JP2018058719A - Manufacturing method of base material for multi-core fiber and manufacturing method of multi-core fiber using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of base material for multi-core fiber and a manufacturing method of muti-core fiber, the methods capable of suppressing unintended deformation from occurring in cores.SOLUTION: A manufacturing method of base material 1P for multi-core fiber includes: a fixing step P1 of fixing, on at least one end of each of plural core coated rods 2, a large-diameter rod 3 having larger outer diameter than each of the core coated rods 2, each core coated rod having an outer peripheral surface of a core rod 10R as a core 10 coated with a clad glass layer 20R as a part of a clad 20; a bundling step P2 of bundling the plural core coated rods 2 together so that the large-diameter rods 3 respectively fixed to the plural core coated rods 2 are arranged adjacent to each other on side surfaces thereof; and an externally depositing step P3 of depositing soot 6 as the other part of the clad 20 on an outer peripheral surface of the plural core coated rods 2.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a method for manufacturing a base material for a multi-core fiber and a method for manufacturing a multi-core fiber using the same, and more particularly to a method suitable for manufacturing a long multi-core fiber.

  An optical fiber used in a widely used optical fiber communication system has a structure in which an outer periphery of one core is surrounded by a clad, and information is transmitted by propagation of an optical signal in the core. . In recent years, with the spread of optical fiber communication systems, the amount of information transmitted has increased dramatically.

  In order to realize an increase in transmission capacity of such an optical fiber communication system, a plurality of signals are transmitted by light propagating through each core using a multi-core fiber in which the outer circumferences of the plurality of cores are surrounded by one clad. It is known.

  As a method for producing a multi-core fiber preform used for producing such a multi-core fiber, it is known to use a perforation method or a stack and draw method as described in Patent Document 1 below. In the drilling method, first, a plurality of through holes are formed in a glass rod serving as a cladding by a drill or the like. Then, the core-covered rod in which the core rod that becomes the core is covered with the clad glass layer that becomes a part of the clad is inserted into each through hole. Thereafter, an unnecessary gap in the through hole is filled by a collapse process to form a multi-core fiber preform. In the stack and draw method, the core-covered rod is inserted into the through hole of the glass tube that is the outer peripheral portion of the cladding, and a plurality of glass rods are inserted into the gap between the glass tube and the core-covered rod. And the unnecessary clearance gap in the through-hole of a glass tube is filled up by a collapse process, and it is set as the preform | base_material for multi-core fibers.

  By the way, in recent years, there is a need for a larger base material for a multi-core fiber than a request for producing a long multi-core fiber. However, in the perforation method, the size of the base material for the multi-core fiber that can be produced is limited by the thickness of the glass rod to be prepared, and when the diameter of the through hole to be formed increases, the perforation tends to be difficult. In the stack and draw method, the size of the base material for the multi-core fiber that can be produced is limited by the thickness of the glass tube to be prepared. When the thickness of the glass tube increases, it tends to be difficult to handle the glass tube.

  In Patent Document 2 below, a plurality of core materials corresponding to a plurality of core-coated rods whose outer shape perpendicular to the longitudinal direction is a regular hexagon are bundled, soot is deposited on the outer periphery by the VAD method, A method of manufacturing a base material for a multi-core fiber that integrates with a core material is described. According to such a method, since the soot which becomes a clad is deposited on the outer side, a thicker base material for a multi-core fiber can be produced without being limited by the diameter of the glass rod or the glass tube.

JP 09-90143 A JP 09-5541 A

  In the manufacturing method of the base material for multi-core fibers described in Patent Document 2, soot is deposited and sintered by the VAD method after a plurality of core-coated rods are brought into close contact and bundled. When the soot deposited in this manner is sintered, the soot contracts during sintering, and the core covering rod may be deformed by the contraction force. When the core covering rod is deformed in this manner, the core of the optical fiber may be deformed and an optical fiber having the intended performance may not be obtained.

  Therefore, the present invention provides a method for manufacturing a base material for a multi-core fiber and a method for manufacturing a multi-core fiber that can prevent unintended deformation from occurring in the core.

