Building a memory bus to switch several full duplex 10 Gb/s switches is not trivial—it is perhaps a network problem in itself. It makes one appreciate the fixed cell sizes of ATM. A switching fabric for large fixed sized packets consisting of many 1024 bit words, could use centralized combinatorial logic to plan routing over a distance of only a few cm. This logic could plan several nanosecond cycles ahead.
Perhaps the data stream from a fiber should go into consecutive DRAM addresses and a gather process, orchestrated by the software, should dispatch the data to the fiber on output. I imagine a path from fiber to DRAM with little switching which means that a particular DRAM receives data from a particular fiber and perhaps a given color range for that fiber. Packet headers would be delivered to the cache of the controlling CPU. The expensive memory crossbar would be traversed on the way to the outgoing link after the software had identified the outgoing link and built appropriate headers in cache.
Early papers on non-blocking crossbars from Bell Labs showed elegant solutions that sometimes could not be deployed because a new call between two customers, whose lines were not busy, could not be accommodated without rerouting calls in progress. The crossbars were relays at the bottom and changing several relays to form a new path would cause intolerable noise for ongoing calls. That problem does not impact us because we are moving digital signals that are discrete in time. The electronic crossbar we imagine here is a sort of systolic array and its controls can be produced by a systolic array of comparators of very small interface numbers, and this array can run a few clocks ahead of the crossbar proper. It is a lot of circuits and the layout may be difficult, but the logic is simple.
See Color switching. Several leads from that note suggest schemes for mechanically separating optical signals, with different steering from moment to moment, but no indication that the signal can be then amplified and sent on its way at the same color on a different fiber. Lambda Switches are closer to what I had in mind.