GB2059944A - Fabrication method of optical fiber preforms - Google Patents
Fabrication method of optical fiber preforms Download PDFInfo
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- GB2059944A GB2059944A GB8031821A GB8031821A GB2059944A GB 2059944 A GB2059944 A GB 2059944A GB 8031821 A GB8031821 A GB 8031821A GB 8031821 A GB8031821 A GB 8031821A GB 2059944 A GB2059944 A GB 2059944A
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- Prior art keywords
- core
- blowing nozzle
- preform
- optical fiber
- gas blowing
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 155
- 238000000034 method Methods 0.000 title claims abstract description 98
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 65
- 239000011521 glass Substances 0.000 claims abstract description 204
- 239000002994 raw material Substances 0.000 claims abstract description 98
- 239000002245 particle Substances 0.000 claims abstract description 60
- 230000002194 synthesizing effect Effects 0.000 claims abstract description 46
- 239000007789 gas Substances 0.000 claims description 297
- 238000007664 blowing Methods 0.000 claims description 185
- 238000005253 cladding Methods 0.000 claims description 95
- 239000005373 porous glass Substances 0.000 claims description 95
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 53
- 239000011261 inert gas Substances 0.000 claims description 22
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- 230000015572 biosynthetic process Effects 0.000 abstract description 14
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- YBMRDBCBODYGJE-UHFFFAOYSA-N germanium dioxide Chemical compound O=[Ge]=O YBMRDBCBODYGJE-UHFFFAOYSA-N 0.000 description 16
- ILAHWRKJUDSMFH-UHFFFAOYSA-N boron tribromide Chemical compound BrB(Br)Br ILAHWRKJUDSMFH-UHFFFAOYSA-N 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 14
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- 229910052681 coesite Inorganic materials 0.000 description 6
- 238000007796 conventional method Methods 0.000 description 6
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- DLYUQMMRRRQYAE-UHFFFAOYSA-N tetraphosphorus decaoxide Chemical compound O1P(O2)(=O)OP3(=O)OP1(=O)OP2(=O)O3 DLYUQMMRRRQYAE-UHFFFAOYSA-N 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 4
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- 238000005192 partition Methods 0.000 description 4
- 229910011255 B2O3 Inorganic materials 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
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- 230000000694 effects Effects 0.000 description 3
- 239000000835 fiber Substances 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 238000012681 fiber drawing Methods 0.000 description 2
- 229910052736 halogen Inorganic materials 0.000 description 2
- 150000002367 halogens Chemical class 0.000 description 2
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- FAQYAMRNWDIXMY-UHFFFAOYSA-N trichloroborane Chemical compound ClB(Cl)Cl FAQYAMRNWDIXMY-UHFFFAOYSA-N 0.000 description 2
- VXEGSRKPIUDPQT-UHFFFAOYSA-N 4-[4-(4-methoxyphenyl)piperazin-1-yl]aniline Chemical compound C1=CC(OC)=CC=C1N1CCN(C=2C=CC(N)=CC=2)CC1 VXEGSRKPIUDPQT-UHFFFAOYSA-N 0.000 description 1
- 229910015844 BCl3 Inorganic materials 0.000 description 1
- 240000008100 Brassica rapa Species 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910052810 boron oxide Inorganic materials 0.000 description 1
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- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 229940119177 germanium dioxide Drugs 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- FAIAAWCVCHQXDN-UHFFFAOYSA-N phosphorus trichloride Chemical compound ClP(Cl)Cl FAIAAWCVCHQXDN-UHFFFAOYSA-N 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 239000005049 silicon tetrachloride Substances 0.000 description 1
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- 239000000126 substance Substances 0.000 description 1
- IEXRMSFAVATTJX-UHFFFAOYSA-N tetrachlorogermane Chemical compound Cl[Ge](Cl)(Cl)Cl IEXRMSFAVATTJX-UHFFFAOYSA-N 0.000 description 1
- 239000012808 vapor phase Substances 0.000 description 1
- 238000001947 vapour-phase growth Methods 0.000 description 1
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
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/01413—Reactant delivery systems
- C03B37/0142—Reactant deposition burners
-
- 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
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/0144—Means for after-treatment or catching of worked reactant gases
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2203/00—Fibre product details, e.g. structure, shape
- C03B2203/10—Internal structure or shape details
- C03B2203/22—Radial profile of refractive index, composition or softening point
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2203/00—Fibre product details, e.g. structure, shape
- C03B2203/10—Internal structure or shape details
- C03B2203/22—Radial profile of refractive index, composition or softening point
- C03B2203/24—Single mode [SM or monomode]
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/04—Multi-nested ports
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/04—Multi-nested ports
- C03B2207/06—Concentric circular ports
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/04—Multi-nested ports
- C03B2207/10—Split ports
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/04—Multi-nested ports
- C03B2207/16—Non-circular ports, e.g. square or oval
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/04—Multi-nested ports
- C03B2207/18—Eccentric ports
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/20—Specific substances in specified ports, e.g. all gas flows specified
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/42—Assembly details; Material or dimensions of burner; Manifolds or supports
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/50—Multiple burner arrangements
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/60—Relationship between burner and deposit, e.g. position
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/60—Relationship between burner and deposit, e.g. position
- C03B2207/64—Angle
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
- Y02P40/57—Improving the yield, e-g- reduction of reject rates
Abstract
In fabricating an optical fiber preform, a synthesizing torch (4) is inclined by 10 DEG to 60 DEG with respect to the rotation axis of a seed rod (2). Moving the rod while rotating it, a glass raw material gas and a flame forming gas are blown out individually from the torch to synthesize glass particles which are deposited onto one end of the rod, so that a cylindrical porous preform is grown in the direction of the rotation axis of the rod. Then the porous preform is heated at a high temperature to vitrify the porous preform into a transparent optical fibre preform. At least one exhaust port (9) is disposed with a distance of 1 mm to 50 mm from the periphery of the porous preform and in the vicinity of the growing surface of the porous preform. In fabricating the porous preform the outer diameter fluctuation is small, and the preform is formed stably without formation of crack on the periphery of the preform. The growing speed is improved easily. The synthesizing torch, e.g. Figure 15a (61) for core is so arranged to produce a glass particle stream deviated from the center area of flame stream. The diameter of a core may be narrowed to 10 mm or less, cladding-to-core-diameter ratio may be increased to be three or more. The mass-production of long-length and low-loss single-mode optical fibers is possible by VAD method. <IMAGE>
Description
SPECIFICATION
Fabrication method of optical fiber preforms
The present invention relates to a fabrication method for optical fiber preforms by a so-called VAD (Vapor-phase Axial Deposition) method.
The fabrication process for optical fiber preforms by the VAD method, is disclosed in U.S. Patent No.
4,062,665. In the VAD method, fine glass particles, synthesized by hydrolysis or thermal oxidation reaction of glass raw material with flame, are attached to and deposited on one end of a seed rod in an axial direction so as to form a cylindrical porous preform. The porous preform is heated at a high temperature and vitrified into a transparent preform.
In a conventional VAD method, for fabricating the cylindrical porous glass preform, a glass synthesizing torch is disposed on or in parallel with the rotation axis of the porous glass preform. Further, an exhaust nozzle for removing residual glass particles not attached to the growing surface of the porous glass preform, is disposed on the side of a reaction vessel. In this case, the growing speed of the porous preform in the axial direction is likely to be slow and in an extreme case the growing speed is higher in the radial direction than in the axial direction. The residual glass particles are additionally attached to the periphery of the upper porous preform, so that the outer diameter of the preform thus obtained greatly fluctuates.Because of this disadvantage, in the conventional VAD method, it was very difficult to improve transmission bandwidth properties of a multi-mode optical fiber by controlling an obtained graded-type refractive index profile by adjusting the dopant concentration in the radial direction of the glass preform and to improve transmission loss properties by the simultaneous formation of core and cladding regions. For this reason, the conventional VAD method fails to take a full advantage of the feasibility of mass-production of optical fibers which is a merit of the VAD method.
Proposed in Electronics Letters, 17th August 1978, Vol. 14, No. 17, pp.534-535, by S. Sudo et al. is an another construction having a main torch and a subsidiary torch in which the main torch is disposed on the rotation axis of the porous preform while the subsidiary torch is disposed inclined to the rotation axis. With this arrangement of those torches, the glass particles from the subsidiary torch are deposited on the peripheral portion of the porous glass preform in a manner that the refraction index profile in the radial direction of the preform is adjustable. This proposal, however, still involves the disadvantage of an undesirable outer diameter fluctuation of the porous glass preform and therefore it was difficult to stably manufacture long-length optical fibers by the VAD method.
Additionally, in case where an amount of the residual glass particles is fairly large, a glass particle layer with a small apparent density is formed by the residual glass particles on the side wall of the porous preform.
Accordingly, the outer diameter of the porous glass preform is remarkably large or there may be formed "cracking" on the peripheral wall of the porous glass preform. As a result, after the preform is vitrified to obtain a transparent preform, it is difficult to use the vitrified preform as an optical fiber preform.
Of the optical fibers, a single-mode optical fiber has an extremely wide transmission bandwidth, and accordingly the single-mode optical fiber is expected as a high-capacity long distance transmission line in the future. There is known a so-called MCVD (Modified Chemical Vapor-phase Deposition) method as a fabrication method for a single-mode optical fiber preform. In this method, a cladding glass layer and a core glass layer are formed on the inner surface of a supporting silica tube and then the assembly of these layers are collapsed to form an optical fiber preform. A resultant single-mode optical fiber has a small transmission loss.In this respect, the MCVD method is available for the manufacturing of, for example, a single-mode optical fiber with a transmission loss in the order of 1 dB/km or less in the wavelength band of 1.55 ,um which has recently attracted attention. In the MCVD method, however, a length of a single-mode optical fiber obtained from a single optical fiber preform is generally 2 to 5 km and even at most 10 km. Therefore, the
MCVD method has problems for the mass-production of single-mode optical fibers.
Another known method of manufacturing the single-mode optical fiber is a so-called rod-in-tube method.
Briefly, in this method, a single-mode optical fiber preform is fabricated first by synthesizing a glass rod to be a core by a so-called plasma method and then by sealing it in a silica tube having proper dimensions. While the rod-in-tube method, when comparing with the MCVD mehtod, is suitable for the mass-production of the optical fibers, the rod-in-tube method has a disadvantage of a large transmission loss. The large transmission loss in the rod-in-tube method is caused largely by the waveguiding properties of the single-mode optical fiber. In the case of the single-mode optical fiber, a relatively large part of optical power propagates through not only a core region but also a cladding region.Accordingly, the optical power, through the propagation, is influenced by imperfections and impurities at the boundaries between a glass rod as the core region and a silica tube as the cladding region, and impurities contained in the silica tube, for example, OH ions and small bubbles. Because ofthis influence, it was difficult to reduce the optical transmission loss less than 5 dB/km.
On the other hand, the VAD method in-which a cylindrical porous preform is first prepared and then is subjected to heating at a high temperature and vitrifying process to form a transparent preform is suitable for the mass-production of optical fibers. In the VAD method, glass raw material gas such as SiCI4, GeCI4, POCI3, BBr3 or the like and flame forming gas such as 2, H2, Ar, He or the like are led to a glass synthesizing torch. Glass fine particles such as SiO2, GeO2, P2O5, B203 or the like synthesized by the flame hydrosis or oxidation reaction of those materials with the glass synthesizing torch are attached and deposited onto a seed rod so as to form a cylindrical porous preform.The cylindrical porous preform thus formed is heated at 1500 to 1700"C by a high temperature heater and is vitrified into a transparent optical fiber preform.
