Salt-Doped Agar-Based Optical Fibers for Electric Current Sensing

This work reports an agar-made, biodegradable optical fiber for electric current measurements. The agar's mineral impurities sustain the charges' flow through the fiber structure, causing refractive index modulation by thermo-optic effect. Moreover, doping the agar solution with NaCl improves the electrical conductivity and sensitivity. We interrogate the sensor response by specklegram analysis, yielding a time-constant reduction in the decaying correlation coefficient curves as the current magnitude increases. Furthermore, oscillations in the speckle pattern manifest for exceeding currents, possibly due to the formation of a dielectric layer within the fiber structure.