Abstract: The influence of the linewidth enhancement factor and cross-gain modulation on the output power of an interferometer based on a semiconductor optical amplifier (SOA) is analyzed.It is found that two output ports of the interferometer do not reach the minimum and maximum simultaneously due to cross-gain modulation.The interferometer has a working range instead of one working point, and this range has a relation with α.The unbalanced state,working range and extinction ratio are discussed.With the increase of α,the degree of unbalanced and work range decrease,while the extinction ratio increases.Experimental results prove the correctness of theoretical analysis.

Key words: semiconductor optical amplifier, interferometer, cross-phase modulation, cross-gain modulation, linewidth enhancement factor, unbalanced state