Capillary optical fibers modified by xerogel layers for chemical detection

Xerogel layers have been used in the development of fiber-optic chemical sensors with the aim of enhancing the interaction of detected chemicals with light waves transmitted in the fiber. In most of fiber-optic sensors xerogels layers have been applied onto the fibers. This paper shows an alternative approach, in which xerogel detection layers are applied onto the walls of holes of silica capillaries. Single capillaries as well as multiple capillaries of microstructure fibers were used as substrates for the application of xerogel layers. Sensitivities of the prepared layers to vapours of water and toluene were determined experimentally. In these experiments, light was coupled into the capillaries and the xerogel layers were brought into contact with gaseous mixtures of the chemicals and nitrogen. Spectral changes of the output light from the capillaries were measured in a wavelength range from 1300 to 1800 nm. Results of these measurements are shown and compared with those obtained for layers applied onto silica fibers. These results show that capillary fibers modified by xerogel layers offer novel means for increasing the detection sensitivity.