Method for determination of the principal modes in a few-mode optical fiber using a multibranch DOE

We propose a method intended for reconstructing a fiber propagation matrix in few-mode regime and determination of the corresponding principal modes. The method is based on the idea of extending the Jones Matrix Eigenanalysis (JME) technique, which provides.the determination of both the propagation matrix and the principal states of polarization in a single-mode fiber, to the basis of spatial modes in a few-mode fiber. We propose that a multibranch diffractive optical element should be used as a correlation filter, which can be implemented by means of a spatial light modulator (SLM). The efficiency of the proposed method is numerically verified for a stepped-index few-mode fiber in the strong coupling regime.