In this work, we present a MEMS-based ATR FTIR spectrometer operating in the wavelength range of 1.8 μm to 6.8 μm. The core engine of the spectrometer is a monolithically integrated scanning Michelson interferometer on a silicon chip. The ATR crystal is illuminated with an IR source and the output light of the crystal is free-space coupled to the MEMS interferometer using micro-optics reflective mirrors and the modulated light from the interferometer is then coupled to an MCT photodetector. The recorded SNR of the spectrometer is about 1000:1 in 10 seconds measurement time with a spectral resolution of 66 cm-1. The spectra of different liquid samples were obtained and the effect of the ATR crystal refractive index on the absorption depth was investigated, showing good agreement with the theoretical model. The proposed miniaturized ATR MEMS spectrometer opens the door for various applications in oil analysis, food safety and health care among others.
Infrared portable spectral sensors are greatly required for rapid and simultaneous analysis of material composition; triggering new applications in the domain of on-site spectroscopy. At the same time, miniaturization of Fourier transform infrared (FTIR) spectrometers based on the silicon technology has been proven to be one of the most promising approaches for wide spectral range applications. In this work, we present a fiber-free MEMS FTIR spectrometer working in the wavelength range of 1.8 μm to 6.8 μm (5500-1470 cm-1). The spectrometer is based on the use of a monolithically integrated scanning Michelson interferometer, assembled with external reflecting micro-optical part, which is responsible for light coupling to and from the MEMS chip. The measured signal-to-noise ratio of the spectrometer is larger than 5000:1 with a spectral resolution of 66 cm-1. The experimental results of measuring the transmission of a polystyrene reference calibration film show four absorption peaks in the Mid Infra-Red (MIR) range at 3.27, 3.5, 5.15, 6.24 μm in close agreement with theoretical predictions.
Air pollution is used to refer to the release of pollutants into the air, where these pollutants are harmful to the human health and our planet. The main source of these pollutants comes from energy production and consumption that release Volatile Organic Compounds (VOCs) such as BTEX and Aldehydes group. Real time monitoring of these VOCs in factories, stations, homes and in the street is important for analysis of the pollution sources fingerprint and for alerting, when exceeding the harmful limits. In this work we report the use of a MEMS FTIR spectrometer in the mid-infrared for this purpose. The spectrometer works in the wavelength range of 1.6 μm - 4.9 μm with a resolution down to 33 cm-1. This covers the absorption spectrum of water vapour, BTEX, Aldehydes and CO2 around 2.65 μm, 3.27 μm, 3.6 μm and 4.3 μm, respectively. The spectra of Toluene with different concentrations are measured, using a multipass gas cell with a physical length of 50 cm and an optical path length of 20 m, showing excellent sensor linearity. The minimum concentration measured is 350 ppb limited by the interference of the side lobes of the strong absorption of water vapour, which can be overcome in the future by humidity compensation. The SNR is measured and found to be 5000:1, corresponding to a detection limit of about 90 ppb. The achieved results open the door for a compact and low-cost solution targeting air pollution monitoring.