JP2012103513A - Optical fiber and laser device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber capable of gradually emitting leakage light which propagates through a clad, and a laser device using the same.SOLUTION: An optical fiber 50 includes a core 51, an inner clad 52 which covers the core 51, a low refractive index layer 60 which covers the inner clad 52, has an average refractive index lower than a refractive index of the inner clad 52, and confines light having a predetermined wavelength to the inner clad 52, and an outer clad 54 which covers the low refractive index layer 60 and has a refractive index higher than the average refractive index of the low refractive index layer 60. A part of the low refractive index layer 60 in a circumferential direction is chipped off in a longitudinal direction of the inner clad 52. The chipped-off part of the low refractive index layer 60 has an average refractive index higher than the average refractive index of the low refractive index layer 60, and functions as a light emitting part 70 for emitting a part of the light confined to the inner clad 52.

Description

  The present invention relates to an optical fiber and a laser device using the same, and more particularly to an optical fiber that can gradually emit leakage light propagating through a clad and a laser device using the same.

  The fiber laser device is used in the fields of processing machines, medical devices, measuring instruments, and the like, and outputs light amplified in an amplification optical fiber. In such a fiber laser device, the output light output from the core of the amplification optical fiber may be input to the core of the delivery fiber and propagated to a desired location by the delivery fiber before being output. .

  However, as described in Patent Document 1 below, in the connection portion between the amplification optical fiber and the delivery fiber, the axis misalignment between the cores, the angle mismatch between the cores, and the mode field difference between the cores In some cases, part of output light output from the amplification optical fiber leaks into the cladding of the delivery fiber and propagates through the cladding of the delivery fiber. In this case, there is a problem that leakage light propagating through the cladding is absorbed by the coating layer of the delivery fiber and the coating layer is burned out. Such a problem also occurs when the output light output from the core of the delivery fiber is reflected at the end of the delivery fiber and leaks to the cladding of the delivery fiber.

  Patent Document 2 listed below describes a technique for emitting leakage light propagating through such a cladding from an optical fiber. Specifically, a light leakage component having a refractive index higher than that of the outermost layer of the optical fiber is provided in contact with the outermost layer near the end of the optical fiber, and light leakage is emitted by the light leakage component. It is to do.

JP 2008-199025 A JP 2001-66483 A

  However, in Patent Document 2, leaked light is emitted out of the optical fiber all at once at a position where the light leakage component is provided. When leaked light is emitted out of the optical fiber at once, the intensity of the emitted light is strong, and there is a risk that the component to which the emitted light is locally heated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber that can gradually emit leakage light propagating through a cladding, and a laser device using the optical fiber.

  An optical fiber according to the present invention covers a core, an inner cladding that covers the core, and the inner cladding. The average refractive index is lower than the refractive index of the inner cladding, and light having a predetermined wavelength is applied to the inner cladding. An optical fiber having a low refractive index layer to be confined and an outer cladding that covers the low refractive index layer and has a refractive index higher than the average refractive index of the low refractive index layer. A portion in the circumferential direction along the outer peripheral surface of the inner cladding is missing along the longitudinal direction of the inner cladding, and a portion where the low refractive index layer is missing is the portion of the low refractive index layer. The average refractive index is higher than the average refractive index, and the light emitting part emits a part of the light confined in the inner cladding.

  According to such an optical fiber, even when a part of the light input to the core or the light output from the core leaks to the inner clad as the leaked light, the leaked light is reflected on the inner side by the low refractive index layer. It is confined to the cladding and propagates through the inner cladding. And since a part of the circumferential direction along the outer peripheral surface of the inner clad in this low refractive index layer is missing along the longitudinal direction of the inner clad to form a light emitting portion, leakage light is emitted from the inner clad. Is gradually emitted from the light emitting portion to the outer cladding while propagating through the light. Therefore, leaked light can be prevented from being emitted from the inner cladding at once, and even when the optical fiber is coated with the coating layer, the coating layer is suppressed from being locally heated and deteriorated by heat. Can be prevented.

  Further, in the above optical fiber, the low refractive index layer has a plurality of low refractive index portions having a refractive index lower than that of the inner cladding and extending along a longitudinal direction of the inner cladding along the circumferential direction. It is preferable that the light emitting portion is not provided with the low refractive index portion.

  Such an optical fiber can be a photonic crystal fiber in which a large number of low refractive index portions are provided in the low refractive index portion, and has the further effect that the width dimension of the light emitting portion can be easily controlled. it can.

