Multiple precisely spaced millimeter-wave signals can be produced from a microchip about the size of a grain of rice, using a stable spectrum of light that carries its precision into the resulting high-frequency electromagnetic signals. The Loughborough University-led team says the approach could eventually support technologies that require tightly controlled frequencies, including future communications and precision timing.
Millimeter waves are being explored for future communications because they offer much more bandwidth, creating more space for transmitting data. Producing these high-frequency signals with the precision and stability needed for advanced technologies remains challenging.
The researchers used a device known as a microcomb. It produces a set of light frequencies with precise spacing between them. A specialized antenna can then convert those optical frequencies into millimeter waves.
Earlier studies had used microcombs to generate a single precise millimeter-wave frequency. Generating many frequencies at once could allow multiple channels to carry data simultaneously, but doing that requires an exceptionally clear and stable microcomb.
The new system was built to provide that stability while producing multiple frequencies at the same time.
A fiber loop helps keep the light stable
Microcombs are typically made by sending laser light into a microresonator, a tiny structure on a chip that traps and circulates light.
The Loughborough design combines the chip-based microresonator with a larger loop of optical fiber. Laser light continually circulates through both parts of the system.
According to the researchers, this arrangement allows the light states to build up efficiently, start on their own and remain stable when the system is disturbed.
The team tested the system during physical disturbances and reported that the microcomb stayed stable even when people were jumping up and down next to it.
The frequencies can be adjusted
The researchers also demonstrated control over the microcomb’s individual frequencies. Some frequencies could be made stronger while others were made weaker.
This provides greater control over the combinations of frequencies produced, which the researchers say could be useful because different applications may require different frequency combinations.
The team also found that the precision and stability of the microcomb were carried through when its optical frequencies were converted into millimeter-wave signals.
Dr. Luke Peters of Loughborough University’s Emergent Photonics Research Center said the controlled signals could be relevant to applications where accuracy and stability are important. He also pointed to precision timing as an area of interest because emerging quantum technologies require extremely accurate timing.
Possible applications remain under development
The researchers say the technology could eventually contribute to faster, higher-capacity 6G networks. They also identify possible uses in radar systems, spectroscopy and astronomical instruments.
Those applications are still some way from real-world systems, and challenges remain before the technology can be used in practice.
The microchip itself is about the size of a grain of rice, but the complete system currently occupies a tabletop laboratory setup. Future versions could potentially become more compact and energy-efficient, with the researchers exploring whether the system could eventually fit inside a shoebox.
Satellite applications are another area of interest because size, weight and power are important considerations there.
Precision timing is being tested
The team is also investigating how accurately the microcomb can operate by testing it against precision clocks.
Collaborations with the National Physical Laboratory and the UK Hub for Quantum Enabled Position, Navigation and Timing are examining potential applications in timing, navigation and positioning.
Dr. Antonio Cutrona, who led the microcomb stability measurements, said the researchers are testing how far the precision and stability of the system can be taken, particularly for technologies that depend on extremely accurate timing.
The study was published in Nature Communications.
