JP2014010258A - 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 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 plurality of groove parts 104 with a depth smaller than a thickness of the clad, and is sectioned into an opening part 104a where the groove part 104 is opened and a non-opening part 104b where the groove part 104 is not opened in a circumferential direction of the clad, and an opening part 105a is present at a position corresponding to a non-opening part 105b in an 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 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. As a specific form of the clad mode removing portion, a ring-shaped groove continuously provided on the outer peripheral surface of the clad as shown in FIG. 9A or intermittently on the outer peripheral surface of the clad as shown in FIG. 9B. The groove part provided automatically is disclosed. Moreover, as shown to Fig.9 (a), such an optical fiber is disclosing that it is easily processed by irradiating a clad with a laser.

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.

  The optical fiber in which the clad mode removing portion for removing the clad mode light as in Patent Document 2 is formed in a groove shape on the outer peripheral surface of the clad is low in cost by irradiating the clad with laser. It is excellent in that it can be manufactured with high accuracy. 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. The clad has a clad mode light removal unit that removes light propagating through the clad. Further, the cladding mode light removal portion includes a plurality of groove portions, the depth of the groove portion is smaller than the thickness of the cladding, and an opening portion where the groove portion opens in the circumferential direction of the cladding, and a non-opening portion where the groove portion does not open. And an opening is present at a position corresponding to the non-opening in the axial direction of the optical fiber.

  Further, in the optical fiber of the present invention, the cladding mode light removal section includes a cladding mode light removal band in which a plurality of grooves are opened at predetermined intervals in a predetermined cross section in the circumferential direction of the optical fiber. It is preferable that the optical fibers are formed at predetermined intervals in the longitudinal direction of the optical fiber, and the non-opening portions in adjacent clad mode light removal bands are shifted from each other in the circumferential direction.

  In the optical fiber of the present invention, it is preferable that the plurality of groove portions have substantially cylindrical shapes whose opening diameters are equal to each other at the surface portion of the optical fiber and the bottom portion of the groove portion.

  In the predetermined cross section in the circumferential direction of the optical fiber, the opening is preferably 70% or more and 95% or less of the circumferential length of the clad portion in the cross section.

  The cladding is preferably set so 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.

  Moreover, it is preferable that the said clad mode light removal part is formed so that it may become 3 cm or more and 7 cm or less in the longitudinal direction of an optical fiber. Further, it is also preferable that the plurality of grooves in the cladding mode light removal portion have openings that are densely formed on the end side. Furthermore, it is preferable that the clad mode light removing portion is formed at the end of the optical fiber.

  The optical cable of the present invention includes the above-mentioned fiber and the end portion of the above-mentioned optical fiber, a housing that fixes the end of the above-mentioned optical fiber at the front end, and a grip that is provided on the rear end side of the housing and grips the above-mentioned optical fiber A part. The optical fiber further includes a coating that surrounds the outer periphery of the cladding, and the gripping portion grips the optical fiber by gripping the coating, and the cladding and the cladding mode light removing portion are exposed at the terminal portion. It is characterized by.

  In the optical cable of the present invention, the optical fiber has a cladding mode light removal portion formed at the end of the optical fiber, and the optical fiber further includes an end cap that is provided in optical contact with the end face and fixed to the housing. Is preferred.

  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 clad mode light removing portion is preferably formed so as to avoid the fixing portion in which the inner tube is fixed to the housing.

  In the optical cable of the present invention, it is preferable that one end side of a glass rod having the same diameter as that of the cladding is connected to the end face of the optical fiber, and the other end side of the glass rod is connected to an end cap.

  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 a perspective view of the optical fiber in one Embodiment of this invention, (b) is sectional drawing in AA of (a), FIG.1 (c) is a side view of (a). (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) is sectional drawing explaining the function of the optical fiber in one Embodiment of this invention. (B) is sectional drawing explaining the optical fiber of a comparative example. (A) is a side view which shows the function of the modification of the optical fiber in this invention. (B) is a side view which shows the function of the other optical fiber contained in this invention shown for a comparison. (A) is sectional drawing which shows the function of the other modification of the optical fiber in this invention. (B) is sectional drawing which shows the function of the other optical fiber contained in this invention shown for a comparison. (A) (b) is a side view which shows another modification of the optical fiber of this invention. (A) (b) is a side view 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. (A) and (b) are the side views explaining the optical fiber concerning a prior art.

