Method for manufacturing an optical fiber preform

Abstract

This invention provides a method for manufacturing an optical fiber preform that prevents foreign matter from being generated at the interface between the core material and the outer mounting layer of the optical fiber preform manufactured by using an optical fiber preform processed on a glass lathe as the core material, thereby improving quality. The method includes the following steps: supporting at least one end of the optical fiber preform using a retaining portion; and processing the optical fiber preform by rotating it while heating it; the optical fiber preform is retained in the retaining portion via a buffer material provided in the retaining portion, the buffer material comprising a component on the side contacting the optical fiber preform and a component on the side contacting the retaining portion, wherein the components on the side contacting the optical fiber preform and the components on the side contacting the retaining portion have different compositions, and the component on the side contacting the optical fiber preform does not contain any of Ca, Mg, Al, K, Na, or Ba.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for manufacturing an optical fiber preform. BACKGROUND

[0002] In recent years, in order to improve productivity, optical fiber preforms have been increasingly large-sized. The optical fiber preform is manufactured, for example, by a well-known method such as a VAD (Vapor Phase Axial Deposition) method or an OVD (Outside Vapor Deposition) method.

[0003] The optical fiber preform manufactured by the method is, for example, processed by a glass lathe such as shown in Fig. 1, in order to adjust the shape for providing to a subsequent process. Further, the optical fiber preform is, for example, processed by a glass lathe such as shown in Fig. 2, in order to adjust the shape for providing to a subsequent process. Figure 1 Fig. 1 is a schematic view of a general glass lathe, and the glass lathe 1 is provided with an outer diameter measurer 4, a heating source 5, and a chuck 6, and holds an optical fiber preform 3 via a dummy rod 2. Typically, for example, a core optical fiber preform of a large diameter manufactured by a VAD method is extended and processed by a glass lathe into a core optical fiber preform of a small diameter, in order to be used as a core material for an OVD method and to add an outer cladding layer. Figure 1

[0004] Generally, in the extension processing by the glass lathe, first, (1) the optical fiber preform 3 and the dummy rod 2 made of quartz glass are held by the respective holding portions 7 in a manner that the respective end faces are opposed to each other, and the end faces opposed to each other are heated to connect them. Next, (2) the holding portion 7 on the optical fiber preform 3 side is opened, and another dummy rod 2 is held by the holding portion 7 in a manner that the end face thereof is opposed to the end face of the optical fiber preform 3, and the end faces are heated to connect them. Thus, the optical fiber preform 3 becomes a shape in which the dummy rods 2 are connected to both ends thereof. In this way, the optical fiber preform 3 held by the glass lathe 1 via the dummy rods 2 is subjected to extension processing or flame polishing processing, and is finished, for example, as a core material for the OVD method.

[0005] When the optical fiber preform manufactured by the OVD method is illuminated from the outside, a foreign matter is sometimes confirmed at the interface between the core material and the outer cladding layer, in the case where the core material is manufactured by extending and processing the optical fiber preform 3 by the glass lathe 1. Such a foreign matter is a problem, and can cause breakage when the optical fiber is drawn, or can cause transmission loss of the optical fiber, and is thus undesirable.

[0006] In Patent Document 1, there is described a method in which, in order to remove the foreign matter generated at the interface as described above, the surface of the optical fiber preform is chemically etched by hydrofluoric acid or the like, and then the glass lathe processing is performed. However, this method has some problems, that is, the cost is increased due to the addition of the chemical etching process, and it is difficult to manage the amount of chemical etching to be uniform in the longitudinal direction, in the case of a large-sized optical fiber preform.​

[0007] Patent Document 1 Japanese Patent Application Laid-Open No. 2010-013352 SUMMARY

[0008] [Problems to be Solved by the Invention]

[0009] The inventors of the present invention analyzed the composition of the foreign matter generated at the interface of the core material and the outer mounting layer, and as a result, found that the main component of the foreign matter was an alkaline earth metal such as Ca. In addition, it was found that when a glass lathe is used to first connect the optical fiber preform with a dummy rod, such foreign matter is generated at a high frequency at the portion of the optical fiber preform held by the glass lathe.

