JP6010587B2 - Method for manufacturing base material for multi-core fiber, and method for manufacturing multi-core fiber using the same - Google Patents

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 the transmission capacity of such an optical fiber communication system, a plurality of signals can be transmitted by light propagating through each core using a multi-core fiber in which the outer periphery of the plurality of cores is surrounded by a single cladding. Are 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 clad using 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 created 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. Further, in the stack and draw method, the size of the base material for the multi-core fiber that can be created is limited by the thickness of the glass tube to be prepared, and when the glass tube becomes large, 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

  However, as described in Patent Document 2, in order to make the outer diameter of the core covering rod into a regular hexagon, it is necessary to cut the prepared cylindrical core covering rod. Therefore, it is conceivable to bundle a plurality of cylindrical core-covered rods (glass rods) and deposit soot on the outer periphery of the bundled core-covered rods.

  However, it has been found that when soot is deposited in this manner, voids are generated between the glass portion derived from the soot and the glass portion derived from the glass rod in the sintering step of converting the soot into a transparent glass body.

  The cause is considered as follows. That is, in the sintering process, when a member in which soot is deposited around a plurality of glass rods is heated, the individual soot positioned on the outer peripheral side of the glass rod is vitrified more quickly than the soot around the glass rod. At the time of transparent vitrification, especially the soot on the outer peripheral side is more easily heated than the soot on the inner peripheral side located in the vicinity of the glass rod, and the transparent vitrification progresses faster. Therefore, the soot on the outer peripheral side causes a viscous flow faster than the soot on the inner peripheral side, and becomes a transparent glass body without a gap. When the soot on the inner peripheral side causes a viscous flow and becomes a transparent glass body, the soot tends to be taken into the glass body on the outer peripheral side already integrated at this time. Thus, the soot on the inner peripheral side is brought closer to the outer peripheral side when it becomes an integral glass, and as a result, the above-mentioned gap is generated.

  Therefore, the present invention provides a method for producing a multi-core fiber preform and a method for producing a multi-core fiber that can suppress the formation of unnecessary gaps.

  The manufacturing method of the base material for multi-core fibers of the present invention includes a bundle step of bundling a plurality of glass rods including a plurality of core-coated rods coated with a clad glass layer whose outer peripheral surface of a core rod serving as a core is a part of the cladding; An external step of depositing soot as another part of the clad on the outer peripheral surface of the bundled glass rods; heating the glass rods deposited with the soot; And a sintering step in which the glass rod is integrated with the transparent glass body, and the softening temperature of the portion in contact with the soot in the glass rod disposed at a position in contact with the soot is such that the deposited soot is transparent It is characterized by being lower than the temperature at the time of vitrification.

  According to such a method for manufacturing a multi-core fiber preform, soot is externally deposited on the outer peripheral surface of a plurality of glass rods including a plurality of bundled core-coated rods. The material can be manufactured. And the softening temperature of the part which contacts soot of the glass rod in which soot accumulates is lower than the temperature in which the soot deposited on the glass rod becomes transparent vitrification. Therefore, in the sintering process, the portion tends to cause viscous flow before the soot, and the soot can be taken into the portion where the viscous flow of the glass rod has occurred. For this reason, soot is taken in one after another from the glass rod side and becomes an integral transparent glass. The formation of unnecessary gaps in the multi-core fiber preform manufactured in this way can be suppressed.

  Further, at least a part of the glass rod disposed at a position in contact with the soot is the core covering rod, and the softening temperature of the cladding glass layer of the core covering rod disposed at a position in contact with the soot is The temperature of the deposited soot is preferably lower than the temperature at which the soot is vitrified.

  According to such a configuration, in the core-covered rod arranged at the position where the soot is attached, it is not necessary that only the outer peripheral portion of the cladding glass layer has a softening temperature lower than that of the soot, and the entire cladding glass layer Can have the same configuration. Therefore, it can suppress that the structure of the core covering rod arrange | positioned in the position to which soot adheres becomes complicated. And since a clad glass layer melts earlier than a soot in a sintering process, the soot can be integrated with the clad glass layer, and a clad in which unnecessary gaps are suppressed can be formed.

