Plastic Optical Fiber Based SPR Sensor for Simultaneous Measurement of Refractive Index and Liquid Level

In this work, a plastic optical fiber (POF) based surface plasmon resonance (SPR) sensor is proposed and demonstrated for simultaneous measurement of refractive index (RI) and liquid level. The sensor probe is fabricated by polishing the POF and drilling several micro-holes with equal pitch along the fiber axial, after depositing a layer of gold film on the polished region, the SPR probe is obtained. The effects of the micro-hole on the sensing performance are investigated and the structural parameters of the micro hole are optimized. Experimental results show that the changes of the liquid RI can be detected by monitoring the wavelength position of the SPR peak, and the liquid level can be measured by monitoring the deepness of the SPR peak. An RI sensitivity of 2024.41 nm/RIU was obtained in the RI range of 1.335-1.40, and a resolution of 5 mm and measurement range of 25 mm for liquid level measurement were achieved for the probe. The proposed sensor is compact in size and has a very small cross sensitivity for the RI and liquid level measurement, which is useful in the biomedical and industrial sensing fields.