Multi-core optical fiber interconnection structure and method for manufacturing multi-core optical fiber interconnection structure

1. A multi-core optical fiber interconnection structure comprising:

a first multi-core optical fiber having a plurality of first cores extending along a first central axis, a first common cladding covering each of the plurality of first cores, and a first marker provided within the first common cladding while being completely separated from both the first central axis and an outer periphery of the first common cladding, to ensure a rotation of the first multi-core optical fiber in a circumferential direction about the first central axis and to function as an index for cutting end portion of the first multi-core optical fiber slantwise relative to the plane normal to the first central axis;

a first ferrule attached to the end portion of the first multi-core optical fiber so that end faces of the first ferrule and the first multi-core optical fiber correspond to each other;

a second multi-core optical fiber having a plurality of second cores extending along a second central axis, a second common cladding covering each of the plurality of second cores, and a second marker provided within the second common cladding while being completely separated from both the second central axis and an outer periphery of the second common cladding, to ensure a rotation of the second multi-core optical fiber in a circumferential direction about the second central axis and to function as an index for cutting end portion of the second multi-core optical fiber slantwise relative to the plane normal to the second central axis; and

a second ferrule attached to the end portion of the second multi-core optical fiber so that end faces of the second ferrule and the second multi-core optical fiber correspond to each other,

wherein both the end faces of the first ferrule and the first multi-core optical fiber are coincident with a common plane which slants relative to a plane normal to the first central axis and both the end faces of the second ferrule and the second multi-core optical fiber are coincident with a common plane which slants relative to a plane normal to the second central axis,

wherein the first and second multi-core optical fibers are arranged so that the plurality of first cores and the plurality of second cores are optically coupled in a one-to-one correspondence relation where the slanted end faces of the first ferrule and the first multi-core optical fiber directly face the slanted end faces of the second ferrule and the second multi-core optical fiber in a state in which the first central axis and the second central axis are on a same straight line, and

wherein the slanted end faces of the first ferrule and the first multi-core optical fiber face the slanted end faces of the second ferrule and the second multi-core optical fiber so as to minimize variation in core pitches of pairs of the first and second cores each in the one-to-one correspondence relation, each of the core pitches being defined along the first and second central axes.

2. The multi-core optical fiber interconnection structure according to claim 1 , wherein the slanted end face of the first multi-core optical fiber and the slanted end face of the second multi-core optical fiber face each other so as to minimize variation in inter-core connection losses of pairs of the first and second cores each in the one-to-one correspondence relation.

3. The multi-core optical fiber interconnection structure according to claim 1 , wherein the slanted end face of the first multi-core optical fiber is slanted in the range of 5° to 11° relative to the plane normal to the first central axis and wherein the slanted end face of the second multi-core optical fiber is slanted in the range of 5° to 11° relative to the plane normal to the second central axis.

4. The multi-core optical fiber interconnection structure according to claim 1 ,

wherein the first marker in the slanted end face of the first multi-core optical fiber is located in an end face region lying farther away from the other end face of the first multi-core optical fiber than a first reference plane including an intersection between the slanted end face of the first multi-core optical fiber and the first central axis and being normal to the first central axis, and

wherein the second marker in the slanted end face of the second multi-core optical fiber is located in an end face region lying nearer to the other end face of the second multi-core optical fiber than a second reference plane including an intersection between the slanted end face of the second multi-core optical fiber and the second central axis and being normal to the second central axis.

5. The multi-core optical fiber interconnection structure according to claim 1 , further comprising

a sleeve for positioning of the first ferrule and the second ferrule, the sleeve having a first opening inserted with at least a tip portion of the first ferrule attached to the end portion of the first multi-core optical fiber, a second opening inserted with at least a tip portion of the second ferrule attached to the end portion of the second multi-core optical fiber, and an inner wall restricting a movement of the first ferrule in a direction perpendicular to the first central axis and a movement of the second ferrule in a direction perpendicular to the second central axis.

6. The multi-core optical fiber interconnection structure according to claim 1 , further comprising: a groove member for positioning of the first multi-core optical fiber and the second multi-core optical fiber.

7. The multi-core optical fiber interconnection structure according to claim 1 , wherein an optical return loss of light on the slanted end face of the first multi-core optical fiber is not less than 30 dB, and an optical return loss of light on the slanted end face of the second multi-core optical fiber is not less than 30 dB.

8. The multi-core optical fiber interconnection structure according to claim 1 , wherein positional deviation amounts between the first cores and the second cores in the one-to-one correspondence relation are not more than 1.6 μm.

9. The multi-core optical fiber interconnection structure according to claim 1 , wherein connection losses between the first cores and the second cores in the one-to-one correspondence relation are not more than 0.4 dB.

