JP2019218250A - Method for manufacturing optical fiber and method for manufacturing optical fiber preform - Google Patents

Abstract

To provide a method for manufacturing an optical fiber, capable of efficiently adding alkali metal or alkaline earth metal to a core part, and a method for manufacturing an optical fiber preform.SOLUTION: The method for manufacturing an optical fiber comprises: the preparation step of preparing a first intermediate constituted of a core formation part consisting of glass and used as the core part and a cladding formation part consisting of glass having a refractive index lower than that of the core part and used as a part of the cladding part and having a gap part extended in the longitudinal direction of the core formation part between an outer layer part and the core formation part; the fine particle charging step of charging glass fine particles including an alkali metal compound or an alkaline earth metal compound in the gap part of the first intermediate to prepare a second intermediate; and the optical fiber manufacturing step of manufacturing the optical fiber having the alkali metal or the alkaline earth metal added to at least the core part using the second intermediate.SELECTED DRAWING: Figure 2

Description

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

  Conventionally, it has been proposed to manufacture an optical fiber or an optical fiber preform using quartz glass to which an alkali metal or an alkaline earth metal is added (see Patent Documents 1 to 5). As a method of adding an alkali metal or an alkaline earth metal to such quartz glass, for example, Patent Documents 1 and 2 disclose vaporized gas of an alkali metal or an alkaline earth metal on the surface of a porous body made of quartz glass. A method of diffusing an alkali metal or an alkaline earth metal from the surface of the porous body by contacting the porous body is disclosed. Patent Documents 3 and 4 disclose that an alkali metal is diffused on the inner surface of the glass pipe by heating the glass pipe while introducing a vaporized gas of the alkali metal into the inside of the glass pipe made of quartz glass. A method is disclosed. Patent Literature 5 discloses a method in which an alkali metal is introduced from the surface into a quartz glass rod by immersing the quartz glass rod in a melt of an alkali metal compound.

JP-A-63-40744 JP 2013-199400 A JP-T-2005-537210 JP 2013-136485 A JP 2013-199401 A

  In general, adding an alkali metal or an alkaline earth metal to quartz glass used as a material in the production of an optical fiber or an optical fiber preform, and diffusing the alkali metal or the alkaline earth metal to the core of the optical fiber, This is effective for reducing the transmission loss of the optical fiber. For this reason, in the production of an optical fiber or an optical fiber preform, in recent years, there has been a demand for efficiently adding an alkali metal or an alkaline earth metal to a core portion.

  The present invention has been made in view of the above circumstances, and provides a method for manufacturing an optical fiber and a method for manufacturing an optical fiber preform capable of efficiently adding an alkali metal or an alkaline earth metal to a core portion. The purpose is to:

  In order to solve the above-mentioned problems and achieve the object, a method for manufacturing an optical fiber according to the present invention is a method for manufacturing an optical fiber including a core portion and a clad portion formed on an outer periphery of the core portion. A core forming portion made of glass and serving as the core portion, and a cladding forming portion made of glass having a lower refractive index than the core portion and serving as a part of the clad portion, and an outer layer portion and the core forming portion A step of preparing a first intermediate having a void extending in the longitudinal direction of the core forming portion between the first intermediate and a glass fine particle containing an alkali metal compound or an alkaline earth metal compound; A fine particle filling step of filling the void portion to form a second intermediate, and using the second intermediate, an optical fiber having an alkali metal or an alkaline earth metal added to at least the core portion. Characterized in that it comprises an optical fiber manufacturing process for forming the.

  Further, in the method for manufacturing an optical fiber according to the present invention, in the above invention, the preparing step includes disposing a core rod including the core forming portion and a glass portion adjacent over the outer periphery of the core forming portion inside a glass pipe. Then, the gap is formed between the outer layer portion of the glass pipe and the core rod, and the clad forming portion is constituted by the glass pipe and the glass portion of the core rod.

  Further, in the method for manufacturing an optical fiber according to the present invention, in the above invention, the preparation step includes providing a hole extending in a longitudinal direction of the core forming portion in the cladding forming portion of the first intermediate body, The gap is formed between an outer layer of the first intermediate and the core forming portion.

  Further, in the method for manufacturing an optical fiber according to the present invention, in the above invention, the glass fine particles are a mixture of the alkali metal compound or the alkaline earth metal compound and quartz glass fine particles.

  Further, in the method for manufacturing an optical fiber according to the present invention, in the above invention, the glass fine particles are obtained by adhering the sublimated alkali metal compound or the alkaline earth metal compound to the surface of quartz glass fine particles. There is a feature.

  Further, in the method for manufacturing an optical fiber according to the present invention, in the above invention, the glass fine particles are obtained by immersing quartz glass fine particles in a solution containing the alkali metal compound or the alkaline earth metal compound, and It is characterized in that a compound or the alkaline earth metal compound is attached to the surface of the quartz glass fine particles.

Further, in the method for manufacturing an optical fiber according to the present invention, in the above invention, the alkali metal compound or the alkaline earth metal compound is K ₂ CO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , Rb ₂ CO _3. , Cs ₂ CO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , KNO ₃ , KCl, NaCl, RbNO ₃ , or RbCl.

  Further, in the method for manufacturing an optical fiber according to the present invention, in the above-described invention, the preparation step is more than an intermediate position between an outer layer portion of the first intermediate and a longitudinal center axis of the core forming portion. The void portion is formed in a region near the core forming portion.

  In the method for manufacturing an optical fiber according to the present invention, in the above invention, the fine particle filling step is characterized by filling the fine glass particles having an average particle diameter of 30 μm to 500 μm.

  Further, in the method for manufacturing an optical fiber according to the present invention, in the above invention, the optical fiber manufacturing step heat-treats the second intermediate while depressurizing the inside of the gap filled with the glass fine particles, A process of melting the core-forming portion and the cladding-forming portion, densifying the filler of the glass fine particles, and drawing an optical fiber in which at least the core portion is doped with an alkali metal or an alkaline earth metal. It is characterized by.

  Further, in the method for manufacturing an optical fiber according to the present invention, in the above invention, the optical fiber manufacturing step heat-treats the second intermediate while depressurizing the inside of the gap filled with the glass fine particles, The core forming part and the clad forming part are melted and the filler of the glass fine particles is densified to prepare an optical fiber preform to which an alkali metal or an alkaline earth metal contained in the filler of the glass fine particles is added. A sintering step and melting the optical fiber preform to which an alkali metal or an alkaline earth metal is added by a heat treatment to draw an optical fiber having an alkali metal or an alkaline earth metal added to at least the core portion. And a drawing step.

  Further, the method for manufacturing an optical fiber preform according to the present invention is a method for manufacturing an optical fiber preform for manufacturing an optical fiber including a core portion and a clad portion formed on the outer periphery of the core portion, A core forming portion made of glass and serving as the core portion, and a clad forming portion made of glass having a lower refractive index than the core portion and being part of the clad portion, wherein an outer layer portion and the core forming portion A step of preparing a first intermediate having a void portion extending in the longitudinal direction of the core forming portion between the first intermediate and a glass fine particle containing an alkali metal compound or an alkaline earth metal compound; A fine particle filling step of filling a void portion to produce a second intermediate, and performing a heat treatment on the second intermediate while reducing the pressure in the void filled with the glass fine particles; A sintering step of melting the lad forming portion and densifying the filler of the glass fine particles to produce an optical fiber preform to which an alkali metal or an alkaline earth metal contained in the filler of the glass fine particles is added. It is characterized by including.

  Further, in the method for manufacturing an optical fiber preform according to the present invention, in the above-described invention, the preparation step includes: mounting a core rod including the core forming portion and a glass portion adjacent over the outer periphery of the core forming portion inside a glass pipe. And the gap portion is formed between the outer layer portion of the glass pipe and the core rod, and the clad forming portion is constituted by the glass pipe and the glass portion of the core rod. .

  Further, in the method for manufacturing an optical fiber preform according to the present invention, in the above invention, in the preparing step, a hole extending in a longitudinal direction of the core forming portion is provided in the cladding forming portion of the first intermediate body. The gap is formed between an outer layer portion of the first intermediate and the core forming portion.

  Further, in the method for producing an optical fiber preform according to the present invention, in the above invention, the glass fine particles are a mixture of the alkali metal compound or the alkaline earth metal compound and quartz glass fine particles. .

  Further, in the method for manufacturing an optical fiber preform according to the present invention, in the above invention, the glass fine particles have the alkali metal compound or the alkaline earth metal compound in a sublimated state adhered to the surface of quartz glass fine particles. Characterized in that:

  Further, in the method for producing an optical fiber preform according to the present invention, in the above invention, the glass fine particles are obtained by immersing quartz glass fine particles in a solution containing the alkali metal compound or the alkaline earth metal compound, It is characterized in that an alkali metal compound or the alkaline earth metal compound is attached to the surface of the quartz glass fine particles.

Further, in the method for manufacturing an optical fiber preform according to the present invention, in the above-mentioned invention, the alkali metal compound or the alkaline earth metal compound may be K ₂ CO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , Rb _2. It is characterized by being CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , KNO ₃ , KCl, NaCl, RbNO ₃ or RbCl.

  Further, in the method for manufacturing an optical fiber preform according to the present invention, in the above-described invention, the preparing step is performed by setting an intermediate position between an outer layer portion of the first intermediate and a longitudinal center axis of the core forming portion. Also, the gap portion is formed in a region near the core formation portion.

  In the method for producing an optical fiber preform according to the present invention, in the above invention, the fine particle filling step is characterized by filling the glass fine particles having an average particle diameter of 30 μm to 500 μm.

  ADVANTAGE OF THE INVENTION According to this invention, there exists an effect which can provide the manufacturing method of the optical fiber which can add an alkali metal or alkaline-earth metal to a core part efficiently, and the manufacturing method of an optical fiber preform.

