JP2019028414A - Optical fiber structure - Google Patents

Abstract

To provide an optical fiber structure having high mechanical strength and high removal efficiency of clad mode light.SOLUTION: An optical fiber structure 60 comprises an optical fiber 10 having a core 11 and a clad 12 and an almost axially symmetrical glass body 20 integrally melted at a part thereof. The glass body 20 has higher refraction index than that of the clad 12 of the optical fiber and also the glass body 20 has a lower softening point than that of the clad 12 of the optical fiber. In addition, an intermediate part 21 of the glass body in the axial direction is formed into an almost cylindrical shape and both ends 22 thereof have such a shape that thickness of the glass body in the radial direction gradually decreases from the intermediate part 21.SELECTED DRAWING: Figure 1

Description

Detailed Description of the Invention

    The present invention relates to an optical fiber structure.

    An optical fiber is used as a transmission medium for propagating laser light and performing processing such as communication, measurement, or metal, and includes a glass core that transmits light, and a glass cladding that covers an outer peripheral surface of the core. And a plastic covering layer for protecting the core and the clad.

    When laser light is incident on an optical fiber and propagated, a part of the laser light may be incident on the clad. If the light incident on the clad has a certain level of high energy, the light may leak and damage the plastic material that is the coating of the optical fiber, the end processing component that fixes the optical fiber, or the like. An optical structure for removing light propagating in the clad from the clad is provided.

    As described above, Patent Document 1 discloses that an optical structure that removes light in a clad when laser light is incident on the clad is formed with a ring-shaped groove on the outer circumference of the clad of the optical fiber.

    Patent Document 2 discloses a structure in which a cladding mode is removed by bonding or fusing a glass tube having a refractive index equal to or higher than that of the optical fiber cladding to the outer periphery of the optical fiber.

JP 2011-118208 A JP 2007-293298 A

    When light is incident on the optical fiber, it is usually assumed that light is incident only on the core region. However, when light is incident on the incident end of the optical fiber from the laser, it may be partially incident on the cladding. In this way, the light incident on the cladding region propagates through the cladding region (cladding mode light), and in particular, an optical fiber is used as a laser beam transmission means of a laser processing apparatus that transmits high energy light of several hundred W to kW class. When used, clad mode light can be a cause of deterioration in processing accuracy.

    Further, there may be a case where a part of the light emitted from the light emitting end enters the clad as return light. A part of the laser light collected by the condensing lens after being emitted from the optical fiber is reflected by the work piece, and the reflected light passes through the condensing lens and returns to the connector side to enter the clad and propagates through the clad. There is a problem that light leaks out of the clad due to the slight bending of the optical fiber and damages the coating layer of the optical fiber and the casing that fixes the optical fiber.

    In order to solve the problems shown in the above [0006] and [0007], a clad mode removing section for removing clad mode light as in Patent Document 1 and Patent Document 2 is provided, and high strength of a laser processing apparatus or the like is provided. It is possible to efficiently remove clad mode light of an optical fiber used as a simple laser light transmission means.

    However, as shown in FIG. 9, the structure described in Patent Document 1 forms a ring-shaped groove processing portion 40 on the clad 12 of the optical fiber 10, so that the strength of the optical fiber 10 is significantly deteriorated and small. The optical fiber can be broken even by an impact. Further, as shown in FIG. 10, the structure described in Patent Document 2 is such that a glass tube 50 is bonded or welded on the clad 12 of the optical fiber 10 as a cladding mode removing portion. There is a high possibility that stress concentrates at both ends of the glass tube 50 in the direction, and the optical fiber breaks. Neither the structure described in Patent Document 1 nor the structure described in Patent Document 2 can be said to have sufficient reliability due to the mechanical strength of the optical fiber.

    The present invention has been made in view of such problems, and an object thereof is to provide an optical fiber structure having high mechanical strength and high cladding mode removal efficiency.

    The optical fiber structure of the present invention is a structure comprising an optical fiber glass having a core and a clad, and a generally axisymmetric glass body melted and integrated in a part of its axial direction. Furthermore, the glass body has a higher refractive index than the cladding of the optical fiber, and the glass body has a lower softening point than the cladding of the optical fiber. Furthermore, the intermediate part in the axial direction of the glass body is generally cylindrical, and both end parts have a shape in which the thickness in the radial direction gradually decreases from the intermediate part.

    In the optical fiber structure according to the present invention, it is preferable that both end portions of the glass body have a shape that gradually decreases the thickness in the radial direction and gradually approaches the optical fiber.

    In the optical fiber structure according to the present invention, it is preferable that the cylindrical outer periphery of at least an intermediate portion of the glass body is roughened.

