Defect-induced resonant tunneling of electromagnetic waves through a polariton gap

– We consider tunneling of electromagnetic waves through a polariton band gap of a 1-D chain of atoms. We analytically demonstrate that a defect embedded in the structure gives rise to the resonance transmission at the frequency of a local polariton state associated with the defect. The optical properties of materials with band gaps in their electromagnetic spectrum have recently attracted a great deal of attention. It was suggested that fundamental electromagnetic processes such as spontaneous emission [1,2], photon-atom interaction [2,3], and optical energy transfer [4] are strongly modified at band gap frequencies. Photonic crystals, which are periodic structures with a macroscopic period [5], present one of the primary examples of systems with electromagnetic band gaps. The periodicity in photonic crystals gives rise to allowed and forbidden bands for electromagnetic waves in basically the same manner as periodicity in the arrangement of atoms causes the band structure for electrons in solids. An important property of photonic crystals is an occurrence of local photon states with frequencies inside band gaps, when the periodic structure is locally distorted. The fact that an isolated defect in an otherwise perfect periodic crystal can give rise to local modes with frequencies in forbidden gaps of a host structure is well known in solid-state physics. Local photons are similar in many aspects to other types of local states: Their frequencies always belong to forbidden gaps; in 3-D systems they split off the continuous spectrum only if the “strength” of a defect exceeds a certain threshold [6-8]; and by changing the type of the distortion one can control the position of the states inside the gap. It is essential, however, that while all other local states appear due to microscopic (of atomic dimensions) defects, local photons require both a macroscopic host structure and its macroscopic distortion. This fact is obviously due to the large wavelengths of electromagnetic waves in frequency regions of interest. () E-mail: [email protected]