JP2013007959A - End face processing method of optical fiber and terminal structure of optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an end face processing method of an optical fiber for easily fusing and connecting a glass block and the optical fiber without working the glass block into a tapered shape.SOLUTION: When the end face processing of an optical fiber 2 is performed, a glass rod 3 with no core clad structure and a glass block 4 with outer diameter which is larger than that of the glass rod 3, and with no core clad structure are prepared. Then, the optical fiber 2 and the glass rod 3 are fused by arc discharge. Then, the glass rod 3 is cut such that the axial length of the glass rod 3 is set to a dimension with which a laser beam R emitted from a core 2a of the optical fiber 2 does not reach an outer peripheral face 3a of the glass rod 3. Afterwards, the glass rod 3 and the glass block 4 are fused by using a CO2 laser to fuse the glass rod 3 and the glass block 4.

Description

  The present invention relates to a method for treating an end face of an optical fiber that transmits high-power light such as laser light, and an optical fiber terminal structure.

  As an end structure of an optical fiber that transmits laser light, for example, one described in Patent Document 1 is known. The terminal structure of an optical fiber described in Patent Document 1 includes an optical fiber having a core and a cladding, and a block-shaped chip (glass block) coupled to the fiber end of the optical fiber. The block-shaped chip has a tip side portion formed in a columnar shape and the like, and a base end side portion formed in a tapered shape toward the tip end, and the end surface of the tip end of the base end side portion is an optical fiber. Bonded to the end face of the fiber end by fusion. Thereby, since the heat capacities of the block-shaped chip and the optical fiber are close, both can be easily fused.

JP 2009-301065 A

  However, in order to prepare a glass block formed in a tapered shape as in the above prior art, a process such as machining or melt-drawing a cylindrical glass block is required, leading to an increase in cost.

  An object of the present invention is to provide an optical fiber end face processing method and an optical fiber end structure capable of easily fusion-bonding a glass block and an optical fiber without processing the glass block into a tapered shape. It is.

  The method for treating an end face of an optical fiber according to the present invention includes an optical fiber having a core / cladding structure, a glass rod having no core / cladding structure, an outer diameter larger than that of the glass rod, and no core / cladding structure. The first step of preparing the glass block, the first fusion step of fusion-connecting the optical fiber and the glass rod, and the first fusion step of fusing and connecting the glass rod and the glass block after performing the first fusion step. And 2 fusion processes.

  As described above, in the optical fiber end surface processing method of the present invention, first, an optical fiber having a core / cladding structure and a glass rod having no core / cladding structure are fusion-bonded, and then the glass rod and the glass rod are used. And a glass block having a large outer diameter and no core / cladding structure. By separately using a glass rod that is thinner than the glass block in this way, the glass block and the optical fiber can be easily fusion-bonded via the glass rod without particularly processing the glass block into a tapered shape. it can. In such an optical fiber terminal structure, the light beam emitted from the core of the optical fiber passes through the glass rod and the glass block while spreading.

  Preferably, the glass rod and the glass block have a uniform refractive index distribution. In this case, melting the glass rod and the glass block does not affect the refractive index of the glass rod and the glass block, so that the quality of the light beam transmitted through the glass rod and the glass block does not deteriorate.

  Preferably, the outer diameter of the glass rod is larger than the core diameter of the optical fiber and smaller than twice the cladding diameter of the optical fiber. In this case, there is no large difference between the outer diameter of the glass rod and the cladding diameter of the optical fiber, and the heat capacities of the glass rod and the optical fiber are close to each other, so that both can be easily fused. Further, when the outer diameter of the glass rod is larger than the cladding diameter of the optical fiber, the glass rod need not be replaced even if the optical fiber is replaced with a thicker one.

  Further, preferably, an antireflection film is formed on the end surface of the glass block opposite to the side to be fused with the glass rod. In this case, reflection of the light beam at the end surface of the glass block opposite to the side to be fused with the glass rod can be prevented.

  Preferably, the refractive index of the glass rod and the glass block is equal to the refractive index of the core of the optical fiber. In this case, reflection of the light beam at the interface between the optical fiber and the glass rod and reflection of the light beam at the interface between the glass rod and the glass block can be prevented.

