Optical fiber for a fiber laser, fiber laser, and production method for optical fiber for a fiber laser

Patent metadata

Field	Value
Publication number	US-11245241-B2
Application number	US-201916594852-A
Country	US
Kind code	B2
Filing date	Oct 7, 2019
Priority date	Oct 30, 2018
Publication date	Feb 8, 2022
Grant date	Feb 8, 2022

Abstract

An optical fiber for a fiber laser includes a core to which a rare-earth element is added, a first cladding formed around the core; and a second cladding formed around the first cladding, and excitation light is guided from at least one end of the first cladding to excite the rare-earth element to output a laser oscillation light. An addition concentration of the rare-earth element to the core is different in a longitudinal direction of the optical fiber for a fiber laser, and a core diameter and a numerical aperture of the optical fiber for a fiber laser are constant in the longitudinal direction of the optical fiber for a fiber laser.

First claim

What is claimed is:

1. An optical fiber for a fiber laser including a core to which a rare-earth element is added, a first cladding formed around the core, and a second cladding formed around the first cladding, in which excitation light is guided from at least one end of the first cladding to excite the rare-earth element to output a laser oscillation light, wherein
an addition concentration of the rare-earth element to the core is different in a longitudinal direction of the optical fiber for a fiber laser,
a core diameter and a numerical aperture of the optical fiber for a fiber laser are constant in the longitudinal direction of the optical fiber for a fiber laser, and
a numerical aperture adjustment element that changes a refractive index of the first cladding is added to the first cladding so that a numerical aperture of the optical fiber for a fiber laser is maintained to be constant in the longitudinal direction of the optical fiber for a fiber laser with respect to change in a numerical aperture of the optical fiber for a fiber laser occurring due to change in a refractive index of the core due to change in the addition concentration of the rare-earth element to the core.

2. The optical fiber for a fiber laser according to claim 1 , wherein
the addition concentration of the rare-earth element to the core in a region closer to the end that guides the excitation light in the longitudinal direction of the optical fiber for a fiber laser is lower than that in an other region.

3. A fiber laser comprising:
the optical fiber for a fiber laser according to claim 1 ;
a tapered fiber bundle connected to an end of the optical fiber for a fiber laser; and
a plurality of light sources that emit excitation light to be guided to the first cladding of the optical fiber for a fiber laser via the tapered fiber bundle.

4. The fiber laser according to claim 3 , wherein
an addition concentration distribution of the rare-earth element is controlled in the longitudinal direction of the optical fiber for a fiber laser so that the temperature of the optical fiber for a fiber laser during rated optical output or maximum optical output is uniform in the longitudinal direction of the optical fiber for a fiber laser.

5. The fiber laser according to claim 3 , wherein
the fiber laser guides excitation light to the first cladding from one direction, and
an addition concentration distribution of the rare-earth element is controlled in the longitudinal direction of the optical fiber for a fiber laser so that the temperature of the optical fiber for a fiber laser during rated optical output or maximum optical output is constant in a length portion of at least 50% and less than 100% from the end that guides the excitation light among the entire length of the optical fiber for a fiber laser and is lower than the constant temperature in a remaining length portion.

6. The fiber laser according to claim 3 , wherein
at least a portion of the optical fiber for a fiber laser is provided on an inner side of a groove formed in a cooling plate formed of a thermoconductive member, the groove being deeper than at least an outer diameter of the optical fiber for a fiber laser, with the aid of a thermoconductive adhesive or a thermoconductive paste.

7. The fiber laser according to claim 6 , wherein
the optical fiber for a fiber laser has a portion in which fibers cross each other, and
the cooling plate is configured such that, in the portion in which the optical fibers for a fiber laser cross each other, a depth of the grooves in which one of the crossing optical fibers for a fiber laser are provided is different from a depth of the groove in which the other crossing optical fibers for a fiber laser are provided so that the crossing optical fibers for a fiber laser do not make contact with each other or such that a bridge formed of a thermoconductive member is provided to extend over the groove in which one of the crossing optical fibers for a fiber laser are provided and the other crossing optical fibers for a fiber laser are provided on the bridge.

8. A fiber laser comprising:
a plurality of the fiber lasers according to claim 3 ; and a beam combiner that combines laser outputs emitted from the plurality of fiber lasers to one optical fiber.

9. A production method for the optical fiber for a fiber laser according to claim 1 , comprising:
allowing a soot to grow while changing the addition concentration of the rare-earth element periodically in an axial direction to manufacture a soot body by a vapor phase axial deposition method;
subjecting the soot body to silica vitrification to manufacture a rod; and
depositing silica glass serving as the first cladding to an outer surface of the rod serving as a core base material in the axial direction by a plasma activated outside vapor deposition method while changing a concentration of the numerical aperture adjustment element included in a raw gas so as to be identical to a period in the axial direction of the rod, of the change in the addition concentration of the rare-earth element included in the core base material to manufacture a preform; and
performing wire drawing while heating the preform.

Assignees

• Fanuc Corp

Inventors

• Takigawa Hiroshi
• Takazane Tetsuhisa

Classifications

• C03B37/02763

  Fibres having axial variations, e.g. axially varying diameter, material or optical properties (rotational spin C03B37/02745) · CPC title

• C03B37/02718

  Thermal treatment of the fibre during the drawing process, e.g. cooling (coating C03C25/10) · CPC title

• C03B37/01211

  by inserting one or more rods or tubes into a tube · CPC title

• H01S3/06729

  Peculiar transverse fibre profile · CPC title

• H01S2301/03

  Suppression of nonlinear conversion, e.g. specific design to suppress for example stimulated brillouin scattering [SBS], mainly in optical fibres in combination with multimode pumping · CPC title