The glass synthesizing torch is generally formed as a multi-layer tube having such an arrangement that a raw material gas blowing nozzle with a centered circular cross section is coaxially surrounded by an inactive gas blowing nozzle for Ar, He or the like, a combustible gas blowing nozzle for H2 or the like, and an auxiliary gas blowing nozzle for 2 or the like, which are disposed in this order. Glass particles, produced by flames blown together with glass raw material gas are sintered and deposited on the seed rod, so that the rod-like glass sintered member is grown in the axial direction. Usually, the synthesizing torch and a flame stream blown out from the torch are disposed coaxially or in parallel with a rotation axis of the seed rod and the porous preform.In case of forming the porous preform for the optical fiber by the synthesizing torch, the produced glass particles are diffused in a direction orthogonal to the rotation axis, or in the horizontal direction. Therefore, it was difficult to reduce the diameter of the porous glass body thus formed to be less than about 40 mm. In this case, it was difficult to make the diameter of the porous glass body less than about 40 mm, even if an area of the raw material gas blowing nozzle at the center of the torch is selected as small as possible or the flame stream is converged as intensively as possible.
As an improvement of the VAD method, the synthesizing torch and the flame stream may be inclined by a given angle with respect to the seed rod and the rotation axis of the porous preform. This improved VAD method could stably fabricate the porous preform as small as about 30 mm in diameter. It was, however, difficult to reduce the diameter of the porous preform to be less than 30 mm. If the porous preform having a diameter of 30 mm is used as the porous glass body for the core and a cladding layer is deposited on the rod-like porous glass body by using the subsidiary torch, a cladding-to-core diameter ratio is approximately 2 at maximum.
As will be discribed in detail layer, it is required that the cladding-to-core diameter ratio be approximately 3 or more in order to form the single-mode optical fiber. In the above-mentioned example, the ratio is about 2 and the thickness of the cladding layer is insufficient for the 3 or more ratio. The ratio may be increased by increasing the thickness of the cladding layer. If the thickness is increased in this way so as to obtain the ratio of 3 or more, the diameter of the porous preform for the cladding exceeds 100 mm. The result is that a stress developed therein possibly cracks the porous preform orthe excessive largeness of the diameter renders it inconvenient to handle the porous preform when it is consolidated or vitrified.Because of those disadvantages, it has not been possible to manufacture the single-mode optical fibers by well taking advantage of the useful feature of the VAD method that the VAD method is suitable for the mass-production of the optical fibers.
In view of the above, it is an object of the invention to provide a fabrication method of an optical fiber preform by an improved VAD method, where the above-mentioned disadvantages are removed.
Another object of the invention is to provide a fabrication method of an optical fiber preform in which a cylindrical porous preform may stably be grown in the axial direction with little fluctuation of the outer diameter of the porous preform.
Yet another object of the invention is to provide a fabrication method of an optical fiber preform in which the fluctuation of the outer diameter of the porous preform is lessened and the above-mentioned glass particle layer with small apparent density is not formed on the periphery of the porous preform, so that a porous preform having a uniform outer diameter may be stably formed without the formation of cracks on the periphery of the porous preform.
Still another object of the invention is to provide a fabrication method of an optical fiber preform in which the porous preform for core of the optical fiber is stably grown in the axial directiion with little fluctuation in the outer diameter and a cladding porous glass body is deposited on the periphery of the porous preform for core to form a low-loss optical fiber preform.
A further object of the invention is to provide a fabrication method of an optical fiber preform suitable for manufacturing a multi-mode optical fiber having a long-length and low-loss, in which a porous preform for core having a large diameter is stably grown in the axial direction with little fluctuation in the outer diameter and without forming a glass particle layer having small apparent density on the periphery of the porous preform.
Still a further object of the invention is to provide a fabrication method of an optical fiber preform for manufacturing graded-index optical fibers having a wide bandwidth and low-loss by controlling a refractive-index profile of the porous preform.
An additional object of the invention is to provide an optical fiber preform fabrication method suitable for manufacturing a single-mode optical fiber having a long-length and low-loss, in which the porous preform for core having a small diameter is stably grown with little fluctuation in the outer diameter and without forming a glass particle layer having a small apparent density on the periphery of the preform.
Another important object of the invention is to provide a fabrication method of a single-mode optical fiber preform which may fabricate on the mass-production basis a single-mode optical fiber preform having a long-length and low-loss by the VAD method.
Yet another important object of the present invention is to provide a torch for core suitable for fabricating the porous glass body for core of the single-mode optical fiber having a small diameter.
According to a first aspect of the present invention, a seed rod is moved while the seed rod being rotated, and a synthesizing torch inclined by 100 to 60 relative to the rotation axis of the seed rod individually blows out glass raw material, environment gas and flame stream including high temperature gas. The glass raw materials are synthesized into glass particles through hydrolysis by flame or thermal oxidation by a high temperature heat source. The glass particles thus synthesized are blown and deposited to one end of the seed rod which moves continuously while rotating, so that a cylindrical porous preform is grown on the rotation axis of the seed rod and is heated at a high temperature to be vitrified into a transparent optical fiber preform.
According to a second aspect of the present invention, at least one exhaust port is disposed with a distance of 1 mm to 50 mm from the periphery of the porous preform and in the vicinity of the growing surface of the porous preform which is fabricated by the deposition of synthesized glass particles as mentioned above. The porous preform is fabricated, while the exhaust port exhausts glass particles not attached to the growing surface of the porous preform, gases produced as a result of the hydrolysis or the thermal oxidation, non-reacted glass raw materials and environment gases.
In the present invention, it is preferable that the synthesizing torch is inclined by 100 to 60 , preferably by 30 to 40 , with respect to the rotation axis of the seed rod, so that the glass particles are obliquely blown and deposited onto one end of the seed rod, and that the above-mentioned exhaust port is disposed with a distance of 1 mm to 50 mm, preferably 5 mm to 10 mm, from the periphery of the porous preform.
In a preferred embodiment of the present invention, the synthesizing torch may be used as a torch for core and form may be formed as a multi-mode optical fiber preform.
In another preferred embodiment of the present invention, the synthesizing torch may be used as a torch for core, and the cylindrical porous glass preform may be used as a porous glass preform for core, and a porous glass preform for cladding is deposited onto the periphery of the porous glass preform for core by a torch for cladding.
In the above embodiment, the torch for core may be inclined by 30 to 50 with respect to the rotation axis and the transparent optical fiber preform may be formed as a single-mode optical fiber.
In order to achieve the above objects for providing a fabrication method of single-mode optical fiber preforms, in the present invention, a porous glass body is attached to and axially deposited on one end of a seed rod and grown by the torch for core which produces fine glass particles for core eccentrically with respect to the center area of the flame stream. The porous glass body is attached to and deposited on the periphery of the porous glass body for core by at least one torch for cladding for producing fine glass particles for cladding so as to form a cladding layer. The obtained porous glass body is heated and vitrified into a transparent glass body. The transparent glass body is sealed in a silica tube, thereby forming a single-mode optical fiber preform.
In another aspect of fabricating a single-mode optical fiber preform according to the present invention, a torch for core which produces fine glass particles eccentrically with respect to the center area of a flame stream is so arranged as to blow the flame stream inclined to a seed rod. The porous glass body for core is grown on one end of the seed rod and in the direction of the axis of the seed rod. A cladding layer is formed on the periphery of the porous glass body for core by at least one torch for cladding. The obtained porous glass body is heated and vitrified into a transparent glass body. The transparent glass body is sealed in a silica tube for jacketting to form a single-mode optical fiber preform.In a preferred embodiment of the present invention, the torch for core is inclined by 30 to 50 with respect to the axis of the seed rod.
It is preferable that the torch for core has a glass raw material gas blowing nozzle and a combustible gas blowing nozzle. The combustible gas blowing nozzle surrounds the glass raw material gas blowing nozzle in such a way that the glass raw material blown out from the glass raw material gas blowing nozzle is deviated from the center of an inner area defined by the combustible gas blowing nozzle, with respect to oxy-hydrogen flame stream blown out from the combustible gas blowing nozzle.
It is also preferable that at least one exhaust port is disposed with a distance of 1 mm to 50 mm from the periphery of the porous preforms for core and cladding and in the vicinity of the growing surface of the porous preforms for core and cladding, and the glass particles not attached to and deposited on the growing surface of the porous preforms for core and cladding, gases produced as a result of the hydrolysis by flame or the thermal oxidation in the torch for core and cladding, and residual non-reacted glass raw material and flame forming gases are exhausted through the exhaust port. Especially, it is preferable that the above-mentioned inclination angle is 30 to 40 and the above-mentioned distance is 5 mm to 10 mm.
According to the present invention, a torch for core has a glass raw material gas blowing nozzle and combustible gas blowing nozzle, which surrounds the glass raw material gas blowing nozzle in such a way that the glass raw material gas blown out from the glass raw material gas blowing nozzle is deviated from the center of an inner area defined by the combustible gas blowing nozzle, with respect to oxy-hydrogen flame stream blown out from the combustible gas blowing nozzle.
Here, it is also preferable that an inert gas blowing nozzle, the combustible gas blowing nozzle and an auxiliary gas blowing nozzle are disposed in this order, surrounding the glass raw material gas blowing nozzle, and the glass raw material gas blowing nozzle is so arranged as to be deviated from the center of the inner area defined by the inert gas blowing nozzle.
Alternatively, a diameter controlling gas blowing nozzle for blowing out diameter controlling gas may be disposed adjacent to the glass raw material gas blowing nozzle in the inner area defined by the inert gas blowing nozzle so as to control the diameter of the porous preform for core, and a subsidiary combustible gas blowing nozzle may be formed adjacent to the diameter controlling gas blowing nozzle.
Additionally, the inert gas blowing nozzle, the combustible gas blowing nozzle and the auxiliary gas blowing nozzle, surrounding the glass raw material gas blowing nozzle, may be disposed in this order, and a controlling gas blowing nozzle may be disposed in the inner area defined by the inert gas blowing nozzle and adjacentto both sides of the glass raw material nozzle, in a mannerthatthe raw material gas blown outfrom the glass raw material gas blowing nozzle is deviated relative to the oxy-hydrogen flame stream, by the controlling gas blown out from the controlling gas blowing nozzle.
Figure 1 is a schematic diagram showing an optical fiber preform fabricating apparatus by a conventional
VAD method;
Figures 2A and 2B, 3A and 38, 4A and 4B, and 5A and 5B are schematic diagrams for illustrating disadvantages of the conventional VAD method;
Figure 6 is a schematic diagram showing an apparatus for fabricating optical fiber preforms according to the invention;
Figures 7A, 7B, 7C and 7D are diagrams for illustrating various aspects of glass particle streams;
Figure 8 is a graphical representation illustrating a surface temperature dependency of GeO2 content;
Figures 9 and 10 are schematic diagrams illustrating operations of two embodiments of gas blowing nozzle according to the invention;;
Figure 11 is a graph for illustrating a theoretical relationship between influence of the absorption loss by
OH ions contained in a silica glass tube and a cladding-to-core diameter ratio;
Figure 12 is a schematic diagram showing an embodiment of an apparatus for fabricating glass preforms by a VAD method according to the present invention;
Figure 13 is a schematic diagram for illustrating steps of sealing a glass preform in a glass tube in the invention;
Figure 14 is a perspective view, partially broken, showing an embodiment of a glass preform fabricating apparatus according to the present invention shown in Figure 12;
Figures 15A and 15B are a cross sectional view and a longitudinal sectional view of an embodiment of a torch for core to be used in the present invention, respectively;;
Figure 16 is a schematic diagram for explaining the formation of a porous glass body for core by the torch for core in the present invention;
Figures 17A and 17B are a cross sectional view and a longitudinal sectional view of an embodiment of a torch for cladding used in the present invention, respectively;
Figure 18 is a graphical representation of a relationship of a diameter of the porous glass body for core with a deviation distance e of the raw material gas blowing nozzle;
Figure 19 is a graphical representation of a relationship of a diameter of the porous glass body for core with an inclined angle of the torch for core; Figures and 20B are cross sectional views of other two embodiments of a torch for core according to the present invention;; Figures IA and 2 IB are a cross sectional view and a longitudinal sectional view of still other embodiments of a torch for core used in the present invention, respectively;
Figure 22 is a graphical representation of a relationship of a diameter of the porous glass body for core with a diameter controlling gas flow rate;
Figure 23 is a schematic diagram illustrating the formation of the porous preform in the present invention; and
Figure 24 is a cross sectional view showing another embodiment of a torch for core used in the presnet invention.
