Gain-equalized few-mode fiber amplifier

摘要

A few-mode rare-earth-doped amplifier fiber has equalized gain for the supported signal transmission modes. The fiber has a raised-index core (31) surrounded by a lower-index cladding region (33). The core has a radius ± 1 and an index difference ”n 1 relative to the surrounding cladding region and is configured to support, at a selected signal wavelength, a set of lower-order fiber modes having an optical field with a diameter greater than 2· ± 1 . The fiber further includes an active region (32,46), doped with a rare-earth dopant, comprising an inner portion (46a) that is coextensive with the core and an outer portion (46b) that surrounds the inner portion and extends into the cladding (33). The active region has an outer radius ± 2 greater than ± 1 that encompasses the optical field of the set of lower-order fiber modes at the selected signal wavelength.