JP2014010427A - Optical fiber and optical cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber with high removal efficiency of clad mode light and high mechanical strength.SOLUTION: An optical fiber 100 includes a core 101, and a clad 102 surrounding an outer periphery of the core 101, and the clad 102 is provided with groove parts 104 formed continuously in a circumferential direction of the optical fiber 100. The clad 102 at the groove part 104 has a large diameter part having a first thickness D1 in a radial direction of the optical fiber 100, and a small diameter part having a second thickness D2 smaller than the first thickness D1 in the radial direction. The plurality of large diameter parts are provided in an axial direction of the optical fiber 100, and the plurality of large diameter parts are provided on a straight line roughly parallel to the axial direction of the optical fiber 100.

Description

  The present invention relates to an optical fiber and an optical cable suitable for transmitting high-intensity laser light.

  As an optical fiber and an optical connector used for transmitting high-intensity light, for example, those described in Patent Document 1 are known. The optical fiber for laser light described in Patent Document 1 includes a core through which laser light propagates, a clad provided on the outer periphery of the core, and a protective layer covering the outer periphery of the clad. A light removing member for removing light propagating through the clad from the clad is formed on the clad exposed portion formed by removing the protective layer.

  Moreover, what was described in patent document 2 is also known as an optical fiber which formed the clad mode removal part which removes the light which propagates a clad from this clad. Here, in an optical fiber having a core and a clad covering the outer peripheral surface of the core, a mode is disclosed in which the clad mode removing portion is formed in a groove shape on the outer peripheral surface of the clad. Further, it is disclosed that such an optical fiber can be easily processed by irradiating a laser to the clad.

JP 2003-139996 A JP 2011-118208 A International Publication No. 08/123609 Pamphlet

  When transmitting light using an optical fiber having a core / cladding structure, it is usually assumed that light is transmitted only in the core region. However, when light enters the optical fiber, the light may enter not only the core region but also the cladding region. The core region is made of a material having a higher refractive index than that of the cladding region, but light transmitted through the core region may slightly leak into the cladding region. In this way, light slightly incident on the cladding region propagates through the cladding region (cladding mode light), and an optical fiber is used as a laser beam transmission means of a laser processing apparatus that transmits kW-class high-intensity light. In some cases, the cladding mode light can be a cause of deterioration in processing accuracy. Such a problem is also pointed out in Patent Document 3.

  In addition, an optical fiber in which a cladding mode removing portion for removing cladding mode light as described in Patent Document 2 is formed in a groove shape on the outer peripheral surface of the cladding can be manufactured at low cost by irradiating the cladding with laser. And it is excellent in that it can be manufactured with high precision. However, an optical fiber used as a high-intensity laser light transmission means such as a laser processing apparatus is required to efficiently remove clad mode light and not to excessively deteriorate the mechanical strength of the optical fiber. .

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical fiber having high cladding mode light removal efficiency and high mechanical strength. Furthermore, an object of the present invention is to provide an optical cable that contributes to the realization of a laser processing apparatus that can perform high-precision processing using such an optical fiber.

  The optical fiber of the present invention is an optical fiber including a core and a clad surrounding the outer periphery of the core, and the clad is provided with a groove formed continuously in the circumferential direction of the optical fiber, and the clad in the groove Has a large diameter portion having a first thickness in the radial direction of the optical fiber and a small diameter portion having a second thickness smaller than the first thickness in the radial direction. A plurality of axial portions are provided, and a plurality of large diameter portions are provided on a straight line substantially parallel to the axial direction of the optical fiber.

  This optical fiber has a groove portion formed continuously in the circumferential direction in the clad, and a plurality of large diameter portions in the groove portion are provided on a straight line substantially parallel to the axial direction. Therefore, since the clad mode light is surely removed by the grooves formed in the axial direction, the removal efficiency of the clad mode light can be increased. The groove portion has a large diameter portion having a first thickness in the radial direction and a small diameter portion having a second thickness smaller than the first thickness in the radial direction. Therefore, when bending stress is applied to the optical fiber, the bending stress concentrates on the large diameter portion, and the shear strength becomes stronger as the outer diameter increases, so by concentrating the bending stress on the large diameter portion. Since the shear strength of the optical fiber is increased, the mechanical strength can be increased.

  In the optical fiber of the present invention, the groove is a plurality of annular grooves formed at predetermined intervals in the axial direction, and the large-diameter portion of each groove is provided on a straight line substantially parallel to the axial direction. It is preferable. Moreover, it is preferable that the cross section of the optical fiber in said groove part is a polygon. Further, it is preferable that the cross-sectional shapes of the plurality of groove portions are substantially equal polygons, and the positions of the corner portions of these cross-sections coincide with each other in the axial direction.

  In the optical fiber of the present invention, the cladding is preferably configured such that the thickness at the bottom of the groove is thicker than the region where the evanescent light of the laser light propagating through the core of the optical fiber penetrates.

