Innovative sensor for refractive index monitoring based on a plastic optical fiber side-polished in a ‘V’-bent structure

Abstract An innovative probe design, based on plastic optical fiber (POF) which has been designed around a side-polished fiber, bent into a ‘V’ shape, is reported. Such a probe offers an innovative approach to monitoring of the surrounding refractive index (RI) of the material under study. The underlying principle is that such a side-polished optical fiber configured in this way can give rise to an enhanced evanescent field. This structure, with the optical fiber slot, was used to fix the side-polished POF. As a result, the POF probe created this way has been optimized using different intersection angles, circular chamfer radius and different polished depths. The maximum sensitivity achieved with the use of this probe reaches 206.4 dB/refractive index unit over the range of RI from 1.33 to 1.40. In the design, the half intersection angle, the circular chamfer radius and the polished depth were set to 30°, 1.12 mm and 194.6 μm, respectively. Such a probe based on inexpensive POF has significant potential for a variety of low-cost, RI sensing applications.