In this paper we report a successful experiment of adaptive polarization mode dispersion (PMD) compensation up to second-order in a 40Gb/s optical time-division multiplexed (OTDM) communication system by using two-stage compensator. In the experiment the PMD monitoring technique based on degree of polarization (DOP) was adopted. And the Particle Swarm Optimization (PSO) algorithm was introduced in adaptive PMD compensation, with the desirable features of fast convergence to the global optimum point for compensation without being trapped in local sub-optima and with good robustness to noise. The comparison was made to estimate the performance effectiveness between PSO algorithms with global neighborhood structure (GPSO) and with local neighborhood structure (LPSO). The LPSO algorithm is shown to be more effective to search global optimum for PMD compensation than GPSO algorithm. The ability of tracking changed PMD using PSO algorithm was also investigated. The two-stage PMD compensator is shown to be effective for both first- and second-order PMD, and the compensator is shown to be bit rate independent. The compensation time is within several hundreds of milliseconds. The response time for recovery from a sharp disturbance is about 11ms.
The principle of adaptive polarization mode dispersion compensation based on signal DOP as the feedback control signals was analyzed. A 40Gbit/s adaptive PMD compensation system was developed and the experiment of second-order PMD compensation was performed. The results show that the system can compensate second-order PMD adaptively with the compensated DGD value up to 30ps within 100ms. The PMD monitoring technique adopted in the experiment was based on measuring DOP, which showed the characteristic of bit-rate independence.
Using the simple inverse Flourier transformation of the target channels, we can get the index modulation structure of the sampled period for the sampled fiber Bragg gratins (FBGs). In this method, the enable channels are identical wavelength operation while the unable channels are almost suppressed completely, and the enable and unable channels can be established at will based on the applications. However, the efficient of the sampled FBGs of which the index modulation is obtained by the simple inverse Fourier transformation is very slow. To get a high efficient, a particle swarm optimization algorithm is applied to design the phase of the target spectrum. Combing the two methods together, a high efficient multi-level phase sampled FBG that each channel is suppressed or not at will, can be obtained. We also use the particle swarms optimizations (PSO) algorithm to optimize the pure phase sampling profiles of the sampled FGB. Results showed that a much high efficient of the FBG can be obtained compared with that obtained from the simple inverse Fourier transformation technology. If appropriate grating period chirp and sampled period chirp is applied to such a grating, a novel FBGs based OADM or interleaver devices with dispersion or dispersion slope compensation can be designed.