JP2010002608A - Laser beam transmitting apparatus and fiber laser oscillator equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam transmitting apparatus in which cladding propagation light of an optical fiber can be completely removed in a short cladding propagation light removing part, and to provide a fiber laser oscillator equipped with the same. <P>SOLUTION: The apparatus is equipped with an optical fiber 1 comprising a light transmitting core 5 extended in the transmitting direction of a laser beam, a light transmitting cladding 4 having a lower refractive index than the core 5 and installed outside the core 5, and a coating 3 provided on the outside of the cladding 4. A cladding exposed part 2 is formed by removing a part of the coating 3 of the optical fiber 1, with a bending of a radius of curvature R imparted to the cladding exposed part 2, and then, a light transmitting member 6 is provided having a refractive index equal to or greater than that of the cladding 4, in a manner coming in contact with the exposed cladding 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser light transmission device that transmits laser light by the light guide effect of an optical fiber and a fiber laser oscillator including the same.

  In order to remove undesirable clad layer propagation light component, the conventional laser light transmission device removes a part of the coating of the optical fiber to expose the clad layer, and the gel having a refractive index higher than the refractive index of the clad layer. By making the clad exposed portion contact with the clad, the clad propagation light is dissipated to the outside (see, for example, Patent Document 1).

Another conventional apparatus dissipates clad propagation light to the outside by bringing a mode stripper having a refractive index equal to or higher than that of the cladding layer into contact with the cladding layer exposed by removing the coating at the end of the optical fiber. The coolant is circulated to exhaust heat (see, for example, Patent Document 2).
In the configuration of Patent Document 2, since the mode stripper in contact with the clad conducts light to the external coolant, the optical fiber itself does not generate heat and measures against overheating damage are taken.

Japanese Patent Laid-Open No. 3-269505 (FIG. 1) Special Table 2000-514930

In the conventional laser light transmission apparatus, in the configuration example of Patent Document 1, the optical fiber with the cladding layer exposed is bent and accommodated in the gel, and although there is no specific description about bending, the coating is generally removed. Since the optical fiber is very brittle, there is a problem that it is difficult to ensure reliability.
Further, when transmitting high power laser light, the gel in contact with the cladding layer generates heat, so that the optical fiber itself generates heat and may be damaged by overheating.

  On the other hand, in the configuration example of Patent Document 2, although measures against overheat damage are taken, in order to completely remove the clad propagation mode, it is necessary to install a mode stripper along the clad layer over a long distance. Therefore, there is a problem that the mode stripper part is increased in size and increases the cost.

  The present invention has been made to solve the above-described problems, and a laser light transmission device capable of high power transmission of 1 kW or more and having a compact cladding propagation component removal function and a fiber laser oscillator including the same The purpose is to obtain.

  The laser light transmission device according to the present invention includes a light-transmitting core extended in the laser light transmission direction, a light-transmitting cladding having a lower bending rate than the core and provided outside the core, In a laser light transmission apparatus comprising an optical fiber comprising a coating provided outside the cladding, the optical fiber has an exposed portion where a portion of the coating is removed over a predetermined length and a refractive index equal to or greater than that of the cladding. And a light transmissive member provided outside the exposed portion of the clad, wherein the clad exposed portion is bent at a radius of curvature within a range that can withstand strength and is in contact with the light transmissive member. It is.

  According to the present invention, by providing an appropriate curvature to the cladding exposed portion (coating removal portion) of the optical fiber, a substantially complete cladding propagation light removal effect can be obtained with a short length.

Embodiment 1 FIG.
FIG. 1 is an overall configuration diagram showing a laser beam transmission apparatus according to Embodiment 1 of the present invention, and FIG. 2 is an enlarged sectional view showing a clad propagation light removing unit 2 (in a broken line frame) in FIG. is there.
1 and 2, an optical fiber 1 is constituted by a coating 3 for external protection, a light-transmissive clad 4 and a core 5, and transmits a laser beam L emitted from a laser oscillator 10.

The core 5 is located at the center of the optical fiber 1 and extends in the transmission direction of the laser light L.
The clad 4 has a lower bending rate than the core 5 and is provided outside the core 5, and the coating 3 is provided outside the clad 4.

In the middle (a part) of the optical fiber 1, a clad propagation light removing part (cladding exposed part) 2 from which a part of the coating 3 is removed is provided.
A light transmissive member 6 having a refractive index equal to or higher than that of the clad 4 is provided outside the clad propagation light removing unit 2.
Furthermore, a cooling member 8 is provided outside the light transmissive member 6 via a light absorbing member 7.

