Sheng Liu

Whispering gallery mode micro-bubble optical cavities are asymmetrical ellipsoids in experimental settings, which makes their modes nondegenerate. A complicated dense spectrum is thus generated. Overlapping and coupled resonances exist in this dense spectrum. In this study, we determined that the orthogonal demodulation Pound-Drever-Hall technique can be used to analyze complicated resonances. Using this method, overlapping weak and strong coupling resonances can be analyzed. Compared to spectrum simplification and the ab initio theory of Fano resonances, this method is repeatable, simple, sensitive, and accurate. The method can increase the measurement range of differential resonance sensing, thus allowing the differential sensing of overlapped resonances.

We present the spectral modulation of an optofluidic microdisk device and investigate the mechanism and characteristics of the microdisk laser in aqueous media. The optofluidic microdisk device combines a solid-state dye-doped polymer microdisk with a microfluidic channel device, whose optical field can interact with the aqueous media. Interesting phenomena, such as mode splitting and single-mode lasing in the laser spectrum, can be observed in two coupled microdisks under the pump laser. We modulated the spectra by changing the gap of the two coupled microdisks, the refractive indices of the aqueous media, and the position of a pump light, namely, selective pumping schemes. This optofluidic microlaser provides a method to modulate the laser spectra precisely and flexibly, which will help to further understand spectral properties of coupled microcavity laser systems and develop potential applications in photobiology and photomedicine.

We report on a novel optical microcavity sensing scheme by using the orthogonal demodulation Pound–Drever–Hall (PDH) technique. We found that larger sensitivity in a broad range of cavity quality factor (Q) could be obtained. Taking microbubble resonator (MBR) pressure sensing as an example, a lower detection limit than the conventional wavelength shift detection method was achieved. When the MBR cavity Q is about 10⁵–10⁶, the technique can decrease the detection limit by one or two orders of magnitude. The pressure-frequency sensitivity is 11.6 GHz/bar at wavelength of 850 nm, and its detection limit can approach 0.0515 mbar. This technique can also be applied to other kinds of microcavity sensors to improve sensing performance.