Patent ID: 7054061

Claim:
A split-band amplifying apparatus comprising: a) a first section for amplifying a long wavelength band of an optical signal; b) a second section having a fiber amplifier for amplifying a short wavelength band of said optical signal, said fiber amplifier comprising: 1) a core having a core cross-section and a refractive index n o ; 2) an active material doped in said core; 3) a depressed cladding surrounding said core, said depressed cladding having a depressed cladding cross-section and a refractive index n 1 ; 4) a secondary cladding surrounding said depressed cladding, said secondary cladding having a secondary cladding cross-section and a refractive index n 2 ; 5) a pump source for pumping said active material to a high relative inversion D, such that said active material exhibits positive gains in said short wavelength band and high gains in said long wavelength band; wherein said core cross-section, said depressed cladding cross-section, and said refractive indices n o , n 1 , and n 2 are selected to produce a roll-off loss curve about a cutoff wavelength λ c , said roll-off loss curve yielding losses at least comparable to said high gains in said long wavelength band and losses substantially smaller than said positive gains in said short wavelength band.