The principle of stimulated emission is primarily used by a semiconductor optical amplifier for amplification of an optical information signal, as the case with laser operation. The figure below depicts the principle of operation of SOA.

Advantages of SOAs

The optical gain provided by SOAs is relatively independent of wavelength of the incident optical signal.

The injection current serves as the pump signal for amplification, not another laser.

Due to compact size, SOAs can be integrated with several waveguide photonic devices on a single planar substrate.

They use the same technology as diode lasers.

SOAs have the ability to operate at operating wavelengths of 1300 nm and 1550 nm with wider bandwidth (up to 100 nm).

They can be configured and integrated to function as pre-amplifiers at the optical receiver end.

SOAs can function as simple logic gates in WDM optical networks.

Limitations of SOAs

SOAs can deliver output optical power up to a few mW only which is usually sufficient for single channel operation in a fiber–optic communication link. However, a WDM system may require up to a few mW power per channel.

Since coupling of the input optical fiber into the SOA integrated chip tends to induce signal loss, SOA must provide additional optical gain in order to minimize the impact of this loss onthe input facet of the active region.

SOAs are highly sensitive to polarization of the input optical signal.

They generate higher noise level in the active medium.

In case multiple optical channels are amplified as required in WDM applications, SOAs can produce severe crosstalk.