Cryptophane-Enhanced Trace Gas Spectroscopy for On-Chip Methane Detection

Sensitivity of on-chip gas sensors is still at least 2-3 orders of magnitude lower than what is needed for applications in atmospheric monitoring, climate research, biomedical research, and industry. In this project, we aim to develop "high-end" on-chip photonic sensors that rely on mid-infrared laser absorption spectroscopy. Our objective is to increase the gas detection sensitivity about 1000 times compared to other on-chip devices to detect methane at concentrations as low as 10 ppb. In order to do so, we work on an original waveguide sensor designs that allows for strong interaction between the guided light and the surrounding gas, as well as on-chip pre-concentration of methane molecules in a thin-film waveguide cladding.

If successful, our integrated sensors will be able to replace the bulky and costly high-end instrumentation, while having considerably lower sample volumes, cost and energy consumption. As such, they are expected to open new fields of applications in research and industry and increase the density of sensor deployment in environmental applications e.g. by organising sensors in networks for better temporal and spatial coverage and data accuracy.

The first half of the project period mainly focused on the development and optimisation of the main building block of the sensor - the integrated photonic waveguide chip. We proposed, fabricated, and experimentally tested several different chip designs where guided light interacts extremely efficiently with the surrounding gaseous environment. We also successfully integrated the waveguide chips in a direct laser absorption spectroscopy setup for detection of methane and acetylene, achieving detection limits in the lower ppm range. So far, this work has resulted in two patent applications under processing, one submitted journal paper, two more manuscripts in preparation, and several invited and contributed conference presentations.

To our best knowledge, we are the first to experimentally demonstrate trace gas detection with a waveguide that provides for a stronger per-length interaction than a free space beam, as well as specific detection of methane down to 2 ppm with an on-chip design. In the remaining years the project will focus on increasing the length and thus the sensitivity of the above designs, on chemical pre-concentration combined with spectroscopic detection, and on the first sensor demonstrator development.