Monolithic integration of semiconductor ring lasers

Abstract

The interest in semiconductor ring lasers (SRLs) has been steadily growing in the last few years because of several unique properties such as ultrafast directional bistability, stable single mode operation and potential for integration. However, most of the mode dynamical behavior as well as the optimum device design are still far from a complete understanding. This thesis reports on the design, technological development and characterization of SRLs emitting at 1.55 um, which are monolithically integrated with a number of other optical elements such as tunable couplers, optical amplifiers, Bragg reflectors and distributed feedback lasers (DFBs). A detailed analysis on the device design is presented with particular emphasis on its robustness with respect to fabrication tolerances and to the optical feedback from the output waveguides. The complete processing technology is developed with a focus on selective dry etching to achieve very accurate control of the waveguide bending losses. Three completely novel and monolithically integrated SRL devices are fabricated and characterized. The first is a master-slave device based on the monolithic integration of an SRL with a DFB that shows highly efficient cavity enhanced four-wave mixing up to detuning frequencies of 1.5 THz. In a second geometry, a Bragg reflector defined on one of the output waveguides selects the lasing mode of the SRL. The device shows world-record wavelength switching speeds as low as 450 ps and strong immunity to thermal fluctuations of the grating. The third device is an SRL with tunable couplers for active Q-switching applications. Pulses as short as 120 ps at a repetition rate of 1.8 GHz are obtained by injecting only a few mA of current into the tuning section