A DISTRIBUTED FIBER OPTIC SENSOR BASED ON CLADDING FLUORESCENCE

A distributed sensor based on an optical fiber whose entire cladding is fluorescent is described. The fiber is formed by cladding fused silica during draw with polydimethyl siloxane into which an organic fluorescent dye, 9,10-diphenylanthracene, has been dissolved. Upon side illumination at a wavelength within the excitation range of the dye, the cladding fluoresces; some of this fluorescence is coupled into guided modes in the fiber core through the evanescent fields of these modes. In the presence of oxygen, fluorescent emission by the dye is diminished. For the sensor described here, the rubbery liquid-like nature of the polydimethyl siloxane cladding allows rapid diffusion of gases, and the intensity of the guided fluorescence is observed to drop by 30 percent in less than 5 s when the ambient atmosphere changes from pure nitrogen to pure oxygen. This oxygen sensor is one successful embodiment of a new technique in fiber optic sensing: distributed cladding fluorescence. The advantages of this sensing technique, and some of the possibilities for new sensors based on this principle, are discussed. © 1990, IEEE