Magnetic Field Sensing With Reflectivity Ratio Measurement of Fiber Bragg Grating

A simple magnetic field sensor by using an optical fiber Bragg grating (FBG) cascaded by a cleaved optical fiber end, which is surrounded with magnetic fluid (MF), is experimentally demonstrated. Magnetic field changes Fresnel reflectivity of the fiber end face through refractive index change of the MF, leading to a modulation to the reflection background in the reflection spectrum of the FBG. By comparing intensity difference between the FBG reflection peak, which is not sensitive to the external magnetic field, and the reflection background, magnetic field measurement is achieved successfully. High accuracy and stability can be realized because influence of power level fluctuation of the optical source on measurement results can be eliminated. Furthermore, temperature can be measured simultaneously from reflection wavelength shift of the FBG that is helpful to further compensate the effect of temperature on magnetic field measurement.