Chip-Based Mid-IR Dual-Comb Spectrometer

Schematic of silicon microresonator generating a frequency comb that samples molecules for chemical identification. (Source: A. Gaeta, Columbia Univ.)

Researchers at Columbia Engi­neering have demons­trated, for the first time, a chip-based dual-comb spectro­meter in the mid-infrared range, that requires no moving parts and can acquire spectra in less than 2 micro­seconds. The system, which consists of two mutually coherent, low-noise, micro­resonator-based frequency combs spanning 2600 nm to 4100 nm, could lead to the development of a spectro­scopy lab-on-a-chip for real-time sensing on the nano­second time scale.

“Our results show the broadest optical bandwidth demons­trated for dual-comb spectro­scopy on an inte­grated platform,” said Alexander Gaeta, David M. Rickey Professor of Applied Physics and of Materials Science. Creating a spectro­scopic sensing device on a chip that can realize real-time, high-through­put detec­tion of trace molecules has been chal­lenging. A few months ago, teams led by Gaeta and Michal Lipson, Higgins Professor of Electrical Engi­neering, were the first to minia­turize dual-frequency combs by putting two frequency comb genera­tors on a single millimeter-sized chip. They have been working on broa­dening the frequency span of the dual combs, and on increasing the reso­lution of the spectro­meter by tuning the lines of the comb.

Now, the researchers focused on the mid-infrared (mid-IR) range, which, because its strong molecular absorp­tion is typi­cally 10 to 1,000 times greater than those in the visible or near-infrared, is ideal for detecting trace molecules. The mid-IR range effec­tively covers the finger­print of many molecules. The team performed mid-IR dual-comb spectro­scopy using two silicon nano­photonic devices as micro­resonators. Their inte­grated devices enabled the direct generation of broadband mid-infrared light and fast acqui­sition speeds for charac­terizing molecular absorp­tion.

“Our work is a critical advance for chip-based dual-comb spectro­scopy for liquid/solid phase studies,” said Mengjie Yu, a PhD student in Gaeta’s lab. “Our chip-scale broadband optical system, essen­tially a photonic lab-on-a-chip, is well-suited for identi­fication of chemical species and could find a wide range of appli­cations in chemistry, biome­dicine, material science, and indus­trial process control.” (Source: Columbia Univ.)

Reference: M. Yu et al.: Silicon-chip-based mid-infrared dual-comb spectroscopy, Nat. Commun. 9, 1869 (2018); DOI: 10.1038/s41467-018-04350-1

Link: Quantum and Nonlinear Photonics (A. Gaeta), Dept. of Applied Physics and Applied Mathematics, Columbia University, New York, USA

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