GB2208114A - Optical fibre preforms - Google Patents

Optical fibre preforms Download PDF

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Publication number
GB2208114A
GB2208114A GB8715461A GB8715461A GB2208114A GB 2208114 A GB2208114 A GB 2208114A GB 8715461 A GB8715461 A GB 8715461A GB 8715461 A GB8715461 A GB 8715461A GB 2208114 A GB2208114 A GB 2208114A
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United Kingdom
Prior art keywords
optical
rod
tube
diameter
fibre
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Withdrawn
Application number
GB8715461A
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GB8715461D0 (en
Inventor
Paul Laurance Scrivener
Eleanor Joan Tarbox
Ian George Sayce
Peter John Wells
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Prysmian Cables and Systems Ltd
Saint Gobain Quartz Ltd
Original Assignee
TSL Group PLC
Prysmian Cables and Systems Ltd
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Application filed by TSL Group PLC, Prysmian Cables and Systems Ltd filed Critical TSL Group PLC
Priority to GB8715461A priority Critical patent/GB2208114A/en
Publication of GB8715461D0 publication Critical patent/GB8715461D0/en
Publication of GB2208114A publication Critical patent/GB2208114A/en
Withdrawn legal-status Critical Current

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Classifications

    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01Manufacture of glass fibres or filaments
    • C03B37/012Manufacture of preforms for drawing fibres or filaments
    • C03B37/01205Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
    • C03B37/01211Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube
    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00Type of glass produced
    • C03B2201/02Pure silica glass, e.g. pure fused quartz
    • C03B2201/03Impurity concentration specified
    • C03B2201/04Hydroxyl ion (OH)
    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2203/00Fibre product details, e.g. structure, shape
    • C03B2203/10Internal structure or shape details
    • C03B2203/22Radial profile of refractive index, composition or softening point
    • C03B2203/24Single mode [SM or monomode]

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

Abstract

There is disclosed a method of making several preforms each to be drawn into an optical fibre, in which initially a large scale rod-in-tube assembly is prepared in which the rod and tube have performed on them the operations needed to achieve the desired cross-sectional geometry of the components to be developed from them in the eventual fibre, the assembly then being drawn into a cane which is separated into lengths, each of which is a preform to be drawn down to a fibre. Also disclosed is a rod-in-tube assembly which may be used in carrying out the method, or otherwise, in which the rod includes an optical core and an inner portion of the optical cladding to a diameter of not less than 1.1 times the diameter of the optical core, and in which the diameter of the rod is at least 800 times the diameter of the theoretical interface in the eventual fibre to be produced from the assembly. There is also disclosed a precursor, which may be a rod-in-tube assembly or a preform, of a monomode optical fibre in which the outer part of the optical cladding and the remainder of the precursor radially outwardly thereof comprises synthetic silica generated as a single body by deposition from a plasma, the synthetic silica having an OH content of less than 2.0 ppm out to a diameter of at least 6 times the diameter of the optical core.

