We report a novel approach for fast measurements of the modal content in few-mode fibers with an interferometric setup based on a scanning Michelson interferometer. A first experimental proof-of-principle is presented which allows us to re-construct the corresponding modes of the fiber under test by evaluating the numerical Hilbert transformations of the experimentally obtained interferograms. Furthermore, the novel interferometric approach is compared to the spatially and spectrally (S2) resolved imaging approach in terms of acquisition speed. It has a great potential to enable real-time measurements by using all-optical instead of numerical Hilbert transformations and state-of-the-art CCD or CMOS cameras. Furthermore, the proposed all-optical Hilbert transformations are not limited by the Nyquist theorem since the transformations are analog and the fringes must not be resolved, which is an additional major benefit in terms of speed. Thus, the interferometric approach will enable for example real-time monitoring of the higher-order mode suppression during the manufacturing of fiber devices and components.
Michael Steinke, Christian Bremauer, Omar de Varona Ortega, Jörg Neumann, Dietmar Kracht, and Peter Wessels, "Interferometric modal content measurements in fibers (Conference Presentation)," Proc. SPIE 10083, Fiber Lasers XIV: Technology and Systems, 100831S (Presented at SPIE LASE: February 02, 2017; Published: 21 April 2017); https://doi.org/10.1117/12.2249827.5383482388001.
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