JPH11271540A - Optical fiber and machining method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber which can stably transmit high-output laser light and to provide the machining method therefor. SOLUTION: This optical fiber 1 has a core 2 and a clad 3 which differ in refractive index from each other. Here, a hollow 4 of specific depth is formed on the incidence end surface 2a of the core 2 on the incidence end 1a of the optical fiber on which converged laser light 10 is made incident. This hollow 4 is formed by isotropically etching the incidence end 1a of the optical fiber 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical fiber,
More particularly, the present invention relates to an optical fiber suitable for transmitting high-power laser light and a processing method thereof.

[0002]

2. Description of the Related Art A quartz glass optical fiber is known as an optical fiber suitable for transmitting high-power laser light. In such a silica glass-based optical fiber, a high-performance laser beam of about several kW can be transmitted with continuous output due to the high performance of silica glass used as a material.

[0003] The upper limit of the output range of laser light that can be transmitted by an optical fiber is determined in consideration of damage to the incident end face of the core due to the collected high-power laser light.
The damage of the incident end face is caused by a relatively low damage threshold of the processing-affected layer generated during the processing of the incident end face. This damage threshold is determined by the material of the optical fiber core or the laser. Different values are taken according to the output pulse waveform of light, the adhesion of dust on the incident end face, the method of finishing the incident end face, and the like.

Here, taking a case where a continuous output laser beam is incident on an optical fiber as an example, the upper limit of the output range of the laser beam is determined by dividing the output of the laser beam by the incident area of the laser beam. Looking at the power density I, a step index (SI) type optical fiber using pure silica glass for the core is about 10 ⁸ W / cm ² , and germanium (G
e) A graded index (GI) type optical fiber using silica doped with (doped) for the core is about 10 ⁶ W
/ Cm ² . The optical fiber for transmitting such high-power laser light has a relatively large diameter in order to suppress the average power density of the laser light at the incident end face of the core.

FIG. 7 shows an example of a processing optical system using an optical fiber. The processing optical system shown in FIG.
And an optical fiber 1 for transmitting a laser beam 10 emitted from a laser 7. Here, an incident lens 8 for condensing the laser light 10 emitted from the laser 7 is provided on the incident end 1a side of the optical fiber 1, and the emitting end 1b of the optical fiber 1 is provided on the emitting end 1b side of the optical fiber 1. An imaging lens 9 for converging the emitted laser light 10 to form an image on a processing point 11 is provided.

In such a processing optical system, the processing point 1
The average power density I _w of the laser light 10 condensed at 1 is given by the following equation (1) based on the average power density I _o at the emission end 1 b of the optical fiber 1 and the imaging magnification m by the imaging lens 9. Required by I _w = I _o · (1 / m) ² (1)

In the above equation (1), the imaging magnification m is the divergence angle θ ₁ of the laser beam 10 at the emission end 1 b of the optical fiber _1.
And the convergence angle θ ₂ of the laser beam 10 by the imaging lens 9, which is obtained by the following equation (2). m = θ ₁ / θ ₂ (2)

Here, according to the above equation (1), the imaging magnification m
Although it is possible to increase the average power density I _w of the laser beam 10 at the work point 11 by a smaller, reducing the imaging magnification m is the lens aperture of the converging optical system such as an imaging lens 9 This leads to an increase and a reduction in working distance.
Therefore, from a practical viewpoint, the average power density I _w of the laser beam 10 at the processing point 11 is increased by increasing the average power density I _o of the laser beam 10 at the emission end 1 b of the optical fiber 1. There is a need.

As described above, the average power density of the laser beam 10 at the incident end 1a of the optical fiber 1
Since there is an upper limit value due to damage to the incident end face 2a, it is impossible to indefinitely increase the average power density I _o of the laser beam 10 at the exit end 1b of the optical fiber 1. For this reason, conventionally, as shown in FIG. 8, for example, by connecting a throat-shaped optical fiber 15 to the incident end 1a side of the optical fiber 1 to increase the incident area of the laser light 10, the optical fiber 1 There is known a method of increasing the output of the laser beam 10 incident on the optical fiber 1 while suppressing the average power density of the laser beam 10 at the incident end 1a as much as possible.

[0010]

As described above, in the prior art, the laser beam 1 at the input end 1a of the optical fiber 1 is conventionally used.
As a method for increasing the output of the laser light 10 incident on the optical fiber 1 while suppressing the average power density of the optical fiber 1 as small as possible, a throat-shaped optical fiber 15 is connected to the incident end 1a side of the optical fiber 1 so that the laser light There has been known a method of increasing the incidence area of No. 10.

