IP Library › Granted Patent US 12678887

Granted Patent B2

US 12678887 · App. 17/627,016 · Granted Jul 14, 2026

Optical fiber, laser generator, laser processing apparatus, and method of manufacturing optical fiber

Inventor: Kensuke Shima (Chiba, JP)

Assignee: Fujikura Ltd.

B23K26/03 C03B37/15 G02B6/03666 G02B6/03688

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Quick Facts

Patent No.: US 12678887
App. No.: 17/627,016
Granted: Jul 14, 2026
Kind: B2

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Abstract

An optical fiber includes: a center core; an inner ring layer, located outside of the center core in a radial direction, that has a refractive index lower than a refractive index of the center core; an outer core, located outside of the inner ring layer in the radial direction, that has a refractive index higher than the refractive index of the inner ring layer; and an outer ring layer, located outside of the outer core in the radial direction, that has a refractive index lower than the refractive index of the outer core. A relative refractive index difference Δ CF between the center core and the inner ring layer varies along a longitudinal direction such that the relative refractive index difference Δ CF at a location along the longitudinal direction is smaller than a relative refractive index difference Δ PF between the outer core and the outer ring layer.

Claims (57)

1 . An optical fiber comprising:

a center core;

an inner ring layer located outside of the center core in a radial direction of the optical fiber, the inner ring layer having a refractive index lower than a refractive index of the center core;

one or more outer cores, each located outside of the inner ring layer in the radial direction and having a refractive index higher than the refractive index of the inner ring layer; and

one or more outer ring layers, each located outside of the outer core in the radial direction and having a refractive index lower than the refractive index of the outer core, wherein

the optical fiber is a single optical fiber extending continuously between opposite ends along a longitudinal direction,

a relative refractive index difference Δ CF between the center core and the inner ring layer varies along the longitudinal direction of the optical fiber such that the relative refractive index difference Δ CF at one or more locations between the opposite ends along the longitudinal direction is smaller than a relative refractive index difference Δ PF between the one or more outer cores and the one or more outer ring layers located adjacently outside of the one or more outer cores in the radial direction,

the relative refractive index difference Δ CF in the one or more locations is locally smaller than:

a refractive index difference Δ C1 between the center core and the inner ring layer in an upstream location located upstream of the one or more locations along the longitudinal direction; and

a relative refractive index difference Δ C2 between the center core and the inner ring layer in a downstream location located downstream of the one or more locations along the longitudinal direction,

so as to allow a portion of light propagating through the center core in the upstream location to be introduced to the outer core in the downstream location,

a difference between the relative refractive index difference Δ CF in the one or more locations and the refractive index difference Δ C1 is greater than a difference between the relative refractive index difference Δ PF in the one or more locations and a refractive index difference Δ P1 between the one or more outer cores and the one or more outer ring layers in the upstream location, and

a difference between the relative refractive index difference Δ CF in the one or more locations and the refractive index difference Δ C2 is greater than a difference between the relative refractive index difference Δ PF in the one or more locations and a refractive index difference Δ P2 between the one or more outer cores and the one or more outer ring layers in the downstream location.

2 . The optical fiber as recited in claim 1 , wherein

a thickness of the inner ring layer is smaller than a thickness of the one or more outer ring layers.

3 . The optical fiber as recited in claim 1 , the optical fiber comprises two or more outer cores and the same number of the outer ring layers.

4 . The optical fiber as recited in claim 3 , wherein,

at the one or more locations, a relative refractive index difference Δ PFn between each of the outer cores and a corresponding one of the outer ring layers located adjacently outside of the outer cores in the radial direction increases along the radial direction.

5 . The optical fiber as recited in claim 1 , wherein

the optical fiber is bent at the location.

6 . A laser generator comprising:

a laser source that generates a laser beam;

the optical fiber as recited in claim 1 , the optical fiber being connected to a downstream side of the laser source to direct the laser beam from the laser source to the center core; and

a fiber bend unit that bends the optical fiber at the location.

