JP2019174502A - Optical device and fiber laser device - Google Patents

Abstract

To eliminate SRS light guided in a clad when a slant type FBG is formed in a core.SOLUTION: An optical device 10 comprises: a core 13a; a clad 13b for covering the core and having a refractive index lower than that of the core; a low refractive index layer 13c for covering the clad and having a refractive index lower than that of the clad; a slant type FBG12 formed in a core; and at least one of clad mode removing sections P1 to P3 for removing clad mode light including SRS light coupled from the core to the clad by the slant type FBG from an inside of the clad.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical device and a fiber laser apparatus.

The maximum output of the fiber laser is limited by stimulated Raman scattering (SRS) that occurs nonlinearly with respect to the laser output.
Patent Document 1 below discloses forming a slant type FBG (Fiber Bragg Grating) in a core in a fiber laser device. With this configuration, it is possible to selectively remove the SRS light from the light propagating in the core, stabilize the signal light propagating in the core, and prevent damage to the excitation light source.

U.S. Pat. No. 9,634,462

  In a high-power fiber laser device, when a slant FBG is formed in the core, the high-power SRS light removed from the core is guided in the cladding. When high-power SRS light is intensively applied to, for example, a protective coating that covers the cladding, this protective coating may generate strong heat. Alternatively, when the SRS light guided in the cladding reaches the excitation light source, the excitation light source may be damaged.

  The present invention has been made in view of such circumstances, and an object of the present invention is to remove light guided in the clad when a slant type FBG is formed in the core.

  In order to solve the above problems, an optical device according to a first aspect of the present invention includes a core, a clad covering the core and having a refractive index lower than that of the core, the clad being covered, and being more than the clad. A clad mode light including a low refractive index layer having a low refractive index, a slant type FBG formed in the core, and SRS light coupled from the core to the clad by the slant type FBG is removed from the clad. And at least one cladding mode removing unit.

  According to the optical device according to the above aspect, the clad mode light including the SRS light released from the core by the slant type FBG is confined in the clad by the low refractive index layer. Then, the clad mode light guided in the clad is removed by the clad mode removing unit. In this way, by removing the SRS light by the cladding mode removing unit, for example, an unintended portion such as a protective coating is irradiated with SRS light to generate strong heat, or the SRS light reaches the excitation light source and the excitation light source becomes It can be prevented from being damaged.

  Here, the optical device includes an optical fiber having the core on which the slant type FBG is formed, the cladding, and the low refractive index layer, and the cladding mode removing unit is provided in the optical fiber. It may be.

  In this case, a slant type FBG and a cladding mode removing unit are provided in one optical fiber. Thereby, the SRS light escaped to the clad by the slant type FBG is quickly removed by the clad mode removing unit.

  The clad mode removing unit may be a clad mode stripper made of a high refractive index material that contacts the outer peripheral surface of the clad and has a refractive index higher than that of the clad.

  In this case, the clad mode stripper including the SRS light can be more reliably removed by using the clad mode stripper having a high ability to remove the clad mode light as the clad mode removing unit.

  In addition, the cladding mode stripper may be configured so that the removing ability of the cladding mode light increases as the distance from the slant type FBG increases along the longitudinal direction of the cladding.

  In this case, the amount of heat generation around the cladding mode stripper becomes more uniform in the longitudinal direction, and large heat generation can be suppressed. Therefore, the durability of the cladding mode stripper can be improved.

  Further, the high refractive index material has a plurality of contact portions arranged at intervals in the longitudinal direction and in contact with the outer peripheral surface of the clad, and a connecting portion for connecting the plurality of contact portions to each other. And each width | variety of the said some contact part in the said longitudinal direction may become large as it distances from the said slant type | mold FBG.

  In this case, it is possible to easily configure a clad mode stripper in which the ability to remove clad mode light increases as the distance from the slant type FBG increases.

  Further, the cladding mode removal portion may be an end face in the longitudinal direction of the cladding.

  In this case, by using the end face of the clad as the clad mode removing section, it is possible to suppress the SRS light from entering other fibers connected to the end face.

  Further, both end faces in the longitudinal direction of the clad may be the clad mode removing portion.

  In this case, both end surfaces of the clad function as clad mode removing portions, so that SRS light can be more reliably removed.

  In addition, an outer peripheral surface of a portion of the cladding covering a region where the slant type FBG is formed in the core is covered with a low refractive index material having a refractive index lower than that of the low refractive index layer. In the longitudinal direction, the cladding mode removing portion and the low refractive index material may be disposed at different positions.

