GB1566991A - Method of forming an optical fibre blank - Google Patents
Method of forming an optical fibre blank Download PDFInfo
- Publication number
- GB1566991A GB1566991A GB1177/78A GB117778A GB1566991A GB 1566991 A GB1566991 A GB 1566991A GB 1177/78 A GB1177/78 A GB 1177/78A GB 117778 A GB117778 A GB 117778A GB 1566991 A GB1566991 A GB 1566991A
- Authority
- GB
- United Kingdom
- Prior art keywords
- tube
- glass
- bath
- blank
- optical fibre
- 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
- 238000000034 method Methods 0.000 title claims description 30
- 239000013307 optical fiber Substances 0.000 title claims description 21
- 239000011521 glass Substances 0.000 claims description 52
- 239000006060 molten glass Substances 0.000 claims description 24
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 16
- 238000010438 heat treatment Methods 0.000 claims description 12
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 11
- 238000005253 cladding Methods 0.000 claims description 11
- 239000000377 silicon dioxide Substances 0.000 claims description 8
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 239000011819 refractory material Substances 0.000 claims description 7
- 239000000835 fiber Substances 0.000 claims description 6
- 230000003287 optical effect Effects 0.000 claims description 6
- 238000000137 annealing Methods 0.000 claims description 5
- 238000001816 cooling Methods 0.000 claims description 5
- KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 claims description 4
- 229910052681 coesite Inorganic materials 0.000 claims description 4
- 229910052906 cristobalite Inorganic materials 0.000 claims description 4
- 229910002804 graphite Inorganic materials 0.000 claims description 4
- 239000010439 graphite Substances 0.000 claims description 4
- 235000012239 silicon dioxide Nutrition 0.000 claims description 4
- 229910052682 stishovite Inorganic materials 0.000 claims description 4
- 229910052905 tridymite Inorganic materials 0.000 claims description 4
- 230000001788 irregular Effects 0.000 claims description 3
- 230000000750 progressive effect Effects 0.000 claims description 3
- 230000001627 detrimental effect Effects 0.000 claims description 2
- 238000002844 melting Methods 0.000 claims description 2
- 230000008018 melting Effects 0.000 claims description 2
- 238000000926 separation method Methods 0.000 claims description 2
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 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
- C03B37/01265—Manufacture of preforms for drawing fibres or filaments starting entirely or partially from molten glass, e.g. by dipping a preform in a melt
- C03B37/01268—Manufacture of preforms for drawing fibres or filaments starting entirely or partially from molten glass, e.g. by dipping a preform in a melt by casting
-
- 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
Description
(54) METHOD OF FORMING AN OPTICAL FIBRE BLANK
(71) We, Société Anonyme dite: COMPAGNIE GENERALE D'ELECTRICITE, a
French Body Corporate of, 54, Rue La Boetie, 75382 Paris Cedex 08, France, 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:
The present invention relates to methods for forming a blank of an optical fibre and to devices for implementing these methods.
A method is known for producing a blank of an optical fibre which consists in inserting a bar of glass into a tube made of glass having a lower refractive index than that of the bar.
An optical fibre is made from this blank by heating it in a furnace to soften the tube and the bar and by stretching it longitudinally.
This method has disadvantages. Indeed, before inserting the bar in the tube, it is necessary to polish carefully the outside surface of the bar which comes in contact with the inside surface of the tube during the stretching. During stretching, it is nonetheless very difficult to obtain a flawless contact surface between the tube and the bar: there are formed on this surface numerous irregular points at which the light transmitted by the fibre is diffused, thus appreciably reducing the optical efficiency of the fibre.
Preferred implementations of the present invention mitigate these disadvantages and provide a very simple method of producing blanks from which high-efficiency optical fibres can be obtained.
The present invention provides a method of forming a blank for an optical fibre, the blank being formed by a tubular cladding constituted by a first glass surrounding a cylindrical core constituted by a second glass, the method comprising effecting successively the following operations:
- heating a first tube constituted by the first glass;
- at least partial filling of the interior of the first tube by the second molten glass, effected by immersing one end of the first tube in a bath of the second molten glass, then sucking up a column of the second glass into the first tube and, lastly removing the first tube from the bath together with the second glass contained therein;
- annealing the first tube filled with the second glass; and
- progressive cooling of the first tube filled with the second glass.
