EP0000282A1 - Verbesserung von optischen Fasern und Gläsern - Google Patents

Verbesserung von optischen Fasern und Gläsern Download PDF

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Publication number
EP0000282A1
EP0000282A1 EP78300096A EP78300096A EP0000282A1 EP 0000282 A1 EP0000282 A1 EP 0000282A1 EP 78300096 A EP78300096 A EP 78300096A EP 78300096 A EP78300096 A EP 78300096A EP 0000282 A1 EP0000282 A1 EP 0000282A1
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Prior art keywords
oxide
glass
alkaline earth
earth metal
core
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EP78300096A
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English (en)
French (fr)
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EP0000282B2 (de
EP0000282B1 (de
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Keith John Beales
William James Duncan
Anthony Gladwyn Dunn
George Reginald Newns
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British Telecommunications PLC
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Post Office
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03622—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 2 layers only
    • G02B6/03627—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 2 layers only arranged - +
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C13/00—Fibre or filament compositions
    • C03C13/04—Fibre optics, e.g. core and clad fibre compositions
    • C03C13/045—Silica-containing oxide glass compositions
    • C03C13/046—Multicomponent glass compositions
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
    • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
    • G02B6/0281—Graded index region forming part of the central core segment, e.g. alpha profile, triangular, trapezoidal core

