This research involves a simulation of four channels coarse wavelength division multiplexing (CWDM) transceiver. The study is done on the effect of the extinction ratio(ER) of the directly modulated laser (DML) diode, the effect of using Erbium doped fiber amplifier (EDFA) in optical fiber links on the quality factor (Q) and the bit error ratio (BER) when using different lengths of fiber. Then a comparison is made between the CWDM network using the amplifier EDFA and the same network without using the amplifier EDFA. In addition, the study is done on the effect of optical fiber length on Q with and without the amplifier EDFA, and we demonstrated the relationship between them diagrammatically.