JPH05196845A - Laser beam injection method - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to provide a laser beam injection method with less reflection loss. A laser beam injection method of converging a laser beam L ₁₀ and injecting the condensed laser beam L ₁₁ into a glass fiber 11 to transmit the laser beam L ₁₁
Linearly polarized light is used for the laser beam L ₁₁ incident on the first core 12 and the laser beam L ₁₁ is incident on the incident end face 12 a of the core 12 of the glass fiber 11 so that the incident angle θ becomes the Brewster angle θ _B. Together with its incident end face 12a
Is formed so that the incident laser beam L ₁₂ is substantially parallel to the axis O ₁₁ of the glass 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 beam injection method which reduces reflection loss when a laser beam is incident on a glass fiber.

[0002]

2. Description of the Related Art In recent years, with the improvement of optical technology, welding using a high-power laser beam has been performed. A laser beam resonator that emits such a high-power laser beam is
They are usually large and heavy and are difficult to move over the material to be welded.

Therefore, as shown in FIG. 5, a laser beam emitted from a laser beam resonator is transmitted to the vicinity of a welded portion through a glass fiber.

Here, FIG. 5 is a conceptual diagram of a method of transmitting a laser beam using a glass fiber.

In FIG. ₁ , the laser beam L ₁ emitted from the laser beam resonator is condensed by the condenser lens 1 to a size equal to or smaller than the diameter of the core of the glass fiber 2,
The optical axis O ₁ is attached to one end face 2a of the glass fiber 2
It is incident so that it is perpendicular to a (incident angle is 0 degree). The incident laser beam is transmitted through the core of the glass fiber 2 and emitted from the other end surface 2b of the glass fiber 2. Laser beam L emitted from glass fiber 2
_{Since 2} diverges as it is, it is condensed again by the condenser lens 3 and is irradiated as a spot S on the welded portion 5a of the material 5. As is known, the glass fiber can be bent freely so that the spot S can be moved onto the material 5 and thus the weld 5a can be freely welded at any position on the material.

[0006]

However, in such a conventional laser beam incidence method, the laser beam is reflected at the incident end face 2a of the laser fiber, and the energy of the laser beam L ₂ is lost. This loss (hereinafter referred to as reflection loss) varies depending on the type of laser and the refractive index of the glass fiber core, and is about several% when a YAG laser and a silica glass core are combined, for example, and the CO laser and the chalcogen glass core. When combined with, it becomes a little less than 20%.

In order to reduce this reflection loss, a non-reflective coating is required by forming a dielectric multilayer film on the incident end face 2a of the glass fiber 2, but the core diameter is only a few hundred μm, so It is difficult and costly to apply antireflection coating to the incident end face 2a.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a laser beam injection method with a small reflection loss.

[0009]

In order to achieve the above object, the present invention provides a laser beam injection method in which a laser beam is converged and the laser beam is incident on a glass fiber for transmission. A linearly polarized laser beam is used, and the laser beam is incident on the incident end face of the glass fiber so as to have a Brewster angle, and the angle of the incident end face is set so that the incident laser beam is substantially aligned with the axis of the glass fiber. It is formed so as to be parallel.

[0010]

According to the above construction, reflection loss is minimized by making the incident angle of the P-polarized laser beam incident on the core of the glass fiber at Brewster's angle, and the P-polarized laser beam is incident with almost no reflection. .. Moreover, since the optical axis of the laser beam incident at the angle of the incident end face is substantially parallel to the axis of the glass fiber, the laser beam is efficiently transmitted because the reflection inside the core is small.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram for carrying out the laser beam injection method according to the present invention.

As shown in the figure, a condenser lens 10 for condensing the laser beam L ₁₀ from the laser beam resonator, and a glass fiber 1 for transmitting the condensed laser beam L _11.
It is composed of 1 and 1. The glass fiber 11 is the core 12
And a clad 13 surrounding the core 12.

The condenser lens 10 is arranged such that the optical axis O ₁₀ thereof is an incident angle θ with respect to the incident end face 12a of the core 12 of the glass fiber 11 being the Brewster angle, and the incident end face 11a of the glass fiber 11 is the laser beam L ₁₁ incident are formed at an angle (cutting angle) .theta.a such that substantially parallel to the axis O ₁₁ of the glass fiber 11.