  In this case, at least two core covering rods are arranged adjacent to each other and in contact with the soot, and the filling glass rods having a smaller diameter than the core covering rods are in contact with the soot. Preferably, the softening temperature of the filling glass rod is lower than the temperature at which the deposited soot becomes transparent vitrified.

  By arranging the small-diameter filling glass rods so as to be in contact with the core coating rods adjacent to each other, the gap between the outer peripheral surfaces of these core coating rods can be filled, and the manufactured multi-core fiber preform The outer peripheral surface can be made closer to a circle. Even in this case, since the softening temperature of the glass rod for filling is lower than the temperature at which the soot becomes transparent vitrified, it is possible to suppress the formation of a gap between the soot and the glass rod for filling in the sintering process. It is possible to suppress the formation of unnecessary gaps in the manufactured multi-core fiber preform.

  Furthermore, in this case, the softening temperature of the filling glass rod is preferably lower than the softening temperature of the clad glass layer of the core-covered rod in contact with the filling glass rod.

  Since the softening temperature of the filling glass rod is lower than the softening temperature of the clad glass layer, the filling glass rod causes viscous flow before the clad glass layer in the sintering process. Therefore, the gap generated between the filling glass rod and the core covering rod before the sintering process can be more appropriately filled with the filling glass rod that has caused viscous flow in the sintering process. Therefore, it is possible to further suppress the formation of unnecessary gaps in the manufactured multi-core fiber preform.

  In addition, the portion of the glass rod that is disposed at a position in contact with the soot may be silica glass to which fluorine is added, and the soot may be pure silica glass.

  In this case, the sintering step is preferably performed in an atmosphere containing a fluorine-based gas.

  In this case, fluorine can be added to the soot when the soot causes a viscous flow, and it is possible to suppress the difference in optical characteristics from the portion of the glass rod in contact with the soot.

  In the bundling step, one end of each glass rod is fixed to a dummy glass rod and the other end of each glass rod is fixed to another dummy glass rod. It is preferable to maintain a state in which a plurality of glass rods are bundled.

  By maintaining the state in which the respective glass rods are bundled in this way, it is possible to deposit soot on the entire outer peripheral surface of the bundled glass rods. Accordingly, the entire bundled glass rod can be used as a base material for a multi-core fiber.

  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 the above. is there.

  According to such a method for producing a multi-core fiber, an unnecessary gap is not formed in the drawn base material for the multi-core fiber, and thus a multi-core fiber in which the formation of an unnecessary gap is suppressed is obtained. Can do.

  As described above, according to the present invention, there are provided a method for manufacturing a multi-core fiber preform and a method for manufacturing a multi-core fiber that can suppress the formation of unnecessary gaps.

It is a figure which shows the multi-core fiber which concerns on 1st Embodiment of this invention. It is a flowchart which shows the manufacturing method of a multi-core fiber. It is a figure which shows a mode that the core covering rod was bound. It is a figure which shows a mode that the dummy glass rod was fixed. It is a figure which shows the mode of an external attachment process. It is a figure which shows the mode after an external attachment process. It is a figure which shows the preform | base_material for multicore fibers. It is a figure which shows the mode of a drawing process. It is a figure which shows the mode after the bundle process in 2nd Embodiment of this invention. It is a figure which shows the mode after the external attachment process in 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 diagram 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 μm 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 the present embodiment, the core 10 is made of silica glass to which a dopant having a high refractive index such as germanium is added, and the cladding 20 is made of silica glass to which 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 bundle process P1, an external process P2, a sintering process P3, and a drawing process P4 as main processes.