10. The multi-core optical fiber interconnection structure according to claim 1 , wherein at least a portion of the slanted end face of the first multi-core optical fiber is in contact with the slanted end face of the second multi-core optical fiber.

11. A method for manufacturing a multi-core optical fiber interconnection structure comprising:

a first multi-core optical fiber at least one end face of which is slanted relative to a plane normal to a first central axis and which has a plurality of first cores extending along the first central axis, a first common cladding covering the plurality of the first cores, and a first marker provided within the first common cladding while being completely separated from both the first central axis and an outer periphery of the first common cladding, to ensure a rotation of the first multi-core optical fiber in a circumferential direction about the first central axis and function as an index for cutting end portion of the first multi-core optical fiber; and

a second multi-core optical fiber at least one end face of which is slanted relative to a plane normal to a second central axis and which has a plurality of second cores extending along the second central axis, a second common cladding covering the plurality of second cores, and a second marker provided within the second common cladding while being completely separated from both the second central axis and an outer periphery of the second common cladding, to ensure a rotation of the second multi-core optical fiber in a circumferential direction about the second central axis and function as an index for cutting end portion of the second multi-core optical fiber,

the method comprising the steps of:

cutting the end portion of the first multi-core optical fiber slantwise relative to the plane normal to the first central axis so as to make the first marker exist in a side or an opposite side where the slanted end face of the first multi-core optical fiber projects, and cutting the end portion of the second multi-core optical fiber slantwise relative to the plane normal to the second central axis so as to make the second marker exist in a side or an opposite side where the slanted end face of the second multi-core optical fiber projects,

arranging the first and second multi-core optical fibers so that the slanted end face of the first multi-core optical fiber and the slanted end face of the second multi-core optical fiber directly face each other in a state in which the first central axis and the second central axis are on a same straight line; and

adjusting relative positions between the slanted end faces of the first and second multi-core optical fibers so as to minimize variation in inter-core connection losses of pairs of the first and second cores each in the one-to-one correspondence relation, in a state in which the first cores and the second cores are each in the one-to-one correspondence relation.

12. The method according to claim 11 , wherein at least a portion of the slanted end face of the first multi-core optical fiber is in contact with the slanted end face of the second multi-core optical fiber.

13. The method according to claim 11 , wherein the adjusting including:

moving at least the first multi-core optical fiber toward the second multi-core optical fiber to reduce an interval between the one end face of the first multi-core optical fiber and the one end face of the second multi-core optical fiber; and

rotating at least the first multi-core optical fiber in a circumferential direction about the first central axis.

14. A multi-core optical fiber interconnection structure comprising:

a first multi-core optical fiber having a plurality of first cores extending along a first central axis, a first common cladding covering the plurality of first cores, and a first marker provided within the first common cladding while being completely separated from both the first central axis and an outer periphery of the first common cladding, to ensure a rotation of the first multi-core optical fiber in a circumferential direction about the first central axis and to function as an index for cutting end portion of the first multi-core optical fiber slantwise relative to the plane normal to the first central axis;

a first ferrule attached to the end portion of the first multi-core optical fiber so that end faces of the first ferrule and the first multi-core optical fiber correspond to each other;

a second multi-core optical fiber having a plurality of second cores extending along a second central axis, a second common cladding covering the plurality of second cores, and a second marker provided within the second common cladding while being completely separated from both the second central axis and an outer periphery of the second common cladding, to ensure a rotation of the second multi-core optical fiber in a circumferential direction about the second central axis and to function as an index for cutting end portion of the second multi-core optical fiber slantwise relative to the plane normal to the second central axis; and

a second ferrule attached to the end portion of the second multi-core optical fiber so that end faces of the second ferrule and the second multi-core optical fiber correspond to each other;

wherein both the end faces of the first ferrule and the first multi-core optical fiber are coincident with a common plane which slants relative to a plane normal to the first central axis and both the end faces of the second ferrule and the second multi-core optical fiber are coincident with a common plane which slants relative to a plane normal to the second central axis,

wherein the first and second multi-core optical fibers are arranged so that the plurality of first cores and the plurality of second cores are optically coupled in a one-to-one correspondence relation where the slanted end faces of the first ferrule and the first multi-core optical fiber directly face the slanted end faces of the second ferrule and the second multi-core optical fiber in a state in which the first central axis and the second central axis are on a same straight line.

15. The multi-core optical fiber interconnection structure according to claim 14 , wherein the slanted end face of the first multi-core optical fiber is slanted in the range of 5° to 11° relative to the plane normal to the first central axis and wherein the slanted end face of the second multi-core optical fiber is slanted in the range of 5° to 11° relative to the plane normal to the second central axis.