  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 perspective view of the optical fiber of the present embodiment, FIG. 1B is a view showing a cross section taken along the line AA, and FIG. 1C is a side view. The optical fiber 100 includes a core 101 and a clad 102 that surrounds the outer periphery of the core. The clad 102 includes a clad mode light removal unit 103 that removes light propagating through the clad. 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 made 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 is formed over a predetermined region in the axial direction (direction X) of the optical fiber 100, and is preferably formed over the circumferential direction (direction θ) of the optical fiber 100.

  The cladding mode light removal unit 103 includes a plurality of groove portions 104. As shown in FIG. 1B, the groove 104 is formed with an opening 104a from the surface of the clad 102, and has a depth D2 smaller than the thickness D1 of the clad 102. The groove portion 104 is typically formed in a column shape in which the outer diameter of the opening portion 104a is substantially constant in the depth direction. The groove 104 is preferably processed smoothly at the bottom 104c of the opening 104a.

  In addition, as shown in FIG. 1C, the cladding mode light removal unit 103 includes an opening 104a in which the groove 104 is opened and a non-opening in which the groove 104 is not opened in the circumferential direction (direction θ) of the cladding 102. It is divided into the section 104b. And the opening part 104a exists in the position corresponding to the non-opening part 104b in the axial direction (direction X) of an optical fiber. For example, with respect to the non-opening portion 104b-1 in the drawing, the opening portion 104a-1 and the opening portion 104a-2 exist in the axial direction (direction X) of the optical fiber. Has an opening 104a-3 and an opening 104a-4. That is, the optical fiber 100 includes at least one opening 104a in any cross section passing through the core 101 (cross section including the straight line AA in FIG. 1A).

  Consider a case where laser light is transmitted using such an optical fiber 100. FIG. 2A is a side view illustrating a state in which light L1 to L5 incident on the clad among the light incident on one end of the optical fiber 100 of the present embodiment is transmitted. FIG. 2B shows light L incident on the clad among light incident on one end of the optical fiber 200 of the comparative example (corresponding to the optical fiber disclosed in the prior art shown in FIG. 9B). It is a side view explaining a mode that '1-L'5 transmits. As such light L1-L5 and L'1-L'5, the case where a part of laser beam radiate | emitted from the core of an optical fiber is reflected from a process target, and injects into an optical fiber again is assumed. . The optical fiber 200 of the comparative example is different from the optical fiber 100 of the present embodiment in that the opening 204a does not exist at a position corresponding to the non-opening 204b in the axial direction (direction X) of the optical fiber. About another structure, the same structure as the optical fiber 100 of this embodiment is provided.

  Of the light incident on one end of the optical fibers 100 and 200, the light not incident on the core (not shown) is transmitted through the cladding 102 and 202 and has a plurality of grooves 104 and 204. 103 and 203 are reached. At this time, the light reaching the grooves 104 and 204 is reflected and scattered at the interfaces with the openings 104a and 204a, and is emitted to the outside of the clads 102 and 202. That is, the cladding mode light is removed.

  At this time, the lights L1 to L5 and L′ 1 to L′ 5 transmitted in the clads 102 and 202 in FIGS. 2A and 2B are considered. The light reaching the openings 104a and 204a of the grooves 104 and 204 is scattered and emitted to the outside of the clad 102, but the light reaching the non-openings 104b and 204b is not emitted to the outside of the clad 102 and 202. Therefore, in the optical fiber 100, the light that has passed through the non-opening portion 104b is reflected and scattered in the opening portion 104a that opens to the corresponding position in the axial direction (direction X) of the optical fiber. All light is removed from the cladding 102.

  On the other hand, in the optical fiber 200, the opening 204a does not exist at a position corresponding to the non-opening 204b in the axial direction (direction X). Therefore, the light L′ 1, L′ 3, and L′ 5 that has reached the opening 204a is removed from the cladding 202, but the L′ 2 and L′ 4 light that has passed through the region of the non-opening 204b is transmitted from the cladding 202. Transmit without being removed.

