Dj. Blumenthal et Nc. Kothari, COHERENT CROSSTALK IN MULTICHANNEL FSK DD LIGHTWAVE SYSTEMS DUE TO 4-WAVE-MIXING IN SEMICONDUCTOR OPTICAL AMPLIFIERS/, IEEE photonics technology letters, 8(1), 1996, pp. 133-135
Coherent crosstalk in multichannel lightwave transmission systems due
to four-wave mixing in semiconductor optical amplifiers is analyzed. F
or direct detection of evenly spaced frequency channels, coherent beat
ing between signal and intermodulation products occurs when the channe
l bit rate is greater than the laser linewidth. Crosstalk and maximum
input power limitations for an FSK/DD system are calculated for up to
100 channels and channel spacing up to 100 GHz. It is shown that the s
pectral hole burning and dynamic carrier heating gain mechanisms must
be included in addition to carrier modulation and gain saturation to a
ccurately predict both incoherent and coherent crosstalk for channel s
pacing greater than 5 GHz. Degradation of the eye pattern due to coher
ent crosstalk is shown to exceed the incoherent contributions by up to
33 dB even when laser phase statistics and bit pattern statistics are
accounted for. The result of this crosstalk mechanism is a predicted
decrease in the maximum input power per channel to -43 dBm for 100 cha
nnels at 100 GHz channel spacing and -52 dBm for 100 channels at 5-GHz
channel spacing for an optical SNR of 23 dB, representing a decrease
in input power per channel of 25 dBm over incoherent crosstalk limitat
ions alone.