Directional bistability in novel semiconductor ring lasers with retro-reflector microcavity

Lasing direction bistability is observed in a novel semiconductor ring laser with very small retro-reflector cavities with equivalent circular radius of 26 and 16 mum and with 4- and 2-port configurations. The optical spectra from both the clockwise and counterclockwise lasing directions demonstrate the characteristic mode hopping that accompanies the flipping of free-running lasing direction with the increase of injection current. Strong bistability is achieved at high currents and also enhanced at lower operation temperature, which indicates that it is driven by the nonlinear mode competition that depends strongly on the intensity of the optical field in the cavity.