[0010] Figure 2 is a detailed view of the chuck 6' of the glass lathe 1 (refer to Figure 1 ). The chuck 6 has a holding portion 7 and a cushion material 8, and holds the glass preform 3 via the cushion material 8.

[0011] As explained in Figure 1 , in the processing using the glass lathe 1, as a first step, the optical fiber preform 3 is held by the holding portion 7 of the chuck 6 by connecting the optical fiber preform 3 with the dummy rod 2. With regard to the holding portion 7, in order to prevent damage to the optical fiber preform 3 or to prevent the optical fiber preform 3 from being attached with dust, the optical fiber preform 3 is generally held via the cushion material 8. However, the holding portion 7 is heated by the heat of the burner flame of the glass lathe 1 or the like, and is high in temperature. In addition, in order to avoid the optical fiber preform 3 from slipping off the holding portion 7, the optical fiber preform 3 is fastened with the cushion material 8 with a strong force. In order to be able to withstand such high temperature and strong force, the cushion material 8 is often a sheet material in which an inorganic filler such as CaC03, which is fine in particle, is mixed in a rubber material, so as to increase the strength.

[0012] It is conceivable that because the optical fiber preform 3 is firmly held by the chuck 6 of the glass lathe 1 via such a Ca-containing cushion material 8, Ca of the cushion material 8 is attached to the surface of the optical fiber preform 3, and because it is heated by the radiant heat of the burner flame of the glass lathe 1, the Ca is dissolved and diffused into the optical fiber preform 3. If such an optical fiber preform 3 is provided as a core material to the OVD method, the dissolved Ca is found as foreign matter at the interface of the core material and the outer mounting layer.

[0013] The present invention was completed in view of the circumstances, and aims to provide a method of manufacturing an optical fiber preform, which does not generate foreign matter at the interface of the core material and the outer mounting layer of an optical fiber preform produced using an optical fiber preform processed by a glass lathe as a core material, and thus can improve the quality.

[0014] [Technical Means for Solving the Problems]

[0015] The manufacturing method of the optical fiber preform of the present application includes the steps of supporting at least one end of the optical fiber preform by a holding portion, and processing the optical fiber preform while rotating and heating it, and the optical fiber preform is held by the holding portion via a buffer material provided to the holding portion, the buffer material includes a part on the side in contact with the optical fiber preform and a part on the side in contact with the holding portion, the part on the side in contact with the optical fiber preform and the part on the side in contact with the holding portion are different in composition, and the part on the side in contact with the optical fiber preform does not contain any of Ca, Mg, Al, K, Na, and Ba.

[0016] In addition, it is preferable in the present application that the part on the side in contact with the optical fiber preform of the buffer material is made of a rubber-based material to which SiO2 or the like is added as a filler, or contains at least one of PTFE (Polytetrafluoroethylene), PFA (Perfluoroalkoxy alkane), and polyimide.

[0017] In addition, it is preferable in the present application that the part on the side in contact with the optical fiber preform of the buffer material contains at least one of cellulose and lignin.

[0018] In the manufacturing method of the optical fiber preform, it is preferable that the part on the side in contact with the holding portion of the buffer material contains at least one of Ca, Mg, Al, K, Na, and Ba.

[0019] In addition, it is desirable in the present application that the buffer material is composed of at least a first material on the side in contact with the optical fiber preform and a second material on the side in contact with the holding portion, the thickness of the first material is 0.1 mm or more and 2.0 mm or less, the thickness of the second material is 1.0 mm or more and 3.0 mm or less, and the total thickness of the buffer material is set to 1.1 mm or more and 4.0 mm or less.

