JP2015125362A - Optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent thermal damage to a cladding in a tip end of an optical fiber.SOLUTION: An optical fiber 1 comprises a core 2, a resin cladding 3, a covering member 4, and a resin filling member with which a clearance between an outer peripheral surface of the core 2 and an inner peripheral surface of the covering member is filled. The resin cladding 3 covers the outer peripheral surface of the core 2 except a tip end 21 of the core 2. The covering member 4 covers the outer peripheral surface of the tip end 21 of the core 2. Furthermore, the covering member 4 has a refractive index lower than that of the core 2, and a thermal conductivity higher than that of the resin cladding 3. The filling member has a refractive index lower than that of the core 2.

Description

  The present invention relates to an optical fiber.

  In general, an optical fiber includes a glass core and a glass cladding. The optical fiber configured as described above is manufactured by drawing an optical fiber preform.

  On the other hand, Patent Document 1 discloses an optical fiber having a clad made of resin. In this optical fiber manufacturing method, a core is first formed by drawing, and a resin is applied to the outer peripheral surface of the core. Thereafter, the clad layer is formed by heating the resin.

  Patent Document 2 discloses a double clad optical fiber. This optical fiber includes a glass core, a glass inner clad, and a resin outer clad. In this optical fiber manufacturing method, a core and an inner cladding are first formed by drawing. And resin is apply | coated to the outer peripheral surface of an inner clad, and an outer clad is formed by heating this resin.

JP2013-221978A JP2013-048214A

  When the optical fiber is used as a component of a fiber laser, that is, when the pumping light travels through the optical fiber, the pumping light is absorbed and the temperature of the optical fiber becomes high. In particular, the temperature of the tip portion on the side where the excitation light is incident becomes high. For this reason, generally, the resin clad having a lower thermal conductivity than the glass clad may be thermally damaged at the tip of the optical fiber.

  An object of the present invention is to prevent thermal damage of the clad at the tip of the optical fiber.

  The optical fiber according to the first aspect of the present invention includes an optical path member, a resinous cladding, a covering member, and a resin filling member that fills a gap between the outer peripheral surface of the optical path member and the inner peripheral surface of the covering member; Is provided. The optical path member is a filament and serves as a light path. The resin clad covers the outer peripheral surface of the optical path member except for the front end portion of the optical path member. The resin clad is made of resin. The covering member covers the outer peripheral surface of the tip portion of the optical path member. The covering member has a lower refractive index than the optical path member, higher thermal conductivity than the resin clad, and the filling member has a lower refractive index than the optical path member.

  According to this configuration, the resin clad is not formed at the tip of the optical path member. For this reason, the thermal damage of the resin clad can be prevented. In addition, a coating member is formed at the tip of the optical path member instead of the resin clad. However, since this coating member has higher thermal conductivity than the resin clad, thermal damage can be prevented.

  The optical path member may be composed of a glass core, or may be composed of a glass core and a glass clad. The glass cladding covers the outer peripheral surface of the core.

  Preferably, the covering member is transparent. According to this configuration, the covering member can further prevent thermal damage.

  Preferably, the covering member has a higher melting point or softening point than the resin clad. According to this configuration, since the covering member has better heat resistance than the resin clad, it is possible to further prevent thermal damage.

  Preferably, the filling member is formed of an ultraviolet curable resin or a thermosetting resin.

  The optical fiber manufacturing method according to the second aspect of the present invention includes the following steps (a) to (d). In step (a), a linear optical path member is prepared in which a portion other than the tip is covered with a resin clad. In step (b), a covering member having a through hole is prepared. In step (c), the tip of the optical path member is disposed in the through hole of the covering member. Step (d) fills the gap between the outer peripheral surface of the optical path member and the inner peripheral surface of the covering member with a resin filler. The covering member has a refractive index lower than that of the optical path member and higher thermal conductivity than that of the resin cladding.

  According to this method, as described above, thermal damage of the resin clad can be prevented. In addition, since the tip is heated and softened in a state where the tip is disposed in the through hole of the covering member, the tip has the same shape as the through hole. That is, the distal end portion of the optical path member and the through hole of the covering member may not have the same shape from the beginning. As a result, the optical fiber can be easily manufactured.