<Bundle process 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 multicore 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, it arrange | positions in the position where the core covering rod 2 is bundled. At this time, the core rods 10R are arranged such that the distance between the centers thereof is the same. Then, the core covering rods 2 arranged at the bundled positions are bound by the binding band 51. The binding band 51 may be made of resin or metal, but is preferably made of resin from the viewpoint of preventing the outer peripheral surface of the core-covered rod 2 from being damaged, and has high heat resistance. Is preferably made of metal. Thus, as shown in FIG. 3, the core covering rods 2 are bound together.

  Although not particularly illustrated, when the core covering rod 2 is bundled, the core covering rod 2 is bundled in a position that should be a space surrounded by the core covering rod 2 (position to be surrounded by the three core covering rods 2). A glass rod for filling may be arranged. In this case, the filling glass rod disposed in the space is preferably made of the same material as that of the clad glass layer.

  Next, dummy glass rods are fixed to both ends of each of the bound core covering rods 2. FIG. 4 is a view showing a state in which the dummy glass rods are fixed to the respective core covering rods 2 as described above. First, one dummy glass rod 52 is fixed to one end of each core covering rod 2 in a state where the core covering rod 2 is bound by the binding band 51. Next, another dummy glass rod 52 is fixed to the other end of each core covering rod 2. This fixing is preferably performed from the viewpoint of preventing impurities from adhering to the core covering rod 2. Thus, by fixing the dummy glass rod 52 to the both ends of each core covering rod 2, the state where each core covering rod 2 was bundled can be maintained. Next, the binding band 51 that has bound each core covering rod 2 is removed. Thus, as shown in FIG. 4, a plurality of core covering rods 2 are bundled.

  In this step, the respective core-covered rods 2 are welded to the dummy glass rod 52 after the respective core-covered rods 2 are bundled using the binding band 51, but such a procedure is not necessarily required. For example, dummy glass rods 52 are fixed at appropriate positions on both ends of one core covering rod 2. Next, another core covering rod 2 is arranged so as to be adjacent to the core covering rod 2 already fixed to the dummy glass rod 52. Fix to the dummy glass rod 52. Furthermore, the last core covering rod 2 is arranged so as to be adjacent to the two core covering rods 2 already fixed to the dummy glass rod 52, and both ends of the arranged last core covering rod 2 are respectively connected to the respective dummy glass rods. It fixes to 52. Thus, even if each core covering rod 2 is fixed to the dummy glass rod 52, a plurality of core covering rods 2 are bundled as shown in FIG.

<External process P2>
FIG. 5 is a diagram showing a state of the external process P2. The external process P2 is performed by, for example, the OVD (Outside vapor deposition method) method, and the soot 3 that becomes a part of the clad 20 is deposited on the outer peripheral surface of each core covering rod 2 bundled in the bundle process P1.

  First, each dummy glass rod 52 is fixed to a chuck of a lathe (not shown), and the bundled core covering rods 2 are rotated about the axis of the dummy glass rod 52. And the soot 3 used as the clad 20 is deposited, rotating the some core covering rod 2 as shown in FIG. At this time, the softening temperature of the clad glass layer 20R is set to be lower than the temperature at which the deposited soot 3 is made into a transparent vitreous described later. For example, when the cladding glass layer 20R is made of silica glass to which fluorine is added as described above, the soot 3 is made of pure silica glass or silica glass to which fluorine having a lower concentration than the cladding glass layer 20R is added. The

The soot 3 to be deposited is introduced into the flame of the oxyhydrogen burner 53 by introducing vaporized SiCl ₄ into the flame of the oxyhydrogen burner 53 by a carrier gas whose flow rate is controlled, and the oxyhydrogen burner 53 is changed from the SiCl ₄ to SiO ₂ (silica glass). The soot 3 of SiO ₂ is deposited so as to cover the outer peripheral surface of each core covering rod 2 while reciprocating a plurality of times in the longitudinal direction of the core covering rod 2. By depositing the soot 3, a porous glass body that becomes a part of the clad 20 is formed. At this time, when the soot 3 is composed of silica glass to which no dopant is added as described above, the soot 3 is deposited without adding any dopant. Further, when a dopant is added to the soot 3, 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. When the soot 3 is composed of silica glass to which fluorine having a lower concentration than the cladding glass layer 20R is added as described above, the vaporized SiF ₄ together with the vaporized SiCl ₄ is put into the flame of the oxyhydrogen burner. Introduce.

