S-shaped oscillation mode lasing in droplet microlasers

The oscillation trajectories of lasing modes can describe both static and dynamic properties of a microlaser, helping determine high-quality (Q) lasing modes and modulate their optical behaviors. Almost all lasing modes for droplet microlasers have a geodesic oscillation path, taking the form of a ring-like curve or a semicircular curve, which is considered the optimal path for achieving the highest gain. However, we have discovered a lasing mode, referred to as the S-mode (SM), with a non-geodesic S-shaped oscillation path in a curable dye-based droplet microlaser. SM exhibits a longer gain length and a smaller free-spectral range than other lasing modes with geodesic oscillation paths, resulting in a high Q-factor up to 9000. Lasing spectra of SM microlasers can be modulated through manipulating the number of SMs and the relative spatial positions of their oscillation paths. Leveraging the oscillation trajectory of SM, out-of-plane lasing coupling is achieved between a microresonator and a tapered fiber positioned atop its dome. Our findings on SM are promising to enrich the understanding of lasing mode theory and inspire the design of other semiconductor-based SM microlasers, which may have practical significance for the design of photonic devices and their on-chip integration.