Spinning Fiber/grating Magneto Optical Characteristics Of The Study

Fiber Bragg gratings (FBGs), as a class of important optical passive devices, hasbeen widely applied in the field of optical fiber communication and fiber optical sensing.Recently, some special FBGs, such as magneto-optical fiber Bragg gratings (MFBGs),spun fiber Bragg gratings (SFBGs), have also attracted more and more attention. TheMFBG has a magnetically tunable photonic band-gap, while the SFBG has a low linearbirefringence. The combination of the magneto-optical effect and fiber spun can makefibers or FBGs possess some new features. In this paper, the spun magneto-opticalfibers (SMOFs) and spun magneto-optical fiber Bragg gratings (SMFBGs) areinvestigated by the coupled mode perturbation theory, including the followinginnovations:1. The theoretical model of SMFBGs is established according to the perturbationtheory, including the magneto-optical effect, linear birefringence, fiber spun and gratingstructure, and the resulting coupled-mode equations are also numerically solved byshooting method. This universal model can also be used to analyze many simplifiedwaveguide structures, such as magneto-optical fiber Bragg gratings,polarization-maintaining fibers, spun fiber Bragg gratings.2. The states of polarization (SOPs) of guided optical waves in SMOFs areinvestigated under control of magnetic field, and then several schemes ofelectromagnetic polarization controllers are proposed. It is shown that, the SOPellipticity of output light, which is directly proportional to the magneto-optical couplingcoefficient, can be obtained by appropriately designing the SMOF parameters such aslinear birefringence, spun rate.3. An integrated experimental platform is set up for measuring the linear andnonlinear properties of magneto-optical fibers. To strictly control the SOPs of input light,a new electromagnetic polarization controller is designed and developed. In ourexperiments on the fiber magneto-optical effect and magneto-optical four-wave mixingeffect, the obtained experimental results are consistent with the theoretical analyses.4. The concept of magnetically-induced circular-polarization dependent loss (MCDL) is proposed for analyzing magnetic field sensitivity of SMFBGs. It is shownthat the magnetic field sensitivity of the SMFBGs spun at high speed is the same as thatof the isotropic MFBG; for the case at appropriately low speed, a larger MCDL peakscan be achieved, which is helpful for measurement free of noise. Compared with thepolarization-dependent loss (PDL) method, the MCDL method has a smallerdependency on linear birefringence and is more convenient for the theoretical analysis.