Description

MAKING OPTICAL FIBRES This invention relates to the manufacture of optical fibres, in particular but not exclusively monomode optical fibres.
A standard requirement for monomode optical fibres is that they should have an outer diameter of 125 yim and contain an optical core having a diameter close to 10 sm.
To achieve the desired optical properties, the optical core is of a higher refractive index and is immediately surrounded by an optical cladding of a lower refractive index. To avoid excessive attenuation of optical power, the material of the core and of the optical cladding must scatter and absorb the transmitted radiation to the minimum possible extent, and typically the diameter of the optical cladding should be at least about 6 times the diameter of the core so that all the guided radiation will be travelling at all times within optically pure material whereby losses are minimised. Outside the optical cladding there is an outer cladding or mechanical cladding which is present. for the purpose of maing the outside diameter of the fibre up to the desired 125 ,um.
The fibre is directly drawn from a preform which. has a structure identical to that of the fibre itself but of course the preform is much shorter and of much greater diameter. The terms "optical core, "optical cladding and "outer cladding" will be used herein in respect of the equivalent components of both the fibre and the preform. For the purposes of this specification, the term "preform" is used to mean a body which includes all the vitreous components which are required to be present in the optical fibre which is to be made from the preform.
Preforms are made individually, typically with an outside diameter of about 30 mm and a length of about 500 mm. There are various ways in which such preforms are made. Normally, these initially involve the preparation of a central rod which includes the optical core and the optical cladding. These components may, for example, be developed inside a support tube by the modified chemical vapour deposition (MCVD) process, the tube then being collapsed so as to form the central rod of the preform, or the central rod including optical core and optical cladding may be formed entirely by deposition without the need for a support tube, for example using the vapour axial deposition (VAD) process.In any event, each central rod has to have its outside dimensions and optical properties precisely measured to ascertain the exact size and location of its optical core, and the refractive index difference between the material defining the optical core and its optical cladding. Because the preform needs to have an outside diameter to optical core diameter ratio of approximately 125:8 as in the eventual fibre, its diameter is achieved by adding outer cladding material to the rod, this being done either by jacketing the rod with one or more silica tubes or by adding further material in the form of layers of vapour deposited material.To achieve the desired concentricity and outside diameter to optical core ratio, each central rod must be carefully matched with a selected jackeing tube and/or precise control of the thickness of the deposited outer cladding material is required. The above steps have to be performed for each individual preform which is produced.
From one aspect, the present invention simplifies and renders more economical the production of preforms which are to be drawn into optical fibres.
From this aspect, the invention provides a method of making several preforms each of which is to be drawn into an optical fibre, comprising preparing a rod-in-tube assembly of substantially greater diameter than the preforms to be made, the preparation including performing upon a rod and a tube each of selected optical characteristics the operations needed to achieve the desired cross-sectional geometry of the components to be developed from them in the eventual fibre and assembling the rod into the tube, drawing the assembly into cane having a diameter much greater than that of a fibre, and separating the cane into lengths each of which is a preform having its cross-sectional geometry determined at the rod and tube stage.
Preferably, the rod includes an optical core having a higher refractive index than the surrounding material and the inner layer of optical cladding, and the ratio of the cross-sectional area of the tube plus the crosssectional area of the inner layer of optical cladding to the cross-sectional area of the optical core is given a predetermined value which is required in the eventual fibre.
In the method according to this aspect of the invention, all measurement and machining processes can be carried out on rod and tube components which are very substantially greater in diameter than the components of a preform and therefore if they are carried out to the same tolerances as hitherto a better result can be obtained in the eventual preform. Furthermore, all measurement and dimension adjusting steps need only to be carried out once, on the large rod and/or tube, in order to achieve the required cross-sectional geometry for all of the individual preforms which are made from the single original rod-in-tube assembly. The method thus offers substantial improvements both in the economy and the quality with which preforms, and hence optical fibre drawn from the preforms, can be made.
The method will be described in more detail in relation to the preparation of preforms for the manufacture of simple monomode optical fibre. However, it should be appreciated that the method could also be applied to the production of preforms for making polarisation-maintaining optical fibres or multiple optical core fibres. In the first instance, the tube would be given three parallel bores lying in a plane, the rod containing the optical core would be placed in the central bore, and rods of material having a different coefficient of expansion from that of the tube material would be placed in the two outer bores. In the second case, to produce a multiple core fibre, rods each containing an optical core would be placed in each of the bores.
It is to be noted that in carrying out a method in accordance with this aspect of the invention, the tube may as a preliminary step be collapsed onto the rod or rods at a relatively high temperature to produce a large but integral rod-in-tube assembly to be drawn to a cane at a later stage, or the collapse and drawing down into cane may be carried out as a single eontinuous operation.
