An accurate method for measuring the proportions of degenerated spatial modes in fibers

Abstract

As a fundamental issue, determining the proportions of spatial modes in multimode fibers has been continuously discussed over the past few years. People have successfully measured the components of spatial modes with different orders but have rarely addressed the measurement of degenerated modes under these spatial modes. In this article, we propose an interference method to measure the proportions of these degenerated modes. This method is based on the discussion of coherent superposition of degenerated modes in multimode fibers. In the experiment, we randomly generate spatial states in two-mode fibers and simulate these phenomena according to the proposed method, which agrees well with the experiment. This measuring method improves the accuracy of mode measurement from mode groups to degenerated modes and may provide a unique perspective for the field of multimode fibers.