Monolithically integrated twin ring diode lasers with quantum-dot active region

Optoelectronic integrated circuits incorporating twin ring diode lasers with InAs/InGaAs/GaAs quantum-dot active region have been fabricated and characterized. Directional control and unidirectional operation of ring diode lasers are demonstrated by forward biasing an S-section waveguide incorporated within the ring cavity. Mode-beating spectra from individual ring diode lasers are observed at three bands near 7.5 GHz, 16.6 GHz, and 25.1 GHz, corresponding to single, double, and triple longitudinal mode spacing in the ring cavity. In addition, mode beating spectra between optically independent integrated twin ring diode lasers are also demonstrated, with minimal linewidth of ~4 MHz.