JP2018186239A - Optical combiner, and fiber laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an optical combiner which can increase an efficiency of transfer of light from an excitation optical fiber to an optical fiber for amplification; and a fiber laser device including the optical combiner.SOLUTION: An optical combiner comprises: an optical fiber 51 for amplification which has a core 52 with an active element added thereto and a clad 53 around the core 52; at least one excitation optical fiber 55; a mid resin part 54 formed between the optical fiber 51 for amplification and the at least one excitation optical fiber 55 so as to touch the optical fiber 51 for amplification and the at least one excitation optical fiber 55; and a common covering film 58 which covers the optical fiber 51 for amplification and the at least one excitation optical fiber 55 on an outer peripheral face side thereof. Supposing that the clad 53 has a refraction index n, the at least one excitation optical fiber 55 has a refraction index n, and the mid resin part 54 has a refraction index n, and the common covering film 58 has a refraction index n, the following relations hold: n≥n; n≥n; n>n; and n>n.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical combiner suitable for transferring pumping light from a pumping optical fiber to an amplification optical fiber, and a fiber laser device including the optical combiner.

  The fiber laser device is used in various fields such as a laser processing field and a medical field because it has excellent light condensing performance, has a high power density, and can obtain light as a small beam spot. In such a fiber laser device, an amplification optical fiber in which an active element is added to the core is used. Further, in the amplification optical fiber, a double clad structure is generally applied in order to allow more excitation light to enter the core. An optical fiber for amplification having a double clad structure has a core to which an active element is added, an inner clad surrounding the core, and an outer clad surrounding the inner clad, and the outer clad has a lower refractive index than the inner clad. The excitation light incident on the inner cladding is reflected to the core side at the interface between the inner cladding and the outer cladding and is incident on the core to excite the active element added to the core.

  For example, Patent Document 1 below discloses an optical combiner in which an amplification optical fiber as described above and a pumping optical fiber through which pumping light transferred to the amplification optical fiber propagates are optically coupled. In this optical combiner, the amplification optical fiber and the excitation optical fiber are aligned along the longitudinal direction, and these are covered with a common coating made of the same resin. In this optical combiner, the outer peripheral surface of the cladding of the amplification optical fiber and the outer peripheral surface of the pumping optical fiber are aligned so as to be close to each other. As described above, the pumping light propagating through the pumping optical fiber can be transferred to the cladding of the amplification optical fiber at a portion where the cladding of the amplification optical fiber and the pumping optical fiber are close to each other.

US Pat. No. 6,826,335

  In the optical combiner described in Patent Document 1, when the amplification optical fiber and the pumping optical fiber are in direct contact with each other, the amplification optical fiber and the pumping optical fiber are scratched on the surface and the mechanical strength is reduced. There are concerns. However, if the outer peripheral surface of the amplification optical fiber and the pumping optical fiber are separated from each other with a common coating, the resin constituting the common coating is also filled between the amplification optical fiber and the pumping optical fiber. Is done. The common coating functions as a polymer cladding that covers the outer peripheral surface of the amplification optical fiber and the outer peripheral surface of the pumping optical fiber. Therefore, the refractive index of this common film is made sufficiently lower than the refractive index of the glass constituting the amplification optical fiber and the excitation optical fiber. For this reason, when the resin constituting the common coating is filled between the amplification optical fiber and the pumping optical fiber, the light propagating through the pumping optical fiber is easily confined in the pumping optical fiber. Therefore, there is a concern that the light transfer efficiency from the pumping optical fiber to the amplification optical fiber is reduced.

  Accordingly, an object of the present invention is to provide an optical combiner capable of improving the light transfer efficiency from the pumping optical fiber to the amplification optical fiber, and a fiber laser device including the optical combiner.

