Enhancement of the sensitivity of magneto-optical fiber sensor by magnifying the birefringence of magnetic fluid film with Loyt-Sagnac interferometer

•Sensitivity is greatly enhanced by 2–3 orders of magnitude.•Loyt-Sagnac interferometer is employed in the configuration.•Birefringence effect instead of refractive index of magnetic fluid is applied.•Theoretical analysis of the Sagnac-interferometer-based model is given. Magnetic field sensor by combing magnetic fluid and optical fiber Loyt-Sagnac interferometer is proposed. The sensor takes advantage of the birefringence effect of magnetic fluid. The relative small birefringence of the magnetic fluid is ‘magnified’ by the properly designed optical fiber Loyt-Sagnac interferometric structure. As compared to the reported MF-based sensors, the achieved sensitivity of the proposed sensor is 592.8pm/Oe, which is enhanced by 1–3 orders of magnitude.