Low-coherence interferometry by intensity correlation

‘Low-coherence interferometry’ is an old technique which has had a wide development recently, and is based on the fact that interference with a path difference much longer that the coherence length gives rise to a ‘channeled spectrum’, which can be detected either by a dispersive spectroscope or by a second interferometer with a variable delay. We have tested an alternative way to detect path differences in this kind of interferometry, by analyzing the output intensity fluctuation correlations by a radiofrequency spectrum analyzer, and Fourier transforming the data. This method is suitable for very long path differences. The experiments have been performed with different lengths of single-mode fibre, in Mach–Zehnder and Fabry–Pérot configurations. Received: 30 March 2000 / Revised version: 17 Juli 2000 / Published online: 20 September 2000