In order to solve the above problems, an optical combiner according to the present invention includes an amplification optical fiber having a core to which an active element is added and a clad surrounding the core, at least one excitation optical fiber, and the amplification optical fiber. An intermediate resin portion disposed between the amplifying optical fiber and the pumping optical fiber so as to be in contact with the pumping optical fiber; a common coating surrounding the outer peripheral surface side of the amplifying optical fiber and the pumping optical fiber; The refractive index of the clad is n ₁ , the refractive index of the pumping optical fiber is n ₂ , the refractive index of the intermediate resin portion is n ₃ , and the refractive index of the common coating is n ₄ , (1) to (4) are satisfied.
n ₁ ≧ n ₂ (1)
n ₁ ≧ n ₃ (2)
n ₃ > n ₄ (3)
n ₂ > n ₄ (4)

In the optical combiner, the intermediate resin portion is disposed between the amplification optical fiber and the pumping optical fiber, so that direct contact between the amplification optical fiber and the pumping optical fiber can be suppressed. For this reason, the optical fiber for amplification and the pumping optical fiber can be prevented from being scratched on the surface and the mechanical strength being lowered. Moreover, the said optical combiner satisfy | fills said Formula (3) and (4). That is, the refractive index n ₄ of the common coating is made lower than the refractive index n ₂ of the pumping optical fiber and lower than the refractive index n ₃ of the intermediate resin portion. For this reason, the light propagating through the excitation optical fiber hardly leaks to the common coating side, and tends to be unevenly distributed on the side where the intermediate resin portion is formed. Moreover, the said optical combiner satisfy | fills the said Formula (2). That is, the refractive index n ₁ of the cladding of the amplification optical fiber is set to be equal to or higher than the refractive index n ₃ of the intermediate resin portion. For this reason, the light propagating through the intermediate resin portion is likely to enter the amplification optical fiber, and the light that has spread to the intermediate resin portion among the light propagating through the excitation optical fiber is likely to be transferred to the amplification optical fiber. Moreover, the said optical combiner satisfy | fills said Formula (1) to (4). In other words, the refractive index n ₁ of the cladding of the amplification optical fiber is the highest refractive index portion. For this reason, the light transferred to the amplification optical fiber is easily confined in the amplification optical fiber. As described above, in the optical combiner of the present invention, the light transfer efficiency from the pumping optical fiber to the amplification optical fiber can be improved.

Moreover, it is preferable to satisfy | fill following formula (5).
n ₃ ≧ n ₂ (5)

By the above equation (5) is satisfied, i.e., by the refractive index n ₃ of the intermediate resin portion is the refractive index n ₂ or more excitation optical fiber, light propagating through the excitation optical fiber is incident on the intermediate resin portion It becomes easy. Further, the light propagating through the intermediate resin portion is likely to enter the amplification optical fiber as described above. Therefore, the light transfer efficiency from the pumping optical fiber to the amplification optical fiber can be further improved.

Moreover, it is preferable to satisfy | fill following formula (6).
n ₁ > n ₃ (6)

When the above formula (6) is satisfied, that is, when the refractive index n ₁ of the cladding of the optical fiber for amplification is higher than the refractive index n ₃ of the intermediate resin portion, the light propagating through the intermediate resin portion And reflection at the interface between the optical fiber for amplification and the cladding of the optical fiber for amplification are suppressed, and the optical fiber for amplification becomes easy to enter. Further, the light propagating through the amplification optical fiber is easily reflected at the interface between the intermediate resin portion and the cladding of the amplification optical fiber, and is difficult to return to the intermediate resin portion side. Therefore, the light transfer efficiency from the pumping optical fiber to the amplification optical fiber can be further improved.

  Moreover, it is preferable that the side opposite to the amplification optical fiber side of the excitation optical fiber is covered in contact with the common coating.

As described above, the refractive index n ₄ of the common coating is lower than the refractive index n ₃ of the intermediate resin portion disposed on the amplification optical fiber side of the pumping optical fiber. Therefore, the side opposite to the amplification optical fiber side of the excitation optical fiber is covered with the common coating without passing through the intermediate resin portion, so that the light propagating through the excitation optical fiber is likely to be unevenly distributed on the amplification optical fiber side. . For this reason, the light transfer efficiency from the pumping optical fiber to the amplification optical fiber can be further improved.

  Further, in a cross section perpendicular to the longitudinal direction, two tangents that are in contact with the outer peripheral surface of the amplification optical fiber and the outer peripheral surface of the excitation optical fiber and do not intersect with each other between the amplification optical fiber and the excitation optical fiber And outside the intermediate region surrounded by the outer peripheral surface of the amplification optical fiber and the outer peripheral surface of the excitation optical fiber, the amplification optical fiber and the excitation optical fiber are covered with the common coating. Preferably it is.

