Pre-detection PMD compensation based on feedback of the first and second RF harmonic tones in an optical fiber transmission system

We propose and demonstrate a noble technique for compensation of polarization-mode-dispersion (PMD) effects on polarization division multiplex (PDM) quadrature phase shift keying (QPSK) systems. The technique uses first and second radio frequency (RF) harmonic tone powers to generate the control signal for the compensation. Optical notch filter is used to filter out one of the sidebands of the optical spectrum to remove the effects of chromatic dispersion (CD) from the detected RF spectrum and then power levels of the RF harmonics vary with the PMD induced differential group delay (DGD) alone. The compensation technique takes control signal from the electrical domain by comparing the slopes of the power of the RF harmonic tones. The compensation is found to be very effective covering the window of whole symbol period. After compensation, the maximum electrical power improvements are 0.76 dB and 0.85 dB for data rate of 40 and 160 Gbps respectively.