Transformation of the radiation fluctuations of a low-coherence source in a two-arm interferometer

We consider fluctuations of the radiation of a low-coherence source trasmitted through a two-arm interferometer and transformed by a square-law detector. It is assumed that the output radiation of the source is a stationary Gaussian narrow-band random process. The fluctuation process at the detector output is presented as the sum of the intensity noise and the interference-component noise. We calculate the relationships between the spectral densities of these components and the degree of their correlation for different delays between the interferometer arms. We show theoretically and confirm experimentally that the power of interference-component fluctuations is nonzero even if the delay between the interferometer arms exceeds the correlation time of the process at the source output. © 2000 Kluwer Academic/Plenum Publishers.