JP2021121839A - Method for connecting optical fiber and method for manufacturing optical fiber connection body - Google Patents

Abstract

To provide a method for connecting an optical fiber capable of suppressing the change of refractive index distribution, and a method for manufacturing an optical fiber connection body.SOLUTION: A method for connecting an optical fiber includes a fusion connection step S2 of fusing and connecting the end surfaces of a pair of optical fibers including a cladding having a diameter of 255 μm or more and 380 μm or less to each other. The fusion connection step comprises: a pre-discharge step S2a of heating the respective end surfaces by discharge toward the respective end surfaces in the state of approaching the respective end surfaces arranged to face each other and be separated or the state of separating the end surfaces by a predetermined distance and contacting the respective end surface; and a discharge step S2b of intermittently heating the respective end surfaces by intermittent discharge toward the contacted respective end surfaces.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for connecting an optical fiber and a method for manufacturing an optical fiber connector.

Generally, in the connection of a pair of optical fibers, it is necessary to optically connect the respective optical fibers. Therefore, for example, the end faces of the respective optical fibers are butted against each other, the central axes of the respective optical fibers are positioned coaxially, and then the respective optical fibers are connected. The following Patent Document 1 describes a connection step for connecting each optical fiber. The connection step described in Patent Document 1 is divided into the following pre-discharge step and main discharge step.

In the pre-discharge step, the end faces of the optical fibers arranged so as to face each other are brought close to each other, and the end faces are heated by the discharge toward the end faces. By heating, the end faces of each optical fiber are softened, fine irregularities on each end face are removed by surface tension, and each end face is shaped into a flat surface. Then, the end faces of the respective optical fibers are brought closer to each other, and the end faces are abutted and connected.

Further, in this discharge step, each end face is further heated by the discharge toward each end face in a state where each end face is pressure-welded. Under heating conditions, each end face is further shaped into a flat surface, the connection is strengthened, and a fiber optic connector is constructed.

Further, Patent Document 2 describes an example of discharging to an optical fiber. The optical fiber connection method described in Patent Document 2 is for facilitating alignment in a stage prior to fusion splicing of a double clad fiber having a non-circular cross section and a single mode fiber having a circular cross section. In the process of making the cross-sectional shape of the double clad fiber circular, intermittent discharge is performed on the double clad fiber by alternately repeating discharge and non-discharge a plurality of times. The non-discharge time in the intermittent discharge is, for example, several tens of μs to several hundreds of μs.

Japanese Unexamined Patent Publication No. 53-39143 Japanese Unexamined Patent Publication No. 2011-203544

Large-diameter optical fibers may be used in recent optical fiber communication systems, fiber laser devices, and the like. The diameter of the clad of a normal optical fiber is, for example, 125 μm, whereas the diameter of the clad of a large-diameter optical fiber is, for example, 200 μm or more.

When the present discharge step described in Patent Document 1 is used for connecting such a large-diameter optical fiber, the heating time in the present discharge step depends on the diameter of the clad in order to shape the end face and strengthen the connection. It needs to be long. If the heating time is long, there is a concern that the refractive index distribution of the optical fiber may change locally around the optical fiber connector. Such a change in the refractive index distribution occurs mainly due to the release of residual stress by heating and the diffusion and sublimation of the dopant.

Here, the release of the residual stress will be described. Generally, in the process of forming an optical fiber by solidifying the optical fiber base material in a molten state to be drawn, the core receives stress from the clad due to the difference between the coefficient of thermal expansion of the core and the coefficient of thermal expansion of the clad, and the stress is applied. Remains in the core. In the optical fiber connection process, when the optical fiber is heated by electric discharge and the core of the optical fiber is melted, the residual stress remaining in the core is released. Due to the release of residual stress, the density distribution of the glass constituting the optical fiber changes, and the refractive index distribution changes.

Next, diffusion and sublimation of the dopant will be described. When one or more kinds of dopants are added to an optical fiber, when the periphery of the end face is heated to the extent that it melts in the optical fiber connection step, the dopant diffuses from the periphery of the end face in the radial direction of the optical fiber or from the end face. Can be sublimated. The refractive index distribution changes due to the diffusion and sublimation of the dopant.

Further, when the intermittent discharge in the optical fiber connection method described in Patent Document 2 is used for connecting a large-diameter optical fiber, heat due to the discharge is generated before the end face is shaped and before the connection at the end face is strengthened. It is transmitted to the core, and there is a concern that the core will melt. There is a concern that the melting of the core causes the dopant to diffuse or sublimate, and the diffusion or sublimation changes the refractive index distribution.

Therefore, an object of the present invention is to provide a method for connecting an optical fiber and a method for manufacturing an optical fiber connector capable of suppressing a change in the refractive index distribution.

In order to solve the above problems, the optical fiber connecting method of the present invention includes a fusion splicing step of fusing and connecting the end faces of a pair of optical fibers having a clad having a diameter of 255 μm or more and 380 μm or less to each other. In the connection step, the end faces are heated by electric discharge toward the end faces in a state where the end faces are brought close to each other or the end faces are separated from each other by a predetermined distance, and the respective end faces are heated. It is characterized by including a pre-discharge step in which the end faces are brought into contact with each other and a main discharge step in which the end faces are intermittently heated by intermittent discharge toward the end faces that are in contact with each other.

Further, the method for manufacturing an optical fiber connector of the present invention includes a step of fusing and connecting the end faces of a pair of optical fibers having a clad having a diameter of 255 μm or more and 380 μm or less by the above-mentioned optical fiber connection method. It is a feature.

