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

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 ΔCF between the center core and the inner ring layer becomes lower than a relative refractive index difference ΔPF 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 ΔCF in the one or more locations is locally smaller than a refractive index difference ΔC1 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 ΔC2 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
• a difference between the relative refractive index difference ΔCF in the one or more locations and the refractive index difference ΔC1 is greater than a difference between the relative refractive index difference ΔPF in the one or more locations and a refractive index difference ΔP1 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 ΔCF in the one or more locations and the refractive index difference ΔC2 is greater than a difference between the relative refractive index difference ΔPF in the one or more locations and a refractive index difference ΔP2 between the one or more outer cores and the one or more outer ring layers in the downstream location.

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 ΔCF between the center core and the inner ring layer becomes lower than a relative refractive index difference ΔPF 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 ΔCF in the one or more locations is locally smaller than a refractive index difference ΔC1 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 ΔC2 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
• a difference between the relative refractive index difference ΔCF in the one or more locations and the refractive index difference ΔC1 is greater than a difference between the relative refractive index difference ΔPF in the one or more locations and a refractive index difference ΔP1 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 ΔCF in the one or more locations and the refractive index difference ΔC2 is greater than a difference between the relative refractive index difference ΔPF in the one or more locations and a refractive index difference ΔP2 between the one or more outer cores and the one or more outer ring layers in the downstream location.