[0020] [Effects of the Invention]

[0021] According to the manufacturing method of the optical fiber preform of the present application, it is possible to avoid attaching a substance that can cause generation of foreign matters to the optical fiber preform and to process it by a glass lathe, and it is possible to suppress generation of foreign matters without increasing the number of steps. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram showing an example of a general glass lathe.

[0023] Figure 2 is a schematic diagram showing an example of a chuck of a general glass lathe.

[0024] Figure 3 This is a schematic diagram showing an example of the chuck of a glass lathe used in an embodiment of the present invention. Detailed Implementation

[0025] The method for manufacturing the optical fiber mother material of the present invention will be described below. The following embodiments are not limited to the invention described in the claims, and various forms can be realized.

[0026] Figure 3 This is an example of a chuck used in the following embodiments of a glass lathe. The chuck 6 includes a holding portion 7 and a buffer material 8. The buffer material 8 includes a base material contact member 9 and a holding portion contact member 10. The base material contact member 9 is the component of the buffer material 8 that contacts the optical fiber base material 3, and the holding portion contact member 10 is the component of the buffer material 8 that contacts the holding portion 7. Thus, the buffer material 8 is composed of the base material contact member 9 (contacting the optical fiber base material 3) and the holding portion contact member 10 (contacting the holding portion), and is constructed by combining components with different compositions.

[0027] The mother material contact component 9 on the side that contacts the optical fiber mother material preferably does not contain CaCO3, specifically does not contain Ca, Mg, Al, K, Na, or Ba, and preferably contains rubber material with added SiO2 as a filler, or contains PTFE, PFA, or polyimide. In addition, it preferably contains paper sheet material such as cellulose or lignin.

[0028] PTFE, PFA, polyimide, etc., have the following characteristics: excellent durability and cleanability, and they are effective in protecting the surface of the optical fiber mother material from the adhesion of substances that cause foreign matter, but they are also prone to slippage. It is possible that the optical fiber mother material 3 will slip off the clamp 6, or the optical fiber mother material 3 will slip off the clamp 6 when it is fused with the dummy rod 2 (dummy glass material).

[0029] On the other hand, paper materials containing cellulose, lignin, etc., while not as durable as PTFE, PFA, and polyimide, are less prone to slippage, so there is no risk of slippage even when holding the optical fiber substrate. If these components are used, they can provide cushioning materials with performance comparable to rubber materials containing CaCO3, and even when in contact with the optical fiber substrate, there is no concern that foreign matter that would dissolve in the optical fiber substrate during subsequent processes will adhere to the optical fiber substrate.

[0030] However, if the buffer material 8 uses only materials that do not contain inexpensive and easily prepared fillers such as CaCO3, the cost burden increases, and the buffer material 8 is consumed quickly due to repeated use. Therefore, by using conventional rubber materials containing CaCO3, specifically Ca, Mg, Al, K, Na, and Ba as fillers on the side that does not contact the optical fiber mother material 3, that is, the side that contacts the retaining part 7, the cost burden can be reduced and the number of times it can be reused can be increased.

[0031] Furthermore, when the mother material contact member 9 on the side of the buffer material 8 that contacts the optical fiber mother material 3 is designated as the first material, and the retaining part contact member 10 on the side that contacts the retaining part is designated as the second material, it is ideal to optimize the thickness of each material. This further optimizes cost and durability. Specifically, it is ideal to have a thickness of 0.1 mm to 2.0 mm for the first material, a thickness of 1.0 mm to 3.0 mm for the second material, and a total thickness of 1.1 mm to 4.0 mm for the buffer material 8. If the thickness of each material deviates from this range, the strength will decrease, or the swaying will increase when the retaining optical fiber mother material is rotated.

[0032] Furthermore, the buffer material 8 in this invention is not limited to being composed only of the first material and the second material, as long as its total thickness is less than 4.0 mm. Other components may also be placed between the first material and the second material.

