JP2000321470A - Optical fiber and laser machining apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the optical fiber which can securely prevent with a simple constitution even high-power light from being reflected. SOLUTION: A columnar quartz block 12 which has an about 10 to 30 mm diameter is fused and connected to both ends of an optical fiber which has its outer peripheral surface coated with a clad 22 and has a core 21 with a diameter of several hundreds of μm. An AR coating 25 is provided on the end surface where the laser light of the quartz block 12 is made incident or emitted. The power density of laser light decreases on the end surface of the quartz block 12 having a large area and hence never damages the AR coating 25. Even high-power laser light can securely be prevented from being reflected without being deformed in the beam shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber in which a clad is provided on an outer peripheral surface of a core and an antireflection coating is applied to an end face through which light enters and exits, and a laser beam machine equipped with the optical fiber.

[0002]

2. Description of the Related Art Conventionally, for example, in a laser beam machine, transmission efficiency in an optical system is reduced due to reflection at an end face of an optical fiber for guiding a laser beam, causing inconvenience due to return light. In an output laser beam machine, since even a very slight reflection may greatly affect the weldability, various methods are employed to prevent reflection at the end face of the optical fiber.

[0003] For example, as described in Japanese Patent Application Laid-Open No. 58-154482, a method is known in which both the input and output end faces of an optical fiber are polished so as to satisfy the condition of Brewster angle incidence. Japanese Patent Application Laid-Open No. 58-154482
According to the method described in the publication, as shown in FIG. 9, for example, a laser beam 51 emitted from an oscillator is condensed on an incident end face 54 of an optical fiber 53 by a condenser lens 52. The incident end face 54 is polished obliquely so that the incident angle becomes the Brewster angle, and there is no Fresnel reflection loss. Similarly, the output end face 55 is also subjected to Brewster angle polishing, and the output light is applied to the processing surface by the condenser lens 56.

However, the method of polishing such that the condition of Brewster angle incidence described in JP-A-58-154482 as shown in FIG. 9 is not suitable for a randomly polarized laser beam. There is a problem. That is, at the Brewster's angle incidence / emission, reflection occurs in polarized light other than p-polarized light, so that reflection cannot be prevented except for linearly polarized laser light. Further, since the angle of Brewster's angle incidence and emission is as large as about 56 °, there is also a problem that the shape of the beam emitted from the end face of the optical fiber is disrupted.

There is also known a method of reflecting the return light at a slight angle to the end face. However, similarly, it is not suitable for a randomly polarized laser beam, and there is a problem that the shape of the emitted beam is distorted.

[0006] Further, a method of directly applying an anti-reflection coating, that is, an AR coating to the core of an optical fiber is also known. However, if the AR coating is directly applied to the core of the optical fiber, the power density is extremely large. Power lasers can damage the AR coating.

Therefore, a configuration described in, for example, Japanese Patent Application Laid-Open No. 7-280154 is known. Japanese Patent Application Laid-Open No. 7-28
No. 1054 discloses a method in which a tip of an optical fiber is fusion-spliced to one end face of a coreless fiber having a flat refractive index distribution and a bending rate equal to the core of the optical fiber, and the coreless fiber is connected to the optical fiber. An end face opposite to the end face is inclined within 0 to 6 degrees with respect to a plane perpendicular to the optical axis, and is provided with an AR coating. And compared to the case where the AR coating is directly applied to the core of the optical fiber,
The leak and the angle in the coreless fiber prevent the interference by the return light.

[0008]

However, in the configuration described in Japanese Patent Application Laid-Open No. 7-28154, there is a possibility that the AR coating may be damaged because the area of the input / output surface of the optical fiber is small.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical fiber and a laser processing machine capable of reliably preventing reflection of high-output light with a simple configuration.

[0010]

According to a first aspect of the present invention, there is provided an optical fiber which guides light and has at least one of a core provided with a cladding on an outer peripheral surface and an end face of the core through which the light enters and exits. And a substantially columnar light-transmitting member having a refractive index substantially the same as the refractive index of the core, and an antireflection coating provided on an end face of the light-transmitting member through which the light enters and exits. An end face of the light transmitting member through which light enters and exits has an area capable of entering and exiting the light at a power density that does not damage the light of the antireflection coating. An optical fiber according to a second aspect is the optical fiber according to the first aspect, wherein the translucent member is quartz. According to a third aspect of the present invention, in the optical fiber according to the first or second aspect, the translucent member is a plane in which an end face through which light enters and exits and an end face connected to the core are parallel. . An optical fiber according to a fourth aspect is the optical fiber according to any one of the first to third aspects, wherein the connection between the core and the translucent member is fusion spliced. An optical fiber according to a fifth aspect is the optical fiber according to any one of the first to third aspects, wherein the connection between the core and the translucent member is an optical contact. According to a sixth aspect of the present invention, in the optical fiber according to any one of the first to fifth aspects, the translucent member has a substantially columnar shape having substantially the same outer diameter as the outer diameter of the cladding on an end face connected to the core. Are provided coaxially.
According to a seventh aspect of the present invention, in the optical fiber according to any one of the first to fifth aspects, the light-transmitting member has a diameter gradually decreasing toward an end face at an end face connected to the core, and a diameter dimension at the end. Is provided with a substantially frustum-shaped cone having substantially the same size as the outer diameter of the cladding. An eighth aspect of the present invention provides a laser processing machine including the optical fiber according to any one of the first to seventh aspects and a laser oscillator.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the configuration of a laser beam machine according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an end portion of an optical fiber of a laser beam machine according to the present invention. FIG. 2 is a perspective view of the same. FIG. 3 is a block diagram showing the laser beam machine.

