Title of Invention

"A METHOD OF MANUFACTURING A POROUS GLASS BASE MATERIAL"

Abstract

A method of manufacturing a porous glass base material, comprising subjecting a glass material to flame hydrolysis in an oxyhydrogen flame to produce glass particles; depositing the produced glass particles wherein, glass particles are deposited in such a manner that a core rod (2) is set to ascend at a substantially constant rate in accordance with deposition of glass particles; a flame flow including glass particles produced by a deposition burner is ejected towards a glass particle deposition surface, from the deposition burner positioned under the glass particle deposition surface so as to form an angle with respect to the glass particle deposition surface, and the flame flow reaches an opposite side to, the deposition burner with respect to the core rod; the glass particles are deposited in such a manner that a depression (6) is formed, by the ejection of the flame flow, in a bottom surface of the object formed by the deposition; and the angle between the core rod (2) disposed vertically and the deposition burner (3) is from 30° to 50°.

Full Text

The present invention relates to a method of manufacturing a porous glass base material. [TECHNICAL FIELD] [0001] The present 'invention relates to a manufacturing method of a porous glass base material by depositing, on a starting member, glass particles which are produced by subjecting a glass material to flame hydrolysis. The present invention particularly relates to a manufacturing -method of a porous glass base material for an optical fiber and a glass base material which achieve an improved deposition ratio of the glass particles. Here, the present application relates to the Japanese patent application identified below. The present application incorporates the following application by reference herein, if applicable. Japanese Patent Application No. 2004-060499 filed on March 4,2004 [BACKGROUND ART] [0002] A synthetic quartz glass has a variety of applications such as optical fibers, mask substrates and lenses. A widely-used manufacturing method of a synthetic quartz glass is the vapor-phase axial deposition (VAD) method. According to the VAD method, a glass material such as SiC14 is subjected to flame hydrolysis in a flame provided by a burner, so that glass particles are produced. The produced glass particles arc deposited on a starting member which ascends at a constant rate while rotating. Thus, a porous glass base material is obtained. The porous glass base material is then dehydrated and vitrified into a transparent glass at a high temperature, thereby manufacturing a synthetic quartz glass. [0003] When the VAD method is employed, a glass rod which is separately formed in advance is used for the starting member, and the glass particles are deposited on the starting member, to form an outer portion. As an alternative example, a core portion corresponding to the starting member and an outer portion may be formed within the same manufacturing process flow. In either way, the glass particles produced by flame hydrolysis are ejected onto the deposition surface of the starting member together with the flame flow, to be attached/deposited thereon. It should be noted that, however, part of the glass particles (approximately half, but may vary depending on the conditions) are not deposited, and emitted outside together with an exhaust gas. [0004] A porous glass base material for an optical fiber fabricated by the VAD method typically has the shape shown in Fig. 1. In the center, a core portion (a) is formed. A first clad portion (b) is then formed on the core portion, and a second clad portion (c) is further formed. Here, the diameters of these deposited layers increase in size in a monotonous manner (see Patent Document 1). [0005] To manufacture the porous glass base material, a core rod 2, which corresponds to the core portion, is first formed by means of a core portion deposition burner 1. On the core rod 2, the first clad portion is deposited by means of a first clad portion deposition burner 3, and the second clad portion is then deposited by means of a second clad portion deposition burner 4. A glass particle flow 5 created by the first clad portion deposition burner 3 hits against the core rod 2, to branch into right and left flows while ascending, as shown by the hatching. The branched flows later move away from the outer surface of the core rod 2 and are finally emitted outside. Here, undepositcd glass particles (soot) are mostly emitted outside together with an exhaust gas, but partly accumulatea on the inner wall of a process chamber. [0006] [Patent Document 1] Unexamined Japanese Patent Application Publication No. 2000-63141 [DISCLOSURE OF THE INVENTION] [PROBLEMS TO BE SOLVED BY THE INVENTION] [0007] A synthetic quartz glass has various uses. In recent years, a synthetic quartz glass of a larger size is highly demanded for optical fibers. Therefore, the amount of undepositied soot increases, which raises the raw material cost. A low deposition ratio of glass particles onto a deposition surface further has the following problem. The undepositied soot accumulate on the inner wall of a process chamber. The soot accumulated on the inner wall comes off, and adheres to the deposition surface. This may cause a bubble within a finished product, resulting in a lower yield. To overcome these problems, a method is desired to raise the deposition ratio of glass particles onto the deposition surface. [0008] An advantage of some aspects of the present invention is to provide a manufacturing method of a porous glass base material and a glass base material which can increase an a deposition ratio of glass particles onto a deposition surface in order to reduce the amount of soot floating within a process chamber, thereby