Impact of finite frequency deviation on the performance of dual-filter heterodyne FSK lightwave systems

A detailed theoretical analysis is given of the impact of finite frequency deviation on the sensitivity of dual-filter heterodyne frequency-shift-keying (FSK) lightwave systems. The analysis provides closed-form signal-to-noise ratio (SNR) results for estimating the bit-error-ratio (BER) performance of the system. These closed-form results provide an insight into the impact of finite frequency deviation 2 Delta f/sub d/, laser linewidth Delta nu , bit rate R/sub b/, and IF filter bandwidths on the system performance. Simulation results indicate that the accuracy of the approximate theory presented is within 1 dB for linewidths up to 22% when BER=10/sup -9/. It is shown that there is a well-defined relationship between the choice of frequency deviation and the tolerable amount of laser phase noise. The sensitivity degradation can be very severe for a fixed linewidth as the frequency deviation gets smaller.<
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