| In Propagation modulation in optical fiber will generate dielectric response base  on optic signal frequency, causing spectral modulation having different frequency  from initial frequency. Dispersion is important a part factor in optic  communications system, medium having the character of dispersion will cause  modulation transformation during the propagation.    System Wavelength Division Multiplexing (WDM) is wavelength  multiplex system capable to and spreading it at an optical fiber. At WDM with  optical fiber dispersion effect nonlinear in optical fiber have to be attention. At the  mentioned related to system performance WDM is effect nonlinear from cross  phase modulation (CPM).    Influence CPM to system WDM, is influence to signal intensity probe  available for experiencing different of phase and change of resulted by signal  intensity is optical fiber dispersion value and distance which used in the optic  communications system. CPM also cause incidence of nonlinear crosstalk, which  would be dominant at high frequency. Level crosstalk CPM tend to be ever   greater for     which more and more narrowing, and |D| higher, fluctuation level  crosstalk CPM and optical fiber type which applied also require to be attention to  in  level crosstalk CPM.  |