Multilayer silver / dielectric thin-film coated hollow waveguides for sensor and laser power delivery applications

Hollow Glass Waveguides (HGWs) incorporating single dielectric thin film designs deposited on silver coated silica hollow waveguides have been used for low-loss transmission of infrared radiation in the 2 – 14 micrometer region. Silver iodide has traditionally been the material of choice as a dielectric thin film in HGWs, with other dielectric thin film materials such as cadmium sulfide and lead sulfide being used as well. The incorporation of multilayer stacks of alternating low and high refractive index dielectric thin films in HGWs has been theoretically shown to further reduce the optical attenuation. Theoretically, lower losses are achieved when the refractive index contrast of the two thin film materials used is high and the number of films incorporated in the HGW film structure increases. Theoretically, such multilayer dielectric stack designs can give rise to the appearance of 1-D photonic bandgap structures with omnidirectional reflection properties as long as critical design parameters are met and scattering contributions due to surface roughness and similar defects are sufficiently low. This study involves the practical design of multilayer dielectric stacks in HGWs, with lead sulfide as a high refractive index material and cadmium sulfide as low refractive index material. The design, optimization, and processing methodology for achieving low-loss multilayer dielectric stacks in HGWs at desired infrared wavelengths is discussed. Characterization of multilayer dielectric coated HGWs includes FTIR spectroscopy for determining the optical response and infrared laser measurements for determining the optical attenuation properties of said multilayer dielectric stack coated HGWs. The experimental loss dependency of dielectric coated HGWs incorporating such metal chalcogenide materials on the particular thin film materials used and number of dielectric layers incorporated is presented and challenges in the current fabrication methodology are discussed.