[0033] The buffer material, which includes the first material and the second material, can be pre-assembled into a sheet, or it can be used after the sheet made of the first material has been wrapped around the optical fiber mother material 3, and then the sheet made of the second material has been further wrapped around the first material without contacting the optical fiber mother material 3. Alternatively, they can be pre-attached to the holding part 7 of the clamp 6.

[0034] The present invention will be described in more detail below with reference to embodiments and comparative examples, but the present invention is not limited to these embodiments in any way.

[0035] [Example]

[0036] First, an optical fiber preform with an effective part length of 600 mm and an average effective part outer diameter of 100 mm, manufactured by sintering a porous glass preform deposited using the VAD method, is held in place using a holding part of a lathe. Second, a dummy rod made of quartz glass with an outer diameter of 80 mm and a length of 500 mm is held in place using another holding part of the lathe with its end faces facing each other.

[0037] Then, while rotating the optical fiber mother material and the dummy rod held by the lathe chuck at 20 rpm, they are simultaneously heated for 5 minutes using an oxyhydrogen flame released from the burner at a flow rate of 400 L / min for hydrogen and 200 L / min for oxygen, and then fused together.

[0038] Next, the retaining part on the fiber optic mother material side is opened, and the opened retaining part holds another dummy rod made of quartz glass with an outer diameter of 80 mm and a length of 500 mm. While rotating both the fiber optic mother material and the dummy rod at 20 rpm, an oxyhydrogen flame released from the burner is used to heat the fiber optic mother material and the dummy rod at a flow rate of 400 L / min of hydrogen and 200 L / min of oxygen for 5 minutes to fuse the two ends together.

[0039] Thus, the optical fiber preform takes the shape with dummy rods connected to both ends. This preform undergoes several extension steps, extending it to a final target diameter of 50 mm and an effective length of 2000 mm. Then, at both ends of the extended preform, dummy rods made of quartz glass with an outer diameter of 40 mm and a length of 500 mm are rotated at 20 rpm while being simultaneously heated with hydrogen at a flow rate of 400 L / min and oxygen at a flow rate of 200 L / min for 5 minutes, after which they are fused to the preform, thus refining it into a core material manufactured using the OVD method.

[0040] As a method for calculating the extension conditions using a glass lathe, when the outer diameter of the glass base material before extension is set as D1, the target outer diameter of the glass base material after extension is set as D2, the burner platform moving speed is set as VB, and the tail fiber moving speed is set as VT,

[0041] VB×D1 2 = (VT+VB)×D2 2 ,

[0042] Therefore, VB is fixed and VT is controlled for extension. In this way, the optical fiber mother material that will become the core material manufactured by the OVD method is obtained.

[0043] The following examples illustrate how optical fiber cores, which are precision-machined into the core material manufactured by the OVD method, are held in a lathe chuck as Comparative Examples 1 to 7 and Examples 1 to 24.

[0044] [Comparative Example 1]

[0045] The optical fiber preform is wrapped with a 2mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler, which serves as a cushioning material to hold the optical fiber preform in the lathe chuck.

[0046] [Comparative Example 2]

[0047] The optical fiber mother material is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with 4MgCO3·Mg(OH)2·4H2O as a filler. Then, a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler is wrapped on top of it. The whole material is used as a buffer to hold the optical fiber mother material in the lathe chuck.

[0048] [Comparative Example 3]

[0049] The optical fiber preform is wrapped with a 0.5 mm thick sheet of acrylonitrile-butadiene rubber with Al(OH)3 as a filler, and then wrapped with a 1.5 mm thick sheet of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole sheet is used as a buffer material to hold the optical fiber preform in the lathe chuck.

[0050] [Comparative Example 4]

[0051] The optical fiber preform is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with Na·K·Al2Si2O5 as a filler, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber preform in the lathe chuck.