  Alternatively, in the optical fiber, the low refractive index layer includes a plurality of low refractive index portions having a lower refractive index than the inner cladding and extending along a longitudinal direction of the inner cladding along the circumferential direction. The light emitting portion is provided with a low refractive index portion having a refractive index lower than that of the inner cladding and having a cross-sectional area smaller than that of the low refractive index portion along the longitudinal direction of the inner cladding. It is preferable.

  According to such an optical fiber, the structure in the cross section perpendicular to the light propagation direction can be made closer to symmetry, so that it is possible to produce a further effect that it is easy to produce a homogeneous fiber.

  Alternatively, in the optical fiber, the low refractive index layer includes a plurality of low refractive index portions having a lower refractive index than the inner cladding and extending along a longitudinal direction of the inner cladding along the circumferential direction. It is preferable that a high refractive index portion having a higher refractive index than the low refractive index portion is provided in the light emitting portion along the longitudinal direction of the inner cladding.

  According to such an optical fiber, since the structure in the circumferential direction can be made closer to symmetry, it is possible to achieve a further effect that it is easy to produce a homogeneous fiber.

  Alternatively, in the optical fiber, the low refractive index layer has a lower refractive index than the inner cladding, extends along the longitudinal direction of the inner cladding, and is provided in a wall shape along the circumferential direction. It is preferably composed of a low refractive index portion.

  According to such an optical fiber, the further effect of confining leaked light more strongly can be achieved.

  In the optical fiber, the low refractive index portion is preferably a hole.

  According to such an optical fiber, since a high numerical aperture (NA) can be secured, it is possible to achieve a further effect of confining leaked light having a larger incident angle.

  Alternatively, in the optical fiber, it is preferable that the low refractive index portion is a low refractive index glass.

  According to such an optical fiber, since the low refractive index portion is glass, it is possible to suppress a decrease in mechanical strength of the optical fiber.

  In the optical fiber, it is preferable that the average refractive index of the light emitting portion is not less than the refractive index of the inner cladding and not more than the refractive index of the outer cladding.

  According to such an optical fiber, light propagating through the inner cladding can be appropriately emitted to the outer cladding.

  Further, in the above optical fiber, the low refractive index layer is missing along the longitudinal direction of the inner cladding at a plurality of locations in the circumferential direction, and each portion where the low refractive index layer is missing. However, it is preferable that the light emitting portion is used.

  According to such an optical fiber, since leakage light can be emitted from a plurality of locations in the circumferential direction of the optical fiber, compared with the case where only one light emitting portion is provided, the light emitting portion per location. If the leakage light intensity is the same, it is possible to easily realize the characteristic of leaking more leakage light.

  The laser device of the present invention includes the above-described optical fiber, and output light is propagated through the optical fiber.

  In such a laser device, an optical fiber can be used as a delivery fiber for output light, and leakage light is gradually generated even when leakage light occurs and the leakage light propagates through the inner cladding of the optical fiber. Can be released.

  The laser apparatus further includes an input optical fiber that has a core and a clad, is end-face connected to the optical fiber, and inputs the output light to the core of the optical fiber. The outer diameter of the clad is preferably set to be equal to or smaller than the outer diameter of the inner clad of the optical fiber.

  According to such a laser apparatus, even when unnecessary leakage light occurs in the input optical fiber and the leakage light is output from the cladding of the input optical fiber, the leakage light is confined in the inner cladding of the optical fiber. Can be made easier.

  Furthermore, in the above laser apparatus, it is preferable that the input optical fiber is an amplification optical fiber in which an active element that causes stimulated emission by light of the predetermined wavelength is added to the core.

  According to such a laser device, a fiber laser device can be configured.

  As described above, according to the present invention, an optical fiber capable of gradually emitting leakage light propagating through a clad along a direction in which light propagates, and a laser apparatus using the optical fiber are provided.

It is a figure which shows the laser apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows the mode of a cross section perpendicular | vertical to the length direction of the optical fiber for amplification of FIG. It is a figure which shows the mode of a cross section perpendicular | vertical to the length direction of the delivery fiber of FIG. It is a figure which shows the mode of the connection of the optical fiber for amplification, and a delivery fiber. It is a figure which shows the mode of a cross section perpendicular | vertical to the length direction of the delivery fiber of the laser apparatus concerning 2nd Embodiment of this invention. It is a figure which shows the mode of a cross section perpendicular | vertical to the length direction of the delivery fiber of the laser apparatus concerning 3rd Embodiment of this invention. It is a figure which shows the mode of a cross section perpendicular | vertical to the length direction of the delivery fiber of the laser apparatus concerning 4th Embodiment of this invention. It is a figure which shows the mode of a cross section perpendicular | vertical to the length direction of the delivery fiber of the laser apparatus concerning 5th Embodiment of this invention. It is a figure which shows the mode of a cross section perpendicular | vertical to the length direction of the delivery fiber of the laser apparatus concerning 6th Embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of an optical fiber according to the present invention and a laser apparatus using the same will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a laser apparatus according to the first embodiment of the present invention.

