Magnetic Field Measurement Based on the Sagnac Interferometer With a Ferrofluid-Filled High-Birefringence Photonic Crystal Fiber

A compact optical fiber magnetic field sensor based on the principle of the Sagnac interferometer is proposed. Different from the conventional ones, a ferrofluid-filled high-birefringence photonic crystal fiber (HB-PCF) is inserted into the Sagnac as a magnetic field sensing element. The refractive index of the ferrofluid filled in the cladding air holes of the HB-PCF will change with respect to the applied magnetic field, and subsequently, the birefringence of the HB-PCF will change, which will affect the shifts of the output interference spectrum in Sagnac. Experiments are carried out to verify the simulation model and the results indicate that the interference spectrum exhibits a red shift with the increment in the magnetic field intensity. The sensitivity of the proposed sensor is up to 0.073 nm/mT for a magnetic field intensity ranging from 10 to 40 mT, while the resolution is 0.001 mT. The proposed magnetic field sensor is attractive due to its compact size, low cost, and immunity to electromagnetic interference beyond what conventional magnetic field sensors can offer.