All-optical modulation format conversion from frequency-shift-keying to phase-shift-keying

We have realized a novel optical modulation format conversion using double-sideband suppressed-carrier modulation. An optical wideband frequency-shift-keying (FSK) signal, generated by an external FSK modulator, can be directly converted into an optical phase-shift-keying (PSK) signal, where the FSK signal having two spectral components was fed to an optical intensity modulator followed by an optical bandpass filter. Optical frequency of the FSK signal was mapped into optical phase of the bandpass filter output whose phase deviation depends on a chirp of the FSK signal. We demonstrated modulation format conversion from FSK to PSK at 10 Gbps, by using a high-speed optical FSK modulator and a dual electrode Mach-Zehnder intensity modulator.