Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
  • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
  • C03B37/01211—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
  • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/02—Pure silica glass, e.g. pure fused quartz
  • C03B2201/03—Impurity concentration specified
  • C03B2201/04—Hydroxyl ion (OH)
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/07—Impurity concentration specified
  • C03B2201/075—Hydroxyl ion (OH)
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
  • C03B2201/12—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with fluorine
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
  • C03B2201/28—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with phosphorus
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
  • C03B2201/31—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with germanium

Definitions

• the present invention relates to a quartz glass tube for use in the production of optical fiber preforms and to an optical fiber preform using said quartz glass tube.
• a quartz glass tube for optical fiber preforms capable of producing high-quality optical fibers with high productivity and at a low cost
• a method for producing an optical fiber preform using said quartz glass tube for preforms and to a quartz glass tube for optical fiber preforms capable of producing a low-loss, high-quality optical fibers at a low cost.
• optical fibers particularly, the single mode optical fibers
• VAD process vapor-phase axial deposition process
• OLED process outer vapor-phase deposition process
• soot body i.e., a porous body obtained by depositing fine silica particles, which is a silica body obtained before vitrifying it into a transparent body, which is referred to herein as spatiala porous soot body
• soot body i.e., a porous body obtained by depositing fine silica particles, which is a silica body obtained before vitrifying it into a transparent body, which is referred to herein as spatial porous soot body
• an optical fiber preform comprising a core portion prepared from a quartz glass doped with germanium and a clad portion formed by a quartz glass doped with chlorine or fluorine.
• the rod in tube method described above is a method for optical fiber preforms which easily enables a large scale and long optical fiber preforms and which is most suitable for mass production and lowering cost, however, for further cost reduction and increasing efficiency, a still yet improvement is required in order to more favorably realize melt welding of the clad tube with the core glass rod to obtain a monolithic body.
• the core glass rod for use in the optical fiber preforms is subjected to melt welding into a monolithic body in a heating furnace in such a state that it is inserted into a quartz glass tube for optical fiber preforms.
• the quartz glass tube for the preforms above is heated to a higher temperature on the outer side as compared to the inner side, and such a distribution in temperature brings about problems. That is, because the temperature distribution is as such that the inner side farther from the heating source becomes lower, if the inner side to be melt welded with the core rod for use in preforms above is set at a temperature sufficiently high as to cause melting, the outer side is heated to an excessively high temperature as to cause deformation, and this leads to the deterioration of dimensional precision.
• the inner side is set at a low heating temperature as such to suppress the melt deformation of the outer side, the melting of the inner side becomes insufficient as to result in an insufficient melting of the inner side, thereby causing a fear that a favorable melt welding of the core glass for preforms can not be performed to obtain a monolithic body.
• the optical fiber preform in accordance with the aforementioned rod in tube method by forming the core portion with a germanium doped quartz glass and the clad portion with a chlorine doped quartz glass, there is found a problem of the high temperature viscosity of the quartz glass tube for preforms in addition to the problem of the difference in refraction index.
• the temperature of the heating furnace must be set at a temperature as high as such in a range of from 2000 to 2500°C in order to sufficiently perform the melt welding thereof with the core glass rod for preforms. This not only increases the cost of producing the heating furnace, but also impairs the working environment.
• chlorine is doped into the entire quartz glass tube for preforms, the problem of temperature distribution differing in the inner and outer side of the quartz glas tube and the core glass tube occurs similar to the case of doping only fluorine.
• germanium doped into the core may diffuse by the heat as to change the distribution in refraction index of the core portion, or the germanium diffused into the clad portion may change the distribution of refraction index inside the clad portion itself, and hence, it is feared that an optical fiber preform having favorable distribution in refraction index may not be obtained.
• the temperature of the outer side of the quartz glass tube as above would be excessively increased as to cause a deformation due to melting, and there remains a problem as such that it would impair the dimensional precision of the outer diameter of the thus obtained optical fiber preform.
• the heating temperature should be set as low as such that the melt deformation of the outer side of the tube is suppressed, the inner side undergoes insufficient melting, and it is therefore difficult to solve the problem of causing a disadvantage as such that a favorable melt welding of the quartz glass tube with the core glass rod cannot be realized in obtaining a monolithic body.
• another object of the present invention is to provide an optical fiber preform capable for producing a low loss optical fiber. It is obtained by melt welding the quartz glass tube for optical fiber preforms above with a core rod for optical fiber preforms into a monolithic body.