    In the optical fiber structure of the present invention, it is preferable that the glass body is borosilicate glass.

    According to the present invention, an optical fiber structure having high mechanical strength and high cladding mode light removal efficiency can be provided.

It is a side view of the optical fiber structure in the embodiment of the present invention. It is an enlarged view of the side view of the optical fiber structure in embodiment of this invention. It is an enlarged view of the side view of the optical fiber structure in embodiment of this invention. It is an enlarged view of the side view of the optical fiber structure in embodiment of this invention. It is a side view which shows another embodiment of this invention. It is an enlarged view of the side view of the optical fiber structure in another embodiment of this invention. It is an enlarged view of the side view of the optical fiber structure in another embodiment of this invention. It is a side view which shows another embodiment of this invention. It is a side view which shows the clad mode removal part in a prior art. It is a side view which shows the clad mode removal part in a prior art.

    DETAILED DESCRIPTION Exemplary 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. 1 is a side view of an optical fiber structure 60 of the present embodiment. The optical fiber 10 includes a core 11, a clad 12, and a plastic coating layer 13. The optical fiber 10 is capable of transmitting a laser beam having a high energy of about several hundred watts to several kW used for laser processing or the like, and can be applied to a laser beam transmission means or the like in a laser processing apparatus. The optical fiber includes a single mode optical fiber designed to propagate a single mode and a multimode optical fiber that propagates a plurality of modes, but any optical fiber can be applied in the embodiment of the present invention.

    In the optical fiber structure, the glass body 20 is formed substantially uniformly in the circumferential direction of the optical fiber 10 at a predetermined position in the axial direction of the optical fiber 10. This structure is disposed in the vicinity of the incident end or the exit end of the optical fiber 10 in the axial direction, and is housed in an optical connector or an appropriate housing to be protected. The axial position of the optical fiber 10 is preferably arranged, for example, at a distance within 10 cm from the incident end of the optical fiber 10 or within 10 cm from the exit end in the axial direction. Further, considering that the optical fiber structure is housed in a connector or an appropriate housing, it is preferable that the optical fiber structure is compact, but a size capable of sufficiently removing the clad mode is required. The maximum outer diameter of the structure is preferably φ0.4 mm to 2.5 mm, and the maximum length is preferably 8 mm to 30 mm.

    When the glass body is integrated on the clad of the optical fiber, the glass body is heated above the strain point of the glass body. However, when the glass body is returned to room temperature after fusion integration, the optical fiber structure 60 can be obtained even if it is gradually cooled at an appropriate temperature gradient. Has a residual stress, and therefore the mechanical strength of the optical fiber structure 60 can be reduced. Residual stress is compressive stress in the axial direction on the optical fiber 10 side, and tensile stress is applied in the axial direction on the glass body 20 side, and these are concentrated at both end portions 22 in the axial direction of the glass body. Breakage can occur. Therefore, in order to alleviate the stress distribution of the glass body, both end portions 22 of the glass body are formed so as to gradually reduce the thickness in the axial direction as shown in FIG. By taking such a shape, the stress concentration of the optical fiber structure 60 is alleviated, and sufficient mechanical strength can be secured.

    The optical fiber structure 60 forms a glass body around the optical fiber. At this time, it is not preferable in terms of transmission characteristics of the optical fiber that the optical fiber is deformed by the influence of the glass body forming process. In order to melt and integrate the glass body into the clad, the glass body is heated to the softening point or higher, but in order to suppress the optical fiber from being deformed by heating, the glass has a softening point lower than that of the clad. Preferably, the glass body is melted and integrated at a temperature lower than the softening point of the clad glass.

    The refractive index of the glass body 20 of the optical fiber structure 60 is larger than that of the optical fiber cladding 12. In this structure, a glass body 20 having a refractive index higher than that of the clad 12 is fused and integrated on the clad and is also in optical contact, so that the light incident on the optical fiber clad 12 is in contact with the clad 12 of the structure. It can be efficiently removed from the clad 12 toward the glass body 20 through the interface of the glass body 20.

    FIG. 2 is a partially enlarged view of the optical fiber structure 60 of the present embodiment. The reduction degree of the thickness of the both end portions 22 in the axial direction of the glass body 20 can be expressed by the contact angle θ between the clad 12 and the glass body 20, and the value of the contact angle θ is preferably small, for example, 45 degrees or less. It is preferable.