Preferably, before said heating, said first tube is disposed coaxially inside a second tube made of refractory material so as to provide radial clearance between the exterior cylindrical surface of said first tube and the interior cylindrical surface of said second tube, the first and second tubes thus being heated together and then immersed in said bath together and wherein said pressure reduction in said first tube is formed by reducing the pressure inside said second tube, said radial clearance being sufficiently small for the suction between said first and second tubes to be smaller than the suction inside said first tube.
The present invention also provides a device for producing a blank of an optical fibre, the device comprising - a first cylindrical tube constituted by a first glass disposed vertically;
- a second cylindrical tube constituted by a refractory material and disposed vertically about said first tube, the first and second tubes being coaxial, so as to provide radial clearance between the exterior cylindrical surface of the first tube and the interior cylindrical surface of the second tube, the lower end of the second tube extending inwardly to form a lip at the lower end on which the lower end of the first tube is laid;
- means for heating the first tube surrounded by the second tube;;
- means for vertically moving said tubes suitable for immersing the lower ends of these tubes in a bath of a second molten glass, said lip leaving an opening of sufficiently large diameter for the second molten glass to enter inside the first tube across its entire interior cross-section;
- heating means for melting said bath; and
- means for reducing the pressure in said second tube, said radial clearance being such that the suction of the glass from this bath between said first and second tubes, when in use is smaller than the suction inside the first tube.
The invention is described hereinbelow by way of a non-limiting example with reference to the accompanying drawing in which the single figure shows a device for performing the method in accordance with the invention.
In this figure, one end of a cylindrical glass tube 1 disposed vertically is immersed in a bath 2 of molten glass. The glass which constitutes the bath 2 has a higher refractive index than that of the glass of the tube 1. The bath 2 is disposed in a crucible 3 supported by a support 4.
A cylindrical tube 5 made of a refractory material e.g. silica is disposed round the tube 1.
The tubes 1 and 5 are coaxial so as to provide a small radial clearance between the outer cylindrical surface of the tube 1 and the inner cylindrical surface of the tube 5.
A thin sheet of carbon 6, e.g. a graphite sheet, is slid into the space corresponding to the axial clearance between the tubes 1 and 5.
The lower end of the tube 1 extends inwardly to form a lip 7 to support the lower end of the tube 1. In the example shown in the figure, the tube 5 is much lower than the tube 1 and its upper end ends in the constriction provided with a tap 8.
A vertical cylindrical furnace 9 surrounds the upper part of the tube 5. Another vertical furnace 10 surrounds the crucible 3 containing the bath 2.
The two furnaces are fixed and their axes are preferably coincident. Means, not shown, are provided to move the tube 5 and the support 4 vertically along the axis of the furnace.
These two furnaces are for example electric furnaces and the furnace 9 is provided with a system, not shown, which is suitable for making its temperature vary as a function of time.
To implement the method in accordance with the invention, a blank of an optical fibre is made by means of the device shown in the figure.
To do this, the tube 1 is inserted in the tube 5 and the carbon sheet 6 is inserted in the space provided radially between the two tubes, these insertions being effected before the formation of the lip 7 at the lower part of the tube 5. This lip 7 can be formed by well-known means.
The tube 1 surrounded by the tube 5 is then disposed in the central part of the furnaces 9 to be heated to a temperature lying between the stress point of the glass which constitutes it and its softening point.
Further. the glass contained in the crucible 3 is melted in the central part of the furnace 10 in order to form the bath 2.
The piston 4 is then raised to bring the bath 2 towards the upper part of the furnace 10 in the position shown in the figure. The tube 5 is then lowered so as to immerse the lower end of the tubes 1 and 5 in the bath 2. Due to the previous heating of the tubes, this immersion is effected without danger of breakage of the tube 1.
A vacuum pump, not shown, is connected to the upper part of the tube 5 in order to lower the pressure in this tube. A column of molten glass drawn from the bath 2 then rises in the interior volume of the tube 1 up to the upper end of this tube. The tap 8 is then closed. It should be observed that the radial clearance provided between the tubes 1 and 5 is sufficiently small for relatively little molten glass to be sucked into the space corresponding to this clearance in relation to this glass sucked inside the tube 1.
Further, the lip 7 of the tube 5 leaves an opening of sufficiently large diameter for the column of molten glass to enter freely across the entire cross-section of the tube 1. In other words the inside diameter of the lip 7 should not be smaller than the inside diameter of the tube 1.
The tube 5 is then raised so as to remove the tube 1 from the bath 2, keeping the tap 8 closed in order to maintain the reduced pressure retaining the column of glass drawn from the bath 2 in the tube 1.
