Photonics: Inverse design; slowing down light; on-chip electro-optic isolator.
Researchers from Harvard University and the Max Planck Institute designed silicon nitride photonic components that are 500 times smaller than conventional designs by using an inverse-design algorithm.
“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, a researcher at the Max Planck Institute, in a press release. “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 device structure evolves through successive iterations of the computational optimization process, resulting in irregular patterns of holes and ridges.
A photonic microchip, next to a 10-euro-cent coin for scale, containing hundreds of inverse-designed components. The close-up images show computer-designed nanostructures, wavelength splitters, mode sorters, and mirrors. The left illustration shows how such devices could be combined and densely packed into integrated photonic circuits on a chip. (Credit: Tony Bi / MPL)
“Inverse design becomes practical when fabrication realities are built into the optimization,” said Kiyoul Yang, assistant professor of electrical engineering at Harvard SEAS, in a press release. “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.”
Next, the researchers will combine the new components with nonlinear optical circuits to generate optical frequency combs. [1]
Researchers from Seoul National University and the University of Seoul developed a programmable photonic IC that can freely control both the speed and shape of optical signals, enabling storage, delay, and control of light within a single chip.
The approach treats the bright mode and dark mode optical states within coupled-resonator-induced transparency (CRIT) systems as a single unified degree of freedom and introduces two controllable loop couplers, allowing resonator structures that were previously fixed after fabrication to be reconfigured as needed.
The researchers theoretically proved that it is possible to control the bandwidth and shape of the passband, as well as the delay and transmission characteristics of signals propagating through the circuit. Numerical simulations showed that the propagation speed of optical pulses can be dynamically adjusted in real time while the circuit is in operation, while 3D electromagnetic simulations showed that the device could be implemented on a silicon nitride platform.
“This research is significant in that it proposes a new design principle that allows the flow of light within photonic integrated circuits to be reconfigured as needed, greatly enhancing design flexibility,” said Namkyoo Park, professor at Seoul National University, in a statement. “We plan to expand this technology toward large-scale programmable photonic integrated circuits based on silicon photonics and photonic AI technologies.” [2]
Researchers from the University of Illinois Urbana-Champaign developed a lithium niobate electro-optic isolator that forces light to propagate only in one direction within a photonic circuit. Unidirectional light propagation can improve robustness to manufacturing defects, protect laser sources, and impart more stability to optical signals within the system.
“Currently, the best commercial optical isolators are built using magneto-optic materials,” said Gaurav Bahl, a professor of mechanical science and engineering in Illinois Grainger Engineering, in a statement. “This approach is okay for relatively large-scale photonic systems such as optical fiber networks, but it cannot be used for integrated photonics. Magnetic and magneto-optic materials are not suitable for processing in foundry facilities, these materials also tend to have high optical loss, and their useful properties have a strong wavelength dependence. However, as we continue to scale up our data centers, there is an increasing need for compact and low-power optical signal routing. And so, chip scale integrated isolator devices that don’t use magnetic materials are becoming increasingly important.”
The on-chip electro-optic isolator can be tuned over many terahertz, enabling the isolation function to be adjusted on demand to suit the wavelength that the rest of the photonic system is using. For the study, the researchers designed the device for the telecom band. It exhibited a figure of merit of nearly 2,000 (about 33 decibels) between forward and backward transmission with extremely low forward loss, comparable with commercial off-chip magnetic isolators.
“As a follow up to this work, we are working on a broadband ‘electro-optic’ isolator that will exhibit nice properties over an extremely wide wavelength range, eliminating the need for tuning,” Bahl added. “Technical innovations such as this isolator can play a key role in solving the big challenges facing nationally critical technologies in AI and computing.” [3]
[1] T. Bi, S. Zhang, E. Bostan, et al. Inverse-designed silicon nitride nanophotonics. Nat Commun 17, 6943 (2026). https://doi.org/10.1038/s41467-026-73390-9
[2] S. Park, B. Chae, H. Park, et al. Fully Programmable Slow Light Based on a Spinor Representation of Generalized Coupled-Resonator-Induced Transparency. Advanced Science (2026): e76378. https://doi.org/10.1002/advs.76378
[3] G.I. Kim, V. Workman, O.E. Örsel, et al. An integrated multi-THz tunable linear isolator based on electro-optic non-reciprocal strong coupling. Nat Commun 17, 6532 (2026). https://doi.org/10.1038/s41467-026-75451-5
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