FIG. 1 is a schematic cross-sectional view showing one configuration example of an optical fiber manufactured by the optical fiber manufacturing method according to the first embodiment of the present invention. FIG. 2 is a flowchart showing an example of the method for manufacturing an optical fiber and the method for manufacturing an optical fiber preform according to Embodiment 1 of the present invention. FIG. 3 is a schematic diagram illustrating a preparation step and a particle filling step of the manufacturing method according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating an example of a second intermediate formed by performing the fine particle filling step of the manufacturing method according to the first embodiment of the present invention. FIG. 5 is a schematic cross-sectional view taken along line AA of the second intermediate shown in FIG. FIG. 6 is a schematic diagram illustrating a drawing step of the manufacturing method according to the first embodiment of the present invention. FIG. 7 is a schematic diagram illustrating a sintering step of the manufacturing method according to the first embodiment of the present invention. FIG. 8 is a schematic diagram illustrating a drawing step using an optical fiber preform in the manufacturing method according to the first embodiment of the present invention. FIG. 9 is a schematic diagram illustrating a preparation step and a fine particle filling step of the manufacturing method according to the second embodiment of the present invention. FIG. 10 is a diagram illustrating an example of a second intermediate formed by performing the fine particle filling step of the manufacturing method according to the second embodiment of the present invention. FIG. 11 is a schematic diagram illustrating a fine particle filling step of the manufacturing method according to the third embodiment of the present invention. FIG. 12 is a schematic diagram illustrating the production of glass fine particles to be filled in the fine particle filling step of the manufacturing method according to Embodiment 3 of the present invention. FIG. 13 is a schematic diagram illustrating a fine particle filling step of the manufacturing method according to the fourth embodiment of the present invention. FIG. 14 is a schematic diagram illustrating the production of glass fine particles to be filled in the fine particle filling step of the manufacturing method according to Embodiment 4 of the present invention. FIG. 15 is a diagram illustrating the position of the void in the first intermediate in the present experiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the embodiment. In each drawing, the same or corresponding elements are denoted by the same reference numerals as appropriate.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing one configuration example of an optical fiber manufactured by the optical fiber manufacturing method according to the first embodiment of the present invention. The optical fiber 1 according to the first embodiment is an optical fiber made of silica-based glass, and includes a core 1a and a clad 1b formed on the outer periphery of the core 1a, as shown in FIG. . Although not shown, a coating is applied to the outer periphery of the cladding 1b. This coating uses what is usually used for an optical fiber.

The core portion 1a is made of quartz glass to which germania (GeO ₂ ) as a dopant for increasing the refractive index and an alkali metal or an alkaline earth metal for reducing transmission loss are added. The clad portion 1b is made of quartz glass obtained by adding the above alkali metal or alkaline earth metal to pure quartz glass to which a dopant for adjusting the refractive index is not added, and has a lower refractive index than the core portion 1a.

  Next, a method for manufacturing an optical fiber and a method for manufacturing an optical fiber preform according to Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 2 is a flowchart showing an example of the method for manufacturing an optical fiber and the method for manufacturing an optical fiber preform according to Embodiment 1 of the present invention. Hereinafter, “the manufacturing method of the optical fiber and the manufacturing method of the optical fiber preform” is appropriately abbreviated as “the manufacturing method”.

  The method for manufacturing an optical fiber according to the first embodiment includes a preparation step, a particle filling step, and an optical fiber manufacturing step. The method for manufacturing an optical fiber preform according to the first embodiment includes a preparation step, a particle filling step, and a sintering step similar to those of the method for manufacturing an optical fiber.

  That is, as shown in FIG. 2, in the manufacturing method according to the first embodiment, first, a preparation step (step S101) for preparing necessary members is performed. FIG. 3 is a schematic diagram illustrating a preparation step and a particle filling step of the manufacturing method according to the first embodiment of the present invention. In the preparation step in the first embodiment, as shown in FIG. 3, a first intermediate 4 having a gap 4a between the glass pipe 2 and the core rod 3 is prepared.

  The glass pipe 2 is a part of the clad portion 1b of the optical fiber 1, and is a high-purity synthetic quartz pipe to which a dopant for adjusting the refractive index is not added. The inner diameter and the outer diameter of the glass pipe 2 are each set so that the cylindrical portion of the glass pipe 2 has an appropriate strength and can form an appropriate gap between the inner surface of the cylindrical portion and the core rod 3. Is set. The length of the cylindrical portion of the glass pipe 2 is set to a length suitable for accommodating the core rod 3. The inner surface of the glass pipe 2 is dry-etched to perform a surface cleaning process. After this surface cleaning process is performed, the lower end 2c of the glass pipe 2 is sealed as shown in FIG. On the other hand, the upper end 2b of the glass pipe 2 is open.

  As shown in FIG. 3, the core rod 3 includes a core forming part 3a and a clad forming part 3b as a glass part adjacent to the outer periphery of the core forming part 3a. The core forming part 3a becomes the core part 1a of the optical fiber 1, and the clad forming part 3b becomes a part of the clad part 1b. The core forming portion 3a is made of quartz glass to which germania is added so as to have a refractive index of the core portion 1a, and the cladding forming portion 3b is made of pure quartz glass so as to have a refractive index of the cladding portion 1b. In the first embodiment, the core rod 3 is manufactured by the VAD method, but may be manufactured by the OVD method, the MCVD method, or the like.

  In this preparation step, the positioning member 5 is arranged at the bottom of the glass pipe 2 before the core rod 3 is arranged inside the glass pipe 2. The positioning member 5 is a disk-shaped member having an outer diameter substantially equal to the inner diameter of the glass pipe 2, and is made of high-purity synthetic quartz glass. Subsequently, as shown in FIG. 3, the core rod 3 is inserted and arranged inside the glass pipe 2. At this time, in the first embodiment, one piece of the glass pipe 2 is set so that the central axis in the longitudinal direction of the cylindrical portion coincides with the central axis in the longitudinal direction of the core rod 3 (that is, the central axis in the longitudinal direction of the core forming portion 3a). Are disposed. The lower end of the core rod 3 in the glass pipe 2 is fitted into a fitting hole (not shown) formed in the positioning member 5. Thereby, the position of the lower end of the core rod 3 in the glass pipe 2 is determined.

  By arranging the core rod 3 inside the glass pipe 2 as described above, a gap 4a is formed between the outer layer 2a of the glass pipe 2 and the core rod 3 in this preparation step, as shown in FIG. . At the same time, in this preparation step, the glass pipe 2 and the glass portion (cladding forming portion 3b) of the core rod 3 around the core forming portion 3a constitute a cladding forming portion of the first intermediate body 4. As a result, the core forming portion made of glass and serving as the core portion 1a of the optical fiber 1 and the cladding forming portion made of glass having a lower refractive index than the core portion 1a and serving as a part of the clad portion 1b of the optical fiber 1 are provided. Is prepared. Such a first intermediate body 4 has a gap 4 a extending in the longitudinal direction of the core forming portion 3 a between the outer layer portion (ie, the outer layer portion 2 a of the glass pipe 2) and the core forming portion 3 a of the core rod 3. Over the outer circumference of the core rod 3. In particular, the gap portion 4a is formed in this preparation step in a region closer to the core forming portion 3a than an intermediate position between the outer layer portion 2a of the first intermediate body 4 and the central axis in the longitudinal direction of the core forming portion 3a. Is preferred.

  After the completion of the above-described preparation step, a fine particle filling step (step S102) is performed as shown in FIG. In the fine particle filling step in the first embodiment, as shown in FIG. 3, a gap 4 a of the first intermediate 4 (specifically, a gap between the inner surface of the glass pipe 2 and the outer layer of the core rod 3). , Glass fine particles 7 are charged and filled.

The glass fine particles 7 are glass fine particles containing an alkali metal compound or an alkaline earth metal compound. In the first embodiment, the glass fine particles 7 are a mixture produced by mixing an alkali metal compound or an alkaline earth metal compound with quartz glass fine particles. The quartz glass fine particles are made of, for example, high-purity quartz glass to which a dopant for adjusting the refractive index is not added. Examples of the above alkali metal compound or alkaline earth metal compound include K ₂ CO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , KNO ₃ , KCl, NaCl, RbNO ₃ , RbCl and the like can be mentioned. The average particle size of the glass fine particles 7 corresponds to the average particle size of the quartz glass fine particles, and is, for example, 30 μm to 500 μm. In the first embodiment, the average particle diameter of the glass fine particles 7 is set to 120 μm as an example.

  Subsequently, in this fine particle filling step, as shown in FIG. 3, a positioning member 6 is inserted into the glass pipe 2, and the core rod 3 in the glass pipe 2 is positioned by the positioning member 6. The positioning member 6 is a disk-shaped member having an outer diameter substantially equal to the inner diameter of the glass pipe 2 and is made of high-purity synthetic quartz glass. As shown in FIG. 3, the positioning member 6 has a fitting hole 6a and a ventilation hole 6b. The fitting hole 6a is a portion where the upper end of the core rod 3 is fitted, and penetrates the positioning member 6 in the first embodiment, but does not have to penetrate. The plurality of ventilation holes 6b are for ensuring air permeability between the outside and the inside of the glass pipe 2. Further, by positioning the positioning member 6 in the glass pipe 2 by making the inside diameter of the ventilation hole 6b enough to allow the glass fine particles 7 to pass through, the glass fine particles 7 are removed from the upper part of the glass pipe 2 via the positioning member 6. Can also be filled. In the first embodiment, the position of the core rod 3 in the glass pipe 2 is determined by fitting the upper end of the core rod 3 into the fitting hole 6a formed in the positioning member 6. At this time, the positioning member 6 positions the core rod 3 in cooperation with the positioning member 5 arranged at the bottom in the glass pipe 2 as shown in FIG.

  In the first embodiment, the glass particles 7 are filled in the voids 4a of the first intermediate 4 as in the above-described fine particle filling step, thereby producing the second intermediate 8 shown in FIG. Thus, the second intermediate 8 used as a material for manufacturing the optical fiber 1 or the optical fiber preform in the first embodiment is obtained (Step S103).

  FIG. 4 is a diagram illustrating an example of a second intermediate formed by performing the fine particle filling step of the manufacturing method according to the first embodiment of the present invention. FIG. 5 is a schematic cross-sectional view taken along line AA of the second intermediate shown in FIG. The second intermediate 8 in the first embodiment is manufactured by filling the glass particles 7 into the voids 4a of the first intermediate 4 shown in FIG. 3, and as shown in FIGS. It is composed of a glass pipe 2, a core rod 3, positioning members 5 and 6, and glass particles 7. In the second intermediate body 8, the upper end of the core rod 3 is fitted in the fitting hole 6 a of the positioning member 6. However, since a plurality of ventilation holes 6b are formed in the positioning member 6 as shown in FIG. 4 in addition to the fitting holes 6a, the outside and the inside of the second intermediate body 8 (for example, the glass fine particles 7 The air permeability with the filled gap 4a) is ensured.

