Investigation of magneto-optical properties of magnetic fluid for fiber optics applications

Abstract

Magnetic fluid (MF) is a novel kind of magneto-optical functional material that possesses diverse magneto-optical properties such as tunable refractive index, birefringence effect, dichroism effect, Faraday effect, field dependent transmission property and so on. It can serve as the magnetically sensitive material playing the key role in magnetic field sensors and magneto-optical devices. There were many reported photonic devices based on MF in the literatures. This thesis focuses on investigating the magneto-optical properties of MF for fiber optics applications. The thesis first reviewed the background knowledge including the MF, optical fibers and optical fiber interferometry. The physical origin of refractive index tunability and birefringence effect of MF are detailedly discussed in preparation for the works in the following Chapters. In the thesis, we have presented three kinds of MF-based magnetic field sensors. The first one is based on the birefringence effect of MF. The MF is inserted into an optical fiber Loyt-Sagnac interferometric configuration in the form of MF film. The sensitivity characteristics of this optical fiber Loyt-Sagnac interferometric configuration are theoretically analyzed and experimentally verified. Finally, a sensitivity of 59.2 pm/Oe is achieved by applying the conclusions drawn from the theoretical analysis to the proposed magnetic field sensing configuration. The second one is based on refractive index tunability of MF and the evanescent field of photonic crystal fiber with air-holes collapse. The evanescent light field interacts with the MF and translates the magnetic field strengths into optical signals. A Mach-Zehnder interferometric configuration formed by cascading two sections of v