Photonic bandgap waveguide structures

Passive optical components based on high-index materials like silicon are becoming increasingly attractive because they allow dense integration. Photonic crystal waveguides support modes due to Bragg reflections as well as modes due to total internal reflection if the waveguide material is made out of the higher refractive medium. We have studied, based on macroporous silicon, the transmission through a 2D-photonic crystal waveguide. These structures are really two-dimensional since they exhibit aspect ratios of more than 100. Their transmission has strong spectral features, resulting from the coupling of index-guided modes with Bragg-guided modes. If both modes have the same symmetry, they interfere with each other and open up spectral gaps (Ministop bands). Moreover, the Bragg-guided modes can exhibit very small group velocities enabling their use for dispersion compensation or gas sensing devices.