  Further, in the first embodiment, the gap portion 4a is moved from the intermediate position between the outer layer portion 2a of the first intermediate body 4 and the longitudinal center axis of the core forming portion 3a shown in FIG. Is formed over the outer periphery of the core rod 3 in a region near the core forming portion 3a. That is, as shown in FIG. 5, the filler of the glass fine particles 7 in the gap 4 a is located at an intermediate position Pc between the outer layer 2 a of the second intermediate 8 and the central axis in the longitudinal direction of the core forming portion 3 a. Also exists in a region near the core forming portion 3a over the outer periphery of the clad forming portion 3b of the core rod 3.

  Thereafter, in the manufacturing method according to the first embodiment, an optical fiber manufacturing process for manufacturing an optical fiber in which at least a core portion is doped with an alkali metal or an alkaline earth metal using the second intermediate body 8, or A sintering step for producing an optical fiber preform in which at least a core forming portion is added with an alkali metal or an alkaline earth metal using the intermediate 2 is performed. Here, the optical fiber manufacturing process includes a case where “an optical fiber is manufactured from the second intermediate body 8 without passing through the optical fiber preform” and a case where “the optical fiber is manufactured from the second intermediate body 8 through the optical fiber base material”. And "manufacturing". Further, the sintering step for manufacturing the optical fiber preform as an object is the sintering step performed in the optical fiber manufacturing step in the case of “manufacturing an optical fiber from the second intermediate 8 via the optical fiber preform”. It is the same as the process.

  That is, when an optical fiber is manufactured from the second intermediate body 8 without passing through the optical fiber preform, the optical fiber manufacturing step includes a drawing step (step S105) illustrated in FIG. In this case, what is produced from the second intermediate 8 is an optical fiber (step S104, optical fiber). Therefore, after producing the second intermediate 8 as described above, the optical fiber is removed from the second intermediate 8. A drawing step (step S105) for drawing is performed.

  In the drawing step of step S105, the second intermediate body 8 is subjected to a heat treatment while depressurizing the inside of the space 4a filled with the glass microparticles 7 in the second intermediate body 8, whereby the core of the second intermediate body 8 is formed. The forming part and the clad forming part are melted and the packing of the glass fine particles 7 is densified, and an optical fiber having at least a core portion to which an alkali metal or an alkaline earth metal is added is drawn.

  FIG. 6 is a schematic diagram illustrating a drawing step of the manufacturing method according to the first embodiment of the present invention. As shown in FIG. 6, in the drawing step of step S105, a lid 100 is placed on the upper end side of the second intermediate body 8, and the inside of the second intermediate body 8 is made airtight. The lid 100 is connected to a gas exhaust pipe 101 communicating with the inside of the second intermediate body 8 in an airtight state. A vacuum pump 102 and a gas exhaust pipe 103 are sequentially connected to the gas exhaust pipe 101. In addition, the lid 100 is provided with a pressure gauge 104 for measuring the pressure inside the second intermediate body 8 in an airtight state. The pressure gauge 104 transmits data of the measurement result of the measured pressure value to the control unit 110. The control unit 110 controls the vacuum pump 102 based on the data of the measurement result of the pressure value, and controls the internal atmosphere (the inside of the glass pipe 2) of the air gap 4 a of the second intermediate body 8 before the drawing step. Atmosphere) can be reduced in pressure.

  Subsequently, the lower end of the second intermediate body 8 is heated to, for example, 2200 ° C. by the heater 105 a of the optical fiber drawing furnace 105 while maintaining the pressure of the internal atmosphere of the second intermediate body 8 in a reduced pressure state. Thereby, the glass pipe 2 constituting the second intermediate body 8, the core rod 3, the positioning members 5, 6 (see FIG. 4), and the filler of the glass microparticles 7 are heated and melted, and the optical fiber F1 is drawn. I do. At this time, the quartz glass fine particles contained in the glass fine particles 7 are densified and sintered to form a transparent glass. At the same time, the metal component (alkali metal or alkaline earth metal) of the alkali metal compound or alkaline earth metal compound contained in the glass microparticles 7 is mixed with the inside of each of the core forming portion 3a and the cladding forming portion 3b of the core rod 3, It diffuses into the inside of the glass pipe 2. As a result, the transparent glass is integrated with the glass pipe 2, the clad forming portion 3b of the core rod 3, and the positioning members 5 and 6 to form a clad portion 1b of the optical fiber 1 to which an alkali metal or an alkaline earth metal is added. Become. The core forming portion 3a of the core rod 3 becomes the core portion 1a of the optical fiber 1 to which an alkali metal or an alkaline earth metal is added.

  After that, the drawn optical fiber F1 is coated on its outer periphery by the coating forming device 106, thereby becoming an optical fiber F2 (optical fiber 1 in FIG. 1). The optical fiber F2 is taken up by the capstan roller 107, and is taken up by the take-up mechanism 109 via the guide roll. As described above, the optical fiber 1 manufactured by the drawing process in step S105 is obtained (step S106), and the present process ends.

  Here, the optical fiber 1 having a cladding outer diameter of 125 μm was manufactured by the drawing step of step S105, and the transmission loss when light was transmitted by the obtained optical fiber 1 was confirmed. As a result, the transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1550 nm was a low value of 0.175 dB / km on average. The transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1310 nm was a good characteristic of 0.309 dB / km on average.

  On the other hand, the optical fiber manufacturing process includes a sintering process (step S107) and a drawing process (step S109) shown in FIG. 2 when an optical fiber is manufactured from the second intermediate 8 via the optical fiber preform. In this case, since what is produced from the second intermediate 8 is the optical fiber preform (step S104, preform), after producing the second intermediate 8 as described above, this second intermediate 8 is used. Sintering step (Step S107) for producing an optical fiber preform by performing an optical fiber preform (Step S108, optical fiber), and thereafter, a drawing step of drawing an optical fiber from the optical fiber preform. (Step S109) is performed.

  In the sintering step of step S107, the second intermediate body 8 is subjected to a heat treatment while reducing the pressure inside the void portion 4a filled with the glass particles 7 in the second intermediate body 8, thereby forming a core of the second intermediate body 8. The forming part and the clad forming part are melted and the filler of the glass microparticles 7 is densified to prepare an optical fiber preform to which the alkali metal or alkaline earth metal contained in the filler of the glass microparticles 7 is added.

  FIG. 7 is a schematic diagram illustrating a sintering step of the manufacturing method according to the first embodiment of the present invention. As shown in FIG. 7, in the sintering step of step S107, similarly to the case of the drawing step of step S105 described above, the lid 100 is placed on the upper end side of the second Is sealed, and the internal atmosphere (the internal atmosphere of the glass pipe 2) such as the gap 4a of the second intermediate body 8 is reduced by the action of the vacuum pump 102. Although not particularly shown in FIG. 7, when the internal atmosphere of the second intermediate body 8 is depressurized, the pressure inside the second intermediate body 8 is measured by the pressure gauge 104, and based on the data of the measured pressure value. The control unit 110 may control the vacuum pump 102.

  In the sintering step, the second intermediate 8 is set in the heating furnace 111 as shown in FIG. The heating furnace 111 heats the second intermediate body 8 from its outer periphery (the outer periphery of the glass pipe 2) in parallel with the above-described depressurization processing of the internal atmosphere of the second intermediate body 8. At this time, the heating furnace 111 sequentially heats the second intermediate body 8 from the lower end 2c to the upper end 2b while moving from the lower end 2c to the upper end 2b along the outer periphery of the glass pipe 2. Thereby, the second intermediate body 8 is sequentially melted from the lower end portion 2c to the upper end portion 2b and reduced in diameter, and the glass pipe 2 constituting the second intermediate body 8, the core rod 3, the positioning members 5, 6, and The filler of the glass fine particles 7 is melted. At this time, the quartz glass fine particles contained in the glass fine particles 7 are densified and sintered to form a transparent glass. At the same time, the metal component (alkali metal or alkaline earth metal) of the alkali metal compound or alkaline earth metal compound contained in the glass microparticles 7 is mixed with the inside of each of the core forming portion 3a and the cladding forming portion 3b of the core rod 3, It diffuses into the inside of the glass pipe 2. As a result, the transparent glass is integrated with the glass pipe 2, the clad forming portion 3b of the core rod 3, and the positioning members 5, 6 to form a transparent clad forming portion to which an alkali metal or an alkaline earth metal is added. The core forming part 3a of the core rod 3 is a transparent core forming part to which an alkali metal or an alkaline earth metal is added.

  In this way, the core forming portion serving as the core portion 1a of the optical fiber 1 and the cladding forming portion serving as the cladding portion 1b of the optical fiber 1 are provided, and the core forming portion and the cladding forming portion (particularly, the outer periphery of the core forming portion) are provided. A transparent optical fiber preform 10 (see FIG. 7) in which an alkali metal or an alkaline earth metal is added to (a portion in the vicinity) is produced.

  Thereafter, in the drawing step of step S109, the optical fiber preform 10 to which the alkali metal or the alkaline earth metal is added is melted by a heat treatment, whereby the alkali metal or the alkaline earth metal is added to at least the core portion. Drawn optical fiber.

  FIG. 8 is a schematic diagram illustrating a drawing step using an optical fiber preform in the manufacturing method according to the first embodiment of the present invention. As shown in FIG. 8, in the drawing step of step S109, the optical fiber drawing furnace 105 is replaced with the optical fiber preform 10 in the same manner as in the case where the second intermediate body 8 in the above-described step S105 is replaced with the optical fiber preform 10. The lower end of the optical fiber preform 10 is heated by the heater 105a to draw the optical fiber F1. After that, the drawn optical fiber F1 is coated with the coating forming device 106 in the same manner as in the case of the above-described drawing step of step S105, thereby becoming the optical fiber F2 (the optical fiber 1 in FIG. 1). . Although not particularly shown in FIG. 8, the optical fiber F2 is taken up by the above-described capstan roller 107, and is taken up by the take-up mechanism 109 via the guide roll. The optical fiber 1 manufactured as described above is obtained (Step S110), and the present process is terminated.

  Here, the optical fiber 1 having a cladding outer diameter of 125 μm was manufactured by the drawing step of step S109, and the transmission loss when light was transmitted by the obtained optical fiber 1 was confirmed. As a result, similarly to the optical fiber 1 manufactured in the above-described step S105, the transmission loss was a low value.

