Over-Stratospheric-Altitude Optical Free Space Links: System Performance Evaluation

The wide bandwidth offered by optical communications systems, is attracting more and more interest in space applications. Investigation has been carried out either on suitable modulations or resilient architectures for communications and Earth Observation (EO) missions. New elements have been introduced: High-Altitude- Platforms (HAP's), whose characteristics allow us to carry out an optical link between unmoving terminals, if GEO satellites are involved. This paper is describing an architecture for EO, based on two HAP's linked via a GEO satellite, whose optical payload offers an inline-like amplification for an overall link that can extend over 80,000 km. The aim of our work is to present a low power consumption system that guarantees the required Bit Error Rate (BER) . Both Direct Detection (DD) and coherent (homodyne and heterodyne) systems will be considered.