Mode-dependent loss characteristic of few-mode magneto-optic Fabry–Pérot configuration with application in sensing and mode-demultiplexing

Optical propagation and reflection behaviors of guided waves in few-mode magneto-optic fibers (FM-MOFs) are investigated by a complete eigenmode representation independent of coordinate systems E mn sl . The variations of eigenmode states, including topological charge of orbital angular momentum (OAM) and circular state of polarization, with the optical propagation and magnetization direction are analyzed by theory and simulation. A few-mode magneto-optic Fabry–Pérot (MOFP) configuration is taken into account for magnetic-field sensing and mode demultiplexing. For the case with m = n = 1 , the magnetization sensitivity of mode-dependent loss (MDL) can reach 9.3 dB/(kA/m) for the yttrium-iron-garnet-based MOFP fiber with a length of 0.1 m and a reflectivity of 0.8. Under appropriate bias magnetic field, the MOFP device may not only be used to compensate the mode dependency of other devices, but also act as a mode demultiplexer, with a mode extinction of 15 dB.