<title>Optimum optical and electrical filter characteristics in optically preamplified direct detection (N)RZ receivers</title>

Abstract

We give optimum values for the bandwidths of realistic optical and electrical filters (optical Fabry-Perot filters and fiber Bragg gratings, electrical Bessel filters and first order RC low pass filters), as well as for realistic NRZ and (33% duty cycle) RZ input pulses for a free space laser communication system employing an optical booster and a direct detection receiver with optical preamplification. Different extinction ratios, the presence of background radiation, and the influence of the booster amplifier's amplified spontaneous emission (ASE) are emphasized. Our results show that the optimum optical filter bandwidth (both for NRZ and RZ) has to be sought in the range of 1.5 to 3 times the data rate. Using the optimum filter bandwidths, RZ coding yields a sensitivity improvement of up to 1.5 dB compared to NRZ transmission. For typical system parameters and link distances higher than several thousand kilometers the booster ASE becomes less important than strong background radiation, while it causes severe sensitivity degradations for shorter distances.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.