JP2005200277A - Method for manufacturing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber capable of more efficiently producing laser light by exciting a core member with a larger amount of exciting light in fiber laser oscillation. <P>SOLUTION: In the method for manufacturing the optical fiber 1, the core member 30 is arranged at a marginal part of a clad member 10 in a section perpendicular to the longitudinal direction of the optical fiber 1, and the core member 30 is helically arranged to the longitudinal direction. One or more core members 30 are arranged in the longitudinal direction of the optical fiber 1 so that the core members 30 are located at the marginal part of the clad member 10 in the section perpendicular to the longitudinal direction of the optical fiber 1. Then, the clad member 10 is heated until the clad member becomes flowable. Furthermore, the center of the section perpendicular to the longitudinal direction of the optical fiber is used as the central axis CZ around which the optical fiber 1 is twisted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing an optical fiber used for fiber laser oscillation having a core member containing a laser active substance and a clad member that transmits excitation light.

Conventionally, for fiber laser oscillators that can obtain very high-quality laser light with high efficiency using pump light with relatively poor beam quality, optical amplifiers that can perform high-speed, large-capacity, and long-distance transmission Various optical fibers to be used have been proposed.
An optical fiber used for a fiber laser is usually a core member at the center of a cross section (a fiber shape with a diameter of about 2 to 12 [μm] doped with rare earth elements (Nd, Er) and the like that transmits single mode laser light). have. The laser beam is confined in the core member by having a clad member having a lower refractive index than the core member (a first clad member that transmits the excitation light) around the core member. Further, the second cladding member having a refractive index lower than that of the first cladding member is provided around the first cladding member, so that the excitation light is confined in the first cladding member.
When the excitation light incident on the optical fiber passes through the core member (when it collides with the core member), the rare earth element in the core member is excited to generate laser light, and single-mode laser light is generated in the core member. Remains. Since this laser beam has a small diameter (depending on the diameter of the core member) and a small divergence angle (depends on the wavelength of the generated laser beam, the refractive index of the core member and the first cladding member, etc.), the beam quality (The beam quality of the laser light is expressed by the product of the radius of the emitted light and the half angle of the spread angle of the emitted light, and the smaller the product, the higher the beam quality).

As shown in FIG. 4A, a conventional general optical fiber 1a (an optical fiber used for fiber laser oscillation) has a longitudinal direction of a cylindrical first clad member 10 (Z-axis direction in FIG. 4A). ), The core member 30 containing the laser active substance is disposed. FIG. 4B shows a cross section perpendicular to the longitudinal direction of the optical fiber 1a (cross section BB in FIG. 4A). As shown in FIG. 4B, in the conventional general optical fiber 1a, the core member 30 is disposed at the center portion of the first cladding member 10 in a cross section perpendicular to the longitudinal direction.
When the excitation light Lin is incident from the end face perpendicular to the longitudinal direction of the optical fiber 1a, the incident excitation light Lin proceeds while being totally reflected in the first cladding member 10. When the excitation light Lin that travels while being totally reflected in the first cladding member 10 collides with the core member 30 (accidentally), the laser light is excited in the core member 30.

In the general optical fiber 1a, the diameter of the core member 30 is set to about 2 to 12 [μm] in order to obtain higher quality laser light, and more pumping is performed for the purpose of obtaining higher output laser light. In order to make light incident, the diameter of the first cladding member 10 is about 100 [μm]. Therefore, the cross-sectional area of the core member 30 with respect to the cross-sectional area of the first cladding member 10 is very small. For this reason, as shown in FIG. 4B, the excitation light Lin does not collide with the core member 30 and circulates along the outer periphery of the first cladding member 10 while being totally reflected in the first cladding member 10. May end up. Further, as shown in FIG. 4C, an optical fiber having a rectangular cross-sectional shape of the first cladding member 10 has been proposed in order to further reduce the pumping light Lin that circulates. In some cases, the excitation light Lin is generated.
Further, since the excitation light Lin has a relatively poor beam quality, it is very difficult to aim the light so as to collide with the core member 30.

Therefore, for example, in the field of the fiber laser oscillation device, as shown in FIG. Excitation light is incident using the prism 54 (the laser light output from the semiconductor laser generator 58 is converted into parallel light by the collimator lens 56 and incident on the prism 54). A fiber laser oscillating device has been proposed in which the laser output is further improved by making it circulate in a spiral shape while reflecting (see, for example, Patent Document 1).
Further, for example, in the field of optical amplifiers, as shown in FIGS. 4D to 4G, the first clad member 10 of the optical fiber has at least three core members 30 and at least two locations in the longitudinal direction. A multi-core fiber 1b has been proposed in which a region 23 having a changed mode field diameter is provided and the gain wavelength characteristic can be flattened not only when the gain is low but also when the gain is high (for example, a patent) Reference 2).
Japanese Patent Laid-Open No. 11-284255 Japanese Patent Laid-Open No. 10-242548

