Modal characteristics and bistability in twin microdisk photonic molecule lasers

We demonstrate coupled-mode characteristics and bistability in photonic molecule lasers composed of evanescent-coupled GaInAsP twin microdisks. First, we show room-temperature continuous-wave operation by photopumping and discuss the unique behavior of coupled modes, i.e., the anticrossing and splitting characteristics of bonding and antibonding modes. Next, we present the clear bistability, which is observed for the antibonding mode by nonuniform pumping with an effective power of nearly 40 μW. It is explained by rate equation analysis, which assumes saturable absorption. The analysis also predicts mode switching by the carrier-induced refractive index change. A micron-sized device with a very low power consumption will allow large scale integration of optical memories, optical flip-flops, and so forth.