Caltech researchers have developed a way to print optical circuits made from the same glass as optical fiber directly onto standard silicon wafers, achieving signal losses at visible wavelengths that approach those of fiber optics. The results are described in a new paper in Nature.

The team, led by Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics at Caltech, adapted germano-silicate glass — the material used in optical fiber — to standard lithography-based chip manufacturing. The waveguides are arranged in spirals, letting light travel meters of optical path within a chip only about two centimeters across, much as fiber is wound around a spool.

A key step is a "reflow" process: because the material has a comparatively low melting temperature, the devices can be placed in a furnace to smooth waveguide surfaces down to the level of individual atoms, suppressing the severe scattering loss that has long limited visible-light photonic chips. At visible wavelengths, the new platform exceeds the previous record set by silicon nitride by a factor of 20, the researchers report — and they say there is room for further improvement.

Lower loss pays off directly in device performance. Lasers built on the platform show more than a 100-fold improvement in how long their emitted light remains coherent. The broad wavelength coverage could also support chip-scale atomic sensors, optical clocks, gyroscopes, ion-trap systems, and lower-energy data-center communications for AI workloads.

"This shift toward fiber-like performance, especially in the visible bands, will enable new technologies that benefit from negligibly low circuit energy loss," Vahala said. The paper, "Towards fibre-like loss for photonic integration from violet to near-infrared," was led by postdoctoral scholar Hao-Jing Chen and graduate student Kellan Colburn, with collaborators at UC Santa Barbara, Leiden University, and the University of Southampton. The work was funded by DARPA, the Air Force Research Laboratory, the Engineering and Physical Sciences Research Council, and Caltech's Kavli Nanoscience Institute.

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