Intel scientists have used silicon manufacturing processes to create a novel 'transistor-like' device that can encode data onto a light beam.
The ability to build a fast photonic (fibre-optic) modulator from standard silicon could lead to very low-cost, high-bandwidth fibre-optic connections among PCs and other electronic devices, and eventually inside computers as well.
As reported in a recent issue of the journal, Nature, Intel researchers split a beam of light into two separate beams as it passed through silicon, and then used a novel transistor-like device to hit one beam with an electric charge, inducing a 'phase shift'. When the two beams of light are re-combined the phase shift induced between the two arms makes the light exiting the chip go on and off at over one gigahertz, 50 times faster than previously produced on silicon. This on and off pattern of light can be translated into the 1s and 0s needed to transmit data.
"This is a significant step toward building optical devices that move data around inside a computer at the speed of light," said Patrick Gelsinger, senior vice president and chief technology officer at Intel. "It is the kind of breakthrough that ripples across an industry over time enabling other new devices and applications."
The modulator device is based on a Mach-Zehnder interferometer, which splits the light along two paths and then recombines it. If a phase shift can be introduced into one of the arms, so that it is 180 degrees out of phase, then the two light beams will interfere destructively when they recombine, which gives a 'zero' at the output. If there is no phase shift, the beams combine constructively, leading to a 'one' at the output. This is a common technique for building modulators.
Rather than using the thermo-optic effect (heat) to change the refractive index of the device, as earlier devices did, Intel's novel phase-shifting technique uses an oxide electrode at the top of the device. When a voltage is applied, charge carriers accumulate next to the electrode, which changes the refractive index locally. This effect is fast because no current actually flows in the device.
Traditionally, commercial optical devices have favoured expensive and exotic materials requiring complex manufacturing. Intel's fabrication of a fast silicon-based optical modulator with performance that exceeds 1 GHz demonstrates the viability of standard silicon as a material for bringing the benefits of high-bandwidth optics to a much wider range of computing and communications applications.
"Just as Superman's X-ray vision allows him to see through walls, if you had infrared vision you could see through silicon," said Mario Paniccia, director of silicon photonics research at Intel. "This makes it possible to route infrared light in silicon, which is the same wavelength typically used for optical communications. The way electrical charges move around in a transistor when voltage is applied can be used to change the behaviour of light as it passes through these charges. This led us to explore manipulating the properties of light, such as phase and amplitude, to produce silicon-based optical devices."
Intel researchers are hoping that they can scale the technology up to 10 GHz or faster in the future.
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