Measurement of self-phase modulation in a semiconductor optical amplifier using a Mach-Zehnder interferometer

Semiconductor optical amplifiers (SOAs) are very attractive for fiber optical communication systems, because of their small size, low power consumption, and optical gain. However, nonlinearities caused by signal induced carrier density modulation must be taken into account. Nevertheless, for some applications like in Sagnac interferometer, they can be used as an useful effect, for optical switching or wavelength converter. Theoretically, they appear as frequency deviation peaks at the leading and trailing edge of a pulse travelling through SOAs. An experimental set-up is used, in order to measure this effect confirming theoretical predictions. Furthermore, signal induced phase shift dependence on bias current of the SOA is presented.