Optically preamplified pulse-position modulation for fibre-optic communication systems

A Chernoff bound is applied, by means of a recently developed moment-generating function (MGF), to the error probability of an optically preamplified pulse-position-modulation (PPM) receiver assuming Gaussian received pulse shapes. Sensitivity results are presented for various length PPM words and also bit-error-rate curves. The results are compared with those obtainable from an equivalent on–off keyed nonreturn-to-zero (OOK NRZ) system and show a possible benefit of 7.1 dB. The work demonstrates the potential of such an optically preamplified PPM receiver by giving results which surpass the fundamental sensitivity limit of an optically preamplified OOK NRZ receiver and approach the sensitivity of coherent detection systems. In particular, the analysis suggests that, at the STM-4 bit rate of 622 Mbit/s, a sensitivity of 25.27 photon/bit is attainable. In addition, a Gaussian approximation is developed from the variance obtainable from the MGF and the results obtained from the Chernoff bound are compared with those obtainable from the approximation.