7 . A laser processing apparatus comprising:

the laser generator as recited in claim 6 ;

a laser emitter that emits the laser beam from the laser generator to a workpiece;

a process monitor that detects a process condition of the workpiece; and

a controller that adjusts a curvature of the optical fiber in the fiber bend unit of the laser generator according to an output from the process monitor.

8 . The optical fiber as recited in claim 1 , wherein

a refractive index distribution in the upstream location is the same as a refractive index distribution in the downstream location.

9 . A method of manufacturing an optical fiber, the method comprising:

preparing a single base optical fiber extending continuously between opposite ends along a longitudinal direction, the single base optical fiber including:

a center core,

an inner ring layer located outside of the center core in a radial direction of the optical fiber, wherein the inner ring layer has a refractive index lower than a refractive index of the center core and includes a dopant that lowers a refractive index,

one or more outer cores, each located outside of the inner ring layer in the radial direction and having a refractive index higher than the refractive index of the inner ring layer, and

one or more outer ring layers, each located outside of the outer core in the radial direction and having a refractive index lower than the refractive index of the one or more outer cores located adjacently inside of the one or more outer ring layers in the radial direction; and

heating one or more locations of the single base optical fiber between the opposite ends along the longitudinal direction of the single base optical fiber to diffuse the dopant in the inner ring layer such that a relative refractive index difference Δ CF between the center core and the inner ring layer becomes lower than a relative refractive index difference Δ PF between the one or more outer cores and the one or more outer ring layers located adjacently outside of the one or more outer cores in the radial direction, and that the relative refractive index difference Δ CF in the one or more locations is locally smaller than a refractive index difference Δ C1 between the center core and the inner ring layer in an upstream location located upstream of the one or more locations along the longitudinal direction and a relative refractive index difference Δ C2 between the center core and the inner ring layer in a downstream location located downstream of the one or more locations along the longitudinal direction, wherein

10 . The method of manufacturing the optical fiber as recited in claim 9 , wherein

the dopant is fluorine.

11 . The method of manufacturing the optical fiber as recited in claim 9 , wherein,

in the single base optical fiber prior to heating the one or more locations, a relative refractive index difference between the one or more outer cores and the one or more outer ring layers located adjacently outside of the one or more outer cores in the radial direction is equal to or greater than a relative refractive index difference between the center core and the inner ring layer.

12 . A method of manufacturing an optical fiber, the method comprising:

preparing a single base optical fiber extending continuously between opposite ends along a longitudinal direction, the single base optical fiber including:

a center core that includes a dopant that increases a refractive index,

an inner ring layer located outside of the center core in a radial direction of the single base optical fiber, wherein the inner ring layer has a refractive index lower than a refractive index of the center core,

one or more outer cores, each located outside of the inner ring layer in the radial direction and having a refractive index higher than the refractive index of the inner ring layer, and

one or more outer ring layers, each located outside of the outer core in the radial direction and having a refractive index lower than the refractive index of the outer core located adjacently inside of each outer ring layer in the radial direction; and

heating one or more locations of the single base optical fiber between the opposite ends along the longitudinal direction of the single base optical fiber to diffuse the dopant in the center core such that a relative refractive index difference Δ CF between the center core and the inner ring layer becomes lower than a relative refractive index difference Δ PF between the one or more outer cores and the one or more outer ring layers located adjacently outside of the one or more outer cores in the radial direction, and that the relative refractive index difference Δ CF in the one or more locations is locally smaller than a refractive index difference Δ C1 between the center core and the inner ring layer in an upstream location located upstream of the one or more locations along the longitudinal direction and a relative refractive index difference Δ C2 between the center core and the inner ring layer in a downstream location located downstream of the one or more locations along the longitudinal direction, wherein

13 . The method of manufacturing the optical fiber as recited in claim 12 , wherein

the dopant is germanium.

14 . The method of manufacturing the optical fiber as recited in claim 12 , wherein,