Quote from above media release:
At major interconnection points, where billions of optical data packets arrive simultaneously, it would be useful if we could control this traffic optically, by slowing some data packets to let others through. This system would work in the same way as traffic congestion calming schemes do on our motorways, when a reduction in the speed limit enables swifter overall flow of traffic.
check these out:
IBM
Slow Light in Optical Fibers Using Stimulated Brillouin Scattering