JP2014010338A - Optical fiber and optical cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber for preventing an adverse effect from being generated by clad mode light removed from a clad.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 has a clad mode light removal part 103 which removes light propagated through the clad 102. The clad mode light removal part 103 has a first area 103a formed on the side close to an end of the optical fiber 100 and a second area 103b formed on the side distant from the end of the optical fiber 100, and is formed such that the removal efficiency of the clad mode light in the first area 103a is lower than that in the second area 103b.

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 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, as described in Patent Document 2, when the depths of the respective grooves are formed almost the same, the clad mode light is removed in a concentrated manner in the groove portion that reaches the first, so that it is removed. There is a problem in that the intensity of the clad mode light is high, which breaks an optical connector or the like that accommodates 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 that prevents adverse effects from being caused by the cladding mode light removed from the cladding. Furthermore, an object of the present invention is to provide an optical cable that contributes to the realization of a highly reliable laser processing apparatus 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 has a clad mode light removal unit that removes clad mode light propagating through the clad. The light removal unit has a first region formed on the side close to the end of the optical fiber, and a second region formed on the side far from the end of the optical fiber, and the cladding of the first region The mode light removal efficiency is lower than that in the second region.

  In this optical fiber, a first region having a low removal efficiency is formed on the side close to the end, and a second region having a high removal efficiency is formed on the side far from the end. Therefore, the clad mode light is gradually removed from the first region close to the end toward the second region, and the clad mode light is not concentrated and removed. Accordingly, since the intensity of the removed clad mode light is suppressed, it is possible to prevent an adverse effect from being caused by the clad mode light.

  In the optical fiber of the present invention, it is preferable that the cladding mode light removal portion is formed so that the removal efficiency continuously increases from the first region toward the second region. In addition, a third region having a lower removal efficiency than the second region is preferably formed on the opposite side of the second region from the first region, and the third region is directed from the third region to the second region. Accordingly, the cladding mode light removal portion may be formed so that the removal efficiency is continuously increased.

  The optical fiber of the present invention further includes a fourth region including a plurality of regions having substantially the same removal efficiency between the first region and the second region, and the removal efficiency of the fourth region is It may be higher than the removal efficiency of the first region and lower than the removal efficiency of the second region.

  The optical fiber of the present invention further includes a fifth region including a plurality of regions having substantially the same removal efficiency between the third region and the second region, and the removal efficiency of the fifth region is third. It may be higher than the removal efficiency of the second region and lower than the removal efficiency of the second region.

  In the optical fiber of the present invention, the clad mode light removal portion is a groove portion formed from the clad toward the core, and is preferably formed such that the removal efficiency increases as the depth of the groove portion increases.

  In the optical fiber of the present invention, the core is made of a material having a higher refractive index than that of the cladding, and the cladding mode light removing portion is made of a material having a higher refractive index than that of the cladding, and the cladding mode light removing portion has the refractive index. It may be formed such that the higher the is, the higher the removal efficiency.

  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 leaks out.

  In the optical fiber of the present invention, the length in the axial direction of the region where the clad mode light removing portion is formed is preferably 3 cm or more and 7 cm or less. Moreover, it is preferable that said clad mode light removal part is formed in the terminal 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 the end portion of the optical fiber, housing the optical fiber at the front end, and fixing the end of the optical fiber. A gripping portion for gripping. 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 removes the cladding and cladding mode light at the terminal portion. The portion is formed to be exposed.

  In the optical cable of the present invention, the optical fiber has a clad mode light removing portion formed at the end of the optical fiber. The optical fiber is provided in an optical contact with the end face and has an end cap fixed to the housing. It is preferable to further provide.

  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 preferably fixed in the housing, and the clad mode light removing portion 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 cladding in the region where the cladding mode light removing portion is not formed, and the other end side of the glass rod is connected to the end surface of the optical fiber of the present invention. It is preferably connected to an end cap.

