Multimode Emission in GaN Microdisk Lasers

Quantum well nanolasers usually show single‐mode lasing, as gain saturation suppresses emissions in other modes. In contrast, for whispering gallery mode microdisk lasers with GaN quantum wells as active material, above threshold multimode laser emission is observed. This intriguing emission feature is manifested in the fact that several modes simultaneously show the characteristic kink in the input–output curve at the onset of lasing. A quantum theory for nanolasers is used to support the experimental finding and to analyze this behavior in the presence of gain saturation. Coupling effects between neighboring modes are identified as the origin of multimode lasing, which initiate photon exchange between modes via population pulsations similar to classical wave‐mixing effects. A reduction of this type of mode coupling with increasing mode spacing is demonstrated. The results can pave the way for multimode application of nanolasers in integrated photonic circuits. Quantum well nanolasers usually show single‐mode lasing. In this paper, multimode laser emission is observed in whispering gallery mode microdisk lasers with GaN quantum wells as active material. The presence of multimode emission despite gain saturation is explained by photon exchange between modes via population pulsations similar to classical wave‐mixing effects.