Hollow glass waveguides (HGWs) have been extensively investigated for the transmission of broadband, high-power radiation, particularly in the mid-infrared. One area of particular interest is the deposition of dielectric thin films within the hollow core of the HGW in order to reduce the losses at desired wavelengths. By implementing a thin film multilayer structure with high index mismatch between adjacent films, it is possible to dramatically improve the losses of the waveguides due to the thin film interference effect. Existing multilayer film research has utilized heavy metal halides, which although provide considerable index contrast, are toxic and unsuitable for clinical applications in which they are often used. Polymer dielectric thin films provide desirable optical properties for HGWs but are hindered by solvent compatibility in the deposition procedure. This work demonstrates implementation of a polymer multilayer dielectric thin film stack within a HGW, using ChemoursTM Teflon AF (n = 1.29) as the low-index material and polystyrene (n = 1.59) as the high-index material. These two polymers were deposited using liquid phase techniques within a HGW; the absorption spectra of waveguide as each layer was deposited on was analyzed in the mid-IR with an FTIR, and straight and bending losses were measured on a CO<sub>2</sub> laser. Appreciable losses were realized with the addition of the second polymer film and the interference bands red-shifted with the second layer, suggesting the successful creation of the multilayer structure.
Hollow glass waveguides (HGWs) have been successfully employed in surgical lasers, temperature and chemical sensors, and other applications requiring transmission of broadband, high-power infrared radiation. The design ofHGWsallows for fine-tuning of the optical response through the deposition of high-quality thin films within the hollowcore. One method of fabricatingHGWs for effective transmission in the infrared is to deposit a reflective metallic layer of silver, and then one or several dielectric layers on top of the silver layer. The addition of appropriate dielectric, or highly transmissive, layers to the HGW has shown to improve throughput and fibers can be modified to transmit optimally at particular wavelengths by altering the types of dielectrics used as well as their individual thicknesses. Increasingly, research in dielectric thin films for HGWs has gravitated towards polymers due to their inertness, ease of deposition, and thickness of film adjusted with concentration of solution instead of deposition kinetics. Poly (methyl methacrylate), polyethylene, and Chemours™ Teflon™ AF are three polymers previously untested as dielectric films in hollow waveguides in the mid-infrared. This work aims to assess the feasibility of these polymers as viable dielectric films in dichroic and multilayer thin-film stack waveguide applications. The three polymers were implemented as HGW dielectric thin films, and the resulting waveguides’ straight and bending losses were measured at CO<sub>2</sub> (λ= 10.6 μm) and Er:YAG (λ= 2.94μm) laser wavelengths.
A dual-core hollow fiber has two separate cores for propagation of light. Such a fiber can have some good applications in laser surgery. The dual-core guide can transmit an infrared laser beam for cutting or ablation while a visible laser beam is simultaneously transmitted as a pilot or aiming beam. The traditional fabrication procedure for a dual-core hollow fiber involves chemical vapor deposition (CVD) growth on silica tubing of an inner cladding layer followed by the deposition of a low index polymer on the outside of the tubing. This will provide a hollow structure that has a clad-core-clad tube. This work provides an alternative approach which involves nesting of two hollow waveguides to establish a dual-core hollow fiber. An Ag/AgI hollow glass fiber is fabricated for transmitting CO<sub>2</sub> laser. Another silica glass tube is selected carefully so that its inner diameter is just slightly larger than the outer diameter of the Ag/AgI hollow fiber. The outer surface of the as-selected glass tubing is coated with a low refractive index polymer. The Ag/AgI hollow fiber was inserted into the polymer coated silica glass tubing to establish an air or silicone oil gap between the two tubes. A visible laser beam is transmitted through the outer tube’s core. The CO<sub>2</sub> laser beam is transmitted through the inner Ag/AgI hollow fiber. The dual-core hollow fibers show good transmission for both the red aiming beam and the CO<sub>2</sub> laser. Therefore this structure can be a good candidate for laser surgery applications.
Hollow glass waveguides (HGWs) have been researched extensively for the efficient transmission of radiation over a
broad spectral range spanning from the visible region to the far-IR. One such HGW film structure consists of a metallic
substrate with overlaying multilayer dielectric thin film stack of alternating high and low refractive index films. The
optical properties of such multilayer thin film stacks are well established and provide a method for developing photonic
bandgap fibers with exceptionally low attenuation losses at a desired wavelength. Transmission losses can be minimized
in multilayer waveguides through two main approaches; either maximizing the number of alternating layer pairs or
maximizing the index contrast between adjacent films. In practice, it has been shown that for liquid-phase deposition-based
procedures, the former approach leads to compounding surface and interface roughness, negating the low-loss
advantage of a multilayer waveguide. Thus, this research focuses on maximizing index contrast between adjacent
dielectrics in an attempt to minimize the number of films required to achieve acceptable transmission characteristics both
in theory and in practice. In this study, multilayer waveguides are fabricated using three dielectric materials: silver
iodide, lead sulfide, and cyclic olefin copolymer. Through exploitation of their high index contrast, these materials are
used to develop low-film-count multilayer waveguides designed for enhanced transmission at both Er:YAG and CO2