It is known that the preparation of preforms by rodin-tube processes inherently involves problems arising from contamination of, and surface imperfections at, the interface between the rod and the tube, see for example GB-A-1333312. That specification discloses that the scattering centres formed by such impurities and defects at the mechanical interface can be reduced by shifting the optical interface between the optical core and the optical cladding inwardly from the mechanical interface by subjecting the central rod which contains the optical core to an ion-exchange process which reduces the refractive index of its outer layer. This results in any contamination or surface defects being in a region where less optical energy is travelling, and hence less attenuation occurs. Nevertheless, it is not believed that the method disclosed in GB-A-1333312 is capable of resulting in optical fibre of telecommunications quality. Throughout this specification the phrase "optical fibre of telecommunications quality" should be taken to mean an optical fibre having an attenuation at 1300 nm (nanometres) which is less than 0.6 dB/km and at 1550 nm which is less than 0.5 dB/km.
Alternatively, the use of a fluxing layer of glass to reduce the deleterious effects of chemical impurities or physical imperfections at the optical fibre interface is disclosed in GB-A-2038311, where typically boron tri chloride and oxygen are passed down the annular gap between rod and tube, while heating the tube to about 15000C. It was proposed in this document that interface imperfections were reduced by mechanisms of vapour phase etching, and conversion of interface layers to advantageously doped glass layers. Improved multimode fibre capable of being used at 850 nm was stated as being made by this method. The method was demonstrated using a rod of 8 mm diameter located inside a tube of OD 20 mm, ID 17 mm, within which a layer of doped glass 0.8 mm thick had been deposited, i.e. providing a final ID of the tube of 15.d mm.
The method disclosed in GB-A-2038311 was not proposed as a means of making a single mode optical fibre of telecommunications quality, and since the method requires heat treatment at temperatures over 1000 0C it would be costly and difficult to engineer for large scale assemblies. The need for such costly and difficult procedures is obviated by the method of the present invention.
We have now found that provided reasonable precautions are taken to maintain clean defect-free surfaces on the rod and inside the tube, it is possible to make a monomode optical fibre of telecommunications quality with the diameter of the rod exceeding 1.1 times the diameter of the core (d) and preferably lying in the range of 1.1xd to 2.8xd, provided a suitably large increase in area occurs between the surface of the rod in the rod-in-tube assembly and what was the surface of the rod in the eventual fibre produced therefrom. For convenience the term "theoretical interface" will be used for what was the surface of the rod in the preform and in the eventual fibre.
A second aspect of the invention enables a substantial improvement in the quality of the optical fibre made by a rod-in-tube method.
From this second aspect, the invention provides an assembly of rod-in-tube for use in making a monomode optical fibre, which fibre comprises an optical core of a given refractive index surrounded by an optical cladding of lower refractive index, the rod and tube defining, at the confronting cylindrical surfaces thereof, the precursor of a theoretical interface in the eventual fibre, the rod including the optical core and an inner portion of the optical cladding out to a diameter of not less than 1.1 times the diameter of the optical core, characterised in that the diameter of the rod is at least 800 times the diameter of the theoretical interface in the eventual fibre to be produced from the rod-in-tube assembly.
It has been found that if the mechanical interface between rod and tube is positioned at more than 1.1 times (but preferably not more than 2.8 times) the diameter of the optical core, and the diameter of the rod is at least 800 times the diameter of the theoretical interface in the eventual fibre then, provided that other customary precautions are taken during the manufacturing process, and as regards the purity of materials employed, monomode optical fibre of telecommunications quality can be produced.
It is believed that the advantage of this aspect of the invention as compared with what is disclosed in GB-A1333312 may arise from the degree of areal expansion of the theoretical interface which occurs during the drawing process when the rod is made large enough. This may have the effect of diluting, or spreading over a much longer length of fibre, whatever level of impurity may exist at the physical interface, and correspondingly reducing the significance of any surface imperfections present at the same interface. The ratio between the surface area of the theoretical interface in a fibre drawn by the rod-intube method and the surface area of the rod in the rodin-tube assembly which gives rise to that theoretical interface is equal to the ratio of the diameter of the rod divided by the diameter of the theoretical interface in the drawn fibre.
Preferably this ratio is not less than 900 and even more preferably exceeds 1000, especially as the rod diameter more closely approaches the minimum ratio of 1.1:1 relative to the optical core diameter.
It has already been mentioned that when preparing preforms from which monomode optical fibre is to be made, it is usual for the high quality of the optical core material and an optical cladding out to a diameter at least 6 times that of the optical core to be developed by a chemical deposition process such as VAD or MCVD. It is also known to develop these two high purity components of the preform by outside vapour deposition (OVD). These processes are sophisticated and time-consuming and the size of the bodies that can be made using them is limited.Given that for very high quality optical fibre the optical cladding needs to be at least 6 times the diameter of the optical core, and that the whole of both these components is usually manufactured by one of the above-mentioned sophisticated chemical vapour deposition processes, this sets a limit on the size of preform that can actually be manufactured, and also means that a preform so manufactured must have at least a predetermined percentage of the sophisticated high purity core and optical cladding material in it.
It has been reported that on an experimental scale optical fibre has been produced in which the ratio of the outside diameter of the optical cladding to that of the optical core was only 3:1, thus reducing the volume of sophisticated quality material required, but it was suggested that the resulting power losses although allowing the resulting fibre to be suitable for certain applications, did not produce fibre having very low attenuation.
