Optical device, laser system, and method for manufacturing optical device

1. An optical device, comprising:

an entrance fiber bundle which is made up of at least one entrance fiber;

an exit fiber; and

a reduced diameter part having (i) an entrance end surface to which the entrance fiber bundle is coupled and (ii) an exit end surface to which the exit fiber is coupled, the exit end surface being narrower in area than the entrance end surface,

a center of the exit end surface deviating from a center of the entrance end surface, in a case where the entrance end surface is viewed from a normal direction of the entrance end surface,

wherein:

the following inequality (1) is satisfied:

D in/10≤ D off≤( D in− D out)/2  (1)

where: Doff indicates a distance between the center of the entrance end surface and the center of the exit end surface; Din indicates a maximum width of the entrance end surface; and Dout indicates a maximum width of the exit end surface, each of Doff, Din, and Dout being obtained in a case where the entrance end surface of the reduced diameter part is viewed from the normal direction of the entrance end surface.

2. An optical device, comprising:

an entrance fiber bundle which is made up of at least one entrance fiber;

an exit fiber; and

a reduced diameter part having (i) an entrance end surface to which the entrance fiber bundle is coupled and (ii) an exit end surface to which the exit fiber is coupled, the exit end surface being narrower in area than the entrance end surface,

a center of the exit end surface deviating from a center of the entrance end surface, in a case where the entrance end surface is viewed from a normal direction of the entrance end surface,

the optical device further comprising:

a GI fiber, which corresponds to the at least one entrance fiber, provided between the at least one entrance fiber and the entrance end surface of the reduced diameter part,

the at least one entrance fiber being coupled to the entrance end surface, via the GI fiber.

3. The optical device as set forth in claim 1 , wherein:

the entrance end surface of and the exit end surface of the reduced diameter part each have a round shape.

4. The optical device as set forth in claim 2 , wherein:

the entrance end surface of and the exit end surface of the reduced diameter part each have a round shape.

5. An optical device, comprising:

an entrance fiber bundle which is made up of at least one entrance fiber;

an exit fiber; and

a reduced diameter part having (i) an entrance end surface to which the entrance fiber bundle is coupled and (ii) an exit end surface to which the exit fiber is coupled, the exit end surface being narrower in area than the entrance end surface,

a center of the exit end surface deviating from a center of the entrance end surface, in a case where the entrance end surface is viewed from a normal direction of the entrance end surface,

wherein:

the entrance fiber bundle is made up of a single entrance fiber; and

a region, in which the single entrance fiber is coupled to the entrance end surface of the reduced diameter part, is variable.

6. A laser system, comprising:

an optical device including (1) an entrance fiber bundle which is made up of a plurality of entrance fibers, (2) an exit fiber, and (3) a reduced diameter part having (i) an entrance end surface to which the entrance fiber bundle is coupled and (ii) an exit end surface to which the exit fiber is coupled, the exit end surface being narrower in area than the entrance end surface, a center of the exit end surface deviating from a center of the entrance end surface, in a case where the entrance end surface is viewed from a normal direction of the entrance end surface; and

a plurality of laser devices each of which includes an exit fiber connected to a corresponding one of the plurality of entrance fibers of the optical device.

7. A laser system, comprising:

an optical device including (1) an entrance fiber bundle which is made up of a single entrance fiber, (2) an exit fiber, and (3) a reduced diameter part having (i) an entrance end surface to which the entrance fiber bundle is coupled and (ii) an exit end surface to which the exit fiber is coupled, the exit end surface being narrower in area than the entrance end surface, a center of the exit end surface deviating from a center of the entrance end surface, in a case where the entrance end surface is viewed from a normal direction of the entrance end surface; and

a single laser device including an exit fiber which is connected to the single entrance fiber of the optical device,

a region, in which the single entrance fiber is coupled to the entrance end surface of the reduced diameter part, being variable.

8. A method of producing an optical device including (1) an entrance fiber bundle which is made up of at least one entrance fiber, (2) an exit fiber, and (3) a reduced diameter part having (i) an entrance end surface to which the entrance fiber bundle is coupled and (ii) an exit end surface to which the exit fiber is coupled, the exit end surface being narrower in area than the entrance end surface,

said method comprising the steps of:

(a) increasing a deviation of a central axis of one end part of an optical rod from a central axis of the other end part of the optical rod while stretching the optical rod; and

(b) cutting out a part of the optical rod which has been stretched in the step (a), the part of the optical rod having both ends which have respective different girths and serving as the reduced diameter part.

9. The laser system as set forth in claim 6 , wherein:

the following inequality (1) is satisfied:

D in/10≤ D off≤( D in− D out)/2  (1)

where: Doff indicates a distance between the center of the entrance end surface and the center of the exit end surface; Din indicates a maximum width of the entrance end surface; and Dout indicates a maximum width of the exit end surface, each of Doff, Din, and Dout being obtained in a case Where the entrance end surface of the reduced diameter part is viewed from the normal direction of the entrance end surface.

10. The laser system as set forth in claim 6 , wherein:

the optical device further comprises:

a plurality of GI fibers, each of which corresponds to the corresponding one of the plurality of entrance fibers, each provided between the corresponding one of the plurality of entrance fibers and the entrance end surface of the reduced diameter part; and

the plurality of entrance fibers are each coupled to the entrance end surface, via the corresponding one of the GI fibers.

11. The laser system as set forth in claim 6 , wherein:

the entrance end surface of and the exit end surface of the reduced diameter part each have a round shape.

12. The laser system as set forth in claim 7 , wherein:

the following inequality (1) is satisfied:

D in/10≤ D off≤( D in− D out)/2  (1)

where: Doff indicates a distance between the center of the entrance end surface and the center of the exit end surface; Din indicates a maximum width of the entrance end surface; and Dout indicates a maximum width of the exit end surface, each of Doff, Din, and Dout being obtained in a case where the entrance end surface of the reduced diameter part is viewed from the normal direction of the entrance end surface.

13. The laser system as set forth in claim 7 , wherein:

the optical device further comprises:

a GI fiber, Which corresponds to the single entrance fiber, provided between the single entrance fiber and the entrance end surface of the reduced diameter part; and

the single entrance fiber is coupled to the entrance end surface, via the GI fiber.

14. The laser system as set forth in claim 7 , wherein:

the entrance end surface of and the exit end surface of the reduced diameter part each have a round shape.