Patent ID: 7054059

Claim:
A method for amplifying an optical signal, the method comprising: providing an input signal having first and second non-overlapping bands of active wavelengths; amplifying said input signal in a first stage having substantially greater gain in said first band than in said second band; amplifying said input signal in a second stage following said first stage, said second stage having substantially greater gain in said second band than in said first band; amplifying said input signal in a third stage following said second stage, said third stage having substantially greater gain in said first band than in said second band; amplifying said input signal in a fourth stage between said second stage and said third stage, said third stage having substantially greater gain in said second band than in said first band; directing pump light into said first stage and said third stage at wavelengths selected to induce Raman amplification of said first band including counter-propagating said pump light into said first stage and said third stage relative to propagation of said optical signal; directing pump light into said second stage and said fourth stage at wavelengths selected to induce Raman amplification of said second band including counter-propagating said pump light into said second stage and said fourth stage relative to propagation of said optical signal; and directing residual pump light at said wavelengths selected to induce Raman amplification of said second hand into said first stage, wherein limited Raman amplification of said second band is induced in said first stage.