Propagation Loss In Three-Dimensional Photonic Crystal Waveguides With Imperfect Confinement

Perfect confinement and efficient propagation of electromagnetic (EM) waves can be realized in waveguides created into a three-dimensional (3D) layer-by-layer photonic crystal that exhibits a complete band gap. However, the difficulty to build very thick 3D photonic crystals in the fundamental optical and infrared regimes by means of current lithography techniques will induce leakage of EM waves away from the waveguide through limited cladding layers. In order to assess the degradation of the optical properties of these photonic crystal waveguides, we build waveguides in a microwave-frequency 3D layer-by-layer photonic crystal and measure the leakage induced propagation loss. We find that this propagation loss exponentially decays with respect to the thickness of the cladding wall of the waveguide. The measurement results can scale to optical and infrared wavelengths and provide useful information for optimal design of photonic crystal structures in these regimes.