Analysis of Intensity and Frequency Noises in Semiconductor Optical Amplifier

A theoretical analysis of the intensity and the frequency noise in semiconductor optical amplifiers (SOA) is given. Amplification of a traveling optical wave is formulated associating with fluctuations on the optical intensity, the optical phase, and the electron numbers based on the classical wave-equation and quantum mechanical modification. Inclusion of the amplified spontaneous emission generated in the SOA is also taken into account. Amounts of noise are expressed in terms of the relative intensity noise (RIN), the spectrum line-width, and the frequency noise. Sensitive dependency of the RIN property on the optical input power is theoretically explained. The RIN increases after passing the SOA, when the optical input power is small enough, but decreases when the optical input power is rather high. On the while, the spectrum line-width is found to be scarcely changed from the input light for conventional operation of the SOA.