Fabrication and characterization of infrared hollow fiber with multi- SiO_2 and AgI inner-coating layers

We report the transmission characteristics of infrared hollow fiber with multi- AgI and SiO(2) inner-coating layers in the mid-infrared region. A three-dielectric-layer hollow glass fiber with a SiO(2)-AgI-SiO(2)-Ag structure was fabricated and low-loss property was obtained in the mid-infrared region. The SiO(2) films were coated by use of the liquid-phase coating method and a semi-inorganic polymer was used as the coating material. For deposition of the AgI film between the two SiO(2) films, a silver film was first plated by use of the silver mirror reaction method. Then the iodination process was conducted to turn the silver layer into silver iodide. A calculation method was also developed to estimate the film thickness of dielectric layers in each fabrication step according to the position of loss peaks in the measured loss spectra. Good agreement between calculated and measured loss spectra was demonstrated by taking into consideration material dispersion and surface roughness of inner-coating films.