Hollow glass waveguide for mid-infrared applications.

摘要

This study is an effort to characterize the optical and mechanical properties of hollow glass waveguides (HGWs) with inner metallic and dielectric layers.; The theoretical base behind the light-guiding principle of a hollow metallic waveguide has been extended to address the optical properties of dielectric-coated hollow metallic waveguides in both straight and bent configurations. The dependencies of attenuation on bore-size, bend radius, and transmitted mode are predicted by this analysis.; HGWs with silver metallic layers and silver iodide dielectric films have been fabricated in bore sizes ranging from 250 {dollar}rmmu m{dollar} to 1000 {dollar}rmmu m.{dollar} The spectral response has been measured, and can be arbitrarily tailored lo show minimum loss at any wavelength between 2 and 11 {dollar}rmmu m.{dollar} Spectroscopic analysis has been used to determine the uniformity and thickness variation in the dielectric layer. Process modifications have reduced this variation from 14% to approximately 1%.; The effect of laser coupling condition has been modeled, and optimum coupling occurs for spot-size to bore-size ratios between 0.55 and 0.64. These theoretical predictions have been verified using laser loss measurements on 530, 700 and 1000 {dollar}rmmu m{dollar} bore waveguides, with the largest bore showing the least sensitivity to launch condition. Continuous {dollar}rm COsb2{dollar} laser power has been transmitted through HGWs with 250, 320, 530, and 700 {dollar}rmmu m{dollar} bore. The 250 and 320 {dollar}rmmu m{dollar} sizes transmitted 35 and 50 W of input power respectively, while both larger sizes successfully transmitted 85 W. Similarly, the larger scores showed the ability to transmit high pulsed energy, up to 80 J.; Laser loss has been shown to be sensitive to input laser beam quality, with most sensitivity observed for small bore waveguides. The preservation of low loss and spatial purity has been achieved by increasing the wall thickness of the substrate tubing. Losses above the theoretically predicted minimum values have been attributed to scattering from film roughness. The roughness of the silver film has been quantified using AFM and rms values can range from 110 nm to 550 nm.; The mechanical properties of the HGW have been evaluated, and the strength and uniformity of unprocessed capillary is excellent for all bore sizes. Various stages of processing have been shown to affect the strength and uniformity of the fabricated waveguides. Reduction in strength values range from 16% to 30%.; Two variations on the HGW have been considered. Theoretical calculations have been made in order to predict the reduction in attenuation achieved through the application of multiple dielectric layers. Primary dielectric layer of low index and high index secondary dielectric offer greatest improvement in transmission. The limiting factor has been determined to be the identification and deposition of transparent dielectric materials with desired refractive indices. The second variant is a dual-core HGW, where the substrate tubing contains a suitable index profile for guiding of light. This allows low-loss transmission of light between the wavelengths of 0.3 and 12 {dollar}rmmu m.{dollar} (Abstract shortened by UMI.)