Patent ID: 7471447

Claim:
An amplifier unit for an optical network, wherein the amplifier unit is coupled to a plurality of optical transmission spans, the amplifier unit comprising: a first pump assembly comprising a first pump assembly sub-group, wherein the first pump assembly sub-group includes a first set of pump radiation sources for Raman pumping the plurality of optical transmission spans, wherein each pump radiation source is adapted to produce radiation having a pump wavelength and a pump power, and wherein the optical transmission spans are adapted to provide Raman amplification of propagating optical data signals when pumped by the set of pump radiation sources; a first optical isolator selectively located within the first pump assembly sub-group between at least one selected pump radiation source and the optical transmission spans to reduce amplified Rayleigh backscatter at the pump wavelength of the selected pump radiation source from feeding back into the selected at least one pump radiation source; wherein the first pump assembly further comprises: a second pump assembly subgroup, which includes a second set of pump radiation sources for Raman pumping the plurality of optical transmission spans, wherein each pump radiation source is adapted to produce radiation having a pump wavelength and a pump power, and wherein the optical transmission spans are adapted to provide Raman amplification of propagating optical data signals when pumped by the first and second sets of pump radiation sources; and a second optical isolator selectively located within the second pump assembly sub-group between at least one second selected pump radiation source, but not all of the pump radiation sources, and the optical transmission spans to reduce amplified Rayleigh backscatter from feeding back into the selected at least one second pump radiation source.