JP5378852B2 - Light source device - Google Patents

Description

  The present invention relates to a light source device using an optical fiber.

  Conventionally, a high-power optical fiber laser using a cascade Raman resonator has been disclosed as a light source device. 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.

  By the way, the optical characteristics of the output optical fiber of the YDFL, the optical fiber of the cascade Raman resonator, and the delivery optical fiber are designed according to the use of each optical fiber. have. For example, an optical fiber for a cascade Raman resonator is designed to have a small mode field diameter in order to efficiently generate a stimulated Raman scattering phenomenon that is a nonlinear optical phenomenon.

  As a result, when these optical fibers are connected by fusion splicing or the like, a connection loss occurs at the connection point due to mismatch of mode field diameters. The light energy lost due to the connection loss is converted into heat energy at the connection point, and the temperature of the connection point is increased. However, when the laser beam has a high output as described above, even if the connection loss is a relatively small value, the amount of heat generated by conversion into thermal energy increases, so protection for protecting the connection point. There has been a problem that the reliability of the apparatus is lowered because the material or the like may become hot and may be damaged or deteriorated.

  The present invention has been made in view of the above, and an object thereof is to provide a highly reliable light source device.

  In order to solve the above-described problems and achieve the object, a light source device according to the present invention includes a light source that outputs light from an output optical fiber having a first mode field diameter, and the first mode field diameter. A connection optical fiber having a different second mode field diameter, a connection to the output optical fiber at a first connection point and a connection to the connection optical fiber at a second connection point, and the first mode field diameter And at least one insertion optical fiber having a third mode field diameter which is a value between the second mode field diameters.

  The light source device according to the present invention is characterized in that, in the above invention, the light source device further includes a protective material formed on at least one of an outer periphery of the first connection point and an outer periphery of the second connection point. And

  In the light source device according to the present invention as set forth in the invention described above, the protective material is a thermally conductive protective material.

  In the light source device according to the present invention as set forth in the invention described above, the protective material has a refractive index higher than at least the outer periphery of the optical fiber to be formed.

  In the light source device according to the present invention, in the above invention, at least one of an outer periphery of the inserted optical fiber in the vicinity of the first connection point and an outer periphery of the connection optical fiber in the vicinity of the second connection point. It further includes a light leakage protective material formed on one side and having a refractive index higher than at least the outer periphery of the optical fiber to be formed.

  Moreover, the light source device according to the present invention is characterized in that, in the above-described invention, the light source device further includes a heat conductive substrate on which at least one of the first connection point and the second connection point is placed. To do.

  According to the present invention, since the amount of heat generated at the connection point of the optical fiber can be reduced, the light source device having high reliability can be realized.

FIG. 1 is a schematic diagram of a light source device according to Embodiment 1. FIG. FIG. 2 is a diagram for explaining a specific structure near the substrate. FIG. 3 is a diagram schematically illustrating an example of the relationship between the mode field diameter of the inserted optical fiber, the connection loss at the connection point, and the temperature of the protective material. FIG. 4 is a diagram illustrating a specific structure in the vicinity of the base material of the light source device according to the modification of the first embodiment.

  Embodiments of a light source device 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 a light source device according to Embodiment 1 of the present invention. The light source device 100 includes an optical fiber laser FL as a light source, a cascade Raman resonator CRR, an insertion 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 optical fiber grating 6 has a center wavelength of 1177 nm, a reflectivity of about 100% in a wavelength band having a width of about 2 nm around the center wavelength and its periphery, 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. Accordingly, the optical fiber gratings 6 and 7 constitute an optical resonator for light having a wavelength of 1117 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 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 as a connection optical fiber, 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. And.