  The melting point of the glass rod may be lower than the melting point of the glass block. In this case, when only the glass rod is melted and the glass rod and the glass block are fused, the glass rod is melted at a low temperature, so that the second fusion process can be easily designed and managed. .

  The refractive index of the glass rod may be larger than the refractive index of the core of the optical fiber. In this case, since the spread of the light beam on the glass rod is suppressed, the glass rod can be lengthened in the axial direction. Therefore, when the glass rod is melted, heat is hardly transmitted to the optical fiber, so that the core / cladding structure of the optical fiber is prevented from collapsing.

  Further preferably, the method further includes a cutting step of cutting the glass rod after performing the first fusing step and before performing the second fusing step. In the second fusing step, The glass block is fusion spliced. In this case, a glass rod having an optimal length can be obtained.

  At this time, in the cutting process, the length of the glass rod in the axial direction is set so that light emitted from the core of the optical fiber and propagating while spreading the glass rod does not reach the outer peripheral surface of the glass rod. Cut the rod. In this case, since the light beam propagating while spreading the glass rod is not reflected by the outer peripheral surface of the glass rod, it is possible to prevent deterioration of the quality of the light beam.

  Preferably, a recess for positioning the glass rod is provided on the end surface of the glass block on the side to be fused with the glass rod, and the glass rod is accommodated in the recess in the second fusion step. Then, the glass rod and the glass block are fused and connected. In this case, the optical fiber can be easily positioned with respect to the glass block via the glass rod. Further, when the glass rod and the glass block are fused, the bonding area between the glass rod and the glass block is increased, so that the fusion strength between the glass rod and the glass block is increased.

  Further preferably, in the second fusion step, the glass rod and the glass block are fusion-bonded by a laser. In this case, at least one of the glass rod and the glass block can be spot-melted and both can be easily fused.

  Further, the present invention is an optical fiber terminal structure having a core / cladding structure, wherein the glass rod is fusion-bonded to the optical fiber and does not have the core / cladding structure, and the glass rod is disposed on the opposite side of the optical fiber. And a glass block having a larger outer diameter than the glass rod and having no core / cladding structure.

  As described above, in the optical fiber terminal structure of the present invention, by separately providing a glass rod that is thinner than the glass block, the glass block and the optical fiber can be connected to the glass rod without particularly processing the glass block into a tapered shape. It can be easily fusion-spliced through.

  Preferably, the length of the glass rod in the axial direction is set such that light emitted from the core of the optical fiber and propagating through the glass rod does not reach the outer peripheral surface of the glass rod. In this case, since the light beam propagating while spreading the glass rod is not reflected by the outer peripheral surface of the glass rod, it is possible to prevent deterioration of the quality of the light beam.

  Preferably, a concave portion for positioning the glass rod is provided on an end surface of the glass block on the side to be fused with the glass rod, and the glass rod is melted with the glass block while being accommodated in the concave portion. Incoming connection. In this case, the optical fiber can be easily positioned with respect to the glass block via the glass rod. Further, when the glass rod and the glass block are fused, the bonding area between the glass rod and the glass block is increased, so that the fusion strength between the glass rod and the glass block is increased.

  According to the present invention, the glass block and the optical fiber can be easily fused and connected without processing the glass block into a tapered shape. Thereby, an increase in cost can be suppressed.

It is sectional drawing which shows one Embodiment of the terminal structure of the optical fiber concerning this invention. It is a figure which shows a mode that the laser beam radiate | emitted from the optical fiber shown in FIG. 1 permeate | transmits a glass rod. It is a graph which shows the relationship between the length of the glass rod shown in FIG. 2, and the maximum diameter of the laser beam which permeate | transmits a glass rod. It is a figure which shows the process of fuse | melting the optical fiber shown in FIG. 1, and a glass rod. It is a figure which shows the process of fuse | melting the glass rod and glass block shown in FIG. As a comparative example, it is sectional drawing which shows the structure where the optical fiber and the glass block were directly fusion-bonded. It is sectional drawing which shows other embodiment of the terminal structure of the optical fiber concerning this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of an optical fiber end face processing method and an optical fiber terminal structure according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a sectional view showing an embodiment of an optical fiber terminal structure according to the present invention. In the drawing, an optical fiber terminal structure 1 of the present embodiment is a terminal structure of an optical fiber 2 that transmits a high-power (several kW) laser beam for laser processing.