Definitions

  • the present invention relates to optical fibres and to glasses suitable for the manufacture of optical fibres.
  • the invention is especially concerned with graded index optical fibres and their production by thermal diffusion using the double crucible drawing technique.
  • the double crucible technique for drawing fibres is ideal.
  • This technique involves melting two glasses, one in a first crucible and the other in a second crucible, the first crucible being located within the second crucible. Both crucibles have drawing nozzles.
  • the fibre thus formed is a clad fibre which is capable of acting as a dielectric optical waveguide.
  • low melting point glasses are required for the double crucible technique.
  • Such glasses are however complex, containing as a rule at least three oxides, and this introduces problems in keeping the glass losses at a sufficiently low level to permit the production of satisfactory optical fibres.
  • US Patent Specification No 3 957 342 describes and claims a family of sodium borosilicate glasses of low softening point and low absorption and scatter loss which have proved highly satisfactory for the production of stepped index optical fibres.
  • the double crucible drawing technique is especially well adapted for the production of graded index fibre by thermal diffusion: see, for example, US Patent Specification No 4 040 807 and Proceedings of the Second European Conference on Optical Fibre Communications, Paris, September 1976, pages 21-26.
  • the core and clad glasses are subjected to a heat treatment which permits inter-diffusion of the mobile oxides in the two glasses, this heat treatment being carried out during the drawing operation by controlling the length of the drawing nozzle in the double crucible.
  • graded index fibre suitable for a wide range of applications can be produced by this process, but the quality is not of the very highest.
  • the present invention is concerned with a family of glasses related to those defined in US Patent Specification No 3 957 342, but modified by the addition of alkaline earth metal oxides. These glasses show considerable potential for the production of high quality graded index fibre by the double crucible method. It is believed that the oxide responsible for the gradation of refractive index is the alkaline earth metal oxide. Glass pairs for fibre core and cladding may readily be produced, the two glasses having significantly different refractive indices. If desired, the glasses may be matched so as to have substantially the same coefficient of thermal expansion, but this is not essential.
  • a four-component glass suitable for the manufacture of optical fibre having a 1 composition calculated by taking a particular notional sodium oxide-boric oxide-silica composition lying within the range defined by region A of Fig 1 of the accompanying drawings, and partially replacing sodium oxide or sodium oxide and silica by one or more alkaline earth metal oxid in such a proportion that the total content of alkaline earth metal oxide in the glass is within the range of from 0 to 20 mole per cent, the composition of the glass lying outside the region of compositions that undergo phase separation or devitrification during optical fibre production.
  • the glass of the invention preferably contains only one alkaline earth metal oxide, and that oxide is preferably calcium oxide or barium oxide.
  • any soda-boro-silicate glass falling within the region A of Fig 1 of the accompanying drawings can be modified by the addition of an alkaline earth metal oxide to form a glass suitable for use in the production of optical fibre.
  • the upper limit for silica has been set at about 70 mole per cent because above this limit difficulties in homogenisation and in melting in silica crucibles are encountered.
  • the lower limit for silica has been set at about 50 mole per cent because of poor glass durability below this value.
  • the lower limit for sodium oxide has been set at 13 mole per cent because of problems due to phase separation of the glass below this limit and .
  • the upper limit has been set at 33 mole per cent because of lack of data on glasses with higher soda content.
  • a glass according to the invention may advantageously be paired with a glass having the corresponding unsubstituted soda-boro-silicate composition to make optical fibre, the glass of the present invention being used for the core and the unsubstituted glass for the cladding.
  • the thermal expansivities of the two glasses may be matched, ie, the proportion of alkaline earth metal oxide in the core glass may be such that the thermal expansion coefficient between O°C and the glass transition temperature of the four-component glass is substantially the same as that of the corresponding soda-boro-silicate glass.
  • the alkaline earth metal oxide is calcium oxide
  • the basis of this relationship is given in detail in Example 1 below.
  • a glass optical fibre having a core and a cladding, the core comprising a first glass, according to the invention, as previously defined, and the cladding comprising a second glass of different refractive index from the first glass and having a soda-boro-silicate composition lying within the range defined by region A of Fig 1 of the accompanying drawings.