  In order to solve the above-described problem, the method for producing a multi-core fiber preform according to the present invention includes at least each of a plurality of core-covered rods coated with a cladding glass layer in which an outer peripheral surface of a core rod serving as a core is part of a cladding. A fixing step of fixing one end face of a large-diameter rod having an outer diameter larger than the outer diameter of the core-covered rod at one end; and a side surface of the large-diameter rod fixed to each of the plurality of core-covered rods A bundling step of bundling the plurality of core covering rods so as to be adjacent to each other, and an external step of depositing soot as another part of the clad on the outer peripheral surface of the plurality of core covering rods. Features.

  According to such a method for manufacturing a multi-core fiber preform, soot is externally deposited on the outer peripheral surfaces of a plurality of bundled core-coated rods, so that a large-diameter multi-core fiber preform can be manufactured. it can. Further, a large-diameter rod having an outer diameter larger than that of the core-covered rod is fixed to end portions of the plurality of core-coated rods, and the plurality of large-diameter rods are bundled so that the side surfaces are adjacent to each other. For this reason, a plurality of core covering rods are bundled apart from each other. Thus, the gap generated when the plurality of core covering rods are separated from each other can suppress the contraction force generated when the soot deposited on the outer peripheral surface of the core covering rod is sintered from acting on the core covering rod. . Therefore, according to the manufacturing method of the base material for multi-core fibers of the present invention, the core covering rod can be prevented from being deformed when the soot is sintered, and unintended deformation can be prevented from occurring in the core. Can do.

  Moreover, it becomes easy to adjust the space | interval of mutually adjacent core covering rods by adjusting the magnitude | size of the outer diameter of a large diameter rod. Therefore, the distance between the cores and the amount of soot entering between the core covering rods adjacent to each other can be easily adjusted.

  Moreover, in the said bundle process, it is preferable to fix the other end surface of each said large diameter rod to a dummy glass rod.

  By fixing the dummy glass rod to the other end of the large-diameter rod, it becomes easy to fix the dummy glass rod to the lathe chuck. For this reason, it becomes easy to rotate the bundled core covering rods about the axis center parallel to the longitudinal direction of the core covering rods, and it becomes easy to perform the external attachment process.

  The distance between the core covering rods adjacent to each other is preferably D / 4 or more, where D is the diameter of the core covering rod.

  In the case of such a configuration, the soot easily enters between the core covering rods adjacent to each other in the external attaching step. For this reason, it becomes easy to put soot in the space surrounded by the core covering rod, and it is possible to suppress the formation of an unnecessary space in the clad.

  In the bundling step, the glass rod for filling, which is a part of the clad, is adjacent to each of the core covering rods in at least one set of the core covering rods adjacent to each other and each of the core covering rods. It is preferable that they are spaced apart.

  As described above, by the bundling process, the filling glass rod serving as the cladding is disposed in the space formed between the outer peripheral surfaces of at least one pair of adjacent core-covered rods. The space is a space in which soot is to be deposited in the external process when the glass rod for filling is not disposed. By arranging the glass rod for filling in this way, it is possible to suppress the volume change when the soot is sintered, compared to the case where all the positions where the glass rod for filling is arranged are filled with soot. Accordingly, it is possible to further suppress the contraction force generated when the soot is sintered from acting on the core covering rod, and thus it is easier to suppress unintended deformation from occurring in the core.

  Moreover, in the said bundle process, it is preferable that the said glass rod for filling is arrange | positioned so that a side surface may contact the side surface of the said large diameter rod.

  By arranging the filling glass rod in this way, it becomes easy to arrange the filling glass rod away from the core coating rod.

  Moreover, the manufacturing method of the multi-core fiber of this invention is equipped with the drawing process which draws the preform | base_material for multi-core fibers manufactured by the manufacturing method of the preform | base_material for multi-core fibers in any one of said.

  According to such a method for producing a multi-core fiber, unintended deformation of the core-covered rod of the multi-core fiber preform is suppressed, so that unintended deformation of the core can be suppressed.

  As described above, according to the present invention, there are provided a method for manufacturing a base material for a multi-core fiber and a method for manufacturing a multi-core fiber that can prevent unintended deformation from occurring in the core.