  In this way, the outer peripheral surface of the amplifying optical fiber and the outer peripheral surface of the pumping optical fiber are covered with a common coating having a refractive index lower than that of the intermediate resin portion, so that the pump optical fiber propagates. Is more likely to be unevenly distributed to the amplification optical fiber side. In addition, light that has shifted to the amplification optical fiber is less likely to leak from the amplification optical fiber. Therefore, the light transfer efficiency from the pumping optical fiber to the amplification optical fiber can be further improved.

  In order to solve the above problems, a fiber laser device of the present invention includes any one of the above optical combiners and a pumping light source that emits pumping light incident on the pumping optical fiber.

  By providing any of the above optical combiners, the light transfer efficiency from the pumping optical fiber to the amplifying optical fiber can be improved.

  As described above, according to the present invention, an optical combiner capable of improving the light transfer efficiency from the pumping optical fiber to the amplification optical fiber and a fiber laser device including the optical combiner are provided.

It is a figure which shows the structure of the fiber laser apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows a cross section perpendicular | vertical to the longitudinal direction of the optical combiner shown in FIG. It is a figure which shows the cross section parallel to the longitudinal direction of a part of each optical fiber connected to the optical combiner shown in FIG. 1, and an optical combiner. It is a figure which shows the cross section perpendicular | vertical to the longitudinal direction of the optical combiner which concerns on 2nd Embodiment of this invention. It is a figure which shows a cross section perpendicular | vertical to the longitudinal direction of the optical combiner which concerns on a modification. It is a figure which shows a cross section perpendicular | vertical to the longitudinal direction of the optical combiner which concerns on another modification.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of an optical combiner and a fiber laser device according to the present invention will be described in detail with reference to the drawings. The embodiments exemplified below are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the spirit of the present invention.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration of a fiber laser device according to the present embodiment. As shown in FIG. 1, the fiber laser device 1 is a resonator type fiber laser device, and includes a pumping light source 20 having a laser diode 21, a pumping optical fiber 25 connected to the laser diode 21, and an optical fiber 30. The first FBG 35 provided in the optical fiber 30, the optical fiber 40, the second FBG 45 provided in the optical fiber 40, and the optical combiner 50 are provided as main components.

  The fiber laser device 1 of this embodiment includes two excitation light sources 20. Each excitation light source 20 includes a laser diode 21. The laser diode 21 of this embodiment is, for example, a Fabry-Perot type semiconductor laser made of a GaAs-based semiconductor, and emits excitation light having a center wavelength of 915 nm. The laser diode 21 is connected to one end of the pumping optical fiber 25, and the other end of the pumping optical fiber 25 is connected to the optical combiner 50. The pumping optical fiber 25 includes a core, a clad that surrounds the outer peripheral surface of the core without a gap, and a coating layer that covers the clad as main components.

  One end of the optical fiber 30 is connected to an optical combiner 50 as will be described later, and a terminating portion 38 that converts light into heat is provided at the other end of the optical fiber 30. The optical fiber 30 includes a core, a clad that surrounds the outer peripheral surface of the core without a gap, and a coating layer that covers the clad. The refractive index of the cladding is set lower than the refractive index of the core. As a material constituting such a core, for example, quartz to which an element such as germanium (Ge) that increases the refractive index is added can be cited. Examples of the material constituting the clad include pure quartz to which no dopant is added. Note that an element such as fluorine (F) that lowers the refractive index may be added to the cladding. Examples of the material constituting the coating layer include an ultraviolet curable resin.

  Further, a photosensitive element such as germanium is added to the core of the optical fiber 30, and the first FBG 35 is provided in the core of the optical fiber 30. The first FBG 35 includes a high refractive index portion having a higher refractive index than a portion other than the first FBG 35 of the core of the optical fiber 30, and a low refractive index portion having a refractive index similar to that of the portion other than the first FBG 35 of the core. It repeats periodically along the longitudinal direction of the core. The repeating pattern of the high refractive index portion is formed by, for example, irradiating ultraviolet light onto a portion that becomes the high refractive index portion. The first FBG 35 formed in this way reflects light of at least a part of the light emitted in the excited state of the active element added to the core 52 of the amplification optical fiber 51 described later. Is configured to do. The reflectivity of the first FBG 35 is higher than the reflectivity of the second FBG 45, which will be described later. Of the light emitted from the active element, light of a desired wavelength is preferably reflected by 90% or more, and is reflected by 99% or more. More preferred. The wavelength of light reflected by the first FBG 35 is, for example, 1060 nm when the active element is ytterbium.