  • composition of the cladding glass is advantageously also the notional composition from which the four-component composition of the core glass is derived by substitution. This is not, however, essential.
  • the thermal expansion coefficients of the core and clad glasses are advantageously substantially equal.
  • the said optical fibre is a graded index fibre and the gradation of refractive index is produced by thermal diffusion.
  • a glass optical fibre having a core and a cladding both made of glasses according to the invention as previously defined, the refractive indices of the core and cladding glasses being different from one another.
  • the said optical fibre is a graded index fibre and the gradation of refractive index is produced by thermal diffusion.
  • the core and clad glasses contain different alkaline earth metal oxides, the oxide of the heavier metal normally being in the core glass.
  • the core glass may contain barium oxide and the cladding glass calcium oxide, or the core glass may contain calcium oxide and the cladding glass magnesium oxide.
  • a graded index glass optical fibre having a core of a glass comprising
  • the thermal expansion coefficients of the core and clad glasses may be matched.
  • Calcium oxide, barium oxide and strontium oxide all behave similarly in glasses and all of these oxides are suitable additives for the core glass of the fibre according to the invention.
  • the dependence of refractive index on alkaline earth metal oxide content is much stronger for barium oxide than for calcium oxide, so that a given molar percentage of barium oxide should give a fibre of higher numerical aperture than could be produced using the same amount of calcium oxide.
  • Magnesium oxide lowers the refractive index slightly and is therefore useful as an additive to cladding glasses.
  • Possible combinations of alkaline earth metal oxides giving the correct refractive index relationships include the following:
  • the alkali metal oxide present in the core and cladding glasses may be either sodium oxide or potassium oxide, giving a further area of choice.
  • the potash-boro-silicate glass system is in many ways similar to the soda-boro-silicate system except that the region of stable glass formation is smaller. If, for example, sodium oxide is used in the core glass and potassium oxide in the clad glass, sodium-potassium exchange can occur in the double crucible in addition to alkaline earth metal oxide diffusion. The provision of several diffusion species enables a better approach to the optimum refractive index profile to be produced.
  • One glass pair which has been tested and found to be promising is one in which the core glass contains barium oxide, sodium oxide, silica and boric oxide and the cladding glass contains calcium oxide, potassium oxide, silica and boric oxide.
  • the core glass contains barium oxide, sodium oxide, silica and boric oxide
  • the cladding glass contains calcium oxide, potassium oxide, silica and boric oxide.
  • oxides may be added to the glasses according to the invention, up to a total of about 5 mole per cent, the only limitation on these additives being that they should not cause substantial worsening of the optical properties, for example, absorption loss of the glass.
  • arsenic trioxide may be added, as described in US Patent Specification No 3 957 342, to stabilise the redox state of the glass, or alumina may be added to improve the chemical durability. The use of the latter additive may be advantageous in the case of glasses containing potassium oxide.
  • the boric oxide, sodium carbonate, potassium carbonate, alumina and silica used in Examples 1 to 4 typically contained from 0.05 to 0.2 ppm by weight of iron, 0.01 to 0.04 ppm by weight of copper, less than 0.05 ppm by weight of chromium and less thnn 0.01 ppm of other transition elements.
  • the ultra-pure calcium carbonate and barium carbonate used contained less than 100 parts by weight in 10 9 of manganese, less than 20 parts by weight in 10 9 of iron, less than 10 parts by weight in 109 of copper, less than 10 parts by weight in 10 9 of nickel, less than 30 parts by weight in 10 9 of chromium and less than 5 parts by weight in 10 9 of cobalt. Less pure materials were used in Examples 5 and 6.
  • Fig 1 of the accompanying drawings points representing two soda-boro-silicate glasses which have been used to produce graded index optical fibre by thermal diffusion with a double crucible are labelled 1 and 2, 1 being the core glass and 2 the cladding glass.
  • Graded index fibre produced from these glasses had a total optical loss of 9-15dB/km, a part of which was of unknown origin, ie, due neither to absorption loss nor to Rayleigh scatter loss..
  • the pulse broadening of this fibre was in the range of from 1-5ns/km.
  • the core displayed a ring structure of uncertain origin.
  • the numerical aperture had a typical value of 0.12. While this fibre is of use for certain applications, it is not ideal for telecommunications purposes.
  • the low pulse broadening is probably caused at least in part by inter-mode coupling which would account for the poor total loss. It is suspected that the visible ring may in some way be produced by thermal mismatch between the core and cladding glasses.