  In this case, the SRS light having a strong power immediately after being reflected by the slant type FBG can be reliably confined in the clad by the low refractive index material, and the vicinity of the slant type FBG can be prevented from generating heat strongly. Further, the SRS light can be removed by the clad mode removing unit at an arbitrary position in the longitudinal direction.

  A fiber laser device according to a second aspect of the present invention includes the optical device, a pumping light source, and a resonator.

  According to the fiber laser device of the above aspect, even when high-power SRS light is generated, heat generation due to the SRS light and failure of the excitation light source can be suppressed by the action of the optical device described above. Therefore, a high-power fiber laser device can be provided.

  In the fiber laser device of the above aspect, the cladding mode removing unit may be disposed in a region where the residual pumping light emitted from the pumping light source does not substantially reach.

  In this case, the cladding mode removal unit is disposed in a region where the residual excitation light does not substantially reach, thereby preventing the excitation light from being unexpectedly removed.

Further, the fiber laser device is a bidirectional pump type including a front pump light source and a rear pump light source, and includes a first combiner provided between the resonator and the front pump light source, the resonator, A second combiner provided between the pumping light source and the rear excitation light source, and the region may be a portion positioned on the output end side of the second combiner.
The fiber laser device is a forward pump type, and the resonator includes an amplification fiber in which an active element that emits light in an excited state is added to a core, and at least a part of the light emitted by the active element. A first FBG that reflects, and a second FBG that reflects light reflected by the first FBG with a lower reflectance than the first FBG, and the region is a portion located on the output end side of the second FBG. There may be.

  According to the above aspect of the present invention, when the slant type FBG is formed in the core, the SRS light guided in the cladding can be removed.

It is a block diagram which shows the structure of the fiber laser apparatus which concerns on 1st Embodiment. It is a schematic diagram of the optical device of FIG. (A) is an enlarged view of the clad mode stripper of FIG. (B) is an enlarged view of a clad mode stripper according to a modification. (A) is explanatory drawing of clad outer diameter ratio. (B) is a graph showing the relationship between the cladding outer diameter ratio and the connection loss. It is a block diagram which shows the structure of the fiber laser apparatus which concerns on the modification of 1st Embodiment. It is a block diagram which shows the structure of the fiber laser apparatus which concerns on 2nd Embodiment. It is a block diagram which shows the structure of the fiber laser apparatus which concerns on the modification of 2nd Embodiment.

(First embodiment)
Hereinafter, the optical device and the fiber laser apparatus of the first embodiment will be described with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent. Further, the present invention is not limited to the following embodiment.

As shown in FIG. 1, a fiber laser apparatus 1A includes a forward pumping light source 2, a first combiner 3, an HR-FBG (High Reflectivity-Fiber Bragg Grating) 4, an amplification fiber 5, and an OC-FBG (Output). Coupler-Fiber Bragg Grating) 6, a second combiner 7, a backward pumping light source 8, an optical device 10, and an output end 9. The amplification fiber 5, the HR-FBG 4, and the OC-FBG 6 constitute a resonator R that generates laser light by the excitation light emitted from the excitation light sources 2 and 8.
The fiber laser device 1 </ b> A is a bidirectional pump type that includes a front pump light source 2 and a rear pump light source 8.

(Direction definition)
As shown in FIG. 2, the optical device 10 includes an optical fiber 13. Hereinafter, the longitudinal direction of the optical fiber 13 is simply referred to as the longitudinal direction. Further, when viewed from the optical fiber 13, the output end 9 side in the longitudinal direction is referred to as + X side, and the resonator R side is referred to as -X side.
Further, when viewed from the amplification fiber 5, the front pumping light source 2 side may be referred to as the front, and the rear pumping light source 8 side may be referred to as the rear.

  As shown in FIG. 1, a plurality of front pumping light sources 2 and rear pumping light sources 8 are arranged with an amplification fiber 5 interposed therebetween. The forward pumping light source 2 emits forward pumping light toward the amplification fiber 5, and the rear pumping light source 8 emits backward pumping light toward the amplification fiber 5. As these excitation light sources 2 and 8, for example, laser diodes can be used.

The first combiner 3 and the second combiner 7 are arranged on both sides of the amplification fiber 5.
The first combiner 3 couples the pumping light emitted from each front pumping light source 2 to one optical fiber and directs it to the amplification fiber 5. The second combiner 7 couples the pumping light emitted from each rear pumping light source 8 to one optical fiber and directs it to the amplification fiber 5.

