OPTICALLY PREAMPLIFIED PULSE-POSITION MODULATION FOR FIBEROPTIC COMMUNICATION-SYSTEMS

A Chernoff bound is applied, by means of a recently developed moment-g enerating function (MGF), to the error probability of an optically pre amplified pulse-position-modulation (PPM) receiver assuming Gaussian r eceived pulse shapes. Sensitivity results are presented for various le ngth PPM words and also bit-error-rate curves. The results are compare d with those obtainable from an equivalent on-off keyed nonreturn-to-z ero (OOK NRZ) system and show a possible benefit of 7.1dB. The work de monstrates the potential of such an optically preamplified PPM receive r by giving results which surpass the fundamental sensitivity limit of an optically preamplified OOK NRZ receiver and approach the sensitivi ty of coherent detection systems. In particular, the analysis suggests that, at the STM-4 bit rate of 622Mbit/s, a sensitivity of 25,27photo n/bit is attainable. In addition, a Gaussian approximation is develope d from the variance obtainable from the MGF and the results obtained f rom the Chernoff bound are compared with those obtainable from the app roximation.