## Telecom Dictionary - Definitions of terms
**Radiation Mode ****- ** Definition and Use
**Radiation Mode - ** For an optical fiber, an unbound mode. *Note:* In an optical fiber, a radiation mode is one having fields that are transversely oscillatory everywhere external to the waveguide, and which exists even at the limit of zero wavelength. Specifically, a radiation mode is one for which
where is the imaginary part (phase term) of the axial propagation constant, integer is the azimuthal index of the mode, *n* (*a*) is the refractive index, where *a* is the core radius, and *k* is the free-space wave number, *k* = 2/, where is the wavelength. Radiation modes correspond to refracted rays in the terminology of geometric optics. *Synonym* **unbound mode.** |