World-First Photonic Time Crystal Revolutionizes Light Control

Researchers have experimentally produced the first all-optical photonic time crystal, a metamaterial designed to alter its optical behavior rapidly and repeatedly over time. According to a study published in Nature, the breakthrough was achieved by an international team from École Polytechnique, Collège de France, and Helmholtz-Zentrum Dresden-Rossendorf (HZDR) using HZDR’s TELBE superradiant terahertz source.

Exploring the Terahertz Technology Frontier at École Polytechnique

At École Polytechnique, assistant professor Yannis Laplace and his team at the Laboratory of Irradiated Solids (LSI) are developing photonic devices to control light in the terahertz frequency range. This underused part of the electromagnetic spectrum sits between conventional electronics and photonics. Research in the field is advancing because terahertz frequencies are 1,000 times faster than those used for electronic components.

“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 the 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.”

Controlling Light Through Time With Metamaterials

Conventional photonic crystals are nanostructured materials containing a repeating optical pattern that determines how photons move through them, functioning similarly to how semiconductors control electrons. While earlier experiments showed that temperature and magnetic fields could change a photonic crystal’s ability to capture light, the optical behavior remained fixed once those conditions were established.

The new device alters its optical properties—such as reflectivity and resonance frequency—dynamically on picosecond timescales. Rather than relying solely on patterns arranged across space, the photonic time crystal introduces a repeating pattern in time. “By extending photonic crystals from space to time, we open a new dimension for light control — and a novel path toward amplification and lasing,” states Tingwen Guo, a PhD student at École Polytechnique and lead author on the publication.

Optical Properties Changed in Picoseconds via TELBE

To build the device, researchers constructed a “plasmonic metamaterial” with support from Thales’ Laboratoire Albert Fert and Polytechnique’s Physics of Interfaces (PICM) laboratory. The material features micrometer-scale gold crenelated structures positioned above an insulating layer and a semiconductor made from a mixture of indium and antimony. When the semiconductor surface is excited, it produces surface plasmons—collective waves of electrons that capture light and maintain its oscillations.

The team exposed the device to terahertz laser pulses produced by the TELBE facility at HZDR’s ELBE accelerator. “TELBE’s unique ability to generate high-field, phase-stable terahertz pulses was critical,” confirms Jan-Christoph Deinert, coordinator of the TELBE facility. “Without this infrastructure, achieving the coherent, ultrafast modulation needed for the PTC regime would have been impossible.”

Theoretical Models and Photon Dissipation

A theoretical model developed by Marco Schiró, a research scientist at Collège de France, and his team supported the experimental findings. The calculations showed that changing the material over time cut photon dissipation in half, reducing the portion of photons that pass through the metamaterial’s surface instead of reflecting.

“The theory not only reproduces the experiment but also provides the basis for guiding future discoveries in this system,” states Schiró.

Frequently Asked Questions

What is a photonic time crystal?

A photonic time crystal is a material that changes its optical properties rapidly and repeatedly over time, introducing a repeating pattern in time rather than just across space.

How fast do photonic time crystals alter light?

The newly developed device alters its optical properties on picosecond timescales, which are on the scale of light’s own oscillations.

What applications could this technology enable?

Researchers indicate the approach could contribute to ultrafast optical computers, advanced telecommunications, and entirely new terahertz lasers for medical imaging and communications.