However, in such a conventional method, it is possible to suppress the average power density of the laser beam 10 at the input end 1a of the optical fiber 1, but the optical fiber 1
It is technically difficult to connect the optical fiber 15 and the throat-shaped optical fiber 15 at the connecting portion 16 in an ideal state. In particular, in the transmission of the high-power laser light 10, the loss at the connecting portion 16, Heat generation of the connecting portion 16 due to a large loss causes a problem.

The present invention has been made in view of the above points, and an optical fiber capable of stably transmitting a high-power laser beam by increasing an incident area of the laser beam, and a processing method thereof. The purpose is to provide.

[0013]

A first feature of the present invention is as follows.
An optical fiber comprising a core and a clad having different refractive indices from each other, the core having an incident end face on which laser light is incident, and a concave part having a predetermined depth is formed on the incident end face.

According to a second feature of the present invention, a step of coating a resist film on an incident end side of an optical fiber having a core and a clad having different refractive indices, and forming a resist film on the incident end face of the core in the resist film. Irradiating the coated resist film with light having a predetermined spot diameter to partially expose the resist film; developing the resist film; and immersing the incident end side of the optical fiber in an etchant to form the resist film. An optical fiber processing method, comprising: a step of etching a portion of the core from which the resist film has been removed; and a step of removing the resist film.

A third feature of the present invention resides in a step of coating a protective film on an incident end side of an optical fiber having a core and a clad having different refractive indices from each other; Irradiating the coated protective film with a laser beam having a predetermined spot diameter to partially remove the protective film; and immersing the incident end side of the optical fiber in an etchant to remove the protective film from the core. An etching method for an optical fiber, comprising: a step of etching the exposed portion; and a step of removing the protective film. In the third aspect of the present invention, it is preferable that the method further includes a step of partially removing the incident end face of the core with the laser beam having the predetermined spot diameter.

According to the first aspect of the present invention, since the concave portion having a predetermined depth is formed in the incident end face of the core of the optical fiber, a higher output than a general optical fiber having a flat incident end face is provided. Laser light can be incident. For this reason, it is possible to increase the average power density of the laser beam at the emission end of the optical fiber, and to reduce the diameter and the long working distance of the imaging lens on the emission end side in a processing optical system or the like at the processing point. The average power density of the laser beam can be increased.

According to the second feature of the present invention, the concave portion is formed by isotropically etching the incident end side of a general optical fiber having a flat incident end surface, so that the concave portion is formed. Simple and inexpensive.

Further, according to the third feature of the present invention, since the etching process can be performed after the incident end face of the core of the optical fiber is partially removed, the concave portion can be made deeper, so that the light Higher output laser light can be incident on the fiber.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1A and 2A to 2E are diagrams showing a first embodiment of an optical fiber and a processing method thereof according to the present invention.

First, the basic structure of an optical fiber will be described with reference to FIGS. Here, FIG. 1A is a partial sectional view showing a first embodiment of an optical fiber according to the present invention, and FIG. 1B is a partial sectional view showing a general optical fiber. As shown in FIGS. 1A and 1B, an optical fiber 1 has a core 2 and a clad 3 having different refractive indexes from each other.
It has. Here, in the first embodiment of the present invention, as shown in FIG.
On the incident end 1a side of the optical fiber 1 into which 0 enters, a depression (recess) 4 having a predetermined depth is formed in the incident end surface 2a of the core 2. The depression 4 is formed by isotropically etching the incident end 1a side of the optical fiber 1 as described later.

Next, the operation of the first embodiment of the present invention having such a configuration will be described.

First, FIG. 1A and FIG.
The principle of the optical fiber 1 shown in FIG. The incident area of the laser light 10 on the incident end 1a side of the optical fiber 1 shown in FIG. 1A is S, and the incident area of the laser light 10 on the incident end 1a side of the general optical fiber 1 shown in FIG. Assuming that the incident area is S ', the incident area S is larger than the incident area S' by the amount of the depression 4, and the following equation (3) is established. S> S '... (3)

Accordingly, the average power density I _i , I _i ′ of the laser beam 10 obtained by dividing the average output or peak output of the laser beam 10 by the incident area S, S ′ of the laser beam 10 is given by the following equation (4). become that way. I _i <I _i ′ (4)

Therefore, assuming that the average power densities I _i and I _i ′ that can be incident on the incident end 1a side of the optical fiber 1 are substantially the same, the optical fiber 1 shown in FIG. )
Laser light 1 having a larger output than the general optical fiber 1 shown in FIG.
0 can be incident. Therefore, it is possible to increase the average power density I _o at the exit end of the optical fiber 1 to be expressed by the following equation (5), forming the exit end 1b side in the machining optical system shown in FIG. 7 thereby increasing the average power density I _w of the laser beam 10 at the work point 11 while achieving a small diameter and a long working distance of the image lens 10. I _o = (output of laser light) / (area of emission end face of core of optical fiber) (5)

Next, referring to FIGS. 2A to 2E, FIG.
A method for processing the optical fiber 1 shown in FIG.

