Simultaneous Demodulation and Clock-Recovery of 40-Gb/s NRZ-DPSK Signals Using a Multiwavelength Gaussian Filter

We demonstrate a novel optical circuit that has the potential of simultaneous demodulation and all-optical clock-recovery of 40-Gb/s wavelength-division-multiplexing nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) signals. A key device of the circuit is an ad hoc periodic fiber Bragg grating filter that simultaneously demodulates the input signals and seeds a series of clock recovery circuits. We report the complete characterization of the proposed scheme in the whole-band using a tunable transmitter. The DPSK demodulated signals show enhanced resilience to chromatic dispersion with respect to the usual NRZ
_ON-OFF
keying format. On the other hand, the recovered clock signals are very stable and have around 200-fs root-mean-square time jitter.