Theoretical Calculation of Amplified Spontaneous Emission in a Distributed Feedback Laser Diode Assisted by a Semiconductor Optical Amplifier

In this paper, the amplified spontaneous emission (ASE) intensity of a distributed feedback laser diode (DFB-LD) amplified by a semiconductor optical amplifier (SOA) is calculated, and the signal-to-spontaneous emission ratio (SSER) is investigated assuming a wavelength tunable laser. Based on a formulization appropriate for an active layer under a low excitation, the theoretical limit of the SSER of the SOA is obtained, and the SSER including the ASEs from both the DFB-LD and the SOA is numerically calculated. The side mode suppression ratio (SMSR) taking the spectral distribution into consideration is also calculated by expanding the same method.