All-Fiber Magneto-Optical Effect Using Nanoparticles Doped Sol-Gel Thin Film Deposited Within Microstructured Fibers

An innovative functionalization method allowing to greatly increase the Faraday effect of microstructured silica-based optical fibers is described. This method relies on the coating of a sol-gel thin film doped with magnetic field sensitive cobalt ferrite nanoparticles around the suspended core of the fiber. By varying the functionalization process parameters, both the film thickness and nanoparticle concentrations can be tailored to optimize the fiber magneto-optical response by a proper adjustment the interaction between the guided mode and the composite film. Experimental measurements in an all-fiber configuration on several samples diversely functionalized show a significant polar magneto-optical effect. A polarization rotation as large as 10° has been measured at 1550 nm when the most efficiently functionalized fiber is located inside a 0.7 cm air gap electromagnet at 1 Tesla. The present method and the developed all-fiber components are very promising candidates for the design of fiber-based sensors of magnetic fields.