CA2436579C - A process for making rare earth doped optical fibre - Google Patents
A process for making rare earth doped optical fibre Download PDFInfo
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- CA2436579C CA2436579C CA002436579A CA2436579A CA2436579C CA 2436579 C CA2436579 C CA 2436579C CA 002436579 A CA002436579 A CA 002436579A CA 2436579 A CA2436579 A CA 2436579A CA 2436579 C CA2436579 C CA 2436579C
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- 238000000034 method Methods 0.000 title claims abstract description 92
- 230000008569 process Effects 0.000 title claims abstract description 78
- 229910052761 rare earth metal Inorganic materials 0.000 title claims abstract description 68
- 150000002910 rare earth metals Chemical class 0.000 title claims abstract description 52
- 239000013307 optical fiber Substances 0.000 title claims description 18
- 239000000835 fiber Substances 0.000 claims abstract description 54
- YBMRDBCBODYGJE-UHFFFAOYSA-N germanium dioxide Chemical compound O=[Ge]=O YBMRDBCBODYGJE-UHFFFAOYSA-N 0.000 claims abstract description 42
- 238000005245 sintering Methods 0.000 claims abstract description 40
- 239000004071 soot Substances 0.000 claims abstract description 40
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 38
- 230000008021 deposition Effects 0.000 claims abstract description 21
- 150000002500 ions Chemical class 0.000 claims abstract description 21
- 238000001035 drying Methods 0.000 claims abstract description 16
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 14
- 230000018044 dehydration Effects 0.000 claims abstract description 13
- 238000006297 dehydration reaction Methods 0.000 claims abstract description 13
- 230000003647 oxidation Effects 0.000 claims abstract description 12
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 12
- 239000000758 substrate Substances 0.000 claims abstract description 8
- 230000000994 depressogenic effect Effects 0.000 claims abstract description 7
- 230000007547 defect Effects 0.000 claims abstract description 6
- 239000010410 layer Substances 0.000 claims description 53
- 238000009826 distribution Methods 0.000 claims description 37
- 239000000203 mixture Substances 0.000 claims description 31
- 239000012792 core layer Substances 0.000 claims description 27
- 238000000151 deposition Methods 0.000 claims description 27
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 20
- -1 germanium halide Chemical class 0.000 claims description 20
- 239000001301 oxygen Substances 0.000 claims description 20
- 229910052760 oxygen Inorganic materials 0.000 claims description 20
- 238000005253 cladding Methods 0.000 claims description 19
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 16
- IEXRMSFAVATTJX-UHFFFAOYSA-N tetrachlorogermane Chemical compound Cl[Ge](Cl)(Cl)Cl IEXRMSFAVATTJX-UHFFFAOYSA-N 0.000 claims description 16
- 229910006113 GeCl4 Inorganic materials 0.000 claims description 13
- 230000003287 optical effect Effects 0.000 claims description 13
- 229910002651 NO3 Inorganic materials 0.000 claims description 11
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 11
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 10
- 239000011521 glass Substances 0.000 claims description 10
- 238000010438 heat treatment Methods 0.000 claims description 9
- 238000010348 incorporation Methods 0.000 claims description 9
- 150000003839 salts Chemical class 0.000 claims description 9
- 239000012159 carrier gas Substances 0.000 claims description 8
- 239000001307 helium Substances 0.000 claims description 8
- 229910052734 helium Inorganic materials 0.000 claims description 8
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims description 8
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 claims description 7
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 7
- 229910052782 aluminium Inorganic materials 0.000 claims description 7
- 239000000460 chlorine Substances 0.000 claims description 7
- 229910052801 chlorine Inorganic materials 0.000 claims description 7
- 239000002904 solvent Substances 0.000 claims description 7
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
- 159000000013 aluminium salts Chemical class 0.000 claims description 6
- 229910000329 aluminium sulfate Inorganic materials 0.000 claims description 6
- 230000003321 amplification Effects 0.000 claims description 6
- 238000009792 diffusion process Methods 0.000 claims description 6
- 239000011261 inert gas Substances 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 6
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 5
- 239000004411 aluminium Substances 0.000 claims description 5
- 230000008859 change Effects 0.000 claims description 5
- 229910052732 germanium Inorganic materials 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 238000005086 pumping Methods 0.000 claims description 2