  As shown in FIG. 1, the laser device 1 is a fiber laser device, and includes a seed light source 10 that outputs seed light, an excitation light source 20 that outputs excitation light, and amplification light that is input by the seed light and the excitation light. Main components are a fiber 30, a combiner 40 that connects the seed light source 10, the excitation light source 20, and the amplification optical fiber 30, and an optical fiber as a delivery fiber 50 that has one end connected to the amplification optical fiber 30. Prepare as.

  The seed light source 10 is composed of, for example, a laser light source composed of a laser diode, or a Fabry-Perot type or fiber ring type fiber laser device. The seed light output from the seed light source 10 is not particularly limited, but when the active element added to the amplification optical fiber 30 in the subsequent stage is ytterbium (Yb) as described later, for example, The laser light has a wavelength of 1070 nm. The seed light source 10 is connected to a seed light propagation fiber 15 including a core and a clad covering the core, and the seed light output from the seed light source 10 is transmitted from the seed light propagation fiber 15. Propagate the core. An example of the seed light propagation fiber 15 is a single mode fiber. In this case, the seed light propagates through the seed light propagation fiber 15 as single mode light.

  The excitation light source 20 is composed of a plurality of laser diodes 21. When the active element added to the amplification optical fiber 30 at the subsequent stage is ytterbium (Yb) as will be described later, for example, excitation light having a wavelength of 915 nm Is output. Each laser diode 21 of the excitation light source 20 is connected to the excitation light propagation fiber 22, and the excitation light output from the laser diode 21 propagates through the excitation light propagation fiber 22. An example of the excitation light propagation fiber 22 is a multimode fiber. In this case, the excitation light propagates through the excitation light propagation fiber 22 as multimode light.

  FIG. 2 is a diagram illustrating a cross-sectional structure perpendicular to the longitudinal direction of the amplification optical fiber 30. As shown in FIG. 2, the amplification optical fiber 30 includes a core 31, a clad 32 that covers the core 31, a resin clad 33 that covers the clad 32, and a coating layer 34 that covers the resin clad 33. The The refractive index of the clad 32 is lower than the refractive index of the core 31, and the refractive index of the resin clad 33 is further lower than the refractive index of the clad 32. The diameter of the core 31 is, for example, 9 μm, the outer diameter of the cladding 32 is, for example, 120 μm, and the outer diameter of the resin cladding is, for example, 250 μm. Examples of the material constituting the core 31 include an element such as germanium that increases the refractive index and a predetermined wavelength that is excited by excitation light output from the excitation light source 20 and output from the seed light source. Quartz to which an active element such as ytterbium (Yb) capable of stimulated emission of light having the same wavelength as the seed light is added. Examples of such an active element include rare earth elements. Examples of rare earth elements include erbium (Er), thulium (Tm), cerium (Ce), neodymium (Nd), and europium (Eu) in addition to Yb. Can be mentioned. In addition to rare earth elements, active elements include bismuth (Bi), chromium (Cr), and the like. Moreover, as a material which comprises the clad 32, the pure quartz to which no dopant is added is mentioned, for example. Moreover, as a material which comprises the resin clad 33, an ultraviolet curable resin is mentioned, for example, As a material which comprises the coating layer 34, the ultraviolet curable resin different from resin which comprises the resin clad 33 is mentioned, for example.

  The combiner 40 connects the seed light propagation fiber 15 and the respective excitation light propagation fibers 22 and the amplification optical fiber 30. Specifically, in the combiner 40, the core of the seed light propagation fiber 15 is end-face connected to the core 31 of the amplification optical fiber 30. Further, in the combiner 40, the cores of the respective excitation light propagation fibers 22 are end-connected to the clad 32 at one end of the amplification optical fiber 30. Thus, the seed light output from the seed light source 10 is input to the core 31 of the amplification optical fiber 30, and the excitation light output from the excitation light source 20 is input to the clad 32 of the amplification optical fiber 30.

  FIG. 3 is a view showing a state of a cross section perpendicular to the length direction of the delivery fiber 50 of FIG. As shown in FIG. 3, the delivery fiber 50 includes a core 51, an inner cladding 52 that covers the core 51, a low refractive index layer 60 that covers the inner cladding 52, and an outer cladding 54 that covers the low refractive index layer 60. And a coating layer 55 that covers the outer cladding 54.

