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Optical Interconnects for Computer Systems. Bhanu Jaiswal University at Buffalo. Introduction. Nature of data traffic in a computer Converse to city traffic Ever increasing data transfer rate Very high data rates restricted by fundamental limitations of current copper interconnects
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Optical Interconnects for Computer Systems Bhanu Jaiswal University at Buffalo
Introduction • Nature of data traffic in a computer • Converse to city traffic • Ever increasing data transfer rate • Very high data rates restricted by fundamental limitations of current copper interconnects • Need for a long term solution
Interconnect Issues • In present computer systems, interconnections handled via parallel electrical busses • Interconnect performance does not increase comparably with the system performance Solutions • Increase performance of present EI • Use completely different physical medium
Problems with Electrical Interconnects • Physical Problems (at high frequencies) • Cross-talk • Signal Distortion • Electromagnetic Interference • Reflections • High Power Consumption • High Latency (RC Delay)
Why Optics ? • Successful long-haul telecommunication system based on fiber optics • Advantages: • Capable to provide large bandwidths • Free from electrical short-circuits • Low-loss transmission at high frequencies • Immune to electromagnetic interference • Essentially no crosstalk between adjacent signals • No impedance matching required
Evolution of Optical Interconnects – Current & Future possibilities This approach to signal transfer is moving from longer-distance applications, such as linking separate computers, to joining chips within a computer
Basic Ingredients SOURCE OPTICAL PATH DETECTOR VCSEL LED’s P-I-N Photodiodes SML Detector Edge-Emitting Laser MQW P-I-N Free-Space Guided Wave
World wide projects • Heriot Watt University – Optically Interconnected Computing (OIC) group • SPOEC Project • DaimlerChrysler, McGill University • Optical Backplanes • UC San Deigo • Optical Transpose Interconnect System Target – Terabits/second
US based research • $70 million program run by US Defence Advanced Research Projects Agency • Companies in business • Primarion Corp. – Thinking inside the box • Agilent Technologies – Optical connecters between computers • Lucent Technologies – Optical Crossbar switch matrix
Optical Backplanes Speed Data In DaimlerChrysler's optical backplane, the beam from a laser diode passes through one set of lenses and reflects off a micromirror before reaching a polymer waveguide, then does the converse before arriving at a photodiode and changing back into an electrical signal. A prototype operates at 1 Gb/s.
Free-Space Interconnects Pack in Data Channels An experimental module from the University of California, San Diego, just 2 cm high, connects stacks of CMOS chips. Each stack is topped with an optics chip [below center] consisting of 256 lasers (VCSELs) and photodiodes. Light from the VCSELs makes a vertical exit from one stack [below, left] and a vertical entry into the other. In between it is redirected via a diffraction grating, lenses, an alignment mirror [center], and another grating. Each of the device's 256 channels operates at 1 Gb/s.
Principal Challenges • Multi-disciplinary field • Device Integration, Interfacing & Packaging • Electronic components – Si CMOS based • Optoelectronic Components – III-V Compound based • Optical components – MicroLens and MicroMirrors based • Misalignment in FSOIs
Conclusions • Interconnect problem significant in ultra deep submicron designs • Performance of Electrical lnterconnects will saturate in a few years • OIs – very promising for future computers • OIs do not aim to completely replace EIs
References • Linking with light - IEEE Spectrum http://www.spectrum.ieee.org/WEBONLY/publicfeature/aug02/opti.html • Optically Interconnected Computing Group http://www.phy.hw.ac.uk/~phykjs/OIC/index.html • Optoelectronics-VLSIsystemintegrationTechnologicalchallenges www.phy.hw.ac.uk/~phykjs/OIC/Projects/ SPOEC/MSEB2000/MSEB2000.pdf
Ref. follows • International Technology Roadmap for Semiconductors (ITRS), 2001 • R. Havemann and J.A Hutchby, “High-Performance Interconnects: An integration Overview”, Proc. Of IEEE, Vol.89, May 2001 • D.A.B Miller, “Physical reasons for optical interconnections”, Int. Journal of Optoelectronics 11, 1997, pp.155-168. • MEL-ARI: Optoelectronic interconnects for Integrated Circuits – Achievements 1996-2000
Thank You for Your Time and Patience !