Referring to FIG. 3, a laser beam machine 33 includes an optical fiber main body 31 and a laser oscillator 32.

As shown in FIGS. 1 to 3, the optical fiber main body 31 has a cladding 22 formed on the outer peripheral surface of a core 21 having, for example, a diameter of about several hundred μm, and a coating member 23 formed on the outer peripheral surface. Optical fiber 1 formed by coating
A cylindrical quartz block 12 having a diameter of about 10 to 30 mm and a length in the axial direction of about 20 to 30 mm, which is a light-transmitting member provided at each end of the optical fiber 11; It is composed of The quartz block 12 uses quartz having substantially the same refractive index as the core 21 as a material so as not to optically form a boundary surface with the core 21 of the optical fiber 11. Further, the quartz block 12 has an area where the laser light is to be expanded and a numerical aperture (N
A) and the bending rate of the quartz block 12 determine the axial length and the diameter, which are the thickness dimensions.

Further, an AR coating 25 which is an anti-reflection coating is applied to the front end surfaces of the quartz blocks 12 provided at both ends of the optical fiber 11.

The optical fiber 11 and the quartz block 1
2 is connected by fusion so that the core 21 and the clad 22 of the optical fiber 11 are not deformed as much as possible so that the beam shape of the laser light is not lost and propagated without loss.

In the optical fiber 11, at least the end faces of the core 21 and the clad 22 from which the covering member 23 has been peeled off are sufficiently polished so that air bubbles do not enter during fusion. Further, the laser beam emitted from the optical fiber 11 is polished vertically so as not to be distorted such as an ellipse.

Further, the fused surface 13 of the quartz block 12 with the optical fiber 11 and the distal end surface 14 on which the AR coating 25 is applied are sufficiently polished in the same manner as the optical fiber 11. Further, the fusion surface 13 and the tip surface 14
Are polished in parallel.

In the laser beam machine 33, one end of the optical fiber main body 31 is opposed to a portion of the laser oscillator 32 from which the laser light is emitted via the first condenser lens 34, that is, one end of the optical fiber main body 31 The end faces of the quartz block 12 provided with the AR coating 25 are opposed to each other. Further, the end of the optical fiber body 31 where the laser light is emitted, that is, the end face of the quartz block 12 on which the AR coating 25 is applied,
A second condenser lens 38 is disposed to face the object 3 to be irradiated.
9 is irradiated with a laser beam.

Next, the operation of the above embodiment will be described.

When the object 39 is irradiated with laser light for processing, the laser light emitted from the laser oscillator 32 is condensed by a first condenser lens 34 and provided at one end of the optical fiber main body 31. AR coating 2 on quarts block 12
Irradiate a relatively wide end face on which 5 is applied. Then, assuming that the laser beam is focused at the numerical aperture (NA) of the optical fiber 11, the quartz block 1 remains at the critical angle of the optical fiber 11.
2 and is focused on the end face 35 of the optical fiber 11.
Since the fused portion of the optical fiber 11 and the quartz block 12 passes through the quartz block 12 while maintaining the critical angle of the optical fiber 11, the AR coating 2
On the fifth side, the numerical aperture (NA) of the ordinary optical fiber 11 alone without the quartz block 12 is equal to the numerical aperture (NA).

Further, the laser light is emitted from the end face of the quartz block 12 on the other end on which the AR coating 25 is applied by guiding the optical fiber 11, and the processed surface of the irradiation object 39 is irradiated by the second condenser lens 38. It is led to.

As described above, in the above-described embodiment, the laser light is input to the end face of the optical fiber 11 by reducing the end face from which the laser light is input and output to a power density at which the AR coating 25 is not damaged by the laser light. Since the quartz block 12 having a diameter much larger than that of the optical fiber 11 having a large area to be emitted is connected, an AR coating 25 for preventing a high-power laser beam such as a laser beam machine 33 from being adversely affected by reflection. Laser light can be input and output without damaging the laser beam.