• the present invention which accomplishes the object above provides a quartz glass tube for use in the production of optical fiber preforms, characterized in that the high temperature viscosity of the quartz glass tube is varied in the wall thickness direction, and that the high tern- perature viscosity in the inner layer side is lower than that of the outer layer side, and an optical fiber preform using said quartz glass tube for optical fiber preforms.
• the quartz glass tube for optical fiber preforms above is, as described above, a high purity quartz glass tube for optical fiber preforms, in which the high temperature viscosity thereof is varied in the wall thickness direction, and that the high temperature viscosity in the inner layer side is lower than that of the outer layer side.
• the viscosity of the inner layer side at 1280 °C is in the range of from 1 x 10 4 to 1 x 10 12 Poise, preferably in the range of from 1 x 10 10 to 1 x 10 12 Poise, and the viscosity of the outer layer side at 1280°C is in the range of from 1 x 10 11 to 1 x 10 13 Poise.
• the quartz glass tube can be produced by a conventionally employed practical methods such as the VAD method, OVD method, or the MCVD method, and can be produced from, for instance, a quartz glass ingot obtained by vitrifying, into a transparent body, a porous silica body prepared by hydrolyzing silicon compound (such as silicon tetrachlo- ride or a siloxane compound), or by vitrifying by Vemeuil's method, into a transparent body, a powder of rock crystal prepared by pulverizing and purifying a naturally occurring rock crystal, or a synthetic quartz glass ingot obtained by a sol-gel process, etc.
• a quartz glass ingot obtained by vitrifying, into a transparent body
• a porous silica body prepared by hydrolyzing silicon compound such as silicon tetrachlo- ride or a siloxane compound
• Vemeuil's method a powder of rock crystal prepared by pulverizing and purifying a naturally occurring rock crystal
• the quartz glass tube is such the high temperature viscosity thereof is varied in the wall thickness direction, and that the high temperature viscosity in the inner layer side is lower than that of the outer layer side.
• a doping agent specifically mentioned are chlorine, germanium, phosphorus, and fluorine, which are used either alone or in combination of two or more selected therefrom.
• at least one selected from chlorine, germanium, phosphorus, and fluorine is doped into the inner layer side of the quartz glass tube.
• At least one selected from chlorine, germanium, and phosphorus is doped together with fluorine into the inner layer side, while doping chlorine into the outer layer side.
• the production cost of the heating furnace for use in the melt welding to obtain a monolithic body can be suppressed, and an optical fiber preform having the desired difference in relative refraction index can be obtained while preventing mal distribution in refraction index attributed to the diffusion of doping agents from occurring.
• OVD method which comprises forming a soot body by depositing fine silica glass particles generated by flame hydrolysis of high purity silicon tetrachloride on a heat-resistant base body to obtain a first porous soot layer; further depositing fine silica particles thereon to obtain a second porous soot layer; subjecting the resulting product to dehydration treatment; vitrifying it into a transparent product and drawing out the heat-resistant base body to obtain a cylindrical quartz glass ingot; and then subjecting the thus obtained quartz glass ingot to a mechanical grinding and the like; and (2) an example of employing VAD method, which comprises forming a soot body by depositing fine silica glass particles generated by flame hydrolysis of high purity silicon tetrachloride on a heat-resistant base body, wherein gases of starting materials differing in composition are supplied separately from a plurality of burners to simultaneously form
• a doping agent is doped as described above, and in doping the doping agents, mentioned are, for example, a method comprising supplying the doping agent to the oxyhydrogen flame together with the gaseous starting material on forming the porous soot body, and a method comprising doping the doping agent in any of the production steps starting from the one before or after the dehydration treatment of the porous soot body to step of vitrifying the body into a transparent body.
• the dehydration treatment is performed at the same time of doping. Accordingly, it is effective to subject the porous soot body to a heat treatment in an atmosphere of gaseous chlorine or gaseous fluorine. Furthermore, in case of producing synthetic quartz, there can be mentioned a method of not incorporating a step of obtaining a porous soot body, such as the direct method (DQ process) or sol-gel process.
• DQ process direct method
• sol-gel process sol-gel process
• a quartz glass tube comprising an inner layer side having a lower high temperature viscosity as compared with the outer layer side can be obtained by preparing, in beforehand, two types of quartz glass tubes differing in high temperature viscosity, and by then melt welding the both tubes into a monolithic body.
• the quartz glass preform using the quartz glass preform for optical .
• the process comprises carefully inserting the core glass rod for optical fiber preforms into the quartz glass tube for preforms; fixing the core glass rod and the quartz glass tube after aligning their circular centers; straightening the entire body for curving, torsion, etc., preferably, after joining the both ends thereof to a quartz glass dummy tube; inserting the resulting body by its lower end into a vertical electric furnace from the upper side of the furnace; and, sequentially heating in zones in the temperature range of from 1700 to 2000°C to melt weld the resulting body into a monolithic body.