  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, 1240 nm, and 1175 nm from the input side. On the other hand, the optical fiber grating 12 includes 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, 1240 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 insertion optical fiber 13 is connected to the output optical fiber 9 at the connection point C7 and 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. 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. Note that the covering portions 9c, 10c, and 13c are removed around the connection points C7 and C8 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. In the grooves 14a and 15a, protective materials 16 and 17 made of a resin such as urethane acrylate prepolymer are formed on the outer periphery of the connection points C7 and C8. The refractive indexes of the protective members 16 and 17 are higher than the refractive indexes of the clad portions 9b, 10b, and 13b of the output optical fiber 9, the optical fiber grating 10, and the insertion optical fiber 13.

Next, the operation of the light source device 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 pumping light that has reached the rare earth element-doped optical fiber 8 optically pumps Yb ions added to the core portion 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. The fluorescence is amplified by the stimulated emission action of Yb ions while reciprocating in the optical resonator formed by the optical fiber gratings 6 and 7 in a single mode, and oscillates at an oscillation wavelength of 1117 nm. The optical fiber laser FL outputs laser light from the output optical fiber 9.

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

  Here, if the output optical fiber 9 and the optical fiber grating 10 having different mode field diameters are directly connected, a large connection loss occurs at the connection point. As a result, the amount of heat generated when the laser light passes through the connection point increases.

  However, in the light source device 100 according to the first embodiment, the intervening optical fiber 13 having a mode field diameter that is between the mode field diameters is interposed between the output optical fiber 9 and the optical fiber grating 10. As a result, the connection loss to be generated is distributed to the connection points C7 and C8, and the amount of heat generated per connection point is also reduced. As a result, damage or deterioration due to the temperature rise of the protective members 16 and 17 that protect the connection points C7 and C8 is suppressed, and the reliability of the device is increased.

  Note that some of the laser light and excitation light output from the output optical fiber 9 may leak at the connection points C7 and C8. 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 the light source device 100 according to the first embodiment, the refractive indexes of the protective members 16 and 17 are higher than the refractive indexes of the cladding portions 9b, 10b, and 13b. Accordingly, the leakage light is promptly emitted to the protective members 16 and 17, and the protective members 16 and 17 promptly emit the leakage light to the outside. As a result, damage to the covering portion 10c is prevented, and the reliability is further 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 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 light source device 100 according to the first embodiment has high reliability.

  Next, a method for setting the mode field diameter of the insertion optical fiber 13 will be described. For example, it is more preferable to set the mode field diameter so that the calorific values at the connection points C7 and C8 are approximately the same.

  FIG. 3 is a diagram schematically showing an example of the relationship between the mode field diameter of the insertion optical fiber 13, the connection loss at the connection points C7 and C8, and the temperatures of the protective members 16 and 17. Lines L1 and L2 indicate connection losses at connection points C7 and C8, respectively. The value a1 indicates the mode field diameter of the output optical fiber 9, and the value a2 indicates the mode field diameter of the optical fiber grating 10. Further, the line L3 is set to an allowable temperature that can ensure desired reliability of the protective materials 16 and 17. When setting the mode field diameter of the insertion optical fiber 13, the mode field diameter may be set between the values a1 and a2 so as to realize a connection loss that does not exceed the allowable temperature of the protective members 16 and 17. . Further, for example, a plurality of insertion optical fibers having different mode field diameters may be connected to further disperse the connection loss.

  In the first embodiment, the protective materials 16 and 17 having a high refractive index are formed on the outer periphery of the connection points C7 and C8. However, a protective material having a high thermal conductivity may be formed. Hereinafter, a light source device according to a modification of the first embodiment provided with such a protective material will be described. This modification includes the same optical fiber laser FL, cascade Raman resonator CRR, intervening optical fiber 13, and base materials 14 and 15 as those in the first embodiment.

