On-chip parallel Fourier transform spectrometer for broadband selective infrared spectral sensing

Optical spectrometers enable contactless chemical analysis. However, decreasing both their size and cost appears to be a prerequisite to their widespread deployment. Chip-scale implementation of optical spectrometers still requires tackling two main challenges. First, operation over a broad spectral range extending to the infrared is required to enable covering the molecular absorption spectrum of a broad variety of materials. This is addressed in our work with an Micro-Electro Mechanical Systems (MEMS)-based Fourier transform infrared spectrometer with an embedded movable micro-mirror on a silicon chip. Second, fine spectral resolution Δλ is also required to facilitate screening over several chemicals. A fundamental limit states that Δλ is inversely proportional to the mirror motion range, which cannot exceed the chip size. To boost the spectral resolution beyond this limit, we propose the concept of parallel (or multi-core) FTIR, where multiple interferometers provide complementary optical paths using the same actuator and within the same chip. The concept scalability is validated with 4 interferometers, leading to approximately 3 times better spectral resolution. After the atmospheric contents of a greenhouse gas are monitored, the methane absorption bands are successfully measured and discriminated using the presented device. Micro-spectrometry: chip-scale optical spectrometer for ubiquitous chemical analysis A chip-scale optical spectrometer using a microelectromechanical system allows selective and contactless chemical analysis in the field by means of infrared spectral sensing. The widespread application of optical spectrometers for chemical analysis has been hampered by their size and cost. However, a team of scientists from Egypt and France was able to overcome the two main challenges to greater deployment of such spectrometers. First, the authors were able to extend the spectrometers’ spectral range to the infrared, thereby allowing analysis of a broad variety of materials. Second, the team could achieve fine spectral resolution, facilitating distinguishing different chemical substances. The authors plan to enhance their system to mid-infrared or even far-infrared wavelengths, and they believe that possible applications include air-quality monitoring, food analysis, precision agriculture and medical diagnosis.