JP2010239037A - Optical fiber laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable optical fiber laser. <P>SOLUTION: The optical fiber laser has: an output optical fiber connected to an optical-fiber resonator including an amplified optical fiber with an amplifying material added thereto, and having a covered portion formed at an outer periphery and removed at an optical output end; and a thermally-conductive protective member formed at the outer periphery at the end of the covered portion adjoining to the optical output end of the output optical fiber. Preferably, the optical fiber laser further has a thermally-conductive base member mounted with the end of the covered portion, and a connecting optical fiber connected to the optical output end of the output optical fiber. The thermally-conductive protective member is formed to be extended to the outer periphery of a point connected to the connecting optical fiber. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical fiber laser.

  Conventionally, a high output optical fiber laser using a cascade Raman resonator has been disclosed as an optical fiber laser. For example, the optical fiber laser disclosed in Non-Patent Document 1 includes a pumping optical fiber laser composed of an ytterbium (Yb) ion-doped optical fiber laser (YDFL) and a cascade Raman resonator. In this optical fiber laser, the pumping optical fiber laser outputs pumping laser light having a wavelength of 1117 nm, and the cascade Raman resonator receives the pumping laser light, and the stimulated Raman scattering phenomenon in the cascade Raman resonator. To generate and output a high-power laser beam having a wavelength of 1480 nm.

  The optical fiber laser using the YDFL or the cascade Raman resonator can also be used as a light source device for various laser processing apparatuses. In this case, the high-power laser beam output from the light source device is transmitted to a desired location by the delivery optical fiber and used for laser processing.

S. G. Grubb, et al., "High-Power 1.48 μm Cascaded Raman Laser in Germanosilicate Fibers," in Optical Amplifiers and Their Applications (1995), paper SaA4.

  However, when the output power of the optical fiber laser as described above is increased, the tip of the covering portion at the output end of the optical fiber on the output side may be damaged, resulting in a problem that the reliability of the apparatus is lowered. .

  The present invention has been made in view of the above, and an object thereof is to provide an optical fiber laser having high reliability.

  In order to solve the above-described problems and achieve the object, an optical fiber laser according to the present invention is connected to an optical fiber resonator including an amplifying optical fiber to which an amplifying substance is added, and a coating portion formed on the outer periphery is provided. An output optical fiber from which the covering portion is removed at the light output end, and a heat conductive protective material formed on the outer periphery of the end of the covering portion in the vicinity of the light output end of the output optical fiber; It is characterized by providing.

  Moreover, the optical fiber laser according to the present invention is characterized in that, in the above-described invention, the optical fiber laser further includes a heat conductive substrate on which the end portion of the covering portion is placed.

  The optical fiber laser according to the present invention may further include a connection optical fiber connected to the light output end of the output optical fiber in the above invention, and the thermally conductive protective material may be connected to the connection optical fiber. It is formed by extending to the outer periphery of the connection point.

  The optical fiber laser according to the present invention is the optical leakage protective material according to the present invention, wherein the optical leakage laser is formed on the outer periphery of the connection optical fiber in the vicinity of the connection point and has a refractive index higher than at least the outer periphery of the connection optical fiber. Is further provided.

  According to the present invention, damage to the end portion of the covering portion of the output optical fiber is prevented, so that it is possible to realize an optical fiber laser with high reliability.

FIG. 1 is a schematic diagram of an optical fiber laser according to the first embodiment. FIG. 2 is a diagram for explaining a specific structure near the substrate. FIG. 3 is an explanatory diagram for explaining leakage light generated in the optical fiber laser shown in FIG.

  Embodiments of an optical fiber laser according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a schematic diagram of an optical fiber laser according to Embodiment 1 of the present invention. The optical fiber laser 100 includes an optical fiber laser FL as a light source, a cascade Raman resonator CRR, an interposing optical fiber 13, and base materials 14 and 15.

The optical fiber laser FL includes semiconductor laser elements 1 ₁ to 1 _n as pumping light sources and a multimode optical fiber 2 that guides pumping light output from the semiconductor laser elements 1 ₁ to 1 _n, where _n is an integer of 2 or more. _{1 to} 2 _n and the pumping light guided by the multimode optical fibers 2 ₁ to 2 _n are coupled and output from the double clad optical fiber 5, TFB (Tapered Fiber Bundle) 3, 4, and each double clad optical fiber 5 Double-clad type optical fiber gratings 6 and 7 connected at connection points C1 and C4, double-clad type rare earth element-doped optical fiber 8 connected to optical fiber gratings 6 and 7 at connection points C2 and C3, and TFB4 And a connected output optical fiber 9.

