JP3142955B2 - Optical fiber for illumination light transmission for laser beam machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to irradiation <br/> Meiko transmission optical fiber for laser processing machine, and more particularly intensity distribution uniform laser processing machine illumination light transmitting optical fiber of the outgoing light It is.

[0002]

2. Description of the Related Art As an optical fiber for transmitting illumination light for a laser beam machine, a fiber having a so-called large diameter having a large core diameter and a refractive index distribution of a step type or a graded type is used. By the way, the intensity distribution of the emitted light from the optical fiber is almost the same as the refractive index distribution when its length is as long as several km. However, looking at the intensity distribution of the emitted light from the optical fiber for transmitting the illumination light for the laser beam machine , the refractive index distribution has the same shape as that of the refractive index distribution even though it is a step type or graded type as described above. And it is hard to say that it is uniform. The reason for this is that the length of the fiber used is often as short as several tens of meters or less, and some are as short as several meters. If such a length is short, unnecessary light is transmitted without being attenuated. In particular, in the case of the step type, a large number of circular modes (modes of spiral propagation in the core) remain, and the emission pattern becomes donut-shaped. In the case of the graded type, there is no such a problem of the circular mode, but the emission pattern of the propagating light has a distribution and is not uniform.

[0003]

However, from the viewpoint of processing a groove having a certain depth in a material with a laser beam,
Since the intensity distribution of the emitted light is required to be constant in the optical fiber for transmitting the illumination light for the laser beam machine , the conventional step-type and graded-type refractive index distribution cannot cope with the above. A new refractive index distribution fiber structure was being studied. In order to develop a new refractive index distribution fiber structure, the present inventors further analyzed the emission pattern of a conventional step type, graded type refractive index distribution optical fiber. Although the above-mentioned circular mode always occurs, the loss of this mode itself is large, and if the length of the optical fiber is long, it attenuates and does not cause a problem.In the case of the graded type, the circular mode leaks out and attenuates. It was found that there was almost no problem even if the fiber length was short after conversion to the normal mode, and it was inferred that if the refractive index distribution was intermediate between the two, the pattern of the emission intensity would be uniform.

[0004]

SUMMARY OF THE INVENTION The present invention has been made from the above viewpoint, a first portion having a refractive index n ₁ of a certain, formed around the first part, the a core consisting of a second portion refractive index which gradually decreases to a small refractive index n ₂ than the refractive index n _1, this was formed around the core, smaller refractive than the refractive index of the refractive index n ₂ It consists of a cladding having a rate n _3, and a first forming the core
Is 50 to 90% of the core diameter, and
Part the refractive index _{n 1} and of 0.2 to 0.6% the relative refractive index difference Δ is the refractive index _{n 2} of the second portion, the first further core
There the refractive index n ₁ and a laser processing machine for irradiation <br/> Meiko transmission optical fiber relative refractive index difference Δ is at least 0.5% of the refractive index n ₃ of the cladding portion.

[0005]

The pattern of the emission intensity is essentially formed at the first portion of the center by making the refractive index distribution of the core a step-type at the first portion at the center and a graded type at the second portion around the first portion. In addition to the uniform step shape, the circular mode generated due to the step type is converted into the normal mode in the second portion, and the emission intensity pattern is uniform as a whole.

[0006]

FIG. 1 is a cross-sectional view of a quartz-based fiber for transmitting illumination light for a laser beam machine according to the present invention, and FIG. 2 is a refractive index distribution diagram thereof. In Fig, 1 has a first portion forming the center of the core, for example, a constant refractive index _{n 1} consisting of GeO ₂ over SiO _2. 2 was formed around the first portion, the second portion forming part of the core, the first part 1 and likewise consists GeO ₂ chromatography SiO _2, the refractive index by adjusting the Ge amount The refractive index n ₂ gradually decreases from the refractive index n ₁
Has been reached. The ratio of the diameter of the first portion forming a part of the core to the core diameter is 50 to 90%, preferably 6 to 90%.
0 to 80%. Further, the refractive index n ₁ and the refractive index n ₂
Is 0.2 to 0.6%. 3 is clad, for example, a F over SiO _2, the refractive index is a small _{n 3} than the refractive index _{n 2,} the relative refractive index difference delta = -0.3 to-1 with the pure silica glass. 3%, relative refractive index difference Δ from refractive index n _{1 of first} portion of core = 0.5 to 1.
It is 9%.