  The amplification fiber 5 includes a core to which one or more kinds of active elements are added, a first cladding that covers the core, a second cladding that covers the first cladding, and a protective coating that covers the second cladding. Have. The amplification fiber 5 is a double clad fiber. As the active element added to the core, rare earth elements such as erbium (Er), ytterbium (Yb), or neodymium (Nd) are used. These active elements emit light in the excited state. Silica glass or the like can be used as the core and the first cladding. As the second cladding, a resin such as a polymer can be used. As the protective coating, a resin material such as an acrylic resin or a silicone resin can be used.

The HR-FBG (first FBG) 4 is formed in the core of an optical fiber that is fusion spliced to the front end of the amplification fiber 5. The HR-FBG 4 is adjusted so as to reflect the light having the wavelength of the signal light out of the light emitted from the active element of the amplification fiber 5 in the excited state with a reflectance of almost 100%. It has a structure in which high refractive index portions are repeated at a constant period along the longitudinal direction.
The OC-FBG (second FBG) 6 is formed in the core of the optical fiber fused to the rear end of the amplification fiber 5. OC-FBG 6 has substantially the same structure as HR-FBG 4, but is adjusted to reflect light with a lower reflectance than HR-FBG 4.

  In the amplification fiber 5, the signal light reflected by the HR-FBG 4 and the OC-FBG 6 reciprocates in the longitudinal direction of the amplification fiber 5. The signal light is amplified along with the reciprocation to become laser light. Thus, in the resonator R, the light is amplified and laser light is generated. Part of the laser light passes through the OC-FBG 6 and reaches the output end 9 via the optical device 10.

(Optical device)
FIG. 2 is a schematic diagram illustrating the configuration of the optical device 10. As shown in FIG. 2, the optical device 10 includes an optical fiber 13 having a core 13a on which a slant type FBG 12 is formed, a clad 13b, a low refractive index layer 13c, and a protective coating 13d. As the core 13a and the clad 13b, a glass clad formed of silica glass or the like can be used. The clad 13b covers the core 13a and has a lower refractive index than the core 13a. The low refractive index layer 13c covers the clad 13b and has a lower refractive index than the clad 13b.

Thus, the optical fiber 13 is a double clad fiber having the clad 13b (first clad) and the low refractive index layer 13c (second clad). The low refractive index layer 13c may be a polymer clad formed of a polymer material.
The protective coating 13d covers the low refractive index layer 13c. As the protective coating 13d, a resin material such as an acrylic resin or a silicone resin can be used. These resin materials used as the protective coating 13d generally generate heat by absorbing light.

  A resonator side fiber (another optical fiber) 17 is fusion-connected to the end portion of the optical fiber 13 on the −X side, and an output side fiber (another optical fiber) 18 is connected to the end portion of the optical fiber 13 on the + X side. Are fusion spliced. Hereinafter, the fusion spliced portion between the optical fiber 13 and the resonator side fiber 17 is referred to as a first connection portion A1, and the fusion spliced portion between the optical fiber 13 and the output side fiber 18 is referred to as a second connection portion A2. The clads of the resonator-side fiber 17 and the output-side fiber 18 are referred to as a resonator-side clad 17b and an output-side clad 18b, respectively.

The first connection part A1 and the second connection part A2 are covered and fixed by the first fixing member 15 and the second fixing member 16, respectively. As the first fixing member 15 and the second fixing member 16, a material having a refractive index higher than that of the cladding 13b is preferably used.
The core 13a of the optical fiber 13, the core 17a of the resonator-side fiber 17, and the core 18a of the output-side fiber 18 are fused together and integrated.

(Slant type FBG)
The slant type FBG 12 is formed by partially irradiating the core 13a with a processing beam (such as an ultraviolet laser beam) and modulating the refractive index. In the present embodiment, in order to form the slant type FBG 12, the low refractive index layer 13c and the protective coating 13d are partially removed, and the processing beam is irradiated to the core 13a through the removed portion. The removed portion is covered with a low refractive index material (recovered portion) 14 after the slant type FBG 12 is formed. For this reason, the outer peripheral surface of the portion of the clad 13 b that covers the region where the slant type FBG 12 is formed in the core 13 a is covered with the low refractive index material 14.
As the low refractive index material 14, a resin material having a refractive index lower than that of the cladding 13b can be used. The refractive index of the resin material constituting the low refractive index material 14 may be equal to or smaller than the refractive index of the low refractive index layer 13c. The low refractive index material 14 prevents the clad mode light from leaking from the portion where the low refractive index layer 13c is removed.

