In this paper, the transmission of signal with DPSK modulation with variation of duty ratio to 66% and 33% is demonstrated and performance of the system is analysed by varying the gain and noise figure value of an EDFA amplifier.Keywords: differential phase shift keying (DPSK), nonreturn-to-zero (NRZ), mach-zehnder modulators (MZM), erbium doped fiber amplifier (EDFA), return-to-zero (RZ), bit error rate (BER)