# Mode coupling

Mode coupling

In the term mode coupling, as used in physics and electrical engineering, the word "mode" refers to eigenmodes of an idealized, "unperturbed", linear system. Most often, these eigenmodes are plane waves. The superposition principle says that eigenmodes of linear systems are independent of each other: it is possible to excite or to annihilate a specific mode without influencing any other mode; there is no dissipation. In most real systems, however, there is at least some perturbation that causes energy transfer between different modes. This perturbation, interpreted as an interaction between the modes, is what is called "mode coupling".

Important applications are:

• In fiber optics[1]
• In lasers (compare mode-locking)[2]
• In condensed matter physics, critical slowing down can be described by a mode-coupling theory.[3]

## References

1. ^ See e.g. J. Zhao, X. Liu, Fiber acousto-optic mode coupling between the higher-order modes with adjacent azimuthal numbers, Opt. Lett. 31, 1609-11 (2006); J. Thomas et al., Cladding mode coupling in highly localized fiber Bragg gratings: modal properties and transmission spectra, Optics Express 19, 325-341 (2011).
2. ^ See e.g. R. Paschotta, Mode coupling, in the online Encyclopedia of Laser Physics and Technology, http://www.rp-photonics.com/mode_coupling.html
3. ^ See e.g. W. Götze, Complex Dynamics of glass forming liquids. A mode-coupling theory, Oxford: Oxford University Press (2009).

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