Patent ID: 8363309

Claim:
An optical amplifier, comprising: a first optical amplifier including a first rare-earth-doped optical medium having an end to which input light is input from an input port, a first light source that generates excitation light, and a first optical multiplexer that is disposed upstream of the first rare-earth-doped optical medium and supplies the excitation light generated by the first light source to the end of the first rare-earth-doped optical medium; an optical isolator receiving the input light; a second optical amplifier including a second rare-earth-doped optical medium having an end to which the input light is input after the input light has been passed through the optical isolator, a second light source that generates excitation light, and a second optical multiplexer that is disposed upstream of the second rare-earth-doped optical medium and supplies the excitation light generated by the second light source to the end of the second rare-earth-doped optical medium, the first optical amplifier and the second optical amplifier being serially connected to each other on an optical path between the input port and an output port with the optical isolator interposed therebetween; a light supplying unit that is disposed on an optical path connecting the input port and the end of the first rare-earth-doped optical medium and supplies amplified spontaneous emission light arising in the first rare-earth-doped optical medium and traveling in a direction opposite to the traveling direction of the input light; and a light input unit that is disposed on an optical path connecting the other, downstream end of the second rare-earth-doped optical medium and the output port and inputs the amplified spontaneous emission light supplied by the light supplying unit via the optical path to the other end of the second rare-earth-doped optical medium.