  Thus, in the axial direction (direction X) of the optical fiber, the presence of the region of the opening 104a at the position corresponding to the region of the non-opening 104b eliminates the cladding mode light in the cladding mode light removal unit 103. Efficiency can be improved.

  Next, the mechanical strength of the optical fiber 100 will be considered. FIG. 3A is a cross-sectional view illustrating a region where stress is concentrated when the optical fiber 100 of the present embodiment is bent. FIG. 3B shows an area where stress is concentrated when bending is applied to the optical fiber 300 of the comparative example (corresponding to the optical fiber disclosed in the prior art shown in FIG. 9A). It is sectional drawing demonstrated. The optical fiber 300 of the comparative example is common to the optical fiber 100 of the present embodiment in that the cladding mode light removal unit 303 includes a plurality of groove portions 304. On the other hand, in the circumferential direction (direction θ) of the clad 302, it is different in that it is not divided into an opening 304a where the groove 304 is open and a non-opening where the groove 304 is not open. In other words, the optical fiber 300 does not have a non-opening in the circumferential direction (direction θ). It can also be said that the groove 304 has an annular opening 304 a formed continuously in the circumferential direction (direction θ) of the optical fiber 300. About another structure, the same structure as the optical fiber 100 of this embodiment is provided.

  When bending is applied to the optical fiber 100 of this embodiment, when attention is paid to the radial direction (direction Z) of the optical fiber 100, the stress F1 is concentrated in a region having a large outer diameter. That is, in the clad mode light removing portion 103 in which the groove portion 104 having the depth D2 is formed in the clad diameter D3, the bending stress can be dispersed to the non-opening portion 104b without concentrating on the bottom portion 105 of the groove portion 104. . Here, since the shear strength of the optical fiber 100 increases as the outer diameter increases, the bending stress is dispersed in the non-opening portion 104b having the cladding diameter D3, so that the optical fiber 100 has higher shear strength. .

  On the other hand, when bending is applied to the optical fiber 300 of the comparative example, the bending stress F2 concentrates on the bottom 305 of the groove 304. That is, since the bending stress F2 is concentrated on the bottom portion 305 having a cladding diameter of D4 (= D3-2 · D2), it can be seen that the shear strength is lower than that of the optical fiber 100.

  As described above, in the optical fiber 100 of the present invention, the clad mode light removing portion 103 has a plurality of groove portions 104 having a depth D2 smaller than the thickness D1 of the clad 102, and the groove portions in the circumferential direction (direction θ) of the clad 102. An opening 104a where the opening 104 is opened and a non-opening 104b where the groove 104 is not opened are opened at a position corresponding to the region of the non-opening 104b in the axial direction (direction X) of the optical fiber 100. Due to the presence of the region of the portion 104a, an effect of achieving both improvement of the cladding mode light removal efficiency and improvement of the 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, unlike the scratches formed when scratched with a scissors or the like, the shear strength of the optical fiber 100 is increased and the mechanical strength can be improved by having a smooth surface. In particular, it is preferable that the bottom portion 105 of the groove portion in the drawing has a rounded and smooth shape. In order to efficiently remove the clad mode light, the depth D2 of the groove 104 is at least 50 μm or more. Although the optimum depth varies depending on the clad thickness, the clad mode light removal efficiency superior to the conventional clad mode light removal portion formed by scratching or wet etching performed on a scissors or the like can be obtained. By satisfying such a condition, the clad mode light removal unit of the present invention can be distinguished from a conventional clad mode light removal unit formed by scratching or wet etching performed on a scissors or the like.

  The plurality of groove portions 104 preferably have substantially cylindrical shapes whose opening diameters are equal to each other at the surface portion of the optical fiber 100 and the bottom portion 104 c of the groove portion 104. In FIG. 2, the light beam is limited for simplicity, but the laser light is transmitted in various modes (transmission paths) in the clad 102. Therefore, the above conditions (that is, the plurality of groove portions are divided into an opening portion in which the groove portion opens in the circumferential direction of the cladding and a non-opening portion in which the groove portion does not open, and the non-opening portion in the axial direction of the optical fiber. The opening 104a is present at a corresponding position), and the depth of the opening 104a is filled from the shallow region to the deep region, thereby reducing the cladding mode light transmitted through the cladding mode light removing unit 103. Can do.

