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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.

Transmission characteristics of infrared hollow fiber with multi- AgI and SiO 2 films are discussed. Three-dielectric-layer hollow glass fiber with SiO 2 /AgI/SiO 2 /Ag structure was fabricated for low-loss delivery of infrared laser light. The first SiO 2 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 2 films, an Ag film was first plated on the SiO 2 film by silver mirror reaction method. Then the iodination process was conducted to turn the silver layer into silver iodide. The second SiO 2 layer was deposited on the AgI layer in the same way as the first SiO 2 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 2 films with the theoretical optimum thicknesses. By optimizing the thickness of the three dielectric layers, low-loss in the loss spectrum of SiO 2 /AgI/SiO 2 /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 2 /AgI/SiO 2 /Ag hollow glass fiber considering material dispersion of dielectric materials is also conducted. Good agreement with the measured data is demonstrated.

We proposed a method to evaluate the material dispersion of the dielectric film in dielectric-coated silver hollow fiber. By taking into consideration the derived material dispersion, the wavelengths of the loss peaks and valleys in the loss spectra of the hollow fiber can be predicted more accurately. Then, we fabricated the dielectric-coated silver hollow fiber according to the parameters obtained by using the improved design method. The measured data showed good agreement with the calculated results. The loss for medical laser of Er :YAG and CO 2 was less than 0.3 dB/m. The loss for green or red pilot beams was around 5 dB/m, which is sufficiently low for the purpose of pilot beam transmission. The derived material dispersion plays an important role in the design and fabrication of the hollow fiber for multiwavelength delivery.

A method is proposed to evaluate the material dispersion of dielectric film in dielectric-coated silver hollow fiber. Cauchy's formulas that characterize the dispersion property were obtained for several commonly used dielectric materials by using the measured data of loss spectra of the hollow fibers. The wavelengths of the loss peaks and valleys in the loss spectra can be predicted more accurately when taking into consideration of the material dispersion. The derived Cauchy's formulas play an important role in the design of infrared hollow fiber for multiwavelength delivery.

We report on AgI/Ag infrared hollow fiber with low-loss in visible region. Improved methods of silver plating and iodination were proposed to fabricate the hollow fiber. The surface roughness of the silver layer and the silver iodide layer was reduced by the pretreatment with an SnCl2 solution and low iodination temperature. Losses for the Er:YAG and green laser light were 0.4 and 7dB/m. The loss property of green laser beam was low to deliver a pilot beam for the invisible infrared laser light. Owing to the smooth and uniform AgI film, the loss spectrum of the hollow fiber showed clear interference peaks in the visible region. An empirical formula for AgI material dispersion was derived, which is of special importance for the design of high-performance AgI/Ag hollow fiber.