  FIG. 4 is a diagram illustrating a specific structure in the vicinity of the base materials 14 and 15 of the light source device according to the modification of the first embodiment. In this modification, in the grooves 14a and 15a of the base materials 14 and 15, heat conductive protective materials 18 and 19 made of, for example, a silicone-based heat conductive compound are formed on the outer periphery of the connection points C7 and C8. ing. Furthermore, the outer periphery of the insertion optical fiber 13 in the vicinity of the connection point C7 and the outer periphery of the optical fiber grating 10 in the vicinity of the connection point C8 are respectively made of a protective material for light leakage made of, for example, the same material as the protective materials 16 and 17. 20 and 21 are formed. The refractive index of the light leakage protective material 20 is higher than the refractive index of the clad portion 13b of the insertion optical fiber 13, and the refractive index of the light leakage protective material 21 is the refractive index of the clad portion 10b of the optical fiber grating 10. Higher than.

  In this modification, since the heat conductive protective members 18 and 19 are formed on the outer periphery of the connection points C7 and C8, even if the heat generation amount is larger, the temperature rise of the heat conductive protective members 18 and 19 is suppressed. Therefore, the reliability is further increased. That is, a light source device with higher output can be realized. Further, since the light leakage protective materials 20 and 21 are formed on the light output side with respect to the connection points C7 and C8, the leakage light can be quickly transferred to the outside in the same manner as the protective materials 16 and 17 in the first embodiment. To release. As a result, damage to the covering portion 10c is prevented, and the reliability is further increased.

  In addition, about the material of the heat conductive protective materials 18 and 19, what has a characteristic which does not absorb the light which leaks in the connection points C7 and C8 is more preferable. Moreover, the thing higher than the refractive index of the clad parts 9b, 10b, and 13b 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. 4, 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. In addition, an aluminum plate having a length of 60 mm, a width of 10 mm, a thickness of 2 mm, a groove width of 2 mm, and a depth of 1 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.

  In the first embodiment, the mode field diameter of the optical fiber grating 10 which is a connection optical fiber is smaller than the mode field diameter of the output optical fiber 9. However, the present invention can also be applied when the mode field diameter of the connecting optical fiber is larger than the mode field diameter of the output optical fiber. In the first embodiment, the light source is an optical fiber laser. However, there is no particular limitation as long as the light source outputs light from the output optical fiber. The connecting optical fiber can also be a delivery optical fiber, for example, and is not particularly limited.

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 9a, 10a, 13a Core part 9b, 10b, 13b Clad part 9c, 10c, 13c Covering part 11 Raman fiber 13 Intervening optical fiber 14, 15 Base material 14a, 15a Groove 16, 17 Protective material 18, 19 Thermal conductive protective material 20, 21 Light leakage protective material 100 Light source device C1-C8 Connection point CRR Cascade Raman resonator FL Optical fiber Laser L1-L3 line

Claims (3)

A light source that outputs light from an output optical fiber having a first mode field diameter;
A connecting optical fiber having a second mode field diameter different from the first mode field diameter;
Connected to the output optical fiber at the first connection point and connected to the connection optical fiber at the second connection point, and is a value between the first mode field diameter and the second mode field diameter. At least one intervening optical fiber having a third mode field diameter;
A thermally conductive substrate on which the first connection point is placed;
And the thermally conductive base material has a groove portion that accommodates the first connection point, and in the groove portion, an outer periphery of the first connection point is made of a silicone-based heat conductive compound. A thermally conductive protective material is formed ,
The silicone-based heat conductive compound includes boron nitride as a filler .   A light leakage protective material having a refractive index higher than at least the outer periphery of the optical fiber to be formed on the outer periphery of the insertion optical fiber in the vicinity of the first connection point where the thermally conductive protective material is formed. The light source device according to claim 1, further comprising: A second base material having a groove for accommodating the second connection point;
In the groove portion of the second base material, a heat conductive protective material made of a silicone-based heat conductive compound is formed on the outer periphery of the second connection point,
The mode field diameter of the insertion optical fiber is set so that the amount of heat generated at the first connection point and the second connection point is approximately the same. Light source device.

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