A microchip about the size of a grain of rice can generate a precisely spaced spectrum of light and convert it into multiple high-frequency millimeter-wave signals, giving researchers a way to produce several controlled frequencies at the same time.
Millimeter waves are attracting interest for future communications because they can provide more bandwidth, creating more space for transmitting data. But producing these signals with the precision and stability needed for advanced technologies remains difficult.
One approach uses a device called a microcomb. It produces a highly precise set of light frequencies arranged at regular intervals. The frequencies are invisible to the human eye, but they can be converted into millimeter waves with a specialized antenna.
Earlier work had demonstrated microcombs producing a single precise millimeter-wave frequency. The new work takes that idea further by producing multiple frequencies at once.
A team led by physicists at Loughborough University, working with international collaborators, built a system that produces a stable, high-quality microcomb and demonstrated that its precisely spaced frequencies can be converted into multiple millimeter-wave signals.
The microcomb uses a larger fiber loop
Microcombs are usually produced by sending laser light into a microresonator, a tiny structure on a microchip that traps and circulates light.
The Loughborough team’s system adds a larger loop of optical fiber to the chip-based microresonator. Laser light continually circulates through both parts of the system.
The arrangement allows the optical states needed to form the microcomb to build up efficiently and remain stable when the system is disturbed.
The researchers also tested how much control they had over the resulting spectrum. They were able to make individual frequencies stronger or weaker, allowing different combinations of frequencies to be produced.
That control is important because different applications can require different sets of signals. The researchers also found that the precision and stability of the optical microcomb were carried through to the millimeter-wave signals generated from it.
The system remained stable during disturbances
The team tested the stability of the microcomb under physical disturbances. According to Dr. Luke Peters of Loughborough University’s Emergent Photonics Research Center, the system remained stable even when people were jumping up and down next to it.
The researchers describe the ability to maintain a stable microcomb as a key part of producing multiple precisely controlled millimeter-wave frequencies.
Peters said the resulting signals could eventually contribute to higher-capacity communications systems, including future 6G networks. The researchers also identify possible uses in radar, spectroscopy and astronomical instruments.
Those applications are not yet ready for real-world use, and the researchers say challenges remain before the technology can be deployed in practical systems.
From a tabletop setup to smaller systems
Although the microchip itself is about the size of a grain of rice, the complete system currently occupies a tabletop laboratory setup.
The researchers are now investigating how the technology could be made smaller and more energy-efficient. They say future versions could potentially be compact enough to fit inside a shoebox.
The team is also interested in whether the technology could eventually be used on satellites, where size, weight and power are important considerations.
Testing the system for precision timing
The researchers are also studying the precision of the microcomb for applications that depend on highly accurate timing.
The team is testing the system against precision clocks and exploring possible uses in timing, navigation and positioning through collaborations with the National Physical Laboratory and the UK Hub for Quantum Enabled Position, Navigation and Timing.
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 researchers are also exploring whether the precision associated with atomic clocks could eventually be brought into more compact technologies for timing, navigation and positioning.
The study was published in Nature Communications.