The tube 5 is raised so as to place the tube 1 in the central zone of the furnace 9 in which a time varying temperature is established so as to anneal the glass constituting the tube 1 and the column drawn off. Once the glass has been annealed, the temperature of the furnace 9 is progressively reduced down to ambient temperature.
Lastly, the tube 1 is separated from the auxiliary tube 5 by breaking the latter if necessary. This separation takes place easily due to the presence of the carbon sheet 6 which prevents any sticking of the outer cylindrical surface of the tube 1 on the inner cylindncal surface of the tube 5.
Thus, a cylindrical blank is obtained which is formed by a tubular glass cladding, corresponding to the tube 1, this cladding surrounding a cylindrical glass core which oorresponds to the column drawn from the bath 2, the glass constituting the core which has a refractive index higher than that of the cladding.
It is sufficient to soften this blank in a furnace and to stretch it longitudinally to obtain an optical fibre. It is observed that the reflection surface of the fibre, i.e. the contact surface between the cladding and the core, comprises very few irregular points on which the light transmitted by the fibre is liable to be diffused. An optical fibre having high efficiency is thus obtained.
By way of an example, numerical characteristics of a device allowing a good quality optical fibre to be produced is given hereinbelow.
- -Constitution of the glass tube I SiO2 : 72%, CaO 13%, Na2O : 11%, MgO : 3% and At203: 1% (by weight).
- Constitution of the glass in the bath 2 SiO2 : 50%, B203 : 20%, CaO : 20%, Na2O : 8% and LizO : 2%.
- Outside diameter of the tube 1 : 14 mm.
- Inside diameter of the tube 5 : 15.3 mm.
Whence radial clearance : 0.65 mm.
- Thickness of the graphite sheet 6 = 0.5 mm.
- Temperature of the bath 2 : 1.020 C.
- Preheating temperature of the tube 1 : 550"C.
(Stress point of the glass of the tube 1 : 510"C).
- Annealing temperature of the tube 1 : 550"C during one hour, then cooling of 50"C per hour down to 350"C, then according to the thermal inertia of the furnace 9.
It should be observed that it is possible to perform the method in accordance with the invention without using an auxiliary tube 5. To do this, the tube 1 is heated directly in the furnace 9, then its lower end is immersed in the bath and the molten glass is sucked up from the bath 2, connecting the interior volume of the tube 1 by pipes to a vacuum source; lastly, the tube 1 filled with molten glass is annealed in conditions identical to those described hereinabove. However, in this case, the tube 1 is liable to be deformed at the moment when the column of molten glass is sucked up. Indeed, the glass of the tube 1 softens in contact with the molten glass and the reduced pressure deforms the softened tube. Such a deformation is detrimental to the optical quality of the finally obtained optical fibre.
The method is therefore preferably performed with the auxiliary tube 5 which, being made of silica, remains perfectly rigid during the forming of the blank. The tube 1 which tends to soften when the molten glass column is sucked up is then protected against the action of the reduced pressure by the tube 5. Indeed, the air pressures on the exterior and interior cylindrical surfaces of the tube 1 are then substantially identical. Thus, consequential deformation of the tube is avoided.
The method in accordance with the invention can be applied to the forming of blanks from which optical fibres for telecommunications can be obtained by stretching.
WHAT WE CLAIM IS:
1. A method of forming a blank for an optical fibre, the blank being formed by a tubular cladding constituted by a first glass surrounding a cylindrical core constituted by a second glass, the method comprising effecting successively the following operations:
- heating a first tube constituted by the first glass;
- at least partial filling of the interior of the first tube by the second molten glass, effected by immersing one end of the first tube in a bath of the second molten glass, then sucking up a column of the second glass into the first tube and, lastly, removing the first tube from the bath, together with the second glass contained therein;
- annealing the first tube filled with the second glass; and
- progressive cooling of the first tube filled with the second glass.
2. A method according to claim 1, wherein the first tube is heated to a temperature higher than the stress point of the first glass, but lower than its softening point
3. A method according to claim 1 or 2, wherein the suction of said column is effected by reducing the air pressure at the other end of the first tube.
4. A method according to claim 1 or 2, wherein, before said heating, said first tube is disposed coaxially inside a second tube made of refractory material so as to provide radial clearance between the exterior cylindrical surface of said first tube and the interior cylindrical surface of said second tube, the first and second tubes thus being heated together and then immersed in said bath together and wherein said pressure reduction in said first tube is formed by reducing the pressure inside said second tube, said radial clearance being
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (11)
1. A method of forming a blank for an optical fibre, the blank being formed by a tubular cladding constituted by a first glass surrounding a cylindrical core constituted by a second glass, the method comprising effecting successively the following operations:
- heating a first tube constituted by the first glass;
- at least partial filling of the interior of the first tube by the second molten glass, effected by immersing one end of the first tube in a bath of the second molten glass, then sucking up a column of the second glass into the first tube and, lastly, removing the first tube from the bath, together with the second glass contained therein;
- annealing the first tube filled with the second glass; and
- progressive cooling of the first tube filled with the second glass.
