Resonantly enhanced nonlinearity in doped fibers for low-power all-optical switching: A review

This paper reviews the state of research in resonantly enhanced nonlinearities in fibers doped with an absorber, of interest for low-power ah-optical switching. A mathematical model is first presented which shows that this type of nonlinearity can be up to nearly a billion times stronger than the intrinsic Kerr effect of silica. In principle, it can induce a phase modulation of rr in the infrared in a subnanometer length of fiber with just a few milliwatts of pump power, with a response time in the nanosecand range. Much shorter response times (picosecond 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 with rare earths (Er3+, Nd3+, Yb3+, and Sm3+), color centers (POHC), and 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 response 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.