The wavelength of the excitation light output from the semiconductor laser elements 1 ₁ to 1 _n is near 915 nm. The rare earth element-doped optical fiber 8 is an amplification optical fiber in which ytterbium (Yb) ions, which are amplification substances, are added to the core portion. The optical fiber grating 6 has a center wavelength of 1117 nm, a reflectance of about 100% in the wavelength band of about 2 nm width around the center wavelength and the periphery thereof, and light with a wavelength of 915 nm is almost transmitted. The optical fiber grating 7 has a center wavelength of 1117 nm, a reflectance at the center wavelength of about 10 to 30%, a full width at half maximum of the reflection wavelength band of about 1 nm, and light with a wavelength of 915 nm is almost transmitted. Therefore, the optical fiber gratings 6 and 7 constitute an optical fiber resonator OR including the rare earth element-doped optical fiber 8 for light having a wavelength of 1117 nm. The output optical fiber 9 is connected to the optical fiber resonator OR through the double clad optical fiber 5 and the TFB 4. The mode field diameter of the output optical fiber 9 is about 9 to 10 μm.

  On the other hand, the cascade Raman resonator CRR includes an optical fiber grating 10, a Raman fiber 11 connected to the optical fiber grating 10 at a connection point C5, and an optical fiber grating 12 connected to the Raman fiber 11 at a connection point C6. .

  In order to efficiently generate stimulated Raman scattering, the Raman fiber 11 has a mode field diameter reduced to about 6 μm to enhance optical nonlinearity. The optical fiber grating 10 includes five optical fiber gratings that reflect light having different wavelengths, and the reflection center wavelengths of the optical fiber gratings are 1480 nm, 1390 nm, 1310 nm, 1239 nm, and 1175 nm from the input side. On the other hand, the optical fiber grating 12 is composed of six optical fiber gratings that reflect light having different wavelengths, and the reflection center wavelengths of the optical fiber gratings are 1480 nm, 1175 nm, 1239 nm, 1310 nm, 1390 nm, and 1117 nm from the input side. ing. In order to ensure connectivity with the Raman fiber 11, the optical fiber gratings 10 and 12 also have a mode field diameter of about 6 μm.

  On the other hand, the distal end portion of the output optical fiber 9 is connected to an insertion optical fiber 13 as a connection optical fiber at a connection point C7. Further, the insertion optical fiber 13 is connected to the optical fiber grating 10 at the connection point C8. The mode field diameter of the insertion optical fiber 13 is about 8 μm which is a value between about 6 μm which is the mode field diameter of the optical fiber grating 10 and about 9 to 10 μm which is the mode field diameter of the output optical fiber 9. Each of the optical fibers is a silica glass optical fiber. The connection points C1 to C8 are all fusion-bonded.

  The connection points C7 and C8 are respectively placed on plate-like base materials 14 and 15 made of aluminum having high thermal conductivity. Next, a specific structure near the base materials 14 and 15 will be described. FIG. 2 is a diagram illustrating a specific structure near the base materials 14 and 15. In FIG. 2, the output optical fiber 9, the optical fiber grating 10, and the insertion optical fiber 13 have a cross-sectional structure along the longitudinal direction. As shown in FIG. 2, the output optical fiber 9 has a structure in which a cladding portion 9b and a covering portion 9c are sequentially formed on the outer periphery of the core portion 9a, and has a light output end portion 9e. Similarly, the optical fiber grating 10 has a structure in which a cladding portion 10b and a covering portion 10c are sequentially formed on the outer periphery of the core portion 10a. Similarly, the insertion optical fiber 13 has a structure in which a cladding portion 13b and a covering portion 13c are sequentially formed on the outer periphery of the core portion 13a, and has a light output end portion 13e. The covering portions 9c, 10c, and 13c have a lower refractive index than the cladding portions 9b, 10c, and 13c, respectively. The covering portions 9c, 10c, and 13c are removed at the connection points C7 and C8 and the periphery thereof for fusion splicing.

