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This document Designing system with Free-space optical (FSO) communication can supply high-speed digital data linkages to rural regions where geography, setup costs, and groundwork safety are major obstacles. Transmission impairments and space loss could be considered major challenges for handling the FSO system. This work has been designed and analyzed a system based on the combination of Dual Polarization Differential Quadrature Phase Shift Keying (DP-DQPSK) and Dense Wavelength Division Multiplexing (DWDM) using the Direct Detection (DD) technique. The proposed system has been utilized with a hybrid transmission medium of Single-Mode Fiber (SMF) with a fixed length of 60 km and FSO with varied lengths of (5, 7, and 9) km. The system was designed with Optisystem software 18 and consist of 64 channels and 14 Gbps of data rate per channel to make the system 5G communication compatible, 3.5 GHz RF electrical signals have been used to modulate the optical carrier. The channels 1,6,12, …,64 were selected as samples among all channels to be investigated and analyzed along with four different atmospheric weather conditions. Additionally, the proposed system is designed to investigate based on different weather attenuation that affected the parameters of Quality Factor (QF) and Bit Error Rate (BER). The significant advantage of the proposed system by using the DD technique, is no reference wave required. Hence, make the system become less complex and possible to be implemented and tested via different weather conditions. Results obtained indicate reverse relation between the QF and both the FSO distance and attenuation. While, BER based parameters showed a direct relation. For light air and haze, the results showed that the system have higher reliability for all the three investigated FSO distances.  For the medium haze, the system has shown capability to transfer as far as 7 km. And for the rain condition, the system capability was set to 5 km.

The demonstration of a higher data rate transmission system was a major aspect to be considered by researchers in recent years. The most relevant aspect to be studied and analyzed is the need for a reliable system to handle nonlinear impairments and reduce them. Therefore, this paper examines the influence of Four-Wave Mixing (FWM) impairment on the proposed high data rate Dual polarization-Differential Quadrature phase shift keying (DP-DQPSK) system using the Optisystem software. In the beginning, the impact of varied input power on the proposed system's performance was evaluated in terms of QF and BER metrics. More power is used to improve system performance. However, increasing power would raise the FWM effects. Accordingly, a −10 dBm input power and the proposed system are used to reduce the impact of FWM. Additionally, a hybrid amplification method is proposed to enhance system performance by utilizing the major amplification methods of erbiumdoped fiber amplifier (EDFA): semiconductor optical amplifier (SOA) and Radio optical amplifier (ROA). The evaluation demonstrates that the OA-EDFA outperformed the other two key amplification techniques of (EDFA-SOA) and (EDFA-ROA) in improving Quality factor (QF) and Bit error rate (BER) system results for all distances up to 720 km. Consequently, the method contributes to minimizing the impact of FWM. In the future, other forms of nonlinearity will be investigated and studied to quantify their impact on the proposed system.