  Also, as shown in FIG. 1A, the cladding mode light removal unit 103 includes a cladding mode light removal zone 103-N (N is the number of grooves 104 having a plurality of openings at predetermined intervals in a predetermined section of the optical fiber 100. The clad mode light removal band 103-N is formed at a predetermined interval in the longitudinal direction (direction X) of the optical fiber 100, and the non-opening portion 104b in the adjacent clad mode light removal band 103-N is included. Are displaced from each other in the circumferential direction (direction θ). Thereby, since the opening 104a exists in the direction X near the non-opening 104b, the light that has passed through the non-opening 104b can be efficiently removed. Moreover, since the groove part 104 can be regularly formed in the longitudinal direction and predetermined | prescribed circumferential direction of the optical fiber 100, shape control and manufacture are easy. A method for manufacturing the optical fiber 100 will be described later.

  In addition, in the predetermined cross section in the longitudinal direction (direction X) of the optical fiber 100, the opening 104a is preferably 70% or more and 95% or less of the circumferential direction (direction θ) of the clad portion in the cross section. Furthermore, the cladding mode light removal unit 103 is preferably formed in a region of 3 cm or more and 7 cm or less in the longitudinal direction (direction X) of the optical fiber 100. As described above, by forming the cladding mode light removing section 103 over a wide range, it is possible to realize high cladding mode light removal efficiency and to prevent the shear strength of the optical fiber 100 from being lowered.

  On the other hand, the clad 102 is set so that the thickness (D1-D2) at the position where the groove portion 104 exists 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 is propagated to a medium with different refractive index, the energy reflectivity of 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 interface. 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).

Here, when the groove 104 is formed in a region where the evanescent wave penetrates, a part of the light propagating through the core 101 is radiated from the groove 104 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 above-mentioned thickness (D1-D2) is a laser propagating through the core 101. It is preferable that the thickness be set so as to be thicker than a region where light evanescent light penetrates.
For example, when a YAG laser (wavelength 1.064 μm) is used as the laser light, the thickness (D1−D2) is 0.3 μm (determined by the above approximation), preferably 1 μm (about the wavelength of propagating light). ) Or more, more preferably 5 μm (5 times the wavelength) or more.

  Next, the modification of this invention is demonstrated using FIGS. 4 to 6, modifications of the above-described optical fiber 100 relating to the cladding mode light removal unit 103 and the groove 104, the opening 104a, and the non-opening 104b included therein will be described.

  4A is a side view showing an optical fiber 400 which is a modification of the optical fiber 100, and FIG. 4B is a side view showing the optical fiber 100 of the present invention described above for comparison. It is. The optical fiber 400 according to this modification is the optical fiber already described in that the openings 404a of the plurality of grooves 404 in the cladding mode light removing unit 403 are formed so as to be dense on the end side of the optical fiber 400. 100.

  At this time, light L6, L7, L′ 6, and L′ 7 propagating in the claddings 402 and 102 and propagating toward the end portions of the optical fibers 400 and 100 will be considered. Lights L6 and L′ 6 both reach the openings 404a and 104a of the grooves 404 and 104 in the optical fibers 400 and 100, and are scattered and emitted to the outside of the claddings 402 and 102.

  On the other hand, in the optical fiber 100, the light L′ 7 passes through the non-opening portion 104b and is not emitted outside the cladding 102. On the other hand, the light L7 reaches the opening 404a of the groove 404 formed densely on the terminal end side of the optical fiber 400, even if it is light that has passed through the region of the non-opening 404b in the optical fiber 400. It is removed from 402. That is, since the light emitted from the end of the optical fiber 400 can be emitted with the cladding mode light reliably removed, for example, if the optical fiber 400 is used as a high-intensity laser light transmission means such as a laser processing apparatus. This can contribute to improvement of laser processing accuracy.