According to such an optical fiber connecting method and an optical fiber connecting body manufacturing method, the clad is melted by the intermittent heating of the end face in this discharge step, and the heat applied to the core can be minimized. When the heat is minimized, the release of residual stress remaining in the core can be suppressed, and the diffusion and sublimation of the dopant can be suppressed when the dopant is added to the optical fiber. Therefore, in the optical fiber connecting method and the optical fiber connecting body manufacturing method of the present invention, changes in the refractive index distribution can be suppressed.

Further, in the intermittent discharge, it is preferable that the discharge for 350 msec and the non-discharge for 50 msec are alternately and repeatedly performed.

In this case, the natural cooling time of the optical fiber is secured by the non-discharging time of 50 msec. Therefore, heat transfer to the center of the core 21 is further suppressed. When the heat transfer is suppressed, the release of the residual stress remaining in the core 21 can be further suppressed, and the diffusion and sublimation of the dopant added to the optical fiber 20 can be further suppressed. Therefore, changes in the refractive index distribution can be further suppressed.

Further, when the diameter of the clad is D and the minimum number of the cycles required for fusion splicing is S when one discharge and one non-discharge are one cycle, the minimum number of the cycles is assumed. The number S is preferably calculated from the following formula.
S = 0.2 × D-46

In this case, the fusion splicing in the optical fiber connector 10 can be even more sufficient.

Further, boron may be added as a dopant to at least one core of the optical fiber.

As described above, according to the present invention, it is possible to provide a method for connecting an optical fiber and a method for manufacturing an optical fiber connector that can suppress a change in the refractive index distribution.

It is a figure which shows the optical fiber connector which concerns on embodiment of this invention. It is sectional drawing which is perpendicular to the longitudinal direction of each optical fiber shown in FIG. It is a flowchart which shows the step of the connection method of an optical fiber. It is a figure which shows the state of the facing step. It is a figure which shows the state of the pre-discharge step. It is a figure which shows the state of this discharge step. It is a figure which shows the relationship between the diameter of a clad and the minimum number of cycles in Example 1-10. It is a figure which shows the relationship between the distance from the end face of the other optical fiber, the average specific refractive index difference, and the coupling efficiency of a basic mode in Example 11 and Comparative Example 1. In Example 12, the refractive index distribution seen from a certain radial direction of the cross section of the core, the first clad, and the second clad at 20 μm and 500 μm from the end face of the other optical fiber in the longitudinal direction of the other optical fiber is shown. The expansion of the relationship between the periphery of the center of the core and the refractive index distribution shown in FIG. 9 is shown. In Comparative Example 2, the refractive index distributions seen from a certain radial direction of the cross section of the core, the first clad, and the second clad at 20 μm and 500 μm from the end face of the other optical fiber in the longitudinal direction of the other optical fiber are shown. The expansion of the relationship between the periphery of the center of the core and the refractive index distribution shown in FIG. 11 is shown. In Comparative Example 3, the refractive index distribution seen from a certain radial direction of the cross section of the core, the first clad, and the second clad at 20 μm and 500 μm from the end face of the other optical fiber in the longitudinal direction of the other optical fiber is shown. The expansion of the relationship between the periphery of the center of the core and the refractive index distribution shown in FIG. 13 is shown.

Hereinafter, preferred embodiments of the optical fiber connecting method and the manufacturing method of the optical fiber connecting body according to the present invention will be described in detail with reference to the drawings. The embodiments illustrated below are for facilitating the understanding of the present invention, and are not for limiting the interpretation of the present invention. The present invention can be modified and improved without departing from the spirit of the present invention. In addition, the present invention may appropriately combine the components in each of the embodiments exemplified below. For ease of understanding, some parts may be exaggerated in each figure.

First, the configuration of the optical fiber connector 10 according to the present embodiment will be described. FIG. 1 is a diagram showing an optical fiber connector 10 according to an embodiment. As shown in FIG. 1, the optical fiber connector 10 of the present embodiment is configured by fusing and connecting a plurality of optical fibers 20 at their respective end faces 40. FIG. 1 shows an example in which a pair of optical fibers 20 are fusion-bonded. The optical fiber connector 10 is used in, for example, an optical fiber communication system, a fiber laser device, or the like. In the optical fiber connector 10, the coating layer is peeled off around the end face 40 as described later, but the appearance of the coating layer being peeled off is omitted in FIG.

FIG. 2 is a cross-sectional view perpendicular to the longitudinal direction of each optical fiber 20 shown in FIG. Each optical fiber 20 has the same configuration as each other. Here, one optical fiber 20 will be described. The optical fiber 20 surrounds the core 21 through which light propagates and the outer peripheral surface of the core 21 over the entire circumference, and the clad 23 that adheres to the outer peripheral surface of the core 21 without gaps and the outer peripheral surface of the clad 23 over the entire circumference. It has a coating layer 27 that surrounds the clad 23 and adheres to the outer peripheral surface of the clad 23 without gaps.

The cross section of the core 21 in the direction perpendicular to the longitudinal direction of the optical fiber 20 is circular, and the core 21 is arranged at the center of the clad 23. Further, the cross section of the clad 23 in the direction perpendicular to the longitudinal direction of the optical fiber 20 is circular. The diameter of the core 21 is, for example, 25 μm or more and 36 μm or less. The diameter of the clad 23 is 255 μm or more and 380 μm or less.

The refractive index of the core 21 is made higher than the refractive index of the clad 23. In the present embodiment, the core 21 is made of silica glass to which a dopant having a high refractive index such as germanium (Ge) is added, and the clad 23 is made of silica glass without any additives. The core 21 is made of silica glass to which a dopant having a high refractive index is added, and the clad 23 is made of silica glass to which a dopant having a low refractive index such as fluorine (F) and boron (B) is added. May be good. Alternatively, the core 21 may be made of silica glass without any additives, and the clad 23 may be made of silica glass to which a dopant having a low refractive index is added. The coating layer 27 is made of, for example, a photocurable resin.