A further aim of the present invention is to enable monomode optical fibre to be produced having very low attenuation, yet containing a low proportion of sophisticated material in its optical cladding.
From this aspect, the invention provides a complete precursor of a monomode optical fibre comprising an optical core of higher refractive index surrounded by an optical cladding of lower refractive index, characterised in that the outer part of the optical cladding and the remainder of the precursor radially outwardly thereof comprises synthetic silica generated as a single body by deposition from a plasma, the synthetic silica having an OH content of less than 2.0 ppm out to a diameter of at least six times the diameter of the optical core.
The synthetic silica is preferably deposited from an electrodeless plasma for example a microwave or radio frequency induced, continuous or pulsed, plasma. Suitably the synthetic silica is deposited from an induction plasma operating at or close to atmospheric pressure for the oxidation of silicon tetrachloride.
The plasma deposited synthetic silica having an OH content of less than 2.0 ppm can serve as optical cladding material and therefore the central part of the precursor needs to include only the optical core and the innermost part of the optical cladding. Consequently, if this central part is made by one of the other more sophisticated chemical vapour deposition processes recently mentioned, then for a given size it will contain a larger diameter optical core and a lesser thickness of optical cladding material. Thus, it can form the basis for a precursor of larger diameter than hitherto. Very low attenuation, indeed sufficiently low to achieve telecommunications quality, can be achieved in the ultimate fibre.
In the embodiments described below the optical core lies in a central rod and the synthetic silica body is a tube machined from synthetic silica produced by deposition from a thermal plasma. The plasma deposition process is such that for the present purposes this tube can be made of as large a diameter as may be required.
Consequently, there is no need for additional sleeving operations in order to build up the outer diameter of the preform to a required value, and so the entire precursor, and consequently the eventual fibre, can be made from only two physical components namely the central rod and the tube, each of which two components can be produced as an integral body.
Hitherto, the tensile strength of optical fibres has been enhanced by specially treating the outer surface of the preform from which they are produced, or having a specially applied outer layer on the preform. In routine commercial production it has been unusual for the fibre to be able reliably to withstand a strain of more than about 1.5% without breaking. Special production procedures involving substantial waste have to be adopted if fibre lengths which will withstand a greater strain are required.
Plasma deposited silica has very good tensile strength and so the use of a plasma deposited silica tube as the outermost component of the precursor gives a substantial improvement in tensile strength of the fibre without the addition of any further layer or tube to the precursor, beyond that which is needed to provide the required optical properties in the preform.
The term "precursor" has been used in relation to the third aspect of the invention since the article may be a preform of a size suitable for direct drawing in an optical fibre drawing tower, or may be a rod-in-tube assembly of substantially greater size as has been discussed in detail in relation to the first aspect of the invention.
In order that the invention may be more clearly understood, a preferred embodiment thereof will now be described, by way of example, with reference to the accompanying drawing, which shows a cross-section through an integral rod-in-tube assembly in accordance with the present invention. A preform produced from a cane drawn from it, and a fibre drawn from the preform, would have the same cross-sectional appearance and relative geometry.
Referring to the drawing, the outer solid-line circle 2 is the outer surface of a plasma deposited silica tube 1, and the inner solid-line circle 4 is the theoretical interface formed between that tube and a central rod 6.
The optical boundaries are different from the physical boundaries, in that the optical core of higher refractive index is defined by the smaller broken-line circle 8 and the optical cladding extends from the circle 8 out at least to the broken line circle 10 which is shown approximately at the six times core diameter position. The optical cladding extends in principle right out to the outer surface 2 of the preform, but in practice significant optical power does not propagate beyond the limits of the circle 10 by virtue of the physical principles involved in monomode optical fibre transmission.
One method for preparing the rod and tube which together form the rod-in-tube assembly illustrated will now be described.
The rod 6 can be produced initially by a VAD process on a VAD machine having a burner set up and supplied to produce germanium oxide doped optical core material. The machine employs one or more than one cladding burner to produce the inner part of the optical cladding, the burner and the material flow rates being configured so that the diameter ratio of the inner optical cladding to the optical core will be not more than 3:1 and preferably will be in the vicinity of 2.5:1. The core and inner cladding are deposited initially in the form of a large diameter body of soot which, after it has been formed, is in known manner dehydrated and fused to solid silica, to produce the finished central rod 6.The external dimensions of the rod are then accurately measured as is its refractive index profile, these measurements then being utilised to compute the required inside diameter and outside diameter figures for the tube 1 with which the rod is to be sleeved. Alternatively a tube of approximately correct dimensions may be made and the rod dimensions adjusted to match it.
The production of the tube used to sleeve the rod is as follows. Using a plasma deposition technique based on silicon tetrachloride, a billet of synthetic silica glass is built up, the billet being made of a sufficient size to form the tube whose dimensions have previously been calculated. The billet is precision machined to for. a cylindrical body having external dimensions as calculated, and it is then bored and internally machined and etched to give it the calculated internal dimensions.
