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.