  At this time, the soot 3 also enters between the core covering rods 2 adjacent to each other and is deposited. Between the core covering rods 2 is between the outer peripheral surfaces of the core covering rods 2 adjacent to each other, and it is not necessary that the core covering rods 2 adjacent to each other are separated from each other. In this way, the oxyhydrogen burner 53 is moved as many times as necessary, so that the required amount of soot 3 is deposited as shown in FIG.

  The soot 3 is deposited on the outer peripheral surfaces of the plurality of core covering rods 2 bundled in this manner. The deposited soot 3 is a porous body.

<Sintering process P3>
After obtaining the core-covered rod 2 on which the soot 3 shown in FIG. 6 is obtained, dehydration is performed as necessary. Dehydration is performed by aging for a predetermined time in a furnace provided with a heater and filled with a gas such as Ar or He.

  Next, a sintering process is performed. In the sintering process, the pressure in the furnace is reduced and the temperature in the furnace is further increased, and the sintering process is performed until the soot 3 changes from a porous body to 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.

  As described above, the softening temperature of the clad glass layer 20R of the core-covered rod 2 is lower than the temperature at which the deposited soot 3 becomes transparent vitrified. Therefore, when the furnace temperature is increased, the clad glass layer 20R becomes higher than the soot 3 The softening temperature is reached first, causing viscous flow. Therefore, the soot 3 in contact with the clad glass layer 20R is taken into the clad glass layer 20R that has caused viscous flow, and then the soot 3 positioned on the outer peripheral side of the soot 3 taken into the clad glass layer 20R. It is captured. Since the temperature in the furnace further increases with time, the soot 3 causes viscous flow while the soot 3 is successively taken into the clad glass layer 20R. For this reason, it is suppressed that a gap is formed between the soot 3 and the clad glass layer 20R, and the soot 3 and the clad glass layer 20R become an integrated transparent glass body.

  At this time, 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 3 becomes another part of the base material clad part 20P. In this way, the multi-core fiber preform 1P is obtained.

In addition, when the clad glass layer 20R is made of silica glass to which fluorine is added as described above, this step is preferably performed in an atmosphere containing a fluorine-based gas. Specifically, fluorine furnaces such as CF ₄ , C ₂ F ₆ , C ₄ F ₈ , CC1 ₂ F ₂ , SiF ₄ , Si ₂ F ₆ , SF ₆ , NF ₃ , and F ₂ are included in the furnace in which this process is performed. Introduce gas. By adopting such a process, there is a tendency that fluorine is added into the soot 3 when the soot 3 becomes transparent glass, and the difference in refractive index between the clad glass layer 20R and the soot added with fluorine in the furnace. Can be reduced. Even in this case, it is difficult for fluorine to be taken into the soot 3 until the soot 3 becomes transparent vitrified, and the clad glass layer 20R is faster to cause viscous flow than the soot 3 becomes transparent vitrified. Thus, the soot 3 can be taken into the clad glass layer 20R.

<Drawing process P4>
FIG. 8 is a diagram showing a state of the drawing process P4. First, as a preparatory stage for performing the drawing process P4, 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 according to the present embodiment, the soot 3 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. The softening temperature of the clad glass layer 20R, which is the portion in contact with the soot 3 of the core covering rod 2 on which the soot 3 is deposited, is lower than the temperature at which the deposited soot 3 becomes transparent glass. Therefore, in the sintering process P3, the clad glass layer 20R tends to cause a viscous flow before the soot 3, and the soot 3 can be absorbed by the clad glass layer 20R that has caused the viscous flow of the core covering rod 2. . For this reason, the soot 3 is united while moving to the core covering rod 2 side. It is possible to suppress the formation of unnecessary gaps in the multi-core fiber preform 1P manufactured in this way. Therefore, according to the manufacturing method of the multi-core fiber preform 1P of the present embodiment, the multi-core fiber preform 1P having no unnecessary space can be produced, or an unnecessary space is generated in the multi-core fiber preform 1P. However, the size of the space can be reduced as compared with the case where the softening temperature of the cladding glass layer 20R and the temperature at which the soot 3 becomes transparent vitrified are the same.