A fabrication method of optical fiber preforms by the conventional VAD method will be described with reference to Figure 1. In Figure 1, reference numeral 201 designates a supplierforsupplying glass raw material gas and flame forming gas. The glass raw material gas may be, for example, silicon tetrachloride SiC14, germanium tetrachloride GeCI4, boron trichloride BCl3, phosphorous oxide trichloride POCI3, phosphorous trichloride PC13, or boron tribromide BBr3. The flame forming gas may be an atmospheric gas composed of combustible gas such as H2, auxiliary gas such as 2 and inactive gas such as Ar, He or N2.
Those gases are individually supplied to a glass synthesizing torch 202. By individually blowing out those gases from the torch 202, fine glass particles such as silicon dioxide SiO2, germanium dioxide GeO2, boron oxide B203 or phosphorous oxide P205 are synthesized by hydrolysis reaction or thermal oxidation reaction.
By blowing the glass fine particles thus synthesized and a flame stream 203 onto a seed rod 204, the glass fine particles are attached to and deposited on the seed rod 204 to form a porous preform 205 around the periphery of the seed rod 204. In Figure 1, reference numeral 206 designates a reaction vessel. An exhaust rate controller 207 is provided for processing the glass raw material gas and the flame forming gas, which reside in the vessel 206, the glass fine particles not attached to the porous preform 205, and the gas resulting from the hydrolysis or the oxidation reaction such as H2O, Hcl, and Cl2. The exhaust rate controller 207 transformes the Cl2 gas into HCI by water shower and neutralizes it by NaOH. The glass fine particles are washed away by the water shower.The porous preform 205 is heated at 1500 to 1700"C by a ring heater 208 of an electric furnace provided on the upper part of the fabricating apparatus and is vitrified into a transparent preform 209. Reference numeral 210 is a protecting vessel of the electric furnace. A pulling-up machine 211 pulls upwardly the seed rod 204, and thus the porous preform 205 growing on the seed rod 204 and the transparent preform 209, while rotating the seed rod 204.
In fabricating the porous preform 205 by using the conventional VAD method, as shown in Figure 2A, the center axis 220 of the synthesizing torch 202 and the stream of the fine glass particles and the flame is coincident with a rotation axis 221 of the porous glass preform 205. Alternatively, the center axis 220 is shifted from the rotation axis 221 in parallel with each other, as shown in Figure 2B.
In fabricating the porous preform 205 with the synthesizing torch 202 disposed as shown in Figure 2A or 2B, it is difficult to keep uniform the shape of a growing surface of the porous preform. For this reason, the outer diameter of the porous preform 230 greatly fluctuates as viewed in the longitudinal direction, as shown in Figure 3A. Further, the growing speed of the porous preform in the axial direction is likely to be very slow.
In an extreme case, the porous preform 231 grows more in the radial direction than in the direction of the rotation axis 221 as shown in Figure 3B. This makes it difficult to fabricate a cylindrical porous preform.
In order to guide undesired glass particles or undesired various gases produced within the reactor vessel 206 as a result of non-reaction or reaction to the exhaust rate controller 207, an exhaust port 212 was formed through the spherical wall of the spherical vessel 206, as shown in Figure 4A, or an exhaust port 213 is formed through the upper cylindrical wall of a cylindrical vessel 216, as shown in Figure 4b.
According to this conventional method, of the fine glass particles 203 synthesized and blown out by the synthesizing torch 202, residual fine glass particles 234 not attached to and disposed on a growing surface 233 of a porous preform 232, are again attached to the peripheral surface of the porous preform 232. As a result, the outer diameter of the porous preform 232 fluctuated in an order of + 2 to i 10 mm. When an amount of the residual fine glass particles is large, a glass particle layer 236 having a small apparent density ranging from 0.05 to 0.1 g/cm3 is formed on the peripheral surface of a normally formed porous preform 235 having an apparent density from 0.2 to 0.5 g/cm3 by the residual fine glass particles, as shown in Figure 5B.
With the additional formation of the layer 236, the outer diameter of the porous preform 235 becomes extremely large and "cracking" is formed on the periphery of the porous preform 235. This makes it difficult to use the transparent vitrified preform as an optical fiber preform.
In order to manufacture optical fibers by a VAD method suitable for manufacturing a long-length optical fiber, the inventors of the present patent application conducted various experiments. Through those experiments, they have found that the above-mentioned defects are effectively removed when the synthesizing torch is inclined with respect to the rotation axis of the porous preform and the exhaust port is disposed in the vicinity of the growing surface of the porous preform. This will be discussed in detail later.
An example of a fabrication method of optical fiber preforms according to the present invention will be described with reference to Figure 6. In Figure 6 illustrating an embodiment of a fabrication apparatus for fabricating transparent glass preforms accoridng to the present invention, reference numeral 1 denotes a reaction vessel, 2 a supporting rod as a seed rod onto which a porous glass body is attached and deposited, 3 a pulling-up machine for raising the support rod 2 while it being rotated and 4 a synthesizing torch. The synthesizing torch is attached to the reaction vessel 1 in such a way that the central axis 4A of the synthesizing torch 4 is inclined with an angle of 0 10 to 60 with respect to the axial direction 2A of the supporting rod 2.It is preferable that the inclination angle 0 is adjustable. Details of the synthesizing torch 4 will be described later. To the torch 4 supplies a supplier 6 glass raw material gas such as SiCI4, GeCI4, POCI3 or BBr3, atmospheric gas such as Ar, He or N2, combustible gas such as H2, and auxiliary gas such as 2 (the latter three gases will generally be referred to as flame forming gases). From the supplier 6, the glass raw material gas is supplied through a glass raw material gas pipe 7 to the torch 4, while at the same time the various flame forming gases are supplied to the torch 4 through flame forming gas pipes 8. Reference numeral 9 designates an exhaust port attached to the reaction vessel 1.Through the exhaust port 9, gas such as H2O, HCI and Cl2 caused by the hydrolysis or thermal oxidation of the flame blown out from the torch 4 in the reaction vessel 1, non-reacted glass raw material gas such as SiC14, GeCI4, POCI3, BBr3 or the like and the atmospheric gas such as Ar, He or N2 are exhausted to an exhaust gas cleaner 10 for processing these gases.
Reference numeral 11 represents a porous preform deposited and grown on the support rod 2, 13 a ring heater for heating the porous preform 11, which is disposed passing through the ring heater 13, at 1 5000C to 1700"C to vitrify and consolidate the porous preform 11 into a transparent preform 14, 15 a supplier for supplying halogen gas for dehydration gas treatment, for example, a mixture of He and Cl2 gases, and 16 a supply port for supplying the dehydration gas into the reaction vessel 1.
In operation, the glass raw material gas containing for example, SiCI4 as major component and the flame forming gases are fed from the supplier 6 through the pipe 7 to the synthesizing torch 4. As a result, glass fine particles containing silicon dioxide SiO2 as major component and GeO2 or P2Os as dopant are deposited on the end face of the supporting rod 2. The supporting rod 2 is moved upwardly while being rotated by the pulling-up machine 3, so as to grow the porous preform 11. Subsequently, the porous preform 11 is heated at, for example, 1 5000C by the consolidating heater 8, so that the transparent preform 14 is formed. In the consolidating step, the dehydration gas, for example, a mixture of He and Cl2 gases is supplied from the supply port 16 into the reaction vessel 1, where OH content is removed from the transparent preform 14.
With the view of reducing the outer diameter fluctuation of the growing porous preform 11, the present invention stabilizes the growth of the porous preform 11 in the axial direction with an arrangement that the central axis 4A of the synthesizing torch 4 and the flame stream 20 is inclined by an angle 0 with respect to the rotation axis 2A of the porous preform 11, as shown in Figure 6.
By using the optical fiber preform fabricating apparatus shown in Figure 6, the porous preform 11 was fabricated under a condition that the synthesizing torch 4 was supplied with oxygen gas at 10 min, hydrogen gas at 5 cumin and glass raw material gas (containing 90 mol % of SiC14 and 10 mol % of GeCI4) at 0.3 4/min. In this fabrication, the following relationship was obtained between an angle (3 and the fluctuation of outer diameter, as shown in Table 1.
TABLE 1
Angle 0 and Fluctuation of outer diameter
Angle H ( ) Outer diameter fluctuation (mm)
0 5-10
10 2-5
20 1-2
30 0.5-1
40 0.5 or less
50 0.5-1
60 2-10
60 or more Preform growth was impossible
With the same supply of the glass raw material gas and combustible gas to the torch as in the above-mentioned case, a relationship shown in Table 2 was obtained between an angle 0 and a growing speed of the porous preform in the axial direction.
TABLE 2
Angle H and growing speed in the axial direction
Angle 0 (") Growing speed in the axial
direction (mm/h)
0 5-20
10 20-30
20 40-45
30 70-75
40 100
50 60-65
60 40-50
60 or more 5 or less
As seen from the results of the above experiments, when the angle 0 is changed from 0 to 60 , the outer diameter fluctuation was minimized at 0 = 400. At the same time, growing speed in the axial direction was increased. Further, when the angle 0 is determined in the angle range of 10 to 60 , it was found that good results were obtained in respect of the outer diameter fluctuation and the axial direction growing speed.
Most preferable, at an angle within a range of 30 to 40 , the growing speed in the axial direction was increased to 70 to 100 mm/hour. A large-sized porous preform was fabricated under this desirable condition which was sufficient to manufacture a long-length optical fiber of 50 to 100 km length.
Here, the relationship of the inclination angle H with the growth of the porous preform will be discussed in detail hereinafter. The porous preform was grown in the stream of the glass particles by attaching and depositing the glass particles on to the porous preform. Experimental results of various states of the glass particle stream when an inclination angle 0 was changed are illustrated in Figures 7Ato 7D. As shown in
Figure 7A, when û = 0 , the fine glass particle stream 21 discharged from the synthesizing torch 4 diverged toward radial direction in the vicinity of the growing surface of the porous preform 11, so that a stagnation point 22 was formed at the center of a plane where the stream diverged.Therefore, the fine glass particles at the center of the growing surface was instably deposited to lessen an amount of the deposited glass particles, with the result that the growth of the preform 11 in the axial direction 2A was instable and the growing speedwas also decreased. When the synthesizing torch 4 was further inclined to increase the angle 0, states of the fine glass particle stream changed, as shown in Figures 7B to 7D. As seen from Figures 7B to 7D, when the inclination angle exceeds 30 , the stagnation point disappeared, so that the porous preform 11 stably grew, the growing speed was increased and the uniformity of the outer diameter was improved.When the inclination angle (3 exceeds 60 , the amount of the deposited glass particles and the growing speed were decreased.
Let us consider a relationship between an inclination angle H and a transmission characteristic of an optical fibers It is well known that in the VAD method, a surface temperature distribution of the porous preform plays an important role in forming a refractive index profile. An amount of GeO2 content in the synthesized fine glass particles increases as the surface temperature of the preform growing surface rises and exhibits a temperature dependency as shown in Figure 8. From this fact, it is deduced that a concentration distribution of GeO2 in the preform and thus finally a refractive index profile of the porous preform can be controlled by adjusting the surface temperature distribution on the growing surface.In order to manufacture the graded index type optical fibers having a wide bandwidth and low-loss by such a control method, the following three conditions are required:
(1) A surface temperature is within a range of 300"C to 8000C, as seen from Figure 8.
