JP2020158349A - Method for manufacturing optical fiber - Google Patents

Abstract

To provide a method for manufacturing an optical fiber having reduced transmission loss.SOLUTION: The method for manufacturing an optical fiber comprises: the high temperature pressing step of heating an optical fiber preform including a core part and a cladding part formed in the outer periphery of the core part at less than 1800 degrees while pressing the preform at 100 MPa or more and 2000 MPa or less; and the drawing step of heating and melting an end portion of the optical fiber preform subjected to the high temperature pressing step at 1800 degrees or more to draw an optical fiber at a drawing speed of 900 m/minute or more.SELECTED DRAWING: Figure 1

Description

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

In recent optical communication systems, there is a strong demand for reduction of transmission loss of optical fibers. One of the reasons is that by reducing the transmission loss of the optical fiber as an optical communication transmission line, the number of repeaters used in a long-distance optical communication system, for example, a submarine line cable can be reduced. This is because there is a great cost advantage in constructing and maintaining a communication system.

In order to reduce the transmission loss of the optical fiber, it is effective to reduce the Rayleigh scattering loss. Rayleigh scattering is caused by the formation of coarse density (density fluctuation) in the glass network due to the strain during transparent vitrification in the manufacturing process of the optical fiber and the influence of the characteristic deterioration region that occurs locally. For the purpose of relaxing the glass network structure, a method of subjecting an optical fiber base material to a high temperature pressurization step called a hot isostatic pressure (HIP) is known (Patent Document 1). According to the HIP treatment, the Rayleigh scattering loss is reduced because the glass network structure in the optical fiber base material is relaxed (Non-Patent Document 1).

Japanese Unexamined Patent Publication No. 5-221674

Maruka Ono et al., "Control of Void Structure of Silica Glass for Realization of Ultra-Low Loss Fiber", Symposium S1012p V03, Proceedings of the 39th Annual Meeting of the Laser Society of Japan, January 2019

All of the HIP treatments conventionally studied relate to the HIP treatment in the optical fiber base material. It is considered that this HIP treatment can realize relaxation of the glass network structure in the optical fiber base material and thereby reduction of Rayleigh scattering loss.

However, an optical fiber is generally manufactured by heating and melting one end of an optical fiber base material in a heating furnace and drawing a line vertically downward from the heating furnace. In the drawing step, the optical fiber base material is heated to about 2000 ° C. Therefore, it is considered that the relaxation effect of the glass network structure by the HIP treatment performed on the optical fiber base material is affected by such a high temperature treatment in the wire drawing process, but it has not been studied in the past.

The present invention has been made in view of the above, and an object of the present invention is to provide a method for manufacturing an optical fiber in which transmission loss is reduced.

In order to solve the above-mentioned problems and achieve the object, the method for manufacturing an optical fiber according to one aspect of the present invention uses an optical fiber base material including a core portion and a clad portion formed on the outer periphery of the core portion. A high-temperature pressurization step of heating to less than 1800 ° C while pressurizing at 100 MPa or more and 2000 MPa or less, and one end of the optical fiber base material subjected to the high-temperature pressurization step are heated to 1800 ° C or higher to melt and 900 m / min or more. It is characterized by including a drawing step of drawing out an optical fiber at the drawing speed of.

The method for producing an optical fiber according to one aspect of the present invention is characterized in that the core portion contains germanium or chlorine.

The method for producing an optical fiber according to one aspect of the present invention is characterized in that the core portion contains an alkali metal.

The method for producing an optical fiber according to one aspect of the present invention is characterized in that the clad portion contains fluorine.

According to the present invention, there is an effect that an optical fiber optical fiber having a reduced transmission loss can be manufactured.

FIG. 1 is a flow chart of a method for manufacturing an optical fiber according to an embodiment. FIG. 2 is a schematic view of the core base material. FIG. 3 is a schematic view of an optical fiber manufacturing apparatus.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiments described below. Further, in each drawing, the same or corresponding components are appropriately designated by the same reference numerals. In addition, for terms not specifically defined in the present specification, G.I. 650.1 and G.M. The definition and measurement method in 650.2 shall be followed.

