  All-optical integrated circuits for computing and information processing have
been pursued for decades as a potential strategy to overcome the speed
limitations intrinsic to electronics. However feasible on-chip integrated logic
units and devices still have been limited by its size, quality, scalability,
and reliability. Here we demonstrate all-passive on-chip optical AND and NAND
logic gates made from a directional emitting cavity connecting two ultrasmall
photonic crystal heterojunction diodes. The measured transmission spectra show
more than 10dB contrast of the logic transport with a high phase tolerance,
agreeing well with numerical simulations. The building of linear, passive, and
ultracompact silicon optical logic gates might pave the way to construct novel
nanophotonic on-chip processor architectures for future optical computing
technologies.