  According to the present invention, since the clad mode light can be dispersed and emitted in the clad mode light removing portion of the optical fiber, the density of the emitted clad mode light can be reduced. Therefore, it is possible to provide an optical fiber that prevents adverse effects from being caused by the cladding mode light removed from the cladding. Furthermore, according to the present invention, it is possible to provide an optical cable that contributes to the realization of a highly reliable laser processing apparatus using such an optical fiber.

It is sectional drawing of the optical fiber in one Embodiment of this invention. It is a side view explaining the manufacturing apparatus of the optical fiber in one Embodiment of this invention. (A) (b) is sectional drawing explaining the structure of the optical cable of this invention. It is sectional drawing of the optical fiber in the modification of this invention. It is sectional drawing of the optical fiber in the modification 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 same description, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  The optical fiber of the present embodiment has a linear shape that extends in the longitudinal direction, and its cross-sectional shape is, for example, a circle. Moreover, the optical fiber of this embodiment is comprised, for example with quartz glass, transmits a laser beam, and can be applied to the laser beam transmission means etc. in a laser processing apparatus. Hereinafter, the optical fiber of this embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view (XZ plane) when the optical fiber of this embodiment is cut along a plane extending in the axial direction. In each figure, the arrow x indicates the axial direction of the optical fiber, the arrow z indicates the radial direction of the optical fiber, and the arrow θ indicates the circumferential direction of the optical fiber.

  The optical fiber 100 includes a core 101 for transmitting laser light and the like, and a clad 102 that covers the core 101. The clad 102 includes a clad mode light removing unit 103 that removes clad mode light propagating in the clad 102. The core 101 is made of a material whose refractive index is higher than that 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 first region 103a, a second region 103b, a third region 103c, a fourth region 103d, and a fifth region 103e. 103 a to 103 e have a function of removing clad mode light in the clad 102. The cladding mode light removal unit 103 is provided at the end of the optical fiber 100. Specifically, for example, the distance between the end face of the optical fiber 100 and the end side end of the cladding mode light removal unit 103 is greater than the distance between the grooves 104 a to 104 e formed in the cladding mode light removal unit 103. Is also getting smaller.

  The first region 103a is provided closer to the end of the optical fiber 100 than the second to fifth regions 103b to 103e. The first region 103a has a plurality of grooves 104a having a depth D1, and the cladding mode light in the cladding 102 is scattered by the grooves 104a and emitted from the cladding 102 to be removed. The groove portion 104 a is, for example, a groove formed continuously in the circumferential direction, and a plurality of the groove portions 104 a are formed at a predetermined interval in the axial direction of the optical fiber 100.

  The second region 103b is provided closer to the base side of the optical fiber 100 than the first region 103a and the fourth region 103d, and closer to the end side of the optical fiber 100 than the third region 103c and the fifth region 103e. It has been. The third region 103c is provided closer to the base side of the optical fiber 100 than the first, second, fourth, and fifth regions 103a, b, d, and e. The fourth region 103d is provided closer to the base side of the optical fiber 100 than the first region 103a and closer to the end side of the optical fiber 100 than the second, third, and fifth regions 103b, c, and e. Yes. The fifth region 103e is provided closer to the base side of the optical fiber 100 than the first, second, and fourth regions 103a, b, and d, and closer to the end side of the optical fiber 100 than the third region 103c. Yes. Similarly to the first region 103 a, the second to fifth regions 103 b to 103 e have groove portions 104 b to e that remove the cladding mode light in the cladding 102, and the groove portions 104 b to 104 e are in the axial direction of the optical fiber 100. Are formed at predetermined intervals. In addition, it is preferable that each groove part 104a-e is processed so that the bottom part may become smooth.

