Abstract

Nonlinear phase shifts in rare earth doped fibres, due to optically induced changes to the imaginary part of the electronic susceptibility associated with dopant absorption transitions, have been proposed as the basis for all-optical switching in communication systems [1.2], where flexible, bit rate- and code format-independent routing of data streams would be required[3]. Previous work has concentrated on neodymium- and erbium-doped fibres [1,4,5], where switching is complicated by the presence of several 4f-4f absorption bands causing a strong variation of the refractive index change with wavelength. Pantell et al [1] found that the phase shift was composed of a resonant term from 4f-4f transitions and a strong, almost wavelength-independent term believed to be from allowed 4f- 5d transitions in the vacuum-UV. Ytterbium has the advantage of a simple electronic structure, with a lone 4f-4f absorption at 980 m conveniently pumpable with diode lasers and sufficiently removed from 1550 nm that the vacuum-UV component dominates.

© 1996 Optical Society of America