Improved Transmission Waveguide Bends in Photonic Crystal

A major drawback of conventional dielectric waveguides is that their bending radii are limited to several millimeters due to the degradation of total internal reflection. Since the guiding of light in a PhC defect waveguides is not given through total internal reflection but the photonic bandgap (PBG) effect they can provide bending within the subwavelength range. Hence, PhC waveguides offer a promising scheme for low loss and ultra-dense optical integration. In this paper we have investigated and optimized 60° and 90° waveguides bends that are implemented in a planar photonic crystal (PhC) with triangular and square lattice symmetry. The in-plane guiding within the planar PhC structure is based on a W1 defect waveguide (a single line defect acting as a light channel in the Γ-K-direction) whereas for the vertical light confinement we rely in a slab waveguide formed by the low index contrast material system InGaAsP/InP. To achieve a reasonable band-gap around 1.55 μm the PhC consists of a lattice of holes with a filling factor of 39%. Key optical design parameters are characterized using 2D Finite difference time domain (FDTD) solution of the full-Wave Maxwell's equations. We show a significant improvement in both the transmission efficiency (up to 97%) and the transmission bandwidth by performing an optimization based on a sensitivity analysis