Fig. 1. Number of microresonators versus Q factor [13–23" target="_self" style="display: inline;">–23] represents a trade-off between the quality factor and the number of resonators. Our work on the top right uniquely combines high optical Q with a large number of resonators.

Fig. 2. Coupling setup. (a) A tunable laser (780 nm) serves as the laser source, and a curved tapered fiber is used to couple oil droplets. (b) A chamber is assembled by two cover slices and a glass slide (thickness: 1 mm). The chamber is filled with deionized water and fluorescent dye. The oil droplets are placed in the water environment to maintain their spherical shape. The fluorescent dye is used for mapping the mode. (c) A vertical microscope is used to observe the coupled droplets. Two fiber rotators are used for the fabrication of the curved tapered fiber. (d) A top view image taken by the vertical microscope and a near-IR camera reveals coupled droplets with a highlighted circumference, with the orange dashed line representing the curved tapered fiber. The coupled resonators are marked by green arrows. (e) The clusters are spatially oriented in a hexagonal lattice configuration [59], where the standard deviation in droplet diameter is 0.5 μm and the standard deviation in resonator-to-resonator distance is 1.5 μm. Each droplet is coupled to the other six droplets with 84% success, as indicated by occasional gaps between droplets.

Fig. 3. Fluorescent mode mapping of a cavity continuum. (a) Spectral mapping of the ensemble’s absorption lines as indicated by its total fluorescent emission. Several absorption lines are chosen to be accompanied by their spatial mapping (b) as correspondingly indicated in micrographs M1–M9. (c) Ensemble’s mode structure with level-crossing events in resonators (−2.5,1),(−4,2),(−2,2),(−3,4), and (−4, 6). The coupled resonators are marked by green arrows. The orange dashed line represents the curved tapered fiber. The wavelength scan took 30 s (see Visualization 1).

Fig. 4. Ways for light to reach a resonator [marked by the blue rectangle, coordinates (−3, 5.5)] (a) through a row of resonators, (b) through a group of resonators, (c) through dark resonators, and (d) correlation between modes. The orange dashed line represents the curved tapered fiber. The wavelength scan took 60 s (see Visualization 1). The coupled resonators are marked by green arrows.

Fig. 5. 2D array of disks with a single disk excited by the waveguide (left-bottom corner of the figure). The inset shows domains where numerical simulations were performed.

Fig. 6. Various propagating paths of light for different excitation wavelengths. The contrast and brightness of the images were modified to enhance the details of the light distribution.

Fig. 7. Energy decay as a function of distance from the tapered fiber. (a) Average of the movie’s frames while the input light is scanning from 771.0 to 771.6 nm. (b) Average over between lines perpendicular to the tapered fiber together with an exponential fit. The orange dashed line represents the curved tapered fiber (see Visualization 2).

Fig. 8. Cavity number. We could measure a cavity continuum containing 402 resonators. The blue line represents the longest distance from the coupling point, where resonances, in the form of a ring of light appearing upon wavelength scan, were still visible. This blue region contains 402 resonators. This number of cavities is currently limited by our camera sensitivity and droplets’ size variations [69]. The green arrows near the tapered fiber describe the resonators coupled to the tapered fiber.

Fig. 9. Variety of mode structures. (a) Collective V-shaped resonance. (b) Individual resonances with multi-ring shapes and continuous tilting during a wavelength scan (see Visualization 2). The orange dashed line represents the curved tapered fiber. The coupled resonators are marked by green arrows.

Fig. 10. Droplet generation: schematic diagram of the system generating oil-in-water droplets. Two 20 mL syringes are charged with deionized water, while a 1 mL syringe is filled with immersion oil. The three syringes are propelled at an identical rate of 100 μL/min. The water acts to compress the oil at the X-junction within a microfluidic chip, thus yielding homogeneous oil-in-water droplets. These collected droplets are then gathered at the base of a test tube due to their higher density compared with water.

Fig. 11. Fluorescent material properties. (Left) Absorption of the fluorescent material is at the optical resonance wavelengths that we study here. (Right) Fluorescent emission is at a wavelength longer than the cut-on wavelength of the long pass filter, where the NIR CCD camera is still sensitive.