Transmission characteristics of infrared hollow fiber with multi- AgI and SiO<sub>2</sub> films are discussed.
Three-dielectric-layer hollow glass fiber with SiO<sub>2</sub>/AgI/SiO<sub>2</sub>/Ag structure was fabricated for low-loss
delivery of infrared laser light. The first SiO<sub>2</sub> film on the silver layer was coated by using liquid phase
coating method. A semi-inorganic polymer was used as the coating material. A smooth vitreous film was
formed by the treatment of a hardener at room temperature and followed by curing treatment. For the
deposition of the AgI film between the two SiO<sub>2</sub> films, an Ag film was first plated on the SiO<sub>2</sub> film by
silver mirror reaction method. Then the iodination process was conducted to turn the silver layer into
silver iodide. The second SiO<sub>2</sub> layer was deposited on the AgI layer in the same way as the first SiO<sub>2</sub> layer.
Fabrication parameters for controlling film thicknesses, such as iodination temperature, silver mirror
reaction time, and solution concentration, are clarified for depositing AgI and SiO<sub>2</sub> films with the
theoretical optimum thicknesses. By optimizing the thickness of the three dielectric layers, low-loss in the
loss spectrum of SiO<sub>2</sub>/AgI/SiO<sub>2</sub>/Ag hollow glass waveguides can be obtained at the target infrared
wavelengths. A method is proposed to evaluate the film thickness of AgI layer based on the positions of
loss peaks and valleys in the loss spectra. Theoretical calculation for loss spectrum of SiO<sub>2</sub>/AgI/SiO<sub>2</sub>/Ag
hollow glass fiber considering material dispersion of dielectric materials is also conducted. Good
agreement with the measured data is demonstrated.