Abstract
Error-rate degradation in a four-channel frequency-shift keying (FSK) direct-detection scheme with equal input power per channel into a dispersion-shifted fiber is discussed. Error-rate performance with and without all other channels modulated was measured. The results show that the error rate is more degraded when the other channels are modulated than when they are unmodulated. This feature is different from that in FSK-alternate-mark-inversion heterodyne detection, indicating that the influence of four-wave mixing (FWM) on error-rate performance is dependent on the detection scheme. Based on the experimental results, error-rate performance in a 100-channel system is also estimated.<>