Space communications employing optical position modulation

Optical technologies for space communications are examined, and in particular the types of optical sources, optical detectors and modulation schemes. An analysis is presented for the pulse position modulation format employing a GaAlAs semiconductor laser and a Si avalanche photodetector. The results, modelling currently available technology, predict a sensitivity of 61 photons/bit for this direct detection PPM system. This sensitivity is approaching that of coherent PCM but is achievable without the complexity of the coherent detection process