High sensitivity fiber optic current sensor based on Fabry-Perot interferometer manufactured by femtosecond laser

Abstract A novel fiber optic current sensor was prepared based on femtosecond laser processing technology and magnetostrictive material Terfenol-D. Its principle is to use the linear stretching of Terfenol-D material under the action of current to cause linear shift in the sensor spectrum. Firstly, we fabricated Fabry–Perot interferometer (FPI 1 ) using femtosecond laser in a tapered few mode fiber. Then, FPI 2 was prepared using the end face of FPI 1 , quartz capillary, and single-mode fiber. When cascading FPI 1 and FPI 2 , by adjusting the air-cavity length of FPI 2 , they form a harmonic vernier effect (HVE) sensor. In HVE sensors, FPI 1 forms a cantilever beam inside the capillary, which is not affected by axial strain. Therefore, when the axial strain acts on the HVE sensor, the effective length of axial strain increases to the entire length of the quartz capillary, greatly amplifying the strain sensitivity. Finally, the Terfenol-D rod is pasted onto the HVE strain sensor, and the strain change coupled to the strain sensor caused by magnetic field changes is detected by measuring the wavelength shift of the sensor. As the magnetic field strength is directly proportional to the current in the energized coil, this sensor can measure current. The experiment found that the current sensitivity of the sensor is 5.30 nm A −1 in the range of 0.5 A–3.3 A, and the linear fitting coefficient is 0.9926. Additionally, the minimum measurable current change of the sensor is 23 mA. The current sensor is of advantages of high sensitivity, stable sensing performance, compact structure, easy fabrication and low cost, meaning wide application prospect.