One-dimensional photonic crystals for eliminating cross-talk in mid-IR photonics-based respiratory gas sensing

L. Fleming; D. Gibson; S. Song; D. Hutson; S. Reid; C. MacGregor; C. Clark

doi:10.1117/12.2247851

24 February 2017 One-dimensional photonic crystals for eliminating cross-talk in mid-IR photonics-based respiratory gas sensing

L. Fleming, D. Gibson, S. Song, D. Hutson, S. Reid, C. MacGregor, C. Clark

Author Affiliations +

Proceedings Volume 10103, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications X; 1010318 (2017) https://doi.org/10.1117/12.2247851
Event: SPIE OPTO, 2017, San Francisco, California, United States

Abstract

Mid-IR carbon dioxide (CO₂) gas sensing is critical for monitoring in respiratory care, and is finding increasing importance in surgical anaesthetics where nitrous oxide (N₂O) induced cross-talk is a major obstacle to accurate CO₂ monitoring. In this work, a novel, solid state mid-IR photonics based CO₂ gas sensor is described, and the role that 1- dimensional photonic crystals, often referred to as multilayer thin film optical coatings [1], play in boosting the sensor’s capability of gas discrimination is discussed. Filter performance in isolating CO₂ IR absorption is tested on an optical filter test bed and a theoretical gas sensor model is developed, with the inclusion of a modelled multilayer optical filter to analyse the efficacy of optical filtering on eliminating N₂O induced cross-talk for this particular gas sensor architecture. Future possible in-house optical filter fabrication techniques are discussed. As the actual gas sensor configuration is small, it would be challenging to manufacture a filter of the correct size; dismantling the sensor and mounting a new filter for different optical coating designs each time would prove to be laborious. For this reason, an optical filter testbed set-up is described and, using a commercial optical filter, it is demonstrated that cross-talk can be considerably reduced; cross-talk is minimal even for very high concentrations of N₂O, which are unlikely to be encountered in exhaled surgical anaesthetic patient breath profiles. A completely new and versatile system for breath emulation is described and the capability it has for producing realistic human exhaled CO₂ vs. time waveforms is shown. The cross-talk inducing effect that N₂O has on realistic emulated CO₂ vs. time waveforms as measured using the NDIR gas sensing technique is demonstrated and the effect that optical filtering will have on said cross-talk is discussed.

Citation Download Citation

L. Fleming, D. Gibson, S. Song, D. Hutson, S. Reid, C. MacGregor, and C. Clark "One-dimensional photonic crystals for eliminating cross-talk in mid-IR photonics-based respiratory gas sensing", Proc. SPIE 10103, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications X, 1010318 (24 February 2017); https://doi.org/10.1117/12.2247851

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