The clad propagation light removal unit 2 has a predetermined length of the clad propagation light removal unit 2 within a range that can withstand strength in order to remove an undesirable clad layer propagation light component transmitted through the clad 4 of the optical fiber 1. While being bent at a radius of curvature R according to D, it is in contact with the light transmissive member 6.
Here, the radius of curvature R of the clad propagation light removing unit 2 is considered to give a gentle bend with a radius of curvature of 100 mm or more to an optical fiber having a clad diameter of 125 μm to 400 μm in consideration of the bending strength of the optical fiber 1.

  Here, the optical fiber 1 is assumed to be, for example, a quartz multimode optical fiber having a core 5 diameter of 20 μm, a cladding 4 diameter of 400 μm, and a coating 3 diameter of 550 μm. L assumes a YAG laser having a wavelength of 1 μm.

In the clad propagation light removing portion 2 of the optical fiber 1, the resin coating 3 is removed over a predetermined length D (for example, D = 15 mm).
In addition, the cladding 4 exposed to the cladding propagation light removing unit 2 is covered and fixed with the light transmissive member 6 while maintaining a predetermined radius of curvature R (for example, R = 150 mm). .

The light transmissive member 6 is made of, for example, sol (optical oil).
The light absorbing member 7 covering the periphery of the light transmissive member 6 is a material having good heat conductivity, and is made of, for example, a black-plated metal (aluminum, copper) or the like.
The cooling member 8 covering the periphery of the light absorbing member 7 is made of a metal with good heat conductivity (aluminum, copper) or the like, and is preferably configured by a water-cooled or air-cooled cooling mechanism.
In addition, the light absorption member 7 and the cooling member 8 may be integrally configured.

  In the configuration of FIGS. 1 and 2, when an undesired clad layer propagation light component propagating through the clad 4 in the optical fiber 1 reaches the clad propagation light removal unit 2, a predetermined radius of curvature R (for example, R = 150 mm) Is efficiently leaked from the clad 4 into the light transmissive member 6 (with a refractive index equal to or higher).

  The optical fiber 1 in the clad propagation light removing unit 2 is in a fragile state as described above because the coating 3 is removed over a predetermined length D (= 15 mm). In the experiment of the inventor, it has been confirmed that when the radius of curvature R is set to 100 mm or more when the diameter of the core 5 is 20 μm and the diameter of the cladding 4 is 400 μm, it can be used safely without any problem.

As a result, the clad propagation light is almost completely dissipated to the outside of the optical fiber 1 at a short distance of the predetermined length D = 15 mm of the clad propagation light removal unit 2.
Hereinafter, the leaked light component is absorbed by the light absorbing member 7, and the heat generation of the light absorbing member 7 caused by the light absorption at this time is cooled by the cooling member 8.
Moreover, since the surface of the clad 4 in the clad propagation light removing unit 2 is in contact with the light absorbing member 7 through the light transmissive member 6, the heat generated by the light absorbing member 7 may directly affect the clad 4. Absent. Therefore, the optical fiber 1 itself does not generate heat.

FIG. 3 is a characteristic diagram showing an experimental result of the optical residual ratio in the clad propagation light removing unit 2, and the horizontal axis indicates the reciprocal [m ^ (− 1)] of the bending radius (curvature radius R) of the optical fiber 1. The vertical axis represents the clad propagation light residual rate [%].
In the horizontal axis of FIG. 3 (the reciprocal of the curvature radius R), “5” corresponds to the curvature radius R = 200 mm, “6.7” corresponds to the curvature radius R = 150 mm, and “10” represents the curvature. This corresponds to a radius R = 100 mm.

  Further, each characteristic curve in FIG. 3 shows the curvature of the optical fiber 1 in the clad propagation light removal unit 2 in a state where the clad propagation light removal unit 2 is set to each predetermined length D (= 20 mm, 15 mm, 10 mm). It shows the result of actual measurement of the relationship between the clad propagation light residual rate.

  As is clear from FIG. 3, at a curvature radius R = 200 mm, the clad propagation light can be almost completely removed at a predetermined length D = 20 mm (residual rate = 0), and at a curvature radius R = 150 mm, It can be seen that the clad propagation light can be removed almost completely at the predetermined length D = 15 mm.

