Pump absorption and amplification uniformity in rod-type, multicore fibers

Pump absorption is one of the most important and, at the same time, overlooked characteristics of double-clad fibers. Most people take it for granted, but it is actually a rather complex and delicate effect. In fact, the problem of pump absorption is only expected to become worse in the new breed of large core, rod-type, multicore fibers. Herein, the pump cladding diameter can reach several millimeters which, combined with the short length of the fiber, are expected to lead to a negligible contribution of mode mixing to pump absorption. Moreover, multicore fibers impose a new constraint to the pump process: amplification uniformity. In a multicore fiber it is important that all the cores emit the same power, but this is affected by the pump propagation and absorption. Therefore, there is an urgent need to study pump absorption and amplification uniformity in these fiber geometries to obtain an optimum pump configuration.