Optical EngineeringNovel all-optical quaternary amplitude shift keying modulation technique based on cross-gain modulation in a semiconductor optical amplifier
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We present a novel all-optical quaternary shift keying (4-ASK) modulation technique based on the cross-gain modulation in a semiconductor optical amplifier (SOA) of a modulated probe with moderate extinction 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 frequency chirp.