(2) In order to obtain a parabolic refractive index distribution of the graded index type, the surface temperature distribution in the radial direction must be of parabolic type.
(3) In order to reduce a fluctuation of the refractive index, an isothermal line of the surface temperature distribution must be orthogonal to the rotation axis.
The above-mentioned relationships among the inclination angle Othe surface temperature distribution and the transmission characteristic will be explained. When 6 < 10", the preform growing surface is flat, as shown in Figure 7A, and the distribution parameter of the surface temperature is apt to increase. The resultant refractive index profile easily takes a fourth power form. Further, a transmission bandwidth of the optical fiber obtained by drawing the transparent glass preform is 100 MHz-km or less. In addition, because of the presence of the stagnation point, the surface temperature distribution changes every moment and a fluctuation of the refractive index increases.Conversely, when û > 60 , the isothermal line excessively inclines with respect to the rotation axis of the porous preform to fail to satisfy the above-mentioned condition (3). As a result, the refractive index fluctuation and the transmission loss of the optical fiber increase. Measurement results of a refractive index distribution (distribution parameter a) of the preform, a fluctuation of the refractive index in the preform (specific refractive index difference: %), a transmission loss (dB/km) at wave length 0.85 lim and a transmission bandwidth (MHz-km) with respect to an inclination angle 6of the synthesizing torch 4 tabulated in Table 3.
TABLE 3
Refractive index and transmission characteristic with respect to inclination angle 6 Inclination angle 8 (") < 10 10 - 60 > 60 Distribution parameter a > 4 3-1.5 < 1.5 Fluctuation of refractive index (%) 0.2 - 0.1 0.05 - 0.01 0.2 - 0.1
Transmission loss (dB/km) > 5.0 < 3.0 > 5.0
Transmission bandwidth MHz-km) < 50 > 100 < 100
As seen from Table 3, at an angle 0 = 10 to 60 , optical fibers with good refractive index and transmission characteristics may be manufactured.
When the angle (3 is changed with a fixed flow rates of the glass raw material and the combustible gas, the outer diameter d (Figure 6) of the porous preform is also adjustable. For example, when (3 = 10 , d = 70 mm(p and when û = 20 , d = 50 mm. Further, d = 60 mm, when 6 = 60".
As described above, the outer diameter fluctuation of the porous preform can remarkably be reduced compared to the conventional method when the synthesizing torch 4 is inclined by 10 to 60 with respect to the rotation axis of the fiber preform. As a result, there is an advantage that the fluctuation of a core-to-outer-diameter ratio, transmission loss, and bandwidth of the optical fibers obtained from the preforms thus formed are improved. Therefore, this fiber preform is effectively used for the fabrication of multi-mode optical fibers. Besides, the stabilization of the growth of the porous preform according to the invention improves the production yield and efficiency of the porous preforms.In addition, since the growing speed in the axial direction is increased, there is an advantage that the optical fiber preform is continuously fabricated in the direction as shown in Figure 6.
Returning now again to Figure 6, the exhaust port 9 is disposed in the vicinity of the growing surface of the porous preform 11 with a distance A from the periphery of the preform 11. With this arrangement, when the distance A is selected to be 1 mm to 50 mm, the outer diameter fluctuation of the porous preform occurred in the conventional method may be remarkably improved. The glass fine particle layer having a small apparent density is not formed on the periphery of the porous preform 11, thus eliminating the formation of "cracking" on the periphery of the porous preform 11. Thus, when the porous preform 11 is vitrified, it provides a stable transparent preform.
The experimental results with respect to the distance A will be described. For simplicity, a simple model shown in Figure 9 was used in which two exhaust ports 30 and 31 were disposed in opposition to each other in the vicinity of the growing surface of the preform when an inclination angle H = 00. For example, in Figure 9, the distance A was 15 mm. Exhaust amounts of the residual glass fine particles 32 and 33 exhausted through the exhaust ports 30 and 31 and various kinds of undesirable gases were adjusted to be equal to blowing amounts of the glass fine particles and the flame stream 20. As a result, the fluctuation of the outer diameter ofthe porous preform 11 formed under this condition was limited within +1 mm. There was not observed the glass fine particle layer having a small apparent density formed by the residual fine particles 32 and 33. The transparent glass preform was fabricated in a stable manner.
On the other hand, when the distance A was selected to be larger than 50 mm in Figure 9, amounts of the residual fine particles and the undesired various gases exhausted from the exhaust ports 30 and 31 were lessened, so that the residual fine particles were attached to the periphery of the porous preform 11. The problem similar to the conventional method was observed again.
When the distance A was selected to be less than 1 mm in Figure 9, the exhaust ports 30 and 31 came in contact with the periphery of the porous preform 11 by a mechanical fluctuation of the position due to the rotation of the porous preform 11 As a result of this, the peripheral surface of the porous preform 11 was undulated, so that there is a problem that the transparent preform thus obtained was hardly used as optical fiber preform.
In order to further enhance the effect resulted from the provision of the exhaust port, three or more exhaust ports may be arranged at an equidistance in the vicinity of the growing surface of the porous preform 11.
Figure 10 shows in detail the exhaust port 9 shown in Figure 9 and its associated portion. In this case, the residual fine particles and undesirable various gases 34 may easily be removed by merely providing a single exhaust port 9 in opposition to the synthesizing torch 4, unlike the embodiment shown in Figure 9. Especially in this case, when an inclination angle 8 ways 30 to 409 and the distance A was 5 to 10 mm, the fluctuation of the outer diameter was improved to +0.5 mm (about 1%) or less.
According to this invention, as described above, the outer diameter fluctuation of the porous preform may be considerably improved compared to the conventional method by the provision of the exhaust port(s) for exhausting the residual fine particles and the undesirable gases which is(are) disposed in the vicinity of the porous preform. Further, the present invention has an advantage that the production yield of the optical fiber preforms by VAD method is improved, since there is no formation of "cracking" in the periphery of the porous preform.
Furthermore, as shown in Figure 5B, there is eliminated the glass fine particle layer having a small apparent density, which is to be formed on the porous preform periphery when the conventional method is used. Accordingly, an additional glass fine particle layer as a cladding layer, for example, may be attached to and deposited on the periphery of a cylindrical porous preform once formed, by using anotehr synthesizing torch, for example, a cladding torch, to fabricate a further thicker cylindrical porous preform, for example, a single-mode optical fiber preform or a multi-mode optical fiber preform having a cladding layer formed as just mentioned in the above, not by a silica tube.
Fabrication method of a transparent preform for single-mode optical fiber according to this invention will be described in detail.
In order to obtain the single-mode optical fiber having a low-loss, it is necessary to make the core diameter as small as possible to select a cladding-to-core diameter ratio to be 3 or more. The reason for this will be given.
Generally, in manufacturing a single-mode optical fiber, the transparent preformsfor core and cladding are stretched in conformity with an inner diameter of a silica glass tube. Then, the stretched transparent preforms are inserted into a silica glass tube and sealed therein (a jacketing process). The single-mode optical fiber preform thus obtained is drawn by a fiber drawing machine into a single-mode optical fiber.The core diameter 2a of an optical fiber when the single-mode optical fiber preform is drawn into an optical fiber having an outer diameter dis given by the following equation:
where 2A is a core diameter of the stretched transparent glass preform, 2B is a cladding diameter, D1 is an outer diameter of the silica glass tube, and D1 is an inner diameter of the silica glass tube.
The single-mode condition for this optical fiber is expressed by the following equation:
where V is a normalized frequency, X is a light source wavelength, n1 and n2 are refractive indexes of the core and cladding regions. Practically, nl = n2 = 1.458. This equation (2) is transformed into
where An = n1 - n2.
As described above in connection with the disadvantage of the rod-in-tube method, in order to obtain a single-mode optical fiber having a low-loss, a sufficiently thick cladding layer must be formed, that is, a cladding-to-core diameter ratio 2B/2A of the preform must be sufficiently large, when the preform is fabricated, since the optical power extends into the cladding region around the core region.
Figure 11 graphically represents theoretical values of OH absorption loss as a function of cladding-to-core diameter ratio with a parameter of cutoff wavelength Xc when the OH content in the silica glass tube 21 is 200 ppm. In order to obtain a single-mode optical fiber having a low-loss at 1.3 Fm or 1.55 ijm wavelength, or in the so-called long wavelength region, the OH ion absorption loss must be 20 dB/km or less. Generally, the cutoff wavelength is selected at about 1.0 to 1.2 Fm. Accordingly, it is seen from Figure 11 that the cladding-to-core diameter ratio must be about 3 or more. If the diameter ratio is about 3 or more, the boundary between the transparent preform and the silica glass tube is also prevented from being contaminated.
According to the conventional VAD method, optical fibers can be mass-produced. However, the conventional VAD method has an extreme difficulty in fabricating a porous glass preform having a cladding-to-core diameter ratio of about 3 or more. For this reason, it was impossible to fabricate a single-mode optical fiber by the conventional VAD method. More specifically, in the conventional VAD method, it is difficult to reduce the diameter of the porous glass body for core to 30 mm or less, mainly due to the torch for core to be used. Accordingly, in order to obtain a cladding-to-core ratio of about 3 or more, the diameter (outer diameter of the cladding) of the porous preform should exceed 100 mm, so that the stress developed in the porous preform possibly cracks the porous preform and the "cracking", when formed, makes it almost impossible to consolidate the preform.Coping with this problem, the inventors carefully studied the structure of a torch for core and conditions for the preform fabrication. Through the study, it was found that the use of a torch for core having a glass raw material gas blowing nozzle deivated from the center area of the combustible gas blowing nozzle makes it easy to form a porous glass body for core having a diameter of 20 mmf or less, and provides a cladding-to-core diameter ratio of 3 or more. The present invention was completed under the recognition of these technical facts.
A fabrication method for fabricating a single-mode optical fiber according to the present invention will be described with reference to Figures 12 and 13. Figure 12 shows an apparatus for fabricating a transparent preform according to the present invention. Figure 13 shows a series of steps of a jacketting process of the transparent glass. In Figure 12, reference numeral 1 designates a reaction vessel, 2 a supporting rod as a seed rod onto which a porous glass body is attached to and deposited, 3 a pulling-up machine for pulling up the supporting rod 2 while rotating the rod 2,4 a torch for core and 5 a torch for cladding. The torch for core 4 is mounted to the vessel 1 with an inclination angle (3 30 to 50D with respect to the axis 2A of the supporting rod 2.It is preferable that the inclination angle is adjustable. The detail of the torch for core 4 will be described later. A supplier 6 supplies to the torches 4 and 5 the glass raw material such as SiCI4, GeCI4, POCKS and BBr3, the atmospheric gas such as Ar, He or N2, the combustible gas such as H2 and the subsidiary gas such as 2 (the latter two will generally be referred to as flame forming gases). The glass raw material gas is supplied from the supplier 6 to the torches 4 and 5 through glass raw material gas pipes 7A and 7B.
Various flame forming gases are supplied through flame forming gas pipes 8A and 8B to the torches 4 and 5.
Reference numeral 9 designates an exhaust port attached to the reaction vessel 1. Through the exhaust port 9, the gases such as H2O, HCI, Cl2 and so on produced by the hydrolysis or the thermal oxidation reaction of the flames blown out from the torches 4 and 5, the non-reacted glass raw material gas such as SiCI4, GeCI4,
POCI3, BBr3 or the like and the gas such as Ar, He, N2 are exhausted to the exhaust gas cleaner 10 for processing these gases.