- VZGDMQKNWNREIO-UHFFFAOYSA-N tetrachloromethane Chemical group ClC(Cl)(Cl)Cl VZGDMQKNWNREIO-UHFFFAOYSA-N 0.000 claims 6
- 150000000917 Erbium Chemical class 0.000 claims 4
- AZDRQVAHHNSJOQ-UHFFFAOYSA-N alumane Chemical class [AlH3] AZDRQVAHHNSJOQ-UHFFFAOYSA-N 0.000 claims 3
- 238000007796 conventional method Methods 0.000 claims 3
- 239000000243 solution Substances 0.000 abstract description 25
- 238000007598 dipping method Methods 0.000 abstract description 9
- JLDSOYXADOWAKB-UHFFFAOYSA-N aluminium nitrate Chemical compound [Al+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O JLDSOYXADOWAKB-UHFFFAOYSA-N 0.000 abstract description 8
- 239000002019 doping agent Substances 0.000 abstract description 7
- VSCWAEJMTAWNJL-UHFFFAOYSA-K aluminium trichloride Chemical compound Cl[Al](Cl)Cl VSCWAEJMTAWNJL-UHFFFAOYSA-K 0.000 abstract description 6
- 230000001476 alcoholic effect Effects 0.000 abstract description 4
- 239000007864 aqueous solution Substances 0.000 abstract description 4
- 230000015572 biosynthetic process Effects 0.000 abstract description 3
- 238000002791 soaking Methods 0.000 abstract 1
- 229910052691 Erbium Inorganic materials 0.000 description 12
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical compound [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 description 12
- 238000012545 processing Methods 0.000 description 6
- 238000001704 evaporation Methods 0.000 description 5
- 230000008020 evaporation Effects 0.000 description 5
- 229910001873 dinitrogen Inorganic materials 0.000 description 4
- HDGGAKOVUDZYES-UHFFFAOYSA-K erbium(iii) chloride Chemical compound Cl[Er](Cl)Cl HDGGAKOVUDZYES-UHFFFAOYSA-K 0.000 description 4
- 239000000146 host glass Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000003153 chemical reaction reagent Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052698 phosphorus Inorganic materials 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
- 241001671983 Pusa Species 0.000 description 2
- 229910020169 SiOa Inorganic materials 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 238000001506 fluorescence spectroscopy Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000011574 phosphorus Substances 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 235000012239 silicon dioxide Nutrition 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 229910017544 NdCl3 Inorganic materials 0.000 description 1
- 239000013543 active substance Substances 0.000 description 1
- 150000001399 aluminium compounds Chemical class 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 150000001805 chlorine compounds Chemical class 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000006735 deficit Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 150000002123 erbium compounds Chemical class 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 150000004820 halides Chemical class 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- ATINCSYRHURBSP-UHFFFAOYSA-K neodymium(iii) chloride Chemical compound Cl[Nd](Cl)Cl ATINCSYRHURBSP-UHFFFAOYSA-K 0.000 description 1
- 230000006855 networking Effects 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 230000005693 optoelectronics Effects 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 238000004017 vitrification Methods 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
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01807—Reactant delivery systems, e.g. reactant deposition burners
- C03B37/01838—Reactant delivery systems, e.g. reactant deposition burners for delivering and depositing additional reactants as liquids or solutions, e.g. for solution doping of the deposited glass
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01807—Reactant delivery systems, e.g. reactant deposition burners
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01853—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
- C03B2201/12—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with fluorine
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
- C03B2201/28—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with phosphorus
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
- C03B2201/31—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with germanium
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
- C03B2201/34—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with rare earth metals, i.e. with Sc, Y or lanthanides, e.g. for laser-amplifiers
-
- 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
- C03B2201/34—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with rare earth metals, i.e. with Sc, Y or lanthanides, e.g. for laser-amplifiers
- C03B2201/36—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with rare earth metals, i.e. with Sc, Y or lanthanides, e.g. for laser-amplifiers doped with rare earth metals and aluminium, e.g. Er-Al co-doped
