Investigation of four wave mixing & cross gain modulation in photonic transmission system

Abstract

This thesis focuses on investigation of two nonlinear effects, four wave mixing (FWM) and cross gain modulation (XGM) in photonic transmission system. The work begins with analyzing the performance for both nonlinear effects in multiple channels of wavelength division multiplexing (WDM) transmission system. It addresses the optical transmission system for long haul transmission. The long haul model of 16 channels RZ and NRZ over 1680 km achieved a good signal to noise ratio. The Q-factor decreases with the growth number of channels for both NRZ and RZ format. This study also examined several modulation formats in DWDM system such as RZ, NRZ and duobinary. It is observed that the Q factor degrades slower for RZ in comparison to NRZ. The duobinary has shown the most efficient format due to its nonlinear and band limitation robustness than traditional modulation formats, such as RZ and NRZ. In the observation, FWM and XGM crosstalk degrades the optical signal transmission characteristic of multiplexing signals system significantly. This could be attributed to the higher power launched into the individual channel that led to the nonlinear effects. The work is designed to optimize the performance for the DWDM system considering the limitation imposed by the nonlinear effects. Preliminarily, in-line optical amplifiers and repeaters are noticed to enhance the system. Other approach known as unequal spacing channel allocation in multichannel transmitter is employed to overcome limitation imposes by FWM and XGM. The observation reveals out that unequal channel spacing advances the Q-factor for the system as compared to equal channel spacing. It is also clearly observed that the adoption of duobinary modulation scheme reduces the impact of FWM in DWDM system. The levels of FWM products are reduced by around 12 dB which offer a prominent performance benefit for the system.