Light propagation in three-dimensional photonic crystals.

We demonstrate the operation of two types of waveguides formed in three-dimensional (3D) photonic crystals (PCs). We first created a vertical waveguide by stacking acceptor-type defects, in which near-infrared light propagates in the stacking direction. Light is transmitted independent of polarization in this waveguide because electromagnetic waves couple to a degenerate mode derived from the structural symmetry of the defects. We then connected horizontal and vertical waveguides to form an L-shaped waveguide, which is able to guide near-infrared light from the horizontal to vertical direction in the 3D PC. We envisage the realization of more complex 3D optical interconnections by optimizing the waveguide structures and increasing the PC period in the vertical direction.