It is sectional drawing which shows the multi-core fiber which concerns on 1st Embodiment of this invention. It is a flowchart which shows the manufacturing method of the multi-core fiber of FIG. It is a perspective view which shows a mode that the large diameter rod was fixed to the edge part of a core covering rod in the fixing process. It is a perspective view which shows a mode that the several core covering rod was bundled in the bundle process. It is a figure which shows the mode of an external attachment process. It is a perspective view which shows the mode after an external attachment process. It is sectional drawing which shows the preform | base_material for multicore fibers. It is a figure which shows the mode of a drawing process. It is sectional drawing along the IX-IX line | wire shown in FIG. It is a perspective view which shows a mode that the several core covering rod was bundled in the bundling process of 2nd Embodiment.

  Hereinafter, preferred embodiments of a method for producing a base material for a multi-core fiber according to the present invention and a method for producing a multi-core fiber using the same will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing a multicore fiber according to a first embodiment of the present invention. As shown in FIG. 1, the multi-core fiber 1 of the present embodiment includes a plurality of cores 10, a clad 20 that surrounds the outer peripheral surfaces of the cores 10 without gaps, an inner protective layer 31 that covers the outer peripheral surface of the clad 20, An outer protective layer 32 covering the outer peripheral surface of the inner protective layer 31. In the present embodiment, a case where the number of cores 10 is three will be described.

  In the multi-core fiber 1 of the present embodiment, the respective cores 10 are arranged at equal intervals apart from each other by a predetermined distance. The diameter of each core 10 is, for example, 6 μm to 10 μm, and the diameter of the clad 20 is, for example, 125 to 230 μm. Moreover, the refractive index of each core 10 is higher than the refractive index of the clad 20, and the relative refractive index difference of each core 10 with respect to the clad 20 is, for example, 0.3% to 0.5%.

  In this embodiment, the core 10 is made of silica glass to which a dopant that increases the refractive index, such as germanium, is added, and the cladding 20 is added to pure silica glass to which no dopant is added or a dopant that decreases the refractive index, such as fluorine. Made of silica glass. Alternatively, the core 10 may be made of pure silica glass to which no dopant is added, and the cladding 20 may be made of silica glass to which a dopant having a low refractive index such as fluorine is added.

  Next, a method for manufacturing the multi-core fiber 1 will be described.

  FIG. 2 is a flowchart showing a method for manufacturing the multi-core fiber 1. As shown in FIG. 2, the manufacturing method of the multi-core fiber 1 includes a fixing process P1, a bundle process P2, an external process P3, a sintering process P4, and a drawing process P5 as main processes.

<Fixing process P1>
FIG. 3 is a perspective view showing a state where the large-diameter rod is fixed to the end portion of the core-covered rod in the fixing step P1. In this step, first, a plurality of core-covered rods 2 are prepared in which the outer peripheral surface of the core rod 10 </ b> R that becomes the core 10 in the multi-core fiber 1 of FIG. 1 is covered with the cladding glass layer 20 </ b> R that becomes a part of the cladding 20. As shown in FIG. 1, in this embodiment, since the number of the cores 10 is three, the three core covering rods 2 are prepared.

  In this embodiment, each core covering rod 2 has the same size and the same configuration. As described above, since the core rod 10 </ b> R becomes the core 10, the core rod 10 </ b> R is made of the same material as the core 10, and the clad glass layer 20 </ b> R is made of the same material as the clad 20.

  Next, one end face of the large-diameter rod 3 having an outer diameter larger than the outer diameter of the core-covering rod 2 is fixed to each end portion of the plurality of core-covering rods 2. In the present embodiment, as shown in FIG. 3, the large-diameter rod 3 is fixed to each of one end and the other end of the core-covered rod 2. These large-diameter rods 3 are preferably welded and fixed to the core-covered rod 2 from the viewpoint of suppressing impurities from adhering to the core-covered rod 2.

  The softening temperature of the large diameter rod 3 is preferably lower than the softening temperature of the clad glass layer 20R of the core covering rod 2. In this case, the cladding glass layer 20R can be suppressed from being softened while the surface of the large-diameter rod 3 is softened. Therefore, unlike the present embodiment, even when some of the core-covered rods 2 are in contact with each other at the end, the core-covered rods 2 that are in contact with each other are welded together by suppressing the softening of the core-covered rod 2. Can be suppressed. Moreover, when welding the large diameter rod 3 to the core covering rod 2, it can suppress that the core covering rod 2 deform | transforms.