  One end of the optical fiber 40 is connected to the optical combiner 50 as will be described later. The optical fiber 40 has the same configuration as the optical fiber 30 except that a second FBG 45 is provided in the core instead of the first FBG 35. The core of the optical fiber 40 is connected to the core 52 of the amplification optical fiber 51 as described later. Further, the second FBG 45 is provided in the core of the optical fiber 40 as described above. Similar to the first FBG 35, the second FBG 45 is formed by periodically repeating a high refractive index portion and a low refractive index portion. The second FBG 45 is configured to reflect light reflected by the first FBG 35 with a lower reflectance than the first FBG 35. When the light reflected by the first FBG 35 is incident, the second FBG 45 reflects this light with a reflectance of about 10%, for example. In the present embodiment, nothing is connected to the other end of the optical fiber 40 opposite to the amplification optical fiber 51 side, but a glass rod or the like may be connected.

  Next, the optical combiner 50 will be described. As shown in FIG. 1, the optical fiber 30 and the pumping optical fiber 25 are connected to one end of the optical combiner 50, and the optical fiber 40 and the other pumping optical fiber 25 are connected to the other end.

  FIG. 2 is a view showing a cross section perpendicular to the longitudinal direction of the optical combiner 50 shown in FIG. FIG. 3 is a diagram showing a cross section parallel to the longitudinal direction of a part of each optical fiber connected to the optical combiner 50 and the optical combiner 50 shown in FIG.

  As shown in FIGS. 2 and 3, the optical combiner 50 includes an amplification optical fiber 51, a pumping optical fiber 55, an intermediate resin portion 54 disposed between the amplification optical fiber 51 and the pumping optical fiber 55, and these. A common coating 58 is provided.

  The amplification optical fiber 51 has a core 52 to which an active element is added and a clad 53 surrounding the core 52. For example, an element such as germanium (Ge) that increases the refractive index and an active element such as ytterbium (Yb) that is excited by excitation light emitted from the excitation light source 20 are added to the core 52 of the amplification optical fiber 51. Quartz. Examples of such active elements include rare earth elements, and examples of rare earth elements include thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), and erbium (Er) in addition to Yb. Can be mentioned. Furthermore, bismuth (Bi) etc. can be mentioned as an active element other than a rare earth element. Examples of the material constituting the clad 53 include pure quartz to which no dopant is added. Note that an element such as fluorine (F) that lowers the refractive index may be added to the clad 53.

  The core 52 of the amplification optical fiber 51 has one end connected to the core 41 of the optical fiber 40 and the other end connected to the core 31 of the optical fiber 30. Therefore, the first FBG 35 is disposed on one side of the amplification optical fiber 51 and is optically coupled to the core 52 of the amplification optical fiber 51. The second FBG 45 is disposed on the other side of the amplification optical fiber 51 and optically coupled to the core 52 of the amplification optical fiber 51. Thus, the first FBG 35, the amplification optical fiber 51, and the second FBG 45 constitute an optical resonator. The cladding 53 of the amplification optical fiber 51 has one end connected to the cladding 42 of the optical fiber 40 and the other end connected to the cladding 32 of the optical fiber 30.

  The excitation optical fiber 55 of the present embodiment is a part constituted by an optical fiber element made of a single glass. The pumping optical fiber 55 has the same configuration as the core 26 of the pumping optical fiber 25. One end of the pumping optical fiber 55 is connected to the core 26 and the cladding 27 of the pumping optical fiber 25, and the other end is connected to the core 26 and the cladding 27 of the other pumping optical fiber 25. Accordingly, the pumping light emitted from each laser diode 21 enters the pumping optical fiber 55 via the pumping optical fiber 25.

