RESONANTLY ENHANCED NONLINEARITY IN DOPED FIBERS FOR LOW-POWER ALL-OPTICAL SWITCHING - A REVIEW

This paper reviews the state of research in resonantly enhanced nonlin earities in fibers doped with an absorber, of interest for low-power a h-optical switching. A mathematical model is first presented which sho ws that this type of nonlinearity can be up to nearly a billion times stronger than the intrinsic Kerr effect of silica. In principle, it ca n induce a phase modulation of rr in the infrared in a subnanometer le ngth of fiber with just a few milliwatts of pump power, with a respons e time in the nanosecand range. Much shorter response times (picosecon d or less) are also possible at the expense of a concomitantly higher switching peak power, although the switching energy remains the same, in the 10-pJ range. The experimental investigations conducted so far w ith rare earths (Er3+, Nd3+, Yb3+, and Sm3+), color centers (POHC), an d transition metal ions (vanadium) are reviewed. They show that a wide range of performance is possible, from 50-mu W switching power and 10 -ms response (in Er3+ grating) to 6-W switching peak power and a respo nse under 25 ns (with POHC). With some of the dopants tested to date, it is readily possible to fabricate fiber switches only 1 cm in length , with a switching power of 15 mW and a 2- to 5-mu s response time. (C ) 1997 Academic Press.