Design of photonic-crystal and wire waveguide interface

The coupling of light between wire-dielectric and photonic-crystal waveguides, characterized by a triangular lattice of air holes, is investigated through a finite-element time domain (FE-TD) approach, in order to optimize the transmission spectrum. The displacement of the inner-hole rows of the photonic-crystal waveguide, on both sides of the interface, has been shown to considerably improve the coupling, resulting in transmission values higher than 90% and 95% over bandwidths of hundreds of nanometers around 1550 nm. The new design approach is successfully proposed for input and output waveguides with width equal to root 3 Lambda, as well as for larger widths, like 2 root 3 Lambda and 3 root 3 Lambda, with Lambda being the period of the photonic crystal.