  Therefore, the multi-core fiber 1 obtained by drawing the base material 1P for such a multi-core fiber can suppress the formation of an unnecessary space and can suppress the deformation of the core 10 and can be in a good communication state. It is possible to prevent the strength from becoming weak unlike the design value.

  Moreover, in the core covering rod 2 of the present embodiment, the softening temperature of the clad glass layer 20R as a whole is lower than the temperature at which the deposited soot 3 becomes transparent glass. Therefore, since only the outer peripheral side portion of the clad glass layer 20R is not configured to be lower than the temperature at which the soot 3 becomes transparent glass, it is possible to prevent the configuration of the core-covered rod from becoming complicated.

  Further, when the soot 3 is pure silica glass, it is not necessary to introduce a gas in which a dopant as an additive is added to the burner for depositing the soot 3 into the flame injected from the oxyhydrogen burner. . For this reason, the external attachment process P3 becomes easy.

  Moreover, in this embodiment, the both ends of each core covering rod 2 are fixed to the dummy glass rod 52, and the bundled state of each core covering rod 2 is maintained. For this reason, soot can be deposited on the whole outer peripheral surface of the bundled core-covered rod 2. Therefore, the bundled core covering rods 2 as a whole can be used as the multi-core fiber preform 1P.

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

  The multi-core fiber manufactured also in the present embodiment is the multi-core fiber 1 described in the first embodiment. Accordingly, the multi-core fiber preform that becomes the multi-core fiber 1 in this embodiment is the multi-core fiber preform 1P.

  Next, the manufacturing method of the multi-core fiber 1 of this embodiment is demonstrated.

  Also in the present embodiment, as in the first embodiment, the method for manufacturing the multi-core fiber 1 includes a bundle process P1, an external process P2, a sintering process P3, and a drawing process P4 as main processes.

<Bundle process P1>
FIG. 9 is a diagram showing a state after the bundle process P1 of the present embodiment. As shown in FIG. 9, the bundling process P1 of the present embodiment is the first embodiment in that the filling glass rod 4 exposed to the outer peripheral side in contact with each of the core covering rods 2 adjacent to each other is further arranged. This is different from the bundle process P1 in FIG.

  The filling glass rod 4 has a smaller diameter than each core-covered rod 2 with which the filling glass rod 4 is in contact. Moreover, in this embodiment, the softening temperature of the glass rod 4 for filling is made lower than the softening temperature of the clad glass layer 20R of the core covering rod 2. When the clad glass layer 20R is silica glass to which fluorine is added as described above, for example, the filling glass rod 4 is made of silica glass to which fluorine having a higher concentration than the clad glass layer 20R is added.

  In the present embodiment, first, the core covering rods 2 are bundled in the same manner as the bundling process P1 of the first embodiment, and then the filling glass rods 4 are arranged so as to contact the core covering rods 2 adjacent to each other. A plurality of glass rods including the core coating rod 2 and the filling glass rod 4 are bound together by a binding band. Thereafter, dummy glass rods 52 are fixed to both ends of each glass rod. This fixing is preferably performed by welding for the same reason as the fixing of the dummy glass rod 52 in the first embodiment. In this way, a plurality of glass rods including a plurality of core covering rods 2 are bundled as shown in FIG.

