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 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 a location of the base optical fiber along a longitudinal direction of the 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.

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

• preparing a 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 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 the each outer ring layer in the radial direction;
• and
• heating one or more locations of the base optical fiber along a longitudinal direction of the 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.