Substrate-Integrated Hollow Waveguides: A New Level of Integration in Mid-Infrared Gas Sensing

Abstract

A new generation of hollow waveguide (HWG) gas cells of unprecedented compact dimensions facilitating low sample volumes suitable for broad- and narrow-band mid-infrared (MIR; 2.5-20 μm) sensing applications is reported: the substrate-integrated hollow waveguide (iHWG). iHWGs are layered structures providing light guiding channels integrated into a solid-state substrate material, which are competitive if not superior in performance to conventional leaky-mode fiber optic silica HWGs having similar optical pathlengths. In particular, the provided flexibility in device and optical design and the wide variety of manufacturing strategies, substrate materials, access to the optical channel, and optical coating options highlight the advantages of iHWGs in terms of robustness, compactness, and cost-effectiveness. Finally, the unmatched modularity of this novel waveguide approach facilitates tailoring iHWGs to almost any kind of gas sensor technology providing adaptability to the specific demands of a wide range of sensing scenarios. Device fabrication is demonstrated for the example of a yin-yang-shaped gold-coated iHWG fabricated within an aluminum substrate with a footprint of only 75 mm × 50 mm × 12 mm (L × W × H), yet providing a nominal optical absorption path length of more than 22 cm. The analytical utility of this device for advanced MIR gas sensing applications is demonstrated for the gaseous constituents butane, carbon dioxide, cyclopropane, isobutylene, and methane.

Mid‐infrared thin‐film diamond waveguides combined with tunable quantum cascade lasers for analyzing the secondary structure of proteins

“…Infrared transmitting waveguides (i.e., predominantly fiberoptic structures) are usually fabricated from IR‐transparent materials including polycrystalline silver halides , amorphous chalcogenide glasses , heavy metal fluorides , tellurium halides , single‐crystalline sapphire , and hollow waveguide structures . Recently, semiconductor waveguides enabling on‐chip MIR sensing schemes have been described including different optical configurations such as planar GaAs/Al 0.2 Ga 0.8 As slab waveguides , GaAs/Al 0.2 Ga 0.8 As strip/ridge waveguides , and HgCdTe waveguide structures .…”

Real-time monitoring of ozone in air using substrate-integrated hollow waveguide mid-infrared sensors

“…In future, a significant size reduction of the sensing device is anticipated by replacing the FTIR spectrometer with a suitable tunable quantum cascade laser (QCL)24343536. Moreover, the sensitivity may be further improved by extending the optical path length via variation of the meandered waveguide channel geometry integrated into the iHWG, as previously demonstrated32.…”

Advances in Mid-Infrared Spectroscopy for Chemical Analysis

“…However, novel detection principles for MIR radiation such as quantum cascade detectors (QCDs) (12,(30)(31)(32) and advanced thin-film (33)(34)(35)(36) and hollow waveguide (HWG) technologies (37)(38)(39) have also contributed to the evolution of conventional MIR spectroscopy into miniaturized chem/bio sensing and assay platforms, as recently reviewed (40,41).…”