Coupling and phase analysis of cavity structures in two-dimensional photonic crystals

An experimental and numerical study of the coupling properties of cavity waveguides and the phase advancement through the coupled cavity waveguides in two-dimensional photonic crystals is presented. We find that the resonance frequency is insensitive to the confinement strength for cavity and for finite size defects. We obtain the coupling constant as a function of the distance between two cavities within the tight-binding formalism experimentally, and show the exponential decay of the coupling strength. By measuring the phase spectra of coupled cavity waveguides (CCW's), we clearly demonstrate that the phase shift across the guiding band is equal to N pi, where N is the number of cavities in the waveguide. This essential behavior is employed to analyze the transmission response of CCW-based Mach-Zehnder interferometer structures introduced recently.