  According to the present invention, thermal damage of the resin clad can be prevented at the tip of the optical fiber.

Side surface sectional drawing of an optical fiber. The front view of an optical fiber. The exploded view of a covering member. The figure which shows the manufacturing method of an optical fiber. Side surface sectional drawing which shows a cooling device. The front view which shows a cooling device. FIG. 6 is a side sectional view of an optical fiber according to Modification 2. FIG. 9 is a side cross-sectional view of an optical fiber according to Modification 3.

  Hereinafter, embodiments of an optical fiber according to the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view of an optical fiber, and FIG. 2 is a front view of the optical fiber.

  As shown in FIGS. 1 and 2, the optical fiber 1 includes a core 2, a resin cladding 3, and a covering member 4. In the present embodiment, the core 2 corresponds to the optical path member of the present invention.

The core 2 is a portion that becomes a light path, and is formed in a filament. The core 2 has a circular cross-sectional shape along the direction orthogonal to the longitudinal direction. That is, the core 2 is formed in a cylindrical shape. The core 2 is made of glass, and preferably made of fluoride glass. For example, the core 2 is made of ZBLAN (ZrF ₄ —BaF ₂ —LaF ₃ —AlF ₃ —NaF) glass or the like. In addition, when the optical fiber 1 is used as a component part of a fiber laser, the core 2 preferably includes a laser medium. As the laser medium, a rare earth element can be exemplified, and preferably erbium can be exemplified.

  The resin clad 3 is configured to cover the outer peripheral surface of the core 2. The resin clad 3 has a refractive index lower than that of the core 2. The resin cladding 3 is preferably made of an ultraviolet curable resin. For example, the resin clad 3 is formed of a fluorine-based acrylic resin or the like.

  The resin clad 3 does not cover the outer peripheral surface of the tip portion 21 of the core 2. Although the length of this front-end | tip part 21 is not specifically limited, For example, it can be set as about 5 mm or more and 20 mm or less.

  The covering member 4 covers the outer peripheral surface of the tip portion 21 of the core 2. That is, the outer peripheral surface of the core 2 excluding the tip portion 21 is covered with the resin clad 3, and the outer peripheral surface of the tip portion 21 is covered with the covering member 4. The covering member 4 includes a first covering portion 41 and a second covering portion 42. The 1st coating | coated part 41 and the 2nd coating | coated part 42 are mutually adhere | attached with the adhesive agent.

  FIG. 3 is an exploded view of the covering member 4. As shown in FIG. 3, the first covering portion 41 has a first pressing surface 411. A groove 412 is formed on the first pressing surface 411. The groove portion 412 extends from one end edge of the first pressing surface 411 to the other end edge. The length of the groove 412 is substantially the same as the length of the tip 21 of the core 2. The cross-sectional shape along the direction perpendicular to the longitudinal direction of the groove 412 is a semicircular shape. The diameter of the groove 412 is substantially the same as the diameter of the tip 21 of the core 2. Half of the tip 21 of the core 2 is accommodated in the groove 412.

  The second covering part 42 has the same shape as the first covering part 41. The second covering part 42 has a second pressing surface 421. A groove 422 is formed on the second pressing surface 421. The groove portion 422 extends from one end edge of the second pressing surface 421 to the other end edge. The length of the groove portion 422 is substantially the same as the length of the tip portion 21 of the core 2. The cross-sectional shape along the direction orthogonal to the longitudinal direction of the groove 422 is a semicircular shape. The diameter of the groove 422 is substantially the same as the diameter of the tip 21 of the core 2. Half of the tip 21 of the core 2 is accommodated in the groove 422. In addition, the 1st and 2nd coating | coated parts 41 and 42 may be a rectangular parallelepiped shape, and may be column shape.

  The 1st coating | coated part 41 and the 2nd coating | coated part 42 are arrange | positioned so that the 1st press surface 411 and the 2nd press surface 421 may oppose. In this state, the groove 412 of the first pressing surface 411 and the groove 422 of the second pressing surface 421 face each other. A through hole of the covering member 4 is formed by the groove portions 412 and 422.

  The covering member 4 has a lower refractive index than the core 2 and a higher thermal conductivity than the resin cladding 3. The thermal conductivity of the covering member 4 is preferably about 0.7 W / (mk) or more, for example.