Further, in Figure 12, 1 1A designates a formed porous glass body for core, 11 B a porous glass body for cladding (a cladding layer) deposited around the porous glass body for core 11A, 12 a porous preform composed of the core and cladding regions, 13 a ring heater for heating the porous preform 12, which passes through the ring heater 13, at 1 5000C to 17000C to vitrify and consolidate the preform 12 into a transparent preform 14, a supplier for supplying halogen gas for dehydration treatment such as a mixture of He and
Cl2 gases, 16 a supply port for supplying the dehydration treatment gas into the reaction vessel 1.
In operation of the apparatus shown in Figure 12, the glass raw material gas containing, for example, SiCI4 as major component and the flame forming gases are supplied to the torch for core 4 from the supplier 6 through the pipes 7A and 8A so as to attach glass fine particles containing SiO2 as major component and
GeO2 and P205 as dopant onto an end face of the supporting rod 2. Then, the supporting rod 2 is pulled up while being rotated by the pulling-up machine 3,so that the porous preform for core 1 1A is grown. At the same time, the cladding torch 5 blows out glass fine particles containing only SiO2 or containing SiO2 as major component and P205 or B203 around the porous preform 1 1A, in a manner that these particles are deposited onto the periphery of the glass body 1 1A.As a result, a porous glass layer 11 B for cladding is formed on the surface of the glass body 1 1A. The porous preform 12 composed of the core region and the cladding region thus formed is heated, for example, at 1 5000C by the vitrifying heater 8, so that a transparent preform 14 having a core glass covered with a cladding glass is formed. In the vitrifying step, the dehydration treatment gas such as a mixture of He and Cl2 gases is supplied from the supply port 16 into the reaction vessel 1 to remove the OH content from the porous preform 14.
A step for jacketting the transparent preform 14 thus fabricated will be described referring to Figure 13. As shown in Figure 13, firstly the transparent glass preform 14 is stretched in conformity to the inner diameter of a silica tube 50. The stretched transparent preform 14' is inserted and sealed into the silica tube 50, so as to form a single-mode optical fiber preform 51. The single-mode optical fiber preform 51 is then drawn by a conventional fiber drawing machine to form a single-mode optical fiber.
Turning now to Figure 14, there is shown a detailed embodiment of an apparatus for fabricating the single-mode optical fiber preform according to the invention. Like numerals are used to designate corresponding portions in Figure 12. In Figure 12, the supplier 6 for supplying the glass raw material, which is of the conventional type, measures the various gases each by a given amount and supplies the measured gases to the core torch 4 and the cladding torch 5. As will be described, the core torch 4 is so arranged that its glass raw material blowing nozzle 41 is deviated from the center area of the blowing nozzle 42 for the flame stream.The core torch 4 is swingable along a groove 43 of the vessel 1 in such a manner that the inclination angle H may be set at a desired value within an angle range of 10 to 60". The set angle H is read by a gauge 44. The exhaust gas cleaner 10 is provided with a spray 45 for spraying water. The sprayed water converts the Cl2 component contained in the exhaust gas into HCI. HCI is neutralized by NaOH. The water from the spray 45 washes away the glass fine particles and the like.
Various embodiments of a torch for core according to the present invention will be described with reference to the drawings. Figure 15A is a front view of an embodiment of a torch for core accoridng to the present invention. Figure 1 5B shows a side view of this embodiment. In Figures 15A and 1 5B, reference numeral 61 denotes a glass raw material blowing nozzle, 62 an inert gas blowing nozzle, 63 a combustible gas blowing nozzle and 64 a subsidiary gas blowing nozzle. As shown in Figures 15A and 15B, the nozzles 61, 62,63 and 64 have rectangular ring-shaped cross sections defined by multi-layered tubes 65, 66, 67 and 68 which also have rectangular cross sections, respectively.As seen from Figures 15A and 15B, the raw material gas blowing nozzle 61 is surrounded by the combustible gas blowing nozzle 63 with the inert gas blowing nozzle 62 intervening therebetween and is deviated by a distance e from the center of the inner area defined by the combustible gas blowing nozzle 63. The combustible gas blowing nozzle 63 is surrounded by the subsidiary combustible gas blowing nozzle 64. Those rectangular rubes 65, 66,67 and 68 may be made of silica glass. The geometrical dimensions of the torch 4 will be seen by using a scale (10 mm) shown in Figure 15A. The exhaust tube 9 is disposed with a distance Afrom the periphery of the core porous glass body 1 1A, as well illustrated in Figure 16.
The core torch 4 having the blowing nozzles 61 to 64 is disposed inclined by an angle Owith respect to the axial direction 2A of the supporting rod 2, as shown in Figure 16. The gases were blown out from the respective nozzles 61,62, 63 and 64 under the following conditions to form the core porous glass body 11A.
In the embodiment,0 = 45 , e = 5 mm and A = 15 mm. In Figure 16, reference numeral 69 designates a glass fine particle stream and 70 an oxy-hydrogen flame.
Raw material gas blowing nozzle 61: SiCI4 (40"C for staturator temperature, 70 cc/min for carrier Ar
gas)
GeCI4 (1 C for saturator temperature, SO cc/min for carrier Ar
gas)
Inert gas blowing nozzle 62: 1.5 cumin for Ar gas
Combusible gas blowing nozzle 63: 2.5 cumin for H2 gas
Auxiliary gas blowing nozzle 64: 7 cumin for 2 Under these conditions, the porous glass body 1 1A for core having a diameter of 18 mm was grown on the end face of the supporting rod 2.
Around the porous glass body 1 1A for core, the cladding layer 11 B was deposited by the cladding torch 5, as shown in Figure 12. A co-axial multi-layer tube torch used in the conventional VAD method may be used for the cladding torch 5. Figure 1 7A is a front view of a four-layeredtubetorch as the cladding torch 5 used in the present embodiment. Figure 17B is a side view of the torch shown in Figure 17A. In Figures 17A and 17B, reference numeral 71 denotes a raw material blowing nozzle, 72 an inert gas blowing nozzle, 73 a combustible gas blowing nozzle, and 74 an auxiliary gas blowing nozzle.Those blowing nozzles 71,72,73 and 74 are defined by four-layered tubes 75, 76,77 and 78, which are made of silica glass, in the form of a co-axial circular ring when viewed in cross section. The cladding torch 5 thus constructed was disposed as shown in Figure 12 and the cladding porous glass body (cladding layer) 11 B was deposited around the core porous glass body 1 1A under the following conditions.
Raw material blowing nozzle 71: SiCI4 (40"C for saturator temperature, 250 cc/min for carrier Ar gas
flow rate)
Inert gas blowing nozzle 72: 1.0 elmin for He gas Combustible gas blowing nozzle 73: 3.5 cumin for H2 gas
Auxiliary gas blowing nozzle 74: 4.5 t/min for 2 gas
Under these conditions, the cladding porous preform 11 B having a diameter of 60 mm was formed around the previously formed core porous glass body having a diameter of 18 mm. The growing speed of the preform 12 in the axial direction was about 40 mm/hour.
The porous preform 12 was heated by a ring-like vitrifying heater 13 provided at the upper portion. At the same time, He gas (10 t/min) and Cl2 gas (0.5 Plmin) were supplied from the dehydration gas supplier 15 to the heating section via the gas supply port 16. In this way, the porous preform 12 was vitrified at 15000C while the OH ions and H2O molecules were removed from the preform 12. A transparent preform 14 thus formed was 30 mm in the outer diameter (diameter of the cladding region) and 9 mm in the diameter of the core region. The refractive index difference An between the core and cladding regions was 0.0029.
When the distance A is selected within a range of 1 to 50 mm, the outer diameter fluctuation of the core porous glass body 1 1A is remarkably improved. In addition, there is no formation of a glass fine particle layer having a small apparent density which is to be formed when the conventional VAD method is used.
Therefore, it does not occur that the core porous glass body 1 1A abnormally grows to have a large outer diameter. Further, the "cracking" on the periphery of the porous glass body 1 1A is prevented to ensure the formation of stable transparent glass body as a result of the consolidation.
In the arrangement of Figure 16, the distance A was selected to be 15 mm. The exhausting amount of the undesired gases such as the residual glass fine particles, the reaction product gas, and the unreacted atmospheric gas exhausted from the exhaust port 9 was adjusted to be comparable with the blowing amounts of the glass fine particle stream 69 and the oxy-hydrogen flame 70. The outer diameter fluctuation of the porous glass body 1 1A fabricated under this condition was improved to be approximately 10.05 mm.
The residual glass fine particles did not form a glass fine particle layer having a small apparent density, so that a stable fabrication of a transparent glass preform was ensured.
In the case that a distance A was 50 mm or more, an amount of the undesirable gas exhausted through the exhaust port 9 was decreased to the residual glass fine particles were attached to the periphery of the core porous glass body 11A. As a resul, the above-mentioned conventional problems were confirmed.
Further, in the case that a distance A was 1 mm or less, a mechanical fluctuation of the position caused by the rotation of the core porous glass body 1 1A made the exhaust port 9 in contact with the periphery of the porous glass body 1 1A. As a result, the periphery of the porous glass body 1 1A was undulated, so that there was a problem that the transparent glass preform thus fabricated is hardly used as optical fiber preform.
By arranging the exhaust port 9 as described above, the glass fine particle layer having a small apparent density was not formed on the peripheral surface of the porous glass body 1 1A for core. Accordingly, the fine glass particle layer for cladding may readily be attached to and deposited on the peripheral surface of the core glass body 1 1A by using the torch 5 for cladding. Further, in this case, if a second exhaust port was disposed, with a distance A' = 1 to 50 mm, as described above, on the periphery of the cladding porous glass body 11 B, the advantages as mentioned above was fully utilized to improve the production yield of single-mode optical fiber preforms by the VAD method.While the embodiments shown in Figures 12 and 14 had only one exhaust port 9, the above-mentioned advantages could be attained, if the distances A and A' between the core and cladding porous glass bodies 1 1A and 11 B and the exhaust port 9 are selected to be within the range from 1 to 50 mm.
The transparent preform 14 thus obtained having an outer diameter of 30 mm was stretched by an oxy-hydrogen burner to form a glass preform 14' having an outer diameter D = 6.7 mm and a core diameter 2A = 2 mm. The glass preform 14' was then sealed in a silica tube 50 having an outer diameter D1 = 26 mm and an inner diameter D2 = 7 mm. In this way, an optical fiber preform 51 was fabricated. The optical fiber preform 51 was then drawn into an optical fiber having an outer diameter of 125 ,um. An inner diameter 2a of the fiber was approximately 9.6 lim when calculated by equation (1). The wavelength satisfying V = 2.405, i.e., a cutoff wavelength fc, was nearly equal to 1.15 lim.This cutoff wavelength was accurately coincident with measured values of an actually manufactured optical fiber. By the above-mentioned method, two single mode optical fibers having a length of about 30 km were obtained from the transparent glass preform 14 having a length of 10 cm. The optical transmission loss of those optical fibers was small; 1 dB/km in average at a wavelength of 1.55 sFtm. The OH absorption loss at a wavelength of 1.39 Fm was about 20 dB/km.
The reason why, in the above-mentioned embodiment, the porous glass body 1 for core having a narrow diameter of about 18 mm could grow by the torch 4 for core shown in Figures 1 SA and 1 SB, as described above, will follow. The torch 4 is inclined by an angle (3 (45 in the present embodiment) with respect to the axial direction 2A, as shown in Figure 16. The raw material gas blowing nozzle 61 is eccentrically located at a lower side portion of the torch 4 and the oxy-hydrogen flame stream 70 flows above the flow 69 from the nozzle 61. With this arrangement, the vertical and horizontal expansions of the glass fine particles 69 is restrained to limit the rising and attaching of the residual glass fine particles.As a result, the glass particles 69 is attached only to the end portion of the porous glass body 11 A, as shown in Figure 16.
