Sensitivity Enhancement for Magnetic Field Sensor Using an Optoelectronic Oscillator Based on Fiber Bragg Grating Fabry-Perot Cavity With Acrylate Adhesive

An enhanced sensitivity magnetic field sensor, utilizing an optoelectronic oscillator (OEO) loop, is both proposed and demonstrated. The critical element of the system is a fiber Bragg grating-Fabry-Perot cavity with acrylate adhesive (FBG-FP-AC), which is composed of two identical FBGs and a sandwich structure. Also, the sandwich structure is fabricated by inserting a thin layer of transparent acrylate adhesive between two sections of single mode fiber (SMF). Furthermore, by bonding the FBG-FP-AC with a Terfenol-D piece, the magnetic field sensor head is formed and is employed in the OEO to implement a single passband microwave photonic filter (MPF). When the external magnetic field varies, the central wavelength of FBG-FP-AC is changed, leading to the shift of the center frequency of the MPF. By detecting the variation of oscillating frequency generated in the OEO, an accurate measurement of the magnetic field can be achieved. Given that Young's modulus and Poisson's ratio of the acrylate adhesive are significantly lower than those of silica, the adhesive cavity is significantly lengthened with the applied external magnetic field. Thus, magnetic-field-induced strain of the Terfenol-D can be effectively magnified. The experimental measurement of the sensitivity of the proposed OEO sensor for magnetic fields reaches 4.86 GHz/mT, which is improved about 7.8 dB compared with the traditional FBG-FP-based OEO sensing structure.