Dispersion Turning Point and Long Sensing Fiber Co-Sensitized Magnetic Field Sensor

The optical fiber magnetic field sensors, which work near the dispersion turning point (DTP) or employ a long sensing fiber for phase difference accumulation, can achieve high sensitivity. However, few reports have combined these two schemes. Herein, this problem is solved by designing a Grin-lens-coupled fiber Mach-Zehnder interferometer (MZI) for magnetic field sensing. The DTP of the fiber MZI is generated by tuning the length of air-gap between two Grin lenses. When the fiber MZI works near DTP, the resonant wavelength has ultra-high sensitivity to the elongation of fiber length. Magnetic field sensing can be performed by combining a long section of single-mode fiber with magnetostrictive material (TbDyFe), which facilitates the accumulation of fiber elongation. Co-sensitized by DTP and long sensing fiber, the maximum sensitivity achieved in the experiment is 37.381 nm/Gs. Much higher sensitivity can be expected by tuning the resonant wavelength close to the DTP or increasing the length of the sensing fiber. Furthermore, this magnetic field sensor features high resonant-wavelength resolution, a tunable dynamic range, and ease of fabrication and operation.