In such an optical fiber connector 10, for example, light propagates through each core 21 in a single mode.

Next, a manufacturing method for manufacturing the optical fiber connector 10 by fusion-connecting the optical fibers 20 by the connection method of the optical fiber 20 for fusion-connecting the optical fibers 20 and the connection method for the optical fiber 20 will be described. FIG. 3 is a flowchart showing a step of a method of connecting the optical fiber 20 and a process of a method of manufacturing the optical fiber connector 10. As shown in FIG. 3, the connection method of the optical fiber 20 includes a facing step S1 and a fusion splicing step S2 as main steps. Further, in the manufacturing method for manufacturing the optical fiber connector 10, the end faces 40 of the pair of optical fibers 20 having a clad 23 having a diameter of 255 μm or more and 380 μm or less are fused and connected to each other by the connection method of the optical fiber 20 shown in FIG. Have a process.

<Opposite step S1>
FIG. 4 is a diagram showing the state of this step S1. This step S1 is a step in which the end faces 40 of the respective optical fibers 20 are arranged so as to face each other and are separated from each other. In this step S1, first, each optical fiber 20 shown in FIG. 1 is set in a fusion splicer (not shown). Before each optical fiber 20 is set in the fusion splicer, the coating layer 27 around the end face 40 of each optical fiber 20 is peeled off. Therefore, the coating layer 27 is not shown in FIG. The length of the region to be peeled off in the longitudinal direction of the optical fiber 20 is, for example, 10 mm from the end face 40. The fusion splicer is arranged in an environment of, for example, a temperature of 25 degrees and a humidity of 40%.

In the fusion splicer, each optical fiber 20 is arranged horizontally, the end faces 40 of each optical fiber 20 are arranged so as to face each other, and the central axis C of each optical fiber 20 is coaxially located. In this state, each optical fiber 20 is set. In order to align the central axes C of the optical fibers 20, for example, the side surfaces of the respective optical fibers 20 may be observed so that the outer peripheral surfaces of the clad 23 of the respective optical fibers 20 are flush with each other.

In this embodiment, the fusion splicer includes a pair of discharge electrodes 50 that heat the end face 40 of the optical fiber 20. In this step S1, each optical fiber 20 is preferably set so that the straight line SL connecting the tips of the pair of discharge electrodes 50 is located between the end faces 40 of the respective optical fibers 20.

In this way, the end faces 40 of each optical fiber 20 are arranged so as to face each other and are separated from each other.

<Fusion connection step S2>
This step S2 is a step in which the end faces 40 of the optical fibers 20 arranged so as to face each other and separated from each other in the facing step S1 are fused and connected. This step S2 includes a pre-discharge step S2a and a main discharge step S2b.

<Pre-discharge step S2a>
FIG. 5 is a diagram showing the state of this step S2a. In this step S2a, the end faces 40 are heated by electric discharge toward the end faces 40 in a state where the end faces 40 arranged so as to face each other and are separated from each other are brought close to each other or the end faces 40 are separated by a predetermined distance. This is a step of bringing the end faces 40 into contact with each other.

Specifically, in a state where one optical fiber 20 is brought close to the other optical fiber 20 so that the end faces 40 arranged so as to face each other and are separated from each other are brought close to each other, the discharge electrode 50 of the fusion splicer is moved in the vertical direction. Vibrate so that it repeatedly swings. Due to the vibration of the discharge electrode 50, the straight line SL connecting the tips of the discharge electrodes 50 moves in a plane perpendicular to the central axis C of each optical fiber 20. Then, while the tip of the discharge electrode 50 is reciprocating in the vertical direction, a high voltage is applied between the pair of discharge electrodes 50 to perform discharge. At this time, when viewed from a direction perpendicular to the central axis C of the optical fiber 20, the discharge electrodes 50 swing in synchronization with each other so that the surface formed by the moving straight line SL covers the entire end surface 40. Is preferable. By swinging the discharge electrode 50 in this way, uneven heating on the end face 40 is suppressed as compared with the case where the surface formed by the moving straight line SL does not cover the end face 40.

When the energy generated by the discharge from the discharge electrode 50 toward each end face 40 is converted into heat, the end faces 40 of the respective optical fibers 20 arranged opposite to each other and separated from each other are heated and softened. At this time, first, the outer peripheral edge of the end face 40 is softened and rounded by surface tension, and fine irregularities on each softened end face 40 are removed to form the end face 40 into a flat surface. Then, the end faces 40 of each optical fiber 20 come closer to each other, and the end faces 40 come into contact with each other and are fused and connected.

In this step S2a, a part of the end face 40 of each optical fiber 20 is fused, and the other part of the end face 40 is not fused. For example, the core 21 of each optical fiber 20 having a low melting point is fused, but the clad 23 of each optical fiber 20 having a high melting point is locally melted, so that each clad 23 is locally fused. There is. Therefore, the connection strength at each end face 40 is weak, and when stress is concentrated on the clad 23 at the end face 40, the optical fiber 20 is easily broken.

In this way, the end faces 40 of each optical fiber 20 are shaped, abutted, and fused and connected.

<Main discharge step S2b>
FIG. 6 is a diagram showing the state of this step S2b. This step S2b is a step of intermittently heating each end face 40 by an intermittent discharge toward each end face 40 that has come into contact with each other.