  The intermediate resin portion 54 is disposed between the amplification optical fiber 51 and the excitation optical fiber 55 so as to be in contact with the amplification optical fiber 51 and the excitation optical fiber 55. The intermediate resin portion 54 is made of, for example, an ultraviolet curable resin. The intermediate resin portion 54 of the present embodiment is disposed in an intermediate region IR between the amplification optical fiber 51 and the excitation optical fiber 55. As shown in FIG. 2, the intermediate region IR is a region surrounded by the two tangents L <b> 1 and L <b> 2, the outer peripheral surface of the amplification optical fiber 51, and the outer peripheral surface of the pumping optical fiber 55. The two tangents L1 and L2 are in contact with the outer peripheral surface of the amplification optical fiber 51 and the outer peripheral surface of the excitation optical fiber 55 in a cross section perpendicular to the longitudinal direction of the optical combiner 50, and the amplification optical fiber 51 and the excitation optical fiber Do not cross each other with 55. As described above, the intermediate resin portion 54 is disposed in the intermediate region IR, and the amplification optical fiber 51 and the excitation optical fiber 55 are covered with the common coating 58 outside the intermediate region IR. Therefore, the side of the pumping optical fiber 55 opposite to the amplification optical fiber 51 side is covered with the common coating 58. Further, the intermediate resin portion 54 of the present embodiment is formed only in a region in the intermediate region IR where the distance between the outer peripheral surface of the amplification optical fiber 51 and the outer peripheral surface of the pumping optical fiber 55 is particularly narrow. Therefore, the intermediate resin portion 54 is formed on a line segment connecting the center of the amplification optical fiber 51 and the center of the excitation optical fiber 55. Further, the length d3 of the intermediate resin portion 54 in the direction perpendicular to the line segment in the cross section perpendicular to the longitudinal direction of the optical combiner 50 is based on the diameter d1 of the amplification optical fiber 51 and the diameter d2 of the pumping optical fiber 55. It is made smaller. In the present embodiment, the diameter d1 of the amplification optical fiber 51 and the diameter d2 of the pumping optical fiber 55 are the same. Further, the thickness t of the intermediate resin portion 54, that is, the distance between the outer peripheral surface of the amplification optical fiber 51 and the outer peripheral surface of the pumping optical fiber 55 is, for example, 10 μm or less. When viewed in the longitudinal direction of the optical combiner 50, the intermediate resin portion 54 is preferably formed continuously between the amplification optical fiber 51 and the pumping optical fiber 55, but is formed intermittently. May be.

  The common coating 58 is a polymer clad that surrounds the outer peripheral surface side of the amplification optical fiber 51 and the outer peripheral surface side of the pumping optical fiber 55. The common coating 58 is made of, for example, an ultraviolet curable resin that is different from the intermediate resin portion 54.

In this embodiment, when the refractive index of the cladding 53 is n ₁ , the refractive index of the pumping optical fiber 55 is n ₂ , the refractive index of the intermediate resin portion 54 is n ₃ , and the refractive index of the common coating 58 is n ₄ , Expressions (1) to (5) hold.
n ₁ ≧ n ₂ (1)
n ₁ ≧ n ₃ (2)
n ₃ > n ₄ (3)
n ₂ > n ₄ (4)
n ₃ ≧ n ₂ (5)

  Next, the operation of the fiber laser device 1 will be described.

  First, excitation light is emitted from the laser diode 21 of each excitation light source 20. This pumping light enters the pumping optical fiber 55 of the optical combiner 50 via the pumping optical fiber 25. The pumping light incident on the pumping optical fiber 55 of the optical combiner 50 gradually shifts to the amplification optical fiber 51 while propagating through the pumping optical fiber 55.

  The excitation light transferred to the cladding 53 of the amplification optical fiber 51 mainly propagates through the cladding 53. Thus, the excitation light propagating through the clad 53 of the amplification optical fiber 51 excites the active element added to the core 52 when passing through the core 52 of the amplification optical fiber 51. The active element in the excited state emits spontaneous emission light in a specific wavelength band. Starting from the spontaneous emission light, signal light including light having a wavelength reflected in common by the first FBG 35 and the second FBG 45 resonates between the first FBG 35 and the second FBG 45. When the resonating signal light propagates through the core 52, the excited active element causes stimulated emission, and the resonating signal light is amplified. Then, when the gain and loss in the optical resonator including the first FBG 35, the amplification optical fiber 51, and the second FBG 45 become equal, a laser oscillation state occurs, and a part of the resonating signal light passes through the second FBG 45. Then, the light is emitted from the end of the optical fiber 40. Note that most of the light that passes through the first FBG 35 from the amplification optical fiber 51 side is converted into heat at the terminal portion 38 and disappears.

  As described above, in the optical combiner 50, the intermediate resin portion 54 is disposed between the amplification optical fiber 51 and the excitation optical fiber 55. For this reason, direct contact between the amplification optical fiber 51 and the pumping optical fiber 55 can be suppressed. Therefore, the amplification optical fiber 51 and the pumping optical fiber 55 can be suppressed from being scratched on the surface and having a reduced mechanical strength.

