Demonstration of multilevel multichannel optical frequency shift keying (FSK) with cleaved-coupled-cavity (C3) semiconductor lasers

We report the first demonstration of multilevel multichannel (4-level, 2-channel) optical frequency shift keying (FSK) using a newly developed cleaved-coupled-cavity (C3) GaInAsP semiconductor laser operating at ~1.3 ¿m. This is made possible because of the very large frequency tuning rate (~10 A/mA) and frequency tuning range (~150 A) achievable with these new lasers. In addition, such a laser is also shown to operate in a highly stable single-longitudinal mode even under high-speed direct frequency modulation.