A Two direction transmission system by using DQPSK-based WDM Technique Concerning various Launch power values.

This paper investigates the design and performance analysis of optical transmission systems based on differential phase shift keying (DPSK). The OptiSystem software created a comprehensive framework for maximizing transmission performance over long distances. In this work, a Non-Return-To-Zero (NRZ) coded High Data Rate (HDR) system with Erbium-Doped Fiber Amplifiers (EDFAs) and Dispersion Compensating Fibers (DCFs) is transmitted at 40 Gbps for long-distance transmission. Since DPSK modulators are more resilient to noise, fiber degradation, and chromatic Dispersion, they are typically utilized by high-speed optical networks for long-distance transmission. Bit Error Rate (BER) and Q-factor (QF) metrics were used to evaluate the transmission's performance and quality against a range of input power levels (1 mW, two mW, four mW, and six mW) for transmission lengths ranging from 60 km to 360 km. System performance and input power are related outcomes where signal strength loss and performance are compromised. However, signal quality deteriorates beyond the 180 km transmission distance due to nonlinear effects (self-phase modulation, seen here) that heavily rely on the transmission power level. Therefore, input power and distance transmission are two key factors that we should balance to ensure the quality of signal information. The optimal input power for distances below 180 km is four mW; beyond this distance, the performance degrades sharply. This study offers valuable perspectives on the power-distance vs signal quality trade-off in a DPSK-based optical system. Additionally, it addresses the issue of signal integrity over long-distance optical links and provides implementation guidance for reliable optical networks.