A Raman amplifier according to the present invention comprises a plurality
of pumping means using semiconductor lasers of Fabry-Perot, DFB, or DBR
type or MOPAs, and pumping lights outputted from the pumping means have
different central wavelengths, and interval between the adjacent central
wavelength is greater than 6 nm and smaller than 35 nm. An optical
repeater according to the present invention comprises the above-mentioned
Raman amplifier and adapted to compensate loss in an optical fiber
transmission line by the Raman amplifier. In a Raman amplification method
according to the present invention, the shorter the central wavelength of
the pumping light the higher light power of said pumping light. In the
Raman amplifier according to the present invention, when a certain pumping
wavelength is defined as a first channel, and second to n-th channels are
defined to be arranged with an interval of about 1 THz toward a longer
wavelength side, the pumping lights having wavelengths corresponding to
the first to n-th channels are multiplexed, and an pumping light having a
wavelength spaced apart from the n-th channel by 2 THz or more toward the
longer wavelength side is combined with the multiplexed light, thereby
forming the pumping light source. The pumping lights having wavelengths
corresponding to the channels other than (n-1)-th and (n-2)-th channels
may be multiplexed, thereby forming the pumping light source. The pumping
lights having wavelengths corresponding to the channels other than
(n-2)-th and (n-3)-th channels may be multiplexed, thereby forming the
pumping light source.
