Fano resonances for localized intrinsic defects in finite-sized photonic crystals

Abstract

Fano resonance spectroscopy (FRS) is used to investigate the photonic resonance properties of the defect states in two-dimensional finite-sized photonic crystals (PCs). This study examines the scattering cross-section spectra by changing the direction of the incident light continuously. The present FRS is applied to the intrinsic localized defect produced by displacing a single rod atom from its regular site, which creates one defect mode within the first gap and two defect modes within the second gap simultaneously. The present examination has made clear the correlation between the asymmetry of the scattering cross-section spectra---characterized by the so-called Fano $q$ value---and the optical energy flows in the PC, in particular, that the optical incoming flux is maximized for ${q}^{\ensuremath{-}1}=0$. This fact demonstrates the presence of the selective capturing of photons at the defect state in the incoming process of light; moreover, it can be recognized merely by knowledge of the $q$ values. The Fano resonances have thus been successfully used to elucidate the resonance nature of the localized defect states in photonic crystals.