Whispering gallery mode (WGM) microcavities can confine light to specific microscale trajectories. This results in ultra-high energy density inside the microcavity, sensitivity to the surrounding microenvironment, and ease of access to optical information. These properties are unique attributes that enable them to be used in a variety of basic research and application areas, such as cavity quantum electrodynamics, nonlinear optics, and laser emission. Doping WGM microcavities with active components can lead to gain-doped WGM microcavities. They show significant advantages in ultra-low-threshold microlasers and thus have potential applications in the fields of sensing and communication. Combining WGM with fluorescence sensing technology not only gains WGM performance but also has the potential to be of substantial research value in sensor sensitivity enhancement and multifunctional sensing. Combining the gain-doped microbottle cavity with fluorescence optimizes the characteristics of the microbottle cavity and incorporates the fluorescence characteristics.

A broadband light source, a spectrometer, and a coupled system were employed to test the resonance spectral properties of the fluorescent microcavity. The coupled system was used to test the whispering gallery mode resonance characteristics of the prepared fluorescent microbottle cavities, and tapered fibers were utilized to couple the fluorescent microcavities to obtain the transmission spectrum curves. From the transmission spectrum, an apparent whispering gallery resonance phenomenon and Lorentz transmission peaks were observed in a specific free spectral range. The fluorescence excitation performance of the prepared gain-doped microbottle cavities was further investigated by building a spatial light path. The laser used in the experiment was adjusted in terms of laser power, and the fluorescent microbottle cavities exhibited different fluorescence brightness when excited by other laser powers. The optimal position of the fluorescent microbottle cavity relative to the laser was found by adjusting the optical three-dimensional stage, and different fluorescence resonance spectral phenomena were detected by changing the angle between the fiber optic probe and the optical path.

Fluorescent microbottle cavities with D_s=125 μm, D_b=382 μm, L_b=760 μm, and curvature Δk of 3×10^-3 μm^-1 were prepared in the experiments. Analyzing the transmission spectrum obtained by the coupled detection system, it can be seen that the fluorescent microbottle cavity showed a high Q factor, and most of its Q factor values are in the order of 10⁴, with a maximum of 4.57×10⁴. The free spectral range (FSR) was measured to be 1.21 nm experimentally and was calculated theoretically to be 1.20 nm. The experimental and theoretical factors were very close and were within the permissible error range. In the transmission spectrum detection process of fluorescent microbottle cavities, two kinds of fluorescent microbottle cavities were prepared by mixing solutions with different mass ratios of UV-curable adhesive (NOA61) to rhodamine B. When the mass ratio of NOA61 to rhodamine B in the fluorescent dye solution was 7∶3, the fluorescent microbottle cavity showed a more obvious fluorescence resonance phenomenon after excitation. When the fiber-optic probe was rotated from 90° to 45°, the most apparent whispering gallery mode resonance phenomenon was observed, and the FSR was 1.21 nm. When the mass ratio of NOA61 to rhodamine B fluorescent dye was adjusted to 8∶2, the fluorescence resonance intensity of the fluorescence spectra of the fluorescent microbottle cavities after excitation was significantly higher than that at the mass ratio of 7∶3. When the fluorescent microbottle cavity was excited at an angle of 135° between the fiber optic probe and the optical path, the resonance mode generated by the fluorescence spectra was not noticeable. The fluorescence intensity of the fluorescence excitation spectrum gradually increased as the angle of the fiber optic probe was rotated from 90° to 45°. At 45°, the fluorescence resonance phenomenon became more intense and pronounced, with an FSR of 1.21 nm.

In this paper, a fluorescence-gained microbottle cavity was fabricated, and its spectral properties were investigated. Theoretical simulations using the time-domain finite-difference method showed that whispering gallery modes can be excited in the microbottle cavity. A fluorescent whispering gallery microbottle cavity with a bottle length of 760 μm and a maximum diameter of 382 μm at the center of the cavity axis was prepared by mixing NOA61 and rhodamine B fluorescent dye, and the resonance phenomenon was measured by the tapered fiber-coupled test system and the spatial light-path excitation system for the prepared fluorescent microbottle cavity. The outcomes demonstrate that the quality factor of the prepared microbottle cavity is 4.57×10⁴, the free spectral range is 1.21 nm, and a strong fluorescence resonance effect was produced when the mass ratio of NOA61 to rhodamine B solution is 8∶2, and the angle between the optical path and the fiber probe is 45°. The proposed microbottle cavities with fluorescence gain were simple to prepare, compact, and sensitive to the environment, and they also have remarkable application prospects in the field of organic lasers.