  In the wire drawing step in step S105 and the sintering step in step S107, the positioning member 6 is not floated by suction of the gas inside the second intermediate body 8 so as not to float. Weights may be placed on the The weight has a structure that does not block the ventilation hole 6b of the positioning member 6, and is preferably made of pure quartz glass.

  On the other hand, when the target product (target object) is an optical fiber preform, the preparation step of step S101 and the fine particle filling step of S102 shown in FIG. 2 are sequentially performed, whereby the second intermediate 8 (FIG. Reference) is produced. Subsequently, the sintering step of step S107 is performed using the second intermediate body 8, thereby producing the optical fiber preform 10 (see FIG. 7). Here, since the target is the optical fiber preform (step S108, preform), the drawing step of step S109 is not performed, and the optical fiber preform 10 obtained by the sintering process described above is treated as the target. Thus, the optical fiber preform 10 as the target is obtained (step S111), and the present process ends.

  In the manufacturing method according to the first embodiment of the present invention, the optical fiber 1 extends in the longitudinal direction of the core forming portion 3a between the core forming portion 3a serving as the core portion 1a and the outer layer portion 2a of the first intermediate body 4. The second gap is filled with glass fine particles 7 obtained by mixing an alkali metal compound or an alkaline earth metal compound with fine silica glass particles, and a filler of glass fine particles 7 is provided so as to surround the core forming portion 3a. The optical fiber 1 or the optical fiber preform 10 is manufactured by manufacturing the intermediate body 8 and performing an optical fiber manufacturing step or a sintering step using the second intermediate body 8.

  For this reason, the alkali metal compound or the alkaline earth metal compound can be directly filled together with the quartz glass fine particles into the clad forming portion which becomes the clad portion 1b of the optical fiber 1, and a larger amount of the alkali metal compound can be used as compared with the conventional method such as the diffusion method. Alternatively, since the alkaline earth metal compound can be included in the vicinity of the outer periphery of the core forming portion 3a, the heat treatment of the second intermediate body 8 in the optical fiber manufacturing process or the sintering process causes the core from the filler of the glass fine particles 7 The alkali metal or alkaline earth metal can be efficiently diffused and added to the forming portion 3a. By performing the drawing step using the second intermediate 8 or the optical fiber preform 10 in which the alkali metal or the alkaline earth metal is added to the core forming portion 3a in this manner, the core portion 1a of the optical fiber 1 is formed. Can be efficiently added with an alkali metal or an alkaline earth metal. Thereby, the periodic structure of the bonding between molecules in the quartz glass constituting the core portion 1a is made uniform, so that the dielectric constant of the quartz glass in the core portion 1a can be stabilized. The occurrence of Rayleigh scattering in the fiber 1 can be suppressed, and the transmission loss of the optical fiber 1 can be reduced.

  In addition, a gap 4a is provided in a region closer to the core forming portion 3a than an intermediate position (see an intermediate position Pc in FIG. 5) between the outer layer portion 2a of the first intermediate body 4 and the longitudinal center axis of the core forming portion 3a. Is formed. For this reason, the region of the first intermediate 4 can be easily filled with the glass particles 7. As a result, the alkali metal or alkaline earth metal can be efficiently diffused and added from the glass microparticles 7 to the core forming portion 3a, and the diffusion of the alkali metal or alkaline earth metal into the outer layer portion 2a can be suppressed. In addition, a decrease in mechanical strength of the drawn optical fiber 1 can be suppressed.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. Also in the second embodiment, the optical fiber 1 shown in FIG. 1 or the optical fiber preform 10 shown in FIG. 7 is manufactured as an object.

  Next, a method for manufacturing an optical fiber and a method for manufacturing an optical fiber preform according to Embodiment 2 of the present invention will be described. In the manufacturing method according to the second embodiment, the respective steps of steps S101 to S111 shown in FIG. 2 are appropriately performed according to the object to be manufactured. The second intermediate produced in the fine particle filling step of S102 is different from the first embodiment.

  FIG. 9 is a schematic diagram illustrating a preparation step and a fine particle filling step of the manufacturing method according to the second embodiment of the present invention. In the preparation step in the second embodiment, as shown in FIG. 9, a first intermediate body 11 composed of a core forming portion 3a and a cladding forming portion 3b and having a void portion 24a in the cladding forming portion 3b is prepared. .

  More specifically, in this preparation step, first, an optical fiber preform composed of the core forming portion 3a and the cladding forming portion 3b is prepared as a material that is a source of the first intermediate 11. In the prepared first preform 11 of the optical fiber preform, the core forming part 3a is a glass part to be the core part 1a of the optical fiber 1, and germania is added so that the refractive index of the core part 1a is obtained. Made of quartz glass. The clad forming part 3b is a glass part that becomes a part of the clad part 1b of the optical fiber 1, and is made of pure silica glass so as to have a refractive index of the clad part 1b. The clad forming part 3b is formed so as to be adjacent over the outer periphery of the core forming part 3a. The outer diameter of the clad forming part 3b is a desired multiple of the diameter of the core forming part 3a. Such an optical fiber preform-like first intermediate 11 is manufactured by the VAD method, but may be manufactured by the OVD method, the MCVD method, or the like.

  Subsequently, the upper and lower ends of the first intermediate body 11 in the form of an optical fiber preform are cut in the radial direction to have a predetermined length (for example, 2 m), and the core forming portion 3a is cut from one cut surface using a drill. A hole of a predetermined length extending in the longitudinal direction (for example, a through hole having a length of 2 m and formed by punching a through hole having a length of 1 m from both ends) is provided in the clad forming portion 3b. As a result, a gap 24a extending in the longitudinal direction of the core forming portion 3a is formed between the outer layer portion 11a of the first intermediate body 11 having the optical fiber preform and the core forming portion 3a. Thus, in the preparation step in the second embodiment, the first intermediate 11 including the core forming portion 3a and the cladding forming portion 3b provided with one or a plurality of void portions 24a is prepared. In the second embodiment, as shown in FIG. 9, four void portions 24a are formed in the clad forming portion 3b of the first intermediate body 11 so as to surround the core forming portion 3a. In addition, the void 24a is one in which one end is heated and sealed after the inner surface is dry-etched to perform a surface cleaning process. For example, as shown in FIG. 9, only the upper end 11 b side of the first intermediate 11 is opened by heating and sealing the lower end 11 c of the first intermediate 11 with a heater (not shown). It is in the state of having done. In particular, the void portion 24a is formed in this preparation step in a region closer to the core forming portion 3a than at an intermediate position between the outer layer portion 11a of the first intermediate body 11 and the longitudinal center axis CL of the core forming portion 3a. Preferably.

After the completion of the above-described preparation step, a fine particle filling step of step S102 is performed as shown in FIG. In the fine particle filling step according to the second embodiment, as shown in FIG. 9, the glass fine particles 7 are charged into the void portion 24 a of the first intermediate body 11 and filled. In the second embodiment, for example, as the glass fine particles 7, a mixture of silica glass fine particles made of high-purity quartz glass having an average particle diameter of 120 μm and high-purity potassium carbonate (K ₂ CO ₃ ) is prepared.

  In the second embodiment, the glass particles 7 are filled in the voids 24a of the first intermediate body 11 as in the fine particle filling step, and the second intermediate body 28 having the filler of the glass particles 7 in the voids 24a is formed. Make it. The obtained second intermediate 28 is used as a material for manufacturing the optical fiber 1 or the optical fiber preform 10 in the second embodiment.

  FIG. 10 is a diagram illustrating an example of a second intermediate formed by performing the fine particle filling step of the manufacturing method according to the second embodiment of the present invention. FIG. 10 is a schematic view of a cross section taken along line BB of the second intermediate body 28 shown in FIG. As shown in FIG. 10, the second intermediate body 28 in Embodiment 2 includes a core forming portion 3a, a cladding forming portion 3b provided with a void portion 24a, and a filler of the glass particles 7 in the void portion 24a. It is constituted by. Here, the void portion 24a is formed by the above-described preparation step such that the core is formed at a position higher than the intermediate position Pc between the outer layer portion 11a of the first intermediate body 11 and the longitudinal center axis CL of the core forming portion 3a shown in FIG. A region near the portion 3a is formed so as to surround the core forming portion 3a. That is, as shown in FIG. 10, the filler of the glass microparticles 7 in the void portion 24a is located between the outer layer portion 11a of the second intermediate member 28 and the longitudinal center axis CL of the core forming portion 3a. It exists in a region closer to the core forming portion 3a than the position Pc so as to surround the core forming portion 3a.

  Thereafter, when the optical fiber is manufactured from the second intermediate 28, the second intermediate 8 of the first embodiment described above is replaced with the second intermediate 28 of the second embodiment, and the drawing step of step S105 is performed. Done. That is, in the drawing step of step S105, the second intermediate 28 is subjected to a heat treatment while depressurizing the inside of the void 24a filled with the glass microparticles 7 in the second intermediate 28, whereby the second intermediate 28 is heated. The core forming portion 3a and the cladding forming portion 3b are melted and the filler of the glass fine particles 7 is densified, and an optical fiber having at least a core portion to which an alkali metal or an alkaline earth metal is added is drawn.

  At this time, the quartz glass fine particles contained in the glass fine particles 7 are densified and sintered to form a transparent glass. At the same time, the metal component (alkali metal or alkaline earth metal) of the alkali metal compound or alkaline earth metal compound contained in the glass microparticles 7 diffuses into the core forming portion 3a and the clad forming portion 3b. As a result, the transparent glass is integrated with the clad forming part 3b to form the clad part 1b of the optical fiber 1 to which the alkali metal or the alkaline earth metal is added. The core forming part 3a becomes the core part 1a of the optical fiber 1 to which an alkali metal or an alkaline earth metal is added. In this way, the optical fiber 1 is manufactured in the drawing process of step S105 in the second embodiment, and the manufactured optical fiber 1 is obtained as a target, and the present process is completed.

  Here, the optical fiber 1 having a cladding outer diameter of 125 μm was manufactured by the drawing process of step S105 in the second embodiment, and the transmission loss when light was transmitted by the obtained optical fiber 1 was confirmed. As a result, the transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1550 nm was a low value of 0.177 dB / km on average. The transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1310 nm was a good characteristic of 0.312 dB / km on average.

  On the other hand, when manufacturing the optical fiber 1 from the second intermediate 28 via the optical fiber preform 10, the second intermediate 8 of the first embodiment described above is replaced with the second intermediate 28 of the second embodiment, and The sintering step of S107 and the drawing step of step S109 are performed.

