Scientists have achieved a major step toward chip-scale ultraviolet light by converting red light into powerful UV within a tiny photonic device. Ultraviolet light, beyond what comes naturally from the sun, plays a central role in modern technology, including sterilization, biological imaging, and chip manufacturing. Researchers also expect tiny sources of UV light on photonic chips to support future advances in quantum computing and ultra-precise atomic clocks. However, shrinking UV light sources to the chip scale has proven difficult because this light quickly loses strength as it travels through optical waveguides, limiting practical designs until now. A Harvard-led team from the lab of Marko Lončar, the Tiantsai Lin Professor of Electrical Engineering, has demonstrated a micron-scale photonic device built on thin-film lithium niobate that produces about 100 times more UV light on a chip than earlier methods. The study, published in Nature Communications, highlights lithium niobate as a promising platform for compact, efficient, and high-power UV generation. Instead of trying to directly guide UV light, the device generates it internally by converting red light into UV. This process, called frequency upconversion, combines two red photons inside the lithium niobate crystal, which is highly efficient at frequency conversion, to produce a single higher-energy UV photon. “Our group is perhaps best known for utilizing lithium niobate for photonic devices that operate at longer, infrared wavelengths – closer to the realm of telecommunications signals,” Lončar said. But he added that this transparent crystalline material, already widely used in integrated photonics, can also guide and generate shorter wavelengths such as UV. “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, former research fellow in the Lončar lab. “We also show that there are some other nonlinear