  Deformed square resonators with the flat sides replaced by circular sides are
proposed and demonstrated to enhance mode Q factors and adjust transverse mode
intervals using the regular ray dynamic analysis and numerical simulations.
Dual-transverse-mode emissions due to the ultrahigh-Q factors with different
wavelength intervals are realized experimentally for AlGaInAs/InP circular-side
square microlasers, and the stationary condition of the dual-mode emission is
satisfied because the high-Q confined modes have totally different mode
numbers. Furthermore, optical frequency combs are generated using the dual-mode
lasing microlaser as a seeding light source by cascaded four-wave mixing in a
highly nonlinear optical fiber.
