Japanese scientists have successfully manipulated light as if it were affected by gravity. By carefully twisting the photonic crystal, the team was able to exploit "pseudogravity" to bend light beams, which could have useful applications in optical systems.


Artist's impression of a black hole and the way its gravity affects light—now simulated in crystals NASA Goddard Space Flight Center/Jeremy Schnittman

One of the quirks of Einstein's general theory of relativity is that light is affected by the fabric of space-time, which itself is distorted by gravity. This is why extremely massive objects, like black holes or entire galaxies, wreak so much havoc on light, bending its path and amplifying distant objects.

In recent research, it was predicted that it should be possible to replicate this effect in photonic crystals. These structures are used to control light in optical devices and experiments, and they are often made by arranging multiple materials into periodic patterns. Theoretically, the twisting of these crystals could deflect light waves in much the same way as cosmic-scale gravitational lensing. This phenomenon is called pseudogravity.

In the new study, the team tested this idea in photonic crystals made of silicon. They distorted the crystal structure so that the originally evenly spaced 200-micron grid cells became increasingly deformed across the surface. Then, light waves in the terahertz range are lasered into the crystal.

The device has two output ports on the opposite side of the laser input port, one above and one below the input port. If pseudo-gravity didn't work, the laser would travel in a straight line and not emerge from either port—but in the twisted crystal, the light waves managed to bend toward the lower ports.

Experimental setup, involving a twisted photonic crystal (DPC), the diagram below illustrates what happens in a normal crystal and in a twisted oneK

The team says the technique could be a very useful way to manipulate light in optical systems and other devices, and could inform studies of related physics.

Associate Professor Masayuki Fujita, one of the authors of the study, said: "This kind of in-plane beam control in the terahertz range can be exploited in 6G communications. Academically, the results show that photonic crystals can exploit gravitational effects and open up new avenues in the field of graviton physics."

The research was published in the journal Physical Review A.