GB1598760A - Optical fibre preforms and their manufacture - Google Patents
Optical fibre preforms and their manufacture Download PDFInfo
- Publication number
- GB1598760A GB1598760A GB23124/78A GB2312478A GB1598760A GB 1598760 A GB1598760 A GB 1598760A GB 23124/78 A GB23124/78 A GB 23124/78A GB 2312478 A GB2312478 A GB 2312478A GB 1598760 A GB1598760 A GB 1598760A
- Authority
- GB
- United Kingdom
- Prior art keywords
- tube
- silica
- potassium
- layer
- alkali metal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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]
- C03B37/018—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] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
-
- 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]
- C03B37/018—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] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01807—Reactant delivery systems, e.g. reactant deposition burners
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
- C03B2201/10—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with boron
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
- C03B2201/28—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with phosphorus
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
- C03B2201/31—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with germanium
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
- C03B2201/50—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with alkali metals
-
- 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
- C03B2203/26—Parabolic or graded index [GRIN] core profile
Description
(54) IMPROVEMENTS IN OR RELATING TO OPTICAL
FIBRE PREFORMS AND THEIR MANUFACTURE
(71) We, THE GENERAL ELECTRIC
COMPANY LIMITED, of 1 Stanhope Gate,
London W1A 1EH, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to optical fibre preforms for the manufacture of multimode optical fibre waveguides composed of vitreous silica containing one or more dopants for modifying the refractive index of the silica, the dopant distribution being such as to give a graded refractive index profile across the cross-section of the waveguide, the refractive index decreasing from the axial region to the peripheral region of the waveguide.The invention also relates to a method of manufacturing such preforms, and to optical fibres produced from the preforms described.
According to the first aspect of the invention, an optical fibre preform for the production of a multimode optical fibre waveguide consists of a vitreous rod composed of an outer layer of substantially pure silica and, surrounded by said outer layer, a core consisting essentially of silica and one or more alkali metal oxides forming an alkali metal silicate glass, wherein the concentration of the alkali metal oxide or oxides is greatest in the axial region of the core and least on the peripheral region of the core contiguous with said outer layer of silica, to impart a graded refractive index profile to the core, said core optionally containing one or more additional glass-forming oxides in a toal proportion not exceeding 5 mole per cent of the silica of the core.
According to the second aspect of the invention, a method of manufacturing an optical fibre preform according to the first aspect includes the steps of forming on the interior surface of a substrate tube of substantially pure vitreous silica, by a chemical vapour deposition process, a vitreous layer consisting of silica with or without one or more additional glass-forming oxides, other than alkali metal oxides, in a substantially uniform concentration throughout said layer and in a total proportion not exceeding 5 mole percent of the silica, then evacuating the tube and introducing a quantity of vapour of at least one alkali metal, or compound decomposable by heat to liberate free alkali metal, into the tube so that said vapour condenses within the tube, closing both ends of the tube and heating the tube to cause vaporisation of the condensate and deposition of a substantially uniform coating of said alkali metal or metals on said layer, then reopening the tube and passing oxygen therethrough while heating the tube progressively from one end to the other end thereof to a sufficiently high temperature, and for a sufficient number of passes of the heating means, to cause oxidation of said alkali metal coating, diffusion of the alkali metal oxide or oxides so formed into said layer, and collapse of the tube to form a rod.
An optical fibre is produced by drawing a preform rod in accordance with the invention, in known manner. It will be understood that, in such a fibre, the optical waveguide is constituted by the core of the preform, the outer layer of substantially pure silica, which is provided by the substrate tube employed in the above-described method of manufacturing the preform, serving only as a support for the waveguide.
In carrying out the chemical vapour deposition process for forming the said layer of vitreous silica, with or without one or more additional oxides as aforesaid, on the interior surface of the substrate tube, a vapour phase reaction mixture of suitable compounds and oxygen, which will react to form silica and, if desired, an additional oxide or oxides, is passed through the bore of the tube while the tube is rotated about its axis and heated externally progressively, from the end at which the vapour mixture enters the bore to the vapour exit end, to a suitable temperature for effecting the said reaction. This procedure results in the progressive deposition of silica, or a mixture of silica and the said oxide or oxides, in finely divided form on the interior surface of the tube, and conversion of this deposit into a vitreous film.A layer of the desired thickness is built up by carrying out a number of passes of the heating means along the tube while the composition of the vapour phase reaction mixture is maintained constant, to deposit a plurality of films all containing the same proportion of additional oxide (if present). For example, 25 to 50 films, each approximately ten microns thick, may be deposited in this way.
The additional oxides which may be incorporated in the silica layer include, for example, phosphorus pentoxide, germanium dioxide or boric oxide. The total proportion of such oxide or oxides introduced is suitably from 0.1 to 5.0 mole per cent of the silica.
