Construction of a dual-core hollow waveguide for visible and mid-infrared light transmission based on PTFE tubing and UV gel

This work proposes a facile approach to fabricate a dual-core hollow waveguide based on two common and low-cost raw materials, namely polytetrafluoroethylene (PTFE) tube and ultraviolet (UV) gel. A silica glass tube is nested inside a heat-shrinkable PTFE tube. After heat treatment at 350 °C, the PTFE tube shrinks and then transforms into the low-index polymer on the outside of the silica tube. The PTFE-coated silica glass tubing is filled with UV gel followed by inserting a typical Ag/AgI mid-infrared (IR) hollow optical fiber. The UV gel is cured by UV radiation, forming a solid low-index layer between the PTFE-coated silica glass tubing and the Ag/AgI hollow optical fiber. A visible laser beam can be transmitted at a loss of 0.4 dB/m through the silica annulus between the low-index PTFE and UV gel layer. A 10.6-μm-wavelength CO₂ laser beam is delivered through the Ag/AgI hollow optical fiber (core size 530 μm) and the transmission loss goes up from 1.63 to 3.22 dB/m as the bending angle increases from 0° to 90°.