1. Optical Interconnects for Computer Systems Bhanu Jaiswal University at Buffalo

2. 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

3. 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

4. Problems with Electrical Interconnects Physical Problems (at high frequencies)  Cross-talk  Signal Distortion  Electromagnetic Interference  Reflections  High Power Consumption  High Latency (RC Delay)

5. 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

6. 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

7. Basic Ingredients SOURCE DETECTOR OPTICAL PATH VCSEL Edge-Emitting Laser LED’s P-I-N Photodiodes SML Detector MQW P-I-N Guided WaveFree-Space

8. 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

9. 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

10. SPOEC Project

11. SPOEC System Layout

12. Test bed developed by the SPOEC project

13. 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.

14. 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.

15. 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

16. 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

17. References Linking with light - IEEE Spectrum 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-VLSI system integration Technological challenges www.phy.hw.ac.uk/~phykjs/OIC/Projects/ SPOEC/MSEB2000/MSEB2000.pdf

18. 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