A P-polarized laser beam L ₁₀ as a linearly polarized laser beam is incident on the condenser lens 10 in the direction of arrow A. The plane of polarization of the P-polarized laser beam L ₁₀ is parallel to the paper surface.

Here, the Brewster angle will be described with reference to FIG. 2. FIG. 2 is a diagram showing the relationship between the incident angle of the laser beam on the transmissive member and the reflection loss.

In the figure, the horizontal axis is the incident angle θ of the laser beam, and the vertical axis is the reflection loss R.

When a reflection loss when a linearly polarized laser beam is incident on the transmitting member (for example, the core 12) is measured, a characteristic curve as shown in the same figure is obtained. P indicates P polarized light,
S indicates S-polarized light.

It can be seen that the S-polarized light monotonically increases with an increase in the incident angle θ, while the P-polarized light takes a minimum value with an increase in the incident angle θ. The incident angle θ _B when the minimum value is obtained is the Brewster angle, and the reflection loss R is substantially “0”. That is, in the S-polarized laser beam, the reflection loss R increases as the incident angle θ increases, while P
When the incident angle θ is the Brewster angle θ _B , the polarized laser beam is not reflected and is completely transmitted. The present invention is
This utilizes that the reflection loss R takes a minimum value when the incident angle θ of the polarized laser beam is the Brewster angle θ _B.

Further, such a P-polarized laser beam can be generated by a laser resonator as shown in FIG. 3, for example.

FIG. 3 is a schematic diagram of a laser resonator for emitting a P-polarized laser beam.

In the figure, a laser medium 14 sandwiched by electrodes (not shown), a semitransparent concave mirror 15 and a total reflection concave mirror 16 for reciprocating and retrieving excitation light, and transmitting members 17, 1
8 and.

The transmissive members 17 and 18 are arranged on the optical axis of the laser beam between the laser medium 14 and the biconcave mirrors 15 and 16, and are arranged so that the incident angle forms the Brewster angle θ _B. There is. Therefore, P of the excitation light on the optical axis
Although the polarized light component is transmitted through the transmissive member, most of the S polarized light component is reflected by the transmissive members 17 and 18, and thus the transmissive member 1
Since the S-polarized light component passing through 7 and 18 is a slight amount, when the pumping light is extracted back and forth between the biconcave mirrors 15 and 16, only the laser beam containing P-polarized light as a main component is obtained. In this way, a P-polarized laser beam is obtained in the direction of arrow B.

Returning to FIG. 1, the condensed P-polarized laser beam L ₁₁ is incident on the incident end face 12a of the core 12 at Brewster's angle θ _B , and the incident laser beam L ₁₂ is incident end face 1
Since 2a is formed at an angle θ _a , it travels in the core 12 parallel to the axis O ₁₁ of the glass fiber 11.

Next, the operation of this embodiment will be described.

The P-polarized laser beam L ₁₀ is focused by the condenser lens 1.
When the laser beam L ₁₀ is converged by 0 and is incident on the core 12 of the glass fiber 11 at the Brewster angle θ _B , there is no reflection loss at the incident end face 12a, so that the laser beam L ₁₀ is incident on the core 12 in a state where the energy is preserved. It The laser beam L ₁₂ incident on the core 12 receives the glass fiber 1
Since it is substantially parallel to the axis O _{11 of} 1, the laser beam can be efficiently transmitted without reflection inside the core 12. As a result, the laser beam L ₁₀ can be incident without reflection without coating the dielectric end face 12a of the core 12 with light, and the laser beam can be efficiently transmitted.

On the other hand, the Brewster angle θ _B , the cutting angle θ _a, etc. differ depending on the type of laser and the material of the core.

First, the relationship between the Brewster angle θ _B , the cutting angle θ _a of the glass fiber and the incident angle θ of the laser beam will be determined.

FIG. 4 is a diagram showing the relationship among the refractive indices n ₁ and n ₂ and the Brewster angle θ _B , the cutting angle θ _a , and the emission angle θ _t . From the figure, Brewster's angle θ _B is expressed by Equation 1.

[0030]

## EQU1 ## θ _B = arctan (n ₂ / n ₁ ) Refractive indices n ₂ and n ₁ , Brewster angle θ _B , and emission angle θ _t
The relationship with is expressed by equation 2.