• the term ..sequentially heating in zones" above is the so-called zone melting, and refers to heating in which the heating zone is gradually moved.
• the core glass rod for optical fiber preforms for use in the production method above for optical fiber preforms is a light transmitting portion, and mentioned is a quartz glass rod or a quartz glass rod having formed on the periphery thereof an optical clad portion. That is, in the present invention, a resonate glass rod" collectively refers to a core rod and to a cladded core rod.
• a core rod without a clad can be formed by a known VAD process, OVD process, etc., while a cladded core rod can be formed by a method comprising jacketing the core rod with a quartz glass tube, by a method comprising forming a clad portion on the periphery of the core rod by means of OVD process and the like, or by a method comprising a combination of the methods above.
• the quartz glass tube for preforms above Since the outer surface of the quartz glass tube for preforms above is maintained at a high precision, it is possible to further superpose a quartz glass tube for dads on the outer surface thereof, i.e., to perform the so-called secondary jacketing and tertiary jacketing, and hence, the quartz glass tube for preforms can be used to efficiently produce a further larger optical fiber preforms.
• a porous soot body was produced in accordance with OVD method by vaporizing a high purity silicon tetrachloride, performing flame hydrolysis in an oxyhydrogen flame, and depositing the resulting product on the periphery of a base body 50 mm in outer diameter being rotated at a rate of 50 rpm.
• To the burner for use in the flame hydrolysis above were supplied 1500 g/h of silicon tetrachloride as the starting material, 1.8 m 3 /h of gaseous hydrogen, and 0.9 m 3 /h or gaseous oxygen.
• a porous soot body about 230 mm in outer diameter and about 3500 mm in length.
• porous soot body was placed inside an electric furnace, was heated at 1100 °C in an atmosphere of mixed gaseous silicon tetrafluoride and gaseous nitrogen, and was treated subsequently at the same temperature in an atmosphere of mixed gaseous chlorine and gaseous nitrogen.
• Porous soot was then deposited on the periphery of the thus obtained porous soot body by means of OVD process, and the resulting product was heated at 1100°C in an atmosphere of mixed gaseous chlorine and gaseous nitrogen.
• the newly obtained porous soot body had an outer diameter of about 400 mm.
• the porous soot body thus obtained was vitrified in gaseous nitrogen at a temperature of 1600 °C to obtain a transparent body as a result, from which the base body was drawn out to produce a cylindrical quartz glass ingot.
• the resulting cylindrical quartz glass ingot had an outer diameter of about 200 mm and an inner diameter of about 50 mm.
• the both ends of the quartz glass ingot were cut, and thus was produced a quartz glass tube 195 mm in outer diameter and 55 mm in inner diameter by mechanically milling and mechanically polishing the inner and outer peripheral surfaces.
• the viscosity of the quartz glass tube was measured, and was found to be 1 x 10 11 Poise at 1280 °C for the inner layer side and 1 x 10 12 Poise at 1280 °C for the outer layer side.
• the viscosity above are values obtained by cutting out samples 3 x 3 x 50 mm in size from the inner layer side and the outer layer side, and then measuring by beam bending method, i.e., by supporting each of the cut out samples by two points under a temperature of 1280°C, and by measuring the quantity of deformation caused by its own weight. Further, the residual OH group concentration of the quartz glass tube was found to be 0.1 ppm.
• a fluorine and chlorine concentration in the inner layer side was found to be of 500 ppm and 3000 ppm, respectively.
• the chlorine concentration for the outer layer side in a region having a thickness of 35 mm as measured from the outer peripheral surface in that experiment was found to be 1000 ppm.
• the viscosity of the quartz glass tube was measured, and was found to be 1 x 10 5 Poise at 1280 °C for the inner layer side and 1 x 10 17 5 Poise at 1280 °C for the outer layer side.
• a cladded core rod for optical fiber preforms was produced by VAD process, which was hot stretched in a vertical electric furnace to obtain a core glass rod 50 mm in outer diameter.
• the core glass rod was carefully inserted into the quartz glass tube above so that it may not be brought into contact with the inner peripheral surface of the tube, and was fixed to the quartz glass tube after aligning the circular center thereof with that of the quartz glass tube.
• the resulting body was placed inside a vertical electric furnace from the lower end, and the lower end was melt welded.
• the inside of the quartz glass tube was reduced in pressure, and was sequentially heated in zones to obtain a monolithic body by melt welding.