In the fiber laser oscillation device described in Patent Document 1, since the exposed core member 30 is wound around the outer peripheral surface of the cylindrical body 52, the core member 30 is estimated to be easily broken.
Further, in the fiber laser oscillation device described in Patent Document 1, it is necessary to enter the excitation light using the prism 54 and to enter the excitation light so as to go around the outer peripheral surface of the cylindrical body 52. When entering light, it is very difficult to circulate all of the incident excitation light (for example, when the diameter of the excitation light is increased, the incident angle to the outer peripheral surface of the cylindrical body 52 is increased within the cylindrical body 52. There may be more excitation light that does not satisfy the angle for total reflection).
Further, the multi-core fiber 1b described in Patent Document 2 has a plurality of core members 30, but as shown in FIGS. 4E to 4G, the core member 30 is disposed substantially at the center of the cross section. Therefore, it is estimated that the probability that the excitation light that circulates along the outer periphery of the first cladding member 10 collides is low.
The present invention was devised in view of such points, and in fiber laser oscillation, an optical fiber that can excite a core member with more pumping light and can obtain laser light more efficiently. It is an object to provide a manufacturing method.

As means for solving the above-mentioned problems, the first invention of the present invention is an optical fiber manufacturing method as described in claim 1.
In the optical fiber manufacturing method according to claim 1, in the cross section perpendicular to the longitudinal direction of the optical fiber, the core member is disposed at the edge of the cladding member, and the core member has a spiral shape in the longitudinal direction. A method of manufacturing an optical fiber arranged to be one or more in the longitudinal direction of the optical fiber so that the core member is positioned at the edge of the cladding member in a cross section perpendicular to the longitudinal direction of the optical fiber. The core member is arranged. Then, the clad member is heated until it can flow. Furthermore, this is a manufacturing method in which the optical fiber is twisted so that the center of the cross section perpendicular to the longitudinal direction of the optical fiber becomes the central axis of twisting.

  If the manufacturing method of the optical fiber of Claim 1 is used, it can manufacture more easily the optical fiber arrange | positioned so that a core member may become spiral shape toward the longitudinal direction at the edge of a clad member. it can.

The best mode for carrying out the present invention will be described below with reference to the drawings.
● [Optical fiber structure (Figure 1)]
FIG. 1A is a schematic external view of an optical fiber 1 manufactured by the “optical fiber manufacturing method” in the present embodiment.
The optical fiber 1 has a core member 30 in the longitudinal direction, and the core member 30 is doped with a laser active material (such as Nd and Er which are rare earth elements). And in the cross section perpendicular | vertical to the longitudinal direction of the optical fiber 1, while the core member 30 is arrange | positioned at the edge part of the clad member 10 (henceforth the 1st clad member 10), the core member 30 is a longitudinal direction It arrange | positions so that it may become a spiral shape.
Further, as shown in FIG. 3A, the outer periphery may be further covered with the second clad member 20, or may be covered with a coating or the like that totally reflects the excitation light Lin.
Further, the refractive index relationship of each member is as follows: the refractive index of the core member 30 (n30)> the refractive index of the first cladding member 10 (n10) ≧ the refractive index of the second cladding member 20 (n20)> the refractive index of air. It is set to be. Note that the second cladding member 20 may be omitted.
Thereby, even if the excitation light (for example, semiconductor laser light) incident from the end face of the optical fiber 1 travels while being totally reflected by the outer peripheral portion of the first cladding member 10, the excitation light collides with the core member 30 more reliably. Thus, the laser active material of the core member 30 can be excited to generate output laser light.

In addition, the optical fiber 1α shown in FIG. 1B has a single core member 30 along the longitudinal direction at the edge of the first clad member 10 with respect to the conventional optical fiber 1a shown in FIG. Are arranged. In the optical fiber 1α shown in FIG. 1B, when the excitation light Lin circulates as shown in FIG. 4B, the probability that the excitation light Lin collides with the core member 30 and is excited than in FIG. 4B. Is estimated to be high.
The optical fiber 1β shown in FIG. 1C has a higher probability that the excitation light Lin collides with the core member 30 and is excited than the optical fiber 1α shown in FIG. This is an example of increasing the number. However, since there are a plurality of core members 30, it is difficult to make the diameter of the output laser light smaller than the diameter obtained by bundling the end faces of the plurality of core members 30.
An optical fiber 1γ shown in FIG. 1 (D) has one core member 30 and one end surface of the optical fiber 1γ and the other end surface of the optical fiber 1β shown in FIG. 1 (C). This is an example of reciprocating a plurality of times in the longitudinal direction. In this case, since the number of the core members 30 is one, the diameter of the output laser light is further reduced, and the beam quality is improved.

  The optical fiber 1 manufactured by the “optical fiber manufacturing method” described below (the optical fiber 1 shown in FIG. 1A) has a pumping light Lin more core than the optical fiber 1α shown in FIG. The probability of exciting the member 30 is high (high efficiency). Further, the diameter of the output laser beam is smaller than that of the optical fiber 1β shown in FIG. 1C (the beam quality is high). Moreover, since the diameter which curves the core member 30 is smaller than the optical fiber (gamma) shown in FIG.1 (D), the core member 30 is hard to bend.

