Low-Loss Hollow Waveguide Fibers for Mid-Infrared Quantum Cascade Laser Sensing Applications

We report on single mode optical transmission of hollow core glass waveguides (HWG) coupled with an external cavity mid-IR quantum cascade lasers (QCLs). The QCL mode results perfectly matched to the hybrid HE11 waveguide mode and the higher losses TE-like modes have efficiently suppressed by the deposited inner dielectric coating. Optical losses down to 0.44 dB/m and output beam divergence of similar to 5 mrad were measured. Using a HGW fiber with internal core size of 300 mu m we obtained single mode laser transmission at 10.54 mu m and successful employed it in a quartz enhanced photoacoustic gas sensor setup