The purpose of the addition of such oxides is to facilitate the deposition of the silica, by depressing the liquidus temperature and thus reducing the temperature of formation of each silica film. The additional oxides, in the small proportions employed, will have only a minor effect on the refractive index of the silica. During the heating procedure for effecting diffusion of the alkali metal oxide, some diffusion of the initally uniformly distributed additional oxide or oxides will inevitably occur, but this will not significantly affect the refractive index gradient produced by the diffusion of the alkali metal oxide.
The alkali metal to be incorporated in the deposited silica layer, which is preferably potassium, sodium or rubidium, may be introduced by distilling the metal vapour into the silica tube. Alternatively, the alkali metal may be introduced in the form of the vapour of a compound which is decomposable on heating to give the free alkali metal and a volatile substance which is nonreactive with silica: for example, alkali metal azides may be employed, the nitrogen produced on decomposition being removed by the oxygen stream subsequently passed through the tube. For the formation of the alkali metal coating on the silica layer, from the condensate in the tube, the tube is heated uniformly, for example in a suitable furnace.
The progressive heating of the silica tube, for the steps of oxidising the alkali metal coating, diffusing the alkali metal oxide into the silica layer, and collapsing the tube, as well as for the previous step of forming the silica layer by a chemical vapour deposition process, is preferably effected by traversing a gas flame along the tube while the latter is rotated about its axis.
The diffusion of the alkali metal oxide or oxides into the deposited silica layer from the interior surface thereof results in the formation of an alkali metal silicate glass (with or without an additional oxide or oxides as aforesaid), in which the concentration of the alkali metal oxide is greatest in the interior surface region of said layer, which becomes the axial region of the preform core on collapsing of the tube, and is least in the peripheral region of said layer contiguous with the substrate silica tube. If the heating for effecting the diffusion and collapsing steps is prolonged, it is possible that a small amount of diffusion of the alkali metal oxide into the substrate tube might take place, but the greater part of this tube will remain as a substantially pure silica outer layer of the preform.
The use of alkali metal oxides as the refractive index-modifying dopants in the graded index core of a preform manufactured by the process described above is advantageous because the alkali metals, or suitable compounds thereof as aforesaid, can be distilled at relatively low temperature, thus facilitating the introduction of these metals into the silica tube, and also because the alkali metal oxides readily diffuse into and combine with silica.
Some specific methods of manufacturing optical fibre preforms in accordance with the invention will be described in the following examples, with reference to the accompanying diagrammatic drawing, which shows, in part-sectional elevation, the arrangement employed for the step of introducing the alkali metal into the silica tube.
Example I
A substrate tube of vitreous silica, of internal diameter 12 mm and external diameter 14 mm, is prepared by chemically cleaning and flame polishing the bore, in conventional manner. The tube is then mounted horizontally in the chucks of a glass-working lathe, and one end of the tube is connected to means for supplying thereto a vapour phase reaction mixture consisting of silicon tetrachloride and oxygen. A gas burner is supported on a carriage arranged to travel in a horizontal direction parallel to the axis of the tube. The vapour mixture is passed through the tube while the latter is rotated at a rate of 60 r.p.m. and the flame is traversed along a 30 cm length of the tube from the vapour entry end to the vapour exit end, suitably at a rate of 10 cm per minute.
Fine silica powder is produced by the resulting reaction and is deposited progressively on the bore of the tube, downstream of the flame, and is progressively converted into a vitreous film by the passage of the flame along the tube. This procedure is continued for 25 passes of the flame to form a vitreous silica layer approximately 250 microns thick over the tube bore. Preferably an arrangement is provided for maintaining a pressure slightly in excess of the ambient atmospheric pressure within the bore of the tube throughout the deposition process, as described in the specification of co-pending Patent Application No. 18160/76, (Serial No. 1,555,562) to ensure that the circularity of the tube is maintained and that the silica layer formed is of uniform thickness and is concentric with the tube.
The tube is then removed from the glass lathe, and indentations are made around the tube at each end of the 30 cm length on the bore of which the silica layer has been deposited. Referring now to the drawing, the said 30 cm length is shown at 1, between the indentations 2, 3, the deposited silica layer being indicated at 4. A baffle arrangement consisting of a number of silica rods, 5, is then introduced into one end of the tube, to lie adjacent to the indentation 2, and 50 mg of potassium metal contained in a silica ampoule or a tube of nickel of stainless steel, 6, is inserted into the same end of the silica tube: the potassium container is broken open at one end immediately before it is introduced into the silica tube. This end of the tube is then closed, at 7.The silica tube is supported horizontally, the open end 8 is connected to a vacuum pump (not shown in the drawing) by which a vacuum of 10-6 torr is applied to the tube, and the closed end and adjacent parts of the tube are surrounded by a series of tubular furnaces 9, 10, 11. The furnace 9 is heated to a temperature of 350C to cause the potassium to evaporate from the container 6. Furnace 10 is maintained at 700"C to heat the baffle 5 and ensure that the potassium vapour distils through it into the tube section 1: the purpose of the baffle is to remove any potassium hydroxide which may be present in the potassium vapour.The furnace 11 is maintained at 150 C to prevent premature condensation of the potassium vapour near the indentation 2, ensuring that the vapour passes well into the tube 1 before condensing: the mass of condensed potassium is shown at 12.