  Further, grooves 14a and 15a are respectively formed on the surfaces of the base materials 14 and 15, and the connection points C7 and C8 are accommodated in the grooves 14a and 15a, respectively. Further, in the groove 14a, a heat conductive protective material 16 made of, for example, a silicone-based heat conductive compound or the like is formed on the outer periphery of the end portion 9ca of the covering portion 9c. In the optical fiber laser 100, the thermally conductive protective material 16 is further extended to the outer periphery of the connection point C7. On the other hand, similarly in the groove 15a, a heat conductive protective material 17 similar to the heat conductive protective material 16 is formed on the outer periphery of the end portion 13ca of the covering portion 13c. This heat conductive protective material 17 is also extended and formed to the outer periphery of the connection point C8. Further, the outer periphery of the insertion optical fiber 13 near the connection point C7 and the outer periphery of the optical fiber grating 10 near the connection point C8 are respectively provided with a light leakage protective material 18 made of a resin such as urethane acrylate prepolymer. , 19 are formed. The refractive index of the light leakage protective material 18 is higher than the refractive index of the cladding portion 13b of the intervening optical fiber 13, and the refractive index of the light leakage protective material 19 is the refractive index of the cladding portion 10b of the optical fiber grating 10. Higher than.

Next, the operation of the optical fiber laser 100 will be described. First, in the optical fiber laser FL, when the semiconductor laser elements 1 ₁ to 1 _n output pumping light having a wavelength near 915 nm, the multimode optical fibers 2 ₁ to 2 _n guide the pumping light, and the TFBs 3 and 4 The guided pumping lights are combined and output to the double clad optical fiber 5. The double clad optical fiber 5 propagates coupled pumping light in multimode. Thereafter, the optical fiber gratings 6 and 7 transmit the pumping light propagated through the double clad optical fiber 5 to reach the rare earth element-doped optical fiber 8.

  The excitation light that has reached the rare earth element-doped optical fiber 8 optically excites Yb ions added to the core of the rare earth element doped optical fiber 8 while propagating in the inner cladding of the rare earth element doped optical fiber 8 in multimode. Fluorescence having a wavelength band including 1117 nm is emitted. This fluorescence is amplified by the stimulated emission action of Yb ions while reciprocating in the single mode in the optical fiber resonator OR formed by the optical fiber gratings 6 and 7, and oscillates at an oscillation wavelength of 1117 nm. The optical fiber laser FL outputs laser light from the optical fiber resonator OR to the output optical fiber 9.

  Next, the laser light output from the output optical fiber 9 passes through the connection point C7, passes through the insertion optical fiber 13 and the connection point C8 in order, and is input from the optical fiber grating 10 to the cascade Raman resonator CRR.

  Here, the output optical fiber 9 is connected to the optical fiber resonator OR through the double clad optical fiber 5 and the TFB 4. A part of the laser light outputted from the optical fiber grating 7 constituting the optical fiber resonator OR leaks from the core portion at a connection point C4 existing between the optical fiber grating 7 and the output optical fiber 9. Further, the residual excitation light propagates in the cladding part (passes through the core part).

  FIG. 3 is an explanatory diagram for explaining leakage light generated in the optical fiber laser 100 shown in FIG. In FIG. 3, reference numerals 5 a, 5 b, and 5 c denote a resin-made outer cladding portion that also functions as a core portion, an inner cladding portion, and a coating of the double-clad optical fiber 5, respectively. Reference numerals 7a, 7b, and 7c denote a core portion, an inner cladding portion, and a resin outer cladding portion that also function as a coating of the optical fiber grating 7, respectively.

  As shown in FIG. 3, a part of the laser light output from the optical fiber grating 7 leaks from the core portion because of the connection loss at the connection point C4, and becomes the leaked light L1. Further, the residual excitation light Lx propagates in the inner cladding part 7b (which also passes through the core part 7a). The leakage light L1 and the residual excitation light Lx propagate through the inner cladding portion 5b (which also passes through the core portion 5a) of the double cladding optical fiber 5 and enter the output optical fiber 9.

