A novel fiber-optic gas-sensing configuration using extremely curved optical fibers and an attempt for optical humidity detection

A novel configuration for optochemical sensors is proposed using a single optical fiber which is extremely curved at an angle of 180 degrees and turned back. Although the curvature of optical fiber caused some loss in the transmission of the incident Light, this loss was not very large. To examine the utility of a sensor head using the curved fiber, all or part of the curved region was coated with a Rhodamine B/hydroxypropyl cellulose humidity sensing film instead of the normal cladding. When the curved fiber was used instead of a straight fiber, the modulation of the incident light by the sensing film was dramatically enhanced, and the change with humidity in the transmission of the incident light through the sensor became much larger. The light signal of the humidity sensor using the curved fiber exhibited a short response time, a high reproducibility, and a smooth dependence on humidity with little hysteresis effect in a wide humidity range. (C) 1998 Elsevier Science S.A. All rights reserved.