The Orbital Angular Momentum Fiber Modes for Magnetic Field Sensing

We have proposed a magnetic field sensor using orbital angular momentum (OAM) L = +/- 1 modes, corresponding to right-and left-handed circular polarization, respectively, in a vortex fiber that supports propagation of these modes. These two circularly polarized OAM modes produce a phase difference under the Faraday effect, which results in the rotation of optical petal when both OAM modes pass through a polarizer. A photodetector is used to detect the intensity variation of the output from the polarizer followed by a slit. By using this method, we have experimentally achieved the superposition of OAM modes with the vector representation of HE21 mode for magnetic field sensing. And a magnetic field sensitivity of 3.31%/T can be reached at the width ratio of the slit to the petal-like pattern of 0.35 +/- 0.02. The obtained experimental results prove the successful implementation of this proof-of-concept principle, showing its potential applications in all-fiber current sensing.