JP6033736B2 - Optical fiber for laser device having optical absorption function - Google Patents

Description

The present invention relates to an optical fiber for a laser device mainly used for a fiber laser device.

For the purpose of application to laser processing and medical applications, fiber lasers are attracting attention because they can easily extract laser light with high efficiency and high beam quality.
A general fiber laser apparatus has a configuration as shown in FIG.
That is, the signal light 2 generated from the signal light source 1 and the pumping light 4 generated from the pumping light source 3 are input to the amplification optical fiber 7 having a core to which a rare earth element is added via the optical coupler 5, and the pumping light. When 4 acts on the rare earth element added to the core, the signal light 2 propagating through the core of the amplification optical fiber 7 is amplified, and the laser light 10 having high energy is obtained.

Part of the excitation light 4 input to the amplification optical fiber 7 propagates through the cladding and reaches the output end of the amplification optical fiber 7. A laser output optical fiber 9 or the like is often connected to the output end of the amplification optical fiber 7, but the clad propagation light is not input to the core of the connection destination optical fiber but is radiated at the connection portion 8. It is normal.

The clad propagating light radiated from the connection portion 8 is absorbed by components existing in the surrounding area, and unexpected heat generation may occur, which may cause damage to the components and the optical fiber.
For this reason, a method is adopted in which the clad propagation light is removed and radiated before reaching the emission end of the amplification optical fiber 7.

As a method of absorbing the clad propagation light, a method of adding a dopant that absorbs the clad propagation light to the clad as in Patent Document 1 and a method of providing a light absorber around the clad as of Patent Document 2 are known. Yes.

  However, the method of adding a dopant as in Patent Document 1 requires the formation of a clad material so that the dopant is uniformly distributed, and there is a problem that it takes much time and cost. In addition, since the dopant is added to the entire cladding, this method is not suitable for absorbing the clad propagation light only at a specific position in the longitudinal direction of the optical fiber.

  On the other hand, the method of providing a light absorber as in Patent Document 2 can provide a light absorber only at a necessary location, so that it is desired to absorb clad propagation light only at a specific position in the longitudinal direction of the optical fiber. This is an effective method. However, since the size of the portion provided with the light absorber is increased, this method is not suitable when downsizing is required.

JP 2002-174739 JP-A-11-274613

An object of the present invention is to provide an optical fiber having a function of absorbing unnecessary propagation light without using a dopant or a light absorber.

The present inventor noticed that when silicon dioxide, which is the main component of quartz glass widely used as a material for optical fibers, is irradiated with radiation, a region in which optical properties are changed due to lack of oxygen is formed. It was clarified that the conventional problem can be solved by absorbing light in the region where the optical characteristics have changed.

The laser device for optical fibers provided by the present invention is silicon dioxide main component, characterized in that the region of the silicon dioxides oxygen is deficient in at least one end of the existing optical fiber was connected to the amplification optical fiber And

In the optical fiber for a laser device of the present invention, the excellent effects described below can be expected.

(1) It is possible to obtain a light absorption function relatively easily and inexpensively without adding new substances / articles for optical fibers such as dopants and light absorbers.

(2) By providing the oxygen-deficient region at an arbitrary position, the clad propagation light can be absorbed only at a specific position in the longitudinal direction of the optical fiber.

It is an example of a general fiber laser apparatus. It is an example of embodiment of the optical fiber used for this invention , and is a case where an oxygen-deficient area | region is formed in the clad | crud of the front-end | tip part of an optical fiber. It is an example of embodiment of the optical fiber used for this invention , and is a case where an oxygen-deficient area | region is formed in the whole clad of an optical fiber. It is an example of embodiment of the optical fiber used for this invention , and is a case where an optical fiber is made into a double clad structure and the oxygen-deficient area | region was formed in the whole 2nd clad. It is an example of embodiment of the optical fiber for laser apparatuses of this invention.

Hereinafter, a basic configuration of an optical fiber used in the present invention will be described with reference to the accompanying drawings.
In FIG. 2, 11 is an optical fiber, 12 is an optical fiber core, 13 is an optical fiber cladding, and 14 is an oxygen-deficient region.
What is characteristic in the present invention is that the main component of the optical fiber 11 is silicon dioxide, and the region 14 in which oxygen of silicon dioxide is deficient exists in the optical fiber.

Oxygen-deficient silicon dioxide usually changes from a state expressed as SiO _{2 in a} chemical formula to a state of SiO _x (0 <x <2). Along with this change, structural defects at the molecular level occur in the material composed mainly of silicon dioxide, and the optical characteristics also change. Due to the change in the optical characteristics, an infrared absorption function is provided, so that light can be absorbed in the oxygen-deficient region. This oxygen-deficient region 14 can be formed by irradiating silicon dioxide with radiation. X-rays and gamma rays are preferable as the radiation.

