IBM touts nanophotonic switch to route data between chip cores

MARCH 17, 2008 -- IBM says its scientists have built the world's smallest nanophotonic switch with a footprint about 100X smaller than the cross section of a human hair. The switch could be used to transfer information inside a computer chip by using photons instead of electrons.

MARCH 17, 2008 -- IBM (search for IBM) says its scientists have built the world's smallest nanophotonic switch with a footprint about 100X smaller than the cross section of a human hair. The switch could be used to transfer information inside a computer chip by using photons instead of electrons.

The switch could significantly speed up chip performance while using much less energy, IBM says.

The switch is a continuation of a series of IBM developments towards an on-chip optical network:


  • In November 2005, IBM scientists demonstrated a silicon nanophotonic device that can significantly slow down and actively control the speed of light.
  • In December 2006 an analogous tiny silicon device was used to demonstrate buffering of over a byte of information encoded in optical pulses, a requirement for building optical buffers for on-chip optical networks.
  • In December 2007, IBM scientists announced the development of an ultra-compact silicon electro-optic modulator, which converts electrical signals into light pulses, a prerequisite for enabling on-chip optical communications.

"This new development is a critical addition in the quest to build an on-chip optical network," said Yurii Vlasov, manager of silicon nanophotonics at IBM's T.J. Watson Research Center. "In view of all the progress that this field has seen for the last few years, it looks that our vision for on-chip optical networks is becoming more and more realistic."

The switch was unveiled in a paper published in the journal Nature Photonics.

IBM says its team demonstrated that the switch has several characteristics that make it suited for on-chip applications. First, the switch is extremely compact. As many as 2,000 would fit side-by-side in an area of 1 sq mm, easily meeting integration requirements for future multi-core processors.

Second, the device is able to route a large amount of data since many different wavelengths can be switched simultaneously. With each wavelength carrying data at up to 40 Gbits/sec, it is possible to switch an aggregate bandwidth exceeding 1 Tbit/sec -- a requirement for routing large messages between distant cores.

Third, IBM scientists showed for the first time that their optical switch is capable of operating within a realistic on-chip environment, where the temperature of the chip itself can change dramatically in the vicinity of "hot-spots," which move around depending upon the way the processors are functioning at any given moment. The IBM scientists believe this temperature-drift-tolerant operation to be one of the most critical requirements for on-chip optical networks.

An important trend in the microelectronics industry is to increase the parallelism in computation by multi-threading, by building large scale multi-chip systems and, more recently, by increasing the number of cores on a single chip. For example the IBM Cell processor that powers Sony's PlayStation 3 gaming console consists of nine cores on a single chip. As users continue to demand greater computing performance, chip designers plan to increase this number to tens or even hundreds of cores.

This approach, however, only makes sense if each core can receive and transmit large messages from all other cores on the chip simultaneously. The individual cores located on today's multi-core microprocessors communicate with one another over millions of tiny copper wires. However, this copper wiring would simply use up too much power and be incapable of transmitting the enormous amount of information required to enable massively multi-core processors.

IBM researchers are exploring an alternative solution to this problem by connecting cores using photons in an on-chip optical network based on silicon nanophotonic integrated circuits. Like a long-haul fiber-optic network, such an extremely miniature on-chip network will transmit, receive, and route messages between individual cores that are encoded as a pulses of light. It is envisioned that by using light instead of wires, as much as 100 times more information can be sent between cores while using 10 times less power and consequently generating less heat.

The work was partially supported by the Defense Advanced Research Projects Agency (DARPA) through the Defense Sciences Office program "Slowing, Storing and Processing Light."

Additional information on this development as well as on the IBM's nanophotonics project can be found on the Web.

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