  • the diffusing species producing the graded index in this glass pair is of course sodium oxide.
  • soda-boro-silicate glasses the problem of obtaining a thermal expansion match between core and cladding end at the same time getting a reasonably large numerical aperture by obtaining a significant difference between core and cladding refractive indices is extremely difficult to solve. ,For this reason it was decided to look into the possibility of modifying the simple soda-boro-silicates by the addition of a further oxide.
  • a core glass was produced having the following composition: sodium oxide 22.30 mole per cent, boric oxide 15.00 mole per cent, silica 54.70 mole per cent, calcium oxide 8 mole per cent.
  • the glass was prepared by the method described in detail in US Patent Specification No 3 957 342, ie, appropriate batch material was melted to produce molten glass, and a mixture of carbon monoxide and carbon dioxide was bubbled through the molten glass in order simultaneously to optimise the redox state of the glass and to homogenise and dry it.
  • the glass also contained about 0.1 mole per cent of arsenic trioxide as a redox buffering oxide, as also described in US Patent Specification No 3 957 342.
  • the glass composition was derived from a notional soda-boro-silicate composition of sodium oxide 25.00 mole per cent, boric oxide 15.00 mole per cent and silica 60.00 mole per cent (indicated by point 3 in Fig 1), the calcium oxide replacing both soda and silica.
  • a graded index fibre was drawn using the four-component glass described above for the core and, for the cladding, a soda-boro-silicate glass of the composition given in the previous paragraph.
  • the fibre was drawn using a Johnson Mathey platinum double crucible with a 10cm npzzle.
  • the core diameter of the fibre was 46 microns.
  • the refractive index profile of the fibre is shown in Fig 2. This is a slightly over-diffused profile, ie, too much diffusion has occurred to give the optimal parabolic refractive index distribution.
  • the extent of diffusion ⁇ which ideally should have a value of from 0.06 to 0.08, was calculated from the measured profile to have a value of 0.20.
  • the quantity ⁇ is given by the equation: where D is the diffusion coefficient (dependent on temperature),
  • the extent of diffusion can be reduced without much difficulty, by, for example, reducing the length of the nozzle, increasing the pulling speed or decreasing the core size. Increasing the amount of diffusion is much more difficult.
  • Fig 3 shows a plot of total loss against wavelength for full numerical aperture launch. From this Figure it can be seen that the total insertion loss of the fibre at 850 to 900 nanometres is 8.2dB/km. The absorption loss at selected wavelengths is indicated on Fig 3 by a series of crosses, showing the scatter loss to be approximately 2.5dB/km which approaches the theoretically predicted loss due to Rayleigh scattering. This means that pulse width measurements on this fibre will give meaningful results. The pulse width of a one-nanosecond pulse after transmission through 1.91km of fibre is shown in Fig 4. From this it can be shown that the pulse broadening for the fibre is 2.8ns/km.
  • the numerical aperture was calculated from the refractive index profile to be 0.18. As will be seen below (Examples 5 and 6) the use of barium oxide instead of calcium oxide in the core glass gives higher numerical aperture values: the use of a higher proportion of calcium oxide has a similar but less marked effect.
  • this glass pair is an extremely good combination to use for high-bandwidth low-loss graded index fibre. Successive lengths of fibre drawn from this glass pair gave completely reproducible properties, as did fibre from different fibre patches.
  • the composition of the core glass was computed from the clad glass composition in accordance with the equation mentioned above, ie, the thermal expansivities of the core and clad glasses are matched. The matching was tested by melting samples of the two glasses, one on top of the other, in a crucible, and then cooling. annealing and sectioning the resulting composite. The sample obtained was free from cracks and exhibited only minor stress at the interface when examined in a strain viewer. This indicates that both glasses had substantially the same thermal expansion coefficient.
  • Fig 10 in terms of expansivity boric oxide and silica can be regarded as the same material so that only the variation of expansivity with sodium oxide and calcium oxide need be cohsidered.
  • the equation of a line of constant expansivity in the soda-lime-silicate system is therefore determined.
  • the equation is content of the binary soda-silicate glass having a given thermal expansion coefficient.
  • a fibre was prepared from a core glass having a composition as described in Example 1 and a cladding glass having the composition sodium oxide 25.00 mole per cent, boric oxide 12.50 mole per cent and silica 62.50 mole per cent.
  • the clad composition is represented by point 4 on Fig 1.
  • the glass was prepared as described in Example 1 and the fibre. was again drawn using a Johnson Mathey platinum double crucible with a 10cm nozzle: the core diameter was 53 microns.