  FIG. 5A is a cross-sectional view showing an optical fiber 500 which is a modification of another optical fiber 100 of the present invention, and FIG. 5B shows a fiber 100 included in the present invention shown for comparison. It is sectional drawing shown. The optical fiber 500 according to this modification is different from the optical fibers according to other embodiments in that the clad mode light removal unit 503 is formed at the end of the optical fiber 500. Here, the end of the optical fiber 500 is, for example, one end of the optical fiber 500 and a position where the distance from the end surface to the cladding mode light removal unit 503 is smaller than the cladding mode light removal unit 503. The optical fiber 100 included in the present invention shown for comparison is different from the optical fiber 500 of the present modified example in that the cladding mode light removal unit 103 is not the end of the optical fiber 100 but is separated by a predetermined distance. In that respect, it differs from the optical fiber 500. In both embodiments, clads 102 ′ and 502 ′ having a predetermined thickness are formed on the bottom portions 105 and 505 of the groove portions 104 and 504.

  At this time, light L8 and L′ 8 incident on the claddings 102 and 502 from the outside will be considered. Lights L8 and L′ 8 are incident on the claddings 102 and 502 with a large incident angle, and then multiple-reflected on the cores 101 and 501 and the side surfaces of the cladding, and are averaged so as to propagate in the cladding at various angles. Light. In general, since the optical system is adjusted so that laser light is condensed toward the cores 101 and 501, the light incident on the clads 102 and 502 is light L8 or L'8 having a large incident angle. This form is typical.

  Here, in the optical fiber 500 according to the present embodiment, since the cladding mode light removal unit 503 is formed at the end of the optical fiber 500, the light L8 enters the cladding mode light removal unit 503 immediately after entering the cladding 502. To reach. That is, the light L8 reaches the cladding mode light removal unit 503 before being averaged into various propagation modes. Here, in order to avoid the loss of light propagating through the core 501 as described above, when the clad 502 ′ having a predetermined thickness is formed on the bottom portion 505 of the groove portion 504 in the optical fiber 500, Light having a small propagation angle (reflection angle at the interface between the clad and air) is not removed by the clad mode light removing unit 503 and may propagate through the clad 102 ′ having a predetermined thickness at the bottom 505. However, by reaching the cladding mode light removal unit 503 before the propagation angle of the light L8 is averaged, the light L8 having a large propagation angle can be reliably guided to the opening 504a of the groove 504.

  On the other hand, in the optical fiber 100 shown in FIG. 5B, the cladding mode light removing unit 103 is formed with a predetermined distance away from the end of the optical fiber 100. Therefore, the incident light L′ 8 is averaged into various propagation modes before reaching the clad mode light removing unit 103. As a result, the light component transmitted through the clad 102 at the bottom 105 of the groove 104 increases, and the removal efficiency of the clad mode light decreases.

  As described above, according to the optical fiber 500 in the present modification, the cladding mode light removal portion 503 is formed at the end of the optical fiber 500, so that the cladding mode light removal efficiency can be improved.

  FIGS. 6A and 6B are views showing still another modification of the optical fiber of the present invention. The optical fibers 600 and 700 in the present embodiment are different from the other embodiments in the specific form of the cladding mode light removal units 603 and 703. The clad mode light removal sections 603 and 703 are clad mode light removal bands 603-N and 703-N (N is a natural number) in which a plurality of grooves 604 and 704 are opened at predetermined intervals in a predetermined cross section of the optical fibers 600 and 700. The cladding mode light removal bands 603-N and 703-N are formed at predetermined intervals in the longitudinal direction (direction X) of the optical fibers 600 and 700, and adjacent cladding mode light removal bands 603-N, The non-opening portions 604b and 704b in 703-N are shifted from each other in the circumferential direction (direction θ).

  6A, the clad mode light removing portion 603 has a plurality of groove portions 604 having a depth smaller than the thickness of the clad 602, and an opening portion 604a in which the groove portion 604 opens in the circumferential direction (direction θ) of the clad 602. And a non-opening portion 604b in which the groove portion 604 is not open. And the opening part 604a exists in the position corresponding to the non-opening part 604b in the axial direction (direction X) of an optical fiber. That is, the optical fiber 600 includes at least one opening 604a in any cross section passing through the core (not shown).

  Here, openings 604a-1 and 604a-2 exist at positions corresponding to a certain non-opening 604b. Of the non-opening 604b, the region 604b-1 corresponds to the opening 604a-1, and the region 604b-2 corresponds to the opening 604a-2. That is, in the present invention, there may be a plurality of regions of the opening 604a existing at positions corresponding to the region of a certain non-opening 604b.