● [Optical fiber manufacturing method (Figure 2)]
Next, an “optical fiber manufacturing method” in the present embodiment will be described with reference to FIGS.
First, as shown in FIG. 2A, the core member 30 is arranged in parallel with the longitudinal direction (Z-axis direction) at the edge of the first clad member 10. The material of the first clad member 10 and the core member 30 is selected from, for example, quartz glass, the same material is selected for the softening point, and the thermal expansion coefficient is substantially the same or the first clad member 10 is larger. It is preferable to select a material of such a kind. 2A includes the core member 30 inside the first clad member 10 so that the excitation light can be incident on the core member 30, but the first clad member 10 of FIG. The core member 30 disposed on the surface may be covered with a second cladding member (not shown).
And it heats until the 1st clad member 10 will be in the state which can flow (it heats to the temperature which can be processed).
Further, the optical fiber 1 is twisted so that the center (central axis CZ) of the cross section perpendicular to the longitudinal direction of the optical fiber 1 becomes the central axis of twisting.
Then, the optical fiber 1 in which the core member 30 having a spiral shape in the longitudinal direction is arranged at the edge of the first cladding member 10 is completed.

Further, as shown in FIG. 2C, more core members can be obtained by arranging a plurality of core members 30 parallel to the longitudinal direction at the edge of the first clad member 10 and heating and twisting in the same manner. An optical fiber 1 having a spiral shape 30 in the longitudinal direction is completed. 2C includes a plurality of core members 30 inside the first clad member 10 so that excitation light can be incident on the core member 30, but the first clad member as shown in FIG. 2D. The plurality of core members 30 arranged on the surface of 10 may be covered with a second cladding member (not shown).
Similarly, when heated and twisted from the state of the optical fiber 1γ in FIG. 1D, an optical fiber 1 in which more core members 30 spiral in the longitudinal direction is completed (in this case, the core member 30). One is himself).

● [Fiber laser oscillator using the manufactured optical fiber (Fig. 3)]
FIG. 3 (A) covers the periphery (side face excluding the end face) of the optical fiber 1 manufactured by the manufacturing method shown in FIG. 2 (C) with a solution-like ceramic precursor (a coating agent such as polysilazane). In this example, the second clad member 20 is formed by firing. In the example of FIG. 3A, the core member 30 includes an excess portion so as to protrude from the end surfaces of the first cladding member 10 and the second cladding member 20.
Then, as shown in FIG. 3B, excitation light Lin (semiconductor laser light or the like) is incident from one end face (incident end face) of the optical fiber 1. A mirror 46 (or coating or the like) that reflects the output laser light Lout is provided at the tip of the core member 30 on the incident end face side so as to be perpendicular to the axial direction of the core member 30.
Further, the core member 30 on the other end face (output end face) of the optical fiber 1 is bundled to reduce the diameter of the output laser light Lout. Then, a collimator lens 42 that converts the output laser light Lout into parallel light and a condenser lens 44 that condenses the output laser light Lout converted into parallel light to a smaller diameter are disposed. The condensed output laser light Lout in this way has high output and accuracy with higher beam quality, and can be used for various applications such as laser processing and laser welding.

The “optical fiber manufacturing method” of the present invention can be variously changed, added, and deleted without changing the gist of the present invention. Further, the shape, configuration, structure, and the like of the optical fiber 1 are not limited to the description of the embodiment.
The numerical values used in the description of the present embodiment are examples, and are not limited to these numerical values.
In this embodiment, a semiconductor laser is used as the excitation light Lin, but various types of excitation light can be used.

  The optical fiber 1 manufactured by the “optical fiber manufacturing method” of the present invention can be applied to various apparatuses using laser light such as a laser processing apparatus.

1 is a schematic external view of an optical fiber 1 manufactured by an “optical fiber manufacturing method” of the present invention. It is a figure explaining the "manufacturing method of an optical fiber" of this invention. It is a figure explaining the example of a fiber laser oscillation apparatus. It is a figure explaining the conventional optical fiber and a fiber laser oscillation apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber 10 1st clad member 20 2nd clad member 30 Core member 42 Collimating lens 44 Condensing lens 46 Mirror Lin Excitation light Lout (Output) laser beam

Claims (1)

In the method of manufacturing an optical fiber, the core member is arranged at the edge of the clad member in a cross section perpendicular to the longitudinal direction of the optical fiber, and the core member is arranged in a spiral shape in the longitudinal direction. There,
In the cross section perpendicular to the longitudinal direction of the optical fiber, one or more core members are arranged in the longitudinal direction of the optical fiber so that the core member is located at the edge of the cladding member,
Heat until the cladding is ready to flow,
Twist the optical fiber so that the center of the cross section perpendicular to the longitudinal direction of the optical fiber is the central axis of the twist,
An optical fiber manufacturing method characterized by the above.

Images