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Multi-core Processors; Optical Inside Makes a Difference



Researchers have taken another step towards implementing on-chip optical networks that use light pulses instead of electrons to move information around inside computer processors. Developed by IBM, the device that makes this possible is a nanophotonic switch which has a footprint about 100X smaller than the cross section of a human hair. The switch speeds up the chip performance and uses less energy.

Nanophotonic switches are key to the development of next-generation high-performance multi-core processors which transmit information internally using pulses of light traveling through silicon instead of electrical signals on copper wires. The IBM team demonstrated that their switch has several critical characteristics which make it ideally suited to on-chip applications:

  • The switch is extremely compact. As many as 2000 would fit side-by-side in an area of one square millimeter, easily meeting integration requirements for future multi-core processors.
  • The device is able to route a huge amount of data since many different wavelengths or "colors" of light can be switched simultaneously. With each wavelength carrying data at up to 40 Gb/s, it is possible to switch an aggregate bandwidth exceeding 1 Tb/s -- a requirement for routing large messages between distant cores.
  • The 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.

Increasing the parallelism in computation by multi-threading, by building large scale multi-chip systems and, by increasing the number of cores on a single chip 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 researches are exploring an alternative solution to this problem by connecting cores using pulses of light 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 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.


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