Optimizing Gas Sensors Based on Quantum Cascade Lasers and Photonic Bandgap Hollow Waveguides

In the present study, bending losses in conventional hollow waveguides (internally Ag/AgI coated) and in photonic bandgap (PBG) hollow waveguides (HWG) are compared based on studies via FT-IR spectroscopy and quantum cascade lasers (QCL). To date, literature on bending losses in hollow waveguides focuses on conventional HWG structures (e.g., silica structural tube with internal Ag/AgI coating), whereas the results discussed here compare relative bending losses in novel photonic bandgap waveguides, a new type of HWG progressively more integrated in gas sensors, versus conventional HWGs for the first time. Photonic bandgap waveguides are expected to exhibit lower polarization-dependent relative bending losses due to radiation propagation via omnidirectional reflection, in contrast to conventional HWGs. Accordingly, photonic bandgap waveguides offer superior flexibility and robustness against bending losses in coiled configurations rendering them promising structures for next-generation miniaturized QCL-based HWG gas sensors.