A SELF-SYNCHRONIZED OPTICALLY PREAMPLIFIED DIGITAL PPM RECEIVER FOR OPTICAL-FIBER COMMUNICATIONS EMPLOYING AN IMPROVED SUBOPTIMUM FILTERINGSCHEME

An optically preamplified digital pulse position modulation (PPM) rece iver with an improved electrical domain filtering regime, involving a matched filter in cascade with a pulse shaping network, is rigorously analysed for the first time. Sensitivity results for various length PP M words, bit error rate curves, and an examination of the pulse shapin g network behaviour are presented. In comparison to an equivalent on-o ff keyed non-return to zero (OOK NRZ) system the results show a possib le benefit of 8.1 dB and in fact surpass the fundamental sensitivity l imit of such a receiver, approaching the sensitivity of coherent detec tion. In particular the analysis suggests that at the STM-4 bit-rate o f 622 Mbit/s a sensitivity of 21.54 photons/bit is attainable. Removin g the pulse shaping network incurs a penalty of 1.9 dB for high PPM co ding levels, though it is lower at the optimum coding level. The optic al fibre PPM power spectral density is derived in a simple fashion and the effect of timing jitter on this detection regime is considered fo r the first time, showing a sensitivity penalty of less than 0.9 dB fo r the parameters considered.