• the melt welding temperature was 1800 °C.
• the distribution of the refraction index of the thus obtained optical fiber preform was measured every 50 mm by using a preform analyzer to found a deviation of ⁇ 0.2 mm or less with respect to the outer diameter. Furthermore, white light was irradiated to the edge plane in a dark room, but no bubbles 0.1 mm or more in size, i.e., the minimum visually observable unit, were observed.
• a porous soot body was produced in accordance with OVD method by vaporizing a high purity silicon tetrachloride, performing flame hydrolysis in an oxyhydrogen flame, and depositing the resulting product on the periphery of a base body 50 mm in outer diameter being rotated at a rate of 50 rpm.
• To the burner for use in the flame hydrolysis above were supplied 1500 g/h of silicon tetrachloride as the starting material, 1.8 m 3 /h of gaseous hydrogen, and 0.9 m 3 /h or gaseous oxygen.
• a porous soot body about 230 mm in outer diameter and about 3500 mm in length.
• porous soot body was placed inside an electric furna- ce, was heated at 1100 °C in an atmosphere of mixed gaseous silicon tetrafluoride and gaseous nitrogen, and was treated subsequently at the same temperature in an atmosphere of mixed gaseous chlorine and gaseous nitrogen.
• Porous soot was then deposited on the periphery of the thus obtained porous soot body by means of OVD process, and the resulting product was heated at 1100°C in an atmosphere of mixed gaseous chlorine and gaseous nitrogen.
• the newly obtained porous soot body had an outer diameter of about 400 mm.
• the porous soot body thus obtained was vitrified in gaseous nitrogen at a temperature of 1600 °C to obtain a transparent body as a result, from which the heat-resistant base body was drawn out to produce a cylindrical quartz glass ingot.
• the resulting cylindrical quartz glass ingot had an outer diameter of about 200 mm and an inner diameter of about 50 mm.
• the both ends of the quartz glass ingot were cut, and thus was produced a quartz glass tube 195 mm in outer diameter and 55 mm in inner diameter by mechanically milling and mechanically polishing the inner and outer peripheral surfaces.
• the viscosity of the quartz glass tube was measured in accordance with the method similar to that used in Example 1 , and was found to be 1 ⁇ 10 10 5 Poise at 1280 °C for the inner layer side and 1 x 10 11 5 Poise at 1280 °C for the outer layer side. Further, the residual OH group concentration of the quartz glass tube was found to be 0.1 ppm.
• a cladded core rod for optical fiber preforms was produced by VAD process, which was hot stretched in a vertical electric furnace to obtain a core glass rod 50 mm in outer diameter.
• the core glass rod was carefully inserted into the quartz glass tube above so that it may not be brought into contact with the inner peripheral surface of the tube, and was fixed to the quartz glass tube after aligning the circular center thereof with that of the quartz glass tube.
• the resulting body was placed inside a vertical electric furnace from the lower end, and the lower end was melt welded.
• the inside of the quartz glass tube was reduced in pressure, and was ⁇ sequentially heated in zones to obtain a monolithic body by melt welding.
• the melt welding temperature was 1800 °C.
• the distribution of the refraction index of the thus obtained optical fiber preform was measured every 50 mm by using a preform analyzer to found a deviation of ⁇ 0.2 mm or less with respect to the outer diameter. Furthermore, white light was irradiated to the edge plane in a dark room, but no bubbles 0.1 mm or more in size, i.e., the minimum visually observable unit, were observed.
• the quartz glass tube for optical fiber preforms according to the present invention is varied in high temperature viscosity in the wall thickness direction in such a manner that the high temperature viscosity in the inner layer side is lower than that of the outer layer side.
• the melt welding temperature for obtaining a monolithic body with a core glass rod for the optical fiber preform can be lowered as to obtain an optical fiber preform with high precision while reducing the construction cost of the heating furnace, and yet, without impairing the working environment.
• an optical fiber preform having favorable distribution of refraction index can be obtained without causing the diffusion of doping agent doped in the core portion.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Manufacture, Treatment Of Glass Fibers (AREA)
• Glass Compositions (AREA)
• Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)

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• 1999
  • 1999-01-18 JP JP00913099A patent/JP4079204B2/ja not_active Expired - Lifetime
  • 1999-10-30 KR KR1019990047866A patent/KR100345358B1/ko not_active Expired - Fee Related
  • 1999-11-08 WO PCT/EP1999/008539 patent/WO2000027767A1/en not_active Ceased
  • 1999-11-08 EP EP99963290A patent/EP1047641A1/de not_active Withdrawn

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