To ensure a clean interface between the rod 6 and the tube 1, each is etched with hydrofluoric acid and dried prior to assembly.
It has been found that even if silicon tetrachloride of the highest purity is not used as feedstock for the plasma the vitreous material deposited from an induction plasma has sufficiently little undesirable metallic inclusions to be satisfactory, and furthermore that by careful control of the inputs to the plasma the OH content of the deposited silica can be kept lower than 2.0 ppm, preferably lower than 1.0 ppm and even more preferably lower than 0.5 ppm, as is desirable when a particularly low optical cladding to core ratio is used in the rod.
The rod and tube, made and prepared as described above, are then assembled together with the rod within and concentric with the tube and a small annular space between them. The large rod-in-tube assembly is complete at this stage, in the sense that it contains all the vitreous components needed in the fibre. Large scale drawing equipment may be employed to simultaneously combine the rod and the tube and draw the combined body down to a cane which in diameter is intermediate the diameter of a fibre and the diameter of the original assembly.
Alternatively, the concentric but separate rod and tube may be subjected only to an optionally slight drawing-down operation sufficient to bond them together concentrically, to leave a unitary rod-in-tube assembly which is still very large in diameter. In a separate operation, this may then be further drawn down to form a cane.
Whichever way the cane is obtained from the preform, it will have a diameter suitable for drawing down into monomode optical fibre in a conventional fibre drawing tower but it may be many metres in length and thus too long to be drawn into fibre in a single operation.
The cane is separated into lengths, each of which constitutes a preform, preferably at least 500 mm long, these then being individually drawn down to fibre in the fibre-drawing tower. It should be noted that all of the concentricity and diameter ratio features of all of the preforms will have been properly determined by the appropriate machining of the billet to form the tube of the rod-in-tube assembly. Thus, the individual measurement, dimension adjustment and assembly steps that are needed individually to sleeve the relatively small preforms conventionally used, which may be roughly the same diameter as, or even smaller in diameter than, the preforms used and made in the present invention, are avoided.Preforms produced in accordance with the invention may also be much longer than hitherto, e.g. 1 metre or more, thus requiring less frequent repreparation of the drawing tower and giving further economy.
The invention will now be further described, in the following examples: Example 1 A plasma-deposited synthetic silica tube is machined to the following dimensions: Outside diameter 102 mm Inside diameter 20.5 mm Length 1120 mm The bore of the tube is machined to be concentric with the outside diameter.
A VAD-produced rod consisting of a core of germanic doped silica and a cladding of synthetic silica is inserted into the tube to form an assembly. The rod has the following characteristics: Outside diameter 17 mm Length 1120 mm Cladding/core ratio 2.63 2 2 Numerical aperture 0.1175 (i.e. (n1 - n2)) where n = refractive index of the core glass n2 = refractive index of the cladding glass The assembly and interface are cleaned with 5g HF and dried with N2.
The tube is subsequently collapsed onto the rod and drawn down to a cane having a diameter of 20 mm.
The cane is severed and a length of the cane is drawn to fibre having a diameter of 125 microns and a fibre core diameter of 8.00 microns. The fibre has a cut off wavelength of 1229 nm, and attenuations at 1300 nm of 0.41 dB/km, and at 1550 nm of 0.26 dB/km.
The areal expansion of the surface of the rod required to produce the theoretical interface created by that surface in the final fibre is 810 times.
Example 2 A composite core rod of germania-doped silica, clad with pure synthetic silica is made by a VAD process.
After dehydration, sintering and stretching, the rod has the following characteristics.
OD 19.2 mm Length 905 mm Cladding : core ratio 2.46 Numerical Aperture 0.1140 The surface of this rod is etched to remove 0.5 mm using 60 HF.
The etched rod is assembled within a tubular body made of plasma synthesised silica of hydroxyl content less than 1 ppm, machined to a cylindrical body of OD 119 mm, ID 21.6, length 905 mm cleaned and etched with hydrofluoric acid. The assembly is collapsed with heating and drawn to cane 18 mm diameter. The produced cane is severed into lengths, each of which is a preform. A preform is drawn to fibre having diameter 125 + 1 Sum. In single mode operation, the fibre has a cut off wavelength of 1226 nm, and an attenuation at 1300 nm of 0.42 dB/km, and at 1550 nm of 0.29 dB/km.
The areal expansion of the surface of the rod required to produce the theoretical interface in the fibre is 947 times.
In the Examples, the optical core is doped to raise its refractive index. It is contemplated that, instead, the outer layer of the rod and at least the inner layer of the tube may be doped to depress their refractive index, e.g. with fluorine in which case the core can be of pure silica.
Among the advantages of the method of this invention may be mentioned 1. The material used for at least 95% of the volume of the fibre can be a bulk high purity product, making repeated characterisation of the bulk glass unnecessary.
2. The core rod for the assembly may be made by a suitable conventional means in a single operation.
3. Since the dimensions of core rod and tubular ingot may be precisely defined prior to collapse/ elongation, it follows that all the resulting fibre will have predictable properties.
4. A rod-in-tube assembly equivalent to over 1000 km of fibre of constant parameters may readily be made.
5. Very precise core concentricity may be readily achieved because the assembly is precisely engineered, and does not rely on difficult deposition or sintering processes for its geometry.
6. Strong fibre results from the use of synthetic silica for the outer region of the fibre. A strong fibre is particularly important for economical fibre manufacture using future high speed fibre drawing techniques.
7. The problem caused by scattering centres at an interface as close as 1.1 times core diameter in rod-in-tube methods in the prior art is reduced, enabling the production of optical fibre of tele communications quality.

