PMD tolerance of 107 Gb/s PM-QPSK system at optimum transmitting power

To provide higher capacity optical fiber networks, a 107 Gb/s transmission system is simulated by using the combined features of polarization multiplexing (PM), quadrature phase shift keying (QPSK) and forward error correction (FEC). The lower tolerance to linear and nonlinear fiber impairments remains a major concern at a higher bit rate. To address the limitations set by the linear impairments, coherent detection of multilevel modulation formats with polarization division multiplexing appears as a promising solution by reducing the symbol rate to one-forth. Electronic dispersion compensation (EDC) and constant modulus algorithm (CMA) are used at the receiver for the linear dispersion compensation and forward error correction (FEC) respectively. Fiber spans each of 90 km are used in this simulation making the transmission length 1980 km. The bit rate of the modulating signals is kept at 26.75 Gb/s and the aggregate transmission rate of 107 Gb/s by utilizing the combined features of PM and QPSK. The power sharing of both the polarization components in the presence of polarization mode dispersion (PMD), fiber nonlinearities and random birefringence is a very important for the system design. In this paper, the PMD tolerance of the system at different transmitting powers with and without the presence of nonlinearities and birefringence are simulated and evaluated in terms of the bit error rate (BER). Transmitting power of 2.518 mW is found as the optimum value for single channel PM-QPSK systems at PMD 0.05 ps/sqrt(km).