A microchip about the size of a grain of rice can generate a highly organized “rainbow” of light, a capability that could eventually support faster, higher-capacity 6G communications and extremely precise timing for quantum technologies.
Physicists at Loughborough University, working with an international research team, demonstrated a system that produces a series of precisely spaced light frequencies. Those optical frequencies can then be converted into multiple high-frequency electromagnetic signals known as millimeter waves.
Millimeter waves are attracting growing interest for future communications because they can provide considerably more bandwidth, giving networks more room to transmit data. A major obstacle, however, has been producing these signals with the precision and stability required for advanced applications.
“The world is becoming increasingly data hungry. We want to send and receive more information, faster and in higher resolution, and millimeter waves could help provide the capacity to do that,” said Dr. Luke Peters, of Loughborough University’s Emergent Photonics Research Centre.
“They could ultimately contribute to faster, higher capacity 6G networks, but the potential goes far beyond communications. These frequencies could also be used in radar systems as well as spectroscopy and astronomical instruments, helping scientists study materials and make extremely precise measurements of the universe.
“These applications are still some way off, and there are challenges to overcome before the technology can be used in real-world systems – but our latest work has tackled a major one.”
Microcombs Could Create Multiple 6G Channels
One method for producing millimeter waves relies on a device known as a microcomb. A microcomb generates an extremely precise set of light frequencies arranged somewhat like the colors in a rainbow, although the light itself is invisible to the human eye. A specialized antenna can then convert those optical frequencies into millimeter waves.
Earlier research demonstrated that microcombs could produce a single precise millimeter wave frequency. Generating many frequencies simultaneously could be far more useful because each could potentially serve as a separate channel for transmitting information at the same time. Achieving that, however, requires a microcomb with exceptional stability and signal quality.
In a new Nature Communications paper, the Loughborough led researchers report a system capable of doing exactly that. Their approach produces a stable, high-quality microcomb that can be converted into several precisely spaced millimeter-wave frequencies simultaneously.
The difference lies in how the microcomb is produced. Conventional systems typically shine laser light into a microresonator, a tiny structure built onto a microchip that traps light and allows it to circulate.
The Loughborough system instead connects the chip-based microresonator to a much larger loop of optical fiber. Laser light continuously travels through both parts of the system, helping the desired optical states form and remain stable.
“We’ve essentially created an incredibly precise and stable ‘rainbow on a chip’, where the loop keeps feeding the light back through the chip, allowing these states to build up efficiently, start on their own and remain stable even when the system is disturbed,” said Dr. Peters.
“It’s remarkably robust too. We’ve even had people jumping up and down next to the system and the microcomb remains stable.”
A Stable and Controllable Rainbow of Light
The researchers also showed that they can manipulate the microcomb’s “rainbow” by increasing or decreasing the strength of individual frequencies. Importantly, the precision and stability of the optical microcomb were preserved after the light was converted into millimeter-wave signals.
That control could allow future systems to generate different combinations of frequencies depending on the application.
“Being able to make individual frequencies stronger or weaker gives us much more control over the signals we produce, because different applications will need different combinations of frequencies,” said Dr. Peters.
“Just as importantly, we’ve shown that the precision of the microcomb carries through to the millimeter waves. That gives us a whole set of highly controlled signals, which is exactly what you need for applications where accuracy and stability matter.
“That same level of precision is valuable for timing. Precision timing sits at the core of emerging quantum technologies, where extreme accuracy is a requirement.”
Shrinking the Technology Beyond the Laboratory
The team is now investigating how the microcomb system could eventually move from a laboratory experiment into practical technology.
Although the central microchip is only about the size of a grain of rice, the entire system currently occupies a tabletop laboratory setup. Researchers believe future versions could become significantly smaller and more energy efficient, potentially compact enough to fit inside a shoebox.
One possibility the team is especially interested in is using the technology aboard satellites, where minimizing size, weight and power consumption is particularly important.
Precision Timing for Quantum Technologies
Researchers are also working to determine the ultimate accuracy of the microcomb system. They are comparing it with precision clocks and investigating possible uses in timing, navigation and position through collaborations with the National Physical Laboratory and as part of broader efforts involving the National Physical Laboratory and the UK Hub for Quantum Enabled Position, Navigation and Timing (QEPNT).
“We’re really excited to see how far we can take the precision and stability of these microcombs, particularly for technologies that rely on extremely accurate timing,” said Dr. Antonio Cutrona, who led the microcomb stability measurements.
“We hope this study and our system open up new ways of bringing the extraordinary precision of atomic clocks into more compact technologies for timing, navigation and position, and it is particularly exciting to explore these possibilities through our wider collaborations with the National Physical Laboratory and the UK Hub for Quantum Enabled Position, Navigation and Timing.”
The study brings together expertise from Loughborough University’s Emergent Photonics Research Centre, the University of Sussex, City University of Hong Kong, QXP Technologies, INRS-EMT, and Swinburne University of Technology and ARC-COMBS.