Direct characterization of any linear photonic device

The paper introduced an efficient and simple method for characterizing any multi-mode linear photonic network, by directly measuring all moduli and phases of the matrix that relates creation operators of the input and output modes. The method employs a readily available standard laser source and photodetectors, and eliminates the need for nonclassical interference and single-photon detectors. It requires 2N-1 configurations for measuring all nontrivial parameters of the matrix describing N-mode linear photonic network. The authors used this method to experimentally characterize an integrated device, a 6×6 fused-fibre coupler, and highlight its precision by comparing measured quantum interference patterns with those predicted using the classically-estimated matrix. The obtained interference patterns are in excellent agreement with those predicted by the measured matrix using our method.