"Light is intangible and, in addition, it travels at great velocity. Nevertheless, it can be confined to a very small space by controllably inserting light into a microscopic container surrounded by reflective walls. The light will then be stored by continuous reflections and cannot escape. In the scientific domain, such a small reflective microcavity is termed a microresonator. These microresonators find applications in all areas where the interaction between light and matter shall be enhanced and studied in a controlled manner. An important area of usage is, for example, the laser diode, which has revolutionized telecommunications and optical data storage in the past few decades." - Michael McKean