If this oxygen-deficient region 14 is formed only in the clad 13 as shown in FIG. 2, the clad propagation light can be efficiently absorbed.
2 shows a case where the oxygen-deficient region 14 is formed in the cladding 13 at the tip of the optical fiber 11, but the entire cladding 13 may be used as the oxygen-deficient region 14 as shown in FIG. However, the oxygen-deficient region 14 may be formed in the clad 13 at the intermediate portion of the optical fiber 11.

In forming the oxygen-deficient region 14 only in the cladding 13 is preferably so as not to adjacent oxygen depletion region 14 and the core 12 of the optical fiber as shown in FIG. This is because when the core 12 and the oxygen-deficient region 14 are adjacent to each other, light propagating through the core 12 at the interface between the core 12 and the oxygen-deficient region 14 is easily absorbed by the oxygen-deficient region 14.

  As a method for preventing the oxygen-deficient region 14 and the core 12 of the optical fiber 11 from being adjacent to each other, the optical fiber 11 may have a double clad structure. That is, the optical fiber 11 is a double clad fiber composed of the core 12, the first clad 13A, and the second clad 13B, and the oxygen deficient region 14 is formed only in the second clad 13B, so that the core 12 and the oxygen deficient region are formed. 14 becomes the optical fiber 11 which is not adjacent.

Actually, in order to obtain the optical fiber 11 in which the oxygen-deficient region 14 is formed only in the clad 13, the radiation is irradiated in the state of the base material that is the material of the optical fiber 11, rather than directly irradiating the optical fiber 11. Is preferred. When a base material to be the clad 13 is irradiated with radiation to form an oxygen-deficient region and an optical fiber is manufactured by a drawing method, which is a general optical fiber manufacturing method, using this base material, oxygen is only in the clad 13. The optical fiber 11 in which the depletion region 14 is formed can be obtained.

When the optical fiber 11 has a double clad structure as shown in FIG. 4 , the oxygen deficient region 14 may be formed by irradiating only the base material to be the second clad 13 </ b> B.

The Example of the optical fiber for laser apparatuses of this invention is shown.
First and second cladding base materials made of quartz glass were prepared, and the entire second cladding base material was irradiated with X-rays to form an oxygen-deficient region.
Drawing is performed using the first and second cladding base materials and the core base material made of quartz glass, the core diameter is 20 μm, the first cladding diameter is 400 μm, the second cladding diameter is 550 μm, and NA = 0.06. An optical fiber was obtained. In this optical fiber, the entire second cladding is an oxygen-deficient region.

The optical fiber thus obtained was cut to a length of 10 mm, and both ends polished, as shown in FIG. 5, fused and connected to the output end side of the amplification optical fiber used in the fiber laser device. Thus, an optical fiber for a laser device of the present invention was produced .
Incorporating the laser device for optical fiber to the fiber laser device was subjected to evaluation tests of the clad propagation light absorption capacity, have an equivalent absorption capacity and when using dopant or light absorber, optical laser apparatus of the present invention It was confirmed that the fiber has a sufficient function as an optical fiber used in the fiber laser device.

The above examples are merely examples of the present invention, and it goes without saying that various modifications and applications are possible within the scope of the idea of the present invention. For example, the optical fiber for a laser device of the present invention can be provided by appropriately changing the core / cladding diameter, the numerical aperture, the range / number of oxygen-deficient regions, etc. according to the fiber laser device used. Needless to say.

DESCRIPTION OF SYMBOLS 1 Signal light source 2 Signal light 3 Excitation light source 4 Excitation light 5 Optical coupler 6 Connection part 7 of optical coupler and optical fiber for amplification 7 Optical fiber for amplification 8 Connection part 9 of optical fiber for amplification and optical fiber for laser emission 9 Laser emission Optical fiber 10 Laser light 11 Optical fiber 12 Optical fiber core 13 Optical fiber cladding 13A Optical fiber first cladding 13B Optical fiber second cladding 14 Oxygen-deficient region

Claims (6)

An optical fiber mainly composed of silicon dioxide, oxygen and there is a region of silicon dioxide depleted to the optical fiber, characterized in that connected to the amplification optical fiber in at least one end of the optical fiber, a laser device use optical fiber. 2. The optical fiber for a laser device according to claim 1, wherein at least a part of light propagating through the optical fiber is absorbed in the oxygen-deficient region. 3. The optical fiber for a laser device according to claim 1, wherein the oxygen-deficient region is formed only in a clad of the optical fiber. The optical fiber for a laser device according to claim 3, wherein the oxygen-deficient region is not adjacent to the core of the optical fiber. The method for producing an optical fiber for a laser device according to any one of claims 1 to 4, wherein the oxygen-deficient region is formed by irradiating a material constituting the optical fiber with radiation. Radiation is irradiated, as a main component silicon dioxide oxygen depletion region is formed, a process of manufacturing the optical fiber using the cladding optical fiber preform, at least one end optical fiber amplifier of the optical fiber And a method of manufacturing an optical fiber for a laser device .

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