  In the optical fiber of the present invention, the length in the axial direction of the region where the groove is formed is preferably 3 cm or more and 7 cm or less. Moreover, it is preferable that said groove part is formed in the terminal of an optical fiber, and it is preferable that said groove part is formed densely in the terminal side of an optical fiber.

  An optical cable of the present invention is provided on the rear end side of the housing, housing the optical fiber and a terminal portion of the optical fiber, and fixing the end of the optical fiber at a front end portion. And a gripping part for gripping the fiber. The optical fiber further includes a covering portion that surrounds the outer periphery of the cladding, and the gripping portion grips the optical fiber by gripping the covering portion, and the cladding and the groove portion are exposed at the terminal portion. It is characterized by.

  In the optical cable of the present invention, the optical fiber has a groove formed at the end of the optical fiber, and the optical fiber further includes an end cap provided in optical contact with the end face and fixed to the housing. preferable.

  The optical cable of the present invention further includes an inner tube that is accommodated in the housing and accommodates the end portion of the optical fiber. The inner tube is fixed in the housing, and the groove is preferably formed so as to avoid a fixing portion in which the inner tube is fixed to the housing.

  In the optical cable of the present invention, the optical fiber is connected to one end side of a glass rod having the same diameter as that of the clad in the region where the groove portion is not formed, and the other end side of the glass rod is connected to the end cap. It is preferable that

  According to the present invention, it is possible to provide an optical fiber having high cladding mode light removal efficiency and high mechanical strength. Furthermore, according to the present invention, it is possible to provide an optical cable that contributes to the realization of a laser processing apparatus capable of performing high-precision laser processing or the like using such an optical fiber.

(A) is sectional drawing of the optical fiber in one Embodiment of this invention. (B) is a side view of the optical fiber in one Embodiment of this invention. (C) is CC sectional drawing of FIG.1 (b). (D) is DD sectional drawing of FIG.1 (b). (E) is EE sectional drawing of FIG.1 (b). (F) is a figure explaining a large diameter part and a small diameter part. (A) is a side view explaining the function of the optical fiber in one Embodiment of this invention. (B) is a side view explaining the optical fiber of a comparative example. (A) and (b) are the side view and sectional drawing explaining the function of the optical fiber in one Embodiment of this invention. (C) (d) is the side view and sectional drawing explaining the optical fiber of a comparative example. (A) is a figure explaining the function of the optical fiber in the modification of this invention. (B) is a figure explaining the function of the optical fiber in another modification of this invention. (C) is a figure explaining the optical fiber of a comparative example. (A)-(h) is a figure explaining the manufacturing method of the optical fiber of this invention. (A) (b) is sectional drawing explaining the structure of the optical cable of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1A is a cross-sectional view (XZ plane) in the axial direction of the optical fiber of this embodiment, and FIG. 1B is a side view (Xθ plane) of the optical fiber. 1 (c), (d), and (e) are a CC sectional view, a DD sectional view, and an EE sectional view, respectively, in FIG. 1 (b). FIG. It is a figure explaining the large diameter part in the said optical fiber, and a small diameter part. In each figure, arrow X indicates the axial direction of the optical fiber, arrow θ indicates the circumferential direction of the optical fiber, and arrow Z indicates the radial direction of the optical fiber.

  The optical fiber 100 includes a core 101 and a clad 102. The clad 102 includes a clad mode light removing unit 103 that removes clad mode light propagating through the clad 102. The optical fiber 100 can transmit high-intensity (for example, several kW) laser light for laser processing, and can be applied to laser light transmission means or the like in a laser processing apparatus.

  The optical fiber 100 is preferably formed of quartz glass. The refractive index of the core 101 is set higher than the refractive index of the clad 102. The outer diameter (core diameter) of the core 101 is, for example, 0.2 mm, and the outer diameter (cladding diameter) of the clad 102 is, for example, 1.0 mm.

  The cladding mode light removal unit 103 includes a plurality of groove portions 104. As shown in FIG. 1B, the groove 104 is an annular groove formed continuously in the circumferential direction. A plurality of groove portions 104 are preferably formed at predetermined intervals in the axial direction of the optical fiber 100. Further, as shown in FIG. 1C, the cross-sectional shapes of the core 101 and the clad 102 in a region where the groove 104 is not provided are circular, and the groove 104 is provided as shown in FIG. The cross-sectional shape of the clad 102 in the region that is formed is a regular hexagon. Moreover, the cross-sectional shape in the some groove part 104 is mutually substantially equal, and as shown in FIG.1 (d) and FIG.1 (e), the cross-sectional shape in each groove part 104 is a regular hexagon. Further, the position of the corner of the cross section in each groove 104 is substantially the same in the axial direction of the optical fiber 100. That is, when the corners X (see FIG. 1 (f)) of the cross section in each groove 104 are connected, the connected line becomes a straight line substantially parallel to the axial direction of the optical fiber 100.