  Although not particularly illustrated in the present embodiment, when the core covering rod 2 is bundled, another glass rod for filling is disposed at a position to be a space surrounded by the core covering rod 2 in a state where the core covering rod 2 is bundled. You may do it. In this case, the filling glass rod disposed in the space is preferably made of the same material as that of the clad glass layer.

  Also in this embodiment, each glass rod may be bundled as shown in FIG. 9 by fixing each glass rod to the dummy glass rod 52 one by one in order.

<External process P2>
In the external attachment process P2 of the present embodiment, the soot 3 that becomes a part of the clad 20 is deposited on the outer peripheral surfaces of a plurality of glass rods including the core covering rod 2 and the filling glass rod 4 bundled in the bundle process P1. . The deposition of the soot 3 is performed in the same manner as the method of depositing the soot 3 on the plurality of core covering rods 2 in which the soot 3 is bundled in the first embodiment.

  As described above, the filling glass rod 4 is disposed so as to be exposed to the outer peripheral side in contact with the core covering rods 2 adjacent to each other, so that the soot 3 is also deposited on the outer peripheral surface of the filling glass rod 4. . That is, in this embodiment, the glass rod 4 for filling is arrange | positioned so that the soot 3 may be contacted. Moreover, since the softening temperature of the glass rod 4 for filling is made lower than the softening temperature of the clad glass layer 20R of the core covering rod 2 as described above, it is inevitably lower than the temperature at which the soot 3 becomes transparent glass. become.

  Thus, as shown in FIG. 10, a necessary amount of soot 3 is deposited.

  In this embodiment, both ends of the core covering rod 2 and the filling glass rod 4 are fixed to the dummy glass rod 52 so that the core covering rod 2 and the filling glass rod 4 are bundled. Is maintained. For this reason, it is possible to deposit soot on the entire outer peripheral surface of the bundled core covering rod 2 and filling glass rod 4. Therefore, the bundled core covering rod 2 and the entire filling glass rod 4 can be used as the multi-core fiber preform 1P.

<Sintering process P3>
The sintering process P3 of the present embodiment is performed in the same manner as the sintering process P3 of the first embodiment. As described above, since the softening temperature of the filling glass rod 4 is set lower than the softening temperature of the clad glass layer 20R of the core covering rod 2, the filling glass rod 4 is first melted. And the glass rod 4 for filling which caused the viscous flow fills the gap between the glass rod for filling and the core covering rod 2. At this time, the soot 3 in contact with the filling glass rod 4 that has caused viscous flow is taken in. Then, when the temperature of the clad glass layer 20R of the core-covered rod 2 reaches the softening temperature and the clad glass layer 20R causes viscous flow, the soot 3 that comes into contact is taken in the same manner as in the sintering step P3 of the first embodiment. Next, the temperature of the soot 3 reaches the softening temperature, the soot 3 also causes viscous flow, and the clad glass layer 20R, the filling glass rod 4, and the soot 3 become an integrated transparent glass body. As described above, since the soot 3 causes viscous flow while being taken into the cladding glass layer 20R and the filling glass rod 4 from the inside, it is suppressed that a gap is formed between the soot 3 and the cladding glass layer 20R and the filling glass rod. The

  Thus, the core rod becomes the base material core part 10P, the clad glass layer 20R becomes a part of the base material clad part 20P, the filling glass rod 4 becomes another part of the base material clad part 20P, and the soot 3 becomes the base material clad part. 20P becomes another part, and the multi-core fiber preform 1P shown in FIG. 7 is obtained.

  Even in the sintering step of this embodiment, when the cladding glass layer 20R is silica glass to which fluorine is added as described above, it is preferable to perform this step in an atmosphere containing a fluorine-based gas.

  Next, a drawing process is performed in the same manner as the drawing process P4 of the first embodiment to obtain the multi-core fiber 1 shown in FIG.