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
- Y02P40/57—Improving the yield, e-g- reduction of reject rates
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Geochemistry & Mineralogy (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Chemical & Material Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Lasers (AREA)
- Glass Compositions (AREA)
- Manufacture, Treatment Of Glass Fibers (AREA)
Abstract
The present invention provides an improved process for making rare earth doped preforms and fibres by a combination of MCVD technique and solution doping method, said method comprising developing matched or depressed clad structure inside a silica glass substrate tube followed by deposition of unsintered particulate layer containing GeO2 and P2O5 for formation of the core and solution doping by soaking the porous soot layer into an alcoholic/aqueous solution of RE-salts containing co-dopants like AlCl3 / Al(NO3)3 in definite proportion, controlling the porosity of the soot, dipping period, strength of the solution and the proportion of the codopants to achieve the desired RE ion concentration in the core and minimise the core clad boundary defects and followed by drying, oxidation, dehydration and sintering of the RE containing porous deposit and collapsing at a high temperature to produce the preform and overladding with silica tubes of suitable dimensions and fibre drawing to produce fibres.
Description
A PROCESS FOR MAKING RARE EARTH DOPED OPTICAL FIBRE
Technical Field The present invention relates to a Process for Making Rare Earth Doped Optical Fibre.
Background Art Rare-earth (RE) doped optical fibres have shown great potential for a number of applications including amplifiers, fibre lasers and sensors. Oxides of rare earths are doped into the core of such fibres as the active substance. Lasing and amplification have been demonstrated at several wavelengths with the incorporation of various rare-earths but for 1o telecommunication applications erbium doped fibre (EDF) remains the most important since the operating wavelength matches with the third low loss optical window.
Erbium doped fibre amplifier (EDFA) operating around 1.53 ~,m low loss window is playing the key role in the present day high capacity communication systems.
It is able to amplify the optical signal directly independent of modulation format.
Optoelectronic repeaters so long used in these systems were 3R devices with the limitations of amplifying the signal in discrete wavelengths. EDFA has the capability to amplify simultaneous optical channels in a single fibre, which has enabled the implementation of WDM
(wavelength division multiplexing) technology with the potential of increasing the bandwidth of long distance transmission systems from Gb/s to Tb/s ranges. It thus exhibits 2o high gain, large bandwidth, low noise, polarisation insensitive gain, substantially reduced cross talk problems and low insertion losses at the operating wavelengths. The success of future high capacity optical networking and transmission systems will depend significantly on the development of efficient EDFA.
Reference may be made to Townsend J.E., Poole S.B., and Payne D.N., Electronics Letters, Vol. 23 (1987) p-329, ' Solution-doping technique for fabrication of rare-earth-doped optical fibre' wherein, the MCVD process is used to fabricate the preform with a step index profile and desired core-clad structure while solution doping is adopted for incorporation of the active ion. The steps involved in the process are as follows:
i. A conventional cladding doped with P205 and F is deposited within a high silica 3o glass substrate tube to develop matched clad or depressed clad type structure.
ii. The core layers of predetermined composition containing index-raising dopant like Ge02 are deposited at a lower temperature to form unsintered porous soot.
iii. The tube with the deposit is immersed into an aqueous solution of the dopant precursor (typical concentration 0.1 M) up to 1 hour. Any soluble form of the dopant ion is suitable for preparation of the solution although rare earth halides have been mostly used.
Technical Field The present invention relates to a Process for Making Rare Earth Doped Optical Fibre.
Background Art Rare-earth (RE) doped optical fibres have shown great potential for a number of applications including amplifiers, fibre lasers and sensors. Oxides of rare earths are doped into the core of such fibres as the active substance. Lasing and amplification have been demonstrated at several wavelengths with the incorporation of various rare-earths but for 1o telecommunication applications erbium doped fibre (EDF) remains the most important since the operating wavelength matches with the third low loss optical window.
