Optical resonators are often called cavities. This term has been taken over from microwave technology, where resonators really look like closed cavities, whereas optical resonators normally have an “open” kind of setup. That difference in geometry is related to the fact that optical resonators are usually very large compared with the optical wavelength, whereas microwave cavities are often not much longer than a wavelength.
Only so-called optical microcavities have dimensions in the micrometer or even sub-micrometer regime, and can tightly enclose a light field in all directions. Microcavities can be realized e.g. with tiny semiconductor or glass structures, such as microtoroids, or as defect structures in photonic crystals.
Even though the term “cavity” is often not completely appropriate, as explained above, many related terms are based on it. Examples are laser cavities (laser resonators), cavity dumping and cavity design (resonator design).
The two basic types of cavities are:
- standing-wave (or linear) cavities, where light bounces back and forth between two end mirrors
- ring cavities, where the light can do round trips in different directions
The article on optical resonators contains more details.
See also: optical resonators, resonator design, resonator modes, stability zones, reference cavities, free spectral range, finesse, bandwidth, Q factor
and other articles in the categories general optics, optical resonators
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