If the low refractive index layer 13c and the protective coating 13d are made of a material that sufficiently transmits the processing light beam, the low refractive index layer 13c and the protective coating 13d may not be removed. In this case, the optical device 10 may not include the low refractive index material 14.
Further, a plurality of slant type FBGs 12 may be provided in the optical device 10.

The slant type FBG 12 transmits light in the wavelength band (for example, 1060 nm) of signal light used as laser light, and releases light in the wavelength band (for example, 1120 nm) of SRS light from the core 13a toward the cladding 13b. It is configured.
As schematically shown in FIG. 2, in the slant type FBG 12 of the present embodiment, the intervals between the refractive index modulation portions in the longitudinal direction are not uniform. Thereby, the wavelength band of the light removed from the core 13a by the slant type FBG 12 becomes large. Therefore, SRS light can be more reliably released toward the clad 13b. In this way, by selectively removing the SRS light from the core 13a and coupling it to the clad 13b, it is possible to stabilize the quality of the signal light and to prevent the excitation light sources 2 and 8 from being damaged.

In the clad excitation type resonator R, when the slant type FBG 12 is disposed in the resonator R, the SRS light is guided in the clad in the resonator R, and the pumping light sources 2 and 8 may be damaged. is there. For this reason, it is preferable that the slant type FBG 12 is disposed outside the resonator R.
The SRS light traveling in the core 13a toward the + X side (output end 9 side) is removed from the core 13a by the slant FBG 12 and travels toward the clad 13b. At this time, the SRS light released by the cladding 13b travels toward the -X side (resonator R side).

  The SRS light that has entered the clad 13b travels in the clad 13b while being repeatedly reflected at the interface between the clad 13b and the low refractive index layer 13c. That is, the SRS light is confined in the clad 13b by the low refractive index layer 13c. A part of the SRS light confined in the cladding 13b is absorbed by the low refractive index layer 13c. For this reason, although the low refractive index layer 13c generates heat, the area of the interface between the cladding 13b and the low refractive index layer 13c increases as the diameter of the cladding 13b increases. Therefore, the larger the diameter of the cladding 13b, the lower the density of light absorbed in the low refractive index layer 13c, and the lower the amount of heat generated in the low refractive index layer 13c.

(Clad mode removal part)
By the way, the higher the output of the fiber laser device 1A, the greater the power of the SRS light confined in the cladding 13b. When this SRS light is applied to a portion that absorbs light, such as a protective coating, the portion strongly generates heat. Alternatively, when high-power SRS light is guided through the cladding 13b and incident on the excitation light sources 2 and 8, the excitation light sources 2 and 8 may fail. Therefore, in order to prevent the generation of heat or failure due to the high-power SRS light, it is required to stably remove the SRS light from the clad 13b.
Therefore, the optical device 10 according to the present embodiment includes clad mode removing portions P1 to P3 that remove clad mode light including SRS light released from the core 13a to the clad 13b by the slant type FBG 12. Details will be described below.

(Clad mode stripper)
The first clad mode removing portion P1 shown in FIG. 2 is a so-called clad mode stripper 11. In the present embodiment, the clad mode stripper 11 refers to a configuration in which a part of the outer peripheral surface of the clad 13b is covered with a high refractive index material 11a having a refractive index higher than that of the clad 13b. The clad mode stripper 11 is formed by intermittently removing the low refractive index layer 13c and the protective coating 13d of the optical fiber 13 along the longitudinal direction and covering the removed portion with a high refractive index material 11a. A resin or the like is used as the high refractive index material 11a. In the clad mode stripper 11, the clad mode light including the SRS light can be removed from the clad 13b to the high refractive index material 11a. Since the high refractive index material 11a irradiated with the SRS light and its surroundings generate heat, a heat radiating part such as a fin or a cooling part may be connected to the high refractive index material 11a.

  FIG. 3A is an enlarged view of the clad mode stripper 11 of FIG. As shown in FIG. 3A, in the cladding mode stripper 11, the low refractive index layer 13c and the protective coating 13d are intermittently removed along the longitudinal direction of the cladding 13b. The high refractive index material 11a enters the removed portion. Thus, the high refractive index material 11a is in intermittent contact with the outer peripheral surface of the clad 13b along the longitudinal direction. A portion of the high refractive index material 11a that is in contact with the clad 13b is referred to as a contact portion 11a2. A plurality of contact portions 11a2 are provided at intervals in the longitudinal direction of the clad 13b. Each contact part 11a2 is mutually connected by the connection part 11a1.