preventing a bubble from being created in a product. [MEANS FOR SOLVING THE PROBLEMS] [0009] The inventors of some aspects of the invention have discovered a way to solve the above-mentioned problems as a result of through researches and studies. A manufacturing method of a porous glass base material according to an aspect of the invention is explained. When a glass material is subjected to flame hydrolysis in an oxyhydrogen flame to produce glass particles and the produced glass particles are deposited, glass particles are deposited in such a manner that a core rod is set to ascend at a substantially constant rate in accordance with deposition of glass particles, a flame flow including glass particles produced by a deposition burner is ejected towards a glass particle deposition surface, from the deposition burner which is positioned under the glass particle deposition surface so as to form an angle with respect to the glass particle deposition surface, and the flame flow reaches an opposite side to the deposition burner with respect to the core rod. This manufacturing method increases the time period during which the contact between the glass particles and the deposition surface is maintained, thereby raising the cposition ratio of the glass particles. Here, the glass particles may be deposited in such a manner that a depression is formed, by the ejection of the flame flow, in a bottom surface of the object formed by the deposition. [0010] The core rod may be a porous glass member formed by depositing and growing glass particles in an axial direction by means of a burner different from the deposition burner, or a transparent glass member which is preferably a quartz glass member. Here, the quartz glass member may contain a dopant evenly or partly in a radial direction. [0011] It is preferable that a shape of the depression formed in the bottom surface is adjusted by changing a flow rate of a glass material supplied to the deposition burner, but the shape of the depression formed in the bottom surface may be adjusted by changing a flow rate of one of a combustion gas and a supporting gas supplied to the deposition burner. Here, an angle between the core rod disposed vertically and the deposition burner is preferably from 30° to 50°. By dehydrating and sintering the porous glass base material manufactured by the manufacturing method described above so as to be vitrified into a transparent glass, a glass base material with excellent optical characteristics can be obtained. [EFFECT OF THE INVENTION] [0012] The porous glass base material obtained by the above-described manufacturing method is dehydrated and sintered into a transparent glass. In this way, quartz glass having superior optical characteristics suitable for a glass base material for an optical fiber can be manufactured at a low cost. [BRIEF DESCRIPTION OF THE DRAWINGS] [0013] Figs. 1A and IB each shows a shape of a porous glass base material produced by the VAD method, where the diameters of the deposited layers increase in size in a monotonous manner. Fig. 2 is a schematic view illustrating how glass particles are generally deposited. Fig. 3 is a schematic view illustrating how glass particles are deposited according to an aspect of the present invention. [BEST MODE FOR CARRYING OUT THE INVENTION] [0014] Hereinafter, some embodiments of the present invention will now be described. The embodiments do not limit the invention according to claims, and all the combinations of the features described in the embodiments are not necessarily essential to means for solving the problems of the invention. [0015] The inventors of some aspects of the invention have found a way to increase the such parameters as the flow rate of the glass material, the flow velocity of the flame provided by the burner, and the temperature of the deposition surface. The inventors solved the above-mentioned problems by adjusting the shape of the deposition surface so as to be suitable for the deposition, specifically speaking, by forming a depression in a bottom surface of an object created by the deposition. [0016] Figs. 1 and 2 clearly show that the bottom part of the porous glass base material which is being created by the deposition is mainly formed by means of the first clad portion deposition burner 3. Here, the first clad portion deposition burner heats the side surface of the core portion to adjust the refractive index distribution, in addition to the formation of the first clad portion. Accordingly, the first clad portion deposition burner 3 demonstrates a lower deposition ratio of glass particles, when compared with the other deposition burners. [0017] This drawback is removed by some aspects of the present invention. To be specific, a depression is formed in a bottom surface of an object created by deposition, so as to increase the deposition ratio of the glass particles ejected from the first clad portion deposition burner 3. In this way, the first clad portion has a larger outer diameter, which increases the deposition ratio of glass particles for the second clad portion. As a consequence, the amount of excess soot floating within the process chamber can be reduced. [0018] The following describes the aspect of the invention in more detail with reference to Fig. 3. To start with, the core rod 2 is formed by means of the core portion deposition burner 1. Then, the first clad portion is formed so as to be wrapped around the core rod 2, by means of the first clad portion deposition burner 3 (hereinafter simply referred to as the burner 3). Here, a depression 6 is formed so as to surround the core rod 2 in the bottom surface of the first clad portion. Note that the shape of the depression 6 can be adjusted by changing the flow rate of the gas supplied to the burner 3. The burner 3 is positioned so as to form an angle