Fabrication of Long Dielectric-Coated Waveguides for the Infrared

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For the application of infrared wave-guides in the industrial and medical fields, we have investigated fabrication methods of long dielectric-coated wave-guides, loss reduction of the wave-guides, and relating electromagnetic problems. Main results are summarized as follows :1. Loss Reduction of Dielectric-Coated Wave-guidesWe have fabricated 2 m long germanium-coated silver wave-guides with circular cross section. Minimum wave-guide loss at 10.6 mum so far obtained is 0.05 dB/m in the wave-guide with 1.5 mm in diameter. It is shown that further loss reduction can be made by using a zinc selenide layer as a coating dielectric and by employing a polyimide tube as a mother tube.2. Fabrication Method of Long Wave-guidesA new method of fabricating long wave-guide is proposed. The cross section of wave-guide is rectangular. The wave-guide is composed of two pairs of metal strips, one of which is coated with a thin dielectric layer. PbF_2 coated rectangular wave-guides with cross section of 1 mm x 1 mm are fabricated and the minimum loss of 0.11 dB/m is attained.3. Total-Reflection-Type Glass Hollow Wave-guidesComplex refractive indices of TiO_2-SiO_2 or GeO_2-based glasses have been measured and simple empirical formulas are obtained to predict complex refractive indices of those glasses which only include weight % of Si or Ge in whole cations. Lower bound of wave-guide loss at 10.6 mum is also clarified.4. Fabrication of Thin Germanium-Coated Wave-guides by Electro-Plating MethodBy using whole electro-plating techniques, thin dielectric-coated wave-guides have been fabricated.