Specifically, in a state where the end faces 40 that are in contact with each other in the step S2a are pressure-contacted, the discharge electrodes 50 are vibrated in the same manner as in the step S2a, and the discharge electrodes 50 are intermittently directed toward the end faces 40. Discharge. By the intermittent discharge, each end face 40 is intermittently heated and softened, the roundness of the outer peripheral edge of the clad 23 is eliminated by softening and pressure welding, and each end face 40 is further shaped into a flat surface. Further, each clad 23 is further melted and fused by heat. Then, when the respective optical fibers 20 are fused and connected, the discharge is stopped.

In the intermittent discharge in this step S2b, for example, the discharge current is set to 24 mA, one discharge time is set to 350 msec, and one non-discharge time, which is the time when discharge is stopped, is set to 50 msec. The discharge for 350 msec and the non-discharge for 50 msec are alternately and repeatedly performed. Here, let D be the diameter of the clad 23, and let S be the minimum number of cycles required for fusion splicing when one discharge and one non-discharge are one cycle. Then, the minimum number S of the cycle is calculated from the following formula.
S = 0.2 × D-46

For example, in a fusion splicer arranged in an environment of a temperature of 25 degrees and a humidity of 40%, one cycle is a cycle in which the discharge current is 24 mA, the discharge time is 350 msec, and the non-discharge time is 50 msec. , Intermittent discharge is performed at least a few seconds S of the cycle.

When the above-mentioned step S2b is performed, the change in the average specific refractive index difference in the region within 400 μm from the end face 40 becomes 0.002% or less in the longitudinal direction of the optical fiber 20. The average specific refractive index difference is the ratio between the average refractive index of the core 21 in the radial direction and the average refractive index of the clad 23 in the radial direction and the average refractive index of the core 21.

It is not necessary to continuously heat the end face 40 of each optical fiber 20 from the pre-discharge step S2a to the main discharge step S2b, but it is preferable to continuously heat the end face 40. By continuously heating, the end face 40 can be maintained in a softened state.

In this way, the respective optical fibers 20 are fused and connected, and the respective cores 21 of the respective optical fibers 20 are optically coupled to each other to manufacture the optical fiber connector 10 shown in FIG. In the optical fiber connection body 10 manufactured in this way, the connection strength at each end face 40 becomes strong, and even if stress is concentrated on the clad 23 at the end face 40, the optical fiber 20 is hard to break. Further, the minimum number S of cycles makes the fusion splicing in the optical fiber connector 10 sufficient.

As described above, the connection method of the optical fiber 20 of the present embodiment includes the fusion connection step S2 in which the end faces 40 of the pair of optical fibers 20 having the clad 23 having a diameter of 255 μm or more and 380 μm or less are fusion-bonded to each other. In the fusion splicing connection step S2, each end face 40 is heated by electric discharge toward each end face 40 in a state where the end faces 40 arranged so as to face each other are brought close to each other or the end faces 40 are separated by a predetermined distance. It includes a pre-discharge step S2a in which each end face 40 is brought into contact with each other, and a main discharge step S2b in which each end face 40 is intermittently heated by intermittent discharge toward each of the contacted end faces 40.

Further, in the method for manufacturing the optical fiber connector 10 of the present embodiment, the end faces 40 of a pair of optical fibers 20 having a clad 23 having a diameter of 255 μm or more and 380 μm or less are fused and connected to each other by the above-mentioned connection method of the optical fiber 20. Provide a step to make it.

According to the method of connecting the optical fiber 20 and the method of manufacturing the optical fiber connector 10, the clad 23 is melted by the intermittent heating of the end face 40 in the present discharge step S2b, and the heat applied to the core 21 is minimized. Can be. When the heat is minimized, the release of the residual stress remaining in the core 21 can be suppressed, and when the dopant is added to the optical fiber 20, the diffusion and sublimation of the dopant added to the optical fiber 20 can be suppressed. Therefore, in the method of connecting the optical fiber 20 and the method of manufacturing the optical fiber connector 10 of the present embodiment, the change in the refractive index distribution can be suppressed.

Further, the basic modes of the light propagating in the core 21 are likely to overlap in the longitudinal direction of the optical fiber 20 by suppressing the change in the refractive index distribution. Therefore, the excitation from the basic mode to the higher-order mode can be suppressed. Further, in the fusion splicing of the large-diameter optical fiber 20, even if the discharge time becomes longer according to the diameter of the clad 23, the natural cooling time of the optical fiber 20 is secured by the intermittent heating of the end face 40. Therefore, the clad 23 is melted, the heat applied to the core 21 is suppressed, the change in the refractive index distribution is suppressed, and the excitation from the basic mode to the higher-order mode can be suppressed.

Further, since the natural cooling time is secured by the intermittent heating of the end face 40, it is not necessary to reduce the value of the discharge current while maintaining the discharge time, and the end face 40 is shaped and melted at the end face 40. Strengthening of incoming connection can be sufficient. Further, for example, when light propagates through the clad 23, the scattering of light at the connection interface can be suppressed and the occurrence of light loss can be suppressed by sufficiently strengthening the fusion splicing described above. Further, since the fusion splicing is sufficiently strengthened, the decrease in the mechanical strength of the optical fiber connector 10 is suppressed, and the optical fiber 20 may be hard to break.

Further, in the method of connecting the optical fiber 20 and the method of manufacturing the optical fiber connector 10 of the present embodiment, in the intermittent discharge, discharge for 350 msec and non-discharge for 50 msec are alternately and repeatedly performed.

Therefore, the natural cooling time of the optical fiber 20 is secured by the non-discharging time of 50 msec. Therefore, heat transfer to the center of the core 21 is further suppressed. When the heat transfer is suppressed, the release of the residual stress remaining in the core 21 can be further suppressed, and the diffusion and sublimation of the dopant added to the optical fiber 20 can be further suppressed. Therefore, changes in the refractive index distribution can be further suppressed.

