Effect of source spectral width and its temporal coherence in the interference pattern of a Mach-Zehnder interferometer

A fiber-based Mach-Zehnder interferometer is designed and tested for its phase characteristics by using a CW tunable laser source. The total phase introduced by the interferometer is modeled by including the linewidth of the input source and the fluctuations of its center wavelength, apart from the path difference in the interferometer. The spectral linewidth of the input laser contributing to the observed interference is found to depend on this path difference. This emphasizes the need for optimal path differences to overcome the coherence limitations of the source. We are thus able to extract the extent of phase correlation present in the input source, and hence its temporal coherence characteristics, from the interference pattern.