  That is, in the sintering step of step S107 in the second embodiment, the second intermediate body 28 is subjected to a heat treatment while reducing the pressure in the space 24a filled with the glass microparticles 7 in the second intermediate body 28. The core forming portion 3a and the cladding forming portion 3b of the second intermediate 28 were melted and the packing of the glass fine particles 7 was densified, and the alkali metal or alkaline earth metal contained in the filling of the glass fine particles 7 was added. An optical fiber preform 10 is manufactured.

  At this time, the quartz glass fine particles contained in the glass fine particles 7 are densified and sintered to form a transparent glass. At the same time, the metal component (alkali metal or alkaline earth metal) of the alkali metal compound or alkaline earth metal compound contained in the glass microparticles 7 diffuses into the core forming portion 3a and the clad forming portion 3b. As a result, the transparent glass is integrated with the clad forming part 3b to form a transparent clad forming part to which an alkali metal or an alkaline earth metal is added. The core forming part 3a is a transparent core forming part to which an alkali metal or an alkaline earth metal is added. In this manner, the transparent optical fiber preform 10 (see FIG. 7) in which an alkali metal or an alkaline earth metal is added to the core forming portion and the clad forming portion (particularly, a portion near the outer periphery of the core forming portion) is obtained. It is made.

  After that, in the drawing step of step S109 in the second embodiment, the optical fiber preform 10 to which the alkali metal or the alkaline earth metal is added is melted by a heat treatment, so that at least the core portion is made of the alkali metal or the alkaline earth. An optical fiber doped with a similar metal is drawn. In this way, the optical fiber 1 is manufactured in the drawing step of step S109 in the second embodiment, and the manufactured optical fiber 1 is obtained as an object, and the present step is completed.

  Here, the optical fiber 1 having a cladding outer diameter of 125 μm was manufactured by the drawing process of step S109 in the second embodiment, and the transmission loss when light was transmitted by the obtained optical fiber 1 was confirmed. As a result, similarly to the optical fiber 1 manufactured in the drawing step of step S105 in the second embodiment, the transmission loss was a low value.

  On the other hand, when the target product (target) is an optical fiber preform, the second intermediate 8 of the first embodiment described above is replaced with the second intermediate 28 of the second embodiment, and the firing in step S107 is performed. A binding step is performed. The optical fiber preform 10 manufactured as described above is obtained as an object, and this step is completed.

  In the manufacturing method according to the second embodiment of the present invention, the longitudinal direction of the core forming portion 3a extends between the core forming portion 3a serving as the core portion 1a of the optical fiber 1 and the outer layer portion 11a of the first intermediate body 11. A void portion 24a is formed by providing a hole to be formed, and the formed void portion 24a is filled with glass particles 7 obtained by mixing an alkali metal compound or an alkaline earth metal compound with quartz glass particles, and the core forming portion is formed. A second intermediate body 28 having a filler of the glass fine particles 7 is produced so as to surround 3a, and an optical fiber manufacturing process or a sintering process is performed using the second intermediate body 28, whereby the optical fiber 1 or the optical fiber The base material 10 is manufactured.

  For this reason, the alkali metal or alkaline earth metal is efficiently diffused and added from the filler of the glass microparticles 7 to the core forming portion 3a by the heat treatment of the second intermediate body 28 in the optical fiber manufacturing process or the sintering process. be able to. By performing the drawing process using the second intermediate body 28 or the optical fiber preform 10 in which the alkali metal or the alkaline earth metal is added to the core forming portion 3a, the core portion 1a of the optical fiber 1 is formed. Can be efficiently added with an alkali metal or an alkaline earth metal. Thereby, similarly to the case of the first embodiment described above, the dielectric constant of the silica-based glass of the core portion 1a can be stabilized, and as a result, the occurrence of Rayleigh scattering in the optical fiber 1 can be suppressed. The transmission loss of the optical fiber 1 can be reduced.

  Further, a void portion 24a is formed in a region closer to the core forming portion 3a than an intermediate position Pc between the outer layer portion 11a of the first intermediate body 11 and the longitudinal center axis CL of the core forming portion 3a. Therefore, the region of the first intermediate 11 can be easily filled with the glass particles 7. Thereby, the alkali metal or the alkaline earth metal can be efficiently diffused and added from the glass fine particles 7 to the core forming portion 3a, and the diffusion of the alkali metal or the alkaline earth metal to the outer layer portion 11a can be suppressed. In addition, a decrease in mechanical strength of the drawn optical fiber 1 can be suppressed.

(Comparative example)
Next, a comparative example for the present invention will be described. In this comparative example, the first intermediate 11 is prepared in the same manner as in the preparation step of the manufacturing method according to Embodiment 2 shown in FIG. 9, and in the fine particle filling step, a glass containing an alkali metal compound or an alkaline earth metal compound is used. Instead of the fine particles 7, high-purity silica glass fine particles not containing an alkali metal compound and an alkaline earth metal compound were filled in the voids 24 a of the first intermediate 11. Other steps were performed in the same manner as in the case of Embodiment 2 to produce a comparative sample for the optical fiber 1 of the present invention. Then, the transmission loss when light was transmitted through the optical fiber of the obtained comparative sample was confirmed.

  As a result, the transmission loss of the optical fiber of the comparative sample when transmitting light having a wavelength of 1550 nm was 0.185 dB / km on average. The transmission loss of the optical fiber of the comparative sample when transmitting light having a wavelength of 1310 nm was 0.330 dB / km on average. From this result, when the quartz glass fine particles not containing the alkali metal compound and the alkaline earth metal compound are filled in the void portions 24a of the first intermediate 11, the glass fine particles 7 containing the alkali metal compound or the alkaline earth metal compound are filled. It was confirmed that the transmission loss of the manufactured optical fiber was higher than that in the case where was filled in the void portion 24a of the first intermediate body 11.

(Embodiment 3)
Next, a third embodiment of the present invention will be described. Also in the third embodiment, the optical fiber 1 shown in FIG. 1 or the optical fiber preform 10 shown in FIG.

  Next, a method for manufacturing an optical fiber and a method for manufacturing an optical fiber preform according to Embodiment 3 of the present invention will be described. In the manufacturing method according to the third embodiment, each of the steps S101 to S111 shown in FIG. 2 is appropriately performed according to the object to be manufactured. The glass particles to be filled are different from those of the first and second embodiments. The manufacturing method according to the third embodiment is the same as the above-described second embodiment except that the glass fine particles to be filled are different.

  FIG. 11 is a schematic diagram illustrating a fine particle filling step of the manufacturing method according to the third embodiment of the present invention. In the fine particle filling step according to the third embodiment, as shown in FIG. 11, glass fine particles 37 instead of the glass fine particles 7 according to the above-described second embodiment are put into the voids 24a of the first intermediate body 11 and filled.

  The glass fine particles 37 are obtained by attaching a sublimated alkali metal compound or alkaline earth metal compound to the surface of quartz glass fine particles. FIG. 12 is a schematic diagram illustrating the production of glass fine particles to be filled in the fine particle filling step of the manufacturing method according to Embodiment 3 of the present invention. When producing the glass microparticles 37 in the third embodiment, first, as shown in FIG. 12, the silica glass microparticles 31 are charged into a glass container 120 made of silica glass, and the alkali metal compound or the alkaline earth The metal particles 32 of the similar metal compound are charged.

The quartz glass fine particles 31 are fine particles made of, for example, high-purity quartz glass to which a dopant for adjusting the refractive index is not added. The average particle size of the quartz glass fine particles 31 is preferably 30 μm to 500 μm. In the third embodiment, the average particle diameter of the quartz glass fine particles 31 is, for example, 120 μm. The metal particles 32 are particles made of an alkali metal compound or an alkaline earth metal compound. Examples of the alkali metal compound or alkaline earth metal compound constituting the metal particles 32 include K ₂ CO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , and SrCO _3. , BaCO ₃ , KNO ₃ , KCl, NaCl, RbNO ₃ , RbCl and the like. In the third embodiment, the metal particles 32 are, for example, high-purity KCl particles (powder).

  On the other hand, as shown in FIG. 12, the glass container 120 and the heating container 121 communicate with each other via the ventilation pipe 122. Further, the glass container 120 is provided with a gas exhaust pipe 124. The heating vessel 121 is provided with a gas introduction pipe 123. The heater 125 is arranged below the heating container 121 and is configured to be able to heat-treat the metal particles 32 in the heating container 121.

  Subsequently, the metal particles 32 charged into the heating container 121 are subjected to a heat treatment by the heater 125, thereby sublimating the metal particles 32 to generate a sublimation gas 32a of an alkali metal compound or an alkaline earth metal compound. As shown in FIG. 12, the sublimation gas 32a is introduced into the glass container 120 from the heating container 121 through the ventilation tube 122 by the carrier gas introduced from the gas introduction tube 123 into the heating container 121. The introduced sublimation gas 32 a flows while being in contact with the quartz glass fine particles 31 in the glass container 120. As a result, the sublimated alkali metal compound or alkaline earth metal compound (hereinafter, referred to as a sublimation metal) is attached (adsorbed) to the surface of the quartz glass fine particles 31. It should be noted that the sublimation gas 32 a after sufficiently contacting the quartz glass fine particles 31 is exhausted from the glass container 120 through the gas exhaust pipe 124.

  In this way, glass fine particles 37 composed of quartz glass fine particles 31 having a sublimation metal of an alkali metal compound or an alkaline earth metal compound adhered to the surface are produced. In the third embodiment, as an example of the glass microparticles 37, a sublimated KCl (sublimation KCl) is attached to the surface of quartz glass microparticles 31 having an average particle diameter of 120 μm. The glass microparticles 37 thus produced are taken out of the glass container 120 and filled in the voids 24a of the first intermediate body 11, as shown in FIG. As a result, a second intermediate body 38 having a filling body of the glass fine particles 37 in the void portion 24a is produced. The obtained second intermediate body 38 is used as a material for manufacturing the optical fiber 1 or the optical fiber preform 10 in the third embodiment.

