Development of new optical fiber toluene sensor

摘要

This paper deals with experimental results on detection of toluene dispersed in water by means of a new and simple plastic optical fiber (POF) sensor. Its sensing part consists of swelling polymer cladding layer such as high density polyethylene (HDPE) with slightly larger refractive index n_2 than that of poly(methyl methacrylate) (PMMA) core with n_1. When is exposed to toluene dispersed in water, HDPE cladding layer causes swelling and the value of n_2 decreases quickly. Then the POF structure in the sensing part changes from leaky-type to guided-one and the output light intensity increases dramatically. By measuring this light intensity change, it becomes possible to detect toluene concentration. In addition, as compared with the popular evanescent-wave detection principle type, this sensor operation does not depend on the wavelength of light source. Therefore, we can use an inexpensive LED or LD in visible region. In experiment, detection of less than 1 wt% toluene in water was easily obtained with fast response about only 1 s. Furthermore, this sensor can detect pure toluene even for a small amount below 1 ml.