  Further, as shown in FIG. 1A, the cladding 102 has a radial thickness R1 in a region where the groove 104 is not provided, and the depth of the groove 104 is R2 smaller than R1. Yes. The groove 104 has an opening 105 formed on the surface of the clad 102 and a bottom 106. Further, as shown in FIG. 1 (f), the cladding 102 in the groove portion 104 has a large diameter portion having a first thickness D 1 in the radial direction of the optical fiber 100 and a first thickness D 1 in the radial direction of the optical fiber 100. And a small diameter portion having a smaller second thickness D2. In the clad 102, the large diameter portion is the corner portion X in the cross section of the groove portion 104, and the small diameter portion is the side portion Y in the cross section of the groove portion 104. In the plurality of groove portions 104 provided in the axial direction of the optical fiber 100, the large diameter portion (corner portion X) is provided on a straight line substantially parallel to the axial direction of the optical fiber 100. Moreover, it is preferable that the groove part 104 is processed so that the bottom part 106 may become smooth.

  Consider a case where laser light is transmitted using such an optical fiber 100. FIG. 2A is a diagram illustrating a state in which light L1 to L5 incident on the clad 102 among the light incident on one end of the optical fiber 100 of the present embodiment is transmitted. FIG. 2B is a diagram for explaining how light L1 'to L5' incident on the clad 202 is transmitted among the light incident on one end of the optical fiber 200 of the comparative example. As such light L1 to L5 and light L1 ′ to L5 ′, a part of the laser light emitted from the cores 101 and 201 of the optical fibers 100 and 200 is reflected from the object to be processed and again the optical fibers 100 and 200. It is assumed that the light is incident on. The optical fiber 200 of the comparative example is different from the optical fiber 100 of the present embodiment in that the groove portion 204 is not continuously formed in the circumferential direction of the optical fiber 200, and other configurations are the same as those of the optical fiber 200 of the present embodiment. The configuration of the fiber 100 is the same.

  Of the light that has entered the optical fibers 100 and 200, the light that has not entered the cores 101 and 201 is transmitted through the clads 102 and 202, and enters the clad mode light removal units 103 and 203 having a plurality of grooves 104 and 204. To reach. At this time, the light reaching the clad mode light removing sections 103 and 203 is reflected and scattered at the interface with the openings 105 and 205 and is emitted to the outside of the clads 102 and 202. That is, the cladding mode light is removed.

  At this time, in FIGS. 2A and 2B, the lights L1 to L5 and the lights L1 'to L5' transmitted through the clads 102 and 202 are considered. Light reaching the openings 105 and 205 of the grooves 104 and 204 is scattered and emitted to the outside of the clads 102 and 202. Here, in the optical fiber 100 of this embodiment, since the groove part 104 is continuously formed in the circumferential direction of the optical fiber 100, all the lights L1 to L5 are removed from the clad 102. On the other hand, for the optical fiber 200 of the comparative example, the light L2 ′ and L4 ′ that have reached the region where the groove portion 204 is not formed in the axial direction (X direction) is transmitted through the cladding 202 without being removed from the cladding 202. To do.

  As described above, in the optical fiber 100, the groove mode 104 is formed continuously in the circumferential direction of the optical fiber 100 in the cladding mode light removal unit 103, so that the cladding mode light removal efficiency in the cladding mode light removal unit 103 is increased. Can be improved.

  Next, the mechanical strength of the optical fiber 100 will be considered. FIG. 3A is a diagram illustrating a region where stress is concentrated when bending is applied to the optical fiber 100 of the present embodiment. FIG. 3B is a diagram for explaining a region where stress is concentrated when the optical fiber 300 of the comparative example is bent. The optical fiber 300 of the comparative example is common to the optical fiber 100 of the present embodiment in that the clad mode light removing unit 303 is provided with a groove 304 formed continuously in the circumferential direction. However, in the optical fiber 300, as shown in FIG. 3D, the cross-sectional shape of the core 301 and the clad 302 in the region where the groove 304 is provided is circular, and the large diameter as in the optical fiber 100 is obtained. This is different from the optical fiber 100 in that it does not have a portion and a small diameter portion. About the other structure of the optical fiber 300, it is the same as that of the structure of the optical fiber 100 of this embodiment.

  When bending is applied to the optical fiber 100 of the present embodiment, as shown in FIG. 3B, the stress F1 is concentrated in a region having a large outer diameter, that is, a corner portion X that is a large diameter portion. As described above, in the clad mode light removal unit 103, the bending stress F1 applied to the small diameter portion (side portion Y) can be reduced by concentrating the stress F1 on the large diameter portion. Here, since the shear strength of the optical fiber 100 increases as the outer diameter increases, the shear strength of the optical fiber 100 can be increased by concentrating the bending stress F1 on the large diameter portion where the cladding thickness is large.

