Crosstalk due to optical fiber nonlinearities in WDM CATV lightwave systems

CrosstaIk in a two-wavelength 1550-nm standard fiber system at subcarrier f requencies 50-800 MHz is investigated. The dependence of the crosstalk on s ubcarrier frequency, wavelength spacing, and optical power is measured and analyzed. The observed crosstalk is attributed to three primary mechanisms: stimulated Raman scattering, cross-phase modulation, and the optical Kerr effect combined with polarization-dependent loss. At wavelength spacing gre ater than 9 nm, stimulated Raman scattering dominates. At wavelength spacin g less than 5 nm, the primary contributor can be the optical Kerr effect wi th polarization dependent loss, except at higher modulation frequencies whe re cross-phase modulation also is significant, At even modest (by CATV stan dards) optical power, the crosstalk is as high as -40 to -45 dB.