Erbium doped fibre amplifier (EDFA) operating around 1.53 ~,m low loss window is playing the key role in the present day high capacity communication systems.
It is able to amplify the optical signal directly independent of modulation format.
Optoelectronic repeaters so long used in these systems were 3R devices with the limitations of amplifying the signal in discrete wavelengths. EDFA has the capability to amplify simultaneous optical channels in a single fibre, which has enabled the implementation of WDM
(wavelength division multiplexing) technology with the potential of increasing the bandwidth of long distance transmission systems from Gb/s to Tb/s ranges. It thus exhibits 2o high gain, large bandwidth, low noise, polarisation insensitive gain, substantially reduced cross talk problems and low insertion losses at the operating wavelengths. The success of future high capacity optical networking and transmission systems will depend significantly on the development of efficient EDFA.
Reference may be made to Townsend J.E., Poole S.B., and Payne D.N., Electronics Letters, Vol. 23 (1987) p-329, ' Solution-doping technique for fabrication of rare-earth-doped optical fibre' wherein, the MCVD process is used to fabricate the preform with a step index profile and desired core-clad structure while solution doping is adopted for incorporation of the active ion. The steps involved in the process are as follows:
i. A conventional cladding doped with P205 and F is deposited within a high silica 3o glass substrate tube to develop matched clad or depressed clad type structure.
ii. The core layers of predetermined composition containing index-raising dopant like Ge02 are deposited at a lower temperature to form unsintered porous soot.
iii. The tube with the deposit is immersed into an aqueous solution of the dopant precursor (typical concentration 0.1 M) up to 1 hour. Any soluble form of the dopant ion is suitable for preparation of the solution although rare earth halides have been mostly used.
iv. Following immersion, the tube is rinsed with acetone and remounted on lathe.
v. The core layer containing the RE is dehydrated and sintered to produce a clear glassy layer. Dehydration is carried out a temperature of 600°C by using chlorine.
The level of OH- is reduced below lppm using C12 / OZ ratio of 5:2 provided the drying time exceeds 30 min.
vi. Collapsing in the usual manner to produce a solid glass rod called preform.
vii. Fibre drawing is conventional.
Reference may also be made to DiGiovanni D.J., SPIE Vol. 1373 (1990) p-2 "Fabrication of rare-earth-doped optical fibre' wherein the substrate tube with the porous core layer is to soaked in an aqueous or alcoholic solution containing a nitrate or chloride of the desired RE ion. The tube is drained, dried and remounted on lathe. The dehydration is carried out by flowing dry chlorine through the tube at about 900°C for an hour.
After dehydration, the layer is sintered and the tube is collapsed to be drawn to fibre.
Another reference may be made to Ainslie B.J., Craig S.P., Davey S.T., and Wakefield B., Material Letters, Vol. 6, (1988) p-139, " The fabrication, assessment and optical properties of high- concentration Nd3+ and Er3+ doped silica based fibres" wherein optical fibres based on A1203 - PZOS. - Si02 host glass doped with high concentrations of Nd3+ and Er3+
have been fabricated by solution method and quantified. Following the deposition of cladding layers P205 doped silica soot is deposited at lower temperature. The prepared 2o tubes are soaked in an alcoholic solution of 1M Al(NO3)3 + various concentrations of ErCl3 and NdCl3 for 1 hour. The tubes are subsequently blown dry and collapsed to make preforms in the usual way. A1 is said to be a key component in producing high RE
concentrations in the core centre without clustering effect. It is further disclosed that Al and RE profile lock together in some way which retards the volatility of RE
ion. The dip at the core centre is observed both for P and GeOa.