  The diameter of the core 51 is, for example, 10 μm, and the outer diameter of the inner cladding 52 is, for example, 130 μm. The outer diameter of the inner cladding 52 is preferably greater than or equal to the outer diameter of the cladding 32 of the amplification optical fiber 30. Examples of the material constituting the core 51 include quartz to which an element such as germanium for increasing the refractive index is added. Examples of the material for the inner cladding 52 include pure quartz to which no dopant is added. Is mentioned.

  The low refractive index layer 60 confines light in the inner cladding 52 when light having a predetermined wavelength such as light having the same wavelength as the seed light or light having the same wavelength as the excitation light is input to the inner cladding 52. It is configured. Specifically, a large number of low refractive index portions extending along the longitudinal direction of the inner cladding 52 are formed along the circumferential direction along the outer peripheral surface of the inner cladding 52. In the present embodiment, each of the low refractive index portions is a hole 61, and a rib 62 is formed between the holes 61. The rib 62 is not particularly limited, and is made of, for example, the same material as that of the inner cladding 52. The air holes 61 are filled with an inert gas such as air or nitrogen. Thus, the average refractive index of the low refractive index layer 60 is made smaller than the average refractive index of the inner cladding 52. The diameter of each hole 61 is not particularly limited as long as light of a predetermined wavelength is input to the inner cladding 52 as long as the light can be confined. For example, the diameter of the hole 61 is 5.0 μm. Similarly, the interval between the holes 61 (the width of the ribs 62) is not particularly limited, but is, for example, about 0.5 μm (the distance between the centers of the holes 61 is 5.5 μm) at the shortest portion.

  Further, the low refractive index layer 60 is missing in a part of the circumferential direction along the outer peripheral surface of the inner cladding 52 as indicated by a broken line in FIG. Specifically, the hole 61 is not formed in the portion indicated by the broken line in FIG. 3, and this portion is a light emitting portion 70 that emits part of the light confined in the inner cladding 52, and It extends along the longitudinal direction of the clad 52. In other words, the light emitting portion 70 is a portion where the gaps 61 are widened so that a part of the light confined in the inner cladding 52 is emitted. The refractive index (average refractive index) of the light emitting portion 70 is set higher than the average refractive index of the low refractive index layer 60. Further, the refractive index of the light emitting portion 70 is not particularly limited as long as a part of the light confined in the inner cladding 52 can be emitted, but it is more than the refractive index of the inner cladding 52. It is preferable from the viewpoint that a part of the light confined in 52 can be appropriately emitted. Since the light emitting portion 70 has such a refractive index, it is made of, for example, the same material as the inner cladding 52. The interval between the air holes 61 sandwiching the light emitting portion 70, that is, the width of the light emitting portion 70 is not particularly limited as long as the light confined in the inner cladding 52 can be emitted. Is done.

  The outer cladding 54 has an outer diameter of, for example, 200 μm, and the outer cladding 54 has a refractive index higher than the average refractive index of the low refractive index layer 60. The outer cladding 54 is made of the same material as that of the inner cladding 52, for example.

  Moreover, the outer diameter of the coating layer 55 is, for example, 300 μm. The covering layer 55 is made of a material having a refractive index higher than that of the outer cladding 54. Examples of such a material include an ultraviolet curable resin.

  As shown in FIG. 1, one end 58 of the delivery fiber 50 is connected to the amplification optical fiber 30 as described above, and nothing is connected to the other end 59, which is a free end. Therefore, in this embodiment, the input optical fiber that inputs light to the delivery fiber 50 is the amplification optical fiber 30.

  FIG. 4 is a diagram illustrating a state of connection between the amplification optical fiber 30 and the delivery fiber 50. For ease of understanding, in FIG. 4, the scale of each part constituting the amplification optical fiber 30 and the delivery fiber 50 is changed from that in FIGS. 2 and 3. As shown in FIG. 4, in the delivery fiber 50, the coating layer 55 is peeled in the vicinity of one end 58. In the amplification optical fiber 30, the resin cladding 33 and the coating layer 34 are peeled in the vicinity of the other end 39 that is the end opposite to the combiner 40. One end 58 of the delivery fiber 50 is connected to the other end 39 of the amplification optical fiber 30, and the core 51 of the delivery fiber 50 and the core 31 of the amplification optical fiber 30 are connected. The clad 52 and the clad 32 of the amplification optical fiber 30 are connected. In the case where the amplification optical fiber 30 that inputs output light to the delivery fiber 50 and the delivery fiber 50 are end-face connected as in the present embodiment, the cladding 32 of the amplification optical fiber 30 is connected as described above. By setting the outer diameter to be equal to or smaller than the outer diameter of the inner cladding 52 of the delivery fiber 50, when the amplification optical fiber 30 and the delivery fiber 50 are connected to the end face, bubbles are formed based on the holes of the delivery fiber. This is preferable because it can be suppressed.

