JPH05288967A - Optical fiber for laser input - Google Patents

Abstract

PURPOSE:To obtain the optical fiber for laser input which gathers light, outputted by a high-output laser light emitting device, in an optical fiber and guides the light. CONSTITUTION:A light guide rod 12 having the same external diameter with an optical fiber 11 of normal constitution having a core part 11A and a clad part 11B is connected to an end surface of the optical fiber 11. The light guide rod 12 which has the same refractive index with the core part 11A of the optical fiber 11 and is equal in external diameter to the clad part 11B is used. At this time, the effective core diameter of the optical fiber 11 is increased from a state of sectional area S2 to a state of sectional area S1, where S1 is the sectional area of the light guide rod and S2 is the sectional area of the core part 11A of the optical fiber 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser input optical fiber for efficiently guiding laser light output from a high power laser emitting device such as a YAG laser.

[0002]

2. Description of the Related Art High-power laser emitting devices such as YAG lasers are widely used in the fields of cutting, machining, medical treatment and the like. The laser light output from this type of laser light emitting device is guided to a cutter, a knife or the like by an optical fiber. FIG. 4 shows a schematic view of a device using the high-power laser emitting device. (A) of a figure is a schematic structure figure of a device, (b) is a longitudinal section of an optical fiber for laser input, and (c) is a side view showing a manufacturing method of an optical fiber for laser input.

In the figure, the laser light output from the high-power laser emitting device 1 is used for cutting and other work in the processing section 2. The laser light is guided by the guiding optical fiber 3 from the high-power laser emitting device 1 to the processing unit 2. At this time, the high power laser light emitting device 1
At the joint portion A between the guide optical fiber 3 and the guide optical fiber 3, a laser input optical fiber 4 as shown in (b) is used so that the laser light is efficiently condensed and guided in the optical fiber. .. The laser input optical fiber 4 is formed in a tapered shape as a whole, and has a core portion 4A at the center and a clad portion 4B around the core portion 4A. Laser light 5
Enters the large diameter portion on the left side of the laser input optical fiber 4, is narrowed down here, and enters the guiding optical fiber 3 from the small diameter portion on the right side. Such a laser input optical fiber 4 is manufactured, for example, by heating an optical fiber 6 having a core and a clad by a burner 7 or the like to soften it and drawing it as shown in (c).

[0004]

By the way, in the conventional optical fiber for laser input as described above, as shown in FIG. 2 (b), the outer diameters of the input side and the output side of the laser beam are different. different. Therefore, there is a problem in that the work of coating or fixing the optical fiber for laser input is relatively complicated. Further, when the preform rod 6 is stretched and manufactured as shown in FIG. 4C, relatively precise outer diameter control is required. Therefore, there is also a problem that an advanced processing technique is required for that purpose. The present invention has been made in view of the above points, and an object thereof is to provide an optical fiber for laser input which has a uniform outer diameter and can efficiently receive laser light.

[0005]

An optical fiber for laser input of the present invention is a light guide rod having the same outer diameter as the optical fiber and the same refractive index as that of the core portion on the end face of the optical fiber having a core portion and a cladding portion. Is connected to expand the effective core diameter of the optical fiber.

[0006]

In this optical fiber for laser input, a light guide rod having the same outer diameter as that of the optical fiber is connected to the end face of the optical fiber having a usual structure having a core portion and a clad portion. The light guide rod has the same refractive index as the core portion of the optical fiber and has the same outer diameter as the cladding portion. At this time, the cross-sectional area of the light guide rod is S1, and the cross-sectional area of the core portion of the optical fiber is S1.
2, the effective core diameter of the optical fiber is the cross-sectional area S2
The state is expanded to the state of the cross-sectional area S1. This makes it possible to obtain a laser input optical fiber for efficiently collecting and guiding the laser light output from the high-power laser emitting device into the optical fiber.

[0007]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of an optical fiber for laser input of the present invention. The optical fiber for laser input shown in the figure has an optical fiber 11 having a core section 11A and a clad section 11B and having an ordinary cross-section.
And a light guide rod 12 having the same outer diameter as the above. Here, the optical fiber 11 is a step index type fiber using, for example, silica glass or multi-component glass. On the other hand, the light guide rod 12 is made of the same glass as the constituent material of the core portion 11A constituting the optical fiber 11, and is made of a material having the same refractive index as that of the core portion 11A. The optical fiber 11 and the light guide rod 12 are integrated by connecting their end faces by a method well known in the art by heat fusion. Therefore, the laser light passing through the central axis portion of the laser input optical fiber having such a configuration has extremely small reflection loss at the connection portion. The reason why the light guiding rod 12 and the core portion 11A of the optical fiber 11 have the same refractive index is to prevent reflection at the interface and increase the incidence efficiency.

