Bojun Yang

Particle swarm optimization used as a control algorithm for adaptive PMD compensation

We introduce particle swarm optimization (PSO) into adaptive polarization-mode dispersion (PMD) compensation in a 40-Gb/s optical time-division-multiplexing communication system. In the searching process for automatic PMD compensation, the PSO algorithm has the merits of rapid convergence to the global optimum, without being trapped in local suboptima, and good robustness to noise. In this letter, we describe how to implement PSO as a component of a control algorithm in adaptive PMD compensation. Performance comparisons between global and local versions of PSO were carried out theoretically and experimentally. We also demonstrate that a time-varying PMD can be successfully tracked using the PSO technique.

Automatic PMD compensation experiment with particle swarm optimization and adaptive dithering algorithms for 10-gb/s NRZ and RZ formats

We demonstrate a 10-Gb/s polarization-mode dispersion (PMD) compensation experiment by using a 4-degree of freedom compensator for both NRZ and RZ formats. The particle swarm optimization method is used as the searching algorithm and an adaptive dithering algorithm is employed in tracking process. The results show that the searching process is finished within several hundreds of milliseconds and the response time for the compensator to recover from a sudden disturbance is less than 20 ms.

Three-stage polarization mode dispersion compensator capable of compensating second-order polarization mode dispersion

The impacts of polarization-dependent dispersion on systems are investigated briefly, based on which a three-stage polarization mode dispersion compensator has been proposed to compensate polarization-dependent chromatic dispersion and the principal states of polarization rotation rate at the same time. The two possible operating points of this compensator are also proposed. Numerical results show that the maximum tolerable polarization mode dispersion value after three-stage compensation has been improved by 17% per bit slot compared with using a two-stage compensator.

The effects of different dispersion compensation ratios on nonlinear single channel and WDM systems

The effects of the compensation ratio with dispersion post-compensation on nonlinear single channel and WDM systems with 10 Gb/s per channel are numerically investigated. When the transmission signal per channel is 10 Gb/s RZ pulse and the amplifier span is 50 km, proper undercompensation can enhance the performance of the nonlinear single channel system and the nonlinear WDM system. But the enhanced distance of the nonlinear WDM system is not as obvious as that of the single channel system, because the cross-phase-modulation effect plays an important role in the nonlinear WDM system.

Analytical theory for pulse broadening induced by all-order polarization mode dispersion combined with frequency chirp and group-velocity dispersion

We derive an analytical expression for the expected root-mean-square (rms) pulse broadening with considering the combined effects of all-order polarization mode dispersion (PMD), group velocity dispersion (GVD) and frequency chirp. It is shown that two commonly used first-order PMD compensators lose their efficiency quickly with chirp parameter increasing if GVD is ignored. When GVD is added, prechirp technique is helpful for the enhancement of PMD tolerance for both uncompensated case and first-order compensators when GVD and PMD coefficient satisfy some special relationship.

Comparison of the Performances of NRZ and RZ WDM Systems with Long Amplifier Spacing and Dispersion Compensation

The performances of NRZ and RZ in nonlinear WDM systems are compared by means of numerical simulation. Self-phase modulation, cross-phase modulation, group velocity dispersion, stimulated Raman scattering and other effects are included in our numerical model. The numerical results show that the performance of NRZ in the nonlinear WDM with dispersion compensation is better than that of RZ. The full dispersion compensation does not well improve the performance of RZ transmission in nonlinear WDM.

The effects of channel separation, input power and cross-phase modulation on nonlinear WDM systems with dispersion compensation

This paper analyzes the effects of channel separation, cross-phase modulation and input power on nonlinear WDM systems with conventional single-mode fiber combined with dispersion-compensating fiber. The conclusions are: (i) The performance of different signal channels depends on the input power and the channel separation. (ii) In general, the shorter the channel separation, the shorter the maximum transmission distance; the larger the input power, the shorter the maximum transmission distance. (iii) Cross-phase modulation plays an important role on the performance of nonlinear WDM with DCF compensation.

The Influence of PMD on the Degree of Polarization Ellipsoid

The effect of PMD on the three axes of the degree of the polarization (DOP) ellipsoid is discussed in the different modulation format systems. The results show that the minimum axis of DOP ellipsoids is suitable for a feedback signal in the compensation systems. In addition, the mitigation performances of DPSK formats are superior to that of OOK format.

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system. A new idea is put up to design a quick single-photon detector. This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs). All of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal. The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector. The single-photon prompt detection can come true for high repetition-rate pulses. The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.

Real-time PMD monitoring using a DOP ellipsoid based on PSO technique

DOP ellipsoid can be used as PMD monitoring signal for automatic PMD compensation. We introduced the particle swarm optimization algorithm into obtaining real-time DOP ellipsoid with high precision only by 100 sampling SOP data.