A vibrating optical fiber tip as a new sensor to monitor organic vapors

A novel transducer concept using a vibrating fiber tip for sensing vapors o f organic compounds is outlined. It is based on a vibrating optical glass f iber, which is excited via a dither piezo tube (DPT), whereby changes of th e vibration of the fiber tip are monitored using position-sensitive detecti on (PSD). The latter consists of a light source in the form of an appropria te laser diode, the emission of which is coupled into the vibrating fiber, and a matching differential photodiode as the detector. The influence of bo th polar and non-polar organic vapors on the vibrating fiber tip has been i nvestigated. Our measurements show that the vibration even of a bare fiber tip (e.g. of a glass fiber without any coating of an active layer) is affec ted by the presence of polar organic vapors, apparently by their influence on the elastic behavior of the fiber. This sensor reaction is influenced by the surface properties of the fiber, because fibers with HMDS-treated surf aces or fibers coated with active layers react intrinsically different from bare fibers. (C) 2000 Elsevier Science S.A. All rights reserved.