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, Christopher Clark

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Citation (Scopus)


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.
Original languageEnglish
Title of host publicationTerahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications X
EditorsLaurence P. Sadwick, Tianxin Yang
PublisherSociety of Photo-Optical Instrumentation Engineers
ISBN (Electronic)9781510606487
ISBN (Print)9781510606470
Publication statusPublished - 24 Feb 2017

Publication series

NameProceedings of SPIE
ISSN (Print)0277-786X
ISSN (Electronic)1996-756C


  • CO2 sensor
  • thin films
  • NDIR
  • mid-IR
  • plasma-assisted DC magnetronsputtering
  • multilayer optical interference filter
  • mid infrared light emitting diodes
  • mid infrared photodiodes
  • capnography
  • surgical anaesthesia
  • nitrous oxide
  • cross-talk
  • one dimensional photonic crystals
  • breath analysis
  • breath emulator


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