  We demonstrate optical performance monitoring of in-band optical signal to
noise ratio (OSNR) and residual dispersion, at bit rates of 40Gb/s, 160Gb/s and
640Gb/s, using slow-light enhanced optical third harmonic generation (THG) in a
compact (80 micron) dispersion engineered 2D silicon photonic crystal
waveguide. We show that there is no intrinsic degradation in the enhancement of
the signal processing at 640 Gb/s relative to that at 40Gb/s, and that this
device should operate well above 1Tb/s. This work represents a record 16-fold
increase in processing speed for a silicon device, and opens the door for slow
light to play a key role in ultra-high bandwidth telecommunications systems.
