Long haul and cost effective optical communication networks having data rate of 100Gbps or beyond is emerging research area for researchers in the field of optical communication. This paper presents and explore an analysis of Wavelength Division Multiplexing (WDM) system in a long haul optical network at 16 x 100_Gbps using advance modulation format of Duo Binary Differential Quadrature Phase Shift Keying (DQPSK) with channel spacing of 200GHz using 194.1THz signal. Significant results of low Bit Error Rate (BER) and High-Quality Factor (Q-factor) over 400Km of standard single mode fiber shows the feasibility of the proposed system for high data rate long haul optical networks.