Further, since the quartz blocks 12 and 12 are provided at both ends of the optical fiber 11 where the laser light enters and exits, the laser coating is provided at the position of the AR coating 25 for preventing reflection when the laser light enters and exits. Since the power density of light is reduced, damage of the AR coating 25 can be reliably prevented.

In the above-described embodiment, the substantially cylindrical quartz block 12 is fused and described.
As shown in FIG. 5 and FIG.
6 and 7, a connecting portion having a diameter substantially equal to the diameter of the optical fiber 11 is integrally formed. A frusto-conical cone having substantially the same diameter as the diameter may be provided. According to the embodiment shown in FIGS. 4 and 5, and the embodiment shown in FIGS. 6 and 7, the operation of fusing with the optical fiber 11 becomes easy, and the manufacturability can be improved.

The optical fiber 11 has a quartz block 12
However, as shown in FIG. 8, for example, as shown in FIG. 8, a quartz block 12 may be connected to the optical fiber 11 by an optical contact, and a portion weak in strength may be reinforced and connected. At the time of this reinforcement, the cladding 22 is fixed so that the interface between the core 21 and the cladding 22 of the optical fiber 11 does not collapse.
Is connected to the quartz block 12. This FIG.
According to the embodiment shown in (1), light can be transmitted without loss without breaking the core 21 and the clad 22. The optical fiber 1
In the case where the diameter of the core 21 is as small as several hundred μm, fusion is suitable.

Furthermore, although quartz has been described as the light transmitting member, any transparent light transmitting member having the same refractive index as the core 21 of the optical fiber 11 and a flat refractive index distribution can be used. May be.

[0028]

According to the present invention, a light-transmissive member having a large area for entering and exiting light by reducing the end face on which light enters and exits to a power density at which the antireflection coating does not damage the light. Is connected to the end face from which the laser beam enters and exits, so that even a high-output laser beam such as a laser beam machine can emit and emit light without damaging an antireflection coating for preventing adverse effects due to reflection.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one end of an optical fiber main body according to an embodiment of the present invention.

FIG. 2 is a perspective view of the same.

FIG. 3 is a block diagram showing the laser beam machine according to the first embodiment;

FIG. 4 is a cross-sectional view of one end of an optical fiber main body showing another embodiment of the present invention.

FIG. 5 is a perspective view of the same.

FIG. 6 is a cross-sectional view of one end of an optical fiber main body, showing still another embodiment of the present invention.

FIG. 7 is a perspective view of the same.

FIG. 8 is a cross-sectional view of one end of an optical fiber main body, showing still another embodiment of the present invention.

FIG. 9 is a block diagram showing a conventional laser beam machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Optical fiber 12 Quartz block which is a translucent member 13 Fusion surface 14 Tip surface 21 Core 22 Cladding 23 Coating member 25 AR coating which is an anti-reflection coating 31 Optical fiber main body 32 Laser oscillator 33 Laser beam machine 34 First collection Optical lens 35 End face 38 Second condensing lens 39 Irradiated object 51 Laser light 52, 56 Condensing lens 53 Optical fiber 54 Incident end face 55 Exit end face

Claims (8)

[Claims] 1. A core having a cladding provided on an outer peripheral surface thereof for guiding light and connected to at least one of end faces of the core through which the light enters and exits, the refraction being substantially the same as the refractive index of the core. A substantially columnar light-transmissive member having a refractive index; and an antireflection coating provided on an end face of the light-transmissive member through which the light enters and exits, and the light of the light-transmissive member enters and exits. An optical fiber, wherein an end face has an area capable of entering and exiting the light at a power density that does not damage the light of the antireflection coating. 2. The optical fiber according to claim 1, wherein the translucent member is quartz. 3. The optical fiber according to claim 1, wherein the translucent member has a plane in which an end face through which light enters and exits and an end face connected to the core are parallel planes. 4. The optical fiber according to claim 1, wherein the connection between the core and the translucent member is fusion splicing. 5. The optical fiber according to claim 1, wherein the connection between the core and the translucent member is an optical contact. 6. The light-transmitting member according to claim 1, wherein an end surface connected to the core is provided with a substantially columnar connection portion having substantially the same outer diameter as the outer diameter of the clad on the same axis. The optical fiber according to any one of the above. 7. The light-transmitting member has a substantially frustum-shaped conical portion on the end face connected to the core, the diameter of which gradually decreases toward the tip and the tip has a diameter substantially equal to the outer diameter of the clad. The optical fiber according to any one of claims 1 to 5, wherein the optical fiber is provided. 8. A laser processing machine comprising: the optical fiber according to claim 1; and a laser oscillator.