Reference may also be made to US Patent No. 5,005,175 (1991) by Desuvire et al., 'Erbium doped fibre amplifier" wherein the fibre for the optical amplifer comprises a single mode fibre doped with erbium in the core having a distribution profile of the RE ion whose radius is less than 1.9 ~,m while the radius of the mode of the pump signal exceeds 3 ~.m. The numerical aperture (NA) of the fibres varies from 0.2 to 0.35 and the core is doped with both A1 and Ge oxides to increase the efficiency. As the radius of the Er doped core region is equal to or less than the radius of the pump mode of the fibre it is claimed that each atom of erbium in the core cross section is exposed to substantially equal levels of the high intensity portion of the pump mode. The fibre with such design is reported to a v~ ~ ~ ~ r .,. . - ~e . - '.
have increased gain and lower threshold compared to the conventional Er doped fibre amplifiers where the radius of the Er doped core is large compared to the radius of the pump mode so that the erbium atoms at the edge of the core do not see a sufficient flux of the pump photons to yield a net gain.
According to US Patent No. 5,491,581 (1996) by G.S. Roba, 'Rare earth doped optical fibre amplifiers' wherein high germania concentration in the core used to enhance the NA
of the fibre is reported to result in generation of residual stress at the core-clad interface due to difference in viscosity and thermal expansion coefficient. Residual stress in turn is believed to produce undesirable increase in background loss of the fibre.
According to US Patent No. 5,778,129 (1998) by Shukunami et.al., 'Doped optical fibre having core and clad structure are used for increasing the amplification band of an optical amplifier using the optical fibre' wherein the porous core layer is deposited after developing the cladding inside a quartz tube by MCVD process and solution doping method is employed to impregnate Er as the active ion into the porous core to be followed by vitrification and collapsing for making the preform. The solution also contains compound of Al, say chlorides, for codoping of the core with Al in order to expand the amplification band. The Er and Al doped glass constitutes first region of the core.
Surrounding this are the second and third regions of the core. The third region contains Ge to increase the refractive index. The second region has an impurity concentration lower 2o than both those of first and third regions and consequently low RI also.
The second region acts as a barrier to prevent diffusion of the active dopant.
Reference may also be made to US Patent No. 5474588 (1995) by Tanaka, D. et.
al., 'Solution doping of a silica with erbium, aluminium and phosphorus to form an optical fibre' wherein a manufacturing method for Er doped silica is described in which silica glass soot is deposited on a seed rod ( VAD apparatus ) to form a porous soot preform, dipping the said preform into an ethanol solution containing an erbium compound, an aluminium compound and a phosphoric ester, and desiccating said preform to form Er, Al and P containing soot preform. The desiccation is carried out for a period ofe24 -240 hours at a temperature of 60° - 70°C in an atmosphere of nitrogen gas or inert gas. This desiccated soot preform is heated and dehydrated for a period of 2.5 - 3.5 hours at a temperature of 950° - 1050°C in an atmosphere of helium gas containing 0.25 to 0.35%
chlorine gas and further heated for a period of 3-5 hours at a temperature of 1400 ° -1600°C to render it transparent, thereby forming an erbium doped glass preform. The segregation of AlCl3 in the preform formation process is suppressed due to the presence of phosphorus and as a result the doping concentration of A1 ions can be set to a high level >3 wt%). The dopant concentration and component ratio of Er, A1 and P ions are claimed to be extremely accurate and homogeneous in the radial as well as in longitudinal directions.
A few of the drawbacks of the above mentioned processes are as follows:
1. Step like RE distribution profile is obtained in the core resulting to poor overlap between the pump signal and the RE ions which lowers the pump efficiency.