  The optical fiber 2 is made of quartz glass. The optical fiber 2 has a core 2a and a clad 2b provided around the core 2a. The refractive index of the core 2a is higher than the refractive index of the clad 2b. The outer diameter (core diameter) of the core 2a is, for example, 0.2 mm, and the outer diameter (cladding diameter) of the cladding 2b is, for example, 1.0 mm.

  A glass rod 3 is fusion spliced (melted and integrated) to the distal end surface of the optical fiber 2. The glass rod 3 is quartz glass that does not have a core / cladding structure like the optical fiber 2. The glass rod 3 is configured to have a heat capacity close to that of the optical fiber 2 as compared with a glass block 4 described later, and the outer diameter of the glass rod 3 is preferably substantially equal to the outer diameter of the optical fiber 2. However, compared to the case where the optical fibers 2 having the core / cladding structure are fusion-bonded, the degree of the influence of the deformation of the junction point due to the fusion-bonding on the beam quality is small. It is not required that the outer diameters match closely.

  From such a viewpoint, the outer diameter of the glass rod 3 is preferably larger than the core diameter of the optical fiber 2 and smaller than twice the cladding diameter of the optical fiber 2. In this case, since the heat capacities of the glass rod 3 and the optical fiber 2 are close to each other, both can be easily fused. Further, when the outer diameter of the glass rod 3 is larger than the cladding diameter of the optical fiber 2, the glass rod 3 does not have to be replaced even if the optical fiber 2 is appropriately replaced with a thicker one depending on the application. Manufacturing cost can be reduced.

  A glass block 4 is fusion-bonded (fused and integrated) to the end surface of the glass rod 3 opposite to the optical fiber 2. The glass block 4 is quartz glass that does not have a core-clad structure like the optical fiber 2. The outer diameter of the glass block 4 is larger than the outer diameter of the glass rod 3. Thereby, the beam density on the front end surface (light beam incident / exit surface) of the optical fiber 2 can be reduced. Further, an antireflection film (AR coating film) 5 for reducing reflection loss is applied to the end face of the glass block 4 opposite to the glass rod 3.

  The laser beam R emitted from the core 2a of the optical fiber 2 propagates inside the glass rod 3 and the glass block 4 while spreading. Here, the axial length of the glass rod 3 is set such that the laser beam R emitted from the core 2 a does not reach the outer peripheral surface (side surface) 3 a of the glass rod 3. Thereby, it is prevented that the laser beam R is reflected by the outer peripheral surface 3a of the glass rod 3 and the beam quality is deteriorated.

Specifically, as shown in FIG. 2, the divergence angle θ of the laser beam R passing through the glass rod 3 is obtained from the following equation using the numerical aperture NA and the refractive index n of the optical fiber 2.
NA = nsinθ

  Here, the core diameter of the optical fiber 2 is 0.2 mm, and the numerical aperture NA of the optical fiber 2 is 0.2. The refractive index n of the optical fiber 2 is 1.45. Therefore, when the clad diameter is 1.0 mm, the limit length of the glass rod 3 for preventing the laser beam R from reaching the outer peripheral surface 3a of the glass rod 3 is 2.9 mm as can be seen from FIG. That is, the axial length of the glass rod 3 needs to be 2.9 mm or less.

  Both the glass rod 3 and the glass block 4 preferably have a uniform refractive index distribution. As a result, even if the glass rod 3 and the glass block 4 are deformed by melting (described later), the refractive index distribution of the glass rod 3 and the glass block 4 is not affected. The quality of the beam R does not deteriorate. As a result, the management accuracy of the fusing conditions is relaxed, so that the manufacturing process can be easily designed and managed.