Further, in the method of connecting the optical fiber 20 and the method of manufacturing the optical fiber connector 10 of the present embodiment, when the diameter of the clad 23 is D and one discharge and one non-discharge are one cycle. Assuming that the minimum number of cycles required for fusion splicing is S, the minimum number of cycles S is calculated from the following equation.
S = 0.2 × D-46

Therefore, if the cycle is at least several S or more with respect to the diameter D of the clad 23, the fusion splicing in the optical fiber connector 10 can be sufficient.

Although the present invention has been described above by taking the above-described embodiment as an example, the present invention is not limited thereto.

For example, boron may be added as a dopant to the core 21 of at least one optical fiber 20.

Further, even if the optical fiber 20 is an amplification optical fiber in which an active element that is excited by excitation light is added to the core, the change in the refractive index distribution is suppressed, so that the optical fiber 20 is used for amplification due to the change in the refractive index distribution. Deterioration of the quality of the optical fiber can be suppressed.

Further, in the intermittent discharge, one discharge time is set to 350 msec, and one non-discharge time, which is the time when the discharge is stopped, is set to 50 msec, but it is not necessary to be limited to this. No. For example, in the above-mentioned intermittent discharge, one discharge time may be longer than one non-discharge time. In this case, the natural cooling time of the optical fiber 20 can be easily reduced within an acceptable range as compared with the case where one discharge time is less than or equal to one non-discharge time. Therefore, it may be possible to perform fusion splicing of a pair of optical fibers more quickly.

Hereinafter, the content of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(Example 1)
In this embodiment, the optical fibers 20 are fused and connected by the method of connecting the optical fibers 20 shown in the embodiment.

First, in this embodiment, a pair of optical fibers 20 were prepared. Each of the prepared optical fibers 20 is made of glass to which the core 21 is added with aluminum (Al), ytterbium (Yb), boron (B) and phosphorus (P) whose refractive index is increased, and the clad 23 is added with any dopant. It was made of uncoated glass, and the coating layer 27 was made of a photocurable resin.

In this example, the diameter of the core 21 was 25 μm and the diameter of the clad 23 was 255 μm.

Next, each of the prepared optical fibers 20 was set in the fusion splicer in the same manner as in the embodiment. Before each optical fiber 20 was set in the fusion splicer, the coating layer 27 of one optical fiber 20 and the coating layer 27 of the other optical fiber 20 were peeled off. The length of the region to be peeled off in the longitudinal direction of the optical fiber 20 was set to 10 mm from the end face 40. The fusion splicer was FSM-100P + manufactured by Fujikura Co., Ltd. The fusion splicer was placed in an environment with a temperature of 25 ° C. and a humidity of 40%. In the intermittent discharge in the present discharge step S2b, the discharge current was set to 24 mA, one discharge time was set to 350 msec, and one non-discharge time was set to 50 msec. Here, one discharge and one non-discharge are regarded as one cycle.

In this embodiment, the optical fibers 20 are fused and connected with the number of cycles being four.

(Example 2)
In this example, the optical fibers 20 were fused and connected in the same manner as in Example 1 using the optical fibers 20 of Example 1 except that the number of cycles was set to 5.

(Example 3)
In this embodiment, a pair of optical fibers 20 different from those in the first embodiment were prepared.

In each of the optical fibers 20 prepared in this embodiment, the core 21 is added with aluminum (Al), ytterbium (Yb), boron (B) and phosphorus (P), which increase the refractive index, to the center side of the core 21. The core 21 is made of glass to which germanium (Ge) is added to the outer peripheral edge side, the clad 23 is made of glass to which no dopant is added, and the coating layer 27 is made of a photocurable resin. rice field.

In this example, the diameter of the core 21 was 28 μm, and the diameter of the first clad was 280 μm.

In this embodiment, the number of cycles is set to 5, and the optical fibers 20 are fused and connected in the same manner as in Example 1.

(Example 4)
In this example, the optical fibers 20 were fused and connected in the same manner as in Example 1 using the optical fibers 20 of Example 3 except that the number of cycles was set to 9.

(Example 5)
In this example, the optical fibers 20 were fused and connected in the same manner as in Example 1 using the optical fibers 20 of Example 3 except that the number of cycles was set to 10.

(Example 6)
In this embodiment, the optical fibers 20 are fused and connected in the same manner as in Example 1 using the optical fibers 20 of Example 3 except that the number of cycles is 15 times.

(Example 7)
In this embodiment, a pair of optical fibers 20 different from those in the first embodiment were prepared.

In each of the optical fibers 20 prepared in this embodiment, the core 21 is added with aluminum (Al), ytterbium (Yb), boron (B) and phosphorus (P), which increase the refractive index, to the center side of the core 21. The core 21 is made of glass to which germanium (Ge) is added to the outer peripheral edge side, the clad 23 is made of glass to which no dopant is added, and the coating layer 27 is made of a photocurable resin. rice field.

In this example, the diameter of the core 21 was 36 μm, and the diameter of the first clad was 380 μm.

In this embodiment, the number of cycles is set to 10 and the optical fibers 20 are fused and connected in the same manner as in Example 1.

(Example 8)
In this embodiment, the optical fibers 20 are fused and connected in the same manner as in Example 1 using the optical fibers 20 of Example 7 except that the number of cycles is 20 times.

(Example 9)
In this embodiment, the optical fibers 20 are fused and connected in the same manner as in Example 1 using the optical fibers 20 of Example 7 except that the number of cycles is 25.

(Example 10)
In this embodiment, the optical fibers 20 are fused and connected in the same manner as in Example 1 using the optical fibers 20 of Example 7 except that the number of cycles is 30.