In the case of an optical fiber for laser input, the laser light 5 enters the light guide rod 12 from the direction shown by the arrow. In this case, the laser light is sent into the optical fiber 11 with the maximum efficiency when input at the angle shown by the broken line in the figure. When the cross-sectional area of the portion of the light guide rod 12 facing the laser light emitting device is S1 and the cross-sectional area of the core portion 11A of the optical fiber 11 is S2, in a state where the light guide rod 12 is not connected to the optical fiber 11. The effective cross-sectional area that can receive the laser light 5 is S2, and the effective cross-sectional area that can receive the laser light when the light guide rod 12 is connected is S1. Since the light guide rod 12 and the core portion 11A of the optical fiber 11 have the same refractive index, the light guide rod 12 extends from the core portion 11A of the optical fiber 11 to each other.
The laser light 5 incident on is not refracted at the connection surface. Therefore, the effective core diameter is expanded to the sectional area ratio S1 / S2 times of both. The light guide rod 12 as described above
The length L is preferably selected based on the following criteria.

FIG. 2 shows a reference diagram for selecting the length L of the light guide rod 12, and FIG. 3 shows a procedure explanatory diagram for selecting the length L. First, in FIG. 2, the optical fiber 1
The refractive index of the first core portion 11A is N1, and the refractive index of the clad portion 11B is N2. In this case, the refractive index of the light guide rod 12 is N1. Here, the incident angle with respect to the central axis 13 of the laser light with respect to the core portion 11A is defined as θ2. In addition, the light guide rod 1 when laser light is incident at this angle
2, the effective core diameter of the optical fiber 11 is R1, the core diameter of the optical fiber 11 is R2, the cross-sectional area of the light guiding rod 12 is S1, the optical fiber 11
The cross-sectional area of the core portion 11A is S2, and the incident angle of the laser light incident on the light guide rod 12 with respect to the central axis 13 is θ1.

Here, as shown in (1) of FIG. 3, the ratio of the input power with and without the light guide rod 12 is
As described above, it is set to be S1 / S2 times. At this time, comparing the triangle ABC and the triangle AEG in FIG. 2, since there is no refraction of the laser light at the connecting portion between the optical fiber 11 and the light guide rod 12, these triangles are similar to each other [FIG. 3 (2)]. .. Further, the formula of the input power shown in FIG. 3 (1) is 2 of the radii R1 and R2 as shown in (3).
It can be expressed as the ratio of powers. Further, as shown in FIG. 3 (4), the length L of the light guide rod 12 is the AF shown in FIG. 2 minus AD.

Further, as shown in FIG. 3 (5), θ1 and θ
The relationship between 2 and the refractive index N1 can be represented by a trigonometric function according to Snell's law. In this case, the refractive index of the laser light in the air was set to "1". Next, as shown in FIG. 3 (6), the relationship between R2, AD, R1, and AF is represented by using θ2, respectively, and if the relationships in FIGS. 3 (7), (8), and (9) are used, 3 (10), L can be represented by the relationship between X and R1 and R2. This X is shown in Fig. 3 (8).
3 corresponds to sin θ2, and its upper limit is determined by the refractive indices N1 and N2 as shown in FIG. 3 (11).

By selecting the length L of the light guiding rod 12 as described above, the effective radius of the optical fiber 11 can be expanded from R2 to R1. The present invention is not limited to the above embodiments. In the above embodiment, the example using the step index optical fiber is shown, but the same can be said for the case using the grade index type optical fiber. Further, the glass material used for the light guiding rod 12 is not limited to the same material as long as it has the same refractive index as that of the core portion of the optical fiber.

[0013]

According to the optical fiber for laser input of the present invention described above, a light guide rod having the same outer diameter as the optical fiber and the same refractive index as that of the core portion is provided on the end face of the optical fiber having the core portion and the cladding portion. Since the connection is made, the effective core diameter can be increased while keeping the outer diameter of the optical fiber constant. This makes coating and terminal treatment easy,
Moreover, it is possible to provide an optical fiber for laser input which has a high laser light input efficiency and is relatively easy to manufacture.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of an optical fiber for laser input of the present invention.

FIG. 2 is a reference diagram for selecting a length L of a light guide rod.

FIG. 3 is a procedure explanatory diagram for selecting the length L of the light guide rod.

4A and 4B are explanatory views for explaining a conventional general laser input optical fiber, FIG. 4A is a configuration diagram of an apparatus using a high-power laser emitting device, and FIG. 4B is a vertical cross-sectional view of the laser input optical fiber. (C) is a side view showing the manufacturing method.

[Explanation of symbols]

 5 laser light 11 optical fiber 11A core part 11B clad part 12 light guide rod L rod length

Claims (1)

[Claims] 1. A light guide rod having the same outer diameter as the optical fiber and the same refractive index as that of the core portion is connected to an end face of the optical fiber having a core portion and a clad portion, and an effective core diameter of the optical fiber. Is an optical fiber for laser input.