A simple analysis technique for heterodyne ASK and FSK lightwavesystems

摘要

An analysis technique for amplitude-shift-keyed (ASK) andfrequency-shift-keyed (FSK) coherent optical communication systems ispresented. The analysis accounts for the phase noise of the transmitterand the local oscillator (LO) lasers, and for additive Gaussian noisestemming from the shot noise and thermal noise. The analysis yields aclosed-form estimate of the bit error rate (BER) as a function of the IFfilter bandwidth, laser linewidth, and bit rate. The accuracy of theanalysis is within 0.4 dB of the sensitivity predicted by more accuratetechniques for ASK, and 0.2 dB for FSK, for optimum and nearly optimumreceivers. This result is valid for a wide range of laser linewidthsfrom 0% to 256% of the bit rate. The Gaussian approximation technique isshown to yield reasonably accurate estimates of the optimum IF bandwidthand of the sensitivity penalty stemming from the phase noise