PERFORMANCE OF LINECODED OPTICAL HETERODYNE FSK SYSTEMS WITH NONUNIFORM LASER FM RESPONSE

A simple theoretical analysis for evaluating the performance of lineco ded optical frequency shift keying (FSK) systems is presented, It acco unts for the combined effects of laser phase noise, receiver noise, an d nonuniform FM response of distributed feedback lasers. A close form expression for the random frequency noise due to the combined effect o f laser nonuniform FM response and phase noise is developed, The analy sis Is carried out for three different linecoding schemes, ie, alterna te mark inversion, Miller code or delay modulation, and Manchester cod ing, to investigate the efficacy of the line coding schemes in counter acting the effect of nonflat FM response, Theoretical and simulation r esults show that the sensitivities of linecoded FSK systems are within 0.7 and 0.4 dB for single-branch and dual-branch detection, respectiv ely, at a bit error Probability of 10(-9) relative to the random non-r eturn to zero FSK with flat FM response.