35-dB nonlinear crosstalk suppression in a WDM analog fiber system by complementary modulation of twin carriers

We investigate, theoretically and experimentally, a novel scheme to suppress the crosstalk between wavelengths in wavelength-division-multiplexing (WDM) analog fiber systems. The idea is based on the fact that crosstalk (due to stimulated Raman scattering and cross-phase modulation combined with group velocity dispersion), is caused by the intensity modulation of one channel affecting a second channel in a WDM system. Then, if an auxiliary carrier (twin) with complementary modulation is introduced very close to the first channel, their combined intensity will be constant and there will be no nonlinear crosstalk induced at the second channel. We have obtained up to 35-dB crosstalk reduction at low modulation frequencies, where crosstalk is most severe.