Optical amplifier and optical amplification method for amplifying wavelength division multiplexed signal light

An optical amplifier for amplifying wavelength division multiplexed signal light which contains respective optical signals of a first wavelength band and a second wavelength band, comprising:

• optical amplifying means for amplifying said wavelength division multiplexed signal light using a rare earth element doped fiber to which excitation light is supplied;
• a first optical circulator having at least three ports, connected to one end of said rare earth element doped fiber;
• and
• a second optical circulator having at least three ports, connected to the other end of said rare earth element doped fiber,
• wherein an optical signal of said first wavelength band is input to said rare earth element doped fiber via said first optical circulator and output from said rare earth element doped fiber via said second optical circulator, and an optical signal of said second wavelength band is input to said rare earth element doped fiber via said second optical circulator, and output from said rare earth element doped fiber via said first optical circulator, the signal light of said respective wavelength bands being propagated in mutually opposite directions inside the rare earth element doped fiber,
• said first optical circulator outputs optical signals of said first wavelength band input to a first port thereof from a second port thereof connected to one end of said rare earth element doped fiber, and outputs optical signals of said second wavelength band which are propagated inside said rare earth element doped fiber and input to said second port from a third port thereof,
• said second optical circulator outputs optical signals of said second wavelength band input to a first port thereof from a second port thereof connected to the other end of said rare earth element doped fiber, and outputs optical signals of said first wavelength band which are propagated inside said rare earth element doped fiber and input to said second port from a third port thereof, and
• at the time of amplifying wavelength division multiplexed signal light which contains respective optical signals of the first wavelength band and the second wavelength band transmitted in the same direction, there is provided;
• demultiplexing means for demultiplexing said wavelength division multiplexed signal light into respective signal lights of the first wavelength band and the second wavelength band, and outputting the demultiplexed signal light of the first wavelength band to the first port of said first optical circulator, and outputting the signal light of the second wavelength band to the first port of said second optical circulator, and
• multiplexing means for multiplexing the optical signal of the second wavelength band output from the third port of said first optical circulator and the optical signal of the first wavelength band output from the third port of said second optical circulator, and outputting the multiplexed signal light.

An optical amplifier for amplifying wavelength division multiplexed signal light which contains respective optical signals of a first wavelength band and a second wavelength band transmitted in the same direction, comprising:

• optical amplifying means for amplifying said wavelength division multiplexed signal light using a rare earth element doped fiber to which excitation means is supplied;
• a first optical circulator connected to one end of said rare earth element doped fiber;
• and
• a second optical circulator connected to the other end of said rare earth element doped fiber,
• wherein an optical signal of said first wavelength band is input to said rare earth element doped fiber via said first optical circulator and output from said rare earth element doped fiber via said second optical circulator, and an optical signal of said second wavelength band is input to said rare earth element doped fiber via said second optical circulator, and output from said rare earth element doped fiber via said first optical circulator.

An optical amplifier for amplifying wavelength division multiplexed signal light which contains respective optical signals of a first wavelength band and a second wavelength band, comprising:

• an optical amplifying unit amplifying said wavelength division multiplexed signal light using a rare earth element doped fiber to which excitation light is supplied;
• a first optical circulator having at least three ports, connected to one end of said rare earth element doped fiber;
• and
• a second optical circulator connected to the other end of said rare earth element doped fiber,
• wherein an optical signal of said first wavelength band is input to said rare earth element doped fiber via said first optical circulator and output from said rare earth element doped fiber via said second optical circulator, and an optical signal of said second wavelength band is input to said rare earth element doped fiber via said second optical circulator, and output from said rare earth element doped fiber via said first optical circulator the signal light of said respective wavelength bands being propagated in mutually opposite directions inside the rare earth element doped fiber, and the wavelength division multiplexed signal light of said first wavelength band and the wavelength division multiplexed signal light of said second wavelength band are transmitted in the same direction.