Self-Phase Modulation in Semiconductor Optical Amplifiers: Impact of Amplified Spontaneous Emission

This paper presents a detailed theoretical and experimental study of the impact of amplified spontaneous emission (ASE) on self-phase modulation in semiconductor optical amplifiers (SOAs). A theoretical model of pulse propagation in SOAs is developed that includes the ASE power and its effect on gain-saturation and gain-recovery. We study the impact of ASE on the nonlinear phase shift, frequency chirp, spectrum, and shape of amplified picosecond pulses at a range of drive currents. We verify our predictions experimentally by launching gain-switched picosecond pulses with 3-mW peak power into a commercial SOA exhibiting 9-ps gain-recovery time at a current of 500 mA. Understanding the impact of ASE on SOAs is important for applications that employs SOAs for all-optical signal processing and as data-network amplifiers.