John Russell saw it for the first time when he was riding a horse along a canal – a mount of water was being pushed along with a boat. The boat stopped but the single peaked wave continued along the canal for several miles, in what he described as a “solitary wave” or “wave of translation”. It was 1834 when this naval engineer observed a macroscopic version of a soliton, a solitary wave that propagates through space without a change in its shape.
Almost two hundred years after Russell’s observation, an international research team – which includes the Técnico professor Marco Piccardo – has published an article in Nature that proposes replicating this phenomenon on the scale of a chip, using pulses of light in semiconductor rings. This size reduction can be crucial, especially in fields where space and efficiency are important, such as environmental monitoring, medical diagnostics and security. The international research team also includes researchers from TU Wien University, Harvard University and a consortium of Italian research institutes.
Marco Piccardo, also a researcher at Instituto de Engenharia de Sistemas e Computadores para os Microsistemas e Nanotecnologias (INESC MN) and co-supervisor of this research, explains: “When we started exploring these semiconductor ring lasers in 2020, we observed interesting physics, like a form of optical turbulence, but the idea of creating solitary pulses in these cavities seemed far-fetched. This breakthrough not only miniaturizes solitons to a handheld scale but also enables their efficient extraction from the cavity, thanks to an active port that we engineered, coupled to the ring.” The outcoupler architecture is further detailed in a companion paper appearing now in Nature Communications.
Soliton lasers, known for generating ultrashort pulses of light, have existed in tabletop systems like fibers but are typically bulky. The groundbreaking discovery by the research team miniaturized soliton lasers into tiny, microscopic rings with completely new applications in a compact form. The laser’s operation within the mid-infrared region of the electromagnetic spectrum places it at a strategic advantage for key applications. The mid-infrared range is particularly important in spectroscopy and sensing, because many substances have their molecular fingerprint here, offering unique opportunities for advancements in environmental monitoring, medical diagnostics, and security. By harnessing this spectrum, the soliton laser technology heralds a new era in precise and compact sensing and spectroscopic tools.
