Analytical modeling and analysis of a coherent OFDM-WDM optical fiber transmission system with raman amplifier in presence of fiber nonlinearities

Abstract

Performance of optical transmission systems are very much limited by fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and crosstalk due to optical amplifiers. Analytical model is developed of a WDM optical fiber link with Raman amplifier and analytical expressions for overall field distribution along the fiber is developed considering SRS, ASE and XPM. Crosstalk power induced by SRS, XPM and ASE is derived and optical signal to crosstalk power ratio (OSCR) at a given distance along the fiber is derived analytically. The performance of optical receiver is found in terms of electrical signal to crosstalk plus noise ratio (SCNR) and bit error rate (BER) taking into considerations crosstalk due to above nonlinear effects, shot noise, thermal noise and beat noise components arising out of beating of signal and crosstalk during photodetection process. A model for a coherent OFDM (CO-OFDM) fiber link with Raman amplifier (RA) at a single optical wavelength is proposed considering OFDM subcarrier modulation followed by optical intensity modulation and coherent detection. Analytical expression is developed for OSCR at the output of the fiber link taking into considerations the crosstalk induced by SRS, XPM, ASE and beat noise components. Receiver analysis is carried out in terms of BER and performance results are evaluated numerically for different system parameters like number of OFDM subcarriers, fiber length, data rate etc. Optimum system parameters for a given BER is evaluated. Results are validated by comparison with experimental results published in literature.

Further, a model for a CO-OFDM-WDM long haul optical fiber system with RA is developed and field distribution along the fiber is found considering RA induced crosstalk and effects of fiber nonlinearities. Analytical expressions are developed for OSCR and OSNR at a given transmission distance. Further, receiver analysis is carried out and performance results are evaluated in terms of electrical SCNR and BER for different data rate, fiber length, number of wavelength channels, number of WDM channel, number of OFDM sub-channel and other system parameters. Power penalty suffered due to SRS induced crosstalk, ASE noise and the effects XPM is numerically evaluated at a given BER. The outcome of this research with provide analytic al tools for performance evaluation and derived of optical fiber transmission system using OFDM and WDM with Raman amplifier.