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** .

This HTML version of FS-1037C was last generated on Fri Aug 23 00:22:38 MDT 1996