  That is, when an optical fiber is manufactured from the second intermediate body 38, the second intermediate body 28 of the second embodiment described above is replaced with the second intermediate body 38 of the third embodiment, and the drawing process of step S105 is performed. Done. At this time, the quartz glass fine particles 31 constituting the glass fine particles 37 are densified and sintered into a transparent glass similarly to the case of the second embodiment, and the sublimation metal (alkaline) adhered to the surface of the quartz glass fine particles 31. Metal or alkaline earth metal) diffuses into the core forming portion 3a and the cladding forming portion 3b. As a result, the transparent glass is integrated with the clad forming part 3b to form the clad part 1b of the optical fiber 1 to which the alkali metal or the alkaline earth metal is added. The core forming part 3a becomes the core part 1a of the optical fiber 1 to which an alkali metal or an alkaline earth metal is added. In this way, the optical fiber 1 is manufactured in the drawing step of step S105 in the third embodiment, and the manufactured optical fiber 1 is obtained as an object, and this step is completed.

  Here, the optical fiber 1 having a cladding outer diameter of 125 μm was manufactured by the drawing step of step S105 in the third embodiment, and the transmission loss when light was transmitted by the obtained optical fiber 1 was confirmed. As a result, the transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1550 nm was a low value of 0.175 dB / km on average. The transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1310 nm was a low value of 0.310 dB / km on average.

  On the other hand, when manufacturing the optical fiber 1 from the second intermediate 38 via the optical fiber preform 10, the second intermediate 28 of the second embodiment described above is replaced with the second intermediate 38 of the third embodiment, and The sintering step of S107 and the drawing step of step S109 are performed.

  At this time, the quartz glass fine particles 31 constituting the glass fine particles 37 are densified and sintered into a transparent glass similarly to the case of the second embodiment, and the sublimation metal (alkaline) adhered to the surface of the quartz glass fine particles 31. Metal or alkaline earth metal) diffuses into the core forming portion 3a and the cladding forming portion 3b. As a result, the transparent glass is integrated with the clad forming part 3b to form a transparent clad forming part to which an alkali metal or an alkaline earth metal is added. The core forming part 3a is a transparent core forming part to which an alkali metal or an alkaline earth metal is added. In this manner, the transparent optical fiber preform 10 (see FIG. 7) in which an alkali metal or an alkaline earth metal is added to the core forming portion and the clad forming portion (particularly, a portion near the outer periphery of the core forming portion) is obtained. It is made.

  Then, in the drawing step of step S109 in the third embodiment, the optical fiber 1 is manufactured using the optical fiber preform 10 as in the case of the above-described second embodiment, and the manufactured optical fiber 1 is And the process ends.

  Here, the optical fiber 1 having a cladding outer diameter of 125 μm was manufactured by the drawing process of step S109 in the third embodiment, and the transmission loss when light was transmitted by the obtained optical fiber 1 was confirmed. As a result, similar to the optical fiber 1 manufactured in the drawing step of step S105 in the third embodiment, the transmission loss was good.

  On the other hand, when the target product (target) is an optical fiber preform, the second intermediate body 28 of the second embodiment is replaced with the second intermediate body 38 of the third embodiment, and the firing in step S107 is performed. A binding step is performed. The optical fiber preform 10 manufactured as described above is obtained as an object, and this step is completed.

  In the manufacturing method according to Embodiment 3 of the present invention, a sublimation metal of an alkali metal compound or an alkaline earth metal compound is adhered to the surface of the quartz glass fine particles 31 to produce glass fine particles 37, and the obtained glass fine particles 37 are used as a core. The space 24a between the forming portion 3a and the outer layer portion 11a of the first intermediate body 11 was filled, and the others were the same as in the second embodiment. For this reason, while enjoying the same operation and effect as the above-mentioned Embodiment 2, compared with the conventional method of attaching and diffusing an alkali metal or alkaline earth metal toward the inner surface of the glass pipe or the outer layer of the glass rod, The area of the glass surface to which the alkali metal or alkaline earth metal is attached can be increased. Thereby, the amount of alkali metal or alkaline earth metal added to the core forming portion 3a and the core portion 1a can be efficiently increased. As a result, the optical fiber 1 in which the alkali metal or the alkaline earth metal is added to the core portion 1a can be easily manufactured, and the optical fiber 1 having the core forming portion 3a to which the alkali metal or the alkaline earth metal is added is provided. The fiber preform 10 can be manufactured efficiently.

(Embodiment 4)
Next, a fourth embodiment of the present invention will be described. Also in Embodiment 4, the optical fiber 1 shown in FIG. 1 or the optical fiber preform 10 shown in FIG. 7 is manufactured as an object.

  Next, a method for manufacturing an optical fiber and a method for manufacturing an optical fiber preform according to Embodiment 4 of the present invention will be described. In the manufacturing method according to the fourth embodiment, the respective steps of steps S101 to S111 shown in FIG. 2 are appropriately performed according to the object to be manufactured. The glass particles to be filled are different from those of Embodiments 1 to 3 described above. The manufacturing method according to the fourth embodiment is the same as the above-described second embodiment except that the glass fine particles to be filled are different.

  FIG. 13 is a schematic diagram illustrating a fine particle filling step of the manufacturing method according to the fourth embodiment of the present invention. In the fine particle filling step in the fourth embodiment, as shown in FIG. 13, glass fine particles 47 instead of the glass fine particles 7 in the above-described second embodiment are charged into the void portion 24 a of the first intermediate body 11 and filled.

  The glass microparticles 47 are obtained by immersing quartz glass microparticles in a solution containing an alkali metal compound or an alkaline earth metal compound, and attaching the alkali metal compound or the alkaline earth metal compound to the surface of the quartz glass microparticles. FIG. 14 is a schematic diagram illustrating the production of glass fine particles to be filled in the fine particle filling step of the manufacturing method according to Embodiment 4 of the present invention. In FIG. 14, a glass container 130 is a container made of quartz glass, and includes an upper flow pipe 131 and a lower flow pipe 132. The lower circulation pipe 132 is provided with an on-off valve 133 for opening or closing the lower circulation pipe 132.

When producing the glass microparticles 47 according to the fourth embodiment, as shown in FIG. 14, first, the on-off valve 133 is closed, and the quartz glass microparticles 31 are put into the glass container 130. In the fourth embodiment, the average particle diameter of the quartz glass fine particles 31 is, for example, 120 μm. Subsequently, the metal solution 42 is filled into the glass container 130 from the upper circulation pipe 131. The metal solution 42 is a solution containing an alkali metal compound or an alkaline earth metal compound, and is prepared by dissolving the alkali metal compound or the alkaline earth metal compound in a solvent such as pure water. Examples of the alkali metal compound or alkaline earth metal compound contained in the metal solution 42 include K ₂ CO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , and SrCO _3. , BaCO ₃ , KNO ₃ , KCl, NaCl, RbNO ₃ , RbCl and the like. In the fourth embodiment, the metal solution 42 is, for example, an aqueous solution of potassium carbonate (K ₂ CO ₃ ).

  In the glass container 130, the quartz glass fine particles 31 are immersed in the metal solution 42, whereby the surface of the quartz glass fine particles 31 is sufficiently impregnated with the alkali metal compound or the alkaline earth metal compound contained in the metal solution 42. Thereafter, the metal solution 42 is discharged from the glass container 130 through the lower flow pipe 132 with the on-off valve 133 opened. In this way, glass particles 47 are produced by impregnating the surface of the quartz glass particles 31 with the alkali metal compound or the alkaline earth metal compound. Next, as shown in FIG. 14, a dry gas 43 such as nitrogen gas is introduced into the glass container 130 from the lower circulation pipe 132, and the glass particles 47 in the glass container 130 are sufficiently dried by the dry gas 43. . The dried gas 43 after drying the glass fine particles 47 is exhausted from the glass container 130 through the upper circulation pipe 131. Thus, the dried glass microparticles 47 are obtained.

In the fourth embodiment, as an example of the glass microparticles 47, one in which potassium carbonate (K ₂ CO ₃ ) is adhered to the surface of quartz glass microparticles 31 having an average particle diameter of 120 μm by impregnation. The glass microparticles 47 thus produced are taken out of the glass container 130 and filled in the voids 24a of the first intermediate body 11, as shown in FIG. As a result, a second intermediate 48 having a filling of the glass fine particles 47 in the void portion 24a is produced. The obtained second intermediate 48 is used as a material for manufacturing the optical fiber 1 or the optical fiber preform 10 in the fourth embodiment.

  That is, when the optical fiber is manufactured from the second intermediate 48, the second intermediate 28 of the second embodiment described above is replaced with the second intermediate 48 of the fourth embodiment, and the drawing process of step S105 is performed. Done. At this time, the quartz glass fine particles 31 constituting the glass fine particles 47 are densified and sintered as in the case of the second embodiment to form a transparent glass, and the alkali metal or alkali adhered to the surface of the quartz glass fine particles 31. The earth metal diffuses into the core forming part 3a and the clad forming part 3b. As a result, the transparent glass is integrated with the clad forming part 3b to form the clad part 1b of the optical fiber 1 to which the alkali metal or the alkaline earth metal is added. The core forming part 3a becomes the core part 1a of the optical fiber 1 to which an alkali metal or an alkaline earth metal is added. In this way, the optical fiber 1 is manufactured in the drawing step of step S105 in the fourth embodiment, and the manufactured optical fiber 1 is obtained as a target, and the present step is completed.

  Here, the optical fiber 1 having a cladding outer diameter of 125 μm was manufactured by the drawing step of step S105 in the fourth embodiment, and the transmission loss when light was transmitted by the obtained optical fiber 1 was confirmed. As a result, the transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1550 nm was a low value of 0.177 dB / km on average. The transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1310 nm was a low value of 0.313 dB / km on average.

  On the other hand, when manufacturing the optical fiber 1 from the second intermediate 48 via the optical fiber preform 10, the second intermediate 28 of the second embodiment described above is replaced with the second intermediate 48 of the fourth embodiment, and The sintering step of S107 and the drawing step of step S109 are performed.

  At this time, the quartz glass fine particles 31 constituting the glass fine particles 47 are densified and sintered as in the case of the second embodiment to form a transparent glass, and the alkali metal or alkali adhered to the surface of the quartz glass fine particles 31. The earth metal diffuses into the core forming part 3a and the clad forming part 3b. As a result, the transparent glass is integrated with the clad forming part 3b to form a transparent clad forming part to which an alkali metal or an alkaline earth metal is added. The core forming part 3a is a transparent core forming part to which an alkali metal or an alkaline earth metal is added. In this manner, the transparent optical fiber preform 10 (see FIG. 7) in which an alkali metal or an alkaline earth metal is added to the core forming portion and the clad forming portion (particularly, a portion near the outer periphery of the core forming portion) is obtained. It is made.