  On the other hand, when bending is applied to the optical fiber 300 of the comparative example, the bending stress F <b> 2 concentrates on the bottom 306 of the groove 304. That is, since the bending stress L2 is concentrated on the bottom portion 306, which is a region where the cladding thickness is small, it can be seen that the shear strength is lower than that of the optical fiber 100 of the present embodiment.

  As described above, in the optical fiber 100 of the present embodiment, the clad 102 is provided with the groove portion 104 formed continuously in the circumferential direction, and the clad 102 in the groove portion 104 is first in the radial direction of the optical fiber 100. A large-diameter portion having a thickness D1 (see FIG. 1 (f)) and a small-diameter portion having a second thickness D2 (see FIG. 1 (f)) smaller than the first thickness D1 in the radial direction. A plurality of the large diameter portions are provided in the axial direction of the optical fiber 100, and the plurality of large diameter portions are provided on a straight line substantially parallel to the axial direction of the optical fiber 100. The effect of achieving both improvement and improvement in mechanical strength can be obtained.

  The surface of the clad 102 and the inner wall of the groove 104 preferably have a smooth surface. That is, the shear strength of the optical fiber 100 is increased and the mechanical strength is improved by having a smooth surface as described above rather than the clad mode light removing portion formed by scratching or the like formed by scratching with a flaw or the like. Can do. In particular, as shown in FIG. 1 and the like, it is preferable that the bottom portion 106 has a rounded and smooth shape. In order to efficiently remove the clad mode light, the depth R2 of the groove 104 (see FIG. 1A) is preferably at least 50 μm or more. The optimum depth R2 varies depending on the clad thickness. However, in the optical fiber 100 of the present embodiment, the clad mode light removal efficiency superior to the conventional clad mode light removal portion formed by flaws or wet etching with scissors or the like. Can be obtained. By satisfying such a condition, the optical fiber 100 of the present embodiment can be distinguished from a conventional clad mode light removal portion formed by scratching by wet scissors or the like or wet etching.

  Moreover, it is preferable that the groove part 104 is an annular groove formed in a plurality at predetermined intervals in the axial direction of the optical fiber 100. In FIG. 2, for the sake of simplification, the light beams L1 to L5 are used to limit the light beam. However, the laser light is transmitted through the clad 102 in various modes (transmission paths). Therefore, the clad mode light that could not be removed by one groove 104 can also be reliably removed by the other grooves 104 provided in the axial direction of the optical fiber 100.

  Furthermore, if the cross section of the optical fiber 100 in the groove portion 104 is polygonal, it has a large diameter portion and a small diameter portion, and the diameter of the clad 102 continuously changes from the large diameter portion to the small diameter portion. . Therefore, the stress applied to the optical fiber 100 can be dispersed so as to gradually decrease from the large diameter portion to the small diameter portion, and the stress applied to the large diameter portion is increased and the stress applied to the small diameter portion is reduced. And mechanical strength can be increased. In order to further reduce the stress applied to the small diameter portion, the large diameter portion is formed in all the groove portions 104 existing in the axial direction of the optical fiber 100, and the large diameter portion is formed in the axial direction of the optical fiber 100. It is preferable that they are provided on a substantially parallel straight line. From the above viewpoint, the cross-sectional shapes of the plurality of groove portions 104 are polygons that are substantially equal to each other, and the positions of the corners of the cross-sections coincide with each other in the axial direction of the optical fiber 100. It is preferable in securing.

  In addition, the length in the axial direction (X direction) of the cladding mode light removal unit 103, which is the region where the groove 104 is formed, is preferably 3 cm or more and 7 cm or less. Thus, by making the length of the cladding mode light removal unit 103 3 cm or more and 7 cm or less, high removal efficiency of the cladding mode light can be realized, and a decrease in the shear strength of the optical fiber 100 can be prevented.

  On the other hand, the clad 102 is configured such that the second thickness D2 at the small diameter portion of the groove portion 104 is thicker than the region where the evanescent light of the laser light propagating through the core 101 of the optical fiber 100 penetrates. Is preferred. When light propagates through a medium with a different refractive index, the energy reflectivity in total reflection is calculated. The reflected light energy is equal to the incident light energy, but the evanescent wave oozes slightly on the opposite side of the boundary surface. It has been known. The penetration depth of this evanescent wave component can be approximated to about λ / 2π (λ is the wavelength at the refractive index of the propagation region). For example, the region where the evanescent light penetrates is λ / 2π from the outer periphery of the core 101. It has become.

