Elimination of cross talk in waveguide intersections

We present general criteria for crossing perpendicular waveguides with near ly 100% throughput and 0% cross talk. Our design applies even when the wave guide width is of the order of the wavelength. The theoretical basis for th is phenomenon is explained in terms of symmetry considerations and resonant tunneling and is then illustrated with numerical simulations for both a tw o-dimensional photonic crystal and a conventional high-index-contrast waveg uide crossing. Cross-talk reduction by up to 8 orders of magnitude is achie ved relative to unmodified crossings. (C) 1998 Optical Society of America.