Noise properties and phase resolution of interferometer systems interrogated by narrowband fiber ASE sources

We present the results of a detailed theoretical and experimental study of the noise properties of various interferometer systems interrogated using narrowband spontaneous emission. The filtering effect of the interferometer is shown to introduce periodic structure in the optical noise spectrum with a period, level, and modulation depth that depends on the exact interferometer configuration and implementation, as well as the source linewidth and spectral shape. Our theoretical analysis, based on the assumption of a Gaussian random process model for the inherent source noise is in good agreement with our experimental results. Finally, using a dual Mach-Zehnder interferometer incorporating a frequency shifter, we show that minimum phase sensitivities of a few tens of μrad/√Hz can be achieved for practical values of length mismatch by optimization of the source linewidth, heterodyne frequency, and interferometer birefringence. We believe the approach to be suitable for a broad range of sensing applications