Magnetic field sensor based on ring WGM resonator infiltrated with magnetic fluid

Abstract

A highly-sensitive magnetic field sensor based on magnetic fluid (MF) infiltrated ring whispering gallery mode (WGM) resonator was proposed and demonstrated in experiment. The resonator was fabricated by attaching a corrosive hollow-core fiber (HCF) to a tapering fiber, which could generate a WGM resonance spectrum. It was firstly demonstrated in theory and experiment that resonance wavelength of the WGM resonator is sensitive to refractive index of medium that infiltrated in the HCF, and the refractive index sensitivity is related to the wall thickness of the HCF. Then, coupling and packaging of the HCF and the tapering fiber were realized by using a simple method, making the sensor robust and portable. When MF was infiltrated in the HCF, since the refractive index of the MF changed with external magnetic field, the WGM resonance valley shifted in wavelength as a function of the magnetic field, which could be used for magnetic field sensing. Experimental results demonstrated that a high sensitivity of 32.4 pm/Gs could be obtained for magnetic field measurement with good linearity. Besides, the proposed sensor behaved simple and robust structure, simple preparation process, low cost, and compact size.