Examination of limonene concentrations using tapered plastic optical fiber sensors

A tapered plastic optic fiber (POF) was developed and demonstrated for monitoring different concentrations of limonene. The working mechanism of the sensor was dependent on the evanescent field interaction between light and the POF tapered region. The tapered POF was fabricated using a polishing-etching method to accomplish different waist diameters of 0.7 mm, 0.65 mm, 0.6 mm, 0.55 mm, and 0.5 mm in a 2 cm sensing region. The experiment was carried out with a blue LED with a wavelength of 400 nm and the output voltage was observed. As the concentration of the limonene solutions increased from 20% to 40%, 60%, 80%, and 100%, the refractive index also increased to 1.39, 1.41, 1.43, 1.44, and 1.47, respectively. The sensitivity of the sensor increased as the tapered waist diameter was reduced. The key benefits of this sensor are its ease of handling and fabrication in comparison to other types of sensors.