"Pseudogravity" in crystals can bend light like black holes
Scientists in Japan have managed to manipulate light as though it was being influenced by gravity. By carefully distorting a photonic crystal, the team was able to invoke “pseudogravity” to bend a beam of light, which could have useful applications in optics systems.
One of the quirks of Einstein’s theory of general relativity is that light is affected by the fabric of spacetime, which itself is distorted by gravity. That’s why objects with extremely high masses, like black holes or entire galaxies, wreak such havoc on light, bending its path and magnifying distant objects.
In recent studies, it was predicted that it should be possible to replicate this effect in photonic crystals. These structures are used to control light in optics devices and experiments, and they’re generally made by arranging multiple materials into periodic patterns. Distortions in these crystals, it was theorized, could deflect light waves in a way very similar to cosmic-scale gravitational lenses. The phenomenon was dubbed pseudogravity.
For the new study, the team put the idea to the test in a photonic crystal made of silicon. They distorted the crystal structure so that the grid’s cells, originally uniform at 200 micrometers apart, became more and more deformed across the surface. Then a laser with light waves in the terahertz range was beamed into the crystal.
The device had two output ports on the opposite side from the laser’s input port, arranged so one was above and one below the input. If pseudogravity wasn’t at work, the laser would have traveled in a straight line and not exited through either port – but in the distorted crystal, the light waves were successfully bent towards the lower port.
The team says this technique could be a very useful way to manipulate light in optics systems and other devices, and could inform the study of related physics.
“Such in-plane beam steering within the terahertz range could be harnessed in 6G communication,” said Associate Professor Masayuki Fujita, an author of the study. “Academically, the findings show that photonic crystals could harness gravitational effects, opening new pathways within the field of graviton physics.”
The research was published in the journal Physical Review A.
Source: Tohoku University