  Next, also in the output optical fiber, since the refractive index of the covering portion 9c is lower than the refractive index of the cladding portion 9b, the leakage light L1 and the residual excitation light Lx propagate through the cladding portion 9b. The leakage light L1 and the residual excitation light Lx are emitted to the outside at the end portion 9ca of the covering portion 9c in the vicinity of the light output end portion 9e of the output optical fiber 9, and at this time, the end portion 9ca is heated.

  As a result of intensive studies by the present inventors, in the case of a high-power optical fiber laser, the end portion 9ca is mainly heated by the residual pumping light Lx as described above, resulting in a high temperature. I found out that it was the cause. On the other hand, in this optical fiber laser 100, since the heat conductive protective material 16 is formed on the outer periphery of the end portion 9ca, the heat of the end portion 9ca is effectively dissipated as heat T1. As a result, the temperature rise of the end portion 9ca is suppressed and damage is prevented.

  Further, when the laser light passes through the connection point C7, a part of the laser light leaks as leakage light L2, as in the case of the connection point C4. When such leaked light propagates through the cladding portions 13b and 10b and reaches the covering portion 10c of the optical fiber grating 10, the covering portion 10c may be damaged. However, in this optical fiber laser 100, the refractive index of the light leakage protective material 18 is higher than the refractive index of the cladding portion 13b. Accordingly, the leakage light L2 is promptly emitted to the light leakage protective material 18, and the light leakage protection material 18 immediately releases the leakage light to the outside. As a result, damage to the covering portion 10c is prevented, and the reliability is further increased.

  As shown in FIG. 2, in this optical fiber laser 100, since the heat conductive protective material 17 is also formed on the outer periphery of the end portion 13ca of the covering portion 13c of the insertion optical fiber 13, it is assumed that the leakage light L1 , L2, even if the residual excitation light Lx reaches the end portion 13ca, the temperature rise of the end portion 13ca is suppressed and damage is prevented. Furthermore, since the light leakage protective material 19 emits leakage light, damage to the covering portion 10c is more reliably prevented.

  Further, in this optical fiber laser 100, an intervening optical fiber having a mode field diameter between the output optical fiber 9 and the optical fiber grating 10 is inserted between the mode field diameters of both. As a result, the connection loss that should occur due to the connection between the output optical fiber 9 and the optical fiber grating 10 is distributed to the connection points C7 and C8, and the amount of heat generated per connection point is also reduced. Furthermore, the heat conductive protective materials 16 and 17 are formed in the outer periphery of each connection point C7 and C8. As a result, even if the calorific value is further increased, the temperature rise of the heat conductive protective materials 16 and 17 is suppressed, so that damage or alteration is suppressed and the reliability of the apparatus is increased.

  Next, in the cascade Raman resonator CRR, when a laser beam having a wavelength of 1117 nm from the optical fiber laser FL is input to the Raman fiber 11 via the optical fiber grating 10, a Raman having a wavelength of 1175 nm corresponding to the first Stokes wavelength of Raman scattering. Scattered light (hereinafter referred to as first Stokes light) is generated and Raman amplified. The amplified first Stokes light is multiple-reflected by the optical fiber resonator formed by the optical fiber gratings 10 and 12 to increase its intensity, and eventually functions as excitation light to generate second Stokes light. Thereafter, third to fifth Stokes lights are sequentially generated by the same action. Here, in the optical fiber grating 12, since the reflectance of the optical fiber grating that reflects light having a wavelength of 1480 nm corresponding to the fifth Stokes light is low, the light having a wavelength of 1480 nm is output from the optical fiber grating 12 to the outside. Since the optical fiber grating 12 has an optical fiber grating having a reflection wavelength of 1117 nm, the laser light having a wavelength of 1117 nm output from the optical fiber laser FL is prevented from being output to the outside of the cascaded Raman resonator CRR. It is efficiently used inside the fiber 11.

  As described above, the optical fiber laser 100 according to the first embodiment has high reliability.

  In addition, about the material of the heat conductive protection materials 18 and 19, what has the characteristic which does not absorb a laser beam is more preferable.

