Photonic crystals can bend light like black holes

A group of researchers from Tohoku University have manipulated the behaviour of light as if it were under the influence of gravity. The findings, which were published in the journal Physical Review A, could help enhance the fields of optics and materials science, along with the development of 6G communications.

Albert Einstein’s theory of relativity established that the trajectory of electromagnetic waves — including light and terahertz electromagnetic waves — can be deflected by gravitational fields. Scientists have now predicted that replicating the effects of gravity — known as pseudogravity — is possible by deforming crystals in the lower normalised energy (or frequency) region.

Professor Kyoko Kitamura from Tohoku University said the researchers set out to explore whether lattice distortion in photonic crystals can produce pseudogravity effects. Photonic crystals possess properties that allow scientists to manipulate and control the behaviour of light, serving as ‘traffic controllers’ for light within crystals. They are made by periodically arranging two or more different materials with varying abilities to interact with and slow down light in a regular, repeating pattern. Pseudogravity effects due to adiabatic changes have also been observed in photonic crystals.

The researchers modified photonic crystals by introducing lattice distortion — a gradual deformation of the regular spacing of elements — which disrupted the grid-like pattern of protonic crystals. This manipulated the photonic band structure of the crystals, resulting in a curved beam trajectory in-medium, akin to a light-ray passing by a large celestial body such as a black hole. The researchers used a silicon distorted photonic crystal with a primal lattice constant of 200 micrometres and terahertz waves, thereby demonstrating the deflection of these waves.

“Much like gravity bends the trajectory of objects, we came up with a means to bend light within certain materials. Such in-plane beam steering within the terahertz range could be harnessed in 6G communication. Academically, the findings show that photonic crystals could harness gravitational effects, opening new pathways within the field of graviton physics,” Kitamura said.

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