The optical combiner 50 satisfies the above formulas (3) and (4). That is, the refractive index n ₄ of the common coating 58 is made lower than the refractive index n ₂ of the pumping optical fiber 55 and lower than the refractive index n ₃ of the intermediate resin portion 54. For this reason, the light propagating through the excitation optical fiber 55 hardly leaks to the common coating 58 side, and tends to be unevenly distributed on the side where the intermediate resin portion 54 is formed. Further, the optical combiner 50 satisfies the above formula (2). That is, the refractive index n ₁ of the clad 53 of the amplification optical fiber 51 is set to be equal to or higher than the refractive index n ₃ of the intermediate resin portion 54. For this reason, the light propagating through the intermediate resin portion 54 is easily reflected on the interface between the intermediate resin portion 54 and the clad 53 and easily enters the amplification optical fiber 51. In this way, light that has propagated through the excitation optical fiber 55 and has spread to the intermediate resin portion 54 is likely to be transferred to the amplification optical fiber 51. The optical combiner 50 satisfies the above formulas (1) to (4). In other words, the refractive index n ₁ of the clad 53 of the amplification optical fiber 51 is the portion with the highest refractive index. For this reason, the light transferred to the amplification optical fiber 51 is easily confined in the amplification optical fiber 51. As described above, in the optical combiner 50, the light transfer efficiency from the pumping optical fiber 55 to the amplification optical fiber 51 can be improved.

Further, the optical combiner 50 satisfies the above formula (5). That is, the refractive index n ₃ of the intermediate resin portion 54 is equal to or higher than the refractive index n ₂ of the pumping optical fiber 55. For this reason, the light propagating through the pumping optical fiber 55 is prevented from being reflected at the interface between the pumping optical fiber 55 and the intermediate resin portion 54 and easily enters the intermediate resin portion 54. Further, the light propagating through the intermediate resin portion 54 is likely to enter the amplification optical fiber 51 as described above. Therefore, the light transfer efficiency from the pumping optical fiber 55 to the amplification optical fiber 51 can be further improved.

Furthermore, from the viewpoint of making light propagating through the intermediate resin portion 54 more easily incident on the amplification optical fiber 51, it is preferable to satisfy the following formula (6).
n ₁ > n ₃ (6)

By satisfying the above equation (6), that is, when the refractive index n ₁ of the cladding 53 of the amplification optical fiber 51 is higher than the refractive index n ₃ of the intermediate resin portion 54, the light propagating through the intermediate resin portion 54 is Reflection at the interface between the intermediate resin portion 54 and the clad 53 of the amplification optical fiber 51 is suppressed, and the incident light is easily incident on the amplification optical fiber 51. Further, the light propagating through the amplification optical fiber 51 is easily reflected at the interface between the intermediate resin portion 54 and the clad 53 of the amplification optical fiber 51 and is difficult to return to the intermediate resin portion 54 side. Therefore, the light transfer efficiency from the pumping optical fiber 55 to the amplification optical fiber 51 can be further improved.

In the optical combiner 50, the side of the pumping optical fiber 55 opposite to the amplification optical fiber 51 side is covered with the common coating 58. As described above, the refractive index n ₄ of the common coating 58 is lower than the refractive index n ₃ of the intermediate resin portion 54 disposed on the amplification optical fiber 51 side of the pumping optical fiber 55. Therefore, the side opposite to the amplification optical fiber 51 side of the excitation optical fiber 55 is covered in contact with the common coating 58 without the intermediate resin portion 54, so that the light propagating through the excitation optical fiber 55 is amplified. It tends to be unevenly distributed on the fiber 51 side. For this reason, the light transfer efficiency from the excitation optical fiber 55 to the amplification optical fiber 51 can be further improved.

  In the cross section perpendicular to the longitudinal direction of the optical combiner 50, the amplification optical fiber 51 and the excitation optical fiber 55 are covered with the common coating 58 outside the intermediate region IR. In this way, the outer peripheral surface of the amplification optical fiber 51 and the outer peripheral surface of the excitation optical fiber 55 other than the portions facing each other are covered with the common coating 58 having a refractive index lower than that of the intermediate resin portion 54, thereby being excited. Light propagating through the optical fiber 55 is more likely to be unevenly distributed to the amplification optical fiber 51 side. Further, the light that has shifted to the amplification optical fiber 51 is less likely to leak from the amplification optical fiber 51. Therefore, the light transfer efficiency from the pumping optical fiber 55 to the amplification optical fiber 51 can be further improved.