As shown in FIG. 2A, first, a resist film 2 is formed on the incident end 1a side of the optical fiber 1 which has been flattened.
Coat 0 and bake.

Next, as shown in FIG. 2 (b), the resist film 20 coated on the incident end face 2a of the core 2 in the resist film 20 has a laser having a predetermined spot diameter corresponding to the diameter of the opening of the depression 4. The resist film 20 is partially exposed to light such as light. Note that, in FIG.
a indicates a photosensitive portion.

Thereafter, as shown in FIG. 2C, the resist film 20 is developed, and a part of the resist film 20 corresponding to the photosensitive portion 20a is removed to form an opening 20b.
As shown in FIG. 2D, the incident end 1a side of the optical fiber 1 is immersed in an etching solution to
The portion where 0 has been removed (the portion opened to the outside via the opening 20b) is etched.

Finally, as shown in FIG. 2E, after cleaning the incident end 1a side of the optical fiber 1, the resist film 20 is peeled off, and the final concave portion 4 is formed on the incident end surface 2a of the core 2. Optical fiber 1 is manufactured.

As described above, according to the first embodiment of the present invention, since the recess 4 having a predetermined depth is formed in the incident end face 2a of the core 2 of the optical fiber 1, the optical fiber 1 has a flat incident end face 2a. Laser light 1 with higher output than general optical fiber 1
0 can be incident. Therefore, the optical fiber 1
Average power density I _o of the laser beam 10 can be increased at the exit end, a small diameter and a long working distance of the imaging lens 10 of the exit end 1b side in the machining optical system shown in FIG. 7 the average power density I _w of the laser beam 10 at the working point 11 can be increased while reducing. Further, since the recess 4 is formed by isotropically etching the incident end 1a side of the general optical fiber 1, the recess 4 is formed.
Can be easily and inexpensively formed.

Second Embodiment Next, an optical fiber according to a second embodiment of the present invention will be described with reference to FIGS. 3 and 4A to 4E. The second embodiment of the present invention differs from the first embodiment in that the method of forming the depression in the incident end face of the core of the optical fiber is different.
Others are the first shown in FIGS. 1A and 2A to 2E.
This is substantially the same as the embodiment. In the second embodiment of the present invention, the same parts as those in the first embodiment shown in FIGS. 1A and 2A to 2E are denoted by the same reference numerals, and detailed description is omitted. I do.

In the second embodiment of the present invention, as shown in FIG. 3, a recess (recess) 4 deeper than the recess 4 of FIG. 1A is formed on the incident end face 2a of the core 2. . The depressions 4 are formed by performing laser processing and etching on the incident end 1a side of the optical fiber 1 as described later.

Hereinafter, FIG. 4A to FIG.
The method for processing the optical fiber 1 shown in FIG. FIG.
As shown in (a), first, a resist film 20 is coated on the incident end 1a side of the optical fiber 1 finished to be flat, and baking is performed.

Next, as shown in FIG. 4B, the resist film 20 coated on the incident end face 2a of the core 2 in the resist film 20 has a laser having a predetermined spot diameter corresponding to the diameter of the opening of the depression 4. By irradiating light to partially remove the resist film 20 to form an opening 20b, and by continuing to irradiate laser light, as shown in FIG.
Is partially removed to form a pilot hole 21. In the case of the core 2 of the optical fiber 1 made of quartz glass, the core 2 of the optical fiber 1 can be removed by short-wavelength laser light having a wavelength of 300 nm or less.

Thereafter, as shown in FIG. 4D, the incident end 1a of the optical fiber 1 is immersed in an etchant to remove the resist film 20 of the core 2 (the opening 20).
b) is etched.

Finally, as shown in FIG. 4 (e), after cleaning the incident end 1a side of the optical fiber 1, the resist film 20 is peeled off, and the concave portion 4 is formed on the incident end surface 2a of the core 2. Optical fiber 1 is manufactured.

