Switchable single-mode microdisk lasers

Stimulated by the non-Hermitian nature of micro- and nanophotonic systems, modal interaction has been proposed to play a more essential role in controlling lasing actions. Here we demonstrate its impact on mode management in microcavity lasers. Single-mode laser emission with extinction ratio above 10 dB has been obtained in twin-microdisks with a radius about 40 µm. Unlike conventional single-mode lasers, here the lasing mode can hop to a nearby lasing mode deterministically without varying the pumping profile or cavity structures. The laser spectra show that the initial lasing mode experiences a negative power slope until it is finally suppressed by the second lasing mode. Interestingly, the characteristics of lasers such as mode spacing and lasing wavelengths remain unchanged. All these observations are intrinsically different from the predictions from the recently developed parity-time symmetric lasers and bistability caused mode switching in microcavities. The corresponding theoretical and numerical calculations show that they are caused by the modal interaction via gain saturation. This type of interaction induced mode switching is found to be quite robust for different materials and cavity shapes. In additional to the twin disks, similar mode switching has also been observed in a single perovskite microrod. Our finding may have applications in optical memory, flip-flop, and other functional devices.