Free-standing thin-film waveguides and slot waveguides offer excellent properties for gas sensing: high air confinement factors resulting in strong light-analyte interaction, reduced material absorption loss, and negligible Fabry-Perot fringes. We demonstrate that such waveguides combined with the sensitive and selective technique of mid-IR laser absorption spectroscopy can detect methane and carbon dioxide down to 300 ppb and 30 ppb levels, respectively. Isotope specific detection of CO2 with excellent 13C isotope ratio accuracy of 0.3‰ has also been shown. The unprecedented sensitivity together with miniature sensor footprint and microlitre sample volumes open new application areas in biology, environmental sensing and industral process monitoring.
Mid-infrared tuneable diode laser absorption spectroscopy (TDLAS) realized with photonic integrated circuits (PICs) has the potential to create small and portable sensing devices with exceptional sensitivity. Here we present a photonic crystal (PhC) W5 waveguide-based sensor, which provides stronger interaction between the light and the analyte than a free space beam, as well as low scattering and material absorption losses. We demonstrate its performance by analysing the transmission spectra of two CO2 isotopes at 4345 nm.
Mid-Infrared (Mid-IR) techniques have gained considerable attention because of their inherent molecular selectivity and their potential for rapid label-free detection in applications such as water quality and environmental monitoring, security, food safety, and point-of-care diagnostics. Waveguide evanescent-field-based Mid-IR spectroscopy can detect analytes at very low concentrations using molecular absorption fingerprints, potentially offering high sensitivity and selectivity over a wide range of compounds. Moreover, significant footprint reduction compared to ATR-based FTIR measurements can be achieved with optical waveguide-based Mid-IR sensing through integration of various optoelectronic and microfluidic components realizing fully packaged lab-on-a-chip systems.
Recently we have developed low-loss chalcogenide optical waveguides and demonstrated waveguiding in the mid-wave and long-wave infrared spectral bands. High contrast GeTe4 and ZnSe channel waveguides were fabricated on bulk substrates and on silicon wafers (with suitable optical isolation layers) using lift-off and dry etching techniques after photolithographically patterning the thin films. These waveguides were exhibiting optical losses as low as 0.6 dB/cm in the mid-wave IR band and were validated for the Mid-IR evanescent wave spectroscopy with water and IPA. We have also demonstrated the effectiveness of simple paper-based fluidics with our waveguides.
In addition, we investigate a new family of free-standing Ta2O5 rib waveguides for trace gas detection with evanescent field overlap with the surrounding medium (air) up to about 70%. The waveguides are being fabricated and the fabrication and characterization results will be presented.
Conference Committee Involvement (2)
Integrated Optics: Devices, Materials, and Technologies XXVI
24 January 2022 | San Francisco, California, United States
Integrated Optics: Devices, Materials, and Technologies XXV
6 March 2021 | Online Only, California, United States
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