The present inventors considered that when an optical fiber base material whose glass network structure has been relaxed by HIP treatment is heated to draw an optical fiber, the temperature rises and the relaxation effect of the glass network structure decreases. Therefore, by drawing out the optical fiber at a high drawing speed of 900 m / min or more at the time of drawing, the reduction of the relaxation effect of the glass network structure due to the HIP treatment is suppressed, and the Rayleigh scattering loss is also reduced in the optical fiber. The present invention has been made with the idea that reduction of transmission loss can be suitably realized.

FIG. 1 is a flow chart of a method for manufacturing an optical fiber according to an embodiment. In this flow, first, in step S101, the core base material preparation step for preparing the core base material is performed. Subsequently, in step S102, a core base material stretching step of stretching the core base material is performed. Subsequently, in step S103, an optical fiber base material manufacturing step of manufacturing an optical fiber base material using the stretched core base material is performed. Subsequently, in step S104, an optical fiber base material high temperature pressurization step (optical fiber base material HIP step) for pressurizing the optical fiber base material at a high temperature is performed. Subsequently, in step S105, an optical fiber drawing step of drawing the optical fiber using the optical fiber base material subjected to the HIP step is performed. Subsequently, in step S106, a coating layer forming step of forming a coating layer on the drawn optical fiber is performed.

Hereinafter, each step will be specifically described. 2A and 2B are schematic views of a core base material prepared in the core base material preparation step of step S101, where FIG. 2A is a side view and FIG. 2B is a top view. The method for preparing the core base material is not particularly limited, but in the present embodiment, the core base material 10 is a columnar glass body produced by using the VAD (Vapor Axial Deposition) method, and the starting material 1 and the starting material 1 are used. It includes a core portion 2 and a clad portion 3.

The starting material 1 has a cylindrical shape. The core portion 2 has a cylindrical shape formed on the outer periphery of the starting material 1. The clad portion 3 is formed on the outer periphery of the core portion 2 and has a cylindrical shape having a lower refractive index than the core portion 2.

The starting material 1 is a member for depositing the soot to be the core portion 2 and the soot to be the clad portion 3 when the VAD method is executed, and is made of, for example, pure quartz glass.

The core portion 2 is made of quartz-based glass to which, for example, germanium (Ge), which is an additive for increasing the refractive index, is added. Chlorine (Cl) or an alkali metal may be added to the core portion 2 instead of germanium. Further, a plurality of types of germanium, chlorine, and alkali metal may be added to the core portion 2. The alkali metal is not particularly limited, but is, for example, sodium (Na) or potassium (K). Chlorine and alkali metals have the effect of reducing the viscosity of glass.

The clad portion 3 is made of, for example, pure quartz glass that does not contain additives that change the refractive index. Further, fluorine (F) may be added to the clad portion 3 as an additive for lowering the refractive index.

The core base material 10 is produced by depositing a soot to be a core portion 2 and a soot to be a clad portion 3 on a starting material 1 by a VAD method, dehydrating the soot, and vitrifying it.

Next, the process of manufacturing the optical fiber base material in step S103 will be described. In the optical fiber base material manufacturing step, an optical fiber base material is produced using the core base material 10 stretched by the core base material stretching step of step S102 using a known method. Specifically, the optical fiber base material is produced by depositing the soot on the stretched core base material 10 by the OVD (Outside Vapor Deposition) method, dehydrating the soot, and vitrifying it. The vitrified portion of the suit is integrated with the clad portion 3 of the stretched core base material 10 to form a clad portion of the optical fiber base material together with the clad portion 3. In the state of the optical fiber base material, the additive of the core portion 2 is also diffused in the starting material 1 and becomes a part of the core portion 2.

