Simultaneous Monitoring of CD and PMD Using RF Tone Power

We propose and demonstrate a novel method for simultaneous chromatic dispersion (CD) and polarization-mode-dispersion (PMD) monitoring using RF spectrum analysis. In this method, the clock frequency of single sideband of the optical signal is removed by using a narrow bandwidth fiber Bragg grating (FBG) notch filter. After photon detection of the filtered optical signal, the clock tone power of the radio frequency (RF) signal is changed with differential group delay (DGD), which is insensitive to the CD variation. Once DGD value is known, CD value can be estimated from the low-frequency RF tone power after the DGD induced RF power variation is removed. This method enables simultaneous CD and PMD monitoring using detected RF spectrum in the tap line without affecting the received data stream and can be implemented without major modification of the transmitter.