Improvement of out-coupling of the oblique waveguide in three-dimensional photonic crystals by introducing a symmetric end structure

An oblique waveguide in a stripe-stacked three-dimensional photonic crystal is a useful structure for interlayer coupling, but has a problem that the out-coupling to free-space is inclined and spatially asymmetric. We propose a new end structure that provides vertical and less-frequency-dependent out-coupling characteristics.