[0052] [Comparative Example 5]

[0053] The optical fiber matrix is ​​made by adding Na(AlSi3O) to acrylonitrile-butadiene rubber. 12 A 0.5mm thick sheet made with CaCO3 as a filler is wrapped around the fiber, and then a 1.5mm thick sheet made with acrylonitrile-butadiene rubber with CaCO3 as a filler is wrapped around it. The whole sheet is used as a buffer material to hold the optical fiber mother material in the lathe chuck.

[0054] [Comparative Example 6]

[0055] The optical fiber mother material is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with 3MgO·4SiO2·H2O as a filler, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole material is used as a buffer to hold the optical fiber mother material in the lathe chuck.

[0056] [Comparative Example 7]

[0057] The optical fiber preform is wrapped with a 0.5 mm thick sheet of acrylonitrile-butadiene rubber with BaSO4 as a filler, and then wrapped with a 1.5 mm thick sheet of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole sheet is used as a buffer material to hold the optical fiber preform in the lathe chuck.

[0058] [Example 1]

[0059] The optical fiber preform is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber preform in the lathe chuck.

[0060] [Example 2]

[0061] The optical fiber mother material is wrapped with a 0.5mm thick sheet made of PTFE, and then wrapped with a 1.5mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0062] [Example 3]

[0063] The optical fiber mother material is wrapped with a 0.5mm thick sheet made of PFA, and then wrapped with a 1.5mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0064] [Example 4]

[0065] The optical fiber mother material is wrapped with a 0.5 mm thick sheet made of polyimide, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0066] [Example 5]

[0067] The optical fiber preform is wrapped with a 0.5mm thick paper sheet made of Towper zip towel (trade name) manufactured by TRY-FU Co., Ltd., and then wrapped with a 1.5mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a cushioning material to hold the optical fiber preform in the lathe chuck.

[0068] [Example 6]

[0069] The optical fiber mother material is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with 4MgCO3·Mg(OH)2·4H2O as a filler. The whole material is used as a buffer to hold the optical fiber mother material in the lathe chuck.

[0070] [Example 7]

[0071] The optical fiber mother material is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with Al(OH)3 as a filler. The whole material is used as a buffer to hold the optical fiber mother material in the lathe chuck.

[0072] [Example 8]

[0073] The optical fiber mother material is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with Na·K·Al2Si2O5 as a filler. The whole material is used as a buffer to hold the optical fiber mother material in the lathe chuck.

[0074] [Example 9]

[0075] The optical fiber mother material is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then coated with acrylonitrile-butadiene rubber with Na(AlSi3O) 12 A 1.5mm thick sheet made of 3·H2O as a filler is used to wrap the fiber optic mother material, which is then used as a buffer material to hold the fiber optic mother material in the lathe chuck.

[0076] [Example 10]

[0077] The optical fiber mother material is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with 3MgO·4SiO2·H2O as a filler. The whole material is used as a buffer to hold the optical fiber mother material in the lathe chuck.

[0078] [Example 11]

[0079] The optical fiber preform is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5 mm thick sheet made of acrylonitrile-butadiene rubber with BaSO4 as a filler. The whole is used as a buffer material to fix the optical fiber preform in the lathe chuck.

[0080] [Example 12]

[0081] The optical fiber preform is wrapped with a 0.5mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5mm thick sheet made of PTFE. The whole is used as a buffer material to hold the optical fiber preform in the lathe chuck.

[0082] [Example 13]

[0083] The optical fiber preform is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5 mm thick sheet made of PFA. The whole is used as a buffer material to hold the optical fiber preform in the lathe chuck.

[0084] [Example 14]

[0085] The optical fiber preform is wrapped with a 0.5 mm thick sheet made of acrylonitrile-butadiene rubber with SiO2 as a filler, and then wrapped with a 1.5 mm thick sheet made of polyimide. The whole is used as a buffer material to hold the optical fiber preform in the lathe chuck.

