Optical fiber sensor for water detection using a side-polished fiber coupler with a planar glass-overlay-waveguide

For monitoring the presence of water at the splicing points of an optical fiber, the water detection sensors based on a side-polished fiber coupler with a commercial microscope-cover-glass are proposed. The sensors are very sensitive to the variation of an upper cladding layer's index on the overlay waveguide. When the sensors detect water, the coupling wavelengths shift to longer wavelength at about 2 nm than that of an air cladding. The variation of an optical loss as a function of the wavelength shift is monitored using an optical time-domain refractometry to detect the installed positions and the immersion locations of the sensors. The advantages of our sensor for these purposes are discussed in. (C) 2002 Elsevier Science B.V. All rights reserved.