Dispersion Compensation for 40-Gb/s Phase-Detected CPFSK Signal Using All-Optical Format Converter for Access Networks

We propose and simulate a dispersion compensator for a 40-Gb/s optical phase-detected signal, which is suitable for access networks. The compensator uses a chirp technique and consists of an asymmetric semiconductor optical amplifier-based Mach-Zehnder interferometer structure and a 40-GHz bandpass filter. A delay-line interferometer demodulator (DLI) is utilized for detection. The compensator converts non-return-to-zero ON-OFF-keying format to continuous-phase frequency-shift keying (CPFSK) so that the produced converted CPFSK format can offer more tolerance against positive and negative residual dispersion compared with the directly generated CPFSK. The chirp with a novel strategy, which is the creation of the out-of-place frequencies, instead of causing signal compression, compensates dispersion. This method can be defined for a CPFSK format composed of the upper sideband (USB) and lower sideband (LSB) signals. Contrary to an optical frequency discriminator receiver, there is no dispersion compensating part in a DLI receiver, but the out-of-place frequencies caused due to the chirp reduce the delay between the USB and LSB signals. We show that the positively chirped converted CPFSK tolerates 120 ps/nm of positive residual dispersion, at a 2-dB power penalty, which is ~ 40 ps/nm more compared with the positive dispersion tolerance of directly generated CPFSK applying a 40-GHz optical bandpass filter.