Doppler shift due to relative movement between satellites must be taken into consideration in intersatellite laser links. The degradation of differential phase-shift keying (DPSK) receiver performance caused by Doppler shift is assessed. In order to simplify the complexity of the receiver, we discuss conditions that will bring the new design concept for a robust laser communication system in space, which does not require precise active control. When the precise active control has to be used, the impact of frequency drifts relative to optical filter's center frequency becomes evident. Optimum bandwidths of optical filters yielding optimum performance over the entire range of frequency shifts are determined to further improve the receiver performance. The results obtained here will be helpful in the design of DPSK/self-homodying intersatellite laser communication systems.
Coupling efficiency of coherent plane waves into single-mode fibers is degraded by the localized deformation of the optics antenna used for reception of optical beams. For transmission-type and reflection-type antennas, the evolution of coupling efficiency with the change of characteristic parameters of the localized distortion are investigated. It is found that the coupling efficiency varies regularly as the increase of the normalized center deepness h/R, the normalized radius a/R, and the normalized center distance d/R. The key principles for selecting optics are determined. The results obtained will be useful in estimation and design of fiber-coupled optical systems in free-space communications.
An IM-DD optical communication system at data rate of 100 Mbps is designed for links between low earth orbiting
(LEO) and geostationary (GEO) satellites. It was constructed with a fibre-coupled LD transmitter and a Si-APD
photodetector. The system used the NRZ format. The transmitter achieves 1W average output power with a
combination of multiplex laser drivers. Due to the transmitter drastically increased output power, it allows
improvement of the link budget with, at the same time, reduced telescope diameter and PAT requirements. The
receiver consisted of a threshold crossing detector and a timing recovery subsystem. It achieved a bit error rate of
10-7 at -47dBm received average signal power.
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