of 30° to 50° against the core rod 2. The angle between the burner 3 and the core rod 2. preferably falls within the above-specified range since the angle of less than 30° only achieves a low deposition ratio and the angle of more than 50° makes it difficult to form the depression 6. [0019] The glass particle flow 5 created by the burner 3 hits against the core rod 2, to branch into right and left flows. The branch flows run through the groove formed by the depression 6, and reach the opposite side, to the burner 3, with respect to the core rod 2, to merge again, as shown by the hatching, and then move away from the deposition surface. Since the glass particle flow 5 runs through the groove formed by the depression 6 as described, the time period during which the contact between the glass particle flow 5 and the deposition surface is maintained increases. As a consequence, a higher deposition ratio is realized for the glass particles. [0020] The shape of the depression 6 can be determined depending on the thickness of the core rod 2 which the glass particle flow 5 hits against, the flow rates and flow velocities of the material gas and combustion gas supplied to the burner 3, the diameter of the burner 3 and the like. However, the best and particularly effective method to adjust the shape of the depression 6 is to increase the flow rate of the glass material gas when compared with a usual rate. [0021] Here, Fig. 3 shows an example where the number of burners 3 to form the first clad portion is one, but the number can be increased. In addition, the core rod 2, which corresponds to the core portion, is formed by means of the core deposition burner 1 within the same manufacturing process flow as the first and second clad portions in Fig. 3, but a quartz glass rod or the like, which is separately formed in advance, may replace the core rod 2. [IMPLEMENTATION EXAMPLE] [0022] IMPLEMENTATION EXAMPLE 1: The flow rates of gases supplied to a burner were set to 12 L/min (Hi) and 14 L/min (Oi), and 2 L/min (Ar), and the flow rate of a glass material (SiCU) was set to 0.8 L/min, which is higher than usual. The burner was placed upward so as to form an angle of 45° with respect to a core rod which is made of a transparent quartz glass and has a diameter of 30 mm. The core rod was set to ascend at a rate of 0.8 mm/min while rotating. Under these conditions, glass particles were deposited onto the core rod, to form a porous glass base material. While the deposition was being conducted, a depression (groove) was formed in the bottom surface of the object created by the deposition so as to surround the core rod as a passage. The flame flow ejected from the burner ran through the groove. Consequently, the deposition ratio of the glass particles reached a very high level of 87%. [0023] COMPARATIVE EXAMPLE 1: Glass particle deposition was performed under the same conditions as in the implementation example 1, except that the flow rate of the glass material (SiCl4) was set at a typical level of 0.45 L/min. No depression was formed in the object created by the deposition, and the diameter of the object increased in a monotonous manner in the longitudinal direction of the porous glass base material. Here, the deposition ratio of the glass particles was 62%. [INDUSTRIAL APPLICABILITY] [0024] A manufacturing method of a porous glass base material according to an aspect of the present invention can enhance the attachment ratiodeposition ratio of glass particles, which contributes to reduction in manufacturing cost of optical fibers. WE CLAIM: 1. A method of manufacturing a porous glass base material, comprising subjecting a glass material to flame hydrolysis in an oxyhydrogen flame to produce glass particles; depositing the produced glass particles wherein, glass particles are deposited in such a manner that a core rod (2) is set to ascend at a substantially constant rate in accordance with deposition of glass particles; a flame flow including glass particles produced by a deposition burner is ejected towards a glass particle deposition surface, from the deposition burner positioned under the glass particle deposition surface so as to form an angle with respect to the glass particle deposition surface, and the flame flow reaches an opposite side to, the deposition burner with respect to the core rod; the glass particles are deposited in such a manner that a depression (6) is formed, by the ejection of the flame flow, in a bottom surface of the object formed by the deposition; and the angle between the core rod (2) disposed vertically and the deposition burner (3) is from 30° to 50°. 2. The method of manufacturing as claimed in one of claim 1, wherein the core rod (2) is a porous glass member formed by depositing glass particles in an axial direction by means of a burner different from the deposition burner. 3. The method of manufacturing as claimed in one of claims 1 to 2, wherein the core rod (2) is a transparent glass member. 4. The method of manufacturing as claimed in claim 3, wherein the transparent glass member is a quartz glass member, and contains a dopant evenly or partly in a radial direction. 5. The method of manufacturing as claimed in one of claims 1 to 4, wherein a shape of the depression formed in the bottom surface is adjusted by changing a flow rate of a glass material supplied to the deposition burner. 6. The method of manufacturing as claimed in one of claims 1 to 5, wherein a shape of the depression formed in the bottom surface is adjusted by changing a flow rate of one of a combustion gas and a supporting gas supplied to the deposition burner. 7. A glass base material formed by dehydrating and sintering the porous glass base material manufactured by the manufacturing method as claimed in one of claims 1 to 6, so as to be vitrified into a transparent glass.