  At this time, the refractive indexes of the glass rod 3 and the glass block 4 are equal to the refractive index of the core 2 a of the optical fiber 2. Thereby, reflection of the laser beam R at the interface between the optical fiber 2 and the glass rod 3 and at the interface between the glass rod 3 and the glass block 4 can be suppressed. Further, since there is no interface having a different refractive index at the connection point, the connection strength can be increased.

  Next, a method for performing the end face processing of the optical fiber 2 to obtain the optical fiber terminal structure 1 will be described.

  First, the end surfaces of the optical fiber 2 and the glass rod 3 are fused and connected by a fiber fusion machine in a state where the end surfaces of the optical fiber 2 and the glass rod 3 are cut vertically using a fiber cutter. Specifically, as shown in FIG. 4A, arc discharge is performed by a pair of discharge electrodes 6 in a state where the end faces of the optical fiber 2 and the glass rod 3 are in contact with each other, and the optical fiber 2 and the glass rod 3 And fuse.

  Next, as shown in FIG. 4B, the glass rod 3 is cut to a desired length using a fiber cutter. At this time, as described above, the length of the glass rod 3 in the axial direction is set such that the laser beam R emitted from the core 2a of the optical fiber 2 does not reach the outer peripheral surface 3a of the glass rod 3. Cut 3

  Next, as shown in FIG. 5, the glass rod 3 is fused and connected to the glass block 4 by a laser. As the laser used at this time, a CO2 laser that can easily manage the intensity and the condensing position is preferable.

  Specifically, the cut surface of the glass rod 3 and the end surface on the opposite side of the antireflection film 5 in the glass block 4 are brought close to each other and the fusion position of the glass block 4 is irradiated with the CO2 laser beam X (FIG. 5). (See (a)). Then, the glass rod 3 is abutted against the glass block 4 (see FIG. 5B). Then, since the CO2 laser beam X comes into contact with the glass rod 3 and the glass block 4, the glass rod 3 and the glass block 4 are in a molten state.

  At this time, the glass rod 3 may be melted before the glass block 4. The glass block 4 having a large heat capacity requires more heat energy than the glass rod 3 having a small heat capacity. For this reason, while the heating necessary to melt the glass block 4 is being applied, the glass rod 3 is excessively melted by the preheating, and the yield in the fusion of the two may be reduced. By melting the glass rod 3 prior to the glass block 4, problems due to the above phenomenon can be prevented.

  Then, the glass rod 3 and the glass block 4 are melt | fused by pushing the glass rod 3 further into the glass block 4 (refer FIG.5 (c)). At this time, the shape of the fused portion of the glass rod 3 may collapse, but since the glass rod 3 does not have a core / cladding structure, the quality of the laser beam R transmitted through the glass rod 3 is not affected. No.

  By the way, as shown in FIG. 6, when the optical fiber 2 is directly fused to the glass block 4, the following problems occur. That is, in order to reduce the energy density of the glass block 4 on the antireflection film 5, it is necessary to make the outer diameter of the glass block 4 sufficiently larger than the outer diameter of the optical fiber 2. However, in this case, since a large heat capacity difference is generated between the optical fiber 2 and the glass block 4, when the optical fiber 2 and the glass block 4 are fused, the optical fiber 2 having a lower heat capacity is melted first. Will begin to do. At this time, if the glass block 4 is melted, the end of the optical fiber 2 is likely to evaporate. Further, if only the optical fiber 2 is melted and fused to the glass block 4, the core / cladding structure of the optical fiber 2 is disturbed, resulting in deterioration of the quality of the laser beam R emitted from the optical fiber 2. End up.

  Therefore, it is conceivable that the heat capacity of the glass block 4 is made closer to the heat capacity of the optical fiber 2 by making the one end side portion of the glass block 4 into a tapered shape. However, it takes considerable cost to process the glass block 4 into a tapered shape.

  On the other hand, in the present embodiment, a glass rod 3 having no core / cladding structure and having a diameter smaller than that of the glass block 4 is separately prepared. First, the optical fiber 2 and the glass rod 3 are fused and connected, and then the glass Since the rod 3 and the glass block 4 are fused and connected, the glass block 4 and the optical fiber 2 can be easily fused via the glass rod 3 without processing the glass block 4 into a tapered shape. Can be connected. Thus, since it is not necessary to process the glass block 4 into a taper shape, it becomes possible to suppress an increase in cost.

