It’s a compact laser chip that emits a special type of ultrafast pulse known as solitons (which occur in the picosecond range, or one thousandth of a nanosecond), and has earned the team that developed it an article published in Nature. Marco Piccardo, a professor at Instituto Superior Técnico and a researcher at INESC Microsistemas e Nanotecnologias (INESC MN), is the third author of the article.
Solitons are peculiar pulses of light that maintain their shape over time and distance, being resistant to disturbances. They are particularly promising due to their applications in ultrafast data transmission and spectroscopy (the study of the absorption and emission of radiation by matter), significantly increasing the speed and efficiency of these systems.
The work demonstrates that, contrary to the idea that solitons could only be produced in more complex and larger systems, two miniature lasers on a single chip – one of which acts as a source and the other as a resonance ring where these pulses are formed – are enough to create stable solitons in the mid-infrared region at the rate of one billion pulses per second (i.e. one gigahertz), with minimal energy consumption.
The idea for this innovation originated in early 2020 during a conversation between Marco Piccardo and physicist Luigi Lugiato (known for the Lugiato-Lefever equation celebrated in the field of quantum optics). “We didn’t expect such a clear path to the creation of bright solitons, let alone in such a practical and integrated device”, says the Técnico professor, who also serves as a guest lecturer at Harvard University.
This is not the first time that the work of Marco Piccardo’s team has been published in Nature. In January 2024, the same research team demonstrated a compact, ring-shaped semiconductor laser capable of producing dark solitons. These dark solitons can be visualised as flashes of darkness that propagate through a continuous stream of light, resembling a “pulsating shadow”). Although they are intriguing from a theoretical standpoint, dark solitons have limited practical applications, as most technological uses favour bright solitons—pulses of intense light traveling over a constant luminous background.
To address this limitation, the team’s recent discovery involves integrating an additional auxiliary laser into the ring. This external laser source allows for the initiation and control of the formation of bright solitons, which have broader applications, all on a compact, chip-integrated platform.
After years of theoretical and experimental studies involving researchers from Harvard, TU Wien and colleagues in Italy, these results pave the way for compact and powerful photonics technologies in the mid-infrared radiation region.
