Polarized stimulated emission from photonic molecule states in coupled microdisk lasers*

Recent studies have demonstrated the engineering of spin coherence via photon-spin interactions in microdisk lasers [S. Ghosh {\it et al.}, Nature (Materials) {\bf 5}, 261 (2006)], motivating the extension of such measurements to pairs of microdisks coupled through the evanescent electromagnetic field. Such coupled microdisks behave like ``photonic molecules'' (PMs) with bonding and antibonding states for the confined photon modes [A. Nakagawa {\it et al.}, Appl. Phys. Lett. {\bf 86}, 04112 (2005)]. We describe the fabrication and optical characterization of different PM geometries, consisting of laterally coupled GaAs/GaAlAs microdisks of both circular and elliptical shape. Steady state photoluminescence measurements reveal bonding and antibonding modes with distinct geometry-dependent polarization characteristics that are consistent with finite-difference time-domain simulations. We also discuss time-resolved optical measurements that probe both carrier and spin dynamics in these PMs.