  Here, when the groove reaches the region where the evanescent light penetrates, a part of the light propagating through the core is radiated from the groove and causes a loss. Therefore, in the clad mode light removing unit 103, in order to efficiently remove the clad mode light without causing a loss in the light propagating through the core 101, the second thickness D2 of the clad 102 in the small diameter portion causes the core 101 to be removed. It is preferable that the thickness of the propagating laser beam is thicker than a region where the evanescent light penetrates. Therefore, for example, when a YAG laser (wavelength: 1.064 μm) is used as the laser light, the second thickness D2 can be set to 0.3 μm or more using the approximation described above, and preferably about the wavelength of the propagation light. 1 μm or more, more preferably 5 μm or more which is about 5 times the wavelength.

  Next, a modification of the present invention will be described with reference to FIG. FIG. 4 is a diagram for explaining a modification example of the clad mode light removing sections 113 and 123 and the groove sections 114 and 124 included in the optical fibers 110 and 120 according to the modification.

  4A and 4B are diagrams showing optical fibers 110 and 120 according to a modification of the present invention, and FIG. 4C is a comparative optical fiber used for comparison with the optical fibers 110 and 120. FIG. The optical fiber 110 according to this modification is different from the optical fiber 100 in that the clad mode light removal unit 113 is formed at the end of the optical fiber 110. Here, the end of the optical fiber 110 is, for example, one end of either end of the optical fiber 110, and the distance from the end surface to the cladding mode light removal unit 113 is formed in the cladding mode light removal unit 113. The position is smaller than the distance between the groove portions 114 to be formed. The optical fiber 400 according to the comparative example is different from the optical fiber 110 according to this modification in that the cladding mode light removal unit 403 is not formed at the end of the optical fiber 400. In the optical fiber 110 and the optical fiber 400, clads 112 and 402 having a predetermined thickness are formed on the bottom portions 116 and 406 of the groove portions 114 and 404, respectively.

  Here, consider the lights L6 and L6 'incident on the claddings 112 and 402 from the outside. Lights L6 and L6 ′ are incident on the clad 112 and 402 at a large incident angle that is an angle greater than or equal to a predetermined value, and then multiple-reflected on the side surfaces of the clad 112 and 402, and propagate in the clad 112 and 402 at various angles. To be averaged. In general, since the optical system is adjusted so as to be condensed toward the cores 111 and 401, the light entering the clad 112 and 402 has a form such as light L6 and L6 ′ incident at a large incident angle. Typical.

  Here, in the optical fiber 110 according to the modification, the clad mode light removal unit 113 is formed at the end of the optical fiber 110, so that the light L 6 is incident immediately after entering the clad 112. To reach. That is, the light L6 reaches the cladding mode light removal unit 113 before being averaged into various propagation modes. Here, as described above, in order to avoid loss of light propagating through the core, when a clad having a predetermined thickness is formed at the bottom of the groove, the propagation angle (reflection at the interface between the clad and air) Light having a small angle may not be removed by the clad mode light removal unit, but may propagate in the clad having a predetermined thickness. However, since the optical fiber 110 reaches the cladding mode light removal unit 113 before the light L6 is averaged, the light L6 having a large propagation angle can be reliably guided to the opening 115 of the groove 114.

  On the other hand, in the optical fiber 400 of the comparative example shown in FIG. 4C, the cladding mode light removal unit 403 is not formed at the end of the optical fiber 400, and the distance from the end of the cladding mode light removal unit 403 is Since it is equal to or greater than the predetermined value, the light L6 ′ is averaged into various propagation modes before reaching the cladding mode light removal unit 403. As a result, the light component transmitted through the clad 402 located inside the bottom portion 406 of the groove 404 increases, and the clad mode light propagating in the clad 402 increases, so the efficiency of removing the clad mode light decreases. Can do.

  As described above, according to the optical fiber 110 according to the present modification, the cladding mode light removal section 113 is formed at the end of the optical fiber 110, so that the cladding mode light removal efficiency can be improved. Furthermore, according to the optical fiber 120 according to another modified example, the grooves 124 are formed densely on the distal end side of the optical fiber 120. That is, in the clad mode light removing portion 123 of the optical fiber 120, the number of the groove portions 124 increases as going toward the end side. For this reason, also in the optical fiber 120, the light L7 can reach the cladding mode light removal unit 123 before being averaged, and the light L7 can be reliably guided to the opening 125 of the groove 124. The same effect as that of the fiber 110 can be obtained.

  Furthermore, the optical fiber according to the present invention can be modified without departing from the spirit of the optical fiber. For example, in FIG. 1, the groove 104 is formed to extend in the θ direction (circumferential direction), but may extend in a direction inclined with respect to the θ direction. Further, the shape of the bottom of the groove is not limited to the shape shown in FIG. 1 and the like, and may be changed as appropriate, for example, by opening in a tapered shape. For example, when opening in a taper shape, it becomes possible to adjust the angle of reflection angle at the groove of the clad mode light, and the clad mode light can be suitably emitted from the clad to the outside.

