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IBM develops tiny nanophotonic switch for optical routing between cores
The move marks another advancement in IBM's quest to develop next-generation high-performance multicore computer chips that transmit information internally using pulses of light through silicon instead of electrical signals on copper wires.
By Ann Steffora Mutschler, Senior Editor -- EDN, 3/17/2008
In another step towards sending information inside a computer chip using light pulses instead of electrons, researchers at IBM in Yorktown Heights, NY, reported today that they’ve created what they believe is the world's smallest nanophotonic switch with a footprint about 100x smaller than the cross section of a human hair.
This development aims to address the trend within the microelectronics industry of 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, even though this approach only makes sense if each core can receive and transmit large messages from all other cores on the chip simultaneously, IBM said.
The individual cores on today’s multicore microprocessors communicate with one another over millions of tiny copper wires, but this copper wiring would simply use up too much power and be incapable of transmitting the enormous amount of information required for massive multi-core processors, the company noted.
As such, IBM said its 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 on-chip network will transmit, receive, and route messages between individual cores that are encoded as a pulses of light, and it is envisioned that using light instead of wires, as much as 100x more information can be sent between cores, while using 10x less power and consequently generating less heat.
This development is key to controlling the flow of information inside chips in the future and is expected to speed chip performance while using less energy.
“This new development is a critical addition in the quest to build an on-chip optical network," Yurii Vlasov, manager of silicon nanophotonics at IBM’s T.J. Watson Research Center, explained in a statement. "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.”
(Source: IBM)
The silicon broadband optical switch, represented by the black boxes in the figure, performs the key role of "directing traffic" within the on-chip optical network.
In a paper published in the April 2008 issue of Nature Photonics, IBM details the development of a silicon broadband optical switch, which is another key component required for on-chip optical interconnects.
Once the electrical signals have been converted into pulses of light, IBM said this switching device performs the key role of "directing traffic" within the network, ensuring that optical messages from one processor core can efficiently get to any of the other cores on the chip.
The IBM scientists demonstrated that the switch has several critical characteristics which make it suited for on-chip applications.
First, the switch is extremely compact: As many as 2,000 switches would fit side-by-side in an area of 1-square-millimeter, thereby meeting integration requirements for future multi-core processors.
Second, 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.
Third, the researchers have 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, and believe this temperature-drift tolerant operation is one of the most critical requirements for on-chip optical networks.
IBM has been working on developments to allow for on-chip optical networks for a number of years. In November 2005, IBM scientists demonstrated a silicon nanophotonic device that can significantly slow down and actively control the speed of light. Then, in December 2006, IBM used an analogous tiny silicon device to buffer more than a byte of information encoded in optical pulses a requirement for building optical buffers for on-chip optical networks. Also, last December, IBM scientists announced the development of an ultra-compact silicon electro-optic modulator, which performs converts electrical signals into the light pulses, a prerequisite for enabling on-chip optical communications, the company concluded.