  • the refractive index profile is shown in Fig 5.
  • the extent of diffusion p was calculated to be 0.05, ie, the fibre is slightly under-diffused.
  • the best loss value on this fibre was found to be 6.5dB/km at 850nm, and the pulse broadening was about 2ns/km.
  • the maximum numerical aperture was 0.197.
  • This glass pair is clearly suitable for use in the production of high-bandwidth low-loss graded index fibre.
  • Use of barium oxide instead of calcium oxide in the core should result in a higher numerical aperture.
  • EXAMPZE 3 Graded-index fibre was produced from a core glass having the composition sodium oxide 17.30 mole per cent, boric oxide 17.50 mole per cent, calcium oxide 8.00 mole per cent, silica 57.20 mole per cent and a clad glass having the composition sodium oxide 20.00 mole per cent, boric oxide 17.50 mole per cent and silica 62.50 mole per cent.
  • the glasses were prepared as described in Example 1.
  • the clad composition is represented by point 5 on Fig 1, and the core composition is derived from that composition by substitution of calcium oxide, to an extent of 8.00 mole per cent, for soda and silica.
  • the fibre was drawn using a Johnson Mathey platinum double crucible with a 10cm nozzle.
  • the core diameter of the fibre was 46 microns. Its refractive index profile is shown in Fig 6 ⁇ this is a slightly under-diffused profile. the A-value being approximately 0.04.
  • the best loss value obtained with this fibre was 6.4dB/km at 850nm.
  • a soda-boro-silicate glass having the composition sodium oxide 22.50 mole per cent, boric oxide 17.50 mole per cent and silica 60.00 mole per cent was chosen as a suitable cladding glass for graded-index fibre and this time a core composition was selected by replacing soda only, not soda and silica, by calcium oxide.
  • the core composition was sodium oxide 15.00 mole per cent, boric oxide 17.50 mole per cent, calcium oxide 7.50 mole per cent and silica 60.00 mole per cent. Both glasses were prepared as described in Example 1.
  • Fibre was drawn from this glass pair using a Johnson Mathey platinum double crucible with a 10cm nozzle.
  • the core diameter was 40 microns.
  • the refractive index profile is shown in Fig 7; the p-value was calculated to be 0.06, which is at the lower end of the ideal range.
  • the maximum numerical aperture was 0.150, and the best loss value was 9.0dB/km at 850nm.
  • this glass pair is exceptionally suitable for the production of low-loss graded-index optical fibre.
  • a core glass having the following composition was prepared: sodium oxide 19.27 mole per cent boric oxide 7.23 mole per cent, barium oxide 12.04 mole per cent, alumina 3.62 mole per cent, silica. 57.82 mole per cent.
  • the clad glass chosen had the following composition: potassium oxide 19.27 mole per cent, boric oxide 7.23 mole per cent, calcium oxide 12.04 mole per cent, alumina 3.62 mole per cent, silica 57.82 mole per cent.
  • the percentages of silica and of boric oxide are the same in core and cladding, and the molar percentages of the monovalent diffusing species (Na + and K + ) and of the divalent diffusing species (Ba2+ and Ca2+) are matched.
  • the alumina was included to improve the chemical durability of the glass.
  • the starting materials used in this Example were not of such high purity as in the previous Examples, and the gas-bubbling stage was omitted. Because of this it was not possible to obtain loss and pulse-broadening measurements on the fibre produced in this run, which was carried out purely in order to obtain a refractive index profile.
  • Fibre having a core diameter of 55 microns was drawn using a Johnson Mathey platinum double crucible with a 10cm nozzle.
  • the refractive index profile is shown in Fig 8.
  • the ⁇ -value was 0.08, the best yet obtained with this class of glasses, and the maximum numerical aperture was 0.21. It will be seen that this glass pair is extremely promising for use in the production of graded-index fibre.
  • Example 5 illustrates the use of barium oxide in the core and calcium oxide in the clad. all other components of the two glasses being the same. As in Example 5, the starting materials were not sufficiently pure for loss and pulse-broadening measurements to be carried out.
  • the core composition was sodium oxide 20.00 mole per cent. . boric oxide 10.00 mole per cent, barium oxide 10.00 mole per cent and silica 60.00 mole per cent, and the clad composition was identical except that 10.00 mole per cent of calcium oxide replaced the 10.00 mole per cent of barium oxide.
  • Fibre having a core diameter of 80 microns was drawn in an Engelhard platinum double crucible with a
  • the refractive index profile is shown in Fig 9.
  • the ⁇ -value was calculated to be about 0.02, ie, the fibre was considerably under-diffused. This is believed to be largely attributable to the fact that it was made in a crucible designed for large-core slightly-graded fibre: use of the Johnson Mathey crucible used in Examples 1 to 5 would be expected. on the basis of previous experiments, to increase significantly the extent of diffusion.
  • the maximum numerical aperture of the fibre was 0.210.

