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Photonic microchips can process data at extremely high speeds and are embedded in a wide variety of today’s technologies. Researchers at the Max Planck Institute for the Science of Light (MPL) and Harvard University have now succeeded in developing three functional components for such chips that are up to 500 times smaller than conventional designs. The researchers used inverse design, a computer algorithm, to achieve this. The results were recently published in Nature Communications.
Photonic microchips are among the key technologies of modern data processing. Their miniaturization, combined with extremely fast data processing compared to electronic components, makes them essential building blocks in telecommunications, large-scale AI data centers, precision measurement and quantum technologies. Light is guided through micrometer-wide-waveguides across chips only a few millimeters wide.
Photonic microchips incorporate various components, such as grating couplers, which couple light from fibers to and from the chip, or ring resonators, tiny circular structures that temporarily store light and strongly increase the light intensity inside the chip. Engineers usually design each component by hand. They start with a familiar geometry and adjust its parameters until the component performs the desired task. This process is time consuming.
In the study recently published in Nature Communications, a team of researchers led by Dr. Pascal Del’Haye, head of the independent research group “Microphotonics” at MPL, and Prof. Kiyoul Yang of Harvard University takes an inverse approach to creating compact, high-performance photonic components for integrated light-based technologies. Using inverse design, the researchers specified what they wanted light to do. This computer algorithm then searched a large space of possible nanostructures for one that does it. The shapes the algorithm finds often look like irregular patterns of holes and ridges. They nonetheless guide light with precision in a chip area that is up to 1000 times smaller than the diameter of a human hair.“
“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 doctoral researcher at MPL. “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.”
The team applied inverse design to thick silicon nitride as a material platform – a material with low optical loss. At the same time, thick silicon nitride can 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,” mentions Pascal Del’Haye. “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, spatial mode sorters and mirrors.
Wavelength splitters separate the colors of light. The smallest version fits into a square of five by five micrometers, taking up fifty to three hundred times less area than the directional-coupler designs that perform the same task.
Mode sorters separate light into spatial channels in a footprint around five hundred times smaller than conventional designs.
As one of examples, inverse-designed mirrors, only a few micrometers across, reflect up to 98.5 percent of incoming light while blocking other spatial modes. Placed in pairs, they form on-chip optical cavities in which light bounces more than one hundred times between the mirrors before escaping.
“Inverse design becomes practical when fabrication realities are built into the optimization,” said Kiyoul Yang, corresponding author at Harvard University. “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.”
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.
Dr. Pascal Del'Haye
Max Planck Institute for the Science of Light, Erlangen
Research group leader ›Microphotonics‹
www.mpl.mpg.de /pascal.delhaye@mpl.mpg.de
Prof. Kiyoul Yang
Assistant Professor, Harvard University
https://seas.harvard.edu / kiyoul@seas.harvard.edu
Original publication in Nature Communications:
Toby Bi, Shuangyou Zhang, Egemen Bostan, Danxian Liu, Aditya Paul, Olga Ohletz, Irina Harder, Yaojing Zhang, Alekhya Ghosh, Abdullah Alabbadi, Masoud Kheyri, Tianyi Zeng, Jesse Lu, Kiyoul Yang & Pascal Del'Haye “Inverse-designed silicon nitride nanophotonics.” Nature Communications 17, 6943 (2026) DOI: https://doi.org/10.1038/s41467-026-73390-9
A photonic microchip, shown next to a 10-euro-cent coin for scale, containing hundreds of inverse-de ...
Copyright: © MPL, Toby Bi
Dr. Pascal Del'Haye and Toby Bi, Research group ›Microphotonics‹.
Copyright: © MPL, Susanne Viezens
Progression of photonic design optimization. The device structure (top view in this image) evolves through successive iterations of the computational optimization process.
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A photonic microchip, shown next to a 10-euro-cent coin for scale, containing hundreds of inverse-de ...
Copyright: © MPL, Toby Bi
Dr. Pascal Del'Haye and Toby Bi, Research group ›Microphotonics‹.
Copyright: © MPL, Susanne Viezens
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