Variational theory for photonic molecules

A new type of artificial molecule is proposed, which consists of coupled defect atoms in photonic crystals, named as photonic molecule. Within the major band gap, the photonic molecule confines the resonant modes that are closely analogous to the ground states of molecular orbitals. By employing the variational theory, the constraint determining the resonant coupling is formulated, that is consistent with the results of both the scattering method and the group analysis. In addition, a new type of photonic waveguide is proposed that manipulates the mechanism of photon hopping between photonic molecules and offers a new optical feature of twin waveguiding bandwidths.