The result of evaluating the removal efficiency of the clad mode light by the optical fiber of the present invention will be described. Here, light was incident on one end of the clad, the intensity of light emitted from the other end of the clad was measured, and the measured intensity of light was compared with the intensity of incident light. The conditions are as follows.
Core diameter: 0.2 mm,
Cladding diameter: 1.0mm
Cross-sectional shape of the optical fiber in the plurality of groove portions: substantially regular hexagonal shape Cladding thickness (second thickness D2) in the small diameter portion of the groove portion: 50 μm
Cladding thickness (first thickness D1) at the large diameter portion of the groove: 58 μm
Cladding mode light removing portion: formed over 5 cm in the axial direction of the optical fiber.
Groove width: 500 μm
As a result, the intensity of the measured light was about 20% of the intensity of the incident light, and it was confirmed that about 80% of the incident light was removed from the cladding (that is, the cladding mode light removal efficiency was about 80%). . The shear strength was 2N.

  On the other hand, when the clad mode light removing portion is an optical fiber having a groove having a circular cross-sectional shape and a diameter of 50 μm, the cladding mode light removing efficiency is about 80%, but the shear strength is 0.8 N. It was confirmed that the shear strength was smaller than that of the optical fiber of the present invention.

  As described above, according to the present invention, it is possible to provide an optical fiber having high cladding mode light removal efficiency and high mechanical strength.

  Next, the manufacturing method of the optical fiber of this invention is demonstrated. The optical fiber manufacturing method of the present invention is not particularly limited as long as a groove having a depth smaller than the thickness of the clad can be formed in the clad mode light removing portion, but laser light is applied to the clad of the optical fiber. It is preferable to form the groove portion by focused irradiation. In this way, unnecessary scratches can be prevented from being applied to the surface of the clad, and the bottom of the groove can be formed into a smooth shape, so that an optical fiber with high mechanical strength can be manufactured.

  As a method of forming the groove as described above, a method of scanning the condensed laser beam and a method of using the laser beam shaped in a line shape are suitable. Also, after irradiating laser light toward the optical fiber from a predetermined direction to form a plurality of line-shaped grooves, the large diameter portion and the small diameter can be easily changed by changing the irradiation direction and repeating the same operation. The groove part provided with the part can be formed.

  A method of manufacturing an optical fiber by laser light irradiation will be described with reference to FIG. Here, among the optical fibers of the present invention, the optical fiber 100 having the above-described clad 102 will be described as an example. First, the optical fiber 100 is prepared, and the optical fiber 100 is gripped by a jig 150 that can move in four directions, that is, the X direction, the θ direction, the Z direction, and the Y direction perpendicular to the X direction and the Z direction. . As the jig 150, for example, a known XYZθ 4-axis control stage as described in JP-A-2007-209992 can be used.

  Then, laser light r is emitted from a laser irradiator (not shown) set to irradiate laser light of a predetermined intensity, and this laser light r is irradiated to the clad 102 for a predetermined time. As a result, a groove 104 having a predetermined depth can be formed in the clad 102. At this time, the optical fiber 100 is irradiated with laser light r having a predetermined angle with respect to the axial direction to form a line-shaped groove in the optical fiber 100.

  Next, the jig 150 is adjusted to move the optical fiber 100 relative to the laser irradiator in the X direction, and the laser beam r is irradiated again to form the groove 104. By repeating such a process, a plurality of groove portions 104 are formed in the clad 102.

  Next, the jig 150 is adjusted, the optical fiber 100 is moved relative to the laser irradiator in the θ direction, the optical fiber 100 is rotated by a predetermined angle around the axis, and the same operation is performed. Line-shaped grooves are further formed so that the grooves are connected. Specifically, for example, when the cross-sectional shape of the groove 104 is a regular hexagon, as shown in FIGS. 5B to 5H, the laser beam r is rotated while rotating the optical fiber 100 by 60 degrees around the axis. Thus, the optical fiber 100 provided with the groove 104 having the large diameter portion and the small diameter portion can be manufactured. Here, since the cross-sectional shape of the portion without the groove portion 104 of the optical fiber 100 is circular, when the focus is set near the center portion (that is, the region near the laser light emitting portion), the deep groove portion 104 is formed, As the focal position is moved away from the center, a shallow groove is formed. That is, by changing the focal position of the laser beam r, the groove portion 104 having the large diameter portion and the small diameter portion can be easily formed, and the optical fiber 100 can be easily processed.

  In this way, the cladding mode light removing unit 103 has the groove 104 formed continuously in the circumferential direction by performing processing while adjusting the laser irradiation position on the cladding 102 and changing the depth of the groove 104. Thus, the clad 102 in the groove portion 104 has a large diameter portion having a first thickness D1 in the radial direction of the optical fiber 100 and a small diameter portion having a second thickness D2 smaller than the first thickness D1 in the radial direction. A plurality of large diameter portions are provided in the axial direction of the optical fiber 100, and the plurality of large diameter portions are provided on a straight line substantially parallel to the axial direction of the optical fiber 100, whereby the optical fiber 100 is manufactured. . Moreover, the optical fibers 110 and 120 shown in the modified example can be manufactured by appropriately changing the irradiation position and direction of the laser light.

