The Gordon—Mollenauer Effect in 112 Gbit/s DP-QPSK Systems

Abstract

Gordon and Mollenauer (G-M) proposed in 1990 that the interplay between the nonlinear Kerr effect and amplified spontaneous emission noise can generate an enhanced level of noise and degrade the performance of optical phase-modulated systems. We systematically investigate the G-M effect in 112 Gbit/s coherent dual polarization quaternary phase shift keying (DP-QPSK) systems through comprehensive simulation. The results show that in the presence or absence of inline dispersion compensation, the G-M effect will seriously damage the system performance. Some of our important conclusions are listed as follows: with the increase in the input power into each span, the G-M effect is enhanced simultaneously; the smaller the span length, the stronger the G-M effect caused by more inter-span interaction; for non-zero dispersion-shifted fibers, different coefficient values will cause a similar amount of G-M effect penalty; by comparing the system performance with different dispersion compensation ratios, one can conclude that different residual dispersions of the same magnitude, no matter whether they are under-compensated or over-compensated, can derogate the overall system performance to a similar degree. In brief, the G-M effect cannot be ignored. We also have a short discussion on how to reduce and compensate for the G-M effect in DP-QPSK systems.

Comparison of the compensation effects of fiber nonlinear impairments with mid-span optical phase conjugation between PDM CO-OFDM system and PDM QPSK system

“…[4] Therefore, compensation of fiber nonlinearity is extremely important for achieving better system performance in long-haul transmission. [5,6] Some methods have already been proposed to compensate for nonlinear impairments such as digital back propagation (BP) and pre-compensation, [6][7][8][9] but the computational complexity is relatively high. Optical phase conjugation (OPC) is a well-known process whereby an optical signal is propagated through a nonlinear medium in the presence of a pump beam to create a 'phase conjugate' signal, typically at a shifted frequency/energy.…”