Photonic Molecules in Photonic Crystals

We propose a photonic molecule consisting of multiple nanocavities in a photonic crystal and demonstrate its lasing and modal characteristics by finite-difference time-domain analysis and by experiments. In the analysis, we show that a point-shift defect and a point-missing defect have s- and p-orbital cavity modes, respectively, and that two adjacent defects exhibit σ- and π-orbital bonding and antibonding modes, which are similar to electronic states in chemical molecules. For such structure, we verify the modal characteristics as photonic molecules, i.e., mode splitting and its dependence on coupling strength, through their fabrication into GaInAsP photonic crystal slabs and the observation of lasing characteristics.