Orthogonal Demodulation Pound-Drever-Hall Technique for Ultra-Low Detection Limit Pressure Sensing

The Measurement of Nanoparticle Concentrations by the Method of Microcavity Mode Broadening Rate

A measurement system for the detection of a low concentration of nanoparticles based on optical microcavities with whispering-gallery modes (WGMs) is developed and investigated. A novel method based on the WGM broadening allows us to increase the precision of concentration measurements up to 0.005 ppm for nanoparticles of a known size. We describe WGM microcavity manufacturing and quality control methods. The collective interaction process of suspended Ag nanoparticles in a liquid and TiO₂ in the air with a microcavity surface is studied.

Highly Sensitive Complicated Spectrum Analysis in Micro-Bubble Resonators Using the Orthogonal Demodulation Pound–Drever–Hall Technique

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.