  The covering member 4 preferably has a higher melting point or softening point than the resin cladding 3. The covering member 4 is preferably transparent. The covering member 4 is preferably made of a crystal material or a glass material. Specifically, it can be formed of calcium fluoride, magnesium fluoride, quartz, or the like.

  Next, a method for manufacturing the optical fiber 1 configured as described above will be described with reference to FIG. FIG. 4 is a diagram for explaining a method of manufacturing the optical fiber 1.

  As shown in FIG. 4, first, the core 2 is formed by drawing the base material made of the material of the core 2 described above (FIG. 4A). More specifically, after the base material is heated and melted, the core 2 is formed by thinly stretching with a drawing device.

  Next, a resin made of the above-described resin clad 3 material is applied to the outer peripheral surface of the core 2. Then, the resin clad 3 is formed by curing the resin by irradiating it with ultraviolet rays for heating (FIG. 4B). The resin clad 3 is not formed on the outer peripheral surface of the tip portion 21 of the core 2. That is, the tip portion 21 of the core 2 is exposed. For example, the tip 21 of the core 2 may be exposed by not applying resin to the tip 21 of the core 2 from the beginning. Alternatively, resin may be applied to the entire outer peripheral surface of the core 2 to form the resin clad 3, and then the resin clad 3 may be peeled off to expose the end portion 21 of the core 2. The resin clad 3 can be removed with an organic solvent.

  As described above, the core 2 is prepared in which the portions other than the tip 21 are covered with the resin clad 3. And the front-end | tip part 21 of the core 2 is pinched | interposed by the 1st coating | coated part 41 and the 2nd coating | coated part 42 (FIG.4 (c)). Specifically, the first covering portion 41 and the second covering portion 42 are arranged so that the first pressing surface 411 and the second pressing surface 421 are opposed to each other. Further, the distal end portion 21 of the core 2 is housed in a groove portion 412 formed on the first pressing surface 411 and a groove portion 422 formed on the second pressing surface 421.

  In this manner, the tip portion 21 is heated in a state where the tip portion 21 of the core 2 is sandwiched between the first covering portion 41 and the second covering portion 42. For example, the tip 21 of the core 2 is heated by a heater or the like via the first cover 41 and the second cover 42. The heating temperature at this time is preferably set to such an extent that the tip portion 21 becomes equal to or higher than the softening point of the core 2, and preferably set to such a degree that the tip portion 21 becomes less than the glass transition point crystallization start temperature of the core 2. In addition, the heating time at this time is preferably about 2 minutes.

  Thus, by heating and softening the distal end portion 21 of the core 2, the distal end portion 21 of the core 2 is deformed so as to match the shapes of the groove portions 412 and 422 of the covering member 4.

  Next, the cooling device for the optical fiber 1 configured as described above will be described with reference to the drawings. FIG. 5 is a side sectional view showing the cooling device for the optical fiber 1, and FIG. 6 is a front view showing the cooling device for the optical fiber 1.

  As shown in FIGS. 5 and 6, the cooling device includes a heat sink 11, a first lid member 12, and a second lid member 13. The heat sink 11 has a groove formed on the upper surface so as to accommodate the optical fiber 1. The heat sink 11 has a flow path 111 through which cooling water for cooling the heat sink 11 flows. The heat sink 11 is formed of a metal material such as aluminum or copper, for example.

  The first lid member 12 is a member for fixing the optical fiber 1 accommodated in the groove of the heat sink 11. The first lid member 12 is fixed to the heat sink 11 in a state where the resin clad 3 of the optical fiber 1 is pressed. For example, the first lid member 12 is fixed to the heat sink 11 with a bolt or an adhesive. With this first lid member 12, the optical fiber 1 is reliably brought into contact with the heat sink 11.

  The second lid member 13 is a member for fixing the optical fiber 1 accommodated in the groove of the heat sink 11. The second lid member 13 is fixed to the heat sink 11 in a state where the covering member 4 of the optical fiber 1 is pressed. For example, the second lid member 13 is fixed to the heat sink 11 with a bolt or an adhesive. By this second lid member 13, the optical fiber 1 is reliably brought into contact with the heat sink 11. The second lid member 13 is a separate member from the first lid member 12, but may be formed integrally with the first lid member 12.

