Theoretical analysis for effect of facet reflections on amplification and noise characteristics in semiconductor optical amplifier

In most cases, the semiconductor optical amplifiers (SOA) are used with anti-reflection coating for its facets to avoid laser oscillation. Providing effects by residual reflection at the facets are theoretically analyzed. When the reflection by the back facet exists, the SOA shows larger amount of the amplified spontaneous emission as well as the larger intensity noise. When the reflection by the front facet exists, amplification ratio is reduced. However, the spectral linewidth of the inputted optical signal is never changed by amplification in the SOA, even the facets have residual reflectivities