Liquid Level Sensor Using Fiber Bragg Grating Assisted by Multimode Fiber Core

A liquid level sensor based on a fiber Bragg grating (FBG) assisted by a section of multimode fiber core (MMFC) was demonstrated. Since the coupling coefficients between the MMFC and the single-mode fiber changes and FBG reflection modes keep still as surrounding liquid level varying, the liquid level can be determined by measuring the power of the FBG reflection core mode. Experimental results show that the sensor achieves a linear sensitivity of 0.29 dB/mm within the liquid level range of 0-30 mm. The refractive index response and the temperature measurement were described. Such a simple, low-cost, and power-detect FBG-based liquid level sensor has great potential in industrial applications.