Algorithm-Designed Photonic Circuits Beyond Human Intuition

Researchers at Harvard SEAS and the Max Planck Institute for the Science of Light used an inverse-design algorithm to create silicon nitride photonic components that are 500 times smaller than conventional designs, including wavelength splitters, spatial mode sorters, and mirrors that reflect up to 98.5% of light. The algorithm incorporates fabrication constraints to ensure compatibility with commercial foundry processes, potentially enabling higher-performance quantum photonic circuits.

News Key Takeaways - Harvard SEAS and Max Planck Institute https://mpl.mpg.de/news/article/beyond-human-intuition-algorithms-create-foundry-ready-photonic-circuits engineering researchers used an inverse-design algorithm to create silicon nitride photonic components that are 500 times smaller than conventional designs. - The research could pave the way for higher-performance quantum photonic circuits and other devices. The extremely fast data-processing capabilities that power today’s telecommunications, large-scale AI data centers, quantum technologies and more, are enabled by photonic microchips – miniaturized semiconductors in which photons, rather than electrons, carry information through micrometer-wide waveguides. Using a computer algorithm, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences SEAS https://seas.harvard.edu/ and the Max Planck Institute for the Science of Light https://mpl.mpg.de/ have developed three new functional components for photonic microchips that are each about 500 times smaller than conventional designs and offer a path toward higher-performance integrated light technologies. The results are published in Nature Communications https://www.nature.com/articles/s41467-026-73390-9 . Photonic microchips are made of many intricate parts, from grating couplers, which transfer light between fibers and waveguides, to ring resonators — tiny circular structures that temporarily store light and increase its intensity inside the chip. The design process for each component is time-consuming and tedious, with engineers typically starting with a familiar geometry and adjusting parameters as they go. A research team co-led by Kiyoul Yang, https://seas.harvard.edu/person/kiyoul-yang SEAS assistant professor of electrical engineering, used a technique called inverse design to take an unconventional approach. Flipping the traditional process upside down, they first specified what they wanted the light to do. A computer algorithm then searched a large space of possible nanostructures for that exact function. The shapes the algorithm finds often look like irregular patterns of holes and ridges, but they nonetheless precisely guide light in a chip area that’s a tiny fraction the width of a human hair. “Inverse design becomes practical when fabrication realities are built into the optimization,” said Yang, who co-led the work with Pascal Del’Haye, head of the microphotonics research group at Max Planck Institute https://mpl.mpg.de/news/article/beyond-human-intuition-algorithms-create-foundry-ready-photonic-circuits . “By including minimum feature sizes and robustness to manufacturing variations in the algorithm itself, we obtain designs that are not only compact but also compatible with a commercial foundry process.” Design and testing of devices The team applied inverse design to silicon nitride – a material with low optical loss that can also help produce clean, laser-like light of many different colors. Previous approaches have mainly focused on silicon and, more recently, on diamond, silicon carbide and lithium niobate. “Thick silicon nitride underpins most of the high-performance integrated photonics we work with, but until now its component library was limited to hand-engineered designs,” Del’Haye said. “These compact, computer-designed components are an important step towards more densely integrated nonlinear and quantum photonic circuits.” The team designed, fabricated and tested three classes of device: wavelength splitters, which separate the colors of light; spatial mode sorters, which separate light into spatial channels; and mirrors. As one of examples, inverse-designed mirrors, only a few micrometers across, reflect up to 98.5% of incoming light while blocking other spatial modes. Placed in pairs, they form on-chip optical cavities in which light bounces more than 100 times between the mirrors before escaping. Future directions The next step is to combine the newly developed components with nonlinear optical circuits. In these building blocks, intense light circulating on a chip can generate optical frequency combs: precise sets of many evenly spaced colors of light used in precision measurement, telecommunications and quantum technologies. “Inverse design lets us define what we want light to do, and the optimization finds a structure that does it, often one no human would have drawn,” said Toby Bi, co-lead author of the study and researcher at the Max Planck Institute. “What is exciting is that the same framework can do three quite different jobs on the same chip: route light by wavelength, sort it by spatial mode, and act as compact mirrors that form on-chip optical cavities.” “ Inverse-designed silicon nitride nanophotonics https://www.nature.com/articles/s41467-026-73390-9 ” was co-authored by SEAS graduate students Egemen Bostan, and Danxian Liu, SEAS fellow and MIT EECS graduate student Aditya Paul, and postdoctoral fellow Tianyi Zeng. The research was supported by the Defense Advanced Research Projects Agency D23AP00251-00 and the Under Secretary of Defense for Research and Engineering FA8721-05-C-0002 . Device fabrication was carried out in part at the Harvard Center for Nanoscale Systems National Science Foundation award No. 1541959 . Topics: AI / Machine Learning /news?topic 521 =521 , Applied Physics /news?topic 551 =551 , Electrical & Computer Engineering /news?topic 556 =556 , Materials Science & Mechanical Engineering /news?topic 1223 =1223 , Optics / Photonics /news?topic 581 =581 , Quantum Engineering /news?topic 536 =536 , Research /news?topic 1271 =1271 , Technology /news?topic 631 =631 Cutting-edge science delivered direct to your inbox. Join the Harvard SEAS mailing list. Scientist Profiles Kiyoul Yang /person/kiyoul-yang Assistant Professor of Electrical Engineering Press Contact Anne J. Manning | amanning@seas.harvard.edu mailto:amanning@seas.harvard.edu