User:Thidhoang/Optical microcavity

An optical microcavity or an optical microresonator is an optical cavity at the microscopic scale, commonly used in experiments with light and matter at the quantum level. Optical cavities are structures designed to trap and enhance light through forming a standing wave of selective frequencies in the structure. Due to their microscale size, optical microcavities can probe quantum effects

Applications and effects
The fundamental difference between a conventional optical cavity and microcavities is the effects that arise from the small dimensions of the system, but their operational principle can often be understood in the same way as for larger optical resonators. Quantum effects of the light's electromagnetic field can be observed. For example, the spontaneous emission rate and behaviour of atoms is altered by such a microcavity, a phenomenon that is referred to as inhibited spontaneous emission. One can imagine this as the situation that no photon is emitted, if the environment is a box that is too small to hold it. This leads to an altered emission spectrum, which is significantly narrowed.

Moreover, nonlinear effects are enhanced by orders of magnitude due to the strong light confinement, leading to the generation of microresonator frequency combs, low-power parametric processes such as down-conversion, second-harmonic generation, four-wave mixing and optical parametric oscillation. Several of these nonlinear processes themselves lead to the generation of quantum states of light. Another field that harnesses the strong confinement of light is cavity optomechanics, where the back-and-forth interaction of the light beam with the mechanical motion of the resonator becomes strongly coupled. Even in this field, quantum effects can start playing a role.

Microcavities have many applications, frequently at present in optoelectronics, where vertical cavity surface emitting lasers VCSEL are probably the best known. Recently, a single photon emitting device was demonstrated by placing a quantum dot in a microcavity. These light sources are interesting for quantum cryptography and quantum computers.

An overview is given in the review article published in the journal Nature.