Patent ID: 8300306

Claim:
A Raman amplifier comprising: first and second optical paths disposed in series with each other, each comprising a Raman-active material having a predetermined Raman shift, the second optical path being downstream from the first optical path with respect to a direction of propagation of a received optical signal; a first pump source connected to the first optical path for emitting and coupling into the first optical path a first pump radiation including at least one first pump frequency; a second pump source connected to the second optical path for emitting and coupling into the second optical path a second pump radiation including at least one second pump frequency; a lowest frequency of the first pump radiation being higher than a highest frequency of the second pump radiation; a residual of the second pump radiation coupled into the first optical path having a power lower by at least 10 dB than the first pump radiation; a residual of the first pump radiation coupled into the second optical path having a power lower by at least 10 dB than the second pump radiation; the lowest frequency of the first pump radiation differing from a highest frequency of the first pump radiation by at most 70% of the Raman shift; and a lowest frequency of the second pump radiation differing from the highest frequency of the second pump radiation by at most 70% of the Raman shift.