  That is, when the predetermined length D of the clad propagation light removing unit 2 is set to 20 mm, the curvature radius R is set to 200 mm or less, and when the predetermined length D is set to 15 mm, the curvature radius R is set. Is set to 150 mm or less, the clad propagation light can be removed.

In addition, when the radius of curvature R is 100 mm, the predetermined length D is 10 mm and about 98% of the clad propagation light can be removed (residual rate = 2 [%]), and the optical fiber 1 is experimentally damaged. It has also been proven not to exist. In this case, the length of the part from which the coating 3 is removed can be set short.
Furthermore, in the case of an optical fiber having a cladding diameter smaller than 400 μm (cladding diameter 125 μm to 400 μm), it was experimentally confirmed that an equivalent cladding propagation light removal effect can be obtained with a gentler bending (a larger radius of curvature). ing.

  As described above, the laser light transmission device according to the first embodiment of the present invention has a light-transmitting core 5 extended in the transmission direction of the laser light L, a lower bending rate than the core 5, 5 is provided with an optical fiber 1 including a light-transmitting clad 4 provided outside 5 and a coating 3 provided outside the clad 4.

The optical fiber 1 has a clad propagation light removing portion (cladding exposed portion) 2 from which a part of the coating 3 is removed over a predetermined length D, and a refractive index equal to or higher than that of the clad 4, and the clad propagation light removing portion 2 The clad propagation light removing portion 2 is bent with a radius of curvature R within a range that can withstand strength and is in contact with the light transmissive member 6. .
That is, the cladding propagation light removing portion 2 is formed by removing a portion of the coating 3 of the optical fiber 1 and bending it at an appropriate value of the radius of curvature R, and the light transmitting member 6 outside the cladding propagation light removing portion 2. Is attached.

In this way, a part of the optical fiber 1 from which the coating 3 has been removed (predetermined length D) is bent with a radius of curvature R that can withstand strength (no problem), and the clad propagation light removal unit 2 can remove the clad propagation light almost completely with a short predetermined length D, and is a laser beam having a compact and efficient clad propagation light removal capability that could not be realized by a conventional apparatus. A transmission apparatus can be realized.
In addition, since the light transmissive member 6 is in contact with the clad 4 exposed in the clad propagation light removing unit 2 and the light absorbing member 7 (heat generating member) is not in direct contact, the clad 4 is overheated. The possibility can also be avoided.

  In addition, since a light absorbing member 7 provided outside the light transmissive member 6 and a cooling member (cooling mechanism) 8 for cooling the light absorbing member 7 from the outside are provided, high-power laser light transmission In the apparatus, even when the clad propagation light power is high, the clad propagation light can be removed while suppressing the temperature rise of the optical fiber 1 itself.

  More specifically, the optical fiber 1 is a quartz multimode optical fiber having a core 5 having a diameter of 20 μm and a cladding 4 having a diameter of 400 μm. The cladding propagation light removing unit 2 has a predetermined length D = 20 mm and a curvature. The radius R is set to 200 mm. Alternatively, the predetermined length D = 15 mm and the radius of curvature R ≦ 150 mm are set.

As a result, the clad propagation light removal unit 2 can remove the clad propagation light almost completely.
When the predetermined length D of the clad propagation light removing unit 2 is set to 10 mm and the radius of curvature R ≦ 100 mm, about 98% of the clad propagation light is removed even if the predetermined length D = 10 mm. Can do.
Furthermore, in the case of an optical fiber having a cladding diameter smaller than 400 μm (cladding diameter 125 μm to 400 μm), it was experimentally confirmed that an equivalent cladding propagation light removal effect can be obtained with a gentler bending (a larger radius of curvature). ing.

Embodiment 2. FIG.
In the first embodiment (FIGS. 1 and 2), the case of the optical fiber 1 having the single-layer clad 4 is shown. However, an optical fiber (DCFF: double-clad fiber) having the two-layer clad 4 is used. It is good also as a structure which can use and can utilize a high output multimode laser diode light as excitation light.
In this case, the same effect as described above can be obtained for the double clad fiber.

The optical fiber 1 having the clad propagation light removing unit 2 is part of the configuration of the fiber laser oscillator, and the fiber laser oscillator is configured using the optical fiber 1 of the first embodiment (FIGS. 1 and 2). May be.
FIG. 4 is a block diagram showing a fiber laser oscillator 10A according to Embodiment 2 of the present invention using an optical fiber 11 having a clad propagation light removing unit 12. In FIG.

