Polarization Mode Dispersion Compensation System Research Articles

Applying the data fusion method to evaluation of the performance of two control signals in monitoring polarization mode dispersion effects in fiber optic links

With increasing distance and bit rate in fiber optic links the effects of polarization mode dispersion (PMD) have been highlighted. Since PMD has a statistical nature, using a control signal that can provide accurate information to dynamically tune a PMD compensator is of great importance. In this paper, we apply the data fusion method with the aim of introducing a method that can be used to evaluate more accurately the performance of control signals before applying them in a PMD compensation system. Firstly, the minimum and average degree of polarization (DOPmin and DOPave respectively) as control signals in monitoring differential group delay (DGD) for a system including all-order PMD are calculated. Then, features including the amounts of sensitivity and ambiguity in DGD monitoring are calculated for NRZ data format as DGD to bit time (DGD/T) varies. It is shown that each of the control signals mentioned has both positive and negative features for efficient DGD monitoring. Therefore, in order to evaluate features concurrently and increase reliability, we employ data fusion to fuse features of each control signal, which makes evaluating and predicting the performance of control signals possible, before applying them in a real PMD compensation system. Finally, the reliability of the results obtained from data fusion is tested in a typical PMD compensator.

Research on PMD compensation in high-speed optical fiber communication network

In order to overcome imperfections in manufacturing process, mechanical stress or temperature which can cause birefringence with difference in the phase and group velocities of the two orthogonal polarized modes, a new adaptive polarization mode dispersion (PMD) compensation method in 80 Gbit/s optical communication is proposed. In the experiment of this paper, through the control of digital signal processor (DSP), the dithering particle swarm optimization (PSO) algorithm is used to extract the best degree of polarization (DOP), the DOP is utilized to compensate three stage PMD of optical fiber. The experiment results show that the high speed polarization monitoring unit seriously decreases the polarization monitoring time for adaptive PMD compensation and makes the PMD compensation system work effectively.

Improved PSO Based Feedback Control Algorithm in the Application of PMD Compensation System

An feedback control algorithm based on improved particle swarm optimization algorithm for adaptive polarization mode dispersion (PMD) compensation has been proposed. In order to achieve the global optima of DOP, the aggregating index has been adjusted to maintain the global searching capability of PSO. The immune clone principle has been adopted to maintain the diversity of the swarm. Compared the eye diagram before and after compensation, the opening of the eye diagram has been improved obviously, which demonstrated the effectiveness of the IPSO based feedback control algorithm..

New control algorithm for automatic PMD compensation system

A new cross-tracking method is proposed to improve the convergent speed of the control algorithm in real-time polarization mode dispersion (PMD) compensation systems. The cross-tracking algorithm is compared with the previously used dithering particle swarm optimization (DPSO) and gradient particle swarm optimization (GPSO) algorithms, and it is proven to offer the best performance among the three algorithms. The transmission of a 43-Gb/s differential quadrature phase-shift keying (DQPSK) signal over a 1 200-km fiber span using a compensator based on digital signal processing (DSP) is demonstrated via the cross-tracking algorithm.

Analysis of Degree of Polarization as a Control Signal in PMD Compensation Systems Aided by Polarization Scrambling

The performance of degree of polarization (DOP) is investigated as a control signal in polarization-mode dispersion (PMD) compensation systems aided by polarization scrambling. The relation between the input and output polarization states of a signal propagating through a polarization scrambler and a PMD-induced optical fiber is described by a 3 times 3 Stokes transfer matrix. The average DOP of the output signal over a period of polarization scrambling is derived as an alternative to the conventional DOP-based control signal, i.e., minimum DOP. In the presence of first- and all-order PMDs, the performance of the average and minimum DOPs in monitoring of differential group delay (DGD) for different data formats (i.e., RZ and NRZ) is evaluated. The performance of the two control signals are further investigated by calculating the outage probability of a feedforward first-order PMD compensation system. The results show that the average DOP outperforms the minimum DOP and also gives a wider DGD monitoring range.

Automatic polarization-mode dispersion compensation by a particle-swarm optimization method and adaptive dithering algorithm

We demonstrate multistage polarization-mode dispersion (PMD) compensation numerically and experimentally by using a particle-swarm optimization (PSO) algorithm in the searching process and an adaptive dithering algorithm in the tracking process. PMD compensation in a 40-Gb/s nonreturn-to-zero (NRZ) system based on the algorithm with a global neighborhood structure in one channel and in two channels is explored numerically. The numerical results show that the PSO algorithm is very efficient for multiple-degree-of-freedom PMD compensation systems. For high-PMD compensation the algorithm with a local neighborhood structure is more efficient than that with a global neighborhood structure. We also investigate the performance of PSO in an experiment, where 4-degree-of-freedom PMD compensation is demonstrated in 10-Gb/s NRZ and return-to-zero (RZ) systems. The total search time with the PSO algorithm is several hundred milliseconds, and the response time for the compensator to recover from a sudden disturbance is less than 20 ms.

An adaptive first-order polarization-mode dispersion compensation system aided by polarization scrambling: theory and demonstration

An adaptive polarization-mode dispersion (PMD) compensation system has been developed to cancel the effects of first-order PMD by producing a complementary PMD vector in the receiver. Control parameters for the PMD compensation system comprised of a polarization controller and a PMD emulator are derived from the nonreturn-to-zero (NRZ) signal in the channel to be compensated. Estimates of the link's differential group delay (DGD) and principal states of polarization (PSPs) based on this signal are reliable when the signal power is equally split between the link's two PSP's; however this condition cannot be assumed. To meet this requirement, we scramble the state of polarization (SOP) of the input signal at a rate much greater than the response time of the PMD monitor signal so that each sample represents many different SOP alignments. This approach allows the effective cancellation of the first-order PMD effects within an optical fiber channel.