Abstract:
Capacity of multi-wavelength 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. Even with the presence of the nonlinear effects, the transmission capacity can further be enhanced by using polarization division multiplexing (PDM) and polarization diversity optical transmission. In this dissertation investigations are carried out to evaluate the performance of PDM and polarization diversity optical transmission systems with optical quadrature phase shift keying (QPSK) modulation using homodyne and self-coherent optical receivers to achieve higher sensitivity. Novel analytical approaches are developed to find the close-form expressions for the signal and cross-polarization induced crosstalk at the output of PDM homodyne coherent and self-coherent receivers. The expressions for bit error rate (BER) are also developed considering the influences of the above channel limitations. Results are evaluated by numerical computations and also by simulations to validate the analytical approaches.
Analytical expressions for signal to crosstalk and noise ratio (SCNR) and BER are also developed considering the effects of polarization mode dispersion (PMD), group velocity dispersion (GVD) and cross-polarization induced crosstalk and angular misalignment at the receiver due to random rotation of the signal state of polarization (SOP) of polarization diversity optical receivers. The probability density function (pdf) of the phase fluctuation due to combined effect of GVD and PMD is determined using non-central moments of the random phase fluctuations due to above system imperfections at the receiver output which are evaluated by numerical simulation. The pdf is used to evaluate the average BER under the influence of different channel impairments with different receiver structures. Power penalties suffered by the system due to XPM, cross-polarization induced crosstalk, GVD and misalignment of principal SOP are numerically evaluated at a given BER of 10-9. Analytical results are validated by results obtained by simulation. Further, new approach to monitor the effect of PMD is presented based on post-detection RF tone power at the output of PDM receiver. Simulations and experiments of optical QPSK transmission system are also carried out to monitor the effect of PMD based on the received RF tone power without and with PDM. Results are found for both PDM and single channel QPSK systems. The findings of this dissertation will be useful for design of optical transmission system with polarization division multiplexing and polarization diversity reception using HCD and SCD receivers.
