DK163425B

DK163425B - Process for preparing a raw material for optical fibres

Info

Publication number: DK163425B
Application number: DK593384A
Authority: DK
Inventors: Hiroo Kanamori; Gotaro Tanaka; Kazunori Chida
Original assignee: Sumitomo Electric Industries; Nippon Telegraph & Telephone
Priority date: 1984-12-11
Filing date: 1984-12-11
Publication date: 1992-03-02
Also published as: DK163425C; DK593384A; DK593384D0

Description

DK 163425BDK 163425B

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Den foreliggende opfindelse angår en fremgangsmåde til fremstilling af et råemne til optiske fibre. Mere specifikt angår det en fremgangsmåde til fremstilling af et optisk fiberråemne, der indeholder fluor.The present invention relates to a process for producing a blank for optical fibers. More specifically, it relates to a process for producing an optical fiber blank containing fluorine.

5 Fluor i silicaglas sænker dets brydningsindex og gør det muligt at fremstille optiske fibre med forskellige fordelinger af brydnings-indexer og forbedrede lystransmissionsegenskaber, fx en optisk fiber, der har en stor forskel i brydningsindex mellem en kerne og en beklædning og således har et stort åbningstal, og en optisk fiber, der 10 omfatter en kerne fremstillet af rent silicaglas, og med forbedret modstandsevne mod bestråling.5 Fluoride in silica glass lowers its refractive index and makes it possible to produce optical fibers with different distributions of refractive indices and improved light transmission properties, e.g., an optical fiber having a large difference in refractive index between a core and a cladding and thus has a large opening number and an optical fiber comprising a core made of pure silica glass, and with improved irradiation resistance.

Der kendes adskillige metoder til fremstilling af et råemne indeholdende fluor til optiske fibre af silicaglastypen, deriblandt en modificeret kemisk dampafsætningsmetode (MCVD) og en ydre plasmadamp-15 afsætningsmetode (POVD). Ud fra et råemne fremstillet ved disse metoder kan der i almindelighed kun trækkes ca. 10 km optisk fiber.Several methods are known for producing a blank containing fluorine for silica glass optical fibers, including a modified chemical vapor deposition method (MCVD) and an outer plasma vapor deposition method (POVD). In general, from a blank prepared by these methods, only approx. 10 km of optical fiber.

Eftersom fremstillingshastighederne ved disse metoder endvidere er lav, er de ikke egnede til masseproduktion af det optiske fiberråemne og således den optiske fiber.Furthermore, since the manufacturing rates of these methods are low, they are not suitable for mass production of the optical fiber blank and thus the optical fiber.

20 Den aksiale dampfaseafsætningsmetode (i det følgende betegnet "VAD"-metoden) kan give et optisk fiberråemne, ud fra hvilket der kan trækkes en optisk fiber med større længde. Et optisk fiberråemne indeholdende fluor fremstilles imidlertid sjældent ved VAD-metoden, eftersom hvis et fluorholdigt materiale simpelthen blandes med gas-25 formigt SiCl^, der er råmaterialet for Si02, opstår der mange ulemper, fx at fluor ikke effektivt sættes til silicaglasset, at det dannede råemne har tendens til at revne, og at afsætningshastigheden af fine glaspartikler nedsættes.The axial vapor phase deposition method (hereinafter referred to as the "VAD" method) can provide an optical fiber blank from which a larger length optical fiber can be drawn. However, an optical fiber blank containing fluorine is rarely produced by the VAD method, since if a fluorine-containing material is simply mixed with gaseous SiCl 2, which is the raw material for SiO 2, there are many disadvantages, e.g. formed blanks tend to crack and the deposition rate of fine glass particles decreases.

FR Bl 2.399.978 beskriver en fremgangsmåde til fremstilling af et 30 silicaglasråemne til anvendelse ved fremstilling af en optisk fiber.FR Bl 2,399,978 discloses a process for producing a silica glass blank for use in producing an optical fiber.

Til dette formål anvendes der en multidysebrænder til at tilføre glasdannende råmateriale, som kan omfatte fluorforbindelser.For this purpose, a multi-nozzle burner is used to supply glass-forming feedstock which may comprise fluorine compounds.

