Fig. 1. (a) Schematic of the HCMW chip. The thickness of the coupling layer is about 30–50 nm, and the metal substrate is about 300 nm thick. The guiding layer that contains a channel for dye solution is 1.1 mm thick. (b) Excitation of UOMs via free-space coupling technique. The right inset shows the image of the HCMW chip before vacuum evaporation.

Fig. 2. Numerically calculated reflectivity spectrum of the simplified HCMW structure, whose parameters are presented above. Inset: Reflectivity spectrum in the range of 540–610 nm, which corresponds to the fluorescence spectrum of the R6G.

Fig. 3. (a) Experimental measurement of the wavelength-dependent resonance dip of the waveguide chip. (b) Numerical simulation by transfer matrix method.

Fig. 4. (a) Schematic of the reflected light cones formed by leakage radiation of the UOMs, while the reflection law generates the spectra reflected beam. (b) Image of the light cones on a screen, where a bright spot corresponding to the reflected beam can be found.

Fig. 5. (a) Energy level diagram of R6G. (b) Schematic of the experimental setup of the optofluidic dye laser.

Fig. 6. (a) Image of the concentric laser cones (red) and the leakage cones of the UOMs (blue) on the screen. (b) Schematic of a specific laser cone and a specific leakage cone of a UOM, where a transverse shift between the two cones’ axes occurs in the incident plane. (c) Emission spectrum of the R6G sample, where the lasing wavelength is 568 nm. The inset figure shows that the lasing threshold of R6G dye is about 2.0  μW/cm2. (d) Fluorescence spectra of R6G solution with concentration of 2.579×10−11  mol/mL emitted from HCMW (black line) and cuvette (red line), respectively.