Many core torches 4 having different deviation distances e of the raw material gas blowing nozzle 61 shown in Figure 16 were manufactured for experiment. The diameters (minimum) of the porous glass body 1 1A of the torches manufactured were measured. The minimum diameters measured in the case of those core torches 4 are shown in Figure 18. The diameter of the core porous glass body 11 A depends sensitively on an angle (3 of the core torch 4 relative to the axis 2A of the porous glass body 1 1A shown in Figure 16, or the supporting rod 2. The porous glass body 11A for core exhibited a minimum diameter when the angle is within an range of 30 to 50".
Figure 19 depicts experimental results when the core torch 4 shown in Figure 1 SA and 1 SB is operated, in which the diameter of the core porous glass body is expressed as a function of an angle 0. Here, the deviation distance 6 was 5 mm in the experiment. As seen from Figure 19, the diameter was minimum in a range of 30 to 500, ranging from about 15 to 18 mm. Further, when the deviation distance 6 was varied within a range of 2 to 5 mm, the result similar to that of Figure 19 was obtained.
As described above, when (3 = 10 to 600, the outer diameter flactuation of the porous glass preform is lessened, while at the same time the growing speed of it in the axial direction increases. For example, when (3 = 30 to 40 , the outer diameter fluctuation was limited within +0.5 to 1 mm and the growing speed was 70 to 100 mm/h. In this case, a large-sized preform corresponding to a long-length optical fiber having a length of 50 to 100 km was obtained. The above was an example when the conventional synthesizing torch was used in the present invention. When a synthesizing torch according to the present invention was used under a condition that a distance A is 5 to 10 mm and an inclination angle n is especially 30 to 40 , the fluctuation of an outer diameter of the core porous preform was improved to within + 0.5 mm.
Figures 20A and 20B are cross sections of other two embodiments of a core torch 4 according to the present invention. In Figures 20A and 20B, reference numeral 81 designates a raw material gas blowing nozzle, 82 an inert gas blowing nozzle, 83 a combustible gas blowing nozzle and 84 an auxiliary gas blowing nozzle. As shown, the blowing nozzles 81,82,83 and 84 have respectively circular or elliptical ring cross sections defined by multi-layered tubes 85,86,87 and 88 having circular or elliptical cross sections. The raw material gas blowing nozzle 81 is surrounded by the combustible gas blowing nozzle 83 via the inert gas blowing nozzle 82 inserted therebetween. The combustible gas blowing nozzle 83 is surrounded by the auxiliary gas blowing nozzle 84.The raw material gas blowing nozzle 81 is located at a position deviated by the deviation distance e from the center of an inner area defined by the combustible gas blowing nozzle 83.
In those embodiments, the raw material gas blowing nozzle 81 is deviated from the combustible gas blowing nozzle 83, so that those embodiments attains the effects similar to those by the core torch in the previous embodiment.
Also in the present embodiment, the multi-layered tubes 85,86,87 and 88 may be formed of silica glass.
The respective geometrical dimensions of the core torch 4 will comparably be measured by using a scale (10 mm) indicated in Figure 20A.
Figure 21A shows a cross section of a further embodiment of a core torch according to the invention, and
Figure 21 B shows a longitudinal sectional view of this torch. In Figures 21A and 21 B, reference numeral 91 is a raw material blowing nozzle, 92 an inactive gas blowing nozzle, 93 a combustible gas blowing nozzle, 94 an auxiliary gas blowing nozzle, 95 a diameter adjusting gas blowing nozzle and 96 a subsidiary combustible gas blowing nozzle. The raw material gas blowing nozzle 91 is disposed depart from the center of the inner area defined by the combustible gas blowing nozzle 93. In addition, the diameter adjusting gas blowing nozzle 85 and the subsidiary combustible gas blowing nozzle 96 are disposed adjacent to the raw material blowing nozzle 91.The diameter adjusting gas nozzle 95 is for controlling the diameter of the porous glass body by the flow rate of adjusting gas to be blown out, for example, Ar gas.
The blowing nozzles 91,95 and 96 are defined by partition walls 98 and 99 provided in a tube 97 having a rectangular cross section. The nozzles 92,93 and 94 having rectangular cross sections are formed by surrounding in succession the rectangular tube 91 with multi-layered tubes 100, 101 and 102 having rectangular cross sections. Those tubes 97,100,101 and 102 and partition walls 98 and 99 may be made of silica glass. The respective geometrical dimensions of the respective portions of the torch 4 for core will comparably be seen by referring to a scale (10 mm) indicated in Figure 21A.
A relationship of the flow rate of the adjusting Ar gas blown out from the diameter adjusting blowing nozzle 96 with the porous glass body 1 1Afor core is illustrated in Figure 22. Figure 22 indicates that a diameter of the porous glass preform is varied by changing a blow rate of the adjusting gas. By taking advantage of this, the porous glass body 11 A having a proper diameter is formed. If the porous glass body 11 B for cladding having a fixed outer diameter is formed around the body 11 A for core by the cladding torch 5, as shown in Figure 12, it is possible to obtain the porous glass body 12 having a desired cladding-to-core diameter ratio.
Taking account of the dimensions of the overall fabricating system and the synthesizing speed per unit time, the dimensions of the core torch 4 may be properly determined.
While the embodiment shown in Figure 12 uses a single torch 5 for cladding for the deposition of the porous glass body 11 B for cladding, use of a plurality of torches for cladding is allowable for ease and stability of the deposition of the porous glass body 11 B for cladding.
Figure 23 shows a porous glass preform fabricating section of the preform fabricating apparatus where two torches 5 - 1 and 5 - 2 for cladding are used to embody the method of the present invention. In Figure 23, as the torch 4 for cladding, use was made of a torch having the same structure as that shown in Figures 21A and 21 B. The torches 5 - 1 and 5 - 2 for cladding were the same as that shown in Figures 17A and 17B having the four-layer tube structure. Those torches 5 - 1 and 5 - 2 are disposed apart from each other along the axial direction 2A of the supporting rod 2.In the glass body formation, the porous glass body 1 1A for core is first formed by the torch 4 for core, then a first porous glass body 11 B - 1 for cladding is formed on the porous glass body 1 IA by the torch 5 - 1 for cladding, and a second porous glass body 11 B-2 for cladding is formed
by the torch 5 - 2 for cladding.
An example of the gas supply conditions to the torches 4, 5 - 1 and 5 - 2 will be given below.
Torch 4 for core:
Raw material gas blowing nozzle 91; SiCI4 (40"C for saturator temperature, 70 cc/min for
carrier Ar gas flow rate)
GeCI4 (20"C for saturator temperature, 50 cc/min for
carrier Ar gas flow rate)
Inert gas blowing nozzle 92: 1.5 e/min for Ar gas
Combustible gas blowing nozzle 93: 2 cumin for H2 gas
Auxiliary gas blowing nozzle 94: 7 elmin for 2 gas
Diameter adjusting gas blowing nozzle 95: 0.4 cumin for Ar gas
Subsidiary combustible gas blowing nozzle 96: 1 cumin for H2 gas
Torch 5- 1 for cladding;
Raw material gas blowing nozzle 71:SiCI4 (40"C for satu rator tem peratu re, 100 cc/min for carrier Ar gas
flow rate)
Inert gas blowing nozzle 72: 1 Clmin for He gas Combustible gas blowing nozzle 73: 3 cumin for H2 gas
Auxiliary gas blowing nozzle 74: 4 cumin for 2 gas
Torch 5 - 2 for cladding:
Raw material gas blowing nozzle 71:SiCI4 (40"C for sate orator temperature, 200 ccm/mi n for carrier Ar
gas flow rate)
Inert gas blowing nozzle 72: 1 cumin for He gas
Combustible gas blowing nozzle 73: 3.5 elmin for H2 gas
Auxiliary gas blowing nozzle 74 4 gamin for 2 gas
Under these conditions of flow rate, the porous glass body 11 A for core having a diameter of 10 mm was formed at a growing speed of about 40 mm/h. A first cladding porous glass body 11 B - 1 having a diameter of about 30 mm was formed around the glass body 11A. A second cladding porous glass body 11 B - 2 having a diameter of about 60 mm was further formed around the first cladding porous glass body 11 B - 1.A transparent glass preform was fabricated after about 10 hours. The transparent glass preform had an outer diameter of 30 mm, a core diameter of 5 mm and an effective length of 15 cm. In this case, the refractive index difference between the core and cladding regions was 0.0044.
The dimension of the silica glass tube 50 was so selected that the core diameter in the optical fiber is 8 Fm.
Then, the transparent glass preform was subjected to the jacketting process shown in Figure 13 and was finally drawn. The optical fiber thus obtained had a cutoff wavelength of 1.13 Fm. Two single-mode optical fibers, each having a length of 25 km, was obtained from the transparent glass preform having a length of 15 cm. The optical transmission loss of this optical fiber was extremely low; abount 0.5 dB/km at a wavelength of 1.55 ism. The OH absorption loss at a wavelength of 1.39 ym was extremely small; 2 dB/km or less.
As described above, in the present invention, the core torch of which the raw material gas blowing nozzle is deviated from the combustible gas blowing nozzle plays an important role in narrowing the porous glass body for core and thus increasing a cladding-to-core diameter ratio. It is to be noted that even in a case of a torch of which the raw material gas blowing nozzle is not deviated geometrically, for example, a torch illustrated in cross section in Figure 24, if the raw material gas blown out from the torch is geometrically deviated, the glass fine particles can substantially be prevented from expanding.
In Figure 24, reference numeral 111 denotes a raw material gas blowing nozzle, 112 an inert gas blowing nozzle, 113 a combustible gas blowing nozzle, 114 an auxiliary gas blowing nozzle, and 115 and 116 control gas blowing nozzles. The blowing nozzles 111, 115 and 116 are defined by partition walls 118 and 119 symmetrically disposed in a tube 117 which is rectangular in cross section. The blowing nozzles 112, 113 and 114 having rectangular cross sections are formed by surrounding the rectangular tube 117 by rectangular multi-tubes 120, 121 and 122. Silica glass may be used for those tubes 117, 120, 121 and 122 and the partition walls 118 and 119. The dimensions at the respective portions of the torch 4 will be seen by using a scale (10 mm) indicated in Figure 24.
An example of the gas supply conditions to the torch 4 for core shown in Figure 24 will be given below.
Raw material gas blowing nozzle: SiC4 (40"C for sate orator temperature, 70 cc/min for
carrier Ar gas flow rate)
GeCI4 (20"C for saturator temperature, 60 cc/min for
carrier Ar gas flow rate)
Inert gas blowing nozzle 112 Ar gas 1.5 cumin Combustible gas blowing nozzle 113 H2 gas 1 cumin Auxiliary gas blowing nozzle 114: 02 gas 7 flmin Control gas blowing nozzle 115: H2 gas elmin Control gas blowing nozzle 116: None
Under these gas supply conditions, the porous glass body was grown in such an arrangement that the control gas blowing nozzle 115 is disposed at an upper location while the nozzle 116 is disposed at a lower location.The porous glass body 11Afor core having a relatively narrow diameter of about 25 mm was obtained. This is because the glass fine particles stream is deviated substantially bellow the oxy-hydrogen stream at the blowing end of the torch 4 for core under the above-mentioned gas supply conditions. In this connection, when the flow rate of H2 gas supplied to the control gas blowing nozzles 115 and 116 is equal, for example, 1 elmin, the diameter of the porous glass body 1 1A for core was approximately 50 mm and accordingly this case failed in narrowing the diameter of the glass body 1 1A. It is evident that the formation of the porous glass body by the torch for core which blows out the raw material deviated relative to the oxy-hydrogen flame stream falls within the scope of the present invention.
As is clear from the foregoing, the present invention has the following advantageous effects:
(1) The porous preform may be grown stably in the axial direction with a small fluctuation (in the order of 11 mm) of the outer diameter of the preform. Especially, when an inclination angle (3 = 30 to 400 and a distance A = 5 to 10 mm, the outer diameter fluctuation is reduced to less than +0.5 mm.
