Development of a new technique to suppress four wave mixing effects in SAC-OCDMA system

Abstract

Multiple access techniques are required to meet the demand for high-speed and large-capacity communications in optical networks, which allow multiple users to share the fiber bandwidth. However, nonlinear effects in optical fiber have become an area of academic research and of huge interest in the optical fiber-based systems. The Four Wave Mixing (FWM) effect is one of the nonlinearities that represent the inelastic scattering that occurs as a result of changes in the refractive index inside the fiber. The FWM occurs when two or more waves are propagated in the same direction in the same fiber. In this thesis, the FWM effect in the Spectral Amplitude Coding (SAC) Optical Code Division Multiple Access (OCDMA) system has been analysed. Many codes have been proposed for SAC-OCDMA systems, such as Optical Orthogonal Code (OOC), Modified Quadratic Congruence Code (MQC), Modified Frequency Hopping Code (MFH), and Double Weight Code (DW). The motivation of this research is to suppress the FWM power in SAC-OCDMA to enhance the system performance. In this research, a new technique is proposed for suppressing the FWM. Moreover, the main idea of the proposed technique is based on adding idle code at the code construction to control the FWM at the sidebands of the signal and filtering the data segment only at the channel part to suppress the FWM power from the original power. This technique is applied for both SAC codes, Random Diagonal Code (RD) and Multi Diagonal Code (MD) because in previous published papers, RD and MD codes were considered recent best performance compared with others. Moreover, in terms of cost, the reported technique is considered cost-effective as the LED light source is used to generate the sideband codes. The results show that the FWM fell approximately 30dB after using the technique. For example, in RD code the FWM power at 40km for fiber length and input power of 15dBm using the SMF fiber type is approximately -55dBm before using the technique; after using the technique at the same parameter values, the FWM power is approximately -90dBm. In other words, with MD code the FWM power before using the technique is approximately -61dBm, after using the technique the value of the FWM power is approximately -81dBm. Moreover, these results have an impact on the Bit Error Rate (BER) well, for example, the value of BER in RD code at the input power -10dBm and 35km fiber length before using the technique was 1.6×10-23, and after using the technique the value of BER became 4.05×10-28. In addition, with MD code the BER value before using the technique was 9.4×10-22, and after using the technique the value of BER was 7.4×10-31.