  When a gap between the optical fiber 1 and the heat sink 11 is generated, heat radiation grease may be used between the optical fiber 1 and the heat sink 11 in order to fill the gap. The heat dissipating grease may contain, for example, silicon as a main component and metal particles.

[Modification]
As mentioned above, although embodiment of this invention was described, this invention is not limited to these, A various change is possible unless it deviates from the meaning of this invention.

Modification 1
In the said embodiment, although the coating | coated member 4 is comprised from two members, the 1st coating | coated part 41 and the 2nd coating | coated part 42, it is not limited to this in particular. For example, the covering member 4 may be composed of one member. In this case, a through hole is formed in the covering member 4, and the tip 21 is heated and softened while the tip 21 is passed through the through hole.

Modification 2
In the said embodiment, although the optical path member is comprised from the core 2, it is not limited to this in particular. For example, as shown in FIG. 7, the optical path member may be composed of a core 2 and a glass cladding 6. That is, the optical path member and the resin clad 3 may be combined to form a double clad fiber. The core 2 can be formed of the same material as in the above embodiment. The glass clad 6 is formed so as to cover the outer peripheral surface of the core 2. The glass cladding 6 can be made of the same material as the core 2, for example. The glass clad 6 has a refractive index lower than that of the core 2 and higher than that of the resin clad 3. The glass clad 6 does not contain a laser medium.

  The resin clad 3 covers the outer peripheral surface of the glass clad 6 except for the tip 61 of the glass clad 6. That is, the resin clad 3 is not formed on the outer peripheral surface of the front end portion 61 of the glass clad 6. The covering member 4 covers the outer peripheral surface of the tip 61 of the glass clad 6.

Modification 3
In the said embodiment, although the front-end | tip part 21 of the core 2 and the coating | coated member 4 were substantially the length of the axial direction, it is not limited to this in particular. For example, the tip portion 21 may be longer than the covering member 4. That is, a gap may be formed between the covering member 4 and the resin clad 3. Thereby, when heating the front-end | tip 21 via the coating | coated member 4 in order to soften the front-end | tip part 21, it can prevent that the resin clad 3 is thermally damaged. When a gap is formed between the covering member 4 and the resin clad 3, as shown in FIG. 8, as in the formation of the resin clad 3, a thermosetting resin or an ultraviolet ray is formed in the gap. A cured resin 5 can be applied and the resin can be cured.

Modification 4
When there is a gap between the optical path member and the covering member 4, the gap may be filled with a resin filling member having a refractive index lower than that of the optical path member. The filling member is preferably formed of an ultraviolet curable resin or a thermosetting resin.

DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Core 3 Resin clad 4 Coating | coated member 41 1st coating | coated part 42 2nd coating | coated part

Claims (7)

An optical path member of a filament that becomes a path of light;
A resin-made cladding that covers the outer peripheral surface of the optical path member except the tip of the optical path member;
A covering member that covers the outer peripheral surface of the tip of the optical path member;
A resin filling member filled in a gap between the outer peripheral surface of the optical path member and the inner peripheral surface of the covering member;
The covering member has a refractive index lower than that of the optical path member and higher thermal conductivity than the resin clad,
The filling member has a lower refractive index than the optical path member,
Optical fiber. The optical path member is composed of a glass core,
The optical fiber according to claim 1. The optical path member is composed of a glass core and a glass clad covering the outer peripheral surface of the core.
The optical fiber according to claim 1. The covering member is transparent,
The optical fiber according to claim 1. The covering member has a higher melting point or softening point than the resin clad,
The optical fiber according to claim 1. The filling member is formed of an ultraviolet curable resin or a thermosetting resin.
The optical fiber according to claim 6.
(A) a step of preparing an optical path member of a filament covered with a resin cladding other than the tip;
(B) preparing a covering member in which a through hole is formed;
(C) disposing a tip portion of the optical path member in a through hole of the covering member;
(D) including a step of filling a resin filling member into a gap between the outer peripheral surface of the optical path member and the inner peripheral surface of the covering member;
The covering member has a lower refractive index than the optical path member and a higher thermal conductivity than the resinous cladding,
Optical fiber manufacturing method

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