Bright, stable frequency combs enabled by racetrack quantum cascade lasers

Harvard researchers and collaborators at TU Wien have developed a racetrack-shaped quantum cascade laser that generates bright, stable mid-infrared frequency combs on a chip, opening a path toward compact dual-comb spectrometers for gas sensing and industrial monitoring. The work was co-led by Ted Letsou and Johannes Fuchsberger and published in Optica.

The device uses radio-frequency injection to lock the laser into a broadband comb state. Unlike conventional straight-bar semiconductor comb lasers, the racetrack design is inherently resistant to optical feedback, a key obstacle to miniaturizing mid-infrared comb systems. In experiments, the comb remained stable even under strong reflected light. 

The platform could enable chip-scale tools for greenhouse gas sensing, industrial process monitoring, and medical diagnostics such as breath analysis. For more information, see the press release from Harvard SEAS.

Artistic rendering by Joshua Mornhinweg.