JP3941063B2 - Fiber laser oscillator - Google Patents

Description

  The present invention relates to a fiber laser oscillating apparatus for generating excitation light in an optical fiber having a core member containing a laser active substance therein, and generating and amplifying laser light inside the core member.

Conventionally, various fiber laser oscillating devices have been proposed that can obtain very high quality laser light with high efficiency by using excitation light having relatively poor beam quality.
As a conventional fiber laser oscillating device, as shown in FIG. 6A, an end face pumped fiber laser oscillating device composed of an optical fiber 10 and condensing lenses 24 and 26 is known. The optical fiber 10 has a core member 12 doped with a rare earth element such as neodymium (Nd), which is a laser active material, in the longitudinal direction, and the core member 12 is covered with a clad member 14. In the example shown in FIG. 6A, the clad member 14 is further covered with a second clad member 16. Here, by appropriately setting the diameter of the core member 12 and the refractive indexes of the core member 12, the clad member 14, and the second clad member 16, a fiber laser oscillation capable of generating high-quality laser light with relatively high efficiency. The apparatus can be realized relatively easily (in this case, assuming that the refractive index of the core member 12 is n1, the refractive index of the cladding member 14 is n2, and the refractive index of the second cladding member 16 is n3), n1>n2> n3).
When pumping light Lin (semiconductor laser or the like) is incident from one end face Ta of the optical fiber 10 through the condenser lens 24, the pumping light Lin repeats total reflection in the clad member 14 of the optical fiber 10 and propagates. The core member 12 is excited. In the excited core member 12, laser oscillation is generated, and only the laser beam Lout that can be totally reflected in the core member 12 from the generated light remains and propagates in the core member 12. Therefore, by using the core member 12 having a small NA (numerical aperture) and a small diameter, it is possible to obtain a very high quality laser beam Lout (the beam quality of the laser beam is determined by the radius and the emission angle of the emitted light) The smaller the product, the higher the beam quality). And the laser beam Lout emitted from the end surface Tb is condensed using the condensing lens 26, and the condensed laser beam Lout is used for various uses.
However, in the end face pump type fiber laser oscillation device shown in the example of FIG. 6A, it is difficult to increase the incident pump light Lin (the area of the end face Ta of one optical fiber 10 is very small). Therefore, it is very difficult to generate the laser beam Lout having a relatively large output.

Therefore, in the prior art disclosed in Patent Document 1, as shown in FIGS. 6B and 6C, the core member 12 is arranged in a plane, and the prisms 4a and 4b are further arranged on the upper surface. A laser beam generator that increases the output of the laser beam to be generated by making the excitation beam Lin incident from a larger area (injecting the excitation beam from the side instead of the end surface of the optical fiber) via 4a and 4b. Proposed. In the prior art disclosed in Patent Document 1, the incident excitation light Lin is reflected at the boundary between the cladding member 14 and the glass flat plate 17 so that the excitation light Lin is confined in the cladding member 14. The incident angle, the refractive index of the prism 4a, etc. are adjusted.
Japanese Patent Laid-Open No. 2001-15835

Generally, in the optical fiber 10 used for the fiber laser oscillation device, the diameter of the clad member 14 is several hundred to 1000 [μm]. When a semiconductor laser is used as the pumping light Lin of the conventional end face pump type fiber laser oscillation device, it is difficult to focus the pumping light having a relatively large output on the fiber end face Ta (the semiconductor laser generally has a beam quality). Because of poor light collection.
Further, in the prior art described in Patent Document 1, since the prisms 4a and 4b must be prepared, the fiber laser oscillation device becomes relatively expensive. The pumping light Lin is incident not from the end face of the optical fiber but from the side surface. When the pumping light is incident, the pumping light Lin is not incident at a predetermined angle with respect to the axial direction of the optical fiber. The excitation light Lin cannot be confined to the light source, and high accuracy is required for the incident angle, and the excitation light Lin needs to be incident as parallel light. For this reason, it is very difficult to use a semiconductor laser having a relatively poor light condensing property as the excitation light Lin.
The present invention has been devised in view of the above points, and provides a fiber laser oscillation device that can receive more excitation light and can obtain a higher-power laser beam. This is the issue.

  The fiber laser oscillation device described in the present embodiment generates laser light by making excitation light incident on an optical fiber having a core member containing a laser active substance in the longitudinal direction and covering the core member with a cladding member. In this fiber laser oscillation device, at any position in the longitudinal direction of the optical fiber, at least a core removing member is left, and excitation light is incident from a clad end surface formed by the cladding removing unit.

