Novel all-optical quaternary amplitude shift keying modulation technique based on cross-gain modulation in a semiconductor optical amplifier

We present a novel all-optical quaternary shift keying 4-ASK modulation technique based on the cross-gain modulation in a semicon- ductor optical amplifier SOA of a modulated probe with moderate ex- tinction ratio. Experimental demonstrations are presented for 20-Gb/s non return to zero NRZ and return to zero RZ 4-ASK signals with different level distributions and extinction ratios. The dispersion tolerance limitations are investigated. RZ 4-ASK signals show better dispersion robustness with accumulated dispersion range from 240 to 350 ps/nm than NRZ 4-ASK signals due to their reduced fre- quency chirp. © 2009 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.3139297