The optical fiber base material manufacturing step is not limited to the one using the OVD method. For example, a method in which a stretched core base material 10 is inserted into a glass tube made of the same material as the clad portion 3 and both are heated and integrated. May be used. In this case, the glass tube is integrated with the clad portion 3 to form a clad portion of the optical fiber base material together with the clad portion 3.

Further, in the core base material preparation step, a core base material having only the starting material 1 and the core portion 2 may be prepared, and all the clad portions of the optical fiber base material may be formed in the optical fiber base material manufacturing step.

Next, the optical fiber base material HIP step of step S104 will be described. In the optical fiber base material HIP step, the optical fiber base material is put into a crucible, and the optical fiber base material is maintained for a certain period of time while being heated and pressurized using, for example, argon gas. The pressurization is, for example, a pressure of 100 MPa or more and 2000 MPa or less. The heating is set to a temperature at which the optical fiber base material does not melt, but is set to an appropriate temperature of less than 1800 degrees, for example. As a result, the glass network structure in the optical fiber base material is relaxed. After that, the inside of the crucible is cooled and depressurized, the temperature is returned to normal temperature and pressure, and then the optical fiber base material is taken out. The optical fiber base material HIP process can be performed using a known HIP apparatus, for example, SYSTEM20J manufactured by Kobe Steel, Ltd.

Next, the optical fiber drawing step of step S105 and the coating layer forming step of step S106 will be described. FIG. 3 is a schematic view of an optical fiber manufacturing apparatus for performing an optical fiber drawing step and a coating layer forming step. The manufacturing apparatus 100 includes a heater 101, a resin coating apparatus 102, an ultraviolet irradiation apparatus 103, a guide roll 104, and a winding apparatus 105.

The heater 101 is provided in a drawing furnace (not shown) in order to heat and melt one end of the HIP-treated optical fiber base material 20. The resin coating device 102 is a device provided with a die for coating an ultraviolet curable resin on the outer periphery of an optical fiber 30 made of glass drawn from an optical fiber base material 20. The resin coating device 102 can coat the ultraviolet curable resin for the primary layer and the ultraviolet curable resin for the secondary layer in layers so that, for example, a coating layer having a two-layer structure of a primary layer and a secondary layer can be formed as a coating layer. It is configured as follows. The ultraviolet irradiation device 103 is a device that irradiates the resin coated on the outer periphery of the optical fiber 30 with ultraviolet rays to cure it to form a coating layer. The ultraviolet irradiation device 103 includes an ultraviolet light source such as a semiconductor light emitting element or a mercury lamp. The guide roll 104 guides the optical fiber 40 on which the coating layer is formed to the winding device 105. The winding device 105 is a device including a bobbin that winds the optical fiber 40. The drawing speed of the optical fibers 30 and 40 is changed depending on the rotation speed of the bobbin.

One end of the optical fiber base material 20 is heated to 1800 ° C. or higher by the heater 101 to melt it, and the optical fiber 30 made of glass is pulled out by the winding device 105 at a drawing speed of 900 m / min or more. Then, the resin coating device 102 applies the resin to the optical fiber 30 made of glass, and the ultraviolet irradiation device 103 cures the optical fiber 30 to form a coating layer.

Here, by drawing out the optical fiber 30 at a high drawing speed of 900 m / min or more, the optical fiber 30 is formed before the relaxation effect of the glass network structure by the HIP treatment on the optical fiber base material 20 is significantly reduced. .. As a result, the relaxation effect is maintained also in the optical fiber 30, so that the manufactured optical fiber 40 has a reduced transmission loss.

In general, it is considered that the lower the drawing speed of the optical fiber, the lower the virtual temperature, and the Rayleigh scattering can be reduced. Therefore, it is preferable to set the drawing speed in the present embodiment so as to obtain a desired transmission loss in consideration of both the maintenance of the effect of the HIP processing and the effect of reducing the virtual temperature.