  Next, an optical cable using the optical fiber of the present invention will be described with reference to FIG. FIG. 6 is a configuration diagram of an optical cable 1 including the optical fiber of the present invention. The optical cable 1 can be mounted with any one of the optical fibers 100, 110, and 120. Here, an example in which the optical fiber 100 is mounted will be described. The optical cable 1 shown in FIG. 6 is used as a laser beam transmission means of a laser beam machine for irradiating and cutting an iron plate such as a vehicle body by irradiating a laser beam of high intensity (for example, 2 kW to 10 kW). obtain.

  The optical cable 1 includes an optical fiber 100 that propagates laser light, a housing 2 that accommodates the end of the optical fiber 100, and a grip portion 3 that is provided on the rear end side of the housing 2 and grips the optical fiber 100.

  The optical fiber 100 preferably includes a covering portion 107 that surrounds the outer periphery of the clad 102, and the grip portion 3 preferably grips the optical fiber 100 by gripping the covering portion 107. In the housing 2, the clad 102 and the clad mode light removing unit 103 are exposed.

  With this configuration, clad mode light, specifically, light that has not been incident on the core 101 due to misalignment (misalignment light) or is emitted from the optical fiber 100 and reflected by the object to be processed (such as an iron plate). Then, the returned light (reflected return light) can be removed from the clad 102 and radiated into the housing 2.

  A cylindrical end cap 4 is connected to the end face of the optical fiber 100. The end cap 4 is formed with a refractive index equivalent to that of the core 101 and has a larger diameter than the core 101. By providing such an end cap 4, the energy density of light at the interface with the outside (air) at the end face of the optical fiber 100 is reduced, so that damage due to adhesion and burning of impurities such as dust hardly occurs. Become. The end cap 4 has a structure in optical contact with the end face of the optical fiber 100 by, for example, fusion. The end cap 4 is housed and fixed in the recess 2 a at the tip of the housing 2.

  The optical cable 1 is preferably accommodated in the housing 2 in a state surrounded by the inner tube 5 that accommodates the terminal portion of the optical fiber 100. The inner tube 5 is made of a material that easily reflects light, such as copper or aluminum. As a result, the cladding mode light removed by the cladding mode light removal unit 103 and the cladding mode light emitted from the cladding mode light removal unit 103 is directly absorbed by the housing 2, thereby preventing damage due to excessive heat generation. Can do. In addition, by reflectively coating the inner wall surface 5a of the inner tube 5, only a part of the light is absorbed by the inner tube 5, and in this case, excessive heat generation of the inner tube 5 can be prevented, Further preferred.

  A cooling space 6 for flowing cooling water is provided between the housing 2 and the inner pipe 5. Further, the housing 2 is formed with an inlet portion 7 for allowing the cooling water to flow into the cooling space 6 and an outlet portion 8 for allowing the cooling water to flow out of the cooling space 6. When the laser processing machine is used, cooling water circulates in the cooling space 6 by a circulation system (not shown) including a cooling fan. Thereby, the inner side pipe | tube 5 is cooled efficiently.

  The inner tube 5 can be fixed in the housing 2. As this fixing method, adhesive fixing with an adhesive S or sealing fixing using a packing such as an O-ring is preferable. By fixing in this way, it is possible to reliably prevent the cooling water from flowing into the inner pipe 5. The cladding mode light removal unit 103 is provided at a position that avoids the region 5 b where the inner tube 5 is fixed to the housing 2. If comprised in this way, it can prevent that an excessive heat | fever is added to the adhesive agent S, O-ring, etc. which were provided in the area | region 5b which fixes the housing 2 and the inner side pipe | tube 5, and transmits a high intensity | strength laser beam. In some cases, damage can be prevented.

  The optical fiber 100 is optically connected to one end side of a glass rod 108 having an approximately the same diameter as the clad 102 and having a refractive index equivalent to that of the core 101 on the end face thereof, and the other end side of the glass rod 108 is connected to the end cap 4. It is preferably optically connected. In this way, the removal efficiency of the cladding mode light can be maintained high, and the fixing portion or region 5b of the end cap 4 located on the distal end side of the optical fiber 100 and the cladding mode light removal portion 103 can be easily separated. be able to. Further, when the optical fiber 100 and the end cap 4 are fusion-spliced, the core 101 can be prevented from being deformed due to the difference in heat capacity between the two, so that the manufacturing yield can be improved. Such an effect is particularly advantageous in that the cladding mode light can be more reliably removed when the cladding mode light removal unit 103 is formed at the end of the optical fiber 100.