[0031]

[Number 2] After determining the _{n 1 sinθ B = n 2 sinθ} t ∴ θ t = arcsin ((n 1 / n 2) sinθ B) more than Buryusuta angle theta _B and the emission angle theta _t,
The relationship between the angle θ _I of the laser beam L ₁₀ with respect to the axis O ₁₁ of the glass fiber 11 shown in FIG. 1 and the cutting angle θ _a will be described.

This cutting angle θ _a is expressed by the equation 3, and the angle θ
_I is represented by Equation 4.

[0033]

## EQU3 ## θ _a = (π / 2) −θ _t

[0034]

## EQU4 ## θ _I = θ _B −θ _{t Using the} above equation, each angle of each glass fiber θ _B , θ _t , θ
_{Find I} and θ _a .

(1) Incident on quartz fiber (wavelength 65
A HeNe laser of 6.3 nm is used.) Since the refractive index n ₁ is 1.0 (air) and the refractive index n ₂ of the core 12 of the glass fiber 11 is 1.46, substituting these into the formulas 1 to 4 , Brewster angle θ _B is 5
5.6 (deg), the emission angle θ _t is 34.4 (deg),
The angle θ _I is 21.2 (deg) and the cutting angle θ _a is 55.6.
(Deg). The reflectance R is ((n ₂ −n ₁ ) /
Since (n ₂ + n ₁ )) ² , the reflectance R at the incident end face is 3.5%.

(2) Incident on chalcogen fiber (using CO laser with wavelength of 5.3 μm) Since the refractive index n ₂ is 2.5, it can be obtained by substituting the equations 1 to 4 as described above. The angle θ _B is 68.2.
(Deg), emission angle θ _t is 21.8 (deg), angle θ
_I is 46.4 (deg) and the cutting angle θ _a is 68.2 (deg).
g). The reflectance R on the incident end face is 18.4.
%.

As described above, in this embodiment, the linearly polarized laser beam is irradiated with the incident end surface 1 of the core 12 of the glass fiber 11.
Since the incident laser beam is formed so as to form a Brewster angle with respect to 2a and the incident laser beam is formed to be substantially parallel to the axis O ₁₁ of the glass fiber 11, reflection is performed by a simple method. It is possible to realize a laser beam injection method with low loss and efficient transmission.

In this embodiment, the laser beam is condensed by using the condenser lens. However, the present invention is not limited to this, and the concave mirror is condensed so that the optical axis of the concave mirror is at Brewster's angle. Good.

[0039]

In summary, according to the present invention, linearly polarized light is used for the laser beam incident on the glass fiber, and the laser beam is incident at a Brewster angle with respect to the incident end face of the glass fiber and the incident end face thereof is also incident. Since the incident laser beam is formed so that the incident laser beam is substantially parallel to the axis of the glass fiber, it is possible to realize a laser beam incident method with less reflection loss.

[Brief description of drawings]

FIG. 1 is a configuration diagram for carrying out a laser beam injection method according to the present invention.

FIG. 2 is a diagram showing a relationship between an incident angle of a laser beam on a transmitting member and reflection loss.

FIG. 3 is a schematic diagram of a laser resonator that emits a P-polarized laser beam.

FIG. 4 is a diagram showing a relationship among a refractive index, a Brewster angle θ _B , a cutting angle θ _a , and an emission angle θ _t .

FIG. 5 is a conceptual diagram of a method of transmitting a laser beam using a glass fiber.

[Explanation of symbols]

 10 condensing lens 11 glass fiber 12 core 13 clad

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Fumio Matsuzaka, No. 1 Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Ishi, Kawashima-Harima Heavy Industries Co., Ltd. Technical Research Institute (72) Masato Hirayama Shin-Nakahara-cho, Isogo-ku, Yokohama, Kanagawa No. 1 Ishi Kawashima Harima Heavy Industries Ltd. Technical Research Institute

Claims (1)

[Claims] 1. A laser beam injection method for converging a laser beam and transmitting the laser beam by injecting the laser beam into a glass fiber, wherein a linearly polarized laser beam is used as the laser beam entering the glass fiber. The laser beam is incident on the fiber at the Brewster angle to the incident end face, and the incident end face is formed so that the incident laser beam is substantially parallel to the axis of the glass fiber. Method.