[0007]

First, a core base material having a diameter of 20 mm and a length of 1700 mm was prepared by the VAD method. The first part is Ge
It was composed of O ₂ —SiO ₂ glass, the diameter of which was 12 mm, the core diameter was 60%, and the refractive index was constant at a relative refractive index difference Δ = about 0.5% as compared with that of pure quartz. The second portion was made of GeO ₂ —SiO ₂ glass similarly to the first portion, but had a diameter of 20 mm, and was 60% of the core diameter to 1% of the outermost circumference.
The Ge amount was gradually reduced toward 00%, and the refractive index was linearly changed to a relative refractive index difference Δ = about 0.5 to 0.1% as compared with that of pure quartz. F-SiO ₂ glass was deposited around the core member by a plasma external method to form a clad portion having a relative refractive index difference Δ = approximately −1% from pure quartz glass. Finished dimensions are outer diameter φ: 25mm, length l: about 6
00 mm. The base material was drawn to a core diameter of 400 μm and a fiber diameter of 500 μm, and a silicone resin was coated thereon as a coating material to give an outer diameter of 700 μm.
When a YAG laser was transmitted through this fiber, the emission pattern was a pattern with almost constant intensity as shown in FIG.

[0008]

The optical fiber for illumination transmission for a laser beam machine according to the present invention comprises a first portion centered on a core and a second portion surrounding the first portion, and the first portion has a constant refractive index. , The refractive index of the second portion has a refractive index distribution that gradually decreases from a refractive index equal to the refractive index of the first portion to a smaller refractive index, and further, the refractive index distribution outside the second portion has a refractive index. The structure in which the cladding having a refractive index smaller than the minimum refractive index of the portion 2 is provided has an effect that the pattern of the emission intensity of the transmission light can be made uniform.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an optical fiber for transmitting illumination light for a laser beam machine according to the present invention.

FIG. 2 is a refractive index distribution diagram of the optical fiber for transmitting illumination light for the laser beam machine shown in FIG. 1;

3 is an emission intensity distribution diagram of the optical fiber for transmitting illumination light for the laser beam machine of FIG. 1. FIG.

[Explanation of symbols]

DESCRIPTION OF REFERENCE NUMERALS 1 First part forming a center of core 2 Second part forming a part of core formed around first part 3 Cladding

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Takashi Tsumanuma 1440, Rokkazaki, Sakura City, Chiba Prefecture Inside the Sakura Plant of Fujikura Electric Wire Co., Ltd. (72) Inventor Chiaki Toritani 1440, Mutsuzaki, Sakura-shi, Chiba Prefecture Inside the Sakura Plant of Fujikura Electric Wire & Cable Co., Ltd. (56) References JP-A-55-153327 (JP, A) JP-A-61-273506 (JP, A) Patent 2754297 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/00 -6/54 B23K 26/00-26/18

Claims (1)

(57) [Claims] _1. A first portion having a constant refractive index n ₁ and a refractive index formed around the first portion, the refractive index of which is gradually reduced from the refractive index n ₁ to a smaller refractive index n ₂ . And a refractive index n ₃ formed around the core and having a refractive index smaller than the refractive index n _2.
Consists of a cladding having a and is 50 to 90% of the diameter core diameter of the first portion forming the core and the refractive index of the first portion n ₁ and the refractive index n ₂ of the second portion The relative refractive index difference Δ is 0.2 to 0.6%, and the relative refractive index difference Δ between the refractive index n ₁ of the first portion of the core and the refractive index n _{3 of the} cladding is at least 0.5%. Laser characterized by the following
-Optical fiber for transmission of illumination light for processing machines .