Chongjin Xie

A comparison between different PMD compensation techniques

We quantify the benefits of using different techniques for compensation of polarization mode dispersion (PMD) in fiber-optic communication systems by means of numerical simulations. This is done both with respect to PMD-induced pulse broadening and in terms of system outage probability for different data formats [nonreturn-to-zero (NRZ) and return-to-zero (RZ)]. Attention is focused on simple and relevant single- and double-stage post-transmission compensators with a few degrees of freedom (DOF). It is generally believed that a PMD compensator with a polarization controller and a variable delay line can only compensate the PMD to the first order. We show, from analytical results, the counterintuitive fact that this scheme can also partially compensate for higher order PMD. We also investigate the benefit of using a polarizer as compensation element where the optical average power can be used as a feedback signal.

Polarization-mode dispersion in high-speed fiber-optic transmission systems

We review recent research related to polarization mode dispersion (PMD) in fiber-optic transmission systems operating at 40 Gb/s and above. We investigate the benefits of using different passive techniques for mitigating the effects of PMD, including more advantageous data formats compared to the conventional nonreturn-to-zero (NRZ) format, soliton transmission, and forward error correction (FEC). We also compare a number of active pre- and posttransmission compensators.

Phase jitter in single-channel soliton systems with constant dispersion

The phase jitter of optical solitons in single-channel communication systems with constant dispersion and distributed amplification is studied in detail. The variational method is used to derive equations that model phase jitter caused by amplifier noise. These equations are solved analytically. Simple formulas are obtained for the phase variance of an ensemble of solitons, which together cover the entire range of practical transmission distances. These formulas are validated for parameters of current interest by numerical solutions of the nonlinear Schroedinger equation.

Soliton robustness to the polarization-mode dispersion in optical fibers

The influences of chromatic dispersion, coupling length, and soliton energy on the soliton robustness to polarization-mode dispersion (PMD) are investigated numerically. We find that both chromatic dispersion and soliton energy have significant effects on the soliton robustness to PMD, and by optimizing chromatic dispersion and soliton energy, soliton pulse broadening can be depressed to within 10% even when the differential group delay is about twice the input pulse width. In addition, a recent experimental result on soliton robustness is numerically verified.

Higher order polarization mode dispersion compensator with three degrees of freedom

We compare several PMD compensation methods, and find that the simple PMD compensator with a variable polarization controller (PC) and a variable time delay line can compensate for not only first, but also higher order PMD.

Influences of polarization-mode dispersion on soliton transmission systems

In soliton transmission systems with polarization-mode dispersion (PMD), random birefringence causes solitons to generate dispersive waves, which degrade soliton transmission systems in two aspects. First, the dispersive waves cause solitons to continuously lose energy, thus induce pulse broadening. Second, the dispersive waves interact with other soliton pulses and cause distortion of a sequence of soliton pulses. Both of these effects induce performance degradation of soliton transmission systems. We study these effects of PMD on both conventional and dispersion-managed (DM) soliton transmission systems. We show that, for conventional soliton systems, although single pulse has robustness to PMD, the interplay between the dispersive waves and solitons would seriously distort a sequence of pulses and make soliton systems worse than linear systems if all other transmission impairments are neglected. We also show that DM solitons are more robust to PMD than both conventional solitons and linear systems due to the enhanced nonlinearity and less sensitivity of DM solitons to perturbations. We further point out that soliton collision-induced polarization scattering causes additional timing jitter and system performance penalty in WDM soliton systems.

Experimental quantification of soliton robustness to polarization mode dispersion in conventional and dispersion-managed systems

We have experimentally quantified the soliton robustness to polarization mode dispersion (PMD) in both conventional and dispersion-managed (DM) soliton systems. Long-term measurements were performed in a computer-controlled system where the PMD characteristics varied randomly with time. Apart from the PMD itself, the performance of both systems depends on the average dispersion while the performance of the DM system also depends on the dispersion map strength. The results show that the robustness can be even more pronounced for DM systems with relatively small dispersion map strengths (0<S<10), compared with conventional systems (S=0), which is an effect of the increased power requirements. The experiments were also compared with numerical simulations.

Robustness of dispersion-managed solitons to the polarization-mode dispersion in optical fibers

The robustness of dispersion-managed (DM) solitons to polarization-mode dispersion (PMD) is studied by numerical simulations. It is shown clearly that DM solitons are robust to PMD, and generally, DM solitons are more robust to PMD than conventional solitons. The robustness of DM solitons depends on both map strength and average group velocity dispersion (GVD). We show that the larger the map strength and average GVD, the more robust are the DM solitons to PMD, which is due to the increased power of DM solitons with the large map strength and average GVD.

Comparison of soliton robustness with respect to polarization-mode dispersion with first-order polarization-mode dispersion–compensated linear systems

Soliton robustness to polarization-mode dispersion (PMD) is compared, both analytically and numerically, with that of linear pulses that use first-order PMD compensation. It is found that soliton robustness to PMD is comparable with first-order PMD compensation and in some cases is even better. The effects of soliton control methods on soliton robustness to PMD were also investigated, and it was found that soliton control methods can significantly improve the solitons robustness to PMD, particularly for long-distance systems.

Polarization-mode dispersion-induced outages in soliton transmission systems

The bit-error-rate (BER) degradation of conventional soliton systems due to polarization-mode dispersion (PMD) is investigated. It is found that the interplay between the dispersive waves generated by PMD and adjacent soliton pulses will seriously degrade the BER of soliton systems, and make them even worse than linear systems if all other transmission impairments are neglected. In order to achieve soliton robustness to PMD, some techniques to eliminate or reduce the dispersive waves must be employed, such as soliton control methods or dispersion-managed solitons. Different systems are estimated and compared in terms of PMD-induced outage probability.