(2) When an inclination angle (3 is within 10" to 609 the growing speed in the axial direction may readily be improved. Especially, when (3 = 30 to 400, the growing speed is increased to 70 to 100 mm/hour and it is easy to fabricate a long length preform corresponding to an optical fiber having a length of 50 to 100 km.
(3) The provision of the exhaust port in the vicinity of the growing surface of the preform with a distance of 1 to 50 mm from the growing surface prevents the formation of the glass fine particle layer having a low apparent density on the periphery of the porous glass preform. As a result, the porous preform grows stably with a uniform outer diameter, without the formation of "cracking" in the peripheral surface of the preform.
(4) A refractive index distribution is controllable by using a temperature distribution on the growing surface of the porous preform. Accordingly, graded-index type optical fibers having a wide bandwidth and low-loss can be fabricated.
(5) A low-loss optical fiber may be manufactured by the steps that the porous preform for core is stably grown in the axial direction with lessened fluctuation of the outer diameter and that the porous preform for cladding is deposited on the preform for core. Accordingly, by using the present invention, a low-loss multi-mode optical fiber or a low-loss single mode optical fiber may be fabricated.
(6) Consequently, the fabrication method according to the invention is suitable for the mass-production of long-length and low-loss optical fibers. This results in reduction of cost of the optical fiber. In this respect, it is expected that the presne invention will contribute to realize a short haul optical transmission system, a subscriber optical transmission network, or the like.
(7) A porous glass body for core having a narrow diameter of less than 20 mm is fabricated readily.
Accordingly, a glass preform for single-mode optical fiber having a cladding-to-core diameter ratio equal to or larger than 3 may be manufactured by the VAD method. This allows the mass-production of long-length and low-loss single mode optical fibers.
(8) The fabrication method of the present invention is also applicable to fabricate preforms for multi-mode optical fibers. In this case, the thickness of the porous glass body for cladding may be thickened, so that there is no need for a subsidiary jacketting silica tube.
The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the artthat changes and modifications may be made without departing from the invention in its broader aspects, and it is the invention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention.
Claims (31)
1. A fabrication method of an optical fiber preform, comprising the steps of:
moving a seed rod while rotating said seed rod;
blowing out a glass raw material gas and a flame forming gas separately from a synthesizing torch inclined by 100 to 60" with respect to the rotation axis of said seed rod to synthesize glass particles and then to deposit said glass particles onto one end of said seed rod which moves while rotating, so that a cylindrical porous preform is grown in the direction of said rotation axis of said seed rod; and
heating said cylindrical porous preform at a high temperature to vitrify said cylindrical porous preform into a transparent optical fiber preform.
2. A fabrication method of an optical fiber preform as claimed in claim 1, wherein said synthesizing torch is a torch.for core and said transparent optical fiber preform is formed as a multi-mode optical fiber preform.
3. A fabrication method of an optical fiber preform as claimed in claim 1, wherein said synthesizing torch is a torch for core, said cylindrical porous preform is a porous preform for core, and a porous preform for cladding is deposited on the periphery of said porous preform for core by a torch for cladding.
4. A fabrication method of an optical fiber preform as claimed in claim 3, wherein said torch for core is inclined by 30 to 50 with respect to said rotation axis and said transparent optical fiber preform is formed as a single-mode optical fiber preform.
5. A fabrication method of an optical fiber preform, comprising the steps of:
moving a seed rod while rotating said seed rod;
blowing out a glass raw material gas and a flame forming gas separately from a synthesizing torch to synthesize fine glass particles from said glass raw material gas through hydrolysis by flame or thermal oxidation by a high temperature heat source, and said glass particles being blown out and deposited to one end of said seed rod which moves while rotating, so that a cylindrical porous preform is grown in the direction of said rotation axis of said seed rod;;
exhausting glass particles not attached on the growing surface of said cylindrical porous preform of said glass particles, gas produced as a result of said hydrolysis or oxidation, non-reacted glass raw material gas and said flame forming gas through at least one exhaust port which is disposed with a distance of 1 mm to 50 mm from the periphery of said cylindrical porous preform formed by the deposition of said glass particles and in the vicinity of a growing surface of said cylindrical porous preform; and
heating said cylindrical porous preform at a high temperature to vitrify said cylindrical porous preform into a transparent optical fiber preform.
6. Afabrication method of an optical fiber preform as claimed in claim 5, wherein said synthesizing torch is inclined by 10 to 60 with respect to the rotation axis of said seed rod, so that said glass particles are obliquely blown out to deposit onto one end of said seed rod.
7. A fabrication method of an optical fiber preform as claimed in claim 6, wherein said exhaust port is disposed opposite to said synthesizing torch with respect to said cylindrical porous preform.
8. A fabrication method of an optical fiber preform as claimed in claim 6, wherein said synthesizing torch is a torch for core and said transparent optical fiber preform is formed as a multi-mode optical fiber preform.
9. A fabrication method of an optical fiber preform as claimed in claim 5, wherein said synthesizing torch is a torch for core, and said cylindrical porous preform is a porous preform for core, and a porous preform for cladding is deposited onto the periphery of said porous preform for core by a torch for cladding.
10. Afabrication method of an optical fiber preform as claimed in claim 9, wherein said torch for core is inclined by 30 to 50 with respect to said rotation axis and said transparent optical fiber preform is formed as a single-mode optical fiber.
11. Afabrication method of an optical fiber preform as claimed in claim 10, wherein said exhaust port is disposed opposite to said torch for core with respect to said cylindrical porous preform.
12. Afabrication method of an optical fiber preform as claimed in claim 1, wherein said synthesizing torch is inclined by 30 to 40 with respect to said rotation axis.
13. Afabrication method of an optical fiber preform as claimed in claim 6, wherein said synthesizing torch is inclined by 30 to 40 with respect to said rotation axis.
14. A fabrication method of an optical fiber preform as claimed in claim 5, wherein said distance is 5 mm to 10 mm.
15. A fabrication method of an optical fiber preform as claimed in claim 14, wherein said synthesizing torch is inclined by 30 to 40 with respect to said rotation axis.
16. A fabrication method of a single-mode optical fiber preform, comprising the steps of:
moving a seed rod while rotating said seed rod;
producing a stream of fine glass particles for core eccentrically with respect to the center area of a flame stream by a torch for core;
attaching and depositing a porous glass body on one end of said seed rod and growing said porous glass body in the axial direction of said seed rod by said torch for core;
producing glass particles for cladding by at least one torch for cladding;
attaching and depositing a porous glass body for cladding on the periphery of said porous glass body for core and growing said porous glass body for cladding in the axial direction of a seed rod, thereby forming a cladding layer;
heating to vitrify the obtained porous glass body into a transparent glass body; and
sealing said transparent glass body in a silica tube.
17. Afabrication method of a single-mode optical fiber preform as claimed in claim 16, wherein said torch for core is disposed inclined by 30 to 50 with respect to said seed rod.
18. A fabrication method of a single-mode optical fiber preform as claimed in claim 16, wherein said torch for core is disposed inclined by 30 to 40 with respect to said seed rod.
19. Afabrication method of a single-mode optical-fiber preform as claimed in claim 16, wherein at least one exhaust port is disposed with a distance of 1 mm to 50 mm from the periphery of said porous preforms for core and cladding and in the vicinity of growing surfaces of said porous preforms for core and cladding, and fine glass particles not attached to and deposited on said growing surfaces of said porous preforms for core and cladding of said fine glass particles, gas produced as a result of hydrolysis by flame or thermal oxidation in said torches for core and cladding and residual non-reacted glass raw material gas and flame forming gas are exhausted through said exhaust port.
20. Afabrication method of a single-mode optical fiber preform as claimed in claim 17, wherein at least one exhaust port is disposed with a distance of 1 mm to 50 mm from the periphery of said porous preforms for core and cladding and in the vicinity of growing surfaces of said porous preforms for core and cladding, and fine glass particles not attached to and deposited on said growing surfaces of said porous preforms for core and cladding of said fine glass particles, gas produced as a result of hydrolysis by flame or thermal oxidation in said torches for core and cladding and residual non-reacted glass raw material gas and flame forming gas are exhausted through said exhaust port.
21. A fabrication method of a single-mode optical fiber preform as claimed in claim 18, wherein said at least one exhaust port is disposed with a distance of 5 mm to 10 mm from the periphery of said porous preforms for core and cladding and in the vicinity of growing surfaces of said porous preforms for core and cladding, and fine glass particles not attached to and deposited on said growing surfaces of said porous preforms for core and cladding of said fine glass particles, gas produced as a result of hydrolysis by flame or thermal oxidation in said torches for core and cladding and residual non-reacted glass raw material gas and flame forming gas are exhausted through said exhaust port.
22. A fabrication method of a single-mode optical fiber preform as claimed in claim 16, wherein said torch for core has a glass raw material gas blowing nozzle and a combustible gas blowing nozzle, and said combustible gas blowing nozzle surrounds said glass raw material gas blowing nozzle in such a manner that a glass raw material gas blown out from said glass raw material gas blowing nozzle is directed to be deviated from the center of an inner area defined by said combustible gas blowing nozzle, with respect to an oxy-hydrogen flame stream blown outfrom said combustible gas blowing nozzle.
23. Afabrication method of a single-mode optical fiber preform as claimed in claim 17, wherein said torch for core has a glass raw material gas blowing nozzle and a combustible gas blowing nozzle, and said combustible gas blowing nozzle surrounds said glass raw material gas blowing nozzle in such a manner that a glass raw material gas blown out from said glass raw material gas blowing nozzle is directed to be deviated from the center of an inner area defined by said combustible gas blowing nozzle, with respect to an oxy-hydrogen flame stream blown out from said combustible gas blowing nozzle.
24. A fabrication method of a single-mode optical fiber preform as claimed in claim 21, wherein said torch for core has a glass raw material gas blowing nozzle and a combustible gas blowing nozzle, and said combustible gas blowing nozzle surrounds said glass raw material gas blowing nozzle in such a manner that a glass raw material gas blown out from said glass raw material gas blowing nozzle is directed to be deviated from the center of an inner area defined by said combustible gas blowing nozzle, with respect to an oxy-hydrogen flame stream blown out from said combustible gas blowing nozzle.
25. A torch for core for fabricating porous preforms for core in use of fabricating single-mode optical fibers, said torch for core comprising a glass raw material gas blowing nozzle and a combustible gas blowing nozzle, said combustible gas blowing nozzle surrounding said glass raw material gas blowing nozzle in such a manner that a glass raw material gas blown out from said glass raw material gas blowing nozzle is directed to be deviated from the center of an inner area defined by said combustible gas blowing nozzle, with respect to an oxy-hydrogen flame stream blown out from said combustible gas blowing nozzle.
26. Atorch for core as claimed in claim 25, wherein an inert gas blowing nozzle, said combustible gas blowing nozzle and an auxiliary gas blowing nozzle are disposed surrounding said glass raw material gas blowing nozzle in this order, and said glass raw material gas blowing nozzle is arranged to be deviated from the center of an inner area defined by said inert gas blowing nozzle.
27. Atorch for core as claimed in claim 26, wherein a diameter controlling gas blowing nozzle is disposed adjacent to said glass raw material gas blowing nozzle in said inner area difined by said inert gas blowing nozzle for blowing out a diameter controlling gas to control the diameter of said porous preform for core and a subsidiary combustible gas blowing nozzle is arranged adjacent to said diameter controlling gas blowing
nozzle.
28. Atorch for core as claimed in claim 25, wherein said inert gas blowing nozzle, said combustible gas
blowing nozzle and an auxiliary gas blowing nozzle are disposed surrounding said glass raw material gas
blowing nozzle in this order, and a controlling gas blowing nozzle is disposed adjacent to both sides of said glass raw material gas blowing nozzle in an inner area defined by said inert gas blowing nozzle, so that said
raw material gas blown out from said glass raw material gas blowing nozzle is deviated relative to said oxy-hydrogen flame stream by a controlling gas blown out from said controlling gas blowing nozzle.
