Optimum optical and electrical filter characteristics in direct detection NRZ or RZ

We give optimum values for the bandwidths of realistic optical filters(optical Fabry-Perot filters and filer Bragg gratings electrical Bessel filters and order RC low pass filters, as well as for realistic NRZ and (50% duty cycle)RZ input pulses for a free space laser communication system employing an optical booster and a direct detection receiver with optical pre-amplification. Different extinction ratios, the presence of background radiation, and the influence of the booster amplifiers amplified spontaneous emission (ASE) ARE emphasized. Our results show that the optimum optical filter bandwidth has to be sought in the range of 1.5 to 3 times the rate. Using optimum filter bandwidth, RZ coding yields a sensitivity improvement of up to 1.5dB compared to NRZ transmission. In this paper we present simulation results of investigations on free space satellite-airborne communication systems with fiber boosted transmitters and fiber pre-amplified direct detection receivers.