Mid infrared gas sensing

Introduction

Many gases are colorless and odorless and therefore are not perceived by the human sense organs. For toxic gases the monitoring in buildings is indispensable, as for example gas leakages can lead to tremendous health damages. But also the detection of nontoxic gases is of utmost importance for many applications as process control or breath analysis for clinical diagnosis. Many gases exhibit absorption lines in specific fingerprint regions in the mid-infrared wavelength range, for example, CO₂ shows high absorption between 4.2 and 4.3 µm. Thus an optical signal at the gas specific wavelength range can interact with the gas and its intensity will be decreased. Optical sensors detect the change in intensity in the fingerprint regions and thus get information about the present gas concentration.

In general, an optical sensor consists of three components: 1. a source that emits radiation in the gas specific wavelength range, 2. a gas cell that provides a large interaction length between the light signal and the gas, 3. a detector that is able to detect even small intensity changes.

Goals

The overall aim of this project is to develop an optical gas sensor on a silicon chip that offers small size and low power consumption. This would open up the way to low-cost mass-production and also allow the implementation of gas sensors into portable devices like mobile phones.

In contrast to free-path optical sensing, our approach is based on integrated photonics where light will be guided inside the silicon chip. The evanescent field can interact with gases in the environment and can thus be used for optical sensing.

Our current research is based on the following topics:

• Integrated silicon based thermal emitter
• 2D integrating cell
• Integrated silicon based MIR detector

References

1. Holst, G. C.; and McHugh, S. W., Review of thermal imaging system performance, Proceedings of SPIE 1689, 78–84, 1992.
2. Hodgkinson, J.; and Tatam, R. P., Optical gas sensing: a review, Measurement Science and Technology 24(1), 12004 (2013).
3. Lai, J. J.; Liang, H. F.; Peng, Z. L.; Yi, X.; Zhai, X. F. (Hg.) (2011): MEMS integrated narrow band infrared emitter and detector for infrared gas sensor: IOP Publishing (276).
4. Soref, R., Mid-infrared photonics in silicon and germanium, Nature Photon. 4(8), 495–497 (2010).

Publikationen

• Fohrmann, L.S.; Petrov, A.Y.; and Eich, M.: Silicon waveguide based broadband thermal emitter for MIR. in Group IV Photonics (GFP), 2014 IEEE 11th International Conference on: S. 185-186, August 2014.
• Fohrmann, L.S.; Petrov, A.Y.; Lang, S.; Jalas, D.; Krauss, T.F.; and Eich, M.;: Single mode thermal emission. Optics Express, 2015.
• Fohrmann, L.S.; Petrov, A.Y.; Sommer, G.; Krauss, T.; and Eich, M.;: Photonic crystal based 2D integrating cell for sensing applications. Proc. SPIE, 2016.