  In FIG. 4, a fiber laser oscillator 10A corresponds to the laser oscillator 10 described above (FIG. 1), and an optical fiber 11 and a clad propagation light removal unit 12 are connected to the optical fiber 1 and the clad propagation light removal unit 2 described above. Each is against.

  10 A of fiber laser oscillators are the optical fiber 11 which consists of a double clad fiber, the clad propagation light removal part 12 provided in a part of optical fiber 11 (near the output end of the laser beam L), and a part of optical fiber 11 A coiled winding part 11a, a laser diode 13 provided at one end of the optical fiber 11, and an FBG (Fiber Bragg Grating) 14 provided before and after the coiled winding part 11a. .

In the fiber laser oscillator 10 </ b> A, the laser oscillator itself that emits the laser light L is configured by the optical fiber 11 having the clad propagation light removing unit 12.
Further, the optical fiber 11 used in the fiber laser oscillator 10A is often composed of a double clad fiber configured to confine the pumping light in the clad.

As shown in FIG. 4, by providing the cladding propagation light removing unit 12 in the vicinity of the emission end of the laser beam L of the fiber laser oscillator 10A, the laser beam L emitted from the fiber laser oscillator 10A includes a cladding propagation component. A good quality beam can be obtained.
In particular, in the case of the optical fiber 11 made of a double-clad fiber, it is possible to apply the above-described ordinary optical fiber 1 by considering the clad 4 as the first clad and the coating 3 as the second clad.

As described above, according to the fiber laser oscillator 10A according to the second embodiment of the present invention, by using the optical fiber 11 having the clad propagation light removing unit 12, the fiber laser oscillator can be used without adding a special configuration. As the laser light L emitted from 10A, a high-quality beam that does not contain a clad propagation component can be obtained.
Further, when the optical fiber 11 made of a double clad fiber is used, an extra pumping light propagating through the first clad is combined by arranging the clad propagation light removing unit 12 in the vicinity of the emission part of the fiber laser oscillator 10A. Can be removed.
Therefore, it is possible to obtain a clean mode laser beam L from which the clad propagation light is removed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram which shows the laser beam transmission apparatus concerning Embodiment 1 of this invention. It is sectional drawing which expands and shows the clad propagation light removal part in FIG. It is explanatory drawing which shows the relationship between the optical fiber curvature in the clad propagation light removal part which concerns on Embodiment 1 of this invention, and a clad propagation light residual rate. It is a block diagram which shows the fiber laser oscillator based on Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,11 Optical fiber, 2, 12 Clad propagation light removal part (clad exposure part), 3 coating | cover, 4 clad, 5 cores, 6 Light transmissive member, 7 Light absorption member, 8 Cooling member, 10A Fiber laser oscillator, 11a Coiled winding part, 13 laser diode, 14 FBG.

Claims (8)

A light-transmitting core extended in the laser light transmission direction;
A light-transmitting cladding having a lower bending rate than the core and provided outside the core;
In a laser beam transmission apparatus comprising an optical fiber comprising a coating provided outside the cladding,
The optical fiber is
A cladding exposed portion in which a part of the coating is removed over a predetermined length;
A light transmissive member having a refractive index equal to or higher than that of the clad and provided on the outside of the clad exposed portion;
The laser light transmission device, wherein the exposed portion of the clad is bent at a radius of curvature within a range that can withstand strength and is in contact with the light transmissive member. A light absorbing member provided outside the light transmissive member;
The laser light transmission apparatus according to claim 1, further comprising a cooling mechanism for cooling the light absorbing member from the outside.   3. The laser light transmission apparatus according to claim 1, wherein a diameter of the clad is set in a range of 125 μm to 400 μm. The radius of curvature of the exposed cladding portion is set within a range of 100 mm to 200 mm,
The laser light transmission apparatus according to claim 3, wherein the predetermined length of the cladding exposed portion is set to 20 mm or less. The radius of curvature of the exposed cladding portion is set within a range of 100 mm or more and 150 mm or less,
The laser light transmission apparatus according to claim 3, wherein the predetermined length of the cladding exposed portion is set to 15 mm or less. The radius of curvature of the exposed cladding portion is set to 100 mm,
The laser light transmission apparatus according to claim 3, wherein the predetermined length of the cladding exposed portion is set to 10 mm or less.   The laser light transmission apparatus according to claim 1, wherein the optical fiber is a double clad fiber.   A fiber laser oscillator comprising the laser beam transmission device according to any one of claims 1 to 7.

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