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EP78300096A 1977-06-28 1978-06-28 Verbesserung von optischen Fasern und Gläsern Expired EP0000282B2 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB2692477 1977-06-28
GB2692477 1977-06-28

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EP0000282A1 true EP0000282A1 (de) 1979-01-10
EP0000282B1 EP0000282B1 (de) 1981-08-26
EP0000282B2 EP0000282B2 (de) 1990-05-16

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EP78300096A Expired EP0000282B2 (de) 1977-06-28 1978-06-28 Verbesserung von optischen Fasern und Gläsern

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US (1) US4275951A (de)
EP (1) EP0000282B2 (de)
CA (1) CA1109083A (de)
DE (1) DE2860976D1 (de)

Cited By (2)

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DE3016116A1 (de) * 1980-04-25 1981-10-29 Nippon Sheet Glass Co. Ltd., Osaka Lichtuebertragende koerper vom stufentyp mit ausgezeichneter wasserbestaendigkeit
EP0081928A1 (de) * 1981-12-03 1983-06-22 BRITISH TELECOMMUNICATIONS public limited company Gläser, Verfahren zur Herstellung und diese enthaltende optische Glasfibern

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US4452508A (en) * 1977-06-28 1984-06-05 British Telecommunications Graded index optical fibres
JPS5851900B2 (ja) * 1978-10-06 1983-11-18 日本板硝子株式会社 高耐水性の光伝送体用ガラス
EP0018110B1 (de) * 1979-04-04 1985-10-09 The Post Office Glas für den Kern einer optischen Faser, dieses Glas enthaltende Fasern und Verfahren zur Herstellung dieses Glases
US4375312A (en) * 1980-08-07 1983-03-01 Hughes Aircraft Company Graded index waveguide structure and process for forming same
JPS6022660B2 (ja) * 1980-09-27 1985-06-03 富士写真光機株式会社 可撓性を有する光学繊維束製造用酸溶出性ガラス
US4345833A (en) * 1981-02-23 1982-08-24 American Optical Corporation Lens array
JPS57200247A (en) * 1981-05-30 1982-12-08 Toshiba Corp Glass fiber of multi-component system for optical communication
NL8103089A (nl) * 1981-06-26 1983-01-17 Philips Nv Optische vezel van het graded index type en werkwijze voor de vervaardiging daarvan.
JPS5874537A (ja) * 1981-10-28 1983-05-06 Fuji Photo Optical Co Ltd 可撓性を有する光学繊維束製造用酸溶出性ガラス
US4686195A (en) * 1986-01-16 1987-08-11 University Of Rochester Method and composition for the manufacture of gradient index glass
US4913518A (en) * 1987-10-22 1990-04-03 Corning Incorporated Fluoroborosilicate glass clad article and night vision device
US4868141A (en) * 1987-10-22 1989-09-19 Corning Incorporated Fluoroborosilicate glass
US5146534A (en) * 1991-11-12 1992-09-08 At&T Bell Laboratories SiO2 -based alkali-doped optical fiber
US6550279B1 (en) 2000-09-01 2003-04-22 Corning Incorporated Process for drawing optical fiber from a multiple crucible apparatus with a thermal gradient
US6588235B2 (en) 2001-08-30 2003-07-08 Corning Incorporated Method of centering a fiber core in a multiple-crucible method
EP1376790A1 (de) * 2002-06-28 2004-01-02 Agilent Technologies, Inc., a corporation of the State of Delaware Wellenlängenkoppler für abstimmbaren Laser
US8366573B2 (en) * 2010-03-04 2013-02-05 Hunt C Timothy Light-emitting components for arrows

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3016116A1 (de) * 1980-04-25 1981-10-29 Nippon Sheet Glass Co. Ltd., Osaka Lichtuebertragende koerper vom stufentyp mit ausgezeichneter wasserbestaendigkeit
EP0081928A1 (de) * 1981-12-03 1983-06-22 BRITISH TELECOMMUNICATIONS public limited company Gläser, Verfahren zur Herstellung und diese enthaltende optische Glasfibern
US4552850A (en) * 1981-12-03 1985-11-12 British Telecommunications Glasses and methods for making them

Also Published As

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EP0000282B2 (de) 1990-05-16
CA1109083A (en) 1981-09-15
DE2860976D1 (en) 1981-11-19
EP0000282B1 (de) 1981-08-26
US4275951A (en) 1981-06-30

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