  The fiber laser oscillation device described in the present embodiment is the fiber laser oscillation device described above, and the core member is shifted from the center to a predetermined position in a cross section perpendicular to the longitudinal direction of the optical fiber.

  Further, the fiber laser oscillation device described in the present embodiment is the fiber laser oscillation device described above, and a plurality of pump lights are emitted from at least one end surface of the optical fiber end surface and the clad end surface formed at an arbitrary position. Incident.

As means for solving the above-mentioned problems, the first invention of the present invention is a fiber laser oscillation device as described in claim 1.
The fiber laser oscillation device according to claim 1, wherein the clad removal portion and the clad end face are formed at an appropriate interval in one optical fiber, and the plural clad end faces and the optical fiber end faces are gathered so as to spread two-dimensionally. A collective end face is formed, and excitation light is incident from the collective end face.

According to a second aspect of the present invention, there is provided a fiber laser oscillation device as set forth in the second aspect.
The fiber laser oscillation device according to claim 2 is the fiber laser oscillation device according to claim 1, wherein the clad end face and the optical fiber end face are polygonal in cross section, and are arranged without gaps on the collective end face. .
According to a third aspect of the present invention, there is provided a fiber laser oscillation device as set forth in the third aspect.
A fiber laser oscillation device according to claim 3 is the fiber laser oscillation device according to claim 1 or 2, wherein the clad removal portion and the clad end face are formed at a plurality of locations in a longitudinal direction. Each of the clad removal portions is exposed from each of the clad end faces by bending the optical fiber to form the collective end face.

If the fiber laser oscillation device described in the present embodiment is used, not only the excitation light is incident from the end face of the optical fiber, but also the excitation light is incident from the clad end face provided at an arbitrary position in the longitudinal direction of the optical fiber. be able to. For this reason, since more excitation light can be incident, a laser beam with higher output can be obtained.
When removing the clad member so as to leave only the core member, the area of the clad end face can be increased and more excitation light can be incident from the clad end face.
Moreover, when removing the clad member, if the clad member having a predetermined thickness is left on the outer periphery of the core member, loss due to damage to the core member and adhesion of dust (diffuse reflection of propagating light, etc.) can be suppressed. .

  Further, according to the fiber laser oscillation device described in the present embodiment, the core member is located at a position deviated from the center at the cladding end face and the fiber end face on which the excitation light is incident. It is easy to make the excitation light incident, the efficiency can be further improved, and a laser beam with higher output can be obtained.

  Further, according to the fiber laser oscillation device described in the present embodiment, since a plurality of excitation lights are incident from at least one end face of the end face of the optical fiber and the end face of the clad, higher output laser light can be obtained.

  According to the fiber laser oscillation device of the first aspect, the pumping light is not incident from the end faces of the optical fiber end face and the clad end face, but the optical fiber end face and the clad end face are collected at the place of the pumping light. For this reason, even when it is difficult to condense the diameter of the pumping light below the diameter of one optical fiber, the pumping light can be incident efficiently, and a laser beam with higher output can be obtained. Can do.

  According to the fiber laser oscillation device of claim 2, the shape of the end face is made polygonal (triangle, quadrangle, hexagon, etc.) so that the end face of the clad and the end face of the optical fiber are arranged as close as possible to the collective end face. ing. For this reason, excitation light can be incident efficiently and a laser beam with higher output can be obtained.

The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an embodiment of a fiber laser oscillation device 1 of the present invention.
[First embodiment (FIG. 1)]
In the first embodiment, the clad end surface S perpendicular to the longitudinal direction is formed by forming the clad removal portion 10R from which the clad member 14 is removed at least at the core member 12 at any position in the longitudinal direction of the optical fiber 10. And the excitation light Lin is also incident from the cladding end surface S. As a result, more pumping light can be made incident than in the conventional end face pumped fiber laser oscillation device, and a laser beam with higher output can be generated.

The optical fiber 10 has a core member 12 containing a laser active substance (rare earth element such as Nd) in the longitudinal direction, and the core member 12 is covered with a clad member 14 having a refractive index lower than that of the core member.
In the example shown in FIG. 1A, the clad end surface S is formed by removing the clad member 14 at two arbitrary locations (clad removal portion 10R) in one optical fiber 10. Note that any number of the clad removal portions 10R may be formed.
FIG. 1B shows the vicinity of the cladding removal portion 10R. The clad end face S is perpendicular to the longitudinal direction of the optical fiber 10, and two clad end faces S that are opposed by one clad removal portion 10R are formed.
In the optical fiber 10 used in the present embodiment, the core member 12 is doped with a rare earth element Nd (neodymium) as a laser active material, and a semiconductor laser having a wavelength of 800 [nm] is used as excitation light. In this case, laser light having a wavelength of 1064 [nm] is generated. The diameter φcore of the core member 12 is about 10 to 100 [μm], and the diameter φclad of the clad member 14 is about several hundred to 1000 [μm]. Further, the diameter φr in the cladding removal portion 10R is formed to be larger by about 0 to several tens [μm] than the diameter of the core member 12.