[0086] [Example 15]

[0087] The optical fiber mother material is wrapped with a 0.05mm thick sheet made of PTFE, and then wrapped with a 2mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0088] [Example 16]

[0089] The optical fiber mother material is wrapped with a 0.1 mm thick sheet made of PTFE, and then wrapped with a 2 mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0090] [Example 17]

[0091] The optical fiber mother material is wrapped with a 1mm thick sheet made of PTFE, and then wrapped with a 2mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0092] [Example 18]

[0093] The optical fiber mother material is wrapped with a 2mm thick sheet made of PTFE, and then wrapped with a 2mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0094] [Example 19]

[0095] The optical fiber mother material is wrapped with a 2.5mm thick sheet made of PTFE, and then wrapped with a 2mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0096] [Example 20]

[0097] The optical fiber mother material is wrapped with a 1mm thick sheet made of PTFE, and then wrapped with a 0.5mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0098] [Example 21]

[0099] The optical fiber mother material is wrapped with a 1mm thick sheet made of PTFE, and then wrapped with a 0.8mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0100] [Example 22]

[0101] The optical fiber mother material is wrapped with a 1mm thick sheet made of PTFE, and then wrapped with a 1mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0102] [Example 23]

[0103] The optical fiber mother material is wrapped with a 1mm thick sheet made of PTFE, and then wrapped with a 2mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0104] [Example 24]

[0105] The optical fiber mother material is wrapped with a 1mm thick sheet made of PTFE, and then wrapped with a 3mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0106] [Example 25]

[0107] The optical fiber mother material is wrapped with a 1mm thick sheet made of PTFE, and then wrapped with a 3.2mm thick sheet made of acrylonitrile-butadiene rubber with CaCO3 as a filler. The whole is used as a buffer material to fix the optical fiber mother material in the lathe chuck.

[0108] Large optical fiber mother material was manufactured by externally mounting 80 kg of glass microparticles onto the core material held in the lathe chuck in Comparative Examples 1-7 and Examples 1-25 using the OVD method, and then sintering it at 1500°C to make it transparent glass.

[0109] Then, shine a halogen lamp on it from the outside to check for any foreign objects at the interface between the core material and the outer mounting layer.

[0110] Table 1 summarizes the composition and thickness of the first and second materials constituting the buffer materials used in Comparative Examples 1 to 7 and Examples 1 to 25, the total thickness of the buffer materials, the occurrence of foreign matter at the interface between the core material of the large optical fiber mother material and the outer mounting layer, and the determination results of whether it can be used as a buffer material.

[0111] The determination of whether a material can be used as a cushioning material depends not only on the presence of foreign matter at the interface, but also on a comprehensive assessment of ease of operation and, consequently, the reusability of the cushioning material. Ease of operation specifically refers to, for example, the ease of holding the optical fiber preform using a lathe chuck. In the table, 0 = no problem, △ = room for improvement but usable, × = unusable.

[0112] [Table 1]

[0113]

[0114] Comparative Examples 1 to 7 confirmed the presence of foreign matter at the interface between the core material and the outer mounting layer, making them unsuitable for use as buffer materials. On the other hand, no such foreign matter was observed in Examples 1 to 25, and all of Examples 1 to 25 were suitable for use as buffer materials. Therefore, it can be concluded that the first material in contact with the optical fiber mother material should not contain Ca, Mg, Al, K, Na, or Ba. It is believed that these substances would adhere to the surface of the optical fiber mother material and melt into the glass due to heating in subsequent processes.

[0115] In Example 1, SiO2 was added as a filler to acrylonitrile-butadiene rubber in the first material, and no foreign matter was detected at the interface between the core material and the outer mounting layer, resulting in good results. In Examples 2 to 5, no foreign matter was generated at the interface, and the cleanliness of PTFE, PFA, polyimide sheets, and paper sheets was high, which was considered good.

