25-channel all-optical gate switches realized by integrating silicon photonic crystal nanocavities.

Silicon-based photonic crystal nanocavities with different lattice pitches were monolithically integrated with a total length of only 200 μm, and were operated as a multi-channel all-optical switch with a large processing density of 42 Tb/s/mm2. A pump light and a signal light were assigned to two cavity modes in each cavity, and in this way all-optical gate switching was achieved in a 25 channel resonant dip with an energy cost in the femtojoule regime. We also demonstrated a wavelength-division multiplexing operation by selecting three neighboring channels, and thus achieved gate switching without inter-channel optical crosstalk. As far as we know, this was the first demonstration of a many-channel all-optical switch that can handle an optical signal with bit-by-bit Gb/s repetition in an integrated photonic crystal chip.