Claims (35)

CLAIMS:
1. A method of making several preforms each of which is to be drawn into an optical fibre, comprising preparing a rod-in-tube assembly of substantially greater diameter than the preforms to be made, the preparation including performing upon a rod and a tube each of selected optical characteristics the operations needed to achieve the desired cross-sectional geometry of the components to be developed from them in the eventual fibre and assembling the rod into the tube, drawing the assembly into cane having a diameter much greater than that of a fibre, and separating the cane into lengths each of which is a preform having its cross-sectional geometry determined at the rod and tube stage.
2. A method as claimed in claim 1, wherein the outside diameter of the tube is at least 100 mm.
3. A method as claimed in claim 1 or claim 2, wherein the tube is at least 750 mm long.
4. A method as claimed in any preceding claim, wherein the cane is separated into lengths each at least 500 mm long.
5. A method as claimed in any preceding claim, wherein the tube is made by machining it from an ingot.
6. A method as claimed in any preceding claim, wherein the rod includes an optical core having a higher refractive index than the surrounding material and the inner layer of optical cladding, and the ratio of the cross-sectional area of the tube plus the cross-sectional area of the inner layer of optical cladding to the crosssectional area of the optical core is given a predetermined value which is required in the eventual fibre.
7. A method as claimed in any preceding claim of making a monomode optical fibre.
8. A rod-in-tube assembly for use in making a monomode optical fibre, which fibre comprises an optical core of a given refractive index surrounded by an optical cladding of lower refractive index, the rod and tube defining, at the confronting cylindrical surfaces thereof, the precursor of a theoretical interface in the eventual fibre, the rod including the optical core and an inner portion of the optical cladding out to a diameter of not less than 1.1 times the diameter of the optical core, characterised in that the diameter of the rod is at least 800 times the diameter of the theoretical interface in the eventual fibre to be produced from the rod-in-tube assembly.
9. An assembly as claimed in claim 8, wherein the rod includes the inner portion of the optical cladding out to a diameter of not more than 2.8 times the diameter of the optical core.
10. An assembly as claimed in claim 8 or 9, wherein the outer diameter of the tube exceeds 800 times the outer diameter of the eventual fibre to be produced from the assembly.
11. An assembly as claimed in any one of claims 8 to 10, in which the tube consists of synthetic silica and at least the inner part thereof has a sufficiently low level of attenuation-inducing contaminant species therein to form the outer part of the optical cladding.
12. An assembly as claimed in any one of claims 8 to 11, in which the diameter of at least one of the confronting cylindrical surfaces lies between 1.5 and 2.8 times the outer diameter of the optical core in the rod.
13. An assembly as claimed in any one of claims 8 to 12, in which the outer diameter of the tube is not less than 900 times the outer diameter of the eventual fibre.
14. An assembly as claimed in any one of claims 8 to 13, in which the diameter of the theoretical interface formed from said cylindrical surfaces is between 1.8 and 2.6 times the outer diameter of the optical core.
15. An assembly as claimed in any one of claims 8 to 14, in which the outer diameter of the tube is more than 1000 times the outer diameter of the eventual fibre.
16. An assembly as claimed in any one of claims 8 to 15, in which the optical core is silica doped with at least one refractive index enhancing element and the tube is of high purity silica.
17. An assembly as claimed in any one of claims 8 to 15, in which the optical core is of pure silica and the outer layer of the rod, and at least the inner layer of the tube, is made from silica doped with a refractive index depressing element.
18. An assembly as claimed in claim 16, in which not less than 95% of the total volume of vitreous material in the assembly is represented by the tube.
19. An assembly as claimed in claim 16, in which more than 97% of the total volume of the vitreous material in the assembly is represented by the tube.
20. A complete precursor of a monomode optical fibre comprising an optical core of higher refractive index surrounded by an optical cladding of lower refractive index, characterised in that the outer part of the optical cladding and the remainder of the precursor radially outwardly thereof comprises synthetic silica generated as a single body by deposition from a plasma, the synthetic silica having an OH content of less than 2.0 ppm out to a diameter of at least six times the diameter of the optical core.
21. A precursor as claimed in claim 20, characterised in that the optical core lies in a central rod and said body is a tube machined from said synthetic silica.
22. A precursor as claimed in claim 21, wherein the outer part of the central rod is of lower refractive index than the optical core and forms the inner part of the optical cladding.
23. A precursor as claimed in claim 20 or claim 21, characterised in that the central rod is made by chemical vapour deposition.
24. A precursor as claimed in claim 23, characterised in that the central rod is made by vapour axial deposition.
25. A precursor as claimed in claim 23, characterised in that the central rod is made by outside vapour deposition.
26. A precursor as claimed in any one of claims 20 to 25, characterised in that the diameter of the rod is less than three times that of the optical core.
27. A precursor as claimed in any one of claims 20 to 26, wherein the rod and tube are concentric but separate.
28. A precursor as claimed in any one of clams 20 to 26, wherein the rod and tube have been bonded together concentrically.
29. A precursor as claimed in any one of claims 20 to 28, having an outside diameter of at leas 100 mm.
30. A precursor as claimed in any one of claims 20 to 29, having a length of at least 750 mm.
31. A preform for drawing directly into an optical fibre, produced by drawing a precursor as claimed in any one of claims 20 to 30 down to a diameter less than that of the precursor but much greater than that of a fibre.
32. Optical fibre drawn from a preform made by a method as claimed in any one of claims 1 to 7.
33. Optical fibre made from a rod-in-tube assembly as claimed in any one of claims 8 to 19.
34. Optical fibre made from a precursor as cline in any one of claims 20 to 30.
35. Optical fibre made from a preform as claImed In claim 31.
GB8715461A 1987-07-01 1987-07-01 Optical fibre preforms Withdrawn GB2208114A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8715461A GB2208114A (en) 1987-07-01 1987-07-01 Optical fibre preforms

