Researchers have achieved the first true on-off optical switching at the nanoscale by precisely controlling light–matter interactions using ultrafast laser pulses and asymmetric metasurfaces.
Image Credit: rangizzz/Shutterstock.com
In nanophotonics, tiny structures manipulate light at incredibly small scales, enabling a range of advanced technologies. One of the most important tools in this field is the optical resonator, which traps and amplifies specific wavelengths of light. Until now, control over these resonances has been more like using a dimmer switch—allowing adjustments in strength or slight shifts in color—but not true switching. Resonators remained fundamentally coupled to light, making full on-off control impossible.
A team led by Andreas Tittl, Professor of Experimental Physics at LMU, working with collaborators from Monash University in Australia, has now overcome this limitation. In a study published in Nature, they describe a method to dynamically control the coupling between nanoresonators and light, turning a resonance on or off within just a few picoseconds.
Making Structures Invisible to Light
Their breakthrough relies on a clever design of metasurfaces—ultrathin materials patterned with nanostructures. Each structure is made of two tiny silicon rods that are intentionally asymmetrical in shape. At a specific wavelength, the optical responses of these rods cancel each other out perfectly, making the structure “invisible” to light—essentially switching the resonance off.
It’s this asymmetry that enables the switching. Because the rods respond differently to varying wavelengths and polarizations, the researchers can selectively excite just one rod with an ultrafast laser pulse lasting only 200 femtoseconds. This pulse temporarily changes its optical properties, disrupts the balance, and causes the resonance to engage with the light—it switches on.
Breaking Symmetry to Control Light
The centerpiece of our work is this deliberate symmetry breaking on extremely short timescales. We generate a perfect optical balance in a structurally asymmetric system. By deliberately disrupting this equilibrium with a laser pulse, we gain a completely new level of freedom for controlling the light-matter interaction. We can generate a resonance at will, quench it, or precisely adjust its bandwidth as with a control knob.
Andreas Tittl, Professor, Experimental Physics, Ludwig-Maximilians-Universität München
Building the metasurfaces in a cleanroom was only part of the challenge. Capturing their behavior in real time required advanced time-resolved spectroscopy.
Only with the aid of our time-resolved spectroscopy approach were we able to experimentally capture these ultrafast processes and watch in real time, how the resonance appears within picoseconds and then disappears again.
Leonardo de S. Menezes, Ludwig-Maximilians-Universität München
“Our measurements showed a huge increase in the coupling with light, while there were scarcely any unwanted energy losses in the material itself. This was the definitive proof that our approach of temporal symmetry breaking works precisely as predicted,” said Menezes, who was in charge of the spectroscopic experiments.
The experiments—mainly carried out by lead authors Andreas Aigner and Thomas Possmayer—demonstrated four distinct switching modes: generating a resonance from an optically “dark” state, completely quenching an existing resonance, and selectively broadening or sharpening the resonance profile. In one case, they increased the resonance’s quality factor (Q-factor) by over 150 %. This level of control was achieved with high precision and speed, while avoiding the energy losses that typically limit other methods.
Redefining Control in Nanophotonics
This ability to directly control the coupling between light and nanostructures marks a significant advance in active nanophotonics. Importantly, the approach isn’t limited to silicon, it can be adapted to other materials and potentially even faster switching techniques, opening the door to a wider range of applications.
With such precise control over when and how resonances appear, this method could pave the way for low-loss, all-optical switches in telecommunications and data processing. It also offers new tools for exploring complex quantum phenomena, including emerging concepts like time crystals.
Journal Reference:
Aigner, A., et al. (2025) Optical control of resonances in temporally symmetry-broken metasurfaces. Nature. doi.org/10.1038/s41586-025-09363-7.