If the refractive index of the core member 12 is appropriately set so that “refractive index of the core member 12> refractive index of air” is satisfied, the cladding removal unit 10R causes the laser light generated inside the core member 12 to be emitted. Since it can be totally reflected inside and confined, at least the core member 12 should be left. Of course, the clad member 14 having a predetermined thickness may be left.
FIG. 1C shows a cross section perpendicular to the longitudinal direction of a general optical fiber 10 used in a fiber laser oscillation device. The outer periphery of the core member 12 (fluoride glass doped with a rare earth element) is covered with a clad member 14 (fluoride glass or the like) (refractive index of the core member 12> refractive index of the clad member 14), and the outer periphery of the clad member 14 is covered. Cover with the second clad member 16 (UV resin or the like) (refractive index of the clad member 14> refractive index of the second clad member 16), and further cover the outer periphery of the second clad member 16 with the covering member 19 (covering resin or the like). Yes. In the present embodiment, the optical fiber 10 is used. However, the optical fiber 10 is not limited to this configuration.
The excitation light Lin is not intended to propagate but is intended to be confined in the clad member 14 and applied to the core member 12, so that the covering member 19 that totally reflects the excitation light Lin may be selected.
The length of the optical fiber 10 from the end face Ta (or Tb) to the clad end face S of the optical fiber 10 and the length of the optical fiber 10 from the clad removal part 10R to the clad removal part 10R are about 5 to 10 [m. ]. If this length is not appropriate, the incident excitation light Lin reaches the end surface S (or the end surfaces Ta and Tb) before exciting the core member 12 and is emitted from the cladding member 14.

Next, components in this embodiment and functions of the components will be described with reference to FIG.
The pumping light incident device 20A is disposed at a position facing one end face Ta of the optical fiber 10, and the pumping light incident device 20B is disposed at a position facing the other end face Tb of the optical fiber 10. Further, the excitation light incidence device 20 </ b> C is disposed at a position substantially opposite to each cladding end surface S.
The excitation light incident device 20C condenses the excitation light emitting means 20 (semiconductor laser array or the like), a collimator lens 22 that converts the emitted excitation light Lin into parallel light, and the excitation light Lin converted into parallel light. And a condensing lens 24. Various other configurations of the lens group including the collimating lens 22 and the condenser lens 24 are conceivable. Then, the cladding removing unit 10R is curved so that each of the excitation light incidence devices 20C can be disposed at a position where each cladding end surface S of the cladding removing unit 10R faces. Then, the excitation light Lin emitted from the excitation light incidence device 20C is incident on the clad end surface S facing the excitation light incidence device 20C.

The excitation light incidence device 20A is provided with a mirror 30a (such as a dichroic mirror) that transmits the excitation light Lin and reflects the laser light Lout generated inside the core member 12 with respect to the excitation light incidence device 20C. The mirror 30 a is disposed in parallel with the end face Ta of the optical fiber 10.
The collimating lens 22 and the condensing lens 24 are the same as the excitation light incident device 20C in that the excitation light Lin emitted from the excitation light emitting means 20 is converted and condensed into parallel light. However, the laser light Lout generated in the core member 12 is emitted from the core member 12 on the end face Ta of the optical fiber 10 to the excitation light incident device 20A.
The laser light Lout emitted from the core member 12 on the end face Ta of the optical fiber 10 is converted into parallel light by the condenser lens 24 (the condenser lens 24 serves as a collimator lens) and reflected by the mirror 30a. The The laser light Lout reflected in the state of parallel light is condensed by the condenser lens 24 and is incident on the core member 12 on the end face Ta (returned to the core member 12 on the end face Ta).

