Semiconductor optical amplifiers: recent advances and applications

Owing to advances in fabrication technology and device design, semiconductor optical amplifiers (SOAs) are evolving as a promising candidate for future optical coherent communication links. This review article focuses on the fundamentals and broad applications of SOAs, specifically for optical channels with advanced modulation formats, as an integrable broadband amplifier in commercial transponders and as a nonlinear medium for optical signal processing. We discuss the basic functioning of an SOA and distortions of coherent signals when SOAs are used as amplifiers. We first focus on the techniques used for low-distortion amplification of phase-modulated signals using SOAs. Then we discuss optical signal processing techniques enabled by SOAs with an emphasis on all-optical wavelength conversion, optical phase conjugation, and phase quantization of coherent optical signals.