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

  First, seed light having a predetermined wavelength is output from the seed light source 10, and excitation light having a predetermined wavelength different from the wavelength of the seed light is output from each laser diode 21 of the excitation light source 20. At this time, the wavelength of the seed light is, for example, 1070 nm as described above, and the wavelength of the excitation light is, for example, 915 nm as described above. The seed light output from the seed light source 10 propagates through the core of the seed light propagation fiber 15 and is input to the combiner 40. Further, the excitation light output from the excitation light source 20 propagates through the excitation light propagation fiber 22 and enters the combiner 40.

  The seed light thus input to the combiner 40 is input to the core 31 of the amplification optical fiber 30 and propagates through the core 31. On the other hand, the excitation light input to the combiner 40 is input to the cladding 32 of the amplification optical fiber 30 and propagates mainly through the cladding 32.

  And when excitation light passes the core 31, it is absorbed by the active element added to the core 31, and excites the active element. The excited active element causes stimulated emission by the seed light, the seed light is amplified by this stimulated emission, and is output from the core 31 at the other end 39 of the amplification optical fiber 30 as output light.

  The output light output from the core 31 of the amplification optical fiber 30 is input to the core 51 of the delivery fiber 50, propagates through the core 51, and is output from the other end 59 of the delivery fiber 50.

  At this time, in the connection portion between the amplification optical fiber 30 and the delivery fiber 50, the axis of the amplification optical fiber 30 is different due to axial misalignment between cores, mismatch of angles between cores, mode field difference between cores, and the like. Some of the output light output from the core 31 may be input to the inner cladding 52 of the delivery fiber 50 as leakage light. Alternatively, the light output from the other end 59 of the delivery fiber 50 may cause full-nel reflection and enter the inner cladding 52 from the other end 59 side. In this case, leaked light input to the inner cladding 52 is confined and propagated in the inner cladding 52 by the low refractive index layer 60. The leakage light propagating through the inner cladding 52 is gradually emitted from the light emitting portion 70 to the outer cladding 54 as it propagates. Then, the leakage light gradually emitted from the light emitting portion 70 to the outer cladding 54 reaches the coating layer 55 and is converted into heat and disappears.

  As described above, according to the optical fiber as the delivery fiber 50 of the present embodiment, a part of the light input to the core 51 and the light output from the core 51 leaks into the inner cladding 52 as leakage light. Even in the case, the leaked light is confined in the inner cladding 52 by the low refractive index layer 60 and propagates through the inner cladding 52. A portion of the low refractive index layer 60 in the circumferential direction along the outer peripheral surface of the inner cladding 52 is missing along the longitudinal direction of the inner cladding 52 and is used as the light emitting portion 70. Is gradually emitted from the light emitting portion 70 to the outer cladding 54 while propagating through the inner cladding 52. Therefore, leakage light can be prevented from being emitted at a short distance in the direction in which light propagates from the inner cladding 52, and even when the optical fiber is coated with the coating layer 55, in the coating layer 55, Since light is gradually converted into heat, it is possible to prevent the coating layer 55 from being burned out.

  Further, as described above, when the outer diameter of the clad 32 of the amplification optical fiber 30 is equal to or smaller than the outer diameter of the inner clad 52 of the delivery fiber 50, it is unnecessary from the clad 32 of the amplification optical fiber 30. Even when light is output, this leaked light can be easily confined in the inner cladding 52 of the delivery fiber 50. For example, when light leaks from the core 31 of the amplification optical fiber 30 and this light propagates through the clad 32 and is output, or when the excitation light propagating through the clad 32 is not used for amplification of the seed light When the excitation light is output, the light output from the cladding 32 can be easily confined in the inner cladding of the delivery fiber 50 as leakage light.

  Further, in the delivery fiber 50 of the present embodiment, the low refractive index layer 60 has holes 61 extending along the longitudinal direction of the inner cladding 52 along the circumferential direction along the outer circumferential surface of the inner cladding 52. Since a large number of light emitting portions 70 are provided in the light emitting portion 70, a high NA can be secured and leaked light having a larger incident angle can be confined.

  Further, according to the laser device 1 provided with such a delivery fiber 50, even if leakage light occurs, the leakage light can be gradually emitted, so that the laser device can be made safe and reliable. it can.

(Second Embodiment)
Next, 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 an equivalent component, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 5 is a view showing a state of a cross section perpendicular to the length direction of the delivery fiber of the laser apparatus according to the second embodiment of the present invention.

