Wavelength division multiplexing (WDM) is a new technology for migrating the core optical transmission network to higher bandwidths. The ability to transfer multiple optical carriers over the same span of fiber promises almost unlimited bandwidth. The multiplexer (mux)/combiner couples together different wavelengths then combines them for transmission into a single mode fiber maintaining the wavelength integrity of each optical carrier. The receive side employs a demultiplexer (demux) or splitter to distribute the optical signal to the wavelength selectors. These devices define the optical bandwidth to recover the original tributary and remove unwanted components. The interaction between adjacent channels in a WDM line signal is Crosstalk between adjacent channels. Because of the closeness of channel spacing, the contents of one channel can cause interference in an adjacent channel. Due to which signal get distort or introducing errors at the receiver after demultiplexing and channel selection. The high WDM system is used for high data rates has range from 2.5 Gbits/s to 40 Gbits/s and channel spacing is 200 GHZ, 100 GHZ, 50 GHZ, 25 GHZ. We can used 2.5 Gbits/s and 10.52 Gbits/.