Wavelength-Routing Switch Fabric Patrick Chiang, Hossein Kakvand, Milind Kopikare, Uma Krishnamoorthy, Paulina Kuo, Pablo Molinero-Fernández Stanford University Optical Routing Seminar 2001

Project Goal Build IP Switch Fabric with 64 by 64 ports, each port signaling at 40Gb/s*16λ=640Gb/s per port

Solution #1—Electrical Switch Fabric As data rate increases, speed becomes dominated by passive electrical model –Channel attenuation--dielectric loss, skin effect –For switch fabric cabinets far (~10m) from line cards, must use fiber for low channel loss –need o/e and e/o f linecard

All Electrical Crossbar For One-Chip Electrical crossbar solution, need –64*2 ports*16λ*2= Gb/s I/O –Power Consumed= 200mW*4096=820W Power Consumed ~ Entire IP Router 40Gb/s *16 λ Crossbar chip

Solution #2—High Speed MEMS Cross-Connect Hide latency Plane 1 OXC Plane K OXC Pulsed Laser Source (Picosecond) on rotary stage Passive MEMS Diffractive gratings (or other optical element) with at least 10ns switching speed MEMS OXC (1  s switching speed) MUX Fiber O/E/O

MEMS Switch Is Too Complex Issues: Need 10-ns switches and 1μs MEMS Difficult to align with large number of planes (K) K=100 planes (i.e.1μs/10ns) Switching speed achievable = 10 ns Assume packet size = 64Bytes 51.2 Gb/s (per channel)  100 MEMS planes, each with 2*1024=2048 Mirrors

Arbiter Different Router Architectures Arbiter Crossbar Switch Electrical Bus

Our proposal: Optical Bus N = 64 ports  64 internal wavelengths K = 16 external WDM wavelengths  16 processing planes VCSEL Array ’ 1 ’ K Input Port 1 ’ 1 ’ K Input Port N 1 - N 1 K Output Port 1 N K Output Port N Passive Optical Bus 1 - N

Passive Wavelength Sorter Input fibers Collimating lens High Dispersion Wavelength Disperser Output fibers Receiver, possibly with spike filter Thermally Expanded Core (TEC) Fiber to couple into fiber better

Advantages Fast Switching: –As fast as VCSEL modulation Scalability: –Can add new planes for new external wavelengths Power: –Passive optical components  minimal power consumption Space: –16 Planes, 64*2 fibers per plane

Open Issues Major Limitations: –Alignment of fibers and other optical elements. –VCSEL arrays with 64 different wavelengths –64-wavelength sorter (dispersion element) –Does not scale with higher port count –Complexity of the arbiter Cost factor: –Alignment of the fibers at the coupler.