A hundred times brighter UV light on a photonic chip

The researchers solved this with a clever conversion process. They started with red light, which has been relatively straightforward to generate on a chip for several years, and converted it into UV. In the process, two red photons convert into a single UV photon. Until now, this approach has produced only minimal light output on chips. This study is the first to generate a useful amount of UV light: several milliwatts, roughly a hundred times more than previous work.

The team worked with thin-film lithium niobate. The chip-scale version of this material was pioneered by a group at Harvard, where the current research was also carried out. The material has drawn considerable attention in recent years for its unusual properties.

Using this material, the researchers built a distinctive waveguide: a nanometre-scale structure on the chip that channels and confines light. They manipulated the waveguide along its entire length of nearly two centimetres. To do so, they first measured its shape to a precision of a few dozen atomic diameters.

With electrodes running along the sides of the waveguide, the team reversed the orientation of the material's crystal structure periodically, up to a thousand of times per millimetre. Alternating voltage on and off along the waveguide creates the pattern that enables the conversion. Each of the roughly 10,000 electrodes per waveguide is unique, tailored to the exact shape of the waveguide at that specific point on the chip.

In earlier work, electrodes were placed some distance away from the waveguide. "In our design, they sit right on it," says Franken. "That required a fabrication process accurate to fifty nanometres across a chip several centimetres long. But it gives us far more control, and the conversion from red to UV works much more efficiently."

The results matter most for technologies that are still bulky, expensive and hard to scale. Quantum computers are a prime example. "If you want to scale systems like that, you need on-chip light sources," says Franken. The same applies to optical atomic clocks, which are so precise that they can even detect differences in gravity. Putting them on a chip makes them compact and practical enough for satellites, for instance.

The technology is not confined to academic papers. The underlying knowledge has been secured in a UT spin-off, Sabratha. The start-up focuses on thin-film lithium niobate and on scaling up these photonic chips for telecom and wireless communication.

Dr Kees Franken was a PhD candidate in the Laser Physics and Nonlinear Optics Group (Faculty of Science and Technology; MESA+) and spent more than two years of his PhD research at Harvard University. He is now CEO of UT spin-off Sabratha and a postdoc in the Nonlinear Nanophotonics Group (Faculty of Science and Technology; MESA+). The researchers describe their technique in the paper Milliwatt-level UV generation using sidewall poled lithium niobate, published today in Nature Communications.

DOI: 10.1038/s41467-026-68524-y