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Endvidere beskriver britisk patentskrift nr. 2.059.944 en fremgangsmåde til fremstilling af råemner til optiske fibre, ved hvilken fremgangsmåde en syntetiseringsbrænder er anbragt med en hældning på fra 10° til 60° i forhold til en podestavs omdrejningsakse. Der 5 tilsættes ikke fluor til råemnet.Further, British Patent No. 2,059,944 discloses a method of producing optical fiber blanks wherein a synthetic burner is disposed at a slope of from 10 ° to 60 ° relative to the axis of rotation of a pod. Fluorine is not added to the blank.

Formålet med den foreliggende opfindelse er at tilvejebringe en forbedret fremgangsmåde til fremstilling af en stav, der kan anvendes ved fremstilling af et optisk fiberråemne, indeholdende fluor ved VAD-metoden.The object of the present invention is to provide an improved method of producing a rod which can be used in the manufacture of an optical fiber blank containing fluorine by the VAD method.

10 Ved den foreliggende opfindelse tilvejebringes således en fremgangsmåde til fremstilling af et råemne til optiske fibre, hvilket råemne indeholder fluor, ved hvilken fremgangsmåde et glasdannende råmateriale flammehydrolyseres ved hjælp af en oxygen/hydrogen-flamme i nærværelse af et gasformigt fluorholdigt materiale til syntetisering 15 af fine glaspartikler, de fine glaspartikler afsættes på spidsen af en roterende podestav til dannelse af et porøst råemne, og det porøse råemne sintres for at omdanne det til et transparent råemne indeholdende fluor, og der til tilføring af det glasdannende råmateriale . og det gasformige fluorholdige materiale anvendes en multidysebræn-20 der, hvilken fremgangsmåde er ejendommelig ved, at det glasdannende råmateriale og oxygengas injiceres fra den første (eller midterste) dyse, det gasformige fluorholdige materiale og oxygengas injiceres fra den anden dyse, der omgiver den første dyse, inaktiv gas injiceres fra den tredje dyse, der omgiver den anden dyse, og hydrogengas 25 injiceres fra den fjerde dyse, der omgiver den tredje dyse. Ved fremgangsmåden ifølge opfindelsen opnås det, at afsætningshastigheden af de fine glaspartikler øges kraftigt, hvorved fremstillingshastigheden for råemnet øges.Thus, the present invention provides a process for producing an optical fiber blank which contains fluorine, wherein a glass-forming raw material is flame hydrolyzed by an oxygen / hydrogen flame in the presence of a gaseous fluorine-containing material for synthesizing 15 fine glass particles, the fine glass particles are deposited on the tip of a rotating graft rod to form a porous blank, and the porous blank is sintered to convert it into a transparent blank containing fluorine and there to feed the glass-forming feedstock. and the gaseous fluorine-containing material is used a multi-nozzle burner, the method being characterized by injecting the glass-forming feedstock and oxygen gas from the first (or middle) nozzle, the gaseous fluorine-containing material and oxygen gas from the second nozzle surrounding the first nozzle. nozzle, inert gas is injected from the third nozzle surrounding the second nozzle, and hydrogen gas 25 is injected from the fourth nozzle surrounding the third nozzle. By the method according to the invention it is obtained that the deposition rate of the fine glass particles is greatly increased, thereby increasing the production rate of the blank.

Opfindelsen illustreres yderligere under henvisning til tegningen, 30 hvor fig. 1 viser en skematisk fremstilling, der illustrerer VAD-metoden; og fig. 2 (I) og (II) viser eksempler på arrangering af dyserne i en brænder. Arrangementet i fig. 2 (II) anvendes ved fremgangsmåden 35 ifølge opfindelsen.The invention is further illustrated with reference to the drawing, in which fig. 1 is a schematic representation illustrating the VAD method; and FIG. 2 (I) and (II) show examples of arranging the nozzles in a burner. The arrangement of FIG. 2 (II) is used in the method 35 of the invention.