(Example)
As an example of the present invention, an optical fiber laser and a cascade Raman resonator having the structure shown in FIG. 1 were produced, and these were connected by fusion splicing through an interpolating optical fiber. And as shown in FIG. 2, the periphery of the connection point of each optical fiber was accommodated in the groove | channel of the base material, and the heat conductive protective material and the light leakage protective material were formed in the predetermined location of the outer periphery. The optical fiber laser was designed to output laser light having a wavelength of 1117 nm and a light intensity of 95 W, and the mode field diameter of the output optical fiber was set to 9.5 μm. On the other hand, in the cascade Raman resonator, the mode field diameter of the optical fiber grating is 6 μm. In addition, the mode field diameter of the inserted optical fiber was 8 μm. Further, an aluminum plate having a length of 60 mm, a width of 10 mm, a thickness of 2 mm, and a groove width and depth of 2 mm was used as the substrate. In addition, T644 manufactured by Commerics of the United States was used as the heat conductive protective material. In addition, Desolite (registered trademark) manufactured by JSR Corporation was used as a protective material for light leakage.

  At this time, the connection loss at the connection point A (corresponding to the connection point C7 in FIG. 1) between the output optical fiber and the insertion optical fiber was 0.3 dB. Further, the connection loss at the connection point B (corresponding to the connection point C8 in FIG. 1) between the insertion optical fiber and the optical fiber grating was 0.27 dB.

  Next, at room temperature, laser light with a wavelength of 1117 nm and a light intensity of 95 W was output from the optical fiber laser, and a laser beam with a wavelength of 1480 nm and an intensity of 47.5 W was output from the cascade Raman resonator. At this time, at the connection point A, it is considered that about 6.34 W of light energy was lost due to the connection loss of the laser light, and a part of the energy was converted into heat. In addition, at the connection point B, it is considered that about 5.34 W of energy is lost in the laser light in consideration of the loss at the connection point A, and a part of the energy is converted into heat.

  And when the temperature of the heat conductive protective material was measured after the temperature fluctuation converged, it was 41 ° C. at the connection point A and 45 ° C. at the connection point B, and neither of the heat conductive protective materials was damaged. . Further, when the temperature of the protective material for light leakage was measured, it was 51 ° C. near the connection point A and 45 ° C. at the connection point B, and no light leakage protective material was damaged. Moreover, there was no damage of the edge part of the coating | coated part of an output optical fiber and an insertion optical fiber.

  In the first embodiment, the output optical fiber is connected to the insertion optical fiber that is a connection optical fiber. However, for example, when the output optical fiber is not connected to another optical fiber and a laser beam is output by providing a connector or the like, the end of the covering portion may be heated, so the present invention can be applied.

1 ₁ to 1 _n semiconductor laser element 2 ₁ to 2 _n multimode optical fiber 3 and 4 TFB
DESCRIPTION OF SYMBOLS 5 Double clad optical fiber 6, 7, 10, 12 Optical fiber grating 8 Rare earth element addition optical fiber 9 Output optical fiber 5a, 7a, 9a, 10a, 13a Core part 5b, 7b Inner clad part 5c, 7c Outer clad part 9b, 10b, 13b Cladding portion 9c, 10c, 13c Covering portion 9ca, 13ca End portion 9e, 13e Light output end portion 11 Raman fiber 13 Interpolated optical fiber 14, 15 Base material 14a, 15a Groove 16, 17 Thermal conductive protective material 18 , 19 Optical leakage protective material 100 Optical fiber laser C1-C8 Connection point CRR Cascade Raman resonator FL Optical fiber laser L1, L2 Leaked light Lx Residual pumping light OR Optical fiber resonator

Claims (4)

An output optical fiber connected to an optical fiber resonator including an amplifying optical fiber to which an amplifying material is added, and having a coating portion formed on an outer periphery, wherein the coating portion is removed at an optical output end;
A thermally conductive protective material formed on the outer periphery of the end portion of the covering portion in the vicinity of the light output end portion of the output optical fiber;
An optical fiber laser comprising:   The optical fiber laser according to claim 1, further comprising a heat conductive substrate on which an end portion of the covering portion is placed. A connection optical fiber connected to the light output end of the output optical fiber;
The optical fiber laser according to claim 1, wherein the thermally conductive protective material is formed to extend to an outer periphery of a connection point with the connection optical fiber.   The optical fiber according to claim 3, further comprising a light leakage protective material formed on an outer periphery of the connection optical fiber in the vicinity of the connection point and having a refractive index higher than at least the outer periphery of the connection optical fiber. laser.

Images