  As shown in FIG. 5, in the optical fiber as the delivery fiber 50 of the present embodiment, the hole 71 as the low refractive index portion having a lower refractive index than the inner cladding 52 is formed in the light emitting portion 70 of the inner cladding 52. It differs from the delivery fiber 50 of 1st Embodiment in the point formed along the longitudinal direction.

  The hole 71 has a cross-sectional area in a plane perpendicular to the length direction smaller than the cross-sectional area of each hole 61 in the low refractive index layer 60. The holes 71 are filled with air, an inert gas, or the like, as with the holes 61. Further, the gap between the holes 71 and the holes 61 adjacent to the holes 71 is wider than the gap between the holes 61. Therefore, the average refractive index of the light emitting portion 70 is set higher than the average refractive index of the low refractive index layer 60.

  The diameter of the hole 71 is not particularly limited as long as a part of the light confined in the inner cladding 52 can be emitted. For example, the diameter of the hole 71 is 2 μm, and the hole 71 is adjacent to the hole 71. Similarly, the distance from the air holes 61 is not particularly limited, but is, for example, 4 μm.

  According to the delivery fiber 50 in the present embodiment, it is possible to easily realize the characteristic of reducing the leaked light emission ratio as compared with a structure without holes.

(Third embodiment)
Next, a third 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 an equivalent component, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 6 is a view showing a state of a cross section perpendicular to the length direction of the delivery fiber of the laser apparatus according to the third embodiment of the present invention.

  The delivery fiber 50 as an optical fiber in the present embodiment is a low refractive index portion 63 in which a hole 61 in the delivery fiber 50 of the first embodiment is filled with low refractive index glass.

  The low refractive index portion 63 has a refractive index lower than that of the inner cladding 52. The relative refractive index difference between the low refractive index portion 63 and the inner cladding 52 is not particularly limited as long as light having a predetermined wavelength is input to the inner cladding 52 as long as the light can be confined. 0.3%. Examples of such a material of the low refractive index portion 63 include quartz to which an element such as fluorine (F) that lowers the refractive index is added.

  According to the delivery fiber 50 according to the present embodiment, since it is not necessary to provide holes in the low refractive index layer 60, it is possible to prevent the mechanical strength of the delivery fiber 50 from being impaired.

(Fourth embodiment)
Next, a fourth 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 an equivalent component, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 7 is a view showing a state of a cross section perpendicular to the length direction of the delivery fiber of the laser apparatus according to the fourth embodiment of the present invention.

  In the delivery fiber 50 as an optical fiber in the present embodiment, the high refractive index portion 72 having a refractive index higher than the average refractive index of the low refractive index layer 60 in the light emitting portion 70 extends along the longitudinal direction of the inner cladding 52. It differs from the delivery fiber 50 of 1st Embodiment in the point currently formed.

  The refractive index of the high refractive index portion 72 is not particularly limited as long as it is higher than the refractive index of the low refractive index layer 60 and can emit part of the light confined in the inner cladding 52. It is preferable that the refractive index is equal to or higher than the refractive index of the outer cladding 54 and equal to or lower than the refractive index of the outer cladding 54. Accordingly, examples of the material of the high refractive index portion 72 include the same material as the material of the inner cladding 52 and quartz to which an element such as germanium that increases the refractive index is added.

  The diameter of the high refractive index portion 72 is, for example, the same diameter as that of the hole 61, and the interval between the high refractive index portion 72 and the hole 61 adjacent to the high refractive index portion 72 is, for example, a hole. The interval is the same as the interval between 61.

  According to the delivery fiber 50 in the present embodiment, the structure in the cross section perpendicular to the light propagation direction can be made closer to the symmetry, so that it is possible to easily produce a homogeneous fiber.

(Fifth embodiment)
Next, a fifth 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 an equivalent component, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 8 is a view showing a state of a cross section perpendicular to the length direction of the delivery fiber of the laser apparatus according to the fifth embodiment of the present invention.

  In the delivery fiber 50 as an optical fiber in the present embodiment, the low refractive index layer 60 has a lower refractive index than the inner cladding 52, extends along the longitudinal direction of the inner cladding 52, and the outer periphery of the inner cladding 52. It differs from the delivery fiber 50 of 1st Embodiment in the point which consists of the low-refractive-index part 67 provided in the wall shape along the circumferential direction along a surface.

  That is, the low refractive index portion 67 has a substantially C-shaped shape in the cross section perpendicular to the longitudinal direction of the delivery fiber 50, and the portion where the low refractive index portion 67 is missing is the portion of the first embodiment. Similar to the delivery fiber 50, the light emitting portion 70 is provided. This low refractive index part 67 is comprised from the material similar to the low refractive index part 63 of 3rd Embodiment, for example.