  Thereafter, in the drawing step of step S109 in the fourth embodiment, the optical fiber 1 is manufactured using the optical fiber preform 10 as in the case of the above-described second embodiment, and the manufactured optical fiber 1 is And the process ends.

  Here, the optical fiber 1 having a cladding outer diameter of 125 μm was manufactured by the drawing step of step S109 in the fourth embodiment, and the transmission loss when light was transmitted by the obtained optical fiber 1 was confirmed. As a result, similar to the optical fiber 1 manufactured in the drawing step of step S105 in the fourth embodiment, the transmission loss was good.

  On the other hand, when the target product (target) is an optical fiber preform, the second intermediate 28 of the second embodiment described above is replaced with the second intermediate 48 of the fourth embodiment, and the firing in step S107 is performed. A binding step is performed. The optical fiber preform 10 manufactured as described above is obtained as an object, and this step is completed.

  In the manufacturing method according to Embodiment 4 of the present invention, glass particles 47 are produced by impregnating the surface of quartz glass particles 31 with an alkali metal compound or an alkaline earth metal compound, and the obtained glass particles 47 are formed into a core. The space 24a between the portion 3a and the outer layer portion 11a of the first intermediate body 11 was filled, and the others were the same as in the second embodiment. For this reason, while enjoying the same operation and effect as the above-mentioned Embodiment 2, compared with the conventional method of attaching and diffusing an alkali metal or alkaline earth metal toward the inner surface of the glass pipe or the outer layer of the glass rod, The area of the glass surface to which the alkali metal or alkaline earth metal is attached can be increased. Thereby, the amount of alkali metal or alkaline earth metal added to the core forming portion 3a and the core portion 1a can be efficiently increased. As a result, the optical fiber 1 in which the alkali metal or the alkaline earth metal is added to the core portion 1a can be easily manufactured, and the optical fiber 1 having the core forming portion 3a to which the alkali metal or the alkaline earth metal is added is provided. The fiber preform 10 can be manufactured efficiently.

(Experiment on the position of the gap filled with glass particles)
Next, an experiment on the position of the void portion in the first intermediate prepared in the preparation step of the manufacturing method according to the present invention will be described. In the present experiment, the first intermediate 11 prepared in the preparation step of the manufacturing method according to the above-described second embodiment is illustrated, and the position of the void 24a formed in the first intermediate 11 is variously changed to perform the step. The preparation process of S101 was performed. Thereafter, the above-described optical fiber manufacturing process is performed, and a sample # of the optical fiber 1 is separately prepared for each position (hereinafter referred to as a hole position) of the void portion 24a filled with the glass fine particles 7 containing the alkali metal compound or the alkaline earth metal compound. 1 to # 4 were manufactured.

  FIG. 15 is a diagram illustrating the position of the void in the first intermediate in the present experiment. As shown in FIG. 15, in the present experiment, the outer diameter of the first intermediate 11 (the outer diameter of the clad forming part 3b) was set to 70 mm, and the distance between the outer layer part 11a of the first intermediate 11 and the core forming part 3a was set. Four void portions 24a were formed in the clad forming portion 3b by changing the hole positions for each sample. In FIG. 15, a hole position P1 is a hole position when the void portion 24a is formed on a circumference having a diameter of 28 mm around the longitudinal center axis CL of the core forming portion 3a. The hole position P2 is a hole position when the void portion 24a is formed on a circumference having a diameter of 30 mm around the center axis CL in the longitudinal direction of the core forming portion 3a. The hole position P3 is a hole position when the gap 24a is formed on a circumference having a diameter of 35 mm around the center axis CL in the longitudinal direction of the core forming portion 3a. The hole position P4 is a hole position when the void portion 24a is formed on a circumference having a diameter of 40 mm around the center axis CL in the longitudinal direction of the core forming portion 3a.

  In this experiment, sample # 1 is a sample of the optical fiber 1 when the gap 24a is formed at the hole position P1. Sample # 2 is a sample of the optical fiber 1 when the gap 24a is formed at the hole position P2. Sample # 3 is a sample of the optical fiber 1 when the void 24a is formed at the hole position P3. Sample # 4 is a sample of the optical fiber 1 in a case where the gap 24a is formed at the hole position P4.

  Subsequently, for each of the samples # 1 to # 4 in this experiment, a measurement of the transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1550 nm and a proof test in which the tensile strain was 1.5% were performed. . Table 1 shows the transmission loss measurement results and the proof test results of samples # 1 to # 4 in this experiment. In Table 1, “average 1550 nm transmission loss” is an average value of the transmission loss of the optical fiber 1 when transmitting light having a wavelength of 1550 nm. The “average breakage rate” is defined as the proof test using samples # 1 to # 4 as optical fibers each having a length of 300 to 600 km and the results (the number of breaks of each of samples # 1 to # 4) per 100 km. It is a thing.

  As shown in Table 1, the average transmission loss of 1550 nm was good in samples # 1 to # 4 regardless of the hole positions P1 to P4 of the gap 24a. Above all, in samples # 1 to # 3 at hole positions P1 to P3, the transmission loss on average was reduced by 1550 nm as compared with sample # 4 at hole position P4 outside these.

  Also, as shown in Table 1, the average breakage of the optical fiber 1 was low in the samples # 1 and # 2 at the hole positions P1 and P2, but the sample # 3 at the hole position P3 outside these holes was lower. , And significantly increased in the sample # 4 at the outer hole position P4. Here, as shown in FIG. 15, both the gap 24a at the hole position P1 and the gap 24a at the hole position P2 are located at the same position as the outer layer 11a of the first intermediate body 11 and the longitudinal center axis CL of the core forming portion 3a. Are formed in a region closer to the core forming portion 3a than the intermediate position Pc. On the other hand, the void portion 24a at the hole position P4 is formed in a region farther from the core forming portion 3a than the intermediate position Pc (that is, a region closer to the outer layer portion 11a). The void portion 24a at the hole position P3 has the same hole position P3 as the intermediate position Pc, but includes a void region located on the outer layer portion 11a side from the intermediate position Pc. Formed in a region far from the forming portion 3a ".

  From the value of the average breaking rate shown in Table 1 and the relative relationship between the hole positions P1 to P4, when the void portion 24a is formed in a region closer to the core forming portion 3a than the intermediate position Pc, the glass in the void portion 24a is formed. Since the filler of the fine particles 7 is located on the core forming portion 3a side (inner side) than the intermediate position Pc, it was confirmed that the mechanical strength of the manufactured optical fiber 1 was improved. On the other hand, when the void portion 24a is formed in a region farther from the core forming portion 3a than the intermediate position Pc, the filler of the glass fine particles 7 in the void portion 24a is closer to the outer layer portion 11a (outer side) than the intermediate position Pc. Therefore, it was confirmed that the mechanical strength of the manufactured optical fiber 1 was lower than the above.

(Experiment on average particle size of glass particles)
Next, an experiment regarding the average particle diameter of the glass fine particles filled in the voids of the first intermediate in the fine particle filling step according to the present invention will be described. In the present experiment, glass fine particles 37 to be filled in the voids 24a of the first intermediate 11 in the fine particle filling step of the manufacturing method according to Embodiment 3 described above are exemplified, and the average particle diameter of the glass fine particles 37 is variously changed. Then, the fine particle filling step of step S102 was performed, and samples of the optical fiber 1 were manufactured according to the average particle diameter of the glass fine particles 37.

  In this experiment, the sample of the optical fiber 1 manufactured with the average particle diameter of the glass fine particles 37 being 10 μm was sample # 5. The sample of the optical fiber 1 manufactured by setting the average particle diameter of the glass microparticles 37 to 30 μm was sample # 6. The sample of the optical fiber 1 manufactured by setting the average particle diameter of the glass microparticles 37 to 120 μm was sample # 7. The sample of the optical fiber 1 manufactured with the average particle diameter of the glass microparticles 37 being 500 μm was sample # 8. The sample of the optical fiber 1 manufactured by setting the average particle diameter of the glass microparticles 37 to 750 μm was sample # 9.

  Here, in the manufacture of sample # 5, since the average particle diameter of the glass fine particles 37 is excessively small, the glass fine particles when the glass fine particles 37 are filled in the voids 24a of the first intermediate body 11 in the fine particle filling step of step S102. 37 has low fluidity, and therefore it is difficult to fill the voids 24a with the glass particles 37. Therefore, in this experiment, it was difficult to stably manufacture the sample # 5 of the optical fiber 1. On the other hand, in the production of Samples # 6 to # 9, since the fluidity of the glass fine particles 37 is good, the glass fine particles 37 are easily filled in the voids 24a of the first intermediate body 11 in the fine particle filling step of Step S102. Was completed. Therefore, in this experiment, samples # 6 to # 9 of the optical fiber 1 could be manufactured stably.

  Subsequently, for each of the samples # 6 to # 9 that were stably manufactured among the samples # 5 to # 9 in this experiment, the transmission loss of the optical fiber 1 when the light having the wavelength of 1550 nm was transmitted was measured. The average value (average 1550 nm transmission loss) was obtained. Table 2 shows the results of the fluidity and the average 1550 nm transmission loss of the glass microparticles 37 of samples # 5 to # 9 in this experiment. With respect to the average 1550 nm transmission loss, except for the sample # 5 in which the flowability of the glass microparticles 37 is poor, only the measurement results of the samples # 6 to # 9, which have good flowability of the glass microparticles 37 and are manufactured stably, are shown. It is shown.

  As shown in Table 2, it was confirmed that samples # 6 to # 8 satisfying the condition that the average particle diameter of the glass microparticles 37 is 30 μm to 500 μm can reduce the average transmission loss of 1550 nm. On the other hand, in sample # 9 in which the glass microparticles 37 exceeded the above conditions, the average 1550 nm transmission loss was higher than in samples # 6 to # 8. This is because the surface area of the entire filler of the glass fine particles 37 becomes smaller as the average particle diameter of the glass fine particles 37 increases. It is considered that it becomes difficult to add an alkali metal or an alkaline earth metal.

  In addition, when the alkali metal or the alkaline earth metal is added to the quartz glass fine particles 31 in Embodiments 3 and 4, when the average particle diameter of the quartz glass fine particles 31 is small, the alkali metal or the alkaline earth metal is excessively added. Quartz glass particles 31, that is, glass particles in an excessively added state can be obtained. In such a case, it is also effective to mix the glass particles in the excessively added state with the quartz glass particles 31 to which no alkali metal or alkaline earth metal has been added. Further, the amount of the alkali metal or alkaline earth metal to be added is controlled by reheating the glass particles in the excessively added state to reduce the amount of the alkali metal or alkaline earth metal compound on the surface of the glass particles by sublimation or the like. Is also possible.

