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New Way to Create Photonic Time Crystals Identified

A new method to create photonic time crystals has been developed by scientists and shows that such bizarre and artificial materials amplify the light that hits them.

An illustration of how a 2D photonic time crystal can boost light waves. Image Credit: Xuchen Wang / Aalto University

Such findings, explained in a study in the journal Science Advances, could result in more effective and strong wireless communications and considerably enhanced lasers.

Initially, time crystals were conceived by Nobel laureate Frank Wilczek in 2012. Mundane, familiar crystals come with a structural pattern that gets repeated in space, but in a time crystal, the pattern repeats in time instead.

Initially, while some physicists doubted that time crystals could exist, recent experiments have proven to be successful in making them. In 2022, scientists at Aalto University’s Low-Temperature Laboratory fabricated paired time crystals that could be beneficial for quantum devices.

Currently, one other team has created photonic time crystals, which are time-based versions of optical materials. The scientists made photonic time crystals that function at microwave frequencies, and they showed that the crystals could help amplify electromagnetic waves.

This ability has possible applications in several technologies, such as lasers, wireless communication, and integrated circuits.

Until now, research performed on photonic time crystals has concentrated on heavy materials—that is, three-dimensional structures. This has proven to be a huge challenge, and the experiments have not gone past model systems with any practical applications.

Hence the team made an attempt to try a new method that included scientists from Aalto University, the Karlsruhe Institute of Technology (KIT), and Stanford University. The new approach was to build a two-dimensional photonic time crystal called a metasurface.

We found that reducing the dimensionality from a 3D to a 2D structure made the implementation significantly easier, which made it possible to realize photonic time crystals in reality.

Xuchen Wang, Study Lead Author and Doctoral Student, Aalto University

Currently, Wang is working at the Karlsruhe Institute of Technology.

The newly-developed method allowed the researchers to fabricate a photonic time crystal and further experimentally confirm the theoretical predictions regarding its behavior.

We demonstrated for the first time that photonic time crystals can amplify incident light with high gain. In a photonic time crystal, the photons are arranged in a pattern that repeats over time. This means that the photons in the crystal are synchronized and coherent, which can lead to constructive interference and amplification of the light.

Xuchen Wang, Study Lead Author and Doctoral Student, Aalto University

The periodic arrangement of the photons implies that they can also interact through means that increase the amplification.

A range of possible applications has been considered by the two-dimensional photonic time crystals. By amplifying electromagnetic waves, they could make wireless transmitters and receivers with more power or efficiency.

Furthermore, Wang notes that coating surfaces with 2D photonic time crystals could aid in signal decay, which is known to be a significant issue in wireless transmission. Also, photonic time crystals can facilitate laser designs by eliminating the requirement for heavy mirrors that are used normally in laser cavities.

One more application arises from finding that 2D photonic time crystals do not just amplify electromagnetic waves that hit them in free space but also waves traveling together with the surface. Surface waves have been utilized for communication between electronic components in integrated circuits.

When a surface wave propagates, it suffers from material losses, and the signal strength is reduced. With 2D photonic time crystals integrated into the system, the surface wave can be amplified, and communication efficiency enhanced.

Xuchen Wang, Study Lead Author and Doctoral Student, Aalto University

Journal Reference:

Wang, X., et al. (2023) Metasurface-based realization of photonic time crystals. Science Advances.


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