Photonic crystals have a photonic band gap (PBG) in which light propagation and emission is prohibited. In particular, three-dimensional (3D) photonic crystals have a complete PBG in all directions, which might allow the complete control of light emission and propagation in devices. Here, we report the first demonstration of light propagation in a 3D photonic-crystal waveguide at optical communication wavelengths. A line defect is introduced into a 3D photonic crystal composed of nine stacked layers, having a complete PBG in the 1.55 μm wavelength region. Light incident on the waveguide edge successfully propagates along the line-defect waveguide. The propagation characteristics agree with the calculated photonic band diagram of the structure. The calculated results indicate that lossless propagation becomes possible by increasing the number of layers in the device. These results are an important step toward the realization of multifunctional 3D photonic chips integrated within a small region.
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