Hollow glass waveguides with CVD-deposited metal and dielectric coatings

Hollow glass waveguides have been fabricated for the delivery of infrared radiation by chemical vapor deposition methods. A molybdenum film is first deposited inside 700- micrometer and 530-micrometer bore silica tubing by the hydrogen reduction of molybdenum chloride. Then, Al ₂O ₃, or TiO ₂ film is deposited onto the molybdenum layer. These dielectric films enhance the reflectivity, and we observe a reduction in loss for the thin- film combination compared with the molybdenum film alone. The thickness uniformity of the dielectric films is estimated to be less than 5% of the desired thickness in a length of 50 cm. A loss spectrum of the Al ₂O ₃/Mo-coated waveguides shows that the losses for the Al ₂O ₃ guide in the 3 - 6 micrometer wavelength region are lower than the loss for the AgI-coated guide fabricated by liquid-phase deposition technique. The chemical vapor deposition techniques can be extended to the fabrication of hollow waveguides with multiple dielectric layers that have much lower losses than current single-layer designs.