Measurement and control of thin film uniformity in hollow glass waveguides

Hollow glass waveguides provide an attractive means for the delivery of IR laser power and for broadband temperature and chemical fiber sensor applications. These waveguides are made using liquid-phase chemistry techniques to deposit a thin dielectric film of AgI over metallic Ag on the inside of small-bore silica tubing. By controlling the thickness of the AgI film, we can tailor the optical response of the guides to give low loss at selected IR laser wavelengths or to produce a broadband response. In either case, the losses depend on the thickness uniformity of the AgI film. Initially, the AgI film thickness varies as much as 14% from end to end of a 6-m long guide. A faster AgI deposition rate reduces this variation to only 1.3% over a 5-m long waveguide. This leads to a reduction in the total loss for the hollow guides in the 2 to 12 mu m region. (C) 1999 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(99)00912-5].