The pumping light incident device 20B transmits a pumping light Lin to the pumping light incident device 20C and reflects the laser light Lout generated inside the core member 12, and an output laser condensing lens. 26 is added. The mirror 30b is disposed at an angle of about 45 ° with the end face Tb of the optical fiber 10.
The collimating lens 22 and the condensing lens 24 are the same as the excitation light incident device 20C in that the excitation light emitted from the excitation light emitting means 20 is converted and condensed into parallel light. However, the laser light Lout generated in the core member 12 is emitted from the core member 12 on the end face Tb of the optical fiber 10 to the excitation light incident device 20B.
The laser light Lout emitted from the core member 12 on the end face Tb of the optical fiber 10 is converted into parallel light by the condenser lens 24 (the condenser lens 24 serves as a collimating lens), and is output by the mirror 30b. Reflected in the direction of the condenser lens 26 (taken out in the direction of the output laser condenser lens 26). The laser beam Lout reflected in the state of parallel light is condensed by the output laser condenser lens 26 and can be used for various applications.

  In the present embodiment, an arbitrary number of cladding end faces S can be formed and more excitation light can be incident on a conventional end face pumped fiber laser oscillation device. In the example shown in FIG. 1C, since four excitation light incidence devices 20C are added to the conventional excitation light incidence devices 20A and 20B, about three times as much excitation light Lin can be incident. High output laser light Lout can be obtained.

[Second embodiment (FIGS. 2 and 3)]
In the second embodiment, the structure of the optical fiber 10 is different from that of the first embodiment.
As shown in FIG. 2, the optical fiber 10 is formed so that the position of the core member 12 is shifted from the center P of the cross section by a predetermined distance D in the cross section perpendicular to the longitudinal direction of the optical fiber 10. Is different. Thereby, the excitation light Lin can be more easily incident from the clad end surface S.
If the core member 12 is located at a position substantially at the center P of the clad end surface S, a part of the excitation light Lin hits the core member 12 curved by the clad removal portion 10R and is reflected, and the clad is appropriately formed. The end surface S may not be reached. However, according to this embodiment, the vicinity of the center of the cladding end surface S is a flat surface, and the core member 12 does not get in the way, so that more excitation light Lin can be incident from the cladding end surface S.

  Also, as shown in FIG. 3, a plurality of excitation light incidence devices 20C are arranged at positions corresponding to the clad end face S (or the end face Ta or Tb of the optical fiber 10) and at an appropriate incident angle. A plurality of excitation lights Lin can be incident from one end face. In this case, even when the pumping light Lin is used, the core member 12 has the cladding end surface S (or the end surface Ta of the optical fiber 10) even if the beam quality is slightly inferior (the condensing diameter error is slightly large or the condensing diameter itself is slightly large) Alternatively, since it is deviated from the center P of Tb), more excitation light Lin can be incident from the cladding end surface S (or the end surface Ta or Tb of the optical fiber 10).

● [Third Embodiment (FIG. 4)]
The third embodiment is different from the first embodiment in the method of bending the cladding removal portion 10R.
As shown in FIG. 4A, the optical fiber 10 is folded by 180 ° at the clad removal portion 10R, and a collective end face SS in which the clad end face S (and the end face Ta or Tb of the optical fiber 10) is bundled is formed. Then, a large output laser beam Lout can be obtained by making the large output pump light Lin having a diameter larger than the diameter of the clad end surface S incident from the collective end surface SS sufficiently wider than the clad end surface S.
Moreover, the shape of the cross section perpendicular | vertical to the longitudinal direction of the optical fiber 10 is preferably a polygonal shape that can be arranged with as little gap as possible. For example, the aggregate end face SS can be formed without a gap by forming the cross-sectional shape into a triangle, or making it a quadrangle or hexagon as shown in FIGS. 4B and 4C.

4B and 4C, the core member 12 is drawn from both ends of the optical fiber 10, and the laser light Lout output from one end face of the core member 12 is converted into parallel light by the condenser lens 24. After (the condensing lens 24 plays the role of a collimating lens), the light is reflected by the mirror 30a, further condensed by the condensing lens 24, and returned to the core member 12. Further, after the laser beam Lout output from the other end face of the core member 12 is converted into parallel light by the collimator lens 22, it is further condensed by the output laser condenser lens 26 to extract the laser beam Lout. In this case, excitation light Lin having a larger output is incident from the collective end face SS from an excitation light incident device (excitation light incident device not including the mirrors 30a and 30b) having the same configuration as the excitation light incident device 20C.
As a result, it is possible to use a pumping light incident device in which the output of the pumping light Lin is large but it is difficult to make the condensing diameter smaller than the diameter φclad of the clad member 14 of the optical fiber 10, and a laser beam with higher output Lout can be obtained.
It is also easy to arrange a plurality of excitation light incidence devices at positions corresponding to the collective end face SS so that more excitation light is incident.

