Photonic band gap 12 Energy gap 10 Negative phase velocity 6 Parallel-plate waveguide 6 Bragg condition 4 Fabry-Perot condition 4 Film preparation 4 Mesoporous materials 4 Multilayer 4 Multilayers 4 Photonic crystals 4 Photons 4 Refractive index 4 Sol-gels 4 Titanium dioxide 4 Alternating layers 2 Amphiphilic molecules 2 Antennas 2 Artificial photosynthesis 2 Band gaps 2 Chemical stability 2 Circular waveguides 2 Coaxial waveguides 2 Composite materials 2 Cross-sectional shape 2 Crystal microstructure 2 Crystalline materials 2 Cut-off 2 Dielectric materials 2 Dielectric waveguides 2