Facile microfluidic fabrication of monodispersed self-coupling microcavity with fine tunability.

Whispering gallery mode (WGM) resonators have received extensive attention because of their nonlinear optical application in lasers and sensors. Optical microcavities are excellent candidates for constructing powerful microlasers and label-free biosensors, owing to their low optical losses and small size. However, most of these microcavity syntheses rely on sophisticated fabrication methods and cannot be manipulated easily. To achieve facile and versatile microcavity fabrication, we present a robust microfluidics method for monodispersed self-coupling optical microcavity fabrication with a fine tunability. The microcavity polydispersity was less than 3%. The optical microcavity size could be varied from 10 to 30 µm with a steady quality factor (Q) of approximately 1000. The lowest laser threshold that we obtained was 0.82 µJ with a microcavity size of 20 µm. The doped fluorescent dye concentration can be tuned precisely from 0.001 to 0.05 wt% to explore an optimized fluorescent background. The experimental results and theoretical simulation match well in terms of Q and the electrometric resonance field intensity. Compared with previous precise and practical fabrication methods, we have demonstrated a facile approach for versatile optical microcavity fabrication. This method can vary the microcavity materials, size, doped fluorescent dye concentration, WGM resonance spectrum, Q factor, and laser threshold easily to adapt to various circumstances and specific applications.