  As described above, according to the manufacturing method of the multi-core fiber preform 1P of the present embodiment, the small-diameter filling glass rods 4 are arranged so as to be in contact with the core coating rods 2 adjacent to each other. A gap between the outer peripheral surfaces of the core covering rod 2 can be filled, and the outer peripheral surface of the manufactured multi-core fiber preform 1P can be made closer to a circle. Even in this case, since the softening temperature of the glass rod 4 for filling is lower than the temperature at which the soot 3 becomes transparent glass, a gap is formed between the soot 3 and the glass rod 4 for filling in the sintering step P3. It is possible to suppress the formation of unnecessary gaps in the manufactured multi-core fiber preform 1P.

  Further, as described above, the softening temperature of the filling glass rod 4 of the present embodiment is lower than the softening temperature of the cladding glass layer 20R of the core-covered rod 2 in contact with the filling glass rod 4. Therefore, as described above, in the sintering process P3, the filling glass rod 4 causes viscous flow before the clad glass layer 20R. For this reason, the gap formed between the filling glass rod 4 and the core coating rod 2 before the sintering step P3 can be more appropriately filled with the filling glass rod 4 that has caused viscous flow in the sintering step P3. . Therefore, it is possible to further suppress the formation of unnecessary gaps in the manufactured multi-core fiber preform 1P.

  Moreover, in this embodiment, the glass rod 4 for a filling is arrange | positioned so that the core covering rod 2 adjacent to each other arrange | positioned in the position which contacts soot 3 may be contacted. Therefore, a narrow gap formed between the outer peripheral surfaces of these core covering rods 2 can be covered with the filling glass rod 4. Moreover, the filling glass rod 4 has a smaller diameter than the core-covered rod 2 with which the filling glass rod 4 contacts. For this reason, the clearance gap between the outer peripheral surface of the core coating rod 2 and the outer peripheral surface of the glass rod 4 for filling is between the outer peripheral surfaces of the core coating rod 2 in the case where the glass rod 4 for filling is not arrange | positioned like 1st Embodiment. Smaller than the gap. For this reason, the soot 3 is easy to fill the gap in the external process P2, and between the glass part derived from the soot 3 and the glass part derived from the core coating rod 2 and the filling glass rod 4 in the sintering process P3. It is possible to suppress the formation of gaps.

  The present invention has been described above by taking the first and second embodiments as examples, but the present invention is not limited to these.

  For example, in the above-described embodiment, the binding band 51 is used when a plurality of glass rods including the core-covered rod 2 are bundled, but they may be bundled by other methods. Moreover, although the both ends of the several glass rod bundled were fixed to the dummy glass rod 52, you may maintain the state with which the glass rod was bundled by the other method.

  In the above embodiment, the multi-core fiber 1 in which each core 10 is directly coated with the clad 20 has been described as an example. However, the MCF may be a so-called trench type MCF. In the trench type MCF, each core is individually covered with an inner clad having a lower refractive index than that of the core, and each inner clad is further individually covered with a trench part 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 an MCF, the core covering 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, and a glass layer serving as a trench portion is formed. The structure is covered with a glass layer serving as a clad. The MCF can be manufactured in the same manner as in the above embodiment except that the core-covered rod having such a structure is used.

  The softening temperature of the filling glass rod 4 described in the second embodiment may be lower than the temperature at which the soot 3 becomes transparent glass, and may be the same as the softening temperature of the cladding glass layer 20R. It may be higher than the softening temperature of 20R.

  Moreover, in the said embodiment, since the manufacturing method which manufactures the multi-core fiber 1 which has the three cores 10 was demonstrated, although the number of the core covering rods 2 was set to three, the number of the cores of a multi-core fiber is not this limitation. 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. In this arrangement, it is considered that the core covering rod 2 arranged in the center does not come into contact with the soot. In this case, the softening temperature of the clad glass layer 20R of the core-covered rod 2 disposed at the center may be higher than the temperature at which the soot becomes transparent glass.

