Harvard Team Achieves Milliwatt UV Light Generation On a Photonic Chip

by Clarence Oxford
Los Angeles CA (SPX) Apr 29, 2026
Researchers at Harvard have demonstrated a chip-scale ultraviolet light source built on thin-film lithium niobate that generates 4.2 milliwatts of on-chip UV power at 390 nanometers wavelength -- approximately 120 times more output power than any previous comparable demonstration on the same material platform.

Ultraviolet light is used across a wide range of modern applications, from surface disinfection and fluorescence imaging of biological materials to photolithography in semiconductor manufacturing. At the chip scale, compact UV sources are expected to enable advances in trapped-ion quantum computers, ultra-precise atomic clocks, and compact environmental sensors capable of monitoring greenhouse gases and atmospheric pollutants.

The core challenge has been that UV light loses power rapidly as it travels through optical waveguides, making it extremely difficult to build practical chip-scale sources at these wavelengths. The Harvard team, working in the lab of Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering, addressed this by converting red light to UV light directly on the chip rather than attempting to deliver UV light from an external source.

In the frequency upconversion process used by the device, two red photons combine inside the lithium niobate crystal to produce a single higher-energy UV photon. Lithium niobate is already a well-established platform for integrated photonics, particularly at infrared and telecommunications wavelengths, but this work demonstrates it can also guide and host light sources at much shorter UV wavelengths.

"When people think about [thin-film lithium niobate], they don't think of it as a UV material, but we show that it is," said co-first author Kees Franken, a former research fellow in the Loncar lab. "We also show that there are some other nonlinear effects happening that we don't fully understand yet."

Efficient frequency conversion in lithium niobate requires a nanofabrication process called poling, in which the crystal grain structures are periodically flipped at precisely controlled intervals along the waveguide. Getting that periodic pattern exactly right -- at sub-micron length scales over centimeter-long devices -- has been the central limitation of earlier attempts.

Previous fabrication approaches faced a fundamental tradeoff. Poling the entire film before etching the waveguides preserved poling quality but eliminated the ability to compensate for fabrication imperfections. Fabricating waveguides first and then poling allowed corrections, but the electrodes had to be placed far from the waveguide, resulting in only partial poling of the film and reduced conversion efficiency.

The Harvard team invented a new technique they call sidewall poling to resolve this tradeoff. Rather than placing electrodes only above the film, they patterned metal electrodes -- shaped as narrow metal fingers -- directly against the sidewalls of the etched waveguide, requiring positioning accuracy of approximately 50 nanometers.

"The key idea was: could we just put the electrodes directly on the waveguide?" said co-first author Soumya Ghosh, a former graduate student in the lab. Placing electrodes at the sidewalls allowed the researchers to fully invert the crystal domains across the entire waveguide cross-section, so that all the light passing through the device sees a uniformly flipped material structure. This maximizes conversion efficiency throughout the waveguide.

The geometry also allowed the team to tailor the poling period along the length of the device, drawing on adapted poling techniques previously developed by the Loncar group and others, to compensate for variations in film thickness and waveguide shape that are unavoidable in cleanroom fabrication.

Earlier thin-film lithium niobate demonstrations at this wavelength range produced only tens of microwatts of UV power -- enough to establish feasibility but far below the threshold for practical applications. The new device's 4.2 milliwatt output represents a step toward real-world usefulness.

Trapped-ion quantum computers require precisely controlled UV light at wavelengths corresponding to specific atomic transitions, and scaling these systems down to chip-level components is considered essential for making the technology practical. "If you want a scalable quantum computer that isn't the size of a truck, you need to scale everything down to the chip level, and this includes the light sources," Franken said.

Ghosh and Franken attributed the advance in part to the Loncar lab's integrated approach to research, combining theoretical design, cleanroom fabrication, and optical characterization within a single group. "The hands-on intuition that we gained for how to make a device, while also keeping the zoomed-out view of what this device is for, and how we were going to characterize it -- that's a big part of what enabled this project for us," Ghosh said.

The paper was co-authored by C.C. Rodrigues, J. Yang, C.J. Xin, S. Lu, D. Witt, G. Joe, G.S. Wiederhecker, and K.-J. Boller. Funding came from the Department of the Air Force, the Office of Naval Research, NASA, and the National Science Foundation.

Research Report:Milliwatt-level UV generation using sidewall poled lithium niobate