Degradation of side-mode suppression ratio in a DFB laser integrated with a semiconductor optical amplifier

The degradation of the side-mode suppression ratio (SMSR) in a monolithically integrated distributed feedback laser and semiconductor optical amplifier (SOA) cavity is investigated. An expression is derived that gives the degradation of the SMSR in the case of a perfectly antireflection-coated SOA facet. The amplified spontaneous emission (ASE) backcoupling can have dramatic effects and degrade the SMSR of single-mode devices to unacceptable levels.