  FIG. 7 is a sectional view showing another embodiment of an optical fiber terminal structure according to the present invention. In the figure, the same or equivalent members as those in the above embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the figure, in the optical fiber terminal structure 1 of the present embodiment, a concave portion 10 having a circular cross section for positioning the glass rod 3 is formed on the end surface (fused surface) opposite to the antireflection film 5 in the glass block 4. Is provided. In this case, when the glass rod 3 and the glass block 4 are fused, even if the glass rod 3 is inserted into the concave portion 10 of the glass block 4 and the fused portion is irradiated with a CO2 laser beam. Alternatively, the glass rod 3 may be inserted into the recess 10 while the CO2 laser beam is irradiated on the recess 10 of the glass block 4.

  At this time, the recess 10 is formed at the center of the fused surface of the glass block 4. Thereby, the optical fiber 2 can be easily positioned at the center of the fused surface of the glass block 4. In addition, you may form the recessed part 10 in the site | part shifted | deviated from the center of the fusion surface of the glass block 4. FIG. In this case, by intentionally bending the optical fiber 2, light propagating in the cladding 2b of the optical fiber 2 (cladding propagation light) can be efficiently removed.

  Thus, by providing the recessed part 10 in the fusion | melting surface of the glass block 4, the optical fiber 2 can be easily positioned with respect to the glass block 4 via the glass rod 3. FIG. Moreover, since the contact area of the glass rod 3 and the glass block 4 increases, both melt | fusion strengths become high. Furthermore, since the molten glass is prevented from flowing to the outer peripheral surface of the glass block 4 when the glass rod 3 and the glass block 4 are fused, the yield of the manufacturing process can be improved.

  The preferred embodiments of the method for treating an end face of an optical fiber and the end structure of the optical fiber according to the present invention have been described above, but the present invention is not limited to the above embodiment.

  For example, in the above embodiment, when the glass rod 3 and the glass block 4 are fused, both the glass rod 3 and the glass block 4 are heated and melted, but at least one of the glass rod 3 and the glass block 4 is melted. What is necessary is just to heat-melt. At this time, by using a laser as a method for fusing the glass rod 3 and the glass block 4, the focal point for irradiating the laser can be set to the glass rod 3, and only the glass rod 3 can be easily heated and melted. In this case, it is not necessary to consider the heat capacity difference between the glass rod 3 and the glass block 4. That is, as described above, it is possible to prevent the glass rod 3 from being excessively melted by preheating while heating necessary to melt the glass block 4 is performed, and the yield in the fusion of both can be prevented from being lowered.

  Moreover, in the said embodiment, although the refractive index of the glass rod 3 and the glass block 4 was made equivalent to the refractive index of the core 2a of the optical fiber 2, by adding fluorine or phosphorus to the glass rod 3 and the glass block 4, for example. The refractive index of the glass rod 3 and the glass block 4 may be smaller than the refractive index of the core 2a of the optical fiber 2. In this case, since melting | fusing point of the glass rod 3 and the glass block 4 becomes low, when fusing the glass rod 3 and the glass block 4, these become easy to fuse | melt. Therefore, it is possible to easily design and manage the fusion process. For example, it becomes possible to reduce the output of the laser to be irradiated. At this time, when only the glass rod 3 is melted as described above, it is desirable that the melting point of the glass rod 3 be lower than the melting point of the glass block 4.

  Moreover, you may make the refractive index of the glass rod 3 and the glass block 4 larger than the refractive index of the core 2a of the optical fiber 2 by adding germanium to the glass rod 3 and the glass block 4, for example. In this case, the spread of the laser beam R in the glass rod 3 and the glass block 4 is suppressed. When the spread of the laser beam R in the glass rod 3 is suppressed, the glass rod 3 can be lengthened, so that the length of the glass rod 3 can be easily managed. In addition, since the heat is not easily transmitted to the optical fiber 2 when the glass rod 3 is melted by the length of the glass rod 3, the core-cladding structure of the optical fiber 2 is prevented from being broken.

