A Novel Fiber Sagnac Interferometer Independent of Eigenfrequency Constraints

Abstract

The fiber Sagnac interferometer (FSI) is widely used in aerospace, inertial navigation, weak magnetic field measurement, and other critical applications. This article proposes a novel FSI model that eliminates the limitation imposed by the crossing time $\tau $ , i.e., the eigenfrequency. This innovation significantly shortens the length of the fiber-optic ring, thereby effectively reducing the system’s backscattering noise. Numerical simulations leveraging Bessel expansions were conducted to analyze the proposed system, demonstrating that the output term is independent of the eigenfrequency. Within a modulation frequency range of 90–120 kHz, the maximum fluctuation of the first harmonic component is only 4.6%, further confirming the system’s immunity to eigenfrequency constraints. The limit sensitivity of the system is then analyzed for applications in weak magnetic field measurement, and the detection sensitivity is up to ${3.7} \times {10}^{-{3}}~\text {fT/Hz}^{\text {1/2}}$ . The proposed system can be applied to any Sagnac interferometer-centered instrument, eliminating eigenfrequency limitations. This is particularly valuable for applications, such as current transformers, inertial measurements, and weak magnetic field detection.