Extremely uniform angular distributions of the three-dimensional emission spectra of photonic quantum ring lasers

We have observed the emission spectra of three-dimensional Rayleigh-Fabry-Perot cavity whispering-gallery modes from photonic quantum ring lasers that give rise to uniform angular mode spacing in space. The observed angular distribution (0 ° ~ 30 °) of the emission modes is linear with respect to the mode number. For example, the average angular mode spacing is 0.95 ° with a standard deviation of 0.098 ° for a 20- (mu)m-diameter laser, whose potential angle-resolving power is promising for angle-sensing applications in the future.