A world-first photonic time crystal can reshape light almost instantly, opening a path toward ultrafast optical technology.
An international research team has created the first experimentally demonstrated all-optical photonic time crystal (PTC), a material whose optical behavior can be altered strongly and repeatedly over extremely short periods of time.
The work, carried out by scientists from École Polytechnique, Collège de France, and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), was published in Nature. The researchers used HZDR’s TELBE superradiant terahertz source to push the material into a previously unexplored form of light-matter interaction in the terahertz range.
The achievement could eventually support ultrafast optical computing, advanced telecommunications, and new types of terahertz lasers.
A New Way to Control Light
Many modern technologies depend on controlling how light behaves when it passes through or interacts with a material. Optical fibers guide information across communication networks, lasers provide precise light sources, and optical sensors are widely used in chemistry and biology.
Researchers at École Polytechnique are now working to extend that control into the terahertz (THz) frequency range. Yannis Laplace, assistant professor at École Polytechnique, and his team at the Laboratory of Irradiated Solids (LSI) are developing photonic devices that can manipulate light at these frequencies.
The terahertz range operates at frequencies around 1,000 times faster than those commonly used by electronic components. Interest in this region is growing because it could offer new ways to observe, analyze, and manipulate matter.
“The THz range represents the frontier between electronic and photonic technologies,” explains Laplace. ”It is a range full of opportunities both for science and for society, yet is still under-developed technologically compared to its electrical and photonic counterparts. Creating photonic crystals could lead the way to the closing of this gap.”
From Photonic Crystals to Photonic Time Crystals
Conventional photonic crystals are nanostructured materials arranged in a repeating optical pattern (like a lattice) that influences how photons move. By controlling the refractive index and geometry of the materials, scientists can block, redirect, or strengthen particular wavelengths of light. In this way, photonic crystals perform a role for photons that is similar to the way semiconductors control electrons.
Earlier experiments by the same research team showed that changing temperature or applying magnetic fields could modify how photonic crystals trapped light. However, those changes remained fixed once they were applied.
The new experiment moves beyond that limitation by introducing a photonic time crystal. In this system, the material’s optical properties (e.g., reflectivity, resonance frequency) change dynamically over picosecond timescales, which are comparable to the oscillation period of the light itself.
“By extending photonic crystals from space to time, we open a new dimension for light control—and a novel path toward amplification and lasing. That could be a game-changer for optical technologies at terahertz frequencies and beyond,” explains Tingwen Guo, PhD student at École Polytechnique and lead author on the publication.
Building a Complex Plasmonic Metamaterial
Producing such rapid changes in photon behavior required the researchers to design a highly specialized device. With assistance from Thales’ Laboratoire Albert Fert and Polytechnique’s Physics of Interfaces (PICM) laboratory, the team built a type of photonic crystal known as a “plasmonic metamaterial.”
The structure contains micrometer-scale, crenelated gold patterns positioned above an insulating layer and a semiconductor made from a mixture of indium and antimony. The gold structures form small cavities that confine photons between the metal and semiconductor layers.
When the surface of the semiconductor is excited, it produces “surface plasmons,” in which electrons move together as a collective wave. This coordinated motion allows the structure to capture light and maintain its oscillations.
Ultrafast Terahertz Modulation
The researchers then directed terahertz laser pulses at the device using TELBE, an intense and frequency-tunable terahertz source located at HZDR’s ELBE accelerator.
The experiment showed that the material’s optical properties, especially its reflectivity, could be changed very strongly within an extremely short period. Achieving both a large effect (like forcing an object to emit a whole different color) and a very rapid response (on the picosecond scale—one billionth of a billionth of a second) had previously been exceptionally difficult.
“TELBE’s unique ability to generate high-field, phase-stable terahertz pulses was critical,” confirmed Jan-Christoph Deinert, the coordinator of the TELBE facility. “Without this infrastructure, achieving the coherent, ultrafast modulation needed for the PTC regime would have been impossible.”
Theory Confirms the Results
The experimental findings were supported by a theoretical model developed by Marco Schiró, Research Scientist at Collège de France, and his team. The model reproduced the observed results and helped explain how photons behaved inside the device.
The researchers also found that the time-based modulation reduced photon dissipation within the metamaterial by half. In other words, a smaller proportion of photons passed through the material without being reflected.
“The theory not only reproduces the experiment but also provides the basis for guiding future discoveries in this system,” rejoiced Schiró.
Toward New Lasers and Optical Technologies
The next challenge is to reduce photon losses even further and increase the number of photons that remain trapped inside the crystal. If the researchers can achieve sufficiently strong amplification, the system could serve as the basis for new lasers with exceptionally flexible and adjustable properties.
Photonic time crystals could ultimately change how light is used in technology, especially in the terahertz range. Their ability to modify light over extraordinarily short timescales could lead to ultrafast lasers for medical imaging and communications.
The same approach could also make it possible to tune the properties of light on demand, such as changing its “color” or intensity almost instantly. This capability may lead to smarter, faster, and more adaptable optical systems.
Reference: “Plasmonic metamaterial time crystal” by Tingwen Guo, Jules Sueiro, Gian Marcello Andolina, Artem Levchuk, Stefano Ponzoni, Romain Grasset, Donald Monthe, Ian Aupiais, Dmitri Daineka, Javier Briatico, Thales VAG de Oliveira, Alexey Ponomaryov, Atiqa Arshad, Arjun Karimbana-Kandy, Gulloo Lal Prajapati, Igor Ilyakov, Jan-Christoph Deinert, Sebastian F. Maehrlein, Luca Perfetti, Marco Schirò and Yannis Laplace, 29 July 2026, Nature.
DOI: 10.1038/s41586-026-10825-9
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