Department of Physics, Bilkent University, Bilkent, Ankara, 06533 TURKEY


       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 waveguides and beam splitters. By using coupled periodic defects, we have experimentally observed a new type of waveguiding in a photonic crystal. A complete transmission was achieved throughout the entire waveguiding band. We have also obtained the dispersion relation for the waveguiding band of the coupled periodic defects from the transmission-phase measurements and from the TB calculations.

     We proposed and demonstrated two different methods to split electromagnetic waves in three-dimensional photonic crystals. By measuring transmission spectra, it was shown that the guided mode in a coupled-cavity waveguide can be split into the coupled-cavity or planar waveguide channels without radiation losses. The flow of electromagnetic waves through output waveguide ports can also be controlled by introducing extra defects into the crystals.