<Bundle process P2>
Next, the core covering rods 2 are bundled so that the side surfaces of the large diameter rods 3 fixed to the core covering rods 2 are adjacent to each other. FIG. 4 is a perspective view showing a state in which a plurality of core covering rods 2 are bundled in the bundle process P2.

  In the present embodiment, the large-diameter rods 3 adjacent to each other are arranged so that the side surfaces thereof are in contact with each other, and the other end surface of each large-diameter rod 3 is fixed to the dummy glass rod 5. Are bundled. For example, the large diameter rod 3 and the dummy glass rod 5 can be fixed by welding the large diameter rod 3 and the dummy glass rod 5. Moreover, the side surface of the large diameter rod 3 adjacent to each other may be welded.

  In this way, by fixing and bundling the large-diameter rods 3 to the end portions of the respective core-covered rods 2, a plurality of core-covered rods 2 are separated and bundled. Further, by fixing each large-diameter rod 3 to the dummy glass rod 5, it is possible to maintain a state in which the plurality of core-covered rods 2 are bundled.

<External process P3>
FIG. 5 is a diagram showing a state of the external process P3. The external process P3 is performed by, for example, an OVD (Outside Vapor Deposition Method) method, and soot that becomes a part of the clad 20 is deposited on the outer peripheral surfaces of the plurality of core-coated rods 2.

  First, each dummy glass rod 5 is fixed to a chuck of a lathe (not shown), and a plurality of core covering rods 2 bundled apart from each other are set to an axial center parallel to the longitudinal direction of the core covering rod 2. Rotate. By fixing the dummy glass rod 5 to the other end of the large diameter rod 3 as described above, it becomes easy to fix the dummy glass rod 5 to a lathe chuck (not shown). For this reason, it becomes easy to rotate the bundled core covering rods 2 as described above, and it becomes easy to perform the external attachment process P3. Then, as shown in FIG. 5, soot that becomes the clad 20 is deposited while rotating the plurality of core covering rods 2. FIG. 6 is a perspective view showing a state after the external attachment process P3, and is a view showing a state in which the soot 6 serving as a part of the clad 20 is deposited on the outer peripheral surface of the plurality of core covering rods 2.

The soot 6 to be deposited introduces the vaporized SiCl ₄ into the flame of the oxyhydrogen burner 53 by the carrier gas whose flow rate is controlled to convert the SiCl ₄ into SiO ₂ (silica glass), and the oxyhydrogen burner 53 The SiO ₂ soot 6 is deposited so as to cover the outer peripheral surface of each core covering rod 2 while reciprocating the core covering rod 2 a plurality of times in the longitudinal direction. By depositing the soot 6, a porous glass body that becomes a part of the clad 20 is formed. At this time, when the clad 20 is made of silica glass to which no dopant is added as described above, the soot 6 is deposited without adding any dopant. When a dopant is added to the clad 20, a gas containing a vaporized SiCl ₄ and a dopant whose amount of addition is controlled is introduced into the flame of the oxyhydrogen burner 53. For example, when the soot 6 is made of silica glass to which fluorine having a lower concentration than the cladding glass layer 20R is added, the vaporized SiF ₄ is appropriately adjusted together with the vaporized SiCl ₄ while the vaporized SiF ₄ is converted to the oxyhydrogen burner 53. Introduce into the flame.

  In this way, the soot 6 is deposited on the outer peripheral surface of the bundled core covering rods 2 on the outer side. At this time, the soot 6 can enter the space surrounded by the core covering rod 2 from the gap between the core covering rods 2 that are separated from each other. Accordingly, in the present embodiment, the soot 6 is also deposited on the outer peripheral surfaces of the core covering rod 2 facing each other, that is, on the outer peripheral surfaces of the core covering rods 2 that are bundled.

  The softening temperature of the deposited soot 6 is more preferably higher than the softening temperature of the cladding glass layer 20R of the core covering rod 2. For example, as described above, when the cladding glass layer 20R is made of silica glass to which fluorine is added, the soot 6 is made of pure silica glass or silica glass to which fluorine having a lower concentration than the cladding glass layer 20R is added. Then, the softening temperature of the cladding glass layer 20R becomes lower than the softening temperature of the deposited soot 6.

