JP3224106B2 - Optical fiber for laser input - Google Patents

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 a laser beam output from a high power laser light emitting device such as a YAG laser.

[0002]

2. Description of the Related Art High-power laser light-emitting devices such as a YAG laser are widely used in the fields of cutting, machining, medical treatment and the like. Laser light output from this type of laser light emitting device is guided by an optical fiber to a cutter, a knife, or the like. FIG. 4 is a schematic diagram of an apparatus using the high-power laser light emitting device. FIG. 1A is a schematic configuration diagram of the device, FIG. 2B is a longitudinal sectional view of a laser input optical fiber, and FIG. 1C is a side view showing a method for manufacturing the laser input optical fiber.

In FIG. 1, a laser beam output from a high-power laser light emitting device 1 is used in a processing section 2 for cutting and other operations. The laser light is guided by the guiding optical fiber 3 from the high-power laser light emitting device 1 to the processing unit 2. At this time, the high-power laser light emitting device 1
At the coupling portion A between the optical fiber for guiding and the optical fiber for guiding 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, 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 optical fiber 4 for laser input, is squeezed here, and enters the optical fiber for guiding 3 from the small-diameter portion on the right side. Such an optical fiber 4 for laser input is manufactured by heating and softening an optical fiber 6 having a core and a clad by a burner 7 or the like, as shown in FIG.

[0004]

By the way, as shown in FIG. 4B, the conventional optical fiber for laser input as described above has outer diameters at the input side and the output side of the laser beam. different. Therefore, there is a problem that the work of applying a coating for fixing the laser input optical fiber and fixing the same is relatively complicated. Further, when the optical fiber 6 is manufactured by drawing as shown in FIG. 4C, relatively precise outer diameter control is required. Therefore, there is also a problem that a high processing technique is required for that purpose. The present invention has been made in view of the above points, and has as its object to provide a laser input optical fiber having a uniform outer diameter and capable of efficiently receiving laser light.

[0005]

According to the present invention, an end face of an optical fiber having a core portion on the laser light incident side has the same outer diameter as the optical fiber and the same refractive index N1 as the core portion .
An optical fiber for laser input, wherein the effective numerical aperture is increased by connecting a light guide rod having a numerical aperture of sin θ1 and a length L represented by the following equation. L = (√ (1-X ² ) / X) · (R1-R2) R1: radius of light guide rod R2: radius of core portion X: X = sin θ1 / N1 (from Snell's law)

[0006]

The length L of the light guide rod is set based on the above equation.
Then, the effective radius of the core of the optical fiber increases.
Therefore, it is necessary to prevent damage to the incident end face of the optical fiber.
Laser light is efficiently incident on the core of the optical fiber
And the light guide rod have the same refractive index.
Reflection at the interface is also blocked. Thus, a laser input optical fiber for efficiently collecting and guiding the laser light output from the high-power laser light emitting device in the optical fiber can be obtained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail 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 according to the present invention. The optical fiber for laser input shown in the figure has an optical fiber 11 having an ordinary cross-sectional configuration having a core portion 11A and a cladding portion 11B.
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 11A constituting the optical fiber 11, and is made of a material having the same refractive index as the core 11A. The end surfaces of the optical fiber 11 and the light guide rod 12 are connected and integrated by a conventionally well-known method by heat fusion. Therefore, the laser light passing through the central axis portion of the laser input optical fiber having such a configuration has very little reflection loss at the connection portion. As described above, the refractive indices of the light guide rod 12 and the core 11A of the optical fiber 11 are made equal.
Then, increasing the incidence efficiency to prevent reflection at the interface
Can be.