  As shown in FIG. 2, in the present embodiment, the clad mode stripper 11 is disposed on the resonator R side viewed from the slant type FBG 12. Thereby, the SRS light which is removed from the core 13a by the slant type FBG 12 and travels toward the resonator R side in the clad 13b can be effectively removed. In particular, by removing most of the SRS light with the cladding mode stripper 11 before the SRS light reaches the first connection part A1, it is possible to prevent the SRS light from entering the resonator-side fiber 17. Therefore, it is possible to suppress the SRS light from reaching the pumping light source 2 and the like through the resonator-side fiber 17 and prevent the pumping light source 2 from being broken. If the refractive index of the high refractive index material 11a is high, a large amount of SRS light can be removed even if the distance between the cladding mode stripper 11 and the slant side FBG 12 in the longitudinal direction is small.

  Here, of the plurality of contact portions 11a2, a portion closer to the slant type FBG 12 is irradiated with higher power clad mode light, and the periphery of the contact portion 11a2 strongly generates heat. On the other hand, the larger the contact area between the contact portion 11a2 and the clad 13b, the greater the power of the clad mode light removed by the contact portion 11a2, and the greater the amount of heat generated in the peripheral portion.

  Therefore, in the present embodiment, as shown in FIG. 3A, the width W1 in the longitudinal direction of each contact portion 11a2 is not uniform. More specifically, the width W1 is larger in the contact portion 11a2 located on the −X side. As a result, the cladding light stripping ability of the cladding mode stripper 11 increases as the distance from the slant type FBG 12 increases. According to this configuration, the heat generation amount of the clad mode stripper 11 becomes more uniform in the longitudinal direction, and the optical fiber 13 can be prevented from generating a large amount of heat locally. As a result, the durability of the optical fiber 13 is improved, and the output of the fiber laser device 1A can be further increased.

  In addition, when the heat generation amount in the end portion on the slant type FBG 12 side in the longitudinal direction (the end portion on the + X side in FIG. 2) of the clad mode stripper 11 is within an allowable range, as shown in FIG. Moreover, the width W1 of each contact portion 11a2 may be uniform.

  As described above, the cladding mode stripper 11 removes the cladding mode light propagating in the cladding 13b. However, when the high refractive index material 11a is irradiated with the high power cladding mode light, the periphery of the high refractive index material 11a is removed. Fever. For this reason, it is preferable to increase the outer diameter of the cladding 13b to increase the area of the interface between the cladding 13b and the high refractive index material 11a. Thereby, the density of the clad mode light irradiated to the said interface becomes small, and the emitted-heat amount per unit area can be reduced.

(Clad end face)
As shown in FIG. 2, in this embodiment, the outer diameter of the clad 13b in the optical device 10 is larger than the outer diameters of the resonator-side clad 17b and the output-side clad 18b. That is, the resonator-side clad 17 b and the output-side clad 18 b are small-diameter clads having a smaller diameter than the clad 13 b of the optical device 10. For this reason, the 1st end surface 13b1 and the 2nd end surface 13b2 are formed in the both ends in the longitudinal direction of the clad 13b. The first end face 13b1 is located at the first connection portion A1 and faces the -X side. The second end face 13b2 is located at the second connection portion A2 and faces the + X side. From these end faces 13b1 and 13b2, clad mode light including SRS light can be removed from the clad 13b. That is, the end faces 13b1 and 13b2 of the clad 13b function as the clad mode removing portions P2 and P3.
Further, in the present embodiment, the end faces 13b1 and 13b2 are covered with the fixing members 15 and 16 having a refractive index higher than that of the cladding 13b. It can be removed more effectively. Even if the fixing members 15 and 16 are not provided, the end faces 13b1 and 13b2 function as the cladding mode removal portions P2 and P3.

The second cladding mode removal portion P2 is the −X side end face 13b1 of the cladding 13b. The third cladding mode removal portion P3 is the + X side end face 13b2 of the cladding 13b.
By removing the cladding mode light at the end faces 13b1 and 13b2 and suppressing the cladding mode light including the SRS light from entering the fibers 17 and 18, the growth of the SRS light in the fibers 17 and 18 is prevented. Can do.
Since the fixing members 15 and 16 irradiated with the cladding mode light including the SRS light generate heat, the fixing members 15 and 16 may be connected to a heat radiating part such as a fin or a cooling part.

