This Spotlight examines an increasingly popular class of optical sensors that comprises microresonators based on the propagation of whispering gallery modes (WGMs). Several 2D and 3D WGM microresonators have already proved their capabilities as general-purpose sensors (especially as biosensors), and they have potential applications outside of research laboratories. Topics include the fundamentals of WGM propagation, types and characterization of microresonators, microfabrication issues, categories of sensing (physical, chemical, and biological), and state of the art sensors.
Whispering gallery mode (WGM) resonators have enabled real-world sensing
applications by measuring physical quantities, such as temperature, mass, and
pressure, as well as chemical and biomedical parameters. In the latter context,
important achievements, such as label-free detection of a single virus, single
molecules, and large objects, such as bacteria, have been recorded. We try to
provide a quick overview of the state of the art of WGM-based sensors.
A summary of the fundamental principles, the mathematical theory, and the
main properties of different types of such resonators is also given.