  Here, the depth of the groove portions 104b to 104e is D2 to D5, respectively. The depths D2, D4, and D5 are all deeper than the depth D1 of the groove 104a, but the depth D3 is approximately the same as the depth D1. The depth D2 of the groove 104b is deeper than any of the depth D1, the depth D3, the depth D4, and the depth D5. Further, the depth D3 of the groove 104c is shallower than the depth D4 and the depth D5. The depth D4 and the depth D5 are approximately the same.

  In such an optical fiber 100, the behavior of the cladding mode light when the cladding mode light enters the optical fiber 100 will be described. Here, as the cladding mode light, for example, a part of the laser light emitted from the core 101 of the optical fiber 100 is reflected from the object to be processed and is incident on the optical fiber 100 again from the end. Of the light that has entered the optical fiber 100, the cladding mode light that has not entered the core 101 is transmitted through the cladding 102. A part of the clad mode light transmitted through the clad 102 reaches the groove 104a of the first region 103a, is reflected and scattered, and is emitted to the outside of the clad 102 and removed. On the other hand, the clad mode light that has not reached the groove 104a propagates in the clad 102 as it is.

  Then, part of the cladding mode light that has not reached the groove 104a reaches the groove 104d in the fourth region 103d, is reflected and scattered, and is emitted to the outside of the cladding 102 and removed. On the other hand, the clad mode light that has not reached the groove 104d propagates in the clad 102 as it is, reaches the groove 104b in the second region 103b, is reflected and scattered, and is removed.

  Here, the removal efficiency of the clad mode light in the optical fiber 100 increases according to the depths D1 to D5 of the groove portions 104a to 104e. That is, the deeper the depths D1 to D5 of the grooves 104a to 104e, the higher the possibility that the cladding mode light propagating in the cladding 102 will reach the grooves 104a to 104e, and the cladding mode light is reflected and scattered and removed. The possibility that Therefore, in this embodiment, the removal efficiency of the cladding mode light is highest in the second region 103b having the deepest groove 104b, and the fourth and fifth regions 103d and e having the grooves 104d and e are next. The first and third regions 103a and 103c having the highest and shallowest groove portions 104a and 104c are the lowest.

  As described above, in the optical fiber 100, the first region 103a having a low removal efficiency is formed on the side close to the end, and the second region 103b having a high removal efficiency is formed on the side far from the end. Therefore, the clad mode light is gradually removed from the first region 103a close to the end portion toward the second region 103b, and the clad mode light is not concentrated and removed. Accordingly, since the intensity of the removed clad mode light can be suppressed, it is possible to prevent an adverse effect from being caused by the clad mode light.

  Also, the optical fiber 100 is formed with a cladding mode light removal portion 103 so that the removal efficiency of the cladding mode light continuously increases from the first region 103a toward the second region 103b. A fourth region 103d including a plurality of grooves 104d having substantially the same removal efficiency is provided between the region 103a and the second region 103b, and the removal efficiency of the fourth region 103d is higher than the removal efficiency of the first region 103a. It is higher than the removal efficiency of the second region 103b. As described above, since the removal efficiency of the cladding mode light gradually increases from the first region 103a toward the fourth region 103d and the second region 103b, the cladding mode light is removed little by little in each region. As a result, a situation in which clad mode light is intensively emitted can be avoided.

  Further, in the optical fiber 100, the clad mode light removing portion 103 is composed of groove portions 104a to 104e formed from the clad 102 toward the core 101, and the removal efficiency increases as the depth of the groove portions 104a to 104e increases. It is formed to become. For this reason, the cladding mode light removal part 103 can be formed with a simple structure.

  Next, the behavior of the clad mode light when the clad mode light propagates from the root side to the end side of the optical fiber 100 in the optical fiber 100 will be described. A part of the cladding mode light propagating from the root side to the terminal side of the optical fiber 100 reaches the groove 104c of the third region 103c, is reflected and scattered, is emitted to the outside of the cladding 102, and is removed. The On the other hand, the cladding mode light that has not reached the groove 104c propagates in the cladding 102 as it is.

