Characterizing a 14 × 14 OAM mode transfer matrix of a ring-core fiber based on quadrature phase-shift interference.

The transfer matrix of light propagating in fibers can quantitatively elucidate the mechanisms of mode coupling, thus having important implications for the knowledge such as the mode division multiplexing communication link characteristics in fibers. However, most methods for measuring the transfer matrix require a prior knowledge of the launched modes at the input and a complex optical system for the characterization at the output of the fiber. In this Letter, we use an interferometric approach for decomposing orbital angular momentum (OAM) modes of the output beams from a ring-core fiber, thereby processing a 14×14 OAM mode transfer matrix of the fiber with merely a camera imaging the mode field at the output of the fiber. The suitability of such a method is validated by the beam reconstruction. Thus, this method is crucial for characterizing the fiber transfer matrix with promising features of fast response and simple operation.