Impact of the material absorption on the modulational instability spectra of wave propagation in high-index glass fibers

Abstract

We examine the behavior of modulational instability (MI) in several classes of high-index glass fibers that are being developed to obtain very high nonlinearities and soften the conditions of generation of highly efficient light sources, namely, telecommunication fibers, air-silica microstructured fibers, tapered fibers, and nonsilica glass fibers. We perform a comparative assessment of their respective performances in MI processes on the basis of three major performance criteria: the level of the input pump power, the fiber length, and the magnitude of the frequency drifts. Indeed, we show that the effectiveness of MI processes in such fibers is not merely influenced by the strength of the nonlinearity, but is also strongly determined by the linear attenuation of waves in the fiber material. In those high-index glass fibers, this attenuation acts as a strong perturbation, causing a frequency drift of the MI sidebands. However, we show that this frequency drift can be totally suppressed by means of a technique based on the concept of a photon reservoir, which feeds in situ the process of MI by continually supplying it the amount of photons absorbed by the fiber.