Newly-developed light amplifying 'photonic time crystals' may improve lasers and telecoms

Researchers 'tinkered' with 2D metamaterials and created "photonic time crystals" that could have revolutionary implications for lasers and transmitters.
Christopher McFadden
Artist's impression of how 2D photonic time crystal can boost light waves.
Artist's impression of how 2D photonic time crystal can boost light waves.

Xuchen Wang / Aalto University 

Researchers have just released a study that explains how they've managed to design a two-dimensional "photonic time crystal" that, they say, could have significant implications for technologies like transmitters and lasers. While their name is similar to that of so-called "time crystals," a phase of matter first suggested in 2012, they are, in fact, not the same thing.

"Time crystals" are particular kinds of crystals whose component atoms exist in a quantum state. This means they behave in ways that seem alien or "strange." "Photonic time crystals," on the other hand, are not found in nature and may not exist in quantum states. Instead, they use light pulses to create a repeating motion pattern (unlike most materials, which have random motion at different energy states).

Since it has been challenging to construct and manipulate 3D "photonic time crystals," the team decided to try something new by making the material even thinner (0.08 inches or 2 millimeters thick). By doing so, the researchers report that their crystals can amplify light at microwave frequencies.

Creating a 2D 'photonic time crystal'

“By modulating or changing the electromagnetic property of the metasurface over time, we were able to create a 2D photonic time crystal,” said Xuchen Wang, a physicist at the Karlsruhe Institute of Technology and the study’s lead author, in an email to Gizmodo. “Reducing photonic time crystals from 3D to 2D can make them thinner, lighter, and easier to manufacture, just like how metasurfaces improved on metamaterials,” he added.

"Photonic crystals" are unique materials that can bend and amplify light in a controlled way. Scientists can create these materials in a lab by adjusting their electromagnetic properties using metamaterials. When light travels through "photonic time crystals," the photons move in a repeating pattern that helps keep them in sync and maintain their coherence. This is similar to how lasers keep quantum bits in a coherent state, which can help prolong their quantum properties.

“In [photonic time crystals], energy is not conserved; hence the states residing in the momentum gap can have exponentially increasing amplitudes,” said Mordechai Segev, a physicist at the Technion Israel Institute of Technology who is unaffiliated with the new paper, in a February interview with Nature Photonics. “This has a huge impact on the physics involved,” he said.

The majority of photonics-dependent devices are involved in the discovery's practical uses. For instance, coating equipment with 2D photonic time crystals could increase wireless transmission strength. Wang told Gizmodo that even though the team's crystal can only amplify microwave frequencies, a slight change in the architecture might enable the crystal to operate at millimeter-wave frequencies, such as those used in 5G communications.

You can read the study for yourself in the journal Science Advances.

Study Abstract:

"Photonic time crystals are artificial materials whose electromagnetic properties are uniform in space but periodically vary in time. The synthesis of these materials and experimental observation of their physics remain very challenging because of the stringent requirement for uniform modulation of material properties in volumetric samples. In this work, we extend the concept of photonic time crystals to two-dimensional artificial structures—metasurfaces. We demonstrate that time-varying metasurfaces not only preserve key physical properties of volumetric photonic time crystals despite their simpler topology but also host common momentum bandgaps shared by both surface and free-space electromagnetic waves. On the basis of a microwave metasurface design, we experimentally confirmed the exponential wave amplification inside a momentum bandgap and the possibility to probe bandgap physics by external (free-space) excitations. The proposed metasurface serves as a straightforward material platform for realizing emerging photonic space-time crystals and as a realistic system for the amplification of surface-wave signals in future wireless communications."

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