When substantially all of the potassium has been distilled into the tube 1, both ends of this tube are sealed at the indentations, and the tube is heated in a furnace at 500"C for approximately ten minutes to effect evaporation of the potassium and redeposition thereof substantially uniformly over the surface of the silica layer 4. The completion of this process is indicated by a uniform brown coloration of the silica layer, apparently due to reaction of the potassium with the silica.
The ends of the tube 1 are then broken open, the tube is mounted in a glass-working lathe and rotated at a rate of 60 r.p.m. while oxygen is passed through the tube and a gas flame is traversed along the tube from the oxygen entry end to the oxygen exit end, at a rate of 5 cm per minute, to heat the tube progressively to a temperature of 1500-1600 C. This procedure results in oxidation of the deposited potassium, as indicated by the disappearance of the brown coloration, followed by diffusion of the potassium oxide into the silica layer 4 and collapse of the tube bore. Usually two or three passes of the flame are sufficient to complete the process, including the complete collapse of the tube to form a rod.
Example 2.
The process described in Example 1 is modified by incorporating phosphorus pentoxide in the initial silica layer formed in the bore of the substrate silica tube by the chemical vapour deposition process. The vapour phase reaction mixture employed for this process consists of silicon tetrachloride, phosphorus oxychloride and oxygen, in the requisite relative proportions to give a phosphorus pentoxide concentration not exceeding 5 mole % in the deposited layer. The composition of the reaction mixture is maintained constant throughout the 25 passes of the flame along the tube, to form a deposited layer of uniform composition.
The remainder of the process, comprising the steps of introducing potassium into the tube, distributing the potassium uniformly over the deposited phosphorus-doped silica layer, oxidising the potassium, diffusing the potassium oxide into the deposited layer, and collapsing the tube, are carried out as described in Example 1.
It will be understood that various modifications may be made in the process as described in the Examples, if desired. Thus, for example, other additional oxides may be incorporated in the deposited silica layer: the length of the substrate tube section 1, and the bore diameter of this tube, may also be varied, the quantity of potassium introduced into the tube being adjusted accordingly.
A preform manufactured by either of the processes of the Examples, or modifications thereof is drawn in known manner to form a multimode optical fibre waveguide having a graded refractive index profile, with an outer supporting layer of substantially pure silica.
WHAT WE CLAIM IS:
1. An optical fibre preform for the production of a multimode optical fibre waveguide, which consists ofa vitreous rod composed of an outer layer of substantially pure silica, which outer layer is to constitute a support for the waveguide, and, surrounded by said outer layer, a core which is to constitute the optical waveguide and which consists essentially of silica and one or more alkali metal
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (12)
1. An optical fibre preform for the production of a multimode optical fibre waveguide, which consists ofa vitreous rod composed of an outer layer of substantially pure silica, which outer layer is to constitute a support for the waveguide, and, surrounded by said outer layer, a core which is to constitute the optical waveguide and which consists essentially of silica and one or more alkali metal
oxides forming an alkali metal silicate glass, wherein the concentration of the alkali metal oxide or oxides is greatest in the axial region of the core and at least in the peripheral region of the core contiguous with said outer layer of silica, to impart a graded refractive index profile to the core, said core optionally containing one or more additional glassforming oxides in a total proportion not exceeding five mole percent of the silica of the core.
2 A method of manufacturing an optical fibre preform according to Claim 1, which includes the steps of forming on the interior surface of a substrate tube of substantially pure vitreous silica, by a chemical vapour deposition process, a vitreous layer consisting of silica with or without one or more additional glass-forming oxides, other than alkali metal oxides, in a substantially uniform concentration throughout said layer and in. a total proportion not exceeding five mole percent of the silica, then evacuating the tube and introducing a quantity of vapour of at least one alkali metal, or compound decomposable by heat to liberate free alkali metal, into the tube so that the said vapour condenses within the tube, closing both ends of the tube and heating the tube to cause vaporisation of the condensate and deposition of a substantially uniform coating of said alkali metal or metals on said layer, then reopening the tube and passing oxygen therethrough while heating the tube progressively from one end to the other end thereof to a sufficiently high temperature, and for a sufficient number of passes of the heating means, to cause oxidation of said alkali metal coating, diffusion of the alkali metal oxide so formed into said layer, and collapse of the tube to form a rod.