  In this way, the oxyhydrogen burner 53 is moved as many times as necessary, and a necessary amount of soot 6 is deposited as shown in FIG.

<Sintering process P4>
After the soot 6 is deposited as shown in FIG. 6 by the external process P3, dehydration is performed as necessary. The dehydration is performed by aging for a predetermined time in a furnace provided with a heater and filled with a gas such as argon (Ar) or helium (He).

  Next, the sintering process P4 is performed. Sintering process P4 is performed until the inside of the furnace is depressurized and the temperature inside the furnace is further increased so that the soot 6 becomes a transparent glass body. The furnace used at this time may be a furnace used for the above dehydration, or may be a furnace different from the furnace used for the above dehydration.

  At this time, as described above, when the softening temperature of the deposited soot 6 is higher than the softening temperature of the clad glass layer 20R of the core-covered rod 2, the soot 6 in contact with the clad glass layer 20R caused viscous flow. The clad glass layer 20R is taken in. Next, the soot 6 positioned on the outer peripheral side of the taken-in soot 6 is taken into the clad glass layer 20R. Since the temperature in the furnace further increases with time, the soot 6 causes viscous flow while the soot 6 is successively taken into the clad glass layer 20R. For this reason, it is suppressed that a gap is formed between the soot 6 and the clad glass layer 20R, and the soot 6 and the clad glass layer 20R become an integral glass body. In addition, when the softening temperature of the deposited soot 6 is not higher than the softening temperature of the cladding glass layer 20R of the core coating rod 2, the order of softening of the cladding glass layer 20R and the soot 6 is different from the above, but the soot 6 and the cladding glass are different. The layer 20R becomes an integral glass body.

  In this step, the core rod 10R of the core covering rod 2 becomes the base material core portion 10P of the base material 1P for the multicore fiber shown in FIG. 7 with almost no change. Further, the clad glass layer 20R of the core covering rod 2 becomes a part of the base material clad part 20P of the multi-core fiber base material 1P, and the soot 6 becomes another part of the base material clad part 20P. In this way, the multi-core fiber preform 1P is obtained.

Note that this step may be performed in an atmosphere containing a fluorine-based gas. Specifically, a fluorine-based gas such as SiF ₄ , CF ₄ , C ₂ F ₆ or the like is introduced into a furnace in which this process is performed. By setting it as such a process, when soot 6 raise | generates a viscous flow, it exists in the tendency for a fluorine to be added in soot 6, and the refractive index of soot 6 can be made small. Even in this case, when the softening temperature of the soot 6 is higher than the softening temperature of the clad glass layer 20R, it is difficult for fluorine to be taken into the soot 6 until the soot 6 causes viscous flow. Since it is faster for the clad glass layer 20R to cause viscous flow than to cause soot, the soot 6 can be easily taken into the clad glass layer 20R as described above.

<Drawing process P5>
FIG. 8 is a diagram showing a state of the drawing process P5. First, as a preparatory stage for performing this process, the multi-core fiber preform 1P is installed in the spinning furnace 110 by the above process.

  Next, the heating unit 111 of the spinning furnace 110 is heated to heat the multi-core fiber preform 1P. At this time, the lower end of the multi-core fiber preform 1P is heated to, for example, 2000 ° C. to be in a molten state. Then, the glass is melted from the base material 1P for the multicore fiber, and the glass is drawn. The drawn molten glass immediately solidifies as it exits the spinning furnace 110, so that the base material core part 10P becomes the core 10 and the base material clad part 20P becomes the clad 20 to form a plurality of cores. 10 and a multi-core fiber strand composed of the clad 20. Thereafter, the multi-core fiber strand passes through the cooling device 120 and is cooled to an appropriate temperature. When entering the cooling device 120, the temperature of the multi-core fiber strand is, for example, about 1800 ° C., but when exiting the cooling device 120, the temperature of the multi-core fiber strand is, for example, 40 ° C. to 50 ° C.

