Gregorian all-reflective optical system

摘要

An optical heterodyne receiver comprises a system of reflectors forming a folded Gregorian configuration for collecting a signal beam, and an optical detector located at the focus of the system. The reflectors comprise a paraboloidal primary reflector and an ellipsoidal secondary reflector facing each other on an optical axis with the focus of the secondary reflector coinciding with the focus of the primary reflector. An auxiliary laser generates a local oscillator beam that is combined with the signal beam after the signal beam emerges from the exit pupil (which is also the aperture stop) of the system, and the resultant is impinged on the detector. A pair of image motion compensators is located as close to the exit pupil as possible for aligning off-axis inputs to the detector. The compensators also ensure that off-axis as well as on-axis inputs are substantially coaxial with the local oscillator beam, thereby maximizing signal detector efficiency. By utilizing a large f/number for the local oscillator beam, it effectively eliminates the need for critical alignment between the signal and the local oscillator beams at the detector.