  Furthermore, in the said embodiment, although the glass rod 3 and the glass block 4 were melt | fused using a laser, you may fuse | melt the glass rod 3 and the glass block 4 with an electric discharge or a heater. In this case, the heater temperature and discharge intensity may be adjusted. At this time, if the melting points of the glass rod 3 and the glass block 4 are lowered as described above, the heating temperature can be lowered. In addition, if only the glass rod 3 is melted by appropriately adjusting the heating time in consideration of the heat capacity difference between the glass rod 3 and the glass block 4, the yield reduction in the fusion process caused by the heat capacity difference between the two. As described above, this can be prevented.

DESCRIPTION OF SYMBOLS 1 ... Optical fiber terminal structure, 2 ... Optical fiber, 2a ... Core, 2b ... Cladding, 3 ... Glass rod, 4 ... Glass block, 5 ... Antireflection film, 10 ... Concave part.

Claims (14)

A preparation step of preparing an optical fiber having a core / cladding structure, a glass rod having no core / cladding structure, and a glass block having an outer diameter larger than that of the glass rod and not having the core / cladding structure; ,
A first fusing step of fusing and connecting the optical fiber and the glass rod;
A method for treating an end face of an optical fiber, comprising: a second fusion step of fusion-connecting the glass rod and the glass block after performing the first fusion step.   2. The method of treating an end face of an optical fiber according to claim 1, wherein the glass rod and the glass block have a uniform refractive index distribution.   3. The method of treating an end face of an optical fiber according to claim 1, wherein an outer diameter of the glass rod is larger than a core diameter of the optical fiber and smaller than twice a cladding diameter of the optical fiber.   The optical fiber according to any one of claims 1 to 3, wherein an antireflection film is formed on an end surface of the glass block opposite to a side to be fused with the glass rod. End face processing method.   The optical fiber end face processing method according to any one of claims 1 to 4, wherein a refractive index of the glass rod and the glass block is equal to a refractive index of a core of the optical fiber.   The method for treating an end face of an optical fiber according to any one of claims 1 to 4, wherein a melting point of the glass rod is lower than a melting point of the glass block.   The optical fiber end face processing method according to claim 1, wherein a refractive index of the glass rod is larger than a refractive index of a core of the optical fiber. After performing the first fusing step, before performing the second fusing step, further comprising a cutting step of cutting the glass rod,
The optical fiber end face processing method according to any one of claims 1 to 7, wherein in the second fusion step, the cut surface of the glass rod and the glass block are fusion-connected.   In the cutting step, the length of the glass rod in the axial direction is set so that light emitted from the core of the optical fiber and propagating through the glass rod does not reach the outer peripheral surface of the glass rod. 9. The method for treating an end face of an optical fiber according to claim 8, wherein the glass rod is cut. A concave portion for positioning the glass rod is provided on an end surface of the glass block to be fused with the glass rod,
The said 2nd melt | fusion process WHEREIN: The said glass rod and the said glass block are fusion-bonded in the state which accommodated the said glass rod in the said recessed part, The Claim 1 characterized by the above-mentioned. Optical fiber end face processing method.   The optical fiber end face processing method according to any one of claims 1 to 10, wherein in the second fusion step, the glass rod and the glass block are fusion-connected by a laser. An optical fiber terminal structure with a core-clad structure,
A glass rod fused and connected to the optical fiber and having no core / clad structure;
An optical fiber terminal structure comprising: a glass block fused and connected to the glass rod on the opposite side of the optical fiber, and having a larger outer diameter than the glass rod and not having the core / cladding structure. .   The length of the glass rod in the axial direction is set such that light emitted from the core of the optical fiber and propagating through the glass rod does not reach the outer peripheral surface of the glass rod. The optical fiber terminal structure according to claim 12. A concave portion for positioning the glass rod is provided on an end surface of the glass block to be fused with the glass rod,
The optical fiber terminal structure according to claim 12 or 13, wherein the glass rod is fusion-bonded to the glass block in a state of being accommodated in the recess.

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