An international team of researchers has experimentally produced the first all-optical photonic time crystal (PTC), a material engineered to alter its optical behavior rapidly and repeatedly over time. Reported in Nature, the achievement was accomplished by scientists from École Polytechnique, Collège de France, and Helmholtz-Zentrum Dresden-Rossendorf (HZDR). According to idw-online.de, the experimental realization marks a world first in creating a material whose optical properties can be strongly and periodically modulated in time at ultrafast scales.
Breakthrough Demonstration of the First All-Optical Photonic Time Crystal
Historically, conventional photonic crystals have relied on spatial modulation. These are nanostructured materials containing a repeating optical pattern or lattice that dictates how photons move through them by arranging materials with different shapes and refractive indexes. While earlier experiments by the team showed that variables like temperature and magnetic fields could change a photonic crystal’s ability to capture light, those conditions remained fixed over time once established. The new device introduces a repeating pattern in time, allowing optical properties such as reflectivity and resonance frequency to be altered dynamically on picosecond timescales.
Engineering the Plasmonic Metamaterial Device
Constructed with support from Thales’ Laboratoire Albert Fert and Polytechnique’s Physics of Interfaces (PICM) laboratory, the new device relies on a form of photonic crystal known as a plasmonic metamaterial
as detailed by sciencedaily.com. The material consists of micrometer-scale gold crenellated structures positioned above an insulating layer and a semiconductor made from a mixture of indium and antimony. The gold structures form tiny cavities designed to confine light between the gold and semiconductor layers.
At the heart of the device, terahertz laser pulses create surface plasmons where electrons form a collective wave. This causes the effective mass of the electrons to oscillate and become heavier as their speed increases, driving the alternation of the material’s optical properties. The entire setup was made possible by HZDR’s TELBE superradiant terahertz source. Jan-Christoph Deinert, the coordinator of the TELBE facility, confirmed that the infrastructure’s unique ability to generate high-field, phase-stable terahertz pulses was critical for achieving the coherent, ultrafast modulation needed for the PTC regime.
Exploring the Terahertz Frontier
The device operates in the terahertz (THz) frequency range, where light oscillates at frequencies of approximately 1,000 billion times per second. Yannis Laplace, an assistant professor at École Polytechnique and researcher at the Laboratory of Irradiated Solids (LSI), noted that terahertz frequencies operate 1,000 times faster than those used for standard electronic components. The THz range represents the frontier between electronic and photonic technologies,
Laplace explained, noting it is full of opportunities for science and society while remaining technologically under-developed compared to electrical and photonic counterparts.
Tingwen Guo, a PhD student at École Polytechnique and lead author on the publication, emphasized the broader implications of the work. By extending photonic crystals from space to time, we open a new dimension for light control — and a novel path toward amplification and lasing,
Guo stated. Researchers have already begun observing signs of photon amplification within the structure and ultimately hope to observe a laser effect, paving the way for new light sources and detectors in the terahertz range.
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