Fabrication of low-loss hollow waveguide with multiple dielectric layers for infrared cavity ring-down spectroscopy

Low-loss hollow waveguides with a multiple dielectric layer are designed and fabricated for use in cavity ring-down spectroscopy (CRDS). Calculations of the waveguide design revealed that hollow waveguides for infrared CRDS system need to have transmission loss of 0.1 dB/m or less. We fabricated rectangular hollow waveguides with multiple dielectric layers to obtain low-loss properties. The waveguides are composed of four glass strips each with a dielectric multilayer deposited on the surface in advance. Experimental results show that the waveguides with double dielectric layers have lower losses at a target wavelength in the infrared than those with a single dielectric layer. The measured transmission loss of a 10-cm long waveguide deposited with a multilayer of Si/Al₂O₃/Ag for the transverse magnetic wave and Al₂O₃/Ag for the transverse electric wave was 0.24 dB at a target wavelength of 5.2 μ m. The loss of the waveguide will be reduced when only the lowest-order mode is excited in the waveguide.