  Further, the intermediate resin portion 54 of the present embodiment is formed only in a part of the intermediate region IR as described above. By reducing the volume of the intermediate resin portion 54 in this way, the distance that the light transferred from the excitation optical fiber 55 to the amplification optical fiber 51 propagates through the intermediate resin portion 54 can be reduced. Therefore, it can be suppressed that light is scattered or absorbed in the intermediate resin portion 54 and lost.

  Further, in the fiber laser device 1, by providing the optical combiner 50, the light transfer efficiency from the pumping optical fiber 55 to the amplification optical fiber 51 can be improved.

(Second Embodiment)
Next, an optical combiner according to a second embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of 1st Embodiment, or equivalent, except the case where it demonstrates especially, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted.

  FIG. 4 is a view showing a cross section perpendicular to the longitudinal direction of the optical combiner according to the present embodiment.

  The optical combiner 50a shown in FIG. 4 differs from the optical combiner 50 of the first embodiment in that the diameter d1 of the amplification optical fiber 51 and the diameter d2 of the pumping optical fiber 55 are different. In the optical combiner 50a, the diameter d1 of the amplification optical fiber 51 is larger than the diameter d2 of the pumping optical fiber 55. The length d3 of the intermediate resin portion 54 in the direction perpendicular to the line segment connecting the center of the amplification optical fiber 51 and the center of the excitation optical fiber 55 in the cross section perpendicular to the longitudinal direction of the optical combiner 50 is It is smaller than the diameter d2 of the optical fiber 55. That is, the length d3 of the intermediate resin portion 54 is smaller than the smaller diameter of the amplification optical fiber 51 and the pumping optical fiber 55. Even in such a form, the light transfer efficiency from the pumping optical fiber 55 to the amplification optical fiber 51 can be improved as in the first embodiment.

  As mentioned above, although the said 1st and 2nd embodiment was demonstrated to the example about this invention, this invention is not limited to these.

For example, in the first and second embodiments described above, a mode that satisfies the above formula (5), that is, an example in which the refractive index n ₃ of the intermediate resin portion 54 is equal to or higher than the refractive index n ₂ of the excitation optical fiber 55 has been described. However, the refractive index n ₃ of the intermediate resin portion 54 may be smaller than the refractive index n ₂ of the pumping optical fiber 55. However, the refractive index n ₃ of the intermediate resin portion 54 is set higher than the refractive index n ₄ of the common coating film. Even in such a form, the light propagating through the excitation optical fiber 55 may be unevenly distributed on the intermediate resin portion 54 side.

  In the first and second embodiments, the example in which the intermediate resin portion 54 is disposed only in a part of the intermediate region IR has been described. However, the intermediate resin portion 54 may be disposed in the entire intermediate region IR. In addition, the intermediate resin portion 54 may be disposed outside the intermediate region IR. FIG. 5 is a diagram illustrating a cross section perpendicular to the longitudinal direction of an optical combiner according to a modification. The optical combiner 50b shown in FIG. 5 is different from the optical combiner 50 of the first embodiment in that an intermediate resin portion 54 is disposed on the entire intermediate region IR and further outside the intermediate region IR. Even in such a form, the light transfer efficiency from the pumping optical fiber 55 to the amplification optical fiber 51 can be improved as in the first embodiment.

  FIG. 6 is a view showing a cross section perpendicular to the longitudinal direction of an optical combiner according to another modification. The optical combiner 50c shown in FIG. 6 is arranged such that the intermediate resin portion 54 covers the surface on the amplification optical fiber 51 side of the outer peripheral surface of the excitation optical fiber 55, and the contact area with the amplification optical fiber 51 is small. Different from the optical combiner 50 of the first embodiment. Even in such a form, the light transfer efficiency from the pumping optical fiber 55 to the amplification optical fiber 51 can be improved as in the first embodiment. However, from the viewpoint of facilitating the uneven distribution of light propagating through the excitation optical fiber 55 on the amplification optical fiber 51 side, the intermediate resin portion 54 is preferably disposed only in the intermediate region IR. Further, the intermediate resin portion 54 may be disposed so as to cover the surface on the pumping optical fiber 55 side of the outer peripheral surface of the amplification optical fiber 51. However, from the viewpoint of making it difficult for light to leak from the amplification optical fiber 51, it is preferable that the area where the amplification optical fiber 51 is covered with the common coating 58 is large. From the viewpoint of facilitating the propagation of light, it is preferable that the area where the excitation optical fiber 55 is covered with the intermediate resin portion 54 is large. Therefore, the intermediate resin portion 54 is arranged so as to cover the outer peripheral surface of the excitation optical fiber 55 as in the modification shown in FIG. 6 rather than arranged so as to cover the outer peripheral surface of the amplification optical fiber 51. Is preferred.