Documents:

5047-DELNP-2006-Abstract-(03-05-2011).pdf

5047-delnp-2006-Abstract-(19-12-2011).pdf

5047-delnp-2006-abstract.pdf

5047-DELNP-2006-Claims-(03-05-2011).pdf

5047-delnp-2006-Claims-(19-12-2011).pdf

5047-delnp-2006-claims.pdf

5047-DELNP-2006-Correspondence Others-(03-05-2011).pdf

5047-DELNP-2006-Correspondence Others-(07-06-2011).pdf

5047-delnp-2006-Correspondence Others-(19-12-2011).pdf

5047-delnp-2006-correspondence-others.pdf

5047-DELNP-2006-Description (Complete)-(03-05-2011).pdf

5047-delnp-2006-Description (Complete)-(19-12-2011).pdf

5047-delnp-2006-description (complete).pdf

5047-delnp-2006-drawings.pdf

5047-DELNP-2006-Form-1-(03-05-2011).pdf

5047-delnp-2006-Form-1-(19-12-2011).pdf

5047-delnp-2006-form-1.pdf

5047-DELNP-2006-Form-2-(03-05-2011).pdf

5047-delnp-2006-Form-2-(19-12-2011).pdf

5047-delnp-2006-form-2.pdf

5047-DELNP-2006-Form-3-(07-06-2011).pdf

5047-delnp-2006-form-3.pdf

5047-delnp-2006-form-5.pdf

5047-DELNP-2006-GPA-(07-06-2011).pdf

5047-delnp-2006-pct-210.pdf

5047-delnp-2006-pct-304.pdf