Physicists at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have unveiled a groundbreaking advancement in photonic technology: a compact, chip-scale laser capable of emitting ultrashort, intense pulses of light within the challenging mid-infrared spectrum. This pioneering device integrates the power and precision of traditionally bulky laser apparatuses into a single semiconductor chip, marking a transformative step forward in mid-infrared photonics and broadening the horizons for environmental sensing, medical diagnostics, and fundamental physics research.
Published recently in the journal Nature, this work introduces the first-ever on-chip generator of picosecond laser pulses within the mid-infrared region that operates independently, without any need for external modulators or complex supplementary components. Central to its function is the creation of an optical frequency comb—a distinct spectrum composed of narrowly spaced lines of coherent light frequencies. This feature augments the device’s utility in precision measurement techniques that rely on spectral benchmarking and calibration, areas critical for next-generation sensing and spectroscopy platforms.
At the heart of this innovation lies the quantum cascade laser (QCL), a semiconductor light source lauded for producing coherent mid-infrared radiation by engineering multiple quantum-well layers that facilitate electron transitions. Unlike traditional mode-locked lasers that generate short pulses through established techniques, QCLs have historically resisted efficient mode-locking owing to their ultrafast carrier dynamics and intrinsic nonlinearities. Previous mid-infrared pulse sources typically depended on intricate external setups, which limited their scalability, tunability, and practicality for widespread applications.
This new device circumvents these limitations by harnessing nonlinear integrated photonics, incorporating innovative ring resonator circuits on-chip that resonate with the primary QCL source. The design draws inspiration from Kerr microresonators—photonic structures famed for producing soliton frequency combs in the near-infrared—with a novel adaptation that applies these principles within the mid-infrared range. By integrating an active laser section with passive and active resonators acting as filters and modulators, the laser chip can directly generate so-called “bright solitons,” ultrashort and stable pulses that maintain their shape through a balance of dispersion and nonlinear effects.
The implications are profound. The device’s broadband emission can capture hundreds to thousands of discreet frequencies simultaneously, a technological leap toward realizing on-chip supercontinuum light sources. Such sources hold promise for revolutionizing environmental gas detection — especially for molecules like carbon dioxide and methane that exhibit strong absorption lines in the mid-infrared — allowing single-chip sensors to differentiate multiple gases in real time with unprecedented sensitivity.
Federico Capasso, the Robert L. Wallace Professor of Applied Physics at SEAS and lead senior author of the study, emphasized the industrial relevance of their achievement: “Not only does this integration represent a new frontier in photonics, but it also brings the possibility of mass production using standard semiconductor fabrication techniques within reach. This scalability is key for transitioning from laboratory demonstrations to real-world deployment in environmental monitoring and medical fields.”
The researchers collaborated with international experts, including the Schwarz group at Vienna University of Technology and a consortium of Italian scientists led by Luigi A. Lugiato, co-author and visionary behind the theoretical foundations of soliton models. Lugiato reflected on the journey linking theory to experiment, highlighting the use of the Lugiato-Lefever equation, an equation initially formulated in the 1980s to model passive Kerr resonators, now extended to describe active, optically driven QCL dynamics in this breakthrough device.
One of the unique challenges overcome in this work lies in synchronizing the coupled ring resonators with the QCL emission under steady operating conditions without incurring complex synchronization setups. The device maintains stable soliton generation over hours, a testament to both the robustness of the design and the precise nanofabrication strategies employed at TU Wien, where the chips were fabricated. The novelty also stems from avoiding traditional mode-locking, instead exploiting nonlinear effects intrinsic to the chip architecture to directly form soliton pulses.
The quantum cascaded layering of semiconductor materials in this device allows fine tailoring of gain and refractive index profiles, which harmonize with the resonators’ optical modes. This synergy enables the laser to navigate its ultra-fast carrier dynamics and nonlinear responses, thereby supporting lasing regimes previously inaccessible in integrated mid-infrared photonics. These advances point toward the feasibility of multi-component, complex photonic chips capable of versatile functionality—once deemed unattainable in this spectral region.
Co-first author Dmitry Kazakov, from Capasso’s group, highlighted the future potential: “By leveraging the interplay between nonlinear optics and quantum cascade physics, we foresee creating fully integrated supercontinuum sources on a chip. This device lays the foundation for generations of broadband emitters that can sample molecular fingerprints across vast spectral ranges, propelling applications in gas sensing, industrial process control, and biomedicine.”
Additional perspectives from co-author Benedikt Schwarz at TU Wien underscore the significance of fabricating and reliably operating multicomponent mid-infrared architectures. Schwarz noted, “Our confidence in controlling integrated nonlinear photonics architectures has raised the bar. The door is now open to explore functionalities such as tunable filtering, switching, and multi-wavelength generation within mid-infrared platforms.”
Timothy Day, Senior VP and General Manager at Leonardo DRS Daylight Solutions, the industrial partner in the collaboration, hailed the findings as a potential “game-changer” for the mid-infrared spectroscopy market. He underscored that employing existing semiconductor manufacturing infrastructure to mass-produce these laser chips could rapidly accelerate their commercialization, boosting applications from advanced pollution monitoring to cutting-edge life sciences research.
Financial backing from agencies including the National Science Foundation and the Department of Defense underscores the strategic importance of this research, which integrates fundamental physics concepts with scalable engineering solutions. Harvard’s Office of Technology Development is currently actively exploring commercialization pathways to bring this revolutionary technology from proof-of-concept to impactful, real-world utilization.
This milestone not only enriches the landscape of mid-infrared photonics but also exemplifies how interdisciplinary collaboration and theory-driven design can unlock novel optoelectronic devices. It opens an exhilarating chapter where chip-based, ultrafast mid-infrared lasers become pivotal tools in sensing, spectroscopy, and beyond.
Subject of Research: Not applicable
Article Title: Driven bright solitons on a mid-infrared laser chip
News Publication Date: 16-Apr-2025
Web References:
https://www.nature.com/articles/s41586-025-08853-y
References:
DOI: 10.1038/s41586-025-08853-y
Image Credits: Runke Luo
Keywords:
Laser spectroscopy, Light sources, Laser light, Quantum cascade lasers, Environmental monitoring, Wavelengths, Solitons, Gas lasers, Applied sciences and engineering, Applied physics, Applied optics, Engineering, Electrical engineering, Materials engineering, Physics, Optics, Nonlinear optics, Quantum optics
