With the increasing requirement of communication rate and capacity, Raman amplifiers are becoming the most
promising technologies in optical communication systems. There are many patents about Raman amplifiers. In this paper,
some important inventions in the patents about Raman amplifiers published since the last 3 years will be presented as
typical examples. This paper will introduce various types of inventions about Raman amplifiers individually: multipleorder
Raman amplifiers, tunable multimode pump sources Raman amplifiers, automatic gain control Raman amplifiers
and lumped Raman amplifiers with a highly-nonlinear medium. These inventions are classified from the principle of Raman
amplification effect, the implementation way, deployment mode and optical materials and devices to realize innovation.
Above all, Raman amplifiers are developing towards greater capacity, lower noise and nonlinearity, higher gain and
longer fiber span lengths.
Keywords: Raman amplifiers, optical transmission, multiple-order, tunable, gain control, optical materials and devices, Amplifiers, amplification, first-order Stokes pumping, first pump source
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