NRZ-DPSK to RZ-BPSK all-optical format conversion using optical filter and SOA-MZI

We propose and demonstrate all-optical format conversion from nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) to return-to-zero binary PSK (RZ-BPSK) at different bit-rates, using a tunable band-pass filter, a semiconductor optical amplifier (SOA) fiber ring laser and an SOA based Mach-Zehnder interferometer (SOA-MZI). The filter acts as the DPSK demodulator and also as the differential decoder. It converts the NRZ-DPSK into the RZ signals, which is equivalent to the data information before differential encoding. The SOA fiber ring laser is used to recover the clock signals from the demodulated RZ signals at different bit-rates. In the subsequent SOA-MZI, the RZ signal is used to modulate the recovered clock signal which is synchronous to the demodulated RZ signal. Thus, the amplitude information is encoded onto the phase of the clock signal, through cross gain modulation (XGM) and cross phase modulation (XPM) effects in the SOA-MZI. The converter can be operated at flexible bit-rates and used as the interface between long-haul WDM and OTDM systems.