As described above, according to the second embodiment of the present invention, the operation and effect of the above-described first embodiment are exhibited, and the incident end face 2a of the core 2 of the optical fiber 1 is partially removed. Since the etching process is performed later, FIG.
The depressions 4 can be made deeper than in the optical fiber processing methods shown in FIGS. 1A to 1E, so that a laser beam 10 with a higher output can be incident on the optical fiber 1.

In the above-described second embodiment, the resist film 20 is used as a protective film for the etching process. However, the present invention is not limited to this, and a peelable paint film or the like is used as a protective film for the etching process. You may do so.

In the first and second embodiments described above, the depression 4 is formed in the incident end face 2a of the core 2 of the optical fiber 1. However, the present invention is not limited to this, and as shown in FIG. The concave surface 5 may be formed by etching, cutting, or the like.

Further, in the above-described first and second embodiments, the incident end face 2a of the core 2 of the optical fiber 1 is used.
Although the concave portion such as the concave portion 4 is formed, if the condensing position of the laser beam 10 on the incident end 1a side of the optical fiber 1 can be adjusted, a projection having a predetermined height is formed on the incident end surface 2a of the core 2. 6
(See FIG. 6) or a convex surface may be formed.
In such an optical fiber 1, since the electric field intensity inside the core 2 of the optical fiber 1 is increased by the light condensing action of the projection 6, etc. It is preferable to shift the focusing position of the laser beam 10 on the side of the incident end 1a of the fiber 1 to the near side (see FIG. 6).

[0041]

As described above, according to the present invention, since a concave portion having a predetermined depth is formed in the incident end face of the core of the optical fiber, it is larger than a general optical fiber having a flat incident end face. Output laser light can be incident. For this reason, it is possible to increase the average power density of the laser beam at the emission end of the optical fiber, and to reduce the diameter and the long working distance of the imaging lens on the emission end side in a processing optical system or the like at the processing point. The average power density of the laser beam can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a first embodiment of an optical fiber according to the present invention.

FIG. 2 is a view for explaining a method of processing the optical fiber shown in FIG. 1;

FIG. 3 is a partial sectional view showing a second embodiment of the optical fiber according to the present invention.

FIG. 4 is a view for explaining a method of processing the optical fiber shown in FIG. 3;

FIG. 5 is a partial sectional view showing a modified example of the optical fiber according to the present invention.

FIG. 6 is a partial sectional view showing another modified example of the optical fiber according to the present invention.

FIG. 7 is a diagram showing an example of a processing optical system using an optical fiber.

FIG. 8 is a view for explaining a conventional method for suppressing the average power density of laser light incident on an optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 1a Incident end 1b Outgoing end 2 Core 2a Incident end face 3 Cladding 4 Depression (depression) 5 Depression (depression) 6 Projection 7 Laser 8 Incident lens 9 Imaging lens 10 Laser light 11 Processing point 15 Throat-shaped optical fiber Reference Signs List 16 connection part 20 resist film 20a photosensitive part 20b opening 21 pilot hole

Claims (8)

[Claims] 1. A core and a clad having different refractive indexes from each other, the core having an incident end face on which laser light is incident, and a concave part having a predetermined depth is formed on the incident end face. Optical fiber. 2. The optical fiber according to claim 1, wherein said concave portion is formed by an etching process. 3. The optical fiber according to claim 1, wherein said concave portion is formed by laser processing and etching. 4. A core and a clad having different refractive indices from each other, wherein the core has an incident end face on which a laser beam is incident, and the incident end face is formed with a convex portion having a predetermined height. Optical fiber. 5. A step of coating a resist film on an incident end side of an optical fiber having a core and a clad having different refractive indices from each other; Irradiating light of a spot diameter to partially expose the resist film; developing the resist film; immersing an incident end side of the optical fiber in an etchant so that the resist film of the core is A method for processing an optical fiber, comprising: a step of etching the removed portion; and a step of peeling the resist film. 6. A step of coating a protective film on an incident end side of an optical fiber having a core and a clad having different refractive indices from each other, wherein the protective film is coated on the incident end face of the core in the protective film. Irradiating a laser beam having a spot diameter to partially remove the protective film, and immersing the incident end side of the optical fiber in an etchant to etch a portion of the core from which the protective film has been removed. A method of processing an optical fiber, comprising: a step of removing the protective film. 7. The method according to claim 6, further comprising the step of partially removing the incident end face of the core with the laser beam having the predetermined spot diameter. 8. The optical fiber processing method according to claim 6, wherein said protective film comprises a resist film or a paint film.