Patent ID: 7813034

Claim:
A Raman amplifier adapted for amplifying an optical signal having frequency in a signal frequency range comprising at least a first and a second optical path disposed in series with each other, each comprising a Raman-active material having a predetermined Raman shift, said amplifier comprising: a first pump source connected to said first optical path, said first pump source being adapted for emitting and coupling into said first optical path a first pump radiation including a first group of pump frequencies between a first minimum pump frequency and a first maximum pump frequency; and a second pump source connected to said second optical path, said second pump source being adapted for emitting and coupling into said second optical path a second pump radiation including a second group of pump frequencies between a second minimum pump frequency and a second maximum pump frequency, a whole of said first and second group of pump frequencies extending over a pump frequency range having a width of at least 40% of said Raman shift; at least a portion of said first group of pump frequencies being excluded from said second group of pump frequencies and at least a portion of said second group of pump frequencies being excluded from said first group of pump frequencies; the couplings between said first and second pump sources and said first and second optical paths being such that a residual of said second pump radiation coupled into said first optical path has a power lower by 10 dB than said first pump radiation, and such that a residual of said first pump radiation coupled into said second optical path has a power lower by 10 dB than said second pump radiation; said first minimum pump frequency and said first maximum pump frequency differing from each other by at most 70% of said Raman shift; and said second minimum pump frequency and said second maximum pump frequency differing from each other by at most 70% of said Raman shift.