2. A method according to claim 1, wherein the first tube is heated to a temperature higher than the stress point of the first glass, but lower than its softening point
3. A method according to claim 1 or 2, wherein the suction of said column is effected by reducing the air pressure at the other end of the first tube.
4. A method according to claim 1 or 2, wherein, before said heating, said first tube is disposed coaxially inside a second tube made of refractory material so as to provide radial clearance between the exterior cylindrical surface of said first tube and the interior cylindrical surface of said second tube, the first and second tubes thus being heated together and then immersed in said bath together and wherein said pressure reduction in said first tube is formed by reducing the pressure inside said second tube, said radial clearance being
sufficiently small for the suction between said first and second tubes to be smaller than to the suction inside said first tube.
5. A method according to claim 4, wherein a carbon sheet is interposed in the space corresponding to said radial clearance.
6. A method of forming a blank of an optical fibre substantially as herein described with reference to the accompanying drawing.
7. A device for producing a blank of an optical fibre the device comprising:
- a first cylindrical tube constituted by a first glass disposed vertically;
- a second cylindrical tube constituted by a refractory material and disposed vertically about said first tube, the first and second tubes being coaxial, so as to provide radial clearance between the exterior cylindrical surface of the first tube and the interior cylindrical surface of the second tube, the lower end of the second tube extending inwardly to form a lip at the lower end on which the lower end of the first tube is laid;
- means for heating the first tube surrounded by the second tube;;
- means for vertically moving said tubes suitable for immersing the lower ends of these tubes in a bath of a second molten glass, said lip leaving an opening of sufficiently large diameter for the second molten glass to enter inside the first tube across its entire interior cross-section;
- heating means for obtaining the melting of said bath; and
- means for reducing the pressure in said second tube, said radial clearance being such that the suction of the glass from this bath between said first and second tubes, when in use, is smaller than the suction inside the first tube.
8. A device according to claim 7, also comprising a carbon sheet disposed in the space corresponding to said radial clearance.
9. A device according to claim 8, wherein said carbon sheet is a sheet of graphite.
10. A device according to claim 7. 8 or 9, wherein said refractory material constituting the second tube is silica.
11. A device for producing a blank of an optical fibre substantially as herein described with reference to and as illustrated in the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7701701A FR2377979A1 (en) | 1977-01-21 | 1977-01-21 | METHOD AND DEVICE FOR MAKING A BLANKET OF OPTICAL FIBER |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1566991A true GB1566991A (en) | 1980-05-08 |
Family
ID=9185765
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1177/78A Expired GB1566991A (en) | 1977-01-21 | 1978-01-12 | Method of forming an optical fibre blank |
Country Status (5)
| Country | Link |
|---|---|
| BE (1) | BE862745A (en) |
| CH (1) | CH619201A5 (en) |
| FR (1) | FR2377979A1 (en) |
| GB (1) | GB1566991A (en) |
| IT (1) | IT1092064B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0474919A1 (en) * | 1990-09-10 | 1992-03-18 | Corning Incorporated | Casting core/clad glass preforms |
-
1977
- 1977-01-21 FR FR7701701A patent/FR2377979A1/en active Granted
-
1978
- 1978-01-09 BE BE1008633A patent/BE862745A/en not_active IP Right Cessation
- 1978-01-11 CH CH27178A patent/CH619201A5/en not_active IP Right Cessation
- 1978-01-12 GB GB1177/78A patent/GB1566991A/en not_active Expired
- 1978-01-20 IT IT19463/78A patent/IT1092064B/en active
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0474919A1 (en) * | 1990-09-10 | 1992-03-18 | Corning Incorporated | Casting core/clad glass preforms |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2377979A1 (en) | 1978-08-18 |
| FR2377979B1 (en) | 1982-10-01 |
| IT7819463A0 (en) | 1978-01-20 |
| IT1092064B (en) | 1985-07-06 |
| CH619201A5 (en) | 1980-09-15 |
| BE862745A (en) | 1978-07-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed [section 19, patents act 1949] | ||
| PCNP | Patent ceased through non-payment of renewal fee |