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8715461A GB2208114A (en) 1987-07-01 1987-07-01 Optical fibre preforms

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GB8715461D0 GB8715461D0 (en) 1987-08-05
GB2208114A true GB2208114A (en) 1989-03-01

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Cited By (9)

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Publication number Priority date Publication date Assignee Title
EP0972752A1 (en) * 1998-07-14 2000-01-19 Lucent Technologies Inc. Large preform for singlemode fiber and method for making same
EP1000908A2 (en) * 1998-10-08 2000-05-17 Heraeus Quarzglas GmbH Method for producing quartz glass preform for optical fibers
WO2001090010A1 (en) * 2000-05-24 2001-11-29 Heraeus Tenevo Ag Method for producing an optical fibre and blank for an optical fibre
KR100345355B1 (en) * 1998-10-09 2002-07-24 신에쯔 세끼에이 가부시키가이샤 Preform for Optical fiber and manufacturing method thereof
US6460378B1 (en) * 2000-02-29 2002-10-08 Xiaoyuan Dong Collapsing a multitube assembly and subsequent optical fiber drawing in the same furnace
US20100034998A1 (en) * 2007-01-19 2010-02-11 Gerhard Schoetz Quartz glass tube as a semifinished product for preform and fiber manufacture, and method for making the quartz glass tube
US20120324958A1 (en) * 2010-07-13 2012-12-27 Chen Yang Methods for manufacturing optical fiber preform and methods for manufacturing optical fiber
WO2020155707A1 (en) * 2019-01-29 2020-08-06 江苏永鼎股份有限公司 Optical fiber preform rod of large size and low loss and preparation method therefor
WO2020181788A1 (en) * 2019-03-11 2020-09-17 江苏永鼎光纤科技有限公司 Method for manufacturing optical fiber preform based on sleeve method

