AN INVESTIGATION OF Q-SWITCHED INDUCED QUENCHING OF THE RESONANT NONLINEARITY IN NEODYMIUM-DOPED FIBERS

A method of reducing the decay time of the population-inversion-depend ent refractive index rare-earth doped fibers is investigated, and its suitability for use in all-optical switching is considered. Normally, the temporal response of this type of nonlinearity is dominated by the slow fluorescent decay from the metastable level present in the doped fiber. However, in this instance, the nonlinearity is rapidly quenche d by the internally generated lasing signal produced by Q-switching a lasing cavity containing the doped fiber, Using this technique the obs erved decay time was reduced from 370 mu s to similar to 1 mu s and a phase modulation of pi-radians was observed, demonstrating that the ef fect could be used to achieve complete optical switching in an interfe rometric device, A model of the temporal behavior of this effect is de veloped using a rate equation analysis, The induced index change is mo deled by summing the effects of individual transitions in the region o f the signal wavelength, and by including the effects of assumed trans itions in the VUV. An extension to this method is discussed in which t he depopulating signal is generated using gain-switched techniques, ob viating the need for intracavity modulation, thus making the depopulat ion mechanism more suitable for practical purposes.