    3 and 4 show shapes that can be realized when the glass body 20 is fused and integrated in the present embodiment. In FIG. 3, the decrease in the thickness of the glass body 20 is not linear, and the end portion 22 of the glass body 20 decreases in thickness while forming a convex surface. In FIG. 4, a part of the intermediate portion 21 of the glass body 20 has a swelled shape, and the thickness is reduced while forming a convex surface at the end portion 22. Also in the shapes shown in FIGS. 3 and 4, the contact angle θ is preferably small, for example, 45 degrees or less. Even in such a shape, there is no problem of mechanical strength, and the effect of removing the cladding mode can be obtained as in the other embodiments.

    As shown in FIGS. 5 and 6, in another embodiment, the shape of both end portions 22 in the axial direction of the glass body 20 forming the optical fiber structure 60 is asymptotically approximated to the cladding 12 of the optical fiber 10 in the axial direction. It is structured. In such a structure, since the concentration of the residual stress in the axial direction is further relaxed, the mechanical strength of the optical fiber structure 60 is further improved.

    Further, as shown in FIG. 7, a part of the intermediate portion 21 of the glass body 20 has a swelled shape, and has a structure in which the thickness is reduced while forming a convex surface at the end portion and gradually approaches the cladding 12 in the axial direction. Can be formed. This structure also has a structure in which the thickness of the glass body decreases at both end portions 22 of the glass body 20 and asymptotically approaches the clad, so that there is no problem of mechanical strength, and the effect of removing the clad mode is another implementation. The same effect as the shape can be obtained.

    FIG. 8 shows still another embodiment. In the optical fiber structure 60, it is desirable that the removed clad mode light is removed without being recombined into the core 11. Further, light incident on the glass body 20 from the clad 12 is reflected inside the glass body 20, and light emitted from the glass body 20 is concentrated on a certain place such as a casing that protects the optical fiber structure 60, and the part is damaged. It is desirable to eliminate the possibility of doing so. In order to realize these, it is preferable that a rough surface processing 30 is performed on the entire circumference of at least a part of the intermediate portion 21 of the glass body 20. By roughening a part of the intermediate portion 21 of the glass body 20 around the entire circumference, the possibility that the glass body 20 will be repeatedly reflected in the glass body 20 and return to the clad 12 is reduced, and the light emitted from the glass body 20 is reduced. The possibility of damaging the housing is reduced. Since the rough surface processing 30 is performed in a place where there is no influence on the strength of the optical fiber 10 itself, the mechanical strength is not deteriorated as compared with the structure in which the optical fiber cladding 12 is directly processed as shown in FIG. . The rough surface processing 30 is formed by a method such as etching using buffered hydrofluoric acid, processing using CO2 laser irradiation, or physical grinding such as sand blasting.

    The glass body 20 has a refractive index higher than that of the optical fiber clad 12 and has a lower softening point. Since the glass body 20 has less residual stress after fusion and integration, the linear expansion coefficient is close to that of the optical fiber clad 12, so that borosilicate An acid glass is preferred. In general, borosilicate glass having a refractive index of 1.471 and a softening point of 820 ° C. is known. Compared with quartz which is a cladding of an optical fiber, the refractive index of quartz is 1. Since it is 458 and a softening point is 1,720 degreeC, it turns out that it is suitable as a glass body which comprises the optical fiber structure of this invention. Further, the linear expansion coefficient that causes the residual stress after processing is about five times that of quartz, and the difference is small compared to other glasses, so that the residual stress can be made relatively small. In general, it is widely used as a heat-resistant glass, and is excellent as the glass body 20 of the present optical fiber structure 60 in view of stable quality and easy availability.

    As described above, since the present invention has a structure with high mechanical strength and can effectively remove the cladding mode of the optical fiber, the industrial utility value is extremely high.

DESCRIPTION OF SYMBOLS 10 Optical fiber 11 Core 12 Clad 13 Coating layer 20 Glass body 21 Glass body intermediate part 22 Glass body edge part 30 Rough surface processing part 40 Groove processing part 50 Jacket tube 60 Optical fiber structure

Claims (4)

    An optical fiber glass having a core and a cladding, and a substantially axisymmetric glass body melted and integrated in a part of its axial direction, and the glass body has a higher refractive index than the cladding of the optical fiber. And the glass body has a softening point lower than that of the cladding of the optical fiber, and an intermediate portion in the axial direction of the glass body is substantially cylindrical, and both end portions of the glass body are lower than the intermediate portions. An optical fiber structure having a shape that gradually decreases the radial thickness.     2. The optical fiber structure according to claim 1, wherein both end portions of the glass body have a shape that gradually decreases the thickness in the radial direction and gradually approaches the optical fiber.     3. The optical fiber structure according to claim 1, wherein at least a part of the glass body in the axial direction has a roughened outer periphery over the entire circumference.     4. The optical fiber structure according to claim 1, wherein the glass body is borosilicate glass.

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