With respect to the optical fiber 20 fused and connected as described above, the leakage of light from the optical fiber connector 10 was visually observed. At this time, visible light was propagated to the optical fiber 20, and the scattering of visible light from the optical fiber connector 10 was visually confirmed through a CCD camera arranged in the fusion splicer. When scattering was confirmed, it was determined that the fusion splicing in the optical fiber connector 10 was insufficient, and when the scattering was too small to be confirmed, it was determined that the fusion splicing in the optical fiber connector 10 was sufficient. Table 1 shows the confirmation results of the diameter of the clad 23, the number of cycles, and scattering in Examples 1-10.

The circles in Table 1 indicate that the scattering is too small to be confirmed as a confirmation result, and the triangles in Table 1 indicate that the scattering is confirmed as a confirmation result. As shown in Table 1, in Examples 2, 5, 6 and 10, it was determined that the fusion splicing in the optical fiber connector 10 was sufficient.

Table 2 shows the results of extracting from Table 1 the diameter of the clad 23 and the minimum number of cycles when it is determined that the fusion splicing in the optical fiber connector 10 is sufficient for the diameter of the clad 23. show. It was determined that the fusion splicing in the optical fiber connector 10 was sufficient if the number was at least the minimum number with respect to the diameter of the clad 23.

FIG. 7 is a diagram showing the relationship between the diameter of the clad 23 and the minimum number of cycles in Table 2. As shown in FIG. 7, it was obtained that the minimum number of cycles had linearity with respect to the diameter of the clad 23.

Here, assuming that the diameter of the clad 23 is D and the minimum number of cycles required to suppress the change in the refractive index distribution is S when one discharge and one non-discharge are one cycle, the cycle is cycled. The result was obtained that the minimum number S of was calculated from the following formula.
S = 0.2 × D-46

Therefore, if the cycle is at least several S or more with respect to the diameter D of the clad 23, the fusion splicing in the optical fiber connector 10 can be even more sufficient.

(Example 11)
First, in this embodiment, a pair of optical fibers different from the pair of optical fibers 20 of the embodiment are prepared.

In this example, one of the prepared optical fibers was a double clad fiber. This optical fiber surrounds the core and the outer peripheral surface of the core over the entire circumference, and surrounds the first clad and the outer peripheral surface of the first clad that are in close contact with the outer peripheral surface of the core over the entire circumference. It has a second clad that adheres to the outer peripheral surface of the clad without gaps, and a coating layer that surrounds the outer peripheral surface of the second clad over the entire circumference and adheres to the outer peripheral surface of the second clad without gaps.

The core consisted of silica glass to which germanium (Ge), which increases the refractive index, was added. The first clad was made of silica glass to which no dopant was added. The second clad was made of a resin having a lower refractive index than the first clad. The coating layer was made of a resin different from the resin constituting the second clad.

In one of the optical fibers of this example, the difference in the specific refractive index between the core and the first clad was 0.115%. The diameter of the core was 28 μm, and the diameter of the first clad was 280 μm.

In this example, the other optical fiber prepared was a triple clad fiber. This optical fiber surrounds the core and the outer peripheral surface of the core over the entire circumference, and surrounds the first clad and the outer peripheral surface of the first clad that are in close contact with the outer peripheral surface of the core over the entire circumference. The second clad that adheres tightly to the outer peripheral surface of the clad, the third clad that surrounds the outer peripheral surface of the second clad over the entire circumference and closely adheres to the outer peripheral surface of the second clad, and the outer peripheral surface of the third clad. Has a coating layer that closely adheres to the outer peripheral surface of the third clad without a gap.

The core consisted of silica glass to which dopants such as boron (B) and germanium (Ge), which increase the refractive index, were added. The first clad was made of silica glass to which no dopant was added. The second clad was made of glass to which fluorine (F), which lowers the refractive index, was added. The third clad was made of a resin having a lower refractive index than the second clad. The coating layer was made of a resin different from the resin constituting the third clad.

In the other optical fiber of this example, the difference in the specific refractive index between the core and the first clad was 0.130%. The diameter of the core was 28 μm, and the diameter of the first clad was 280 μm.

Next, each of the optical fibers prepared in this embodiment was set in the fusion splicer in the same manner as in the embodiment. Before each optical fiber was set in the fusion splicer, the second clad and coating layer of one optical fiber and the third clad and coating layer of the other optical fiber were peeled off. The length of the peeled region in the longitudinal direction of the optical fiber was set to 10 mm from the end face. In the present discharge step S2b of this embodiment, in the intermittent discharge in the present discharge step S2b with respect to one end of one optical fiber, the discharge current is set to 24 mA, one discharge time is set to 350 msec, and one time. The non-discharge time was set to 50 msec. Here, when one discharge and one non-discharge are regarded as one cycle, the number of cycles is set to 10. In this example, it was observed by the leakage of light in the optical fiber connector 10 as described above.

After confirming that the change in the refractive index distribution was suppressed, the refractive index distribution at the end face of the other optical fiber was measured in the longitudinal direction of the other optical fiber, and the average specific refractive index difference was measured. The coupling efficiency of the basic mode was also calculated from the overlap integral of the electrolytic distribution of the basic mode estimated from the refractive index distribution. The overlap integral was calculated by the electrolytic distribution of the other optical fiber and the electrolytic distribution at the end face of one optical fiber.

FIG. 8 shows the relationship between the distance from the end face of the other optical fiber in the longitudinal direction of the other optical fiber, the difference in the average refractive index, and the coupling efficiency of the basic mode in this embodiment. The vertical axis on the left side of FIG. 8 shows the average refractive index difference (%), the vertical axis on the right side of FIG. 8 shows the coupling efficiency of the basic mode, and the horizontal axis of FIG. 8 shows the distance (μm) from the end face. ..

