Integrated Semiconductor Ring Lasers

[摘要] The concept of a semiconductor laser with a circular resonator, its advantages and particular problems are discussed. The pillbox resonator is introduced and its operation on whispering gallery modes is illustrated using a computer model. The experimental evidence of the guiding mechanism is shown, leading to the first demonstration of continous wave operation in a semiconductor ring laser with a threshold current of 24mA. The parameters of the GaAs/AlGaAs material that are relevant for the low threshold current operation are presented and all aspects of the fabrication procedure are covered, emphasizing the processes that led to smooth sidewalls and the low loss circular cavity. A further reduction of the threshold current to 12.5mA is shown, which is owing to a coating of silicon nitride that supresses the non-radiative recombination current and reduces the scattering loss. The excess bending loss is calculated to be 3dB/360 and found to be independent of the radius between 30mum and 145mum. The influence of the Y-junction on the operation characteristic is studied and shown to cause kinks in the L-I curve; it is also held responsible for the relatively low differential quantum efficiency (0.02-0.04) of the devices. Strip-loaded guiding is demonstrated for radii between 300mum and 600mum and proposed as a solution for the problem of degradation that is caused by etching through the active layer. The integration capability of the structure is demonstrated by the succesful operation of a circuit comprising of a ring laser, a low-loss waveguide and a detector, and an optoelectronic integrated circuit featuring a ring laser and a field-effect transistor. The material parameters that are involved in performing these complicated functions are discussed and modeled numerically.

[发布机构] University:University of Glasgow

[关键词] Electrical engineering, Condensed matter physics, Optics