Optic fibre is one of the most popular medium used in communication to propagate light through a glass (wave guide). In the future communication industry it require high data rate and Wave length multiplexing (WDM) and densewave lengthmultiplexing (DWDM) are the best alternative type of optical fibre that can carry multiple services with high data rate. Right this time WDM/DWDM is more preferable due to several advantages, but it has also several limitations of non-linear effects like Self-Phase Modulation (SPM), Cross-Phase Modulation (XPM) and Four-Wave Mixing (FWM) may occur. In this thesis, the WDM 100GHz channel spacing /DWDM 50GHz channel spacing are analysed with the following input parameters; varying Bit rate (5, 10 and 15) Gb/s,varying input power (0, 5 and 10)dBm and with Bessel optical filter (BOF) and Gaussian optical filters (GOF) at Optical fiber length (0-60) km without EDFA and (0-180)km with EDFA has been done to investigate the maximum bit rate by reducing channel over lapping probability . In this research analysis the architecture model that uses two separate DWDM, DWDM1 and DWDM2 combined with power combiner and the channel spacing between the twomultiplexers (MUX) is 100GHz has good performance than other models. Opti-System simulator is used for verifying various measurements, plots and all other graphical analysis. Keywords: BER, channel spacing, DWDM, WDM, FWM, OSNR, Q-Factor, Opti-System.