  The laser beam R emitted from the core 101 of the optical fiber 100 propagates through the glass rod 108 and the end cap 4 while spreading. Here, the length of the glass rod 108 in the axial direction may be set such that the laser beam R does not reach the outer peripheral surface (side surface) 108 a of the glass rod 108. This prevents the laser beam R from being reflected by the outer peripheral surface 108a of the glass rod 108 and degrading the beam quality.

When the divergence angle of the laser beam passing through the glass rod 108 is B, the divergence angle B is obtained from the following equation using the numerical aperture NA and the refractive index n of the optical fiber 100.
NA = nsinB

  Here, when the core diameter of the optical fiber 100 is 0.2 mm, the numerical aperture NA of the optical fiber 100 is 0.2, the refractive index n of the core 101 is 1.45, and the cladding diameter is 1.0 mm, the laser beam R In order not to reach the outer peripheral surface 108a of the glass rod 108, the length of the glass rod 108 may be 2.9 mm.

  The optical fiber and the optical cable of the present invention can be changed as appropriate without departing from the spirit of the present invention. That is, as the optical fiber, in addition to a core having a circular cross section, a core having a rectangular cross section may be used, and the cross section of the core is not particularly limited. Further, as the types of optical fibers, all types of optical fibers such as quartz optical fibers and plastic optical fibers can be used.

  DESCRIPTION OF SYMBOLS 100 ... Optical fiber, 102 ... Cladding, 103 ... Cladding mode light removal part, 104 ... Groove part, 105 ... Opening part, 106 ... Bottom part, 107 ... Covering part, 108 ... Glass rod, 108a ... Outer peripheral surface, 1 ... Optical cable, 2 ... Housing, 3 ... Holding part, 4 ... End cap, 5 ... Inner tube, 5a ... Inner wall surface, 5b ... Fixing part, 6 ... Cooling space, 7 ... Inlet part, 8 ... Outlet part, D1 ... Large diameter part, D2 ... small diameter part, R ... laser beam, X ... corner part, Y ... side part.

Claims (12)

An optical fiber comprising a core and a clad surrounding the outer periphery of the core,
The clad is provided with a groove formed continuously in the circumferential direction of the optical fiber,
The clad in the groove has a large diameter portion having a first thickness in the radial direction of the optical fiber, and a small diameter portion having a second thickness smaller than the first thickness in the radial direction,
A plurality of the large diameter portions are provided in the axial direction of the optical fiber, and the plurality of large diameter portions are provided on a straight line substantially parallel to the axial direction of the optical fiber.
An optical fiber characterized by that. The groove portion is a plurality of annular grooves formed at predetermined intervals in the axial direction, and the large diameter portion of each groove portion is provided on a straight line substantially parallel to the axial direction.
The optical fiber according to claim 1. The cross section of the optical fiber in the groove is polygonal,
The optical fiber according to claim 2. The cross-sectional shapes of the plurality of grooves are polygons that are substantially equal to each other, and the positions of the corners of the cross-section coincide with each other in the axial direction.
The optical fiber according to claim 3. The cladding is configured such that the thickness at the bottom of the groove is thicker than the area where the evanescent light of the laser light propagating through the core of the optical fiber penetrates.
The optical fiber according to any one of claims 1 to 4, wherein: The axial length of the region where the groove is formed is 3 cm or more and 7 cm or less,
The optical fiber according to any one of claims 1 to 5, wherein: The groove is formed at the end of the optical fiber.
The optical fiber according to any one of claims 1 to 6. The groove is formed densely on the end side of the optical fiber,
The optical fiber according to claim 1, wherein the optical fiber is an optical fiber. The optical fiber according to any one of claims 1 to 8,
A housing for accommodating the end portion of the optical fiber, and fixing the end of the optical fiber at the front end;
A grip portion provided on the rear end side of the housing and gripping the optical fiber;
The optical fiber further includes a covering portion that surrounds the outer periphery of the cladding,
The gripping part grips the optical fiber by gripping the covering part,
The clad and the groove are exposed at the terminal portion,
An optical cable characterized by that. The optical fiber is an optical fiber according to claim 7 or 8,
The optical fiber further includes an end cap that is provided in optical contact with the end face and is fixed to the housing.
The optical cable according to claim 9. The optical cable is further accommodated in the housing, further comprising an inner tube that accommodates the end portion of the optical fiber,
The inner tube is fixed in the housing, and the groove is formed so as to avoid a fixing portion in which the inner tube is fixed to the housing.
The optical cable according to claim 9 or 10, wherein The optical fiber is connected to one end side of a glass rod having the same diameter as that of the clad in a region where the groove portion is not formed on the end face of the optical fiber, and the other end side of the glass rod is connected to the end cap. It is connected,
The optical cable according to claim 10.

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