Optical fiber with improved cross-sectional profile and optical gain media using same

Abstract

An optical fiber gain medium has a core region in which a signal propagates, and a cladding region surrounding the core into which a pump signal is coupled. The gain medium also includes a plurality of doped regions each of which has a different effect on the gain profile of the gain medium. In a first embodiment, two doped regions are located in the cladding region at different radial distances from the core. Each of the two doped regions has a different absorption characteristic such that it absorbs signal energy in a different wavelength region of the gain band. The relative contributions may be controlled by controlling a number of different factors, including type of dopant, density of dopant, radial width of the doped regions, and relative separation between the doped regions, and their positioning relative to evanescent portions of different wavelength bands. In another embodiment, the different doped regions include dopant in the core and in a cladding region, and each dopant is pumped by a separate pump source. The relative contributions of the different dopants to the gain in the different wavelength ranges may be controlled by type of dopants used, density of doping, location of the dopant region in the cladding relative to the core and evanescent portions of different wavelength bands, and relative pump power and pump wavelengths provided to each doped region.