Broadband frequency combs in the long-wavelength infrared (LWIR, 8–13 µm) hold great promise for high-precision sensing and spectroscopy, but achieving comb operation in this regime has been limited by strong material dispersion and fabrication constraints. This talk presents recent advances enabling an on-chip LWIR quantum-cascade laser (QCL) frequency comb with unprecedented bandwidth through precise dispersion engineering. I will first introduce the background in dual-comb spectroscopy, fundamental comb theory, and traditional dispersion characterization techniques. Building on this foundation, I will describe a new dispersion-characterization approach that quantifies bias-dependent group-velocity dispersion in LWIR QCLs and the subsequent implementation of an air-dielectric double-chirped mirror (DCM) providing tailored broadband compensation. I will then delve into the key fabrication challenges—deep subwavelength etching, high-aspect-ratio structures, and thermal management—that were overcome to realize the integrated device, which achieves record-broadband, coherent comb emission near 9.6 µm with a single narrow beatnote. These results highlight a powerful platform for dispersion-controlled LWIR photonics and chart a path toward octave-spanning, chip-scale combs across the mid- to far-infrared.

Tianyi Zeng is a postdoctoral researcher at Harvard University’s School of Engineering & Applied Sciences, working with Prof. Kiyoul Yang on integrated nonlinear laser devices. His research focuses on developing high-performance silicon nitride and aluminum oxide nanophotonic platforms for ultrafast and nonlinear photonics, achieving record-low optical losses and broadband gain. He received his Ph.D. in Electrical Engineering from MIT under Prof. Qing Hu, where he demonstrated ultrabroadband long-wave infrared quantum cascade laser frequency combs with integrated dispersion compensation. Tianyi’s work bridges semiconductor nanofabrication, III-V and solid-state lasers, and nonlinear integrated photonics. He is also co-founding a startup to commercialize an integrated chip-scale optical circuit switch and amplifier—technology aimed at enabling high-speed, energy-efficient AI data-centers.

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