[FoRK] optical delay lines

Eugen Leitl eugen at leitl.org
Thu Feb 10 02:26:38 PST 2011

I need to connect two parts of a building with 10 GBit. The cheap optics over
multimode is specced to support at least 300 m. At 10 GBit, a bit is roughly
3 cm in vacuum, slightly shorter in glass. So 300 m is an optical FIFO, very
much like acoustic mercury delay lines of yore, and can accomodate your
standard 1500 Byte MTU.

Slightly more expensive optics over monomode can cover 40 or even 70 km at
such speeds.  Recent 40 GBit/s and 100 GBit/s Ethernet standard tells us at
least an order of magnitude higher storage density is possible.

If the packet headers directly select the optical crossbar, you do not need
to buffer more than a few bits within a photonic router. In any cases the
routing decision has to be made within less than 10-100 gate delays, even
using slow light medium.

Effectively, for LoS applications the router is a smart mirror for your light
stream, directing it nearer towards the target. Figuring out the optimal
header encoding layout is left as an exercise to the reader.

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