  In the first to fourth embodiments, the core 1a is made of silica glass to which germania is added, and the clad 1b is made of pure silica glass. However, the present invention is not limited to this. is not. For example, the core 1a may be made of pure quartz glass, and the cladding 1b may be made of quartz glass to which a dopant (for example, fluorine) for lowering the refractive index is added. Also, the present invention can be applied to an optical fiber in which a rare earth element such as yttrium or erbium is added to the core 1a.

  Further, in the above-described first to fourth embodiments, the optical fiber 1 (single-core optical fiber) including the single core portion 1a in the cladding portion 1b is illustrated, but the present invention is not limited to this. . For example, the optical fiber 1 according to the present invention may be a multi-core optical fiber including a plurality of cores 1a in a cladding 1b.

  Further, in the above-described second to fourth embodiments, four void portions 24a are formed in the region of the clad forming portion 3b, but the present invention is not limited to this. For example, one void portion 24a may be formed in the region of the clad forming portion 3b, or two or more (a plurality of) void portions 24a may be formed. Further, the gap 24a is not limited to the above-described columnar shape, and may have another shape such as a cylindrical shape.

  In the fourth embodiment described above, the potassium carbonate aqueous solution obtained by dissolving a potassium carbonate salt in pure water is used as the metal solution 42 for attaching the alkali metal compound or the alkaline earth metal compound to the surface of the quartz glass fine particles by impregnation. However, the present invention is not limited to this. In the present invention, the alkali metal compound or alkaline earth metal compound may be other than potassium carbonate (eg, potassium chloride salt), and the solvent of the metal solution 42 may be other than pure water (eg, formic acid or formaldehyde, etc.). ). That is, a combination of an alkali metal compound or an alkaline earth metal compound and a solvent can be appropriately selected in consideration of solubility and the like.

  The present invention is not limited by the above-described embodiments. The present invention includes a configuration in which the above-described components are appropriately combined. For example, in the gap 4a between the glass pipe 2 and the core rod 3 of the first intermediate body 4 in the first embodiment, glass particles 7 which are a mixture of an alkali metal compound or an alkaline earth metal compound and quartz glass particles are provided. Alternatively, glass fine particles (glass fine particles 37 in the third embodiment or glass fine particles 47 in the fourth embodiment) obtained by attaching an alkali metal compound or an alkaline earth metal compound to the surface of quartz glass fine particles may be filled. In addition, other embodiments, examples, operation techniques, and the like performed by those skilled in the art based on the above-described embodiments are all included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Optical fiber 1a Core part 1b Cladding part 2 Glass pipe 2a Outer layer part 2b Upper end part 2c Lower end part 3 Core rod 3a Core forming part 3b Cladding forming part 4 First intermediate body 4a, 24a Gap part 5, 6 Positioning member 6a Fitting hole 6b Vent holes 7, 37, 47 Glass fine particles 8, 28, 38, 48 Second intermediate 10 Optical fiber preform 11 First intermediate 11a Outer layer 11b Upper end 11c Lower end 31 Quartz glass fine particles 32 Metal particles 32a Sublimation gas 42 Metal solution 43 Dry gas 100 Lid 101, 103 Gas exhaust pipe 102 Vacuum pump 104 Pressure gauge 105 Optical fiber drawing furnace 105a Heater 106 Coating forming device 107 Capstan roller 108 Guide roll 109 Winding mechanism 110 Control unit 111 Heating furnace 120 Glass container 121 Heating container 1 Reference Signs List 22 Vent pipe 123 Gas introduction pipe 124 Gas exhaust pipe 125 Heater 130 Glass container 131 Upper flow pipe 132 Lower flow pipe 133 Open / close valve CL Longitudinal central axis F1, F2 Optical fiber Pc Intermediate position P1, P2, P3, P4 Hole position

Claims (20)

A method for manufacturing an optical fiber including a core portion and a clad portion formed on the outer periphery of the core portion,
A core forming portion made of glass and serving as the core portion, and a clad forming portion made of glass having a lower refractive index than the core portion and being part of the clad portion, wherein an outer layer portion and the core forming portion A preparing step of preparing a first intermediate having a void portion extending in the longitudinal direction of the core forming portion between the first intermediate body;
A fine particle filling step of preparing a second intermediate by filling glass fine particles containing an alkali metal compound or an alkaline earth metal compound into the voids of the first intermediate;
An optical fiber manufacturing step of manufacturing an optical fiber in which at least the core portion is doped with an alkali metal or an alkaline earth metal, using the second intermediate,
A method for manufacturing an optical fiber, comprising:   The preparing step includes disposing a core rod including the core forming portion and a glass portion adjacent to the outer periphery of the core forming portion inside a glass pipe, and forming the gap between an outer layer portion of the glass pipe and the core rod. 2. The method according to claim 1, wherein the cladding is formed by the glass pipe and the glass portion of the core rod.   In the preparing step, a hole extending in a longitudinal direction of the core forming portion is provided in the clad forming portion of the first intermediate body, and the hole is provided between an outer layer portion of the first intermediate body and the core forming portion. The method for manufacturing an optical fiber according to claim 1, wherein a void is formed.   The method for producing an optical fiber according to any one of claims 1 to 3, wherein the glass fine particles are a mixture of the alkali metal compound or the alkaline earth metal compound and quartz glass fine particles.   The glass fine particles according to any one of claims 1 to 3, wherein the sublimated alkali metal compound or the alkaline earth metal compound is adhered to the surface of quartz glass fine particles. Manufacturing method of optical fiber.   The glass particles are immersed in a solution containing the alkali metal compound or the alkaline earth metal compound, and the alkali metal compound or the alkaline earth metal compound is adhered to the surface of the quartz glass particles. The method for producing an optical fiber according to any one of claims 1 to 3, wherein The alkali metal compound or the alkaline earth metal compound may be K ₂ CO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , KNO ₃ , KCl, NaCl, RbNO ₃ or the method of manufacturing an optical fiber according to any one of claims 1 to 6, characterized in that the RbCl,.   The preparing is characterized in that the gap is formed in a region closer to the core forming portion than an intermediate position between an outer layer portion of the first intermediate and a longitudinal center axis of the core forming portion. A method for manufacturing the optical fiber according to claim 1.   The method of manufacturing an optical fiber according to any one of claims 1 to 8, wherein in the fine particle filling step, the glass fine particles having an average particle diameter of 30 µm to 500 µm are filled. The optical fiber manufacturing process,
The second intermediate is heat-treated while depressurizing the inside of the gap filled with the glass fine particles, melting the core forming portion and the clad forming portion and densifying the filled body of the glass fine particles, The method for producing an optical fiber according to any one of claims 1 to 9, further comprising a step of drawing an optical fiber in which an alkali metal or an alkaline earth metal is added to a core portion. The optical fiber manufacturing process,
The second intermediate body is subjected to a heat treatment while depressurizing the inside of the gap filled with the glass fine particles, thereby melting the core forming part and the clad forming part and densifying the filled body of the glass fine particles, A sintering step of producing an optical fiber preform to which an alkali metal or an alkaline earth metal contained in a filler of fine particles is added,
An optical fiber preform to which an alkali metal or an alkaline earth metal is added is melted by a heat treatment, and a drawing step of drawing an optical fiber having an alkali metal or an alkaline earth metal added to at least the core portion,
The method for producing an optical fiber according to any one of claims 1 to 9, comprising: A method for manufacturing an optical fiber preform for manufacturing an optical fiber including a core portion and a clad portion formed on the outer periphery of the core portion,
A core forming portion made of glass and serving as the core portion, and a clad forming portion made of glass having a lower refractive index than the core portion and being part of the clad portion, wherein an outer layer portion and the core forming portion A preparing step of preparing a first intermediate having a void portion extending in the longitudinal direction of the core forming portion between the first intermediate body;
A fine particle filling step of preparing a second intermediate by filling glass fine particles containing an alkali metal compound or an alkaline earth metal compound into the voids of the first intermediate;
The second intermediate body is subjected to a heat treatment while depressurizing the inside of the gap filled with the glass fine particles, thereby melting the core forming part and the clad forming part and densifying the filled body of the glass fine particles, A sintering step of producing an optical fiber preform to which an alkali metal or an alkaline earth metal contained in a filler of fine particles is added,
A method for producing an optical fiber preform, comprising:   The preparing step includes disposing a core rod including the core forming portion and a glass portion adjacent to the outer periphery of the core forming portion inside a glass pipe, and forming the gap between an outer layer portion of the glass pipe and the core rod. The method for manufacturing an optical fiber preform according to claim 12, wherein a clad forming part is formed by the glass pipe and the glass part of the core rod while forming a part.   In the preparing step, a hole extending in a longitudinal direction of the core forming portion is provided in the clad forming portion of the first intermediate body, and the hole is provided between an outer layer portion of the first intermediate body and the core forming portion. The method for manufacturing an optical fiber preform according to claim 12, wherein a void is formed.   The method for producing an optical fiber preform according to any one of claims 12 to 14, wherein the glass fine particles are a mixture of the alkali metal compound or the alkaline earth metal compound and silica glass fine particles. .   The glass fine particles according to any one of claims 12 to 14, wherein the sublimated alkali metal compound or the alkaline earth metal compound is adhered to the surface of quartz glass fine particles. A method for producing an optical fiber preform.   The glass particles are immersed in a solution containing the alkali metal compound or the alkaline earth metal compound, and the alkali metal compound or the alkaline earth metal compound is adhered to the surface of the quartz glass particles. The method for producing an optical fiber preform according to any one of claims 12 to 14, wherein: The alkali metal compound or the alkaline earth metal compound may be K ₂ CO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , KNO ₃ , KCl, NaCl, RbNO ₃ or the method of manufacturing an optical fiber preform according to any one of claims 12 to 17, characterized in that the RbCl,.   The preparing is characterized in that the gap is formed in a region closer to the core forming portion than an intermediate position between an outer layer portion of the first intermediate and a longitudinal center axis of the core forming portion. A method for manufacturing an optical fiber preform according to claim 12.   The method for producing an optical fiber preform according to any one of claims 12 to 19, wherein, in the fine particle filling step, the glass fine particles having an average particle diameter of 30 µm to 500 µm are filled.

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