A microbubble resonator is a device used in photonics and optical physics for the precise manipulation of light waves. It consists of a micro-sized, gas-filled spherical cavity (the "microbubble") typically embedded within a solid material. The microbubble acts as a resonator for light waves, allowing them to circulate within the cavity with minimal loss.
The principles underlying microbubble resonators are similar to those of other optical resonators, such as Fabry-Perot cavities and whispering gallery mode (WGM) resonators. Light waves entering the microbubble resonator can be confined within the cavity due to total internal reflection at the interface between the gas-filled microbubble and the surrounding solid material. This confinement leads to the formation of standing wave patterns, known as whispering gallery modes, along the inner surface of the microbubble.
Microbubble resonators offer several advantages over other types of resonators, including their small size, high quality (Q) factors, and low optical losses. These properties make them promising candidates for a variety of applications, including:
Sensing: Microbubble resonators can be used as highly sensitive detectors for various physical and chemical parameters, such as temperature, pressure, refractive index, and molecular binding events. Changes in these parameters can be detected by monitoring shifts in the resonance frequencies or linewidths of the whispering gallery modes.
Laser sources: Microbubble resonators can be used to generate laser light by incorporating gain media, such as doped fibers or semiconductor materials, into the cavity. The high-Q factors of microbubble resonators enable the efficient buildup of optical gain, leading to the generation of coherent laser radiation.
Nonlinear optics: The strong confinement of light within microbubble resonators enhances nonlinear optical effects, such as second-harmonic generation, four-wave mixing, and Raman scattering. These effects can be exploited for applications in optical signal processing, frequency conversion, and quantum information science.