  In FIG. 6B, the cladding mode light removal band 703-N (N is a natural number) is formed at a predetermined interval in the longitudinal direction (direction X) of the optical fiber 700, but in the longitudinal direction (direction X). It is inclined from the vertical direction (direction θ). That is, the predetermined cross section of the optical fiber 700 in which the cladding mode light removal band 703-N is to be formed is not limited to a direction perpendicular to the longitudinal direction (direction X) of the optical fiber 700. In addition, the cladding mode light removal band 705-N is formed continuously with the cladding mode light removal band 705-N being inclined with respect to the direction perpendicular to the longitudinal direction (direction X) of the optical fiber 700. May be. What is necessary is just to form in the longitudinal direction of the optical fiber 700 at predetermined intervals.

  The optical fiber of the present invention can be modified without departing from the spirit of the optical fiber. For example, in FIG. 1B, the groove 104 is formed to be parallel to the direction Z, but may be formed to be inclined with respect to the direction Z. In addition, the outer diameter of the opening 105a may not be constant in the depth direction, and may be opened in a tapered shape. By doing so, the reflection angle of the clad mode light at the groove 104 can be adjusted, and the clad mode light can be suitably emitted from the clad 102 to the outside.

The result of evaluating the clad mode light removal efficiency of the optical fiber of the present invention will be described. That is, light was incident on one end of the clad, the intensity of light emitted from the clad at the other end was measured, and compared with the incident light intensity. The conditions are as follows.
・ Core diameter: 0.2mm, clad diameter 1.0mm
・ Clad thickness at the bottom of the groove: about 50 μm ・ Clad mode light removal part: formed over 5 cm in the axial direction of the optical fiber ・ Interval (pitch) between optical fiber removal bands: 250 μm
・ Width of groove: 500 μm
As a result, it was confirmed that about 80% of the incident light was removed from the cladding. (That is, the cladding mode light removal efficiency is about 80%.) The shear strength was 2N.

  On the other hand, when the clad mode removal portion is roughened by polishing the clad surface with scissors (No. 80) (conventional form: comparative example), the clad mode light removal efficiency is about 70%, and the shear strength is 0.8N.

  In addition, when the cladding mode removal portion has a form having an annular opening in which grooves are continuously formed in the circumferential direction of the optical fiber (a form shown in FIG. 3B), the cladding mode light removal efficiency is The shear strength was about 80N.

  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 of the present invention is not particularly limited as long as a groove portion having a depth smaller than the thickness of the cladding can be formed in the cladding mode light removing portion. It is preferable to form by doing. In this way, unnecessary scratches can be prevented from being applied to the cladding surface other than the groove, and the bottom of the groove can be formed in a smooth shape, so that the mechanical strength of the optical fiber can be prevented from being lowered.

  This will be described with reference to FIG. First, the optical fiber 100 with the cladding 102 exposed is prepared, and the optical fiber 100 is held by a jig 110 that can move in the XYZθ directions. As such a jig 110, for example, a known XYZθ 4-axis control stage as described in JP-A-2007-209992 can be used.

  Then, the clad 102 is irradiated with a laser beam r emitted from a laser irradiator (not shown) set to irradiate a laser beam with a predetermined intensity for a predetermined time. As a result, a groove 104 having a predetermined depth can be formed in the clad 102. At this time, if the laser beam r is irradiated in a plurality of times and the depth of the groove 104 is controlled by the number of times of irradiation, the laser beam intensity does not need to be excessively increased, and the shape control of the groove 104 is easy. It becomes. That is, when a plurality of groove portions 104 are formed in the clad 102, the depths can be formed to be substantially equal to each other.

  Next, the jig 110 that holds the optical fiber 100 is adjusted, the optical fiber 100 is moved relative to the laser irradiator in the X direction and the θ 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.

  For example, to manufacture the optical fiber 100 shown in FIG. 1, as shown in FIG. 7B, first, the laser beam r is irradiated to form the groove portion 104-1, and then the optical fiber 100 is moved in the direction X. The laser beam is irradiated again. By repeating this, the groove parts 104-1 and 10-2 are formed. Next, the optical fiber is rotated in the θ direction and moved in the X direction, and the same operation is performed. As a result, the grooves 104-2-1-2 can be formed in the optical fiber 100 ′ at positions shifted in the direction X and the direction θ with respect to the grooves 104-1 to 104-4.