The outer diameters of the resonator-side cladding 17b and the output-side cladding 18b are, for example, about 125 μm to 250 μm.
The outer diameter of the clad 13b of the optical fiber 13 is, for example, about 250 μm to 600 μm.

  FIG. 4A is a schematic diagram showing a traveling path of the cladding mode light Lc in the vicinity of the first connection portion A1 or the second connection portion A2. As shown in FIG. 4A, the clad mode light Lc travels in the longitudinal direction while repeating reflection on the outer peripheral surface of the clad 13b. For this reason, a part of the cladding mode light Lc leaks from the end faces 13b1 and 13b2 of the cladding 13b. In this specification, the loss of the clad mode light Lc due to light leaking from the end faces 13b1 and 13b2 of the clad 13b is referred to as “connection loss” in this specification. The connection loss depends on the area of the end face 13b1 or the end face 13b2. The areas of the end faces 13b1 and 13b2 depend on the outer diameter ratio between the clads connected by the connection portions A1 and A2.

  That is, the connection loss depends on the outer diameter ratio. As shown in FIG. 4A, the diameter of the clad 13b of the optical fiber 13 is defined as a dimension a, and the diameter of the resonator-side cladding 17b or the output-side cladding 18b is defined as a dimension b. The value of a ÷ b is referred to as the cladding outer diameter ratio a / b. In FIG. 4B, the horizontal axis indicates the cladding outer diameter ratio a / b, and the vertical axis indicates the connection loss (dB). As shown in FIG. 4B, the connection loss value increases as the cladding outer diameter ratio a / b increases.

  For example, when the diameter (dimension a) of the cladding 13b of the optical fiber 13 is 180 μm and the diameter (dimension b) of the resonator-side cladding 17b or the output-side cladding 18b is 125 μm, the cladding outer diameter ratio a / b is 180 ÷ 125 = 1.44. From the graph shown in FIG. 4B, when the cladding outer diameter ratio a / b is 1.44, the connection loss is about 3 dB.

  For example, when the diameter (dimension a) of the cladding 13b of the optical fiber 13 is 300 μm and the diameter (dimension b) of the resonator-side cladding 17b or the output-side cladding 18b is 125 μm, the cladding outer diameter ratio a / b is 300 ÷ 125 = 2.4. From the graph shown in FIG. 5B, when the cladding outer diameter ratio a / b is 2.4, the connection loss is about 7.5 dB.

  Thus, as the diameter of the clad 13b of the optical fiber 13 is increased, the connection loss is increased and the ability to remove the clad mode light in the second connection portion A2 is increased. Furthermore, as described above, the heat generation amount per unit area in the low refractive index material 14 or the clad mode stripper 11 is suppressed as the diameter of the clad 13b of the optical fiber 13 is increased. Therefore, it is preferable that the outer diameter of the clad 13b of the optical fiber 13 constituting the optical device 10 is large. For example, the cladding outer diameter ratio a / b is preferably 1.44 or more.

  When forming the slant type FBG 12, the outer diameter of the clad 13b of the optical fiber 13 is preferably 500 μm or less, for example, in order to irradiate the core 13a with the processing light beam with high accuracy.

  As described above, according to the optical device 10 of the present embodiment, the SRS light released from the core 13a by the slant type FBG 12 is confined in the clad 13b by the low refractive index layer 13c. Then, the SRS light propagated in the clad 13b is removed by the clad mode removing portions P1 to P3. In this way, by removing the SRS light by the cladding mode removing portions P1 to P3, for example, the unintended portion such as the protective coating 13d is irradiated with the SRS light to generate strong heat, or the SRS light is applied to the excitation light sources 2 and 8. It is possible to prevent the excitation light sources 2 and 8 from damaging and reaching.

  In addition, the slant type FBG 12 and the clad mode removing portions P1 to P3 are provided in one optical fiber 13. Thereby, the SRS light released to the clad 13b by the slant type FBG 12 is quickly removed by the clad mode removing portions P1 to P3. Moreover, since the optical device 10 is configured by one optical fiber 13, the optical device 10 can be easily applied to different types of fiber laser apparatuses.