In the fusion splicing step S2, when the optical fiber is melted by electric discharge, the residual stress remaining in the core is released. In this example, as shown by the solid line in FIG. 8, the result was obtained that the average specific refractive index difference was reduced by releasing the residual stress in the range of the distance from the end face in the range of 0 μm to 400 μm. Further, as shown by the broken line in FIG. 8, it is considered that the change in the average specific refractive index difference due to the diffusion and sublimation of the added dopant was suppressed in the range of the distance from the end face of 50 μm or more and 400 μm or less. In addition, the result was that the decrease in light binding efficiency was suppressed.

(Comparative Example 1)
In this comparative example, the same pair of optical fibers as in Example 11 was prepared.

Each optical fiber of this comparative example was set in a fusion splicer in the same manner as in Example 11. In this comparative example, the main discharge step S2b was performed under conditions different from the conditions of the main discharge step S2b shown in Example 11. In the present discharge step S2b of this comparative example, the discharge current was set to 24 mA and the one discharge time was set to 1750 msec in the discharge in the present discharge step S2b with respect to one end of one optical fiber. In the present discharge step S2b of this comparative example, when one discharge time is 350 msec and one discharge is one cycle, the number of cycles is continuously set to five, and the non-discharge is Not done. In this comparative example, it was observed by the leakage of light in the optical fiber connector 10 as described above.

After confirming that the change in the refractive index distribution was suppressed, the average specific refractive index difference and the coupling efficiency of the basic mode were calculated in the same manner as in Example 11.

FIG. 8 shows the relationship between the distance from the end face of the other optical fiber in the longitudinal direction of the other optical fiber, the difference in the average refractive index, and the coupling efficiency in the basic mode in this comparative example.

Unlike the eleventh embodiment, the average refractive index difference increases due to the release of the residual stress toward the distance from the end face in the range of 400 μm to 0 μm, and the average specific refractive index difference and the distance in the region where the distance is 400 μm. The result was obtained that the difference from the average specific refractive index difference in the region where was 0 μm was 0.002% or more. Further, as shown by the alternate long and short dash line in FIG. 8, it is considered that a change in the average specific refractive index difference occurs due to diffusion and sublimation of the added dopant in the range of 50 μm or more and 500 μm or less from the end face. In addition, the result was that the light binding efficiency was reduced.

(Example 12)
First, in this embodiment, a pair of optical fibers different from the pair of optical fibers 20 of the embodiment are prepared.

In this embodiment, the configuration of one optical fiber is the same as the configuration of the optical fiber of Example 11.

In one of the optical fibers of this example, the difference in the specific refractive index between the core and the first clad was 0.115%. The diameter of the core was 28 μm, and the diameter of the first clad was 280 μm.

In this embodiment, the other optical fiber is a double clad fiber. This optical fiber surrounds the core and the outer peripheral surface of the core over the entire circumference, and surrounds the first clad and the outer peripheral surface of the first clad that are in close contact with the outer peripheral surface of the core over the entire circumference. It has a second clad that adheres to the outer peripheral surface of the clad without gaps, and a coating layer that surrounds the outer peripheral surface of the second clad over the entire circumference and adheres to the outer peripheral surface of the second clad without gaps.

The core is a silica glass in which aluminum (Al), ytterbium (Yb), boron (B) and phosphorus (P), which increase the refractive index, are added to the central side of the core, and germanium (Ge) is added to the outer peripheral edge side of the core. It consisted of. The first clad was made of glass to which no dopant was added. The second clad was made of a resin having a lower refractive index than the first clad. The coating layer was made of a resin different from the resin constituting the third clad.

In this example, in the other optical fiber, the difference in the specific refractive index between the core and the first clad was 0.125%. The diameter of the core was 28 μm, and the diameter of the first clad was 280 μm.

Next, each of the optical fibers prepared in this embodiment was set in the fusion splicer in the same manner as in the embodiment. Before each optical fiber was set in the fusion splicer, the second clad and coating layer of one optical fiber and the second clad and coating layer of the other optical fiber were peeled off. The length of the peeled region in the longitudinal direction of the optical fiber was set to 10 mm from the end face. In this embodiment, for one end of one optical fiber, in the intermittent discharge in the present discharge step S2b, the discharge current is 24 mA, one discharge time is 350 msec, and one non-discharge time is 50 m. It was set to seconds. Here, when one discharge and one non-discharge are regarded as one cycle, the number of cycles is set to 10. In this example, it was observed by the leakage of light in the optical fiber connector 10 as described above.

After confirming that the change in the refractive index distribution was suppressed, the refractive index distribution at the end face of the other optical fiber was measured in the longitudinal direction of the other optical fiber, and the average specific refractive index difference was measured.

FIG. 9 shows the refractive index distribution seen from the radial direction of the cross section of the core, the first clad, and the second clad at 20 μm and 500 μm from the end face of the other optical fiber in the longitudinal direction of the other optical fiber. The vertical axis of FIG. 9 shows the specific refractive index difference (%), and the horizontal axis of FIG. 9 shows the distance (μm) from the center of the core in the radial direction of the core. FIG. 10 shows an enlarged view of the graph around the center of the core shown in FIG. The solid lines shown in FIGS. 9 and 10 show the distribution of the refractive index at 500 μm from the end face. The broken lines shown in FIGS. 9 and 10 show the distribution of the refractive index at 20 μm from the end face. From FIG. 10, it was obtained that the refractive index distribution shown by the solid line was almost the same as the refractive index distribution shown by the broken line.

