ABSTRACT
Semiconductor Optical Amplifier (SOA) is a kind of optical amplifier of which optical gain is provided by the stimulated emission in semiconductor where the population of free carriers is inverted. The development of SOA was closely related to that of the semiconductor laser. SOAs are compact, electrically pumped devices. Additionally, SOAs can be integrated monolithically with laser diodes, optical modulators, photodiodes, and passive waveguides including multi-mode interference couplers and arrayed waveguide devices. High chip–fiber coupling losses make SOA performances poor because the fiber-to-fiber gain decreases due to the chip–fiber coupling losses at both the input and the output sides. Polarization insensitive SOAs can be used as linear optical amplifiers, optical gate switches, and nonlinear elements for all optical processing. Multi-channel amplification is required for inline amplifiers in wavelength division multiplexing systems. When SOAs are used as the multi-channel amplifiers, system penalties can be caused due to inter-channel crosstalk and nonlinear distortions in the saturated regime.
