Optical amplification device and optical amplification method

1 . An optical amplification device comprising:

an optical waveguiding unit including a plurality of optical transmission paths containing an optical amplification medium having a gain in a wavelength band of signal light;

an excitation light introducing unit configured to introduce, to the optical waveguiding unit, excitation light that excites the optical amplification medium, from both ends of the optical waveguiding unit; and

a residual excitation light introducing unit configured to introduce, to the optical waveguiding unit, residual excitation light being output from both the ends of the optical waveguiding unit and having a wavelength component of the excitation light, wherein

the optical amplification medium is formed of a plurality of cores to which a rare-earth ion is added, and

the optical waveguiding unit includes a multi-core optical fiber including the plurality of optical transmission paths formed of the plurality of cores.

2 . The optical amplification device according to claim 1 , wherein

the plurality of optical transmission paths include:

a first optical transmission path in which first signal light among the signal light propagates in a first direction from a first end to a second end of the optical waveguiding unit; and

a second optical transmission path in which second signal light among the signal light propagates in a second direction from the second end to the first end of the optical waveguiding unit.

3 . The optical amplification device according to claim 2 , wherein

the excitation light introducing unit includes:

a first excitation light introducing unit configured to introduce, to the optical waveguiding unit, first excitation light that excites the optical amplification medium, from the first end of the optical waveguiding unit; and

a second excitation light introducing unit configured to introduce, to the optical waveguiding unit, second excitation light that excites the optical amplification medium, from the second end of the optical waveguiding unit, and

the residual excitation light introducing unit includes:

a first residual excitation light introducing unit configured to introduce, to the optical waveguiding unit from the first end, first residual excitation light being output from the second end of the optical waveguiding unit and having a wavelength component of the first excitation light; and

a second residual excitation light introducing unit configured to introduce, to the optical waveguiding unit from the second end, second residual excitation light being output from the first end of the optical waveguiding unit and having a wavelength component of the second excitation light.

4 . The optical amplification device according to claim 2 , wherein

the multi-core optical fiber is formed of a double-clad structure, and

the excitation light introducing unit introduces the excitation light to the optical waveguiding unit by a clad excitation method.

5 . The optical amplification device according to claim 1 , wherein

the multi-core optical fiber is formed of a double-clad structure, and

the excitation light introducing unit introduces the excitation light to the optical waveguiding unit by a clad excitation method.

6 . The optical amplification device according to claim 3 , wherein

the first excitation light introducing unit includes:

a first excitation light generating unit configured to generate the first excitation light; and

a first optical coupling unit configured to couple the first excitation light to the optical waveguiding unit,

the second excitation light introducing unit includes:

a second excitation light generating unit configured to generate the second excitation light; and

a second optical coupling unit configured to couple the second excitation light to the optical waveguiding unit,

the first residual excitation light introducing unit includes a first residual excitation light coupling unit configured to couple the first residual excitation light to the optical waveguiding unit, on a side close to the first end, and a first residual excitation light separating unit configured to separate the first signal light and the first residual excitation light from each other, on a side close to the second end, and

the second residual excitation light introducing unit includes a second residual excitation light coupling unit configured to couple the second residual excitation light to the optical waveguiding unit, on a side close to the second end, and a second residual excitation light separating unit configured to separate the second signal light and the second residual excitation light from each other, on a side close to the first end.

7 . The optical amplification device according to claim 6 , wherein

the first excitation light introducing unit and the second residual excitation light introducing unit further include a first optical control unit, and

the first optical control unit includes a first terminal to which the first excitation light is input, a second terminal from which the first excitation light is output and to which the second residual excitation light is input, and a third terminal from which the second residual excitation light is output.

8 . The optical amplification device according to claim 6 , wherein

the second excitation light introducing unit and the first residual excitation light introducing unit further include a second optical control unit, and

the second optical control unit includes a first terminal to which the second excitation light is input, a second terminal from which the second excitation light is output and to which the first residual excitation light is input, and a third terminal from which the first residual excitation light is output.

9 . The optical amplification device according to claim 6 , wherein

each of the first optical coupling unit, the second optical coupling unit, the first residual excitation light separating unit, and the second residual excitation light separating unit is an optical coupling/separating unit of a space propagation type including a space optical system, and

each of the first residual excitation light coupling unit and the second residual excitation light coupling unit is a residual excitation light coupling unit of an optical waveguiding type.