  The multi-core fiber strand coming out of the cooling device 120 passes through the coating device 131 containing the ultraviolet curable resin that becomes the inner protective layer 31, and is coated with the ultraviolet curable resin. Further, when passing through the ultraviolet irradiation device 132 and being irradiated with ultraviolet rays, the ultraviolet curable resin is cured and the inner protective layer 31 is formed. Next, the multi-core fiber coated with the inner protective layer 31 passes through the coating device 133 containing the ultraviolet curable resin to be the outer protective layer 32 and is coated with the ultraviolet curable resin. Further, when passing through the ultraviolet irradiation device 134 and being irradiated with ultraviolet rays, the ultraviolet curable resin is cured and the outer protective layer 32 is formed, and the multi-core fiber 1 shown in FIG. 1 is obtained.

  Then, the direction of the multi-core fiber 1 is changed by the turn pulley 141 and is taken up by the reel 142.

  Thus, the multi-core fiber 1 shown in FIG. 1 is manufactured.

  As described above, according to the manufacturing method of the multi-core fiber preform 1P of the present embodiment, the soot 6 is externally deposited on the outer peripheral surface of the bundled core-coated rods 2 and thus has a large diameter. The base material 1P for multi-core fibers can be manufactured. In addition, according to the manufacturing method of the multi-core fiber preform 1P of the present embodiment, the large-diameter rod 3 having an outer diameter larger than that of the core-covered rod 2 is fixed to the end portions of the plurality of core-coated rods 2, thereby The rods 3 are bundled so that the side surfaces are adjacent to each other. Therefore, the plurality of core covering rods 2 are bundled apart from each other. In this way, the gap generated when the plurality of core covering rods 2 are separated from each other is caused by the contraction force generated when the soot 6 deposited on the outer peripheral surface of the core covering rod 2 is sintered acting on the core covering rod 2. Can be suppressed. Therefore, according to the method for manufacturing the multi-core fiber preform 1P of the present embodiment, the core covering rod 2 can be prevented from being deformed when the soot 6 is sintered, and unintended deformation occurs in the core 10. This can be suppressed.

  When a plurality of core-covered rods 2 are bundled with the large-diameter rods 3 fixed to the ends as described above, the core-covered rods adjacent to each other are adjusted by adjusting the size of the outer diameter of the large-diameter rods 3. It becomes easy to adjust the interval of 2. Therefore, the distance between the cores 10 of the multi-core fiber 1 and the amount of the soot 6 entering between the core covering rods 2 adjacent to each other can be easily adjusted.

  In the present embodiment, the outer peripheral surfaces of the core covering rods 2 adjacent to each other are entirely separated from each other. Therefore, the soot 6 can enter between the core covering rods 2 in the external attachment process P3. For this reason, formation of an unnecessary space in the clad 20 can be suppressed. From the viewpoint of facilitating the soot 6 to enter between the adjacent core covering rods 2 in the external process P3, the distance x between the adjacent core covering rods 2 is D when the diameter of the core covering rod 2 is D. / 4 or more is preferable. FIG. 9 is a cross-sectional view taken along line IX-IX shown in FIG. Thus, by increasing the distance between the core covering rods 2 adjacent to each other to some extent, the soot 6 can be easily inserted into the space surrounded by the core covering rod 2 and an unnecessary space is prevented from being formed in the clad 20. can do. However, the distance between the core covering rods 2 adjacent to each other may be less than D / 4.

  According to the manufacturing method of the multi-core fiber 1 of the present embodiment, unintended deformation of the core-covered rod 2 of the multi-core fiber preform 1P is suppressed, so that unintended deformation of the core 10 is suppressed. be able to.

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of 1st Embodiment, or an equivalent component, the overlapping description is abbreviate | omitted except the case where it attaches | subjects the same referential mark and demonstrates in particular.

  The multi-core fiber manufactured in this embodiment is the same as the multi-core fiber 1 manufactured in the first embodiment, and the base material for multi-core fiber manufactured in this embodiment is the same as that in the first embodiment. This is the same as the manufactured multi-core fiber preform 1P. Moreover, the manufacturing method of the multi-core fiber 1 in the present embodiment includes the fixing process P1, the bundle process P2, the external process P3, the sintering process P4, and the drawing process P5 as main processes, as in the first embodiment. .

<Fixing process P1>
The fixing process P1 of the present embodiment is the same as the fixing process P1 of the first embodiment.

