Investigation and Suppression of Four Wave Mixing in WDM Systems

Abstract

In optical fiber communication, non-linear effects deteriorate the performance of the communication system. This is because of the condition that degrading effects of non-linearities start to emerge at high launched powers in ultra-dense wavelength division multiplexing and FWM is the major deteriorating issue as it becomes severe at low frequency spacing and at minimum pulse broadening (Dispersion) values. The major emphasis of this dissertation is to investigate the emergence of FWM in WDM system at different distances and to study the behaviour of the system for different WDM channels. Performance of the proposed system is evaluated in terms of Q-factor, BER and FWM. Results revealed that maximum FWM emerges for 3.125 GHz WDM channel spacing and reduced as the spacing between channels increased. Moreover, small optical fiber effective areas exhibit more FWM and also more four wave mixing power induced in dispersion compensation fiber (DCF) as compared to single mode fiber (SMF). Performance analysis of high capacity and high speed WDM has been done by incorporating different line-coding and advanced modulation formats. A 96 channels WDM system is investigated for different distances and validated in terms of Q- factor, BER. Results revealed that DRZ is maximum tolerant to FWM effects and NRZ is maximum prone to FWM. A suppression method for FWM using an optical phase conjugation (OPC) is proposed. Comparison of placements of OPC in two different cases has been done and it is observed that placement of OPC after laser source performs exceptionally well and suppresses FWM with ease of maintenance.