Ultralow threshold and single-mode lasing in microgear lasers and its fusion with quasi-periodic photonic crystals

The GaInAsP microgear laser is a kind of microdisk laser but has a rotationally symmetric grating, which matches with the profile of the whispering gallery mode. In this study, we achieved the room temperature continuous-wave lasing with a threshold photopump power of 14 muW for the smallest gear diameter of 2.02 mum. We also observed the single-mode lasing in a deep grating device, where the pi-phase-shifted nonlasing mode completely disappeared. The experimental results were well explained by a three-dimensional finite-difference time-domain calculation and a consideration on the surface recombination. In addition, to increase the variety of the microgear, we proposed its fusion with a quasi-periodic photonic crystal (QPC), which also has a rotational symmetry. We theoretically estimated a sufficiently high Q of 21600 for a QPC gear with a point defect of 1.6-mum diameter, which is the smallest limit for a normal microdisk at a wavelength of 1.5-1.6 mum.