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 of organic compounds is outlined. It is based on a vibrating optical glass fiber, which is excited via a dither piezo tube (DPT), whereby changes of the vibration of the fiber tip are monitored using position-sensitive detection (PSD). The latter consists of a light source in the form of an appropriate laser diode, the emission of which is coupled into the vibrating fiber, and a matching differential photodiode as the detector. The influence of both polar and non-polar organic vapors on the vibrating fiber tip has been investigated. 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 affected 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 surfaces or fibers coated with active layers react intrinsically different from bare fibers.