  Similarly, as described above, the area where the amplification optical fiber 51 is covered with the common coating 58 is preferably large, and the area where the excitation optical fiber 55 is covered with the intermediate resin portion 54 is preferably large. . Therefore, from the viewpoint of suppressing light from leaking from the amplification optical fiber 51 while transferring light from the excitation optical fiber 55 to the amplification optical fiber 51 via the intermediate resin portion 54, the intermediate resin portion 54 and the excitation optical fiber 55. Is preferably larger than the contact area between the intermediate resin portion 54 and the amplification optical fiber 51.

  Moreover, although the fiber laser apparatus 1 gave and demonstrated the example provided with the two excitation light sources 20 in the said embodiment, the number of the excitation light sources 20 with which a fiber laser apparatus is provided is not specifically limited. Further, the number of pumping optical fibers 25 is appropriately changed according to the number of pumping light sources 20, and the number of pumping optical fibers 55 of the optical combiner 50 connected to the pumping optical fiber 25 is also changed appropriately. In addition, the pumping optical fiber 55 has been described by taking an example made of a single glass, but the pumping optical fiber 55 may have portions with different refractive indexes.

  In the above embodiment, the example in which the outer shape of the amplification optical fiber 51 is circular has been described. However, the outer shape of the amplification optical fiber 51 may be polygonal.

  As described above, according to the present invention, an optical combiner capable of improving the light transfer efficiency from the pumping optical fiber to the amplifying optical fiber and a fiber laser device including the optical combiner are provided. It is expected to be used in fields such as fiber communications.

DESCRIPTION OF SYMBOLS 1 ... Fiber laser apparatus 20 ... Excitation light source 50 ... Optical combiner 51 ... Amplifying optical fiber 52 ... Core 53 ... Cladding 54 ... Intermediate resin part 55 ... Excitation light Fiber 58 ... Common coating

Claims (6)

An amplifying optical fiber having a core doped with an active element and a clad surrounding the core;
At least one pumping optical fiber;
An intermediate resin portion disposed between the amplification optical fiber and the excitation optical fiber so as to be in contact with the amplification optical fiber and the excitation optical fiber;
A common coating surrounding the outer peripheral surface side of the amplification optical fiber and the excitation optical fiber;
With
When the refractive index of the cladding is n ₁ , the refractive index of the excitation optical fiber is n ₂ , the refractive index of the intermediate resin portion is n ₃ , and the refractive index of the common coating is n ₄ , the following formula (1) An optical combiner characterized in that (4) holds.
n ₁ ≧ n ₂ (1)
n ₁ ≧ n ₃ (2)
n ₃ > n ₄ (3)
n ₂ > n ₄ (4) The optical combiner according to claim 1, wherein the following formula (5) is satisfied.
n ₃ ≧ n ₂ (5) The optical combiner according to claim 1 or 2, wherein the following expression (6) is satisfied.
n ₁ > n ₃ (6) 4. The optical combiner according to claim 1, wherein a side of the excitation optical fiber opposite to the amplification optical fiber is covered with the common coating. 5. Two tangents that are in contact with the outer peripheral surface of the amplification optical fiber and the outer peripheral surface of the excitation optical fiber and do not intersect with each other between the amplification optical fiber and the excitation optical fiber in a cross section perpendicular to the longitudinal direction; The amplification optical fiber and the excitation optical fiber are covered with the common coating on the outer side of the intermediate region surrounded by the outer peripheral surface of the amplification optical fiber and the outer peripheral surface of the excitation optical fiber. The optical combiner according to claim 4. An optical combiner according to any one of claims 1 to 5,
An excitation light source that emits excitation light incident on the excitation optical fiber;
A fiber laser device comprising:

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