  A part of the cladding mode light that has not reached the groove 104c reaches the groove 104e in the fifth region 103e, and is reflected, scattered, and removed. On the other hand, the clad mode light that has not reached the groove 104e propagates in the clad 102 as it is, reaches the groove 104b in the second region 103b, is reflected and scattered, and is removed.

  Thus, in the optical fiber 100, the third region 103c having a lower removal efficiency than the second region 103b is formed on the opposite side of the second region 103b to the first region 103a. The removal efficiency continuously increases from the third region 103c toward the second region 103b. Further, a fifth region 103e including a plurality of groove portions 104e having substantially the same removal efficiency is provided between the third region 103c and the second region 103b, and the removal efficiency of the fifth region 103e is the third region 103c. It is higher than the removal efficiency of the second region 103b. Thus, since the removal efficiency of the cladding mode light gradually increases from the third region 103c toward the fifth region 103e and the second region 103b, the end of the optical fiber 100 is the light emitting end. Even when the clad mode light propagates from the base side to the end side of the optical fiber 100, the clad mode light slightly passes from the third region 103c toward the fifth region 103e and the second region 103b. Since the cladding mode light is not removed in a concentrated manner, the same effect as when light is incident on the optical fiber 100 can be obtained.

  Further, in the optical fiber 100, the cladding mode light removal unit 103 is formed at the end of the optical fiber 100, so that light incident on the optical fiber 100 is removed immediately after entering the cladding 102. The unit 103 is reached. Therefore, since the light reaches the clad mode light removal unit 103 before the light is averaged into various propagation modes, the light having a large propagation angle can be reliably guided to the grooves 104a to 104e. The same effect can be obtained when the grooves 104a to 104e are densely formed at the end of the optical fiber 100. On the other hand, when the cladding mode light removal unit 103 is not formed at the end of the optical fiber 100, the light incident on the optical fiber 100 reaches the cladding mode light removal unit after being averaged. The light component transmitted through the clad 102 inside the grooves 104a to 104e increases, and the removal efficiency of the clad mode light can be lowered.

  By the way, it is preferable that the length in the axial direction (X direction) of the cladding mode light removing portion 103, which is a region where the groove portions 104a to 104e are formed, is 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, it is preferable that the clad 102 is configured such that the thickness of the clad 102 in the groove portions 104a to 104e is thicker than a region where the evanescent light of the laser light propagating through the core 101 of the optical fiber 100 penetrates. is there. 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 can be approximated to about λ / 2π (λ is the wavelength at the refractive index of the propagation region). For example, the region where evanescent light penetrates is λ / 2π from the outer periphery of the core 101. Yes.

  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 order to efficiently remove the clad mode light without causing a loss in the light propagating through the core 101 in the clad mode light removal unit 103, the clad 102 has a thickness at the bottom of the grooves 104a to 104e. It is preferable that the laser beam is thicker than a region where evanescent light of the laser light propagating through the core 101 of the fiber 100 penetrates. Therefore, for example, when a YAG laser (wavelength: 1.064 μm) is used as the laser light, the thickness of the clad 102 in the groove portions 104a to 104e can be set to 0.3 μm or more by using the above-described approximation, and preferably propagates. The thickness may be about 1 μm or more, which is about the wavelength of light, and more preferably 5 μm or more, which is about 5 times the wavelength.

  Furthermore, the optical fiber according to the present invention can be modified without departing from the spirit of the optical fiber. That is, in the above description, an example in which the cladding mode light removal unit 103 includes a plurality of grooves 104a to 104e has been described. It is also possible to configure a light removal unit.