29. Afabrication method of an optical fiber preform, substantially as herein described with reference to the accompanying drawings.
30. A fabrication method of a single-mode optical fiber preform, substantially as herein described with
reference to the accompanying drawings.
31. A torch for core for fabricating porous preforms for core in use of fabricating single-mode optical fibers, substantially as herein described with reference to the accompanying drawings.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12953079A JPS6044258B2 (en) | 1979-10-09 | 1979-10-09 | synthesis torch |
| JP3480A JPS5696740A (en) | 1980-01-07 | 1980-01-07 | Preparation of optical fiber matrix |
| JP3380A JPS5938171B2 (en) | 1980-01-07 | 1980-01-07 | Manufacturing method of optical fiber base material |
| JP9384180A JPS6041627B2 (en) | 1980-07-11 | 1980-07-11 | Manufacturing method of optical fiber base material |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2059944A true GB2059944A (en) | 1981-04-29 |
| GB2059944B GB2059944B (en) | 1983-11-30 |
Family
ID=27453081
Family Applications (3)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8031821A Expired GB2059944B (en) | 1979-10-09 | 1980-10-02 | Fabrication method of optical fibre preforms |
| GB08301030A Expired GB2128981B (en) | 1979-10-09 | 1983-01-14 | Fabrication method of optical fiber preforms |
| GB08301031A Expired GB2128982B (en) | 1979-10-09 | 1983-01-14 | Fabrication method of optical fiber preforms |
Family Applications After (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08301030A Expired GB2128981B (en) | 1979-10-09 | 1983-01-14 | Fabrication method of optical fiber preforms |
| GB08301031A Expired GB2128982B (en) | 1979-10-09 | 1983-01-14 | Fabrication method of optical fiber preforms |
Country Status (5)
| Country | Link |
|---|---|
| DE (1) | DE3036915A1 (en) |
| FR (1) | FR2467180B1 (en) |
| GB (3) | GB2059944B (en) |
| IT (1) | IT1133839B (en) |
| NL (1) | NL189814C (en) |
Cited By (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0067050A1 (en) * | 1981-06-04 | 1982-12-15 | Corning Glass Works | Method of forming an optical waveguide fiber |
| EP0072069A1 (en) * | 1981-08-03 | 1983-02-16 | Koninklijke Philips Electronics N.V. | Method of producing preforms for drawing optical fibres and apparatus for the continuous production of optical fibres |
| FR2513987A1 (en) * | 1981-10-01 | 1983-04-08 | Western Electric Co | METHOD AND DEVICE FOR MANUFACTURING A LIGHT GUIDE PREFORM |
| EP0089560A1 (en) * | 1982-03-12 | 1983-09-28 | Nippon Telegraph And Telephone Corporation | Process for the production of optical fiber preforms |
| EP0105926A1 (en) * | 1982-04-26 | 1984-04-25 | Western Electric Co | Vapor-phase axial deposition system. |
| GB2129418A (en) * | 1982-11-02 | 1984-05-16 | Heraeus Schott Quarzschmelze | Manufacture of elongate glass elements having refractive index distribution |
| EP0150247A1 (en) * | 1984-01-31 | 1985-08-07 | Nippon Telegraph And Telephone Corporation | Method of fabricating optical fiber preforms |
| US4568370A (en) * | 1982-09-29 | 1986-02-04 | Corning Glass Works | Optical fiber preform and method |
| EP0185106A1 (en) * | 1983-06-17 | 1986-06-25 | Sumitomo Electric Industries Limited | Method of producing a rod containing fluorine |
| EP0154500A3 (en) * | 1984-02-27 | 1986-10-29 | Nippon Telegraph And Telephone Corporation | Method, apparatus and burner for fabrication an optical fiber preform |
| EP0463783A1 (en) * | 1990-06-25 | 1992-01-02 | AT&T Corp. | Method and apparatus for making glass |
| EP0474242A2 (en) * | 1990-09-07 | 1992-03-11 | Sumitomo Electric Industries, Ltd. | Method for producing glass article |
| US6018964A (en) * | 1997-02-28 | 2000-02-01 | Nikon Corporation | Method for manufacturing quartz glass |
| EP1209129A2 (en) * | 2000-11-24 | 2002-05-29 | Heraeus Quarzglas GmbH & Co. KG | Process and apparatus for producing a quartz glass article |
| USD907292S1 (en) | 2013-09-25 | 2021-01-05 | Bic-Violex Sa | Shaving blade cartridge |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57100934A (en) * | 1980-12-12 | 1982-06-23 | Nippon Telegr & Teleph Corp <Ntt> | Manufacturing of optical fiber preform |
| JPS57100933A (en) * | 1980-12-12 | 1982-06-23 | Nippon Telegr & Teleph Corp <Ntt> | Preparation of base material for optical fiber |
| DE3219544A1 (en) * | 1982-05-25 | 1983-12-01 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Process for the production of an optical waveguide |
| JPS6126532A (en) * | 1984-07-13 | 1986-02-05 | Sumitomo Electric Ind Ltd | Production of base material for optical fiber |
| JPS61197439A (en) * | 1985-02-27 | 1986-09-01 | Furukawa Electric Co Ltd:The | Production of porous glass rod and devices therefor |
| USD415315S (en) | 1998-04-24 | 1999-10-12 | The Gillette Company | Razor cartridge |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4135901A (en) * | 1974-12-18 | 1979-01-23 | Sumitomo Electric Industries, Ltd. | Method of manufacturing glass for optical waveguide |
| FR2313327A1 (en) * | 1975-06-06 | 1976-12-31 | Quartz & Silice | VERY HIGH PURITY GLASS PREPARATION PROCESS USED IN PARTICULAR FOR THE MANUFACTURE OF OPTICAL FIBERS |
| CH620181A5 (en) * | 1975-08-16 | 1980-11-14 | Heraeus Schott Quarzschmelze | Process for the preparation of synthetic quartz glass, apparatus to carry out the process, and the use of the synthetic quartz glass |
| JPS52121341A (en) * | 1976-04-06 | 1977-10-12 | Nippon Telegr & Teleph Corp <Ntt> | Production of optical fiber base materials and production apparatus fo r the same |
| JPS5927728B2 (en) * | 1977-08-11 | 1984-07-07 | 日本電信電話株式会社 | Manufacturing method of sooty glass rod |
| JPS54112218A (en) * | 1978-02-20 | 1979-09-03 | Nippon Telegr & Teleph Corp <Ntt> | Production of optical fiber |
| JPS54116429A (en) * | 1978-03-03 | 1979-09-10 | Hitachi Ltd | Production of material for optical fiber |
-
1980
- 1980-09-30 DE DE19803036915 patent/DE3036915A1/en active Granted
- 1980-10-02 GB GB8031821A patent/GB2059944B/en not_active Expired
- 1980-10-07 NL NLAANVRAGE8005546,A patent/NL189814C/en not_active IP Right Cessation
- 1980-10-08 FR FR8021512A patent/FR2467180B1/en not_active Expired
- 1980-10-09 IT IT25227/80A patent/IT1133839B/en active
-
1983
- 1983-01-14 GB GB08301030A patent/GB2128981B/en not_active Expired
- 1983-01-14 GB GB08301031A patent/GB2128982B/en not_active Expired
Cited By (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0067050A1 (en) * | 1981-06-04 | 1982-12-15 | Corning Glass Works | Method of forming an optical waveguide fiber |
| EP0072069A1 (en) * | 1981-08-03 | 1983-02-16 | Koninklijke Philips Electronics N.V. | Method of producing preforms for drawing optical fibres and apparatus for the continuous production of optical fibres |
| FR2513987A1 (en) * | 1981-10-01 | 1983-04-08 | Western Electric Co | METHOD AND DEVICE FOR MANUFACTURING A LIGHT GUIDE PREFORM |
| EP0089560A1 (en) * | 1982-03-12 | 1983-09-28 | Nippon Telegraph And Telephone Corporation | Process for the production of optical fiber preforms |
| EP0105926A1 (en) * | 1982-04-26 | 1984-04-25 | Western Electric Co | Vapor-phase axial deposition system. |
| EP0105926A4 (en) * | 1982-04-26 | 1984-10-29 | Western Electric Co | Vapor-phase axial deposition system. |
| EP0178032A1 (en) * | 1982-04-26 | 1986-04-16 | AT&T Corp. | Vapor-phase axial deposition system |
| US4568370A (en) * | 1982-09-29 | 1986-02-04 | Corning Glass Works | Optical fiber preform and method |
| GB2129418A (en) * | 1982-11-02 | 1984-05-16 | Heraeus Schott Quarzschmelze | Manufacture of elongate glass elements having refractive index distribution |
| US5049175A (en) * | 1982-11-02 | 1991-09-17 | Heraeus Quarzschmelze Gmbh | Method of manufacturing a glass body having a non-uniform refractive index |
| EP0185106A1 (en) * | 1983-06-17 | 1986-06-25 | Sumitomo Electric Industries Limited | Method of producing a rod containing fluorine |
| AU571032B2 (en) * | 1983-06-17 | 1988-03-31 | Nippon Telegraph & Telephone Corporation | Producing optical fibres |
| EP0150247A1 (en) * | 1984-01-31 | 1985-08-07 | Nippon Telegraph And Telephone Corporation | Method of fabricating optical fiber preforms |
| EP0154500A3 (en) * | 1984-02-27 | 1986-10-29 | Nippon Telegraph And Telephone Corporation | Method, apparatus and burner for fabrication an optical fiber preform |
| US4801322A (en) * | 1984-02-27 | 1989-01-31 | Nippon Telegraph & Telephone Corporation | Method, apparatus and burner for fabricating an optical fiber preform |
| EP0463783A1 (en) * | 1990-06-25 | 1992-01-02 | AT&T Corp. | Method and apparatus for making glass |
| EP0474242A2 (en) * | 1990-09-07 | 1992-03-11 | Sumitomo Electric Industries, Ltd. | Method for producing glass article |
| EP0474242A3 (en) * | 1990-09-07 | 1992-04-01 | Sumitomo Electric Industries, Ltd. | Method for producing glass article |
| US5207813A (en) * | 1990-09-07 | 1993-05-04 | Sumitomo Electric Industries, Ltd. | Method for producing glass article |
| US6018964A (en) * | 1997-02-28 | 2000-02-01 | Nikon Corporation | Method for manufacturing quartz glass |
| EP1209129A2 (en) * | 2000-11-24 | 2002-05-29 | Heraeus Quarzglas GmbH & Co. KG | Process and apparatus for producing a quartz glass article |
| EP1209129A3 (en) * | 2000-11-24 | 2004-07-28 | Heraeus Quarzglas GmbH & Co. KG | Process and apparatus for producing a quartz glass article |
| USD907292S1 (en) | 2013-09-25 | 2021-01-05 | Bic-Violex Sa | Shaving blade cartridge |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3036915C2 (en) | 1987-01-22 |
| GB2059944B (en) | 1983-11-30 |
| GB2128982B (en) | 1984-10-31 |
| GB2128982A (en) | 1984-05-10 |
| GB8301030D0 (en) | 1983-02-16 |
| DE3036915A1 (en) | 1981-04-23 |
| FR2467180B1 (en) | 1986-07-11 |
| GB2128981B (en) | 1984-10-10 |
| IT8025227A0 (en) | 1980-10-09 |
| FR2467180A1 (en) | 1981-04-17 |
| NL189814C (en) | 1993-08-02 |
| GB8301031D0 (en) | 1983-02-16 |
| NL8005546A (en) | 1981-04-13 |
| IT1133839B (en) | 1986-07-24 |
| GB2128981A (en) | 1984-05-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Effective date: 20001001 |