Photonic crystals are three dimensional periodic structures having the property of reflecting the electromagnetic (EM) waves in all dimensions, for a certain range of frequencies. Defects or cavities around the same geometry can also be built by means of adding or removing material. The electrical fields in such cavities are usually enhanced, and by placing active devices in such cavities, one can make the device benefit from the wavelength selectivity and the large enhancement of the resonant EM field within the cavity. We used three-dimensional photonic crystals to demonstrate resonant cavity enhanced detectors and antennas, and waveguiding.
We have demonstrated the resonant cavity enhanced (RCE) effect by placing microwave detectors in defect structures built around dielectric and metallic based photonic crystals. A power enhancement factor of 3450 was measured for planar cavity structures built around dielectric based photonic crystals. A resonant antenna was also built around the same structure. We measured a maximum directivity of 310, and a power enhancement of 180 at the resonant frequency of the cavity. The measured radiation patterns agree well with our theoretical results.
We used the defect structures to demonstrate waveguiding around layer-by-layer photonic crystals. An air gap introduced between two photonic crystal walls was used as the waveguide. We observed full (100%) transmission of the electromagnetic (EM) waves through these planar waveguide structures within the frequency range of the photonic band gap. The dispersion relations obtained from the experiment were in good agreement with the predictions of our waveguide model. By using coupled periodic defects, we have also experimentally observed a new type of waveguiding in a photonic crystal. A complete transmission was achieved throughout the entire waveguiding band.