Fiber-Optic Current Sensor Based on Ohmic Heating of Tin Sphere with Embedded Silicon Fabry-Perot Interferometer

A fiber-optic Fabry-Perot interferometer (FPI) is proposed and demonstrated as an electric current sensor based on ohmic heating with temperature self-compensation. The sensing head is fabricated by attaching a silicon pillar on the fiber tip as the FPI and inserted into a molten tin (Sn) sphere as the conducting medium. Two copper electrodes are also inserted into the Sn sphere and serve as the electrodes for current measurement. The electric current loaded on the Sn sphere will lead to a temperature rise that is measured with high resolution by the silicon FPI. A fiber Bragg grating is incorporated in the vicinity of the sensing head for temperature compensation. Both theoretical analysis and experimental results indicate that the peak or valley wavelengths of the silicon FPI have a linear response to the square of the measured current. The current responsivity of 1.83 nm/A² has been experimentally obtained, with a resolution of 1.28 × 10^-3 A at around 0.3 A.