Harvard’s SEAS creates single-chip laser that emits mid infrared pulses

17 Apr 2025

First on-chip, picosecond MIR laser pulse generator to requires no external components.

The research team in the Capasso lab.

Physicists in Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) have created a compact laser that emits extremely bright, short pulses of light in the “useful” mid-infrared wavelength range, packing the performance of larger photonic devices onto a single chip.

The research described in Nature, the research is the first demonstration of an on-chip, picosecond, mid-infrared laser pulse generator that requires no external components to operate. The device can make an optical frequency comb, a spectrum of light consisting of equally-spaced frequency lines, used today in precision measurements. The new laser chip could one day speed the creation of highly sensitive, broad-spectrum gas sensors for environmental monitoring, or new types of spectroscopy tools for medical imaging.

The paper’s senior author is Prof. Federico Capasso. Supported by the U.S. National Science Foundation and Department of Defense, the research was a collaboration with the Schwarz group at Vienna University of Technology; a consortium of Italian scientists led by Luigi A. Lugiato; and Leonardo DRS Daylight Solutions, led by Timothy Day.

“This is an exciting new technology that integrates on-chip nonlinear photonics to generate ultrashort pulses of light in the mid-infrared; no such thing existed until now,” Capasso said. “What’s more, such devices can be readily produced at industrial laser foundries using standard semiconductor fabrication.”

“It’s a key step to creating a supercontinuum source, which can generate thousands of different frequencies of light, all in one chip,” said Dmitry Kazakov, co-first author and research associate in Capasso’s group.

Fabricating multicomponent architectures

Microscope image of the quantum cascade photonic integrated chip.

Fundamental to the new feat of nanophotonic engineering is the quantum cascade laser, which generates coherent beams of mid-infrared light by layering together different nanostructured semiconductor materials. Unlike other semiconductor lasers that have relied for decades on mode-locking to generate their pulses, quantum cascade lasers remain notoriously difficult to pulse due to their inherently ultra-fast dynamics.

The new pulse generator seamlessly combines, into a single device, several concepts in nonlinear integrated photonics and integrated lasers to make specific types of picosecond light pulses called solitons. In designing their chip architecture, the researchers took inspiration from a seemingly unrelated type of modulator called a Kerr microresonator.

“Our measurements were non-traditional when it came to quantum cascade laser research,” said co-first author Theodore Letsou, a graduate student at MIT and research fellow in Capasso’s group. “We merged two types of fields and took what the Kerr resonator community does and applied it to our systems.”

“The most significant impact of our new work is the confidence it has given us in fabricating multicomponent architectures,” said paper co-author Benedikt Schwarz, professor at TU Wien (Vienna, Austria). “We’re already developing new architectures to enable functionalities previously thought impossible.” The researchers drew on a foundational theory published in the 1980s that established a framework for passive Kerr resonators. One of the new paper’s co-authors is Luigi Lugiato, who worked on repurposing his original equation to describe the dynamics of the mid-IR laser system.

“This is an exciting culmination of a journey that began with the Lugiato-Lefever equation,” said Lugiato, professor emeritus at the University of Insubria, Italy. “What started as a model for passive systems has evolved into a unified framework for soliton frequency combs in all kinds of cavities. That path led us to predict solitons in optically driven quantum cascade lasers above threshold – now confirmed by this experiment.” The new mid-infrared laser can reliably maintain pulse generation for hours at a time. Crucially, it can also be mass-produced using existing industrial fabrication processes, which could greatly increase the speed of its widespread adoption. The chips were made at TU Wien.

“This technology promises to be a real game-changer in the field of mid-infrared spectroscopy,” said paper co-author Timothy Day, Senior Vice President and General Manager of Leonardo DRS’ Daylight Solutions business unit. “The ability to leverage existing fabrication processes to produce these devices in commercial volumes could really enable what’s next in several markets, including environmental monitoring, industrial process control, life sciences research and medical diagnostics.”