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. |