Single mode optical waveguide with expanded rare-earth doped region

Abstract

A single mode optical waveguide includes a first region having a relatively high refractive index, a second region having a relatively low refractive index disposed adjacent to the first region, and a dopant region overlapping the first and second regions. Preferably, the first and second regions are circular regions which are concentric with respect to one another. Moreover, the dopant material in the dopant region advantageously can have a non-uniform dopant gradient. In addition, a predetermined percentage of dopant material defining the dopant region is disposed coincident with the second region. Preferably, the predetermined percentage is greater than or equal to 10 percent and, most preferably, the predetermined percentage is greater than or equal to 50 percent. Alternatively, the first region corresponds to an inner core of a dual core optical fiber, while the second region corresponds to an outer core of the dual core optical fiber.