US Patent 7634164 Fiber optic article with inner region

A fiber optic article can comprise a core, an inner region disposed about the core and a cladding disposed about the inner region. The index of refraction of the cladding can be less than that of the inner region, and the index of refraction of the inner region can be less than that of the core. The fiber can include a second cladding disposed about the cladding, where the second cladding has an index of refraction that is less than the index of refraction of the cladding. The inner region can have a non circular outer perimeter that includes at least one inwardly oriented section. The article can be elongate along a longitudinal axis and can include at least one longitudinally extending region, such as a stress inducing region, for providing birefringence and the inwardly oriented region can face the longitudinally extending region. The fiber optic article can include active material for providing light responsive to the article receiving pump light, such as, for example, one or more rare earths. The rare earths can include erbium and ytterbium.