  According to the delivery fiber 50 in the present embodiment, it is possible to achieve a further effect that leakage light is more strongly confined in the circumferential direction other than the light emitting portion 70 in the circumferential direction of the cross section.

(Sixth embodiment)
Next, a sixth 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 an equivalent component, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 9 is a view showing a state of a cross section perpendicular to the length direction of the delivery fiber of the laser apparatus according to the sixth embodiment of the present invention.

  As shown in FIG. 9, in the delivery fiber 50 in the present embodiment, the low refractive index layer 60 is missing along the longitudinal direction of the inner cladding 52 at a plurality of locations in the circumferential direction along the outer circumferential surface of the inner cladding 52. Each of the portions where the low refractive index layer 60 is missing is a light emitting portion 70, which is different from the delivery fiber 50 of the first embodiment.

  Each light emitting unit 70 has the same configuration as the light emitting unit 70 in the first embodiment.

  According to such a delivery fiber 50, since leakage light can be emitted from a plurality of locations in the circumferential direction of the delivery fiber, only one light emitting portion 70 is provided as in the delivery fiber in the first embodiment. Compared with the case where it is, the intensity | strength of the leakage light discharge | released from each light emission part 70 can be made weak.

  As mentioned above, although this invention was demonstrated to the 1st-6th embodiment as an example, this invention is not limited to these.

  For example, in the above embodiment, the laser device of the present invention has been described as an example of a fiber laser device. However, the present invention is not limited to this, for example, the laser device of the present invention is a solid-state laser device, and the light of the present invention. The fiber may be used as a delivery fiber for a solid state laser device.

  Moreover, in the said embodiment, although demonstrated by the example in which the optical fiber of this invention is used as the delivery fiber 50, the optical fiber of this invention may be applied other than a delivery fiber.

  In the above embodiment, the amplification optical fiber 30 is directly connected to the optical fiber as the delivery fiber 50, and the amplification optical fiber 30 is used as an input optical fiber for inputting light to the delivery fiber 50. However, another optical fiber having a core and a clad may be interposed between the amplification optical fiber 30 and the delivery fiber 50, and the other optical fiber may be used as the input optical fiber.

  In the above embodiment, the outer diameter of the clad 32 of the amplification optical fiber 30 connected to the one end 58 of the delivery fiber 50 is set to be equal to or smaller than the inner clad 52 of the delivery fiber 50. However, the present invention is not limited to this. The outer diameter of the clad 32 of the amplification optical fiber 30 connected to the delivery fiber 50 may be larger than the outer diameter of the inner clad 52 of the delivery fiber 50.

  Moreover, you may fill the hole 71 of 2nd Embodiment with the material similar to the high refractive index part 72 of 4th Embodiment. Furthermore, holes similar to the holes 71 of the second embodiment may be formed in the light emitting section 70 of the third embodiment, and a high refractive index portion similar to the high refractive index portion 72 of the fourth embodiment is provided. May be.

  Further, the light emitting portion 70 of the fifth embodiment may be formed with a hole similar to the hole 71 of the second embodiment, and a high refractive index portion similar to the high refractive index portion 72 of the fourth embodiment is provided. Alternatively, the entire light emitting portion 70 may be filled with the same material as the high refractive index portion 72 of the fourth embodiment.

  Also, in the delivery fibers 50 of the second to fifth embodiments, a plurality of light emitting portions 70 may be provided as in the sixth embodiment.

  Further, the low refractive index portion 67 of the fifth embodiment may be formed by holes. However, in this case, it is preferable to provide a plurality of light emitting portions 70 as described above from the viewpoint of ensuring strength.

  Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

  An optical fiber similar to the delivery fiber of the first embodiment was produced. In this optical fiber, the core diameter was 10 μm, the outer diameter of the inner cladding was 130 μm, the outer diameter of the outer cladding was 200 μm, and the outer diameter of the coating layer was 300 μm. Further, 76 holes having a diameter of 5.0 μm were formed in the low refractive index layer, and the distance between the centers of the holes was set to 5.5 μm. And the light emission part from which the space | interval of a void | hole was 6 micrometers apart was provided. The material of the core is quartz to which 3% by mass of germanium is added, the material of the inner cladding and the outer cladding is pure quartz to which no dopant is added, and the material of the coating layer is an ultraviolet curable resin. . The material of the light emitting part was the same material as the inner cladding.

  Next, the same amplification optical fiber as in the first embodiment was prepared. This amplification optical fiber had a core diameter of 9 μm, a cladding outer diameter of 120 μm, and a resin cladding of 250 μm. The material of the core of this optical fiber for amplification is quartz to which 3% by weight of germanium and 1% by weight of ytterbium are added, and the material of the inner and outer claddings is pure quartz to which no dopant is added, The material of the resin cladding was an ultraviolet curable resin.

