PMD insensitive CD monitoring based on RF power ratio measurement utilizing FBG filter

In this paper, we propose a chromatic dispersion (CD) monitoring technique based on fiber Bragg grating (FBG) filtering and RF power ratio measurement. This method can measure CD value without the effects of polarization-mode dispersion (PMD) and received power for non-return-to-zero (NRZ) phase-modulated signals. A narrowband FBG notch filter is placed at the optical carrier wavelength, such that the radio frequency (RF) clock power decreases with CD. On the other hand, RF clock power increases with CD in the absence of notch filter. By using the RF power ratio of the filtered and non-filtered signals, PMD effects can be eliminated and CD measurement sensitivity will be increased. The simulation results show that the proposed method is efficient for measuring CD in 57-Gbit/s NRZ differential 8-level phase-shift keying (D8PSK) and 38-Gbit/s NRZ differential quadrature phase-shift keying (DQPSK) systems. It is shown that CD measurement sensitivity is increased by 20% to 0.12 dB/(ps/nm) in the CD measurement range (0∼200-ps/nm).