Optical Interconnects Speeding Up Computing Matt Webb PICTURE HERE

In the near future All logic operations solved using with optics Have to start somewhere Picture of something to signify amazing computing speeds

Why do we care? Problems with scaling of electrical interconnects (EI) Ex: Telecommunications already moved away from electrical lines Performance between chips is already affected by EI Near future will be a problem on chips

Solutions Several possibilities New architectures Minimize interconnections New design approaches Emphasize interconnection layout New medium for interconnection Optics

Background Research on optical interconnections has been going on for >20 years With optoelectronic digital computing Development of SEED’s and VCSEL’s Practical to implement SEED/VCSEL picture?

Aspect ratio limitations

Bandwidth limitations

Delay limitations

Typical model Laser diode driver Transimpedance Amplifier

Latency vs. Length 3Gb/s, 0.25μm CMOS

Power consumption vs. Length

Channels vs. Length

Scaling of OI transmitter/receiver Only viable if technology for the design of TX/RX can keep up with future generations of silicon technology

Timing for optical signals Virtually independent of temperature Virtually no degradation of signal on the scale of meters Slower propagation, but very reliable and predictable Could eliminate high power clock circuits

Benefits of OI Optoelectronic devices can be used as impedance transformers No inductance on an optical line Do not generate or detect radio- frequency signals or interference Long or short does not matter

More benefits Larger synchronous zones, even on multiple chips Allows “fire-hose” architectures Lower power dissipation after “break-even length” 100μm – 10’s of cm

Benefits cont. Voltage isolation Increasingly important due to smaller power supplies Larger density for long distance on- chip and off-chip interconnects No need for hierarchy of interconnects

Main Challenges for OI Young and expensive Systems that could take advantage of optics will most likely have different architectures than today's Problems and benefits are misperceived by those not involved in recent research

Receivers Power dissipation Small capacitance Larger noise immunity “Receiverless”

Transmitters Quantum-well modulators VCSEL’s LED’s Si based optoelectronic devices

Technology Absence of low-cost and practical How to integrate III-V devices Compatibility Hybrid integration Solder-bonding

Misperceptions Wavelength is too large Not true for longer interconnect lengths Conversion of optics to electronics is inefficient Power, area, and time Current generation of technology

Conclusions Use of OI could solve many of the problems faced in today’s electrical systems Much work remains to make the technolgy feasible When it’s all said and done OI’s are the future