The infrared light was being converted to
green light in a process known as third
harmonic generation - though this was
completely unexpected at first.
Image: University of Sydney
A seemingly impossible sparkle of green light from a silicon chip has opened up a whole new field of possibilities for communications devices, including exponentially shrinking the hardware needed to guarantee high quality internet connection.
"When I saw the green light on the camera, I was extremely puzzled," said Dr Christian Grillet of the University of Sydney. "We were using infrared light, not green. And besides, silicon does not transmit light at that wavelength!"
Dr Grillet's colleague Dr Christelle Monat was in the labs in the School of Physics at the time: "I didn't believe the camera. I had to look with my own eyes. It was as strange as seeing a house-brick suddenly emit light."
The effect was real, however, and was published in the journal Nature Photonics. Their infrared laser was being converted to green light - light of higher energy - in a process known as third harmonic generation.
Asked about the potential of this discovery, Dr Monat says: "One could imagine that a small green light indicator could help users of numerous internet applications. This could be used to immediately inform companies such as Skype of a problem in the clarity of their connections, thereby allowing them to fix this in real-time, all without the end-user even noticing."
The key to this unlikely event was a regular pattern of sub-microscopic air holes in the researchers' silicon chip, creating what is known as a photonic crystal. At the time of the discovery Dr Monat and Dr Grillet were assisting PhD student Bill Corcoran with experiments on slow light, itself a very novel and surprising phenomenon.
Corcoran explains: "The experiments use specially designed photonic crystals from our colleagues at St Andrews in Scotland. They allow us to slow the laser light used for telecommunications to 1/40th of its usual speed.
"As the light slows down, the energy from the laser is greatly concentrated. This energy can be used like traffic lights on the road to control the movement of large amounts of optical data through networks much more efficiently."
The researchers work in a field known as photonics. They say that converting infrared to green light adds another important tool to the impressive suite of capabilities of silicon, already the material of choice for the micro-electronics industry.
"Being able to control light on a chip, along wires no wider than one hundredth of the width of a human hair, represents the first step to realise all sorts of operations with significantly better performance than electronics alone," Dr Monat explains. "And if we can do that in silicon, even more complex and exciting architectures become possible by integrating and marrying both the photonic and electronic worlds."
The research team's paper, Green light emission in silicon through slow-light enhanced third-harmonic generation in slow light photonic-crystal waveguides, is published in Nature Photonics.
Editor's Note: Original news release can be found here.
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