Qi, Yanli, Zheng, Zhexuan, Banakar, Mehdi, Wu, Yangbo, Gangnaik, Anushka, Rowe, David, Mittal, Vinita, Butement, Jonathan, Wilkinson, James S, Mashanovich, Goran and Nedeljković, Miloš (2021) Integrated switching circuit for low-noise self-referenced mid-infrared absorption sensing using silicon waveguides. IEEE Photonics Journal, 13 (6), [6600110]. (doi:10.1109/JPHOT.2021.3121331).
Abstract
We report a new method of accurately measuring the mid-infrared absorption of fluid analytes using on-chip waveguides that allows measurements to be referenced for noise and drift reduction whilst using only a single external detector. A silicon-on-insulator waveguide circuit integrated with a microfluidic channel is made in which a pair of switches alternate light between an evanescent absorption sensor waveguide and a reference waveguide at a rate of a few kHz, thus allowing low frequency common noise components to be removed from the measurement, and leading to a reduction in the noise floor by a factor of 11 compared to a simple waveguide absorption sensor. The device was verified by using it to detect an Isopropyl alcohol (IPA) absorption peak at a wavelength of 3.77 μm.
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