<Bundle process P2>
FIG. 10 is a perspective view showing a state in which the plurality of core covering rods 2 are bundled in the bundling step P2 of the present embodiment. In the present embodiment, the same number of core coated rods 2 as the plurality of core coated rods 2 of the first embodiment are prepared as in the first embodiment, and the same number of filling glass rods 7 as the core coated rods 2 are prepared.

  The diameter of the glass rod 7 for filling of this embodiment is made smaller than the diameter of the core covering rod 2. Further, the filling glass rod 7 becomes a part of the clad 20. Therefore, the filling glass rod 7 is made of the same material as that of the clad glass layer 20R. Or the glass rod 7 for filling may be comprised from the glass whose softening temperature is lower than the clad glass layer 20R. In this case, when the clad glass layer 20R is made of pure silica glass, the filling glass rod 7 is made of, for example, silica glass to which fluorine is added, and the clad glass layer 20R is made of silica glass to which fluorine is added. In this case, the filling glass rod 7 is made of, for example, silica glass to which fluorine having a higher concentration than the cladding glass layer 20R is added.

  In this step, the prepared plurality of core covering rods 2 and the plurality of glass rods for filling 7 are arranged at a position where they are bundled. At this time, the filling glass rods 7 are arranged so as to be separated from each other and adjacent to the core covering rods 2 adjacent to each other. Specifically, a plurality of core-covered rods 2 to which the large-diameter rods 3 are fixed are arranged in the same manner as in the first embodiment, and the filling glass rod 7 has two side-by-side large-diameter rods 3 adjacent to each other. It arrange | positions so that it may contact | connect with the side surface. After arranging the core covering rod 2 and the filling glass rod 7 to which the large-diameter rod 3 is fixed in this way, the end surface of the large-diameter rod 3 and the end surface of the filling glass rod 7 are fused to the end surface of the dummy glass rod 5. Worn and fixed. In this way, the plurality of core covering rods 2 and the plurality of filling glass rods 7 are bundled. Thus, in each of the pairs of core covering rods 2 adjacent to each other, the filling glass rod 7 which is a part of the clad 20 is adjacent to each of the core covering rods 2 adjacent to each other and separated from each core covering rod. Arranged. In this step, the side surfaces of the large-diameter rods 3 adjacent to each other or the side surfaces of the large-diameter rod 3 and the side surfaces of the core-covered rod 2 may be welded.

  In the present embodiment, after the bundling process P2, the external attachment process P3 and the sintering process P4 are performed in the same manner as in the first embodiment to obtain the multi-core fiber preform 1P. Furthermore, the drawing process P5 is performed in the same manner as in the first embodiment, and the multi-core fiber 1 is obtained.

  According to this embodiment, the glass rod 7 for filling can be arrange | positioned in the space formed between the outer peripheral surfaces of the mutually adjacent core coating rod 2 by arrange | positioning the glass rod 7 for filling as mentioned above. it can. The space is a space in which the soot 6 is to be deposited in the external process P3 when the glass rod 7 for filling is not disposed. By arranging the filling glass rod 7 in this manner, the volume change when the soot 6 is sintered is suppressed as compared with the case where all the positions where the filling glass rod 7 is arranged are filled with the soot 6. be able to. Accordingly, it is possible to further suppress the contraction force generated when the soot 6 is sintered from acting on the core covering rod 2, and thus it is easier to suppress unintended deformation from occurring in the core 10.

  In the present embodiment, the filling glass rods 7 are arranged as described above in each of the sets of core covering rods 2 adjacent to each other. However, the filling glass rod 7 may be disposed adjacent to each core covering rod 2 and spaced apart from each core covering rod 2 in at least one pair of core covering rods 2 adjacent to each other.

  As mentioned above, although this invention was demonstrated to the example for embodiment, this invention is not limited to these.

  For example, the relationship among the softening temperature of the clad glass layer 20R, the softening temperature of the filling glass rod 7, the softening temperature of the soot 6, the softening temperature of the large diameter rod 3, and the softening temperature of the dummy glass rod 5 should be adjusted as appropriate. Can do.