  Next, the prepared optical fiber and the amplification optical fiber are connected to each other, and seed light and excitation light are input to the amplification optical fiber, and a part of the excitation light is used as excess excitation light. 5 W was output from the other cladding, and input to the inner cladding of the optical fiber.

  And the temperature of the coating layer of an optical fiber was measured at normal temperature. As a result, the coating layer of the optical fiber rose only up to 60, and no thermal damage occurred.

  Thus, according to the optical fiber of the present invention, it is considered that the excitation light input to the inner cladding is gradually emitted.

  ADVANTAGE OF THE INVENTION According to this invention, the optical fiber which can discharge | release the leak light which propagates a clad gradually, and a laser apparatus using the same are provided.

DESCRIPTION OF SYMBOLS 1 ... Laser apparatus 10 ... Seed light source 15 ... Seed light propagation fiber 20 ... Excitation light source 21 ... Laser diode 22 ... Excitation light propagation fiber 30 ... Amplification optical fiber 31 ... Core 32 ... Clad 33 ... Resin clad 34 ... Coating layer 40 ... Combiner 50 ... Delivery fiber 51 ... Core 52 ... Inner cladding 54 ... Outer cladding 55 ... Covering layer 60 ... Low refractive index layer 61 ... Hole 62 ... Rib 63, 67 ... Low refractive index part 70 ... Light emitting part 71 ... Hole 72 ..High refractive index part

Claims (12)

The core,
An inner cladding covering the core;
A low refractive index layer covering the inner cladding, having an average refractive index lower than the refractive index of the inner cladding, and confining light of a predetermined wavelength in the inner cladding;
An outer cladding that covers the low refractive index layer and has a refractive index higher than the average refractive index of the low refractive index layer;
An optical fiber comprising:
A portion of the circumferential direction along the outer peripheral surface of the inner cladding in the low refractive index layer is missing along the longitudinal direction of the inner cladding,
The portion where the low refractive index layer is missing is a light emitting portion that has a higher average refractive index than the average refractive index of the low refractive index layer and emits part of the light confined in the inner cladding. An optical fiber characterized by The low refractive index layer has a refractive index lower than that of the inner cladding, and a plurality of low refractive index portions extending along the longitudinal direction of the inner cladding are provided along the circumferential direction.
The optical fiber according to claim 1, wherein the light emitting portion is not provided with the low refractive index portion. The low refractive index layer has a refractive index lower than that of the inner cladding, and a plurality of low refractive index portions extending along the longitudinal direction of the inner cladding are provided along the circumferential direction.
The light emitting portion is provided with a low refractive index portion having a refractive index lower than that of the inner cladding and having a cross-sectional area smaller than that of the low refractive index portion along the longitudinal direction of the inner cladding. The optical fiber according to claim 1. The low refractive index layer has a refractive index lower than that of the inner cladding, and a plurality of low refractive index portions extending along the longitudinal direction of the inner cladding are provided along the circumferential direction.
2. The light according to claim 1, wherein a high refractive index portion having a higher refractive index than the low refractive index portion is provided in the light emitting portion along a longitudinal direction of the inner cladding. fiber.   The low refractive index layer has a refractive index lower than that of the inner cladding, extends along the longitudinal direction of the inner cladding, and includes a low refractive index portion provided in a wall shape along the circumferential direction. The optical fiber according to claim 1.   The optical fiber according to claim 1, wherein the low refractive index portion is a hole.   The optical fiber according to claim 1, wherein the low refractive index portion is low refractive index glass.   8. The optical fiber according to claim 1, wherein the average refractive index of the light emitting portion is equal to or higher than a refractive index of the inner cladding and equal to or lower than a refractive index of the outer cladding.   The low refractive index layer is missing along the longitudinal direction of the inner cladding at a plurality of locations in the circumferential direction, and each portion where the low refractive index layer is missing is the light emitting portion. The optical fiber according to any one of claims 1 to 8, wherein the optical fiber is formed. Comprising the optical fiber according to any one of claims 1 to 9,
A laser apparatus in which output light is propagated by the optical fiber. An optical fiber for input that has a core and a clad, is end-face connected to the optical fiber, and inputs the output light to the core of the optical fiber;
The laser device according to claim 10, wherein an outer diameter of the clad of the input optical fiber is equal to or smaller than an outer diameter of the inner clad of the optical fiber. 12. The laser device according to claim 11, wherein the input optical fiber is an amplification optical fiber in which an active element that causes stimulated emission by light of the predetermined wavelength is added to the core.

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