Optical amplifier and controlling method for Raman amplifier

An optical amplifier comprising:

• a rare earth doped fiber amplifying section in which a rare earth doped fiber amplifier can be disposed;
• a Raman amplifying section being capable of amplifying light in an amplifying band that said rare earth doped fiber amplifier can amplify and light in an adjacent band located outside the amplifying band, the adjacent band being capable of locating A channels;
• and
• a pumping light source supplying pumping light to said Raman amplifying section and capable of changing wavelength of the pumping light, wherein
• in the case where a number of operating channels is equal to or less than A, the wavelength of the pumping light is controlled such that light within the amplifying band and the adjacent band is amplified by said Raman amplifying section, without amplification of the amplifying band by the rare earth doped fiber amplifier, and
• in the case where the number of operating channels is greater than A, the wavelength of the pumping light is controlled such that light within the adjacent band, but not the amplifying band is provided by the rare earth doped fiber amplifier.

An apparatus comprising:

• a Raman amplifier capable of amplifying signal light of an entire band being composed of an amplifying band of a rare earth doped fiber amplifier and a band, which can have the number of allowable channels A, located out of the amplifying band of the rare earth doped fiber amplifier, in accordance with Raman pumping light;
• means for controlling wavelength of the pumping light such that signal light of the entire band is amplified by the Raman amplifier, without amplification of the amplifying band being provided by the rare earth doped fiber amplifier, when a number of operating channels is equal to that of allowable channels A or less;
• an
• means for controlling the wavelength of pumping light such that the signal light of the band located out of the amplifying band of the rare earth doped fiber amplifier, but not the amplifying band, is amplified by the Raman amplifier, and amplification of the amplifying band of the rare earth doped fiber amplifier is provided by the rare earth doped fiber amplifier;
• when the number of operating channels becomes greater than the number of allowable channels A.

A method comprising:

• providing a Raman amplifier to amplify a signal light having a number of operating channels in accordance with Raman pumping light of the Raman amplifier, the Raman amplifier capable of amplifying light in an amplifying band of a rare earth doped fiber amplifier and light in an adjacent band located outside the amplifying band, the adjacent band being capable of locating A channels;
• when the number of operating channels of the signal light is equal to or less than A, controlling wavelength of the Raman pumping light so that signal light within the amplifying band and the adjacent band is amplified by the Raman amplifier, without amplifying the signal light by the rare earth doped fiber amplifier;
• and
• when the number of operating channels of the signal light is greater than A, controlling wavelength of the Raman pumping light so that signal light within the adjacent band, but not the amplifying band, is amplified by the Raman amplifier, and amplifying signal light within the amplifying band by the rare earth doped fiber amplifier.

An apparatus comprising:

• a Raman amplifier to amplify a signal light having a number of operating channels in accordance with Raman pumping light of the Raman amplifier, the Raman amplifier capable of amplifying light in an amplifying band of a rare earth doped fiber amplifier and light in an adjacent band located outside the amplifying band, the adjacent band being capable of locating A channels;
• means, when the number of operating channels of the signal light is equal to or less than A, for controlling wavelength of the Raman pumping light so that signal light within the amplifying band and the adjacent band is amplified by the Raman amplifier, without amplifying the signal light by the rare earth doped fiber amplifier;
• and
• means, when the number of operating channels of the signal light is greater than A, for controlling wavelength of the Raman pumping light so that signal light within the adjacent band, but not the amplifying band, is amplified by the Raman amplifier, and for amplifying signal light within the amplifying band by the rare earth doped fiber amplifier.

An apparatus comprising:

• an optical amplifier comprising
• a Raman amplifier section amplifying a signal light having a number of operating channels in accordance with Raman pumping light of the Raman amplifier section;
• a rare earth doped fiber amplifier section having an amplifying band, wherein
• the Raman amplifier section is capable of amplifying light in the amplifying band and light in an adjacent band located outside the amplifying band,
• the adjacent band is capable of locating A channels,
• the rare earth doped fiber amplifier section is provided when the number of operating channels of the signal light greater than A, and, when the number of operating channels of the signal light is greater than A, the rare earth doped fiber amplification amplifies signal light within th amplifying band;
• and a controller which
• when the number of operating channels of the signal light is equal to or less than A, controls wavelength of the Raman pumping light so that signal light within the amplifying band and the adjacent band if amplified by the Raman
• amplifier section, without amplifying the signal light by the rare earth doped fiber amplifier section, and
• when the number of operating channels of the signal light is greater th A controls wavelength of the Raman pumping light so that signal light within the adjacent band, but not the amplifying band, is amplified by the Raman amplifier section.