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GB1554314A (en) * 1975-08-16 1979-10-17 Heraeus Schott Quarzschmelze Manufacture of light-conducting fibres
GB2043619A (en) * 1979-03-07 1980-10-08 Standard Telephones Cables Ltd Optical fibre and optical fibre preform manufacture
GB2109367A (en) * 1981-11-17 1983-06-02 Pirelli General Plc Manufacture of a preform for optical fibres by the rod in tube method
EP0125828A1 (en) * 1983-05-02 1984-11-21 Sumitomo Electric Industries Limited Optical fiber and process for producing the same
EP0159046A2 (en) * 1984-04-20 1985-10-23 Sumitomo Electric Industries Limited Method for producing glass preform for single mode optical fiber

Patent Citations (5)

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Publication number Priority date Publication date Assignee Title
GB1554314A (en) * 1975-08-16 1979-10-17 Heraeus Schott Quarzschmelze Manufacture of light-conducting fibres
GB2043619A (en) * 1979-03-07 1980-10-08 Standard Telephones Cables Ltd Optical fibre and optical fibre preform manufacture
GB2109367A (en) * 1981-11-17 1983-06-02 Pirelli General Plc Manufacture of a preform for optical fibres by the rod in tube method
EP0125828A1 (en) * 1983-05-02 1984-11-21 Sumitomo Electric Industries Limited Optical fiber and process for producing the same
EP0159046A2 (en) * 1984-04-20 1985-10-23 Sumitomo Electric Industries Limited Method for producing glass preform for single mode optical fiber

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6105396A (en) * 1998-07-14 2000-08-22 Lucent Technologies Inc. Method of making a large MCVD single mode fiber preform by varying internal pressure to control preform straightness
EP0972752A1 (en) * 1998-07-14 2000-01-19 Lucent Technologies Inc. Large preform for singlemode fiber and method for making same
EP1000908A2 (en) * 1998-10-08 2000-05-17 Heraeus Quarzglas GmbH Method for producing quartz glass preform for optical fibers
EP1000908A3 (en) * 1998-10-08 2001-05-02 Heraeus Quarzglas GmbH Method for producing quartz glass preform for optical fibers
KR100345355B1 (en) * 1998-10-09 2002-07-24 신에쯔 세끼에이 가부시키가이샤 Preform for Optical fiber and manufacturing method thereof
US6460378B1 (en) * 2000-02-29 2002-10-08 Xiaoyuan Dong Collapsing a multitube assembly and subsequent optical fiber drawing in the same furnace
WO2001090010A1 (en) * 2000-05-24 2001-11-29 Heraeus Tenevo Ag Method for producing an optical fibre and blank for an optical fibre
CN1298646C (en) * 2000-05-24 2007-02-07 赫罗伊斯·坦尼沃有限责任公司 Method for producing optical fibre and blank for optical fibre
US20100034998A1 (en) * 2007-01-19 2010-02-11 Gerhard Schoetz Quartz glass tube as a semifinished product for preform and fiber manufacture, and method for making the quartz glass tube
US8544299B2 (en) * 2007-01-19 2013-10-01 Heraeus Quarzglas Gmbh & Co. Kg Quartz glass tube as a semifinished product for preform and fiber manufacture, and method for making the quartz glass tube
US20120324958A1 (en) * 2010-07-13 2012-12-27 Chen Yang Methods for manufacturing optical fiber preform and methods for manufacturing optical fiber
US9086524B2 (en) * 2010-07-13 2015-07-21 Yangtze Optical Fibre And Cable Joint Stock Limited Company Methods for manufacturing optical fiber preform and methods for manufacturing optical fiber
WO2020155707A1 (en) * 2019-01-29 2020-08-06 江苏永鼎股份有限公司 Optical fiber preform rod of large size and low loss and preparation method therefor
WO2020181788A1 (en) * 2019-03-11 2020-09-17 江苏永鼎光纤科技有限公司 Method for manufacturing optical fiber preform based on sleeve method

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