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Ved den foreliggende opfindelse injiceres det fluorholdige materiale sammen med et gasformigt glasråmateriale (fx SiCl^, GeCl^, etc.)» hydrogengas, oxygengas og inaktiv gas fra en multidysebrænder (i det følgende benævnt "brænder") til syntetisering af fine glaspartikler, 5 og materialerne flammehydrolyseres i en oxygen/hydrogenflamme til dannelse af et porøst råemne indeholdende fluor.In the present invention, the fluorine-containing material is injected together with a gaseous glass raw material (e.g. SiCl 2, GeCl 2, etc.) hydrogen gas, oxygen gas and inert gas from a multi-nozzle burner (hereinafter referred to as "burner") for synthesizing fine glass particles. and the materials are flame hydrolyzed in an oxygen / hydrogen flame to form a porous blank containing fluorine.

Det er kendt, at når de fine glaspartikler syntetiseres under et højt oxygenpartialtryk, sønderdeles det fluorholdige materiale grundigt, og der syntetiseres tilstrækkeligt med fine glaspartikler, og der 10 tilsættes effektivt yderligere fluor til det dannede råemne.It is known that when the fine glass particles are synthesized under a high oxygen partial pressure, the fluorine-containing material is thoroughly decomposed and sufficiently fine glass particles are synthesized and additional fluorine is effectively added to the formed blank.

Hvis oxygenpartialtrykket reduceres ved at sænke oxygengassens strømningshastighed, bliver komponentatomer i det fluorholdige materiale såsom carbonatomer ikke oxideret fuldstændigt under sønderdelingen af det fluorholdige materiale og afsætning på det porøse råemne. Endvi-15 dere nedsættes syntetiseringshastigheden af de fine glaspartikler.If the oxygen partial pressure is reduced by lowering the flow rate of the oxygen gas, component atoms in the fluorine-containing material such as carbon atoms are not completely oxidized during the decomposition of the fluorine-containing material and deposition on the porous blank. Furthermore, the rate of synthesis of the fine glass particles is decreased.

Ved at injicere glasråmaterialerne og det fluorholdige materiale separat, forbedres afsætningshastigheden af de fine glaspartikler kraftigt, hvilket er tydeligt ud fra de i tabel I viste resultater.By injecting the glass raw materials and the fluorine-containing material separately, the deposition rate of the fine glass particles is greatly improved, which is evident from the results shown in Table I.

Tabel ITable I

20 Eksperiment Dysearran- Brydningsindex- Forhold af afsætnings- nr. gement forskel hastighed af fine glas-20 Experiment Nozzle Arrangement- Refractive Index- Ratio of outlet no. Gement difference speed of fine glass

Fig. 2 partikler 1 [I] -0,13 1,0 25 2 [II] -0,13 1,2 I arrangement [I] af dyserne i fig. 2 er en dyse 3' til SiCl^, CCI2F2 og oxygengas, en dyse 6 er til oxygengas, en dyse 5 er til inaktiv gas, og en dyse 4 er til hydrogengas.FIG. 2 particles 1 [I] -0.13 1.0 25 2 [II] -0.13 1.2 In arrangement [I] of the nozzles of FIG. 2 is a nozzle 3 'to SiCl 2, CCl 2 F 2 and oxygen gas, a nozzle 6 is to oxygen gas, a nozzle 5 is to inert gas, and a nozzle 4 is to hydrogen gas.

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4 I arrangement [II] af dyserne i fig. 2 er en dyse 3" til S1CI4 og oxygengas, og en dyse 6' er til CCI2F2 og oxygengas. I eksperiment 1 er strømningshastighederne af gasserne som følger: Første dyse: S1CI4, 250 ml/sek 5 - CC12F2, 250 ml/sek O2, 200 ml/sek4 In arrangement [II] of the nozzles of FIG. 2 is a nozzle 3 "for S1Cl4 and oxygen gas, and a nozzle 6 'is for CCI2F2 and oxygen gas. In Experiment 1, the flow rates of the gases are as follows: First nozzle: S1Cl4, 250 ml / sec 5 - CC12F2, 250 ml / sec O2 , 200 ml / sec

