An automated chemical process for tapering highly multimoded plastic optical fibre tapers was developed. On-line monitoring was performed whilst varying the solvent composition to optimize taper formation, in order to obtain repeatable, optically clear and mechanically robust tapers in a minimum time period. A model of the process is presented in terms of fibre core radius and core/cladding refractive index. A relationship between core radius, cladding refractive index and numerical aperture was derived that had application for dynamic prediction and compensation of optical parameters. When characterized with a range of refractive indices, the tapered POF sensor exhibited two distinct regions: the water/alcohol region below 1.4 refractive index units, and the oil region above 1.4 suggesting the sensor's use as an oil-in-water, or water-in-oil sensor. From 95% confidence limits, the accuracy of the POF was ±0.006 refractive index units (to 2 standard deviations) or 0.4% above 1.4. Tapered POP is sensitive to refractive index providing a cheap, easy-to-handle and rugged throwaway sensor for water and beverage process and quality monitoring.
- Optical fibre