Analysis and compensation of PMD effects in high speed fiber-optic transmission systems using different modulation and detection scehemes

Abstract

Polarization Mode Dispersion (PMD) is a serious barrier that limits high-speed optical fiber telecommunication systenls. PMD is the result of random birefringence in single-mode fibers along the transmission path. This leads to wavelength-dependent polarization states and phases at the output that eventually results in inter-symbol interference and system performance degradation. In this thesis work, analytical models have been developed to assess and compensate for the effect of PMD considering different modulation and detection schemes; such as, intensity modulation-direct detection (lM-DD), continuous phase frequency shift keying (CPFSK) directand heterodyne detection. Based on the analytical model, the average BER performance of an IMDD optical transmission system is evaluated considering Maxwellian distribution for the differential group delay (DOD). The probability density functions (pdfs) of the random output signal phase fluctuation due to PMD in a CPFSK direct- and heterodyne detection system are analytically developed. The pdf of the signal phase fluctuation is used to evaluate the average BER as a function of mean DOD. As the passive PMD mitigation techniques do not require any dynamically adjusted components, and are bit rate independent, an analytical model of PMD compensation technique is also developed with several Iinecoding to make the single channel optical transmission system more tolerant to PMD. The impact and compensation of PMD in multi-channel optical transmission system is also analytically investigated considering the interaction of cross-phase modulation (XPM) and PMD. XPM changes the state-of-polarization (SOP) of the channels through nonlinear polarization rotation and induces nonlinear time dependent phase shift' for polarization components that leads to amplitude modulation of the propagating waves in a wavelength division multiplexing (WDM) system. The angle between the SOP changes randomly and as a result PMD causes XPM modulation amplitude fluctuation random in the perturbed channel. The pdf of the random angle fluctuation between the SOP of pump and probe due to PMD is determined analytically and the impact of PMD on XPM in a two channel pump-probe configuration is evaluated. To mitigate the PMD in a multi-channel transmission system, a high-birefringent adjustable linear chirped Bragg grating (LCFBO) based PMD compensation scheme is developed and its performance is evaluated using the optimum system parameters. The results of this research work will find applications iri the design of WDM transmission systems in presence of fiber nonlinear effects and PMD.