large clear aperture to fit the PAT performance testing system. The PAT subsystem has a large field of view for the acquisition and a high angular accuracy for the fine tracking. To resolve the conflict between large field of view and fine angular resolution, a large-aperture double-focus laser collimator is proposed and its optical design and mechanical structure are described. The collimator mainly consists of a primary lens, a reflector, a beam-splitting plate, a secondary lens, two compensating lenses, two imaging sensors and a laser. The primary lens directly forms the long focal length arm of the collimator. The combination of the primary lens and the secondary lens form the short focal length arm of the collimator. The collimator has an angular resolution <0.75 μrad and a 10 mrad field of view. For the collimator, the incident beam is focused on the two imaging sensors by its two arms, and the beam emitted from the laser is collimated and transmitted. The collimator is combined with an optical scanner and a fine beam deflector to test and verify the PAT performance of the inter-satellite laser communication terminal in a full physical manner.