  Here, the removal efficiency of the clad mode light increases in accordance with the refractive index of the medium. That is, when the clad mode light removing portion 103 is not made of the groove portions 104a to 104e and is made of a material having a higher refractive index than the clad 102, the higher the refractive index, the higher the possibility that the clad mode light is emitted and removed. Therefore, when the grooves 104a to 104e are not provided, the refractive index of the second region 103b is set highest, the refractive indexes of the fourth and fifth regions 103d and e are set next higher, If the refractive index of the third regions 103a and 103c is the lowest, the removal efficiency of the cladding mode light is the highest in the second region 103b, and the removal efficiency of the fourth and fifth regions 103d and e is the next. The removal efficiency of the first and third regions 103a and 103c is the lowest, and the same effect as that obtained when the grooves 104a to 104e are provided can be obtained.

  The core 101 is made of a material having a higher refractive index than the clad 102, and the clad mode light removing unit 103 is made of a material having a higher refractive index than the clad 102. Therefore, when the cladding mode light removal unit 103 is formed so that the removal efficiency is higher as the refractive index is higher, the cladding mode light can be removed little by little, as in the case where the grooves 104a to 104e are provided. Therefore, it is possible to avoid a situation where clad mode light is intensively emitted.

  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 concentrated 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. 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, and the groove portions 104 a to 104 e will be collectively described as the groove portion 104. 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. A line-shaped groove is further formed so that the grooves are connected. In addition, by appropriately changing the irradiation position and direction of the laser beam, it is possible to manufacture optical fibers having different groove positions and depths.

  Next, an optical cable using the optical fiber of the present invention will be described with reference to FIG. FIG. 3 is a configuration diagram of an optical cable 1 including the optical fiber of the present invention. Here, an example in which the optical fiber 100 is mounted will be described. The optical cable 1 shown in FIG. 3 is used as a laser beam transmission means of a laser processing machine that irradiates a high intensity (for example, 2 kW to 10 kW) laser beam and welds / cuts an iron plate such as a vehicle body. 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.

  As described above, 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, in the above embodiment, as shown in FIG. 1, the first region 103 a and the third region 103 c with low cladding mode light removal efficiency are provided on the terminal side and the base side of the optical fiber 100. An example has been described in which the second region 103b having high cladding mode light removal efficiency is provided between the region 103a and the third region 103c. However, for example, as shown in the optical fiber 200 including the core 201 and the clad 202 in FIG. 4, regions corresponding to the third region 103 c and the fifth region 103 e may not be provided.

  Specifically, in the optical fiber 200, the first region 203a having the groove portion 204a having the lowest removal efficiency of the cladding mode light is provided at the end of the optical fiber 200, and the removal efficiency is at the base side of the first region 203a. A second region 203b having a groove portion 204b higher than the groove portion 204a is provided, and a third region 203c having a groove portion 204c having a removal efficiency higher than that of the groove portion 204b is provided on the base side of the second region 203b.

  In such an optical fiber 200, the first region 203a having a low removal efficiency is formed on the side close to the end portion, and the third region 203c having a high removal efficiency is formed on the side far from the end portion. The mode light is gradually removed from the first region 203a close to the end toward the second region 203b and from the second region 203b toward the third region 203c. The light is not concentrated and removed. Accordingly, since the intensity of the removed clad mode light is suppressed, it is possible to prevent an adverse effect from being caused by the clad mode light.

  Further, in the case where the end of the optical fiber is the light exit end, for example, as shown in the optical fiber 300 including the core 301 and the clad 302 in FIG. 5, the first region 103 a and the fourth region in the above embodiment are used. The region corresponding to the region 103d may not be provided.

  Specifically, in the optical fiber 300, the first region 303a having the groove 304a having the highest removal efficiency of the cladding mode light is provided at the end of the optical fiber 300, and the removal efficiency is on the base side of the first region 303a. A second region 303b having a groove 304b lower than the groove 304a is provided, and a third region 303c having a groove 304c having a removal efficiency lower than that of the groove 304b is provided on the base side of the second region.