3. A method according to Claim 2, wherein the said chemical vapour deposition process is carried out by passing a vapour phase reaction mixture af suitable compounds and oxygen, which will react to form silica and possibly a said additional oxide or oxides, through the bore of the silica tube while the tube is rotated about its axis and heated externally progressively, from the end at which the vapour mixture enters the bore to the vapour exit end, to a suitable temperature for effecting the said reaction and for depositing a film of vitreous silica, with or without said additional oxide or oxides, on the interior surface of the tube.
4. A method according to Claim 3, wherein a plurality of said films, each approximately ten microns thick, are deposited by repeated passes of the heating means along the tube while the composition of the vapour phase reaction mixture passed therethough is maintained constant.
3. A method according to Claim 2,3 or 4, Xein an additional oxide consisting of phosphorus pentoxide or germanium dioxide or boric oxide is incorporated in the said silica layer.
6. A method according to any of the preceding Claims 2 to 5, wherein a said additional oxide or oxides is or are incorporated in the said silica layer in a total proportion from Q.1 to 5.Q mole pereent of the silica.
7. A method according to any of the preceding Claims 2 to 6, wherein the said alkali metal introduced into the evacuated tube and deposited as a coating on the said layer is potassium, sodium or rubidium.
8. A method according to any of the preceding Claims 2 to 7, wherein the said alkali metal is introduced into the tube in the form of the vapour of an alkali metal azide, and the nitrogen produced on decomposition thereof is removed by the oxygen stream subsequently passed through the tube.
9. A method according to any of the preceding Claims Z to 8, wherein the progressive heating of the tube, for the steps of oxidising the alkali metal coating, diffusing the alkali metal oxide into the silica layer, and collapsing the tube, is effected by traversing a gas flame along the tube while the tube is rotated. about its axis.
10. A method accordng to Claim 2, for the manufacture of an optical fibre preform, carried out substantially as hereinbefore described in Example 1 or Example 2.
11. An optical fibre preform manufactured by a method according to any of the preceding Claims 2 to 10.
12. An optical fibre waveguide manufactured by drawing an optical fibre preform according to Claim 1 or Claim 11.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB23124/78A GB1598760A (en) | 1978-05-26 | 1978-05-26 | Optical fibre preforms and their manufacture |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB23124/78A GB1598760A (en) | 1978-05-26 | 1978-05-26 | Optical fibre preforms and their manufacture |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1598760A true GB1598760A (en) | 1981-09-23 |
Family
ID=10190505
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB23124/78A Expired GB1598760A (en) | 1978-05-26 | 1978-05-26 | Optical fibre preforms and their manufacture |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB1598760A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4597787A (en) * | 1984-11-13 | 1986-07-01 | Ispra Fibroptics Industries Herzlia Ltd. | Manufacture of optical fibre preforms |
| US4715875A (en) * | 1984-11-13 | 1987-12-29 | Ispra Fibroptics Industries Herzlia Ltd. | Manufacture of optical fibre preforms |
| US7426327B2 (en) | 2005-11-23 | 2008-09-16 | Corning Incorporated | Low attenuation non-zero dispersion shifted optical fiber |
| US7469559B2 (en) | 2002-08-28 | 2008-12-30 | Corning Incorporated | Method for making low loss optical fiber |
| WO2013077263A1 (en) * | 2011-11-21 | 2013-05-30 | 住友電気工業株式会社 | Optical fiber preform, method for producing optical fiber, and optical fiber |
-
1978
- 1978-05-26 GB GB23124/78A patent/GB1598760A/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4597787A (en) * | 1984-11-13 | 1986-07-01 | Ispra Fibroptics Industries Herzlia Ltd. | Manufacture of optical fibre preforms |
| US4715875A (en) * | 1984-11-13 | 1987-12-29 | Ispra Fibroptics Industries Herzlia Ltd. | Manufacture of optical fibre preforms |
| US7469559B2 (en) | 2002-08-28 | 2008-12-30 | Corning Incorporated | Method for making low loss optical fiber |
| US7524780B2 (en) | 2002-08-28 | 2009-04-28 | Corning Incorporated | Low loss optical fiber and method for making same |
| US7426327B2 (en) | 2005-11-23 | 2008-09-16 | Corning Incorporated | Low attenuation non-zero dispersion shifted optical fiber |
| WO2013077263A1 (en) * | 2011-11-21 | 2013-05-30 | 住友電気工業株式会社 | Optical fiber preform, method for producing optical fiber, and optical fiber |
| US9036972B2 (en) | 2011-11-21 | 2015-05-19 | Sumitomo Electric Industries, Ltd. | Optical fiber preform, method for producing optical fiber, and optical fiber |
| US9229160B2 (en) | 2011-11-21 | 2016-01-05 | Sumitomo Electric Industries, Ltd. | Optical fiber preform, method for producing optical fiber, and optical fiber |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |