Boffins shrink light-twister to silicon scale, multiply bandwidth 10x

This could be how light becomes a more common data carriage medium

Twisted light image - University of Rochester

We've known for some time that the orbital angular momentum (OAM) of light (colloquially known as “twisted light”) can be modulated to carry information, but until now, it's only been demonstrated on large-scale laboratory lasers.

That's changed with work from the State University of New York at Buffalo and the Polytechnic University of Milan, with boffins building and demonstrating a micron-scale OAM semiconductor.

If it worked at scale and in the field, an OAM scheme could be added to existing modulation, getting what Buffalo reckons would be a tenfold increase in capacity.

In “twisted light”, the wavefront presents as a helix (there's a decent Wikipedia entry). Giving different beams different orbital values – different twists – means they can share a medium like an optical fibre without interfering with each other.

To shrink the effect down small enough to be useful in a communication system, the boffins crafted an on-chip “microring” that's 9 microns in diameter (below).

The microring vortex laser

Image: University at Buffalo

Its particular trick: when pumped with a laser, this microring preserves OAM in one direction. Physics World explains the materials in the “clock face” pattern shown above are chosen for their refractive index, so light can only flow in one direction through the microring: “The outer wall of the microring also has a periodic modulation of the refractive index, which causes the circulating light to propagate upwards and emerge from the ring and into free space”.

In their paper in Science (abstract) the researchers say the microring laser has a sideband suppression of 40dB.

The microring currently needs to be pumped by an external semiconductor laser, so the next stage of the work will be to integrate everything into a single unit.

As well as the obvious communications applications, the researchers reckon since OAM is a quantum property that can undergo “teleportation”, the devices could be useful in quantum crypto or computing applications. ®

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