[0116] In the comparison of Examples 6 to 14, Examples 6 to 11 demonstrate sufficient restoring force when the cushioning material is clamped and flattened using a clamp and then released. On the other hand, Examples 12 to 14, while sufficient for use as cushioning material, exhibit weaker restoring force compared to Examples 6 to 11. The rebound force of the cushioning material is one of the forces that hold the parent material in place. The fact that the cushioning material retains its restoring force after clamping increases the likelihood of its good reuse. Therefore, Examples 6 to 14 can be considered qualified as cushioning materials, with Examples 6 to 11 being particularly excellent in terms of restoring force, further increasing the likelihood of good reuse. Therefore, to increase the likelihood of good reuse of the cushioning material, it is preferable that the second material contains Ca, Mg, Al, K, Na, and Ba. Fillers composed of these elements can improve the strength or restoring properties of the material, making it easy to reuse the cushioning material even after clamping with a strong force, offering economic advantages.

[0117] In the comparison of Examples 15 to 25, in Examples 15, 19-21, and 25, a permissible degree of oscillation was observed when the optical fiber mother material was rotated while being held in place. On the other hand, no such oscillation was observed in Examples 16-18 and 22-24. Therefore, it can be said that Examples 15-25 are qualified as buffer materials, with Examples 16-18 and 22-24 being particularly excellent in terms of ease of holding, thus improving ease of operation. Therefore, it is preferable that the thickness of the first material is 0.1 mm to 2.0 mm or less, the thickness of the second material is 1.0 mm to 3.0 mm or less, and preferably the total thickness of these buffer materials is 1.1 mm to 4.0 mm or less. If the thickness of each material deviates from this range, the strength will decrease, or the oscillation will increase when the optical fiber mother material is rotated while being held in place.

[0118] Furthermore, the present invention is not limited to the described embodiments and can be freely modified and improved as appropriate.

[0119] [Explanation of Symbols]

[0120] 1 Glass lathe

[0121] 2. Dummy stick

[0122] 3. Optical fiber parent material

[0123] 4. Outer diameter measuring instrument

[0124] 5. Heating source

[0125] 6. Chuck

[0126] 7. Holding section

[0127] 8. Buffer material

[0128] 9. Base material contact parts

[0129] 10. Holding part contact component

Claims

1. A method for manufacturing an optical fiber preform, comprising the following steps: At least one end of the optical fiber housing is supported using a retaining portion; and The optical fiber mother material is rotated on one side and heated on the other to process it; and The optical fiber mother material is held in place by a buffer material at the holding portion. The buffer material includes a component on the side that contacts the optical fiber matrix and a component on the side that contacts the retaining portion. The components on the side that contact the optical fiber mother material and the components on the side that contact the retaining part have different compositions. The components on the side in contact with the optical fiber matrix do not contain any of Ca, Mg, Al, K, Na, or Ba. The component on the side that contacts the retaining part is made of rubber material; The component on the side in contact with the retaining part contains at least one of Ca, Mg, Al, K, Na, and Ba.

2. The method for manufacturing optical fiber mother material according to claim 1, wherein the component of the buffer material on the side in contact with the optical fiber mother material is made of a rubber material with SiO2 added as a filler.

3. The method for manufacturing optical fiber mother material according to claim 1, wherein the component of the buffer material on the side in contact with the optical fiber mother material comprises at least one of PTFE, PFA, and polyimide.

4. The method for manufacturing optical fiber mother material according to claim 1, wherein the component of the buffer material on the side in contact with the optical fiber mother material comprises at least one of cellulose and lignin.

5. The method for manufacturing optical fiber mother material according to claim 4, wherein the component of the buffer material on the side in contact with the optical fiber mother material is a paper sheet.

6. The method for manufacturing an optical fiber preform according to any one of claims 1 to 5, wherein the buffer material is composed of at least a first material on the side in contact with the optical fiber preform and a second material on the side in contact with the retaining portion, wherein the thickness of the first material is 0.1 mm or more and 2.0 mm or less, the thickness of the second material is 1.0 mm or more and 3.0 mm or less, and the total thickness of the buffer material is 1.1 mm or more and 4.0 mm or less.

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