Moreover, the clad mode light containing SRS light can be more reliably removed by providing the several clad mode removal parts P1-P3.
Further, by using the end faces 13b1 and 13b2 of the clad 13b as the clad mode removing portions P2 and P3, it is possible to make the SRS light incident on the resonator side fiber 17 or the output side fiber 18 connected to the end faces 13b1 and 13b2. Can be suppressed. Therefore, for example, it is possible to prevent high-power SRS light from entering the excitation light sources 2 and 8 and from entering the device connected to the tip of the output side fiber 18.

Further, as shown in FIG. 2, the outer peripheral surface of the portion of the clad 13 b that covers the region where the slant type FBG 12 is formed in the core 13 a is covered with the low refractive index material 14. When the low refractive index material 14 is formed of a material having a refractive index lower than that of the low refractive index layer 13 c, the SRS light having a strong power immediately after being reflected by the slant type FBG 12 is further reduced by the low refractive index material 14. It can be surely confined in the cladding 13b. Thereby, it can suppress that the vicinity of slant type FBG12 generates heat strongly.
Moreover, the cladding mode removal parts P1-P3 are arrange | positioned in the position different in the longitudinal direction with the low refractive index material 14, and this arrangement | positioning can be set arbitrarily. Therefore, the clad mode light can be removed by the clad mode removing portions P1 to P3 at an arbitrary position.

  Note that the cladding mode removal units P1 to P3 included in the optical device 10 are arranged in a region where the residual pumping light emitted from the pumping light sources 2 and 8 does not substantially reach in the fiber laser device 1A. The “region in which the residual excitation light does not substantially reach” in the present embodiment is, for example, a portion of the fiber laser device 1A that is located closer to the output end 9 than the second combiner 7. In this region, since the excitation light is sufficiently absorbed by the core, it is possible to prevent the excitation light from being unexpectedly removed by disposing the cladding mode removal portions P1 to P3 in the region.

  As described above, the slant type FBG 12 is also preferably arranged outside the resonator R. Therefore, it is preferable that the optical device 10 having the slant type FBG 12 and the clad mode removing portions P1 to P3 is disposed outside the resonator R.

The configurations of the fiber laser apparatus 1A and the optical device 10 are not limited to the example in FIG. 1, and may be changed as appropriate. For example, the clad mode stripper 11 may be arranged on the + X side (output end 9 side) of the slant type FBG 12. In this case, the SRS light included in the reflected light from the output end 9 can be effectively removed.
Alternatively, as shown in FIG. 5, the clad mode stripper 11 may be arranged on both sides in the longitudinal direction of the slant type FBG 12.

(Second Embodiment)
Next, a second embodiment according to the present invention will be described. The basic configuration is the same as that of the first embodiment. For this reason, the same code | symbol is attached | subjected to the same structure, the description is abbreviate | omitted, and only a different point is demonstrated.
The fiber laser device 1B of the present embodiment is a one-side excitation type that does not have a backward excitation light source. That is, the fiber laser device 1B is a forward pump type fiber laser device.

  As shown in FIG. 6, the fiber laser device 1B includes a pumping light source 2, a first combiner 3, an HR-FBG 4, an amplification fiber 5, an OC-FBG 6, an optical device 10, an output end 9, It has. The HR-FBG 4, the amplification fiber 5, and the OC-FBG 6 constitute a resonator R. The optical device 10 is disposed between the OC-FBG 6 and the output end 9. The optical device 10 includes a slant type FBG 12 and a clad mode stripper (first clad mode removing portion) 11 disposed on both sides in the longitudinal direction. Although not shown, the first connection portion A1 and the second connection portion A2 include end faces of optical fibers as second and third cladding mode removal portions, respectively.

  Also in this embodiment, in order to prevent the excitation light from being unintentionally removed, the cladding mode removal unit is arranged in a region where the residual excitation light does not substantially reach. Here, the “region in which the residual excitation light does not substantially reach” in the present embodiment is a portion of the fiber laser device 1B that is located closer to the output end 9 than the OC-FBG 6, for example. In this region, since the excitation light is sufficiently absorbed by the core, it is suitable as a position for providing the cladding mode removal portion.

  Although detailed description is omitted, the fiber laser device 1B of the present embodiment can also obtain the same operational effects as those of the first embodiment.