  In such an optical fiber 300, since the clad mode light propagates from the root side to the terminal side, the third region 303c on the most base side travels toward the second region 303b and then the second region 303b. In this case, the clad mode light is not concentrated and removed from the first region 303a. Therefore, in the optical fiber 300, the same effect as the optical fiber 100 and the optical fiber 200 can be obtained.

  Moreover, as an optical fiber according to the present invention, in addition to a core having a circular cross-sectional shape, a core having a rectangular cross-sectional shape may be used, and the cross-sectional shape 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.

  100, 200, 300 ... optical fiber, 101, 201, 301 ... core, 102, 202, 302 ... clad, 103a, 203a, 303a ... first region, 103b, 203b, 303b ... second region, 103c, 203c , 303c: third region, 103d: fourth region, 103e: fifth region, 104a, 104b, 104c, 104d, 104e, 204a, 204b, 204c, 304a, 304b, 304c ... groove portion, 107: covering portion 108 ... Glass rod, 108a ... outer peripheral surface, 1 ... optical cable, 2 ... housing, 3 ... gripping part, 4 ... end cap, 5 ... inner tube, 5a ... inner wall surface, 5b ... fixing part, 6 ... cooling space, 7: entrance part, 8 ... exit part, D1, D2, D3, D4, D5 ... depth, R ... laser beam.

Claims (15)

An optical fiber comprising a core and a clad surrounding the outer periphery of the core,
The clad has a clad mode light removing unit for removing clad mode light propagating through the clad,
The cladding mode light removal unit has a first region formed on a side near the end of the optical fiber and a second region formed on a side far from the end of the optical fiber, Formed so that the removal efficiency of the cladding mode light in the first region is lower than that in the second region;
An optical fiber characterized by that. The cladding mode light removal portion is formed so that the removal efficiency is continuously increased from the first region toward the second region.
The optical fiber according to claim 1. A third region having a lower removal efficiency than the second region is formed on the opposite side of the second region to the first region.
The optical fiber according to claim 1 or 2, wherein The cladding mode light removal portion is formed so that the removal efficiency is continuously increased from the third region toward the second region.
The optical fiber according to claim 3. A fourth region including a plurality of regions having substantially the same removal efficiency is further provided between the first region and the second region, and the removal efficiency of the fourth region is the first region. Higher than the removal efficiency of the second region, lower than the removal efficiency of the second region,
The optical fiber according to claim 2. A fifth region including a plurality of regions having substantially the same removal efficiency is further provided between the third region and the second region, and the removal efficiency of the fifth region is the third region. Higher than the removal efficiency of the second region, lower than the removal efficiency of the second region,
The optical fiber according to claim 4. The clad mode light removal portion is a groove formed from the clad toward the core, and is formed such that the removal efficiency increases as the depth of the groove increases.
The optical fiber according to any one of claims 1 to 6. The core is made of a material having a refractive index higher than that of the cladding, and the cladding mode light removing portion is made of a material having a refractive index higher than that of the cladding, and the cladding mode light removing portion has a higher refractive index. It is formed so that the removal efficiency becomes higher,
The optical fiber according to any one of claims 1 to 6. 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 oozes out.
The optical fiber according to claim 7. The axial length of the region where the cladding mode light removal portion is formed is 3 cm or more and 7 cm or less,
The optical fiber according to any one of claims 1 to 9, wherein: The cladding mode light removal portion is formed at the end of the optical fiber,
The optical fiber according to any one of claims 1 to 10, wherein: The optical fiber according to any one of claims 1 to 11,
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 clad mode light removing portion are exposed in the terminal portion,
An optical cable characterized by that. The optical fiber is the optical fiber according to claim 11,
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 12. 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 cladding mode light removing portion 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 12 or 13, characterized in that The optical fiber is connected to one end side of a glass rod having the same diameter as that of the cladding in a region where the cladding mode light removing portion is not formed, and the other end side of the glass rod is connected to the end face of the optical fiber. Connected to the end cap,
The optical cable according to claim 13.

Images