Anden dyse: O2, 1800 ml/sekSecond nozzle: O2, 1800 ml / sec

Tredje dyse: N2, 1500 ml/sekThird nozzle: N2, 1500 ml / sec

Fjerde dyse: 1¾. 4000 ml/sek 10 I eksperiment 2, som er ifølge opfindelsen, er strømningshastigheden af gasserne som følger: Første dyse: S1CI4, 250 ml/sek O2, 200 ml/sek 15 Anden dyse: O2, 1800 ml/sek GCI2F2, 250 ml/sekFourth nozzle: 1¾. 4000 ml / sec 10 In Experiment 2, according to the invention, the flow rate of the gases is as follows: First nozzle: S1Cl4, 250 ml / sec O2, 200 ml / sec 15 Second nozzle: O2, 1800 ml / sec GCI2F2, 250 ml /SEC

Tredje dyse: N2, 1500 ml/sekThird nozzle: N2, 1500 ml / sec

Fjerde dyse: H2, 4000 ml/sekFourth nozzle: H2, 4000 ml / sec

Disse resultater kan forklares ved, at når S1CI4 og CCI2F2 injiceres 20 samtidigt, begrænses dannelsen af Si02-kerner på grund af dannelse af S1F4 og lignende, medens når de injiceres separat, dannes Si02-ker-nerne på hensigtsmæssig måde, således at afsætningen af fast fase lettes.These results can be explained by the fact that when S1Cl4 and CCl2F2 are injected simultaneously, the formation of SiO2 nuclei due to formation of S1F4 and the like is restricted, while when injected separately, the SiO2 nuclei are formed appropriately so that the deposition of solid phase is facilitated.

Specifikke eksempler på det fluorholdige materiale er CCI2F2, CF4, 25 SFg, C2Fg, S1F4, etc. Mængden af tilsat fluor forøges, når strømningshastigheden af det fluorholdige materiale forøges. Den maksimale strømningshastighed kan være begrænset, eftersom for høj en strømningshastighed forårsager adskillige vanskeligheder såsom revnedannelse i det dannede råemne, asymmetri i råemnet omkring dets akse 30 etc. Der foretrækkes derfor især et fluorholdigt materiale indeholdende flere fluoratomer pr. molekyle, og S1F4, C2Fg, CF4 og SFg foretrækkes.Specific examples of the fluorine-containing material are CCI2F2, CF4, SFG, C2Fg, S1F4, etc. The amount of fluorine added increases as the flow rate of the fluorine-containing material increases. The maximum flow rate can be limited since too high a flow rate causes several difficulties such as cracking in the formed blank, asymmetry in the blank around its axis 30, etc. Therefore, a fluorine-containing material containing more than one fluorine atom is preferred. molecule, and S1F4, C2Fg, CF4 and SFg are preferred.

Claims

Liquid-containing material 200-500 ml / sec 10 preferably 300-400 ml / sec Oxygen gas 4,000-12,000 ml / sec preferably 6,000-8000 ml / sec Hydrogen gas 4,000-15,000 ml / sec preferably 5,000-8,000 ml / sec. The ratio of the oxygen flow rate to the hydrogen flow rate is usually from 0.5-2, preferably from 0.5-1. The ratio of the flow rates of the fluorine-containing material to the glass raw material is from 0.5-1.5, preferably from 0.7-1. The diameter of each nozzle varies as a function of other conditions such as the gas flow rates. The figures show typical diameters of the nozzles, but the present invention is not limited to these diameters. 25 PATENT REQUIREMENTS

A process for producing a blank for optical fibers which contains fluorine, wherein a glass-forming raw material is flame hydrolyzed by an oxygen / hydro-flame in the presence of a gaseous fluorine-containing material for synthesizing fine glass particles, the fine glass particles are deposited on the tip of a rotating graft rod to form a porous blank (1), and the porous blank (1) sintered to convert it into a transparent blank containing fluorine and to supply the glass forming raw material and the gaseous fluorine-containing material are used a multi-nozzle burner (2), characterized in that the glass-forming raw material and oxygen gas are injected from the first (or middle) nozzle (3 "), the gaseous fluorine-containing material and oxygen gas are injected from the second nozzle (6). ') surrounding the first nozzle (3 "), inert gas is injected from the third nozzle (5) surrounding the second nozzle, and hydrogen gas is injected from the fourth nozzle (4) surrounding the third nozzle.

Process according to claim 1, characterized in that the fluorine-containing material is at least one material selected from the class consisting of SFg, CF4, C2Fg, S1F4 and CCI2F2.