[Fourth embodiment (FIG. 5)]
The fourth embodiment is a fiber laser oscillation device having the simplest configuration in which the pumping light incidence device 20C is disposed at a position facing the cladding end surface S of the plurality of cladding removal portions 10R without using the mirrors 30a and 30b. It is an example.
In the configuration of the fourth embodiment, the number of cladding end faces S and the number of excitation light incidence devices 20C may be selected so that laser light Lout having a target output can be obtained.

As described above, if the fiber laser oscillation device 1 according to the present embodiment is used, the pumping light Lin can be incident from a plurality of locations of the single optical fiber 10, so that the total pumping light Lin is increased. Therefore, the laser beam Lout having a higher output can be obtained.
Further, when the diameter φclad of the clad member 14 is increased in order to increase the excitation light Lin, the relative ratio of the cross-sectional area of the core member 12 to the cross-sectional area of the clad member 14 is reduced, and total reflection is performed in the clad member 14. However, the probability of excitation by hitting the core member 12 is lowered, and the oscillation efficiency is lowered. However, in the fiber laser oscillation device 1 shown in the present embodiment, since it is not necessary to increase the diameter φclad of the clad member 14, high oscillation efficiency can be maintained.
Further, in the conventional fiber laser oscillation device that makes the excitation light incident from the side surface, an apparatus (such as a prism) for making the incident light from the side surface of the optical fiber 10 and an adjustment for confining the incident excitation light Lin (to the excitation light prism) In this embodiment, the pumping light Lin is incident from the end face of the optical fiber 10, although it is estimated that various cost increase factors and error factors such as the beam quality of the pumping light are included. With a simpler configuration, the cost can be reduced and the error factor can be reduced.

The fiber laser oscillation device 1 of the present invention is not limited to the shape, configuration, structure, and the like described in the present embodiment, and various modifications, additions, and deletions can be made without changing the gist of the present invention.
The numerical values used in the description of the present embodiment are examples, and are not limited to these numerical values.
In the present embodiment, a semiconductor laser is used as the excitation light Lin, but the present invention is not limited to this.

  The fiber laser oscillation device 1 of the present invention can be applied to various devices using laser light such as a laser processing device.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram (1st Embodiment) of one Embodiment of the fiber laser oscillation apparatus 1 of this invention. It is a figure explaining the structure of the optical fiber 10 in 2nd Embodiment. In 2nd Embodiment, it is a figure explaining the example which injects several excitation light Lin from one end surface. It is a figure explaining 3rd Embodiment. It is a figure explaining 4th Embodiment. It is a figure explaining the conventional fiber laser oscillation apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fiber laser oscillation apparatus 10 Optical fiber 10R Clad removal part 12 Core member 14 Clad member 16 2nd clad member 19 Coating | coated member 20A-20C Excitation light incident device 20 Excitation light emitting means 22 Collimating lens 24 Condensing lens 26 Output laser condensing Lens 30a, 30b Mirror S Clad end face Ta, Tb Optical fiber end face Lin Excitation light Lout (Output) Laser light

Claims (3)

A fiber laser oscillating device for generating laser light by making excitation light incident on an optical fiber having a core member containing a laser active substance in the longitudinal direction and covering the core member with a cladding member,
At a plurality of locations in the longitudinal direction of one optical fiber from one optical fiber end surface to the other optical fiber end surface, a clad removal portion that leaves at least a core member and a clad end surface formed by the clad removal portion are formed at a plurality of locations. Has been
The length of the part not including the cladding removal part from the optical fiber end face to the cladding end face and the part not including the cladding removal part from the cladding end face to the cladding end face are opposite to the excitation light incident from the optical fiber end face or the cladding end face. It is set to a length that can excite the core member before reaching the side cladding end face or optical fiber end face,
A collective end face is formed by gathering a plurality of clad end faces and optical fiber end faces so as to spread two-dimensionally , and has a configuration in which excitation light is incident on the collective end face.
A fiber laser oscillation device. The fiber laser oscillation device according to claim 1,
The cross-sectional shape perpendicular to the axis of the optical fiber is formed in a polygon, and a plurality of cladding end faces and optical fiber end faces are arranged without gaps at the collective end face.
A fiber laser oscillation device.   The fiber laser oscillation device according to claim 1 or 2,
  Each of the clad removal portions is separated from each of the clad end surfaces by bending the optical fiber in which the clad removal portion and the clad end surface are formed at a plurality of positions in the longitudinal direction to form the collective end surface. Exposed,
A fiber laser oscillation device.

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