Surface structure for efficiently coupling into photonic crystal slab waveguides with a triangular lattice of air holes

Highly efficient coupling outer electromagnetic (EM) waves into photonic crystal (PhC) waveguides (PhCWs) is critical to the applications of PhCs in photonic integrated circuits. We investigate and simulate an efficient way of coupling EM waves into PhCWs of air holes array by using surface dielectric margin based on all-PhCs structure. Good matching of modal field profiles on both sides of the interface is obtained by adjusting the surface dielectric margin along the propagation direction. The coupling efficiency can be highly enhanced by suppressing the surface field propagating along the transverse margin at the interface. The numerical results using finite-difference time-domain simulations show that the bandwidth for coupling efficiency larger than 90% can be as broad as about 100nm.