In the case of a laser input optical fiber, the laser light 5 enters the light guide rod 12 from the direction indicated by the arrow. In this case, when the laser beam is input at the angle indicated by the broken line in the figure, it is sent into the optical fiber 11 with the maximum efficiency. 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 11A of the optical fiber 11 is S2, when the light guide rod 12 is not connected to the optical fiber 11, The effective sectional area that can receive the laser light 5 is S2, and the effective 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 11A of the optical fiber 11 have the same refractive index, the core 11A of the optical fiber 11 is separated from the light guide rod 12.
Is not refracted at the connection surface. Therefore, the effective core diameter is increased to the cross-sectional area ratio S1 / S2 times of both. The light guide rod 12 as described above is used.
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.
The refractive index of the core portion 11A is N1, and the refractive index of the cladding portion 11B is N2. In this case, the refractive index of the light guide rod 12 is N1. Here, the incident angle of the laser beam with respect to the core portion 11A with respect to the central axis 13 is defined as θ2. Also, the light guide rod 1 when the laser beam enters at this angle
2, the effective core radius is R1, and the core half of the optical fiber 11 is
The diameter is R2, the cross-sectional area of the light guide rod 12 is S1, the cross-sectional area of the core 11A of the optical fiber 11 is S2, and the incident angle of the laser beam incident on the light guide rod 12 with respect to the central axis 13 is θ1.
And

Here, as shown in FIG. 3A, the ratio of the input power when the light guide rod 12 is provided and when it is not provided,
As described above, the setting is made to be S1 / S2 times. At this time, comparing the triangle ABC and the triangle AEG in FIG. 2, these triangles are similar to each other because there is no refraction of the laser beam at the connection portion between the optical fiber 11 and the light guide rod 12 [FIG. 3 (2)]. . Also, the equation of the input power shown in FIG. 3 (1) is, as shown in FIG.
It can be expressed as a power ratio. Further, as shown in FIG. 3D, the length L of the light guide rod 12 is obtained by subtracting AD from AF shown in FIG.

As shown in FIG. 3 (5), θ1 and θ1
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 beam in the air was "1". Next, as shown in FIG. 3 (6), the relationship among R2, AD, R1, and AF is represented using θ2, and the relationship between FIGS. 3 (7), (8), and (9) is used. As shown in 3 (10), L can be represented by the relationship between X and R1 and R2. Note that this X is shown in FIG.
The upper limit is determined by the refractive indices N1 and N2 as shown in FIG. 3 (11).

As described above, by selecting the length L of the light guide rod 12, the effective radius of the optical fiber 11 can be increased from R2 to R1. The present invention is not limited to the above embodiments. In the above embodiment, an example in which a step index optical fiber is used has been described, but the same can be said for a case where a grade index type optical fiber is used. Further, the glass material used for the light guide rod 12 only needs to have the same refractive index as the core of the optical fiber, and does not necessarily have to be the same material.

[0013]

According to the optical fiber for laser input of the present invention described above, the end face of the optical fiber having the core portion has the same outer diameter as the optical fiber and the same refractive index as the core portion.
Since the light guide rods having dimensions are connected, the effective core diameter can be enlarged while keeping the outer diameter of the optical fiber constant. This makes it possible to provide an optical fiber for laser input that is easy to coat and terminate, has high laser light input efficiency, and is relatively easy to manufacture.

[Brief description of the drawings]

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

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

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

4A and 4B are explanatory diagrams illustrating a conventional general laser input optical fiber, in which FIG. 4A is a configuration diagram of a device using a high-output laser light emitting device, FIG. 4B is a longitudinal sectional view of the laser input optical fiber, (C) is a side view showing the manufacturing method.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/24-6/42 G02B 6/10

Claims (1)

(57) [Claims] 1. An end face of an optical fiber having a core portion on an incident side of a laser beam, which has the same outer diameter as the optical fiber , has the same refractive index N1 as the core portion , and has a numerical aperture sin θ1
An optical fiber for laser input, wherein a light guide rod having a length L represented by the following formula is connected to increase an effective core diameter of the optical fiber. L = (√ (1-X ² ) / X) · (R1-R2) R1: radius of the light guide rod R2: radius of the core portion X: X = sin θ1 / N1 (from Snell's law)