Physics and applications of defect structures in photonic crystals

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. 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. The transmission, phase, and delay time characteristics of the various coupled-cavity structures were measured and calculated. We observed the eigenmode splitting, waveguiding through the coupled cavities, splitting and switching of electromagnetic waves in waveguide ports, and Mach-Xender interferometer effect in such structures. The corresponding field patterns and the transmission spectra were obtained from the finite-difference-time-domain (FDTD) simulations. We developed a theory based on the classical wave analog of the tight-binding (TB) approximation in solid state physics. Experimental results are in good agreement with the FDTD simulations and predictions of the TB approximation.