(Comparative Example 2)
In this comparative example, the same pair of optical fibers as in Example 12 was prepared.

Each optical fiber of this comparative example was set in a fusion splicer in the same manner as in Example 12. In this comparative example, the main discharge step S2b was performed under conditions different from the conditions of the main discharge step S2b shown in Example 12. In the present discharge step S2b of this comparative example, the discharge current was set to 24 mA and the one discharge time was set to 1750 msec in the discharge in the present discharge step S2b with respect to one end of one optical fiber. In the present discharge step S2b of this comparative example, when one discharge time is 350 msec and one discharge is one cycle, the number of cycles is continuously set to five, and the non-discharge is Not done. In this comparative example, it was observed by the leakage of light in the optical fiber connector 10 as described above.

After confirming that the change in the refractive index distribution was suppressed, the average specific refractive index difference was calculated in the same manner as in Example 12.

FIG. 11 shows the refractive index distribution seen from the radial direction of the cross section of the core, the first clad, and the second clad at 20 μm and 500 μm from the end face of the other optical fiber in the longitudinal direction of the other optical fiber. The vertical axis of FIG. 11 shows the specific refractive index difference (%), and the horizontal axis of FIG. 11 shows the distance (μm) from the center of the core in the radial direction of the core. FIG. 12 shows an enlarged view of the graph around the center of the core shown in FIG. The solid lines shown in FIGS. 11 and 12 show the distribution of the refractive index at 500 μm from the end face. The broken lines shown in FIGS. 11 and 12 show the distribution of the refractive index at 20 μm from the end face. Comparing this comparative example with that of Example 12, it was obtained that the increase in the specific refractive index difference of the optical fiber around the center of the core was remarkable. In particular, when the refractive index distribution shown by the broken line in FIG. 12 was compared with the refractive index distribution shown by the broken line in FIG. 10, the result was obtained that the increase in the specific refractive index difference was remarkable.

(Comparative Example 3)
In this comparative example, the same pair of optical fibers as in Example 12 was prepared.

Each optical fiber of this comparative example was set in a fusion splicer in the same manner as in Example 12. In this comparative example, the main discharge step S2b was performed under conditions different from the conditions of the main discharge step S2b shown in Example 12. In the main discharge step S2b of the present comparative example, the discharge current is 24 mA, one discharge time is 350 msec, and one non-discharge time in the discharge in the present discharge step S2b with respect to one end of one optical fiber. Was set to 20 msec. Here, when one discharge and one non-discharge are regarded as one cycle, the number of cycles is set to 10. In this comparative example, it was observed by the leakage of light in the optical fiber connector 10 as described above.

FIG. 13 shows the refractive index distribution seen from the radial direction of the cross section of the core, the first clad, and the second clad at 20 μm and 500 μm from the end face of the other optical fiber in the longitudinal direction of the other optical fiber. The vertical axis of FIG. 13 shows the specific refractive index difference (%), and the horizontal axis of FIG. 13 shows the distance (μm) from the center of the core in the radial direction of the core. FIG. 14 shows an enlarged view of the graph around the center of the core shown in FIG. The solid lines shown in FIGS. 13 and 14 show the distribution of the refractive index at 500 μm from the end face. The broken lines shown in FIGS. 13 and 14 show the distribution of the refractive index at 20 μm from the end face. As compared with Example 12, the result was obtained that the difference in the specific refractive index of the optical fiber around the center of the core was remarkably increased. In particular, when the refractive index distribution shown by the broken line in FIG. 14 was compared with the refractive index distribution shown by the broken line in FIG. 10, the result was obtained that the increase in the specific refractive index difference was remarkable.

As described above, when Example 12 was compared with Comparative Examples 2 and 3, it was obtained that the increase in the difference in the refractive index around the center of the core was suppressed.

Therefore, it was shown that the change in the refractive index distribution can be suppressed by the method for connecting the optical fiber 20 and the method for manufacturing the optical fiber connector 10 in the present invention.

According to the present invention, a method for connecting an optical fiber and a method for manufacturing an optical fiber connector are provided, and are expected to be used in the field of optical fiber and the like.

10 ... Optical fiber connector 20 ... Optical fiber 21 ... Core 23 ... Clad 27 ... Coating layer 40 ... End face

Claims (5)

It is provided with a fusion splicing step for fusing and connecting the end faces of a pair of optical fibers having a clad having a diameter of 255 μm or more and 380 μm or less.
The fusion splicing step
In a state where the end faces are arranged so as to face each other and are separated from each other, or in a state where the end faces are separated by a predetermined distance, the end faces are heated by electric discharge toward the end faces and the end faces are brought into contact with each other. Pre-discharge step and
The main discharge step of intermittently heating each end face by an intermittent discharge toward each of the contacted end faces,
A method for connecting an optical fiber, which comprises. The method for connecting an optical fiber according to claim 1, wherein in the intermittent discharge, discharge for 350 msec and non-discharge for 50 msec are alternately and repeatedly performed. When the diameter of the clad is D and the minimum number of the cycles required for fusion splicing is S when one discharge and one non-discharge are one cycle, the minimum number S of the cycle is assumed. Is calculated from the following formula S = 0.2 × D-46
The method for connecting an optical fiber according to claim 1 or 2, wherein the optical fiber is connected. The method for connecting an optical fiber according to any one of claims 1 to 3, wherein boron is added as a dopant to at least one core of the optical fiber. The optical fiber connecting method according to any one of claims 1 to 4 comprises a step of fusing and connecting the end faces of a pair of optical fibers having a clad having a diameter of 255 μm or more and 380 μm or less. A method for manufacturing an optical fiber connector.

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