Further, for example, when an alkali metal, for example, potassium is added to the core portion 2 and fluorine is added to the clad portion 3, the virtual temperature of the core portion 2 becomes low, so that compressive stress is applied to the core portion 2 and the clad portion 3 is subjected to compressive stress. It can be in a state where tensile stress is generated. Therefore, it is considered that the effect of the HIP treatment on the optical fiber base material can be more easily maintained even in the core portion of the optical fiber after drawing. In order to reduce the transmission loss of the optical fiber, it is particularly important to reduce the Rayleigh scattering loss in the core portion, so it is preferable that compressive stress is generated in the core portion 2.

(Example 1)
As Example 1, ITU-T G.M. A single mode optical fiber compliant with 652 was manufactured. A VAD device was used to make additive-free silica soot. This suit was dehydrated and vitrified while adding chlorine in a dehydrating and vitrifying apparatus to prepare a transparent vitrified core base material. Germanium was added so that this core base material could be used as the core portion of the optical fiber base material. As a result, the difference in specific refractive index Δ with respect to the pure silica glass of the core base material was set to 0.35%. A silica soot was externally attached to this core base material. A clad portion was formed by vitrifying the silica soot externally attached to the core base material. The optical fiber base material thus produced was subjected to HIP treatment using the HIP apparatus SYSTEM20J manufactured by Kobe Steel. Specifically, the optical fiber base material is put into the crucible, heated to 1500 ° C. using argon gas, pressurized to 150 MPa and maintained for 2 hours, and then the inside of the crucible is cooled and depressurized at room temperature. After returning to normal pressure, the optical fiber base material was taken out. Subsequently, an optical fiber was manufactured from the optical fiber base material by using the apparatus having the configuration shown in FIG. Specifically, the lower end of the optical fiber base material was heated to 1900 ° C., and the drawing was performed at a drawing speed of 900 m / min to manufacture an optical fiber. The manufactured optical fiber had a light transmission loss of 0.166 dB / km at a wavelength of 1.55 μm.

(Examples 2 to 6, Comparative Examples 1 to 3)
As Examples 2 to 6, an optical fiber was manufactured in the same process as in Example 1. However, in Examples 2 to 6, the additives for the core portion and the clad portion, the temperature and pressure in the HIP treatment, and the drawing speed were appropriately changed. Further, in Comparative Examples 1 to 3, the optical fiber was manufactured in the same process as in any of Examples 2 to 6 except that the HIP treatment was not performed. Table 1 shows the production conditions and the transmission loss of the produced optical fiaver in Examples 1 to 6 and Comparative Examples 1 to 3. As shown in Table 1, the transmission loss of Examples 1 to 6 subjected to the HIP treatment was lower than the transmission loss of Comparative Examples 1 to 3. Further, in Examples 1 to 6, the higher the temperature, the higher the pressure, or the higher the drawing speed in the HIP treatment, the lower the transmission loss. Further, when potassium was added to the core portion as in Example 6, the transmission loss was lower than in Examples 1 and 2 having the same HIP temperature, HIP pressure, and drawing speed.

The present invention is not limited to the above embodiments. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

1 Starting material 2 Core part 3 Clad part 10 Core base material 20 Optical fiber base material 30, 40 Optical fiber 100 Manufacturing equipment 101 Heater 102 Resin coating equipment 103 Ultraviolet irradiation equipment 104 Guide roll 105 Winding equipment

Claims (4)

A high-temperature pressurizing step of heating an optical fiber base material having a core portion and a clad portion formed on the outer periphery of the core portion to less than 1800 ° C. while pressurizing at 100 MPa or more and 2000 MPa or less.
A wire drawing step of heating one end of the optical fiber base material subjected to the high temperature pressurization step to 1800 degrees or more to melt it and drawing out the optical fiber at a drawing speed of 900 m / min or more.
A method for manufacturing an optical fiber, which comprises. The method for manufacturing an optical fiber according to claim 1, wherein the core portion contains germanium or chlorine. The method for manufacturing an optical fiber according to claim 1 or 2, wherein the core portion contains an alkali metal. The method for manufacturing an optical fiber according to any one of claims 1 to 3, wherein the clad portion contains fluorine.

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