  The configuration of the fiber laser device 1B is not limited to the example of FIG. 7, and may be changed as appropriate. For example, as shown in FIG. 7, the optical device 10 may be disposed between the amplification fiber 5 and the OC-FBG 6, that is, in the resonator R. Even in this case, by arranging the optical device 10 in a region where the pumping light is sufficiently absorbed by the core in the amplification fiber 5 and the residual pumping light does not substantially reach, the same effect as the first embodiment can be obtained. Obtainable.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, although the fiber laser apparatuses 1A and 1B of the embodiment have one output end 9, an optical fiber or the like may be further connected to the end of the output end 9. Further, a beam combiner may be connected to the tip of the output end 9 so that laser beams from a plurality of fiber laser devices are bundled.

In the above embodiment, as shown in FIG. 2, the clad mode removing portions P1 to P3 and the slant type FBG 12 are provided in one optical fiber 13. However, the optical fiber 13 may be divided. Good. In other words, the optical device 10 may have a structure in which the first optical fiber having at least one of the cladding mode removing portions P1 to P3 and the second optical fiber having the slant type FBG 12 are fusion-connected.
Further, the optical device 10 in this specification may be employed in a MOPA (Master Oscillator Power Amplifier) type fiber laser apparatus.

  In addition, the constituent elements in the above-described embodiment can be appropriately replaced with known constituent elements without departing from the gist of the present invention, and the above-described embodiments and modifications may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1A-1C ... Fiber laser apparatus 2 ... Front pumping light source (pumping light source) 5 ... Amplifying fiber 8 ... Back pumping light source (pumping light source) 10 ... Optical device 11 ... Cladding mode stripper 11a ... High refractive index material 11a1 ... Connection part 11a2 ... Contact part 12 ... Slant type FBG 13 ... Optical fiber 13a ... Core 13b ... Clad 13c ... Low refractive index layer 13d ... Protective coating 13b1 ... First end face (end face) 13b2 ... Second end face (end face) 13d ... Protective cover 14 ... Low refractive index material P1 to P3 ... Clad mode removal part R ... Resonator

Claims (12)

The core,
A clad covering the core and having a lower refractive index than the core;
A low refractive index layer covering the cladding and having a lower refractive index than the cladding;
A slant type FBG formed on the core;
An optical device comprising: at least one cladding mode removing unit that removes cladding mode light including SRS light coupled from the core to the cladding by the slant FBG from the cladding. An optical fiber having the core on which the slant FBG is formed, the clad, and the low refractive index layer;
The optical device according to claim 1, wherein the cladding mode removing unit is provided in the optical fiber.   The said clad mode removal part is a clad mode stripper comprised by the high refractive index material which contacts the outer peripheral surface of the said clad, and has a refractive index higher than the refractive index of this clad. Optical devices.   4. The optical device according to claim 3, wherein the cladding mode stripper is configured such that the removing ability of the cladding mode light increases as the distance from the slant type FBG increases along the longitudinal direction of the cladding. The high refractive index material is
A plurality of contact portions arranged at intervals in the longitudinal direction and in contact with the outer peripheral surface of the cladding;
A connecting portion for connecting the plurality of contact portions to each other;
The optical device according to claim 4, wherein a width of each of the plurality of contact portions in the longitudinal direction increases as the distance from the slant type FBG increases.   The optical device according to claim 1, wherein the cladding mode removal portion is an end face in a longitudinal direction of the cladding.   The optical device according to claim 6, wherein both end faces in the longitudinal direction of the clad are the clad mode removing portions. Of the cladding, the outer peripheral surface of the portion covering the region where the slant type FBG is formed in the core is covered with a low refractive index material having a lower refractive index than the low refractive index layer,
The optical device according to claim 1, wherein in the longitudinal direction of the clad, the clad mode removing portion and the low refractive index material are arranged at different positions. The optical device according to any one of claims 1 to 8,
An excitation light source;
A fiber laser device comprising: a resonator;   The fiber laser device according to claim 9, wherein the cladding mode removing unit is disposed in a region where the residual pumping light emitted from the pumping light source does not substantially reach. The fiber laser device is a bidirectional pump type including a front pump light source and a rear pump light source, and includes a first combiner provided between the resonator and the front pump light source, the resonator, and the rear pump light source. A second combiner provided between the light source and
The fiber laser device according to claim 10, wherein the region is a portion located on an output end side with respect to the second combiner. The fiber laser device is a forward pump type,
The resonator is
An amplifying fiber in which an active element that emits light in an excited state is added to the core;
A first FBG that reflects at least part of the light emitted by the active element;
A second FBG that reflects light reflected by the first FBG with a lower reflectance than the first FBG;
The fiber laser device according to claim 10, wherein the region is a portion located on an output end side with respect to the second FBG.

Images