  By adjusting the laser irradiation position and the groove depth to the clad in this way, the clad mode light removing portion in the optical fiber has a plurality of grooves having a depth smaller than the thickness of the clad, and the circumferential direction of the clad In the (direction θ), the opening is divided into an opening in which the groove is open and a non-opening in which the groove is not open, and is opened at a position corresponding to the non-opening in the axial direction (direction X) of the optical fiber. It can be formed so that there is a part. Moreover, the optical fiber shown in the modification can be manufactured by appropriately changing the irradiation position and direction of the laser beam.

  Next, an optical cable using the optical fiber of the present invention will be described with reference to FIG. FIG. 8 is a configuration diagram of an optical cable 1 including the optical fiber of the present invention. In addition, the optical cable 1 demonstrates the example which mounts the optical fiber 100. FIG. The optical cable 1 shown in FIG. 8 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.

100, 200, 300, 400, 500, 600, 700 ... optical fibers 102, 202, 302, 402, 502, 602, 702 ... clad 103, 203, 303, 403, 503, 603, 703 ... clad mode light removal unit 104, 204, 304, 404, 504, 604, 704 ... grooves 105a, 205a, 305a, 405a, 505a, 605a, 705a ... openings 105b, 205b, 405b, 505b, 605b, 705b ... non-openings 1 ... optical cable 2 ... Housing 3 ... Holding part 4 ... End cap 5 ... Inside 6 ... Cooling space 7 ... Inlet part 8 ... Outlet part

Claims (12)

An optical fiber comprising a core and a clad surrounding the outer periphery of the core,
The clad has a clad mode light removing portion that extends in an axial direction of the optical fiber and removes light propagating through the clad,
The cladding mode light removal portion includes a plurality of groove portions, and the depth of the groove portion is smaller than the thickness of the cladding, and the opening portion in which the groove portion opens in the circumferential direction of the cladding and the non-opening groove portion. Divided into openings,
The optical fiber, wherein the opening is present at a position corresponding to the non-opening in the axial direction of the optical fiber. The clad mode light removal portion includes a clad mode light removal zone in which the groove portion has a plurality of openings at predetermined intervals in a predetermined cross section in the circumferential direction of the optical fiber,
The clad mode light removal band is formed at a predetermined interval in the longitudinal direction of the optical fiber, and the non-openings in the adjacent clad mode light removal bands are shifted from each other in the circumferential direction. The optical fiber according to claim 1.   3. The optical fiber according to claim 1, wherein the plurality of groove portions have the same opening diameter at a surface portion of the optical fiber and a bottom portion of the groove portion. The predetermined opening in the circumferential direction of the optical fiber, the opening is 70% or more and 95% or less of the circumference of the cladding in the cross section. An optical fiber as described in 1. The thickness of the said clad is set so that the thickness in the said bottom part of the said groove part may become thicker than the area | region which the evanescent light of the laser beam which propagates the said core of the said optical fiber oozes out. The optical fiber according to any one of the above. The length in the axial direction of the cladding mode light removal portion is 3 cm or more and 7 cm or less,
The optical fiber according to any one of claims 1 to 5, wherein: The optical fiber according to any one of claims 1 to 6, wherein the clad mode light removing unit is formed at a terminal of the optical fiber. The optical fiber according to any one of claims 1 to 7, wherein the plurality of groove portions are formed densely on a terminal side of the optical fiber. A 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 optical cable, wherein the clad and the clad mode light removing portion are exposed at the terminal portion. The optical fiber is a fiber according to claim 7 or 8,
The optical fiber according to claim 9, further comprising an end cap that is provided in optical contact with the end face and is fixed to the housing. The optical cable is further accommodated in the housing, further comprising an inner tube that accommodates the end portion of the optical fiber,
11. 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 described in 1. The optical fiber is connected to one end side of a glass rod having substantially the same diameter as the clad, and the other end side of the glass rod is connected to the end cap on the end face of the optical fiber. Item 11. The optical cable according to Item 10.

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