Birth of silicon's optical age
ANAND PARTHASARATHY
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Photons of light may soon replace electrons as information carriers.
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PHOTON POWER: Semiconductor optical amplifier developed at the Center for Integrated Photonics. (Inset) a scanning electron microscope's view of its innards... a step towards all-optical photonics networks.
THE WORLDWIDE web is largely an optical network where hundreds of kilometres of glass fibre carry data to and fro.
Electro-optical modulators — devices which convert optical information into electrical, and vice versa — are used in thousands on the Internet. Ironically, inside the millions of personal computers, which connect to the Net, copper is still the preferred connection material, and today's processors which house nearly a billion transistors on a matchbox-sized slab of silicon, use micro-thin tracks of copper to carry the bits of data.
More efficient
It would be more efficient to replace the copper connections with photons or beams of light. But electro-optical modulators have been too large to fit into the chip — till now.
Just 18 months ago, the world's biggest chip maker, Intel announced in the British journal, Nature, the birth of `the optical age of silicon.'
During the Intel Developer Forum in San Francisco, Intel's engineers unveiled the first-ever optical modulator realised on a fingernail-sized piece of silicon. (The Hindu, February 18, 2004). The resultant light beam could switch at 1 billion times a second (1 giga hertz).
Fifteen months later, this vision of the future became a reality when scientists at the Centre for Integrated Photonics (CIP) at Adastral Park, near Ipswich in the East of England, delivered commercially viable samples of a Semiconductor Optical Amplifier (SOA), which could switch 40 times faster.
Transmission system
Clearly, the time has come to consider an all-optical data transmission system.
Getting silicon to behave like an optical component as the researchers at Intel and CIP have done is only the first step. The bigger challenge is to make silicon behave like a laser.
At centres like Cornell University, the University of California, Los Angeles (UCLA) and at Intel, scientists have fallen back on the Raman Effect, first postulated by Sir C.V. Raman in 1928.
Raman effect
The Effect, which says light is tremendously amplified when passing through certain transparent materials, has been seized by these scientists to create what is known as the Raman silicon laser (The Hindu on February 18).
The Raman laser is a fundamental scientific breakthrough that may well bring the days of an all-optical communication system nearer.
This has become an urgency because as Gordon Moore, author of the famous Moore's law explained to this correspondent during a global conference call on the 40th anniversary of the law in April this year, we may have at best another 20 years before electronics on silicon hits a physical wall.
That is when photonics will have to step in.
However, silicon lasers and modulators notwithstanding, a pure photonics silicon chip is not going to happen tomorrow. First, we need to see all-optical gates for logic, the units, which do the math.
Photonics interconnect
The Massachusetts Institute of Technology (MIT) in its annual survey of `Ten emerging technologies' in 2005, suggests that the first photonics interconnects will appear between chips, rather than within the chips.
The ultimate goal — photons of lights replacing electrons on computer chips, may be a decade or more away. Meanwhile, photonics development centres like CIP have already kick-started the transition from lab to factory, and many of their semiconductor photonics products are seeing their way into a new generation of optical information systems.
Photonics network
On a wet day in May, I peeped through a porthole in one of CIP's many optical prototype labs, where dozens of optical building blocks had been strapped together to create a rudimentary photonics network.
The numbers rolling over the numeric displays told me the data was being optically shifted at close to 50 billion times a second. One hardly noticed the messy clutter of the lab setting:
This was a thrilling preview of the not-too-distant optical future. I came away feeling I had truly `seen the Light'.
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