  Moreover, in the manufacturing method of the base material for multi-core fibers of this invention, the softening temperature of the part which contacts the soot 3 in the glass rod arrange | positioned in the position which contacts the soot 3 is lower than the temperature at which soot turns into transparent glass. It ’s fine. Therefore, for example, only the vicinity of the outer peripheral surface of the cladding glass layer 20R of the core-covered rod 2 or the filling glass rod 4 may have a softening temperature lower than the temperature at which the soot 3 becomes transparent glass. Further, as long as the softening temperature of the portion of the core-covered rod 2 that comes into contact with the soot 3 is lower than the temperature at which the soot 3 becomes transparent vitrified, the one in the vicinity of the outer peripheral surface of the cladding glass layer 20R or the filling glass rod 4 The softening temperature of the part does not have to be lower than the temperature at which the soot 3 becomes transparent glass.

  Moreover, the dopant added in order to make the softening temperature of the clad glass layer 20R and the filling glass rod 4 lower than the temperature at which the soot 3 becomes transparent glass is not limited to fluorine. For example, germanium (Ge), chlorine (Cl), boron (B), phosphorus (P), etc. can be mentioned as a dopant.

  As described above, according to the present invention, a method for manufacturing a base material for a multi-core fiber and a method for manufacturing a multi-core fiber capable of suppressing the formation of unnecessary gaps are provided. Can be used.

DESCRIPTION OF SYMBOLS 1 ... Multi-core fiber 1P ... Base material for multi-core fibers 2 ... Core coating rod 3 ... Soot 4 ... Glass rod for filling 10 ... Core 10P ... Base material core part 10R- ..Core rod 20 ... Clad 20P ... Base material clad 20R ... Clad glass layer 51 ... Bundling band 52 ... Dummy glass rod 53 ... Oxyhydrogen burner

Claims (7)

A bundle step of bundling a plurality of glass rods including a plurality of core-covered rods coated with a clad glass layer whose outer peripheral surface of a core rod to be a core is a part of a clad;
An external step of depositing soot as another part of the clad on the outer peripheral surfaces of the bundled glass rods;
A sintering step of heating the plurality of glass rods on which the soot is deposited to form the soot and the glass rod as an integral transparent glass body;
With
The softening temperature of the portion in contact with the soot of the glass rod is placed in contact with soot deposited the soot rather lower than the temperature at which the transparent glass,
At least a portion of the glass rod disposed at a position in contact with the soot is the core-covered rod;
The softening temperature of the cladding glass layer, the multi-core fiber preform which deposited the soot is characterized by low Ikoto than the temperature at the time of vitrification of the core coated rods which are placed in contact with the soot Manufacturing method. These cores are arranged such that at least two core covering rods are arranged adjacent to each other and in contact with the soot, and a glass rod for filling smaller in diameter than the core covering rods is in contact with the soot. Placed in contact with the covering rod,
The method for producing a base material for a multi-core fiber according to claim 1 , wherein a softening temperature of the glass rod for filling is lower than a temperature at which the deposited soot becomes transparent vitrified. The base material for multi-core fibers according to claim 2 , wherein the softening temperature of the glass rod for filling is lower than the softening temperature of the clad glass layer of the core-covered rod in contact with the glass rod for filling. Method. The portion of the glass rod that comes into contact with the soot is in contact with the soot is silica glass doped with fluorine;
The method for producing a base material for a multi-core fiber according to any one of claims 1 to 3 , wherein the soot is pure silica glass. The method for manufacturing a base material for a multi-core fiber according to claim 4 , wherein the sintering step is performed in an atmosphere containing a fluorine-based gas. In the bundling step, one end of each glass rod is fixed to a dummy glass rod and the other end of each glass rod is fixed to another dummy glass rod. The method for producing a base material for a multi-core fiber according to any one of claims 1 to 5 , wherein the glass rod is kept in a bundled state. Method of manufacturing a multicore fiber, characterized in that it comprises a drawing step of drawing the preform for the multicore fiber produced by the production method of the multi-core fiber preform according to any one of claims 1 to 6.

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