  In the above embodiment, the multi-core fiber 1 in which each core 10 is directly covered with the clad 20 has been described as an example. However, the multi-core fiber may be a so-called trench type multi-core fiber. In the trench type multi-core fiber, each core is individually coated with an inner clad having a lower refractive index than the core, and each inner clad is individually coated with a trench portion having a lower refractive index. The element composed of the core, the inner cladding, and the trench portion may be referred to as a core element. All the core elements are covered with a clad having a higher refractive index than the trench and a lower refractive index than the core. When manufacturing such a multi-core fiber, the core coated rod is coated with a glass layer serving as an inner cladding, and a glass layer serving as an inner cladding is coated with a glass layer serving as a trench portion, thereby forming a glass layer serving as a trench portion. Is covered with a glass layer serving as a cladding. A multi-core fiber can be manufactured in the same manner as in the above embodiment except that a core-coated rod having such a structure is used.

  In the first embodiment, the large-diameter rod 3 is fixed to the dummy glass rod 5, and in the second embodiment, the large-diameter rod 3 and the filling glass rod 7 are fixed to the dummy glass rod 5. The core covering rod 2 was bundled. However, the method of bundling the plurality of core-covered rods 2 is not limited to these, and the dummy glass rod 5 is not an essential component. For example, the thick rods 3 may be bundled with a binding band or the like. When the large-diameter rod 3 is bundled using a binding band, the binding band may be made of resin or metal, but is preferably made of metal from the viewpoint of high heat resistance.

  In the above embodiment, the case where the large-diameter rod 3 is fixed to both ends of each core-covered rod 2 is described as an example. However, the large-diameter rod 3 is fixed to at least one end of the core-covered rod 2. It should be done.

  Moreover, in the said embodiment, since the manufacturing method which manufactures the multi-core fiber 1 which has the three cores 10 was demonstrated, the number of the core covering rods 2 was set to three, and the number of the glass rods 7 for filling in 3rd Embodiment is also three. It was However, the number of cores of the multicore fiber is not limited to this. For example, a multi-core fiber having a 1-6 core arrangement in which one core is arranged at the center of the clad and six cores are arranged at equal intervals around the core may be used. In this case, one core covering rod 2 is arranged at the center, and six core covering rods 2 are arranged around it.

  As described above, according to the present invention, a method for manufacturing a multi-core fiber base material and a method for manufacturing a multi-core fiber that can prevent unintended deformation from occurring in the core are provided. Can be used.

DESCRIPTION OF SYMBOLS 1 ... Multi-core fiber 1P ... Base material 2 for multi-core fiber ... Core coating rod 3 ... Large diameter rod 5 ... Dummy glass rod 6 ... Soot 7 ... Glass rod 10 for filling ... Core 10P ... Base material core part 10R ... Core rod 20 ... Cladding 20P ... Base material cladding part 20R ... Clad glass layer

Claims (6)

A large-diameter rod having an outer diameter larger than the outer diameter of the core-coated rod at at least one end of each of the plurality of core-coated rods coated with a clad glass layer whose outer peripheral surface is a part of the cladding. A fixing step of fixing one end face of
A bundling step of bundling the plurality of core covering rods such that side surfaces of the large diameter rods fixed to each of the plurality of core covering rods are adjacent to each other;
An external step of depositing soot to be another part of the clad on the outer peripheral surface of the plurality of core-coated rods;
The manufacturing method of the preform | base_material for multi-core fibers characterized by comprising. The method for manufacturing a base material for a multi-core fiber according to claim 1, wherein in the bundling step, the other end face of each of the large-diameter rods is fixed to a dummy glass rod. The method for producing a base material for a multicore fiber according to claim 1 or 2, wherein a distance between the core covering rods adjacent to each other is D / 4 or more, where D is a diameter of the core covering rod. In the bundling step, the glass rod for filling, which is a part of the clad, is adjacent to each core covering rod and separated from each core covering rod in at least one pair of the core covering rods adjacent to each other. The method for manufacturing a multi-core fiber preform according to any one of claims 1 to 3, wherein the multi-core fiber preform is arranged. 5. The method for manufacturing a base material for a multi-core fiber according to claim 4, wherein in the bundling step, the glass rod for filling is arranged such that a side surface is in contact with a side surface of the large-diameter rod. A method for producing a multi-core fiber, comprising a drawing step of drawing the base material for a multi-core fiber produced by the method for producing a preform for a multi-core fiber according to any one of claims 1 to 5.

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