10 . The optical amplification device according to claim 7 , wherein

each of the first optical coupling unit, the second optical coupling unit, the first residual excitation light separating unit, and the second residual excitation light separating unit is an optical coupling/separating unit of a space propagation type including a space optical system, and

each of the first residual excitation light coupling unit and the second residual excitation light coupling unit is a residual excitation light coupling unit of an optical waveguiding type.

11 . The optical amplification device according to claim 8 , wherein

each of the first optical coupling unit, the second optical coupling unit, the first residual excitation light separating unit, and the second residual excitation light separating unit is an optical coupling/separating unit of a space propagation type including a space optical system, and

each of the first residual excitation light coupling unit and the second residual excitation light coupling unit is a residual excitation light coupling unit of an optical waveguiding type.

12 . The optical amplification device according to claim 9 , wherein

the optical coupling/separating unit includes a dichroic mirror, and

the residual excitation light coupling unit includes an excitation light combiner.

13 . An optical amplification method comprising:

introducing signal light to a plurality of optical transmission paths containing an optical amplification medium having a gain in a wavelength band of the signal light;

introducing, to the plurality of optical transmission paths, excitation light that excites the optical amplification medium, from both ends of the plurality of optical transmission paths; and

introducing, to the plurality of optical transmission paths, residual excitation light being output from both the ends of the plurality of optical transmission paths and having a wavelength component of the excitation light, wherein

the introducing the signal light to the plurality of optical transmission paths includes introducing the signal light to a multi-core optical fiber including the plurality of optical transmission paths formed of a plurality of cores to which a rare-earth ion is added.

14 . The optical amplification method according to claim 13 , wherein

the introducing the signal light to the plurality of optical transmission paths includes:

introducing first signal light among the signal light to a first optical transmission path included in the plurality of optical transmission paths, from a first end of the plurality of optical transmission paths; and

introducing second signal light among the signal light to a second transmission path included in the plurality of optical transmission paths, from a second end of the plurality of optical transmission paths.

15 . The optical amplification method according to claim 13 , wherein the multi-core optical fiber is formed of a double-clad structure, and

the introducing the excitation light to the plurality of optical transmission paths includes introducing the excitation light to the plurality of optical transmission paths by a clad excitation method.

16 . The optical amplification method according to claim 14 , wherein

the introducing the excitation light to the plurality of optical transmission paths includes:

introducing first excitation light that excites the optical amplification medium, from the first end of the plurality of optical transmission paths; and

introducing second excitation light that excites the optical amplification medium, from the second end of the plurality of optical transmission paths, and

the introducing the residual excitation light to the plurality of optical transmission paths includes:

introducing, to the plurality of optical transmission paths from the first end, first residual excitation light being output from the second end of the plurality of optical transmission paths and having a wavelength component of the first excitation light; and

introducing, to the plurality of optical transmission paths from the second end, second residual excitation light being output from the first end of the plurality of optical transmission paths and having a wavelength component of the second excitation light.

17 . The optical amplification method according to claim 16 , wherein

the introducing the first excitation light to the plurality of optical transmission paths includes generating the first excitation light and coupling the first excitation light to the plurality of optical transmission paths, and

the introducing the second excitation light to the plurality of optical transmission paths includes generating the second excitation light and coupling the second excitation light to the plurality of optical transmission paths.

18 . The optical amplification method according to claim 16 , wherein

the introducing the first residual excitation light to the plurality of optical transmission paths includes separating the first signal light and the first residual excitation light from each other and coupling the first residual excitation light to the plurality of optical transmission paths, and

the introducing the second residual excitation light to the plurality of optical transmission paths includes separating the second signal light and the second residual excitation light from each other and coupling the second residual excitation light to the plurality of optical transmission paths.

19 . The optical amplification method according to claim 17 , wherein

the introducing the first excitation light to the plurality of optical transmission paths includes coupling the first excitation light to the plurality of optical transmission paths by a space optical system, and

the introducing the second excitation light to the plurality of optical transmission paths includes coupling the second excitation light to the plurality of optical transmission paths by a space optical system.

20 . The optical amplification method according to claim 18 , wherein

the introducing the first residual excitation light to the plurality of optical transmission paths includes separating the first signal light and the first residual excitation light from each other by a space optical system and coupling the first residual excitation light to the plurality of optical transmission paths by an optical waveguide, and

the introducing the second residual excitation light to the plurality of optical transmission paths includes separating the second signal light and the second residual excitation light from each other by a space optical system and coupling the second residual excitation light to the plurality of optical transmission paths by an optical waveguide.