Fiber amplifiers with depressed cladding and their uses in Er-doped fiber amplifiers for the S-band

摘要

A fiber amplifier in a depressed cladding or W-profile fiber. The fiber has a core doped with the active material and defined by a core cross-section and a refractive index n_o. A depressed cladding of index n₁ surrounds the core and a secondary cladding of index n₂ surrounds the depressed cladding. The fiber amplifier is pumped to a level of high relative inversion, such that the active material exhibits positive gains in a short wavelength band and high gains in a long wavelength band. The core cross-section, the depressed cladding cross-section and the refractive indices n_o, n₁, and n₂ are selected to obtain a roll-off loss curve about a cutoff wavelength lambda_c. The roll-off loss curve yields losses at least comparable to the high gains in the long wavelength band and losses substantially smaller than the positive gains in the short wavelength band.