2., Step like RE distribution requires high numerical aperture (NA) of the core or confinement of the RE in the central region (say 50% of the total core area) for increase to in pump efficiency which in turn leads to the following disadvantages:
i) Doping of RE 'only in selected portion of the core is extremely difficult and affects the repeatability of the process due to the sensitivity of the method to process parameters during various stages of processing such as deposition, solution doping, drying and sintering.
ii) Increasing the NA of the fibre with simultaneously reducing the core area requires high germania concentration in a small core which enhances the possibility of formation of the dip at the centre due to evaporation during sintering &
collapsing.
iii) For preforms with high NA (>0.20) high germania concentration in the core lowers 2o the viscosity of the glass and makes the process very sensitive to temperature especially during the stages of porous soot layer deposition and sintering.
iv) Increase in temperature sensitivity during porous soot deposition leads to variation in composition and soot density along the length of the tube.
v) High germania concentration in the core results to generation of residual stress at the core-clad interface due to difference in viscosity and thermal expansion coefficient. Residual stress produces tmdesirable increase in background loss of the fibre.
vi) Residual stress is believed to introduce polarisation mode dispersion (PMD) which results in serious capacity impairments including pulse broadening. Since the 3o magnitude of PMD at a given wavelength is not stable passive compensation becomes impossible.
v. The core layer containing the RE is dehydrated and sintered to produce a clear glassy layer. Dehydration is carried out a temperature of 600°C by using chlorine.
The level of OH- is reduced below lppm using C12 / OZ ratio of 5:2 provided the drying time exceeds 30 min.
vi. Collapsing in the usual manner to produce a solid glass rod called preform.
vii. Fibre drawing is conventional.
Reference may also be made to DiGiovanni D.J., SPIE Vol. 1373 (1990) p-2 "Fabrication of rare-earth-doped optical fibre' wherein the substrate tube with the porous core layer is to soaked in an aqueous or alcoholic solution containing a nitrate or chloride of the desired RE ion. The tube is drained, dried and remounted on lathe. The dehydration is carried out by flowing dry chlorine through the tube at about 900°C for an hour.
After dehydration, the layer is sintered and the tube is collapsed to be drawn to fibre.
Another reference may be made to Ainslie B.J., Craig S.P., Davey S.T., and Wakefield B., Material Letters, Vol. 6, (1988) p-139, " The fabrication, assessment and optical properties of high- concentration Nd3+ and Er3+ doped silica based fibres" wherein optical fibres based on A1203 - PZOS. - Si02 host glass doped with high concentrations of Nd3+ and Er3+
have been fabricated by solution method and quantified. Following the deposition of cladding layers P205 doped silica soot is deposited at lower temperature. The prepared 2o tubes are soaked in an alcoholic solution of 1M Al(NO3)3 + various concentrations of ErCl3 and NdCl3 for 1 hour. The tubes are subsequently blown dry and collapsed to make preforms in the usual way. A1 is said to be a key component in producing high RE
concentrations in the core centre without clustering effect. It is further disclosed that Al and RE profile lock together in some way which retards the volatility of RE
ion. The dip at the core centre is observed both for P and GeOa.
Reference may also be made to US Patent No. 5,005,175 (1991) by Desuvire et al., 'Erbium doped fibre amplifier" wherein the fibre for the optical amplifer comprises a single mode fibre doped with erbium in the core having a distribution profile of the RE ion whose radius is less than 1.9 ~,m while the radius of the mode of the pump signal exceeds 3 ~.m. The numerical aperture (NA) of the fibres varies from 0.2 to 0.35 and the core is doped with both A1 and Ge oxides to increase the efficiency. As the radius of the Er doped core region is equal to or less than the radius of the pump mode of the fibre it is claimed that each atom of erbium in the core cross section is exposed to substantially equal levels of the high intensity portion of the pump mode. The fibre with such design is reported to a v~ ~ ~ ~ r .,. . - ~e . - '.
have increased gain and lower threshold compared to the conventional Er doped fibre amplifiers where the radius of the Er doped core is large compared to the radius of the pump mode so that the erbium atoms at the edge of the core do not see a sufficient flux of the pump photons to yield a net gain.
According to US Patent No. 5,491,581 (1996) by G.S. Roba, 'Rare earth doped optical fibre amplifiers' wherein high germania concentration in the core used to enhance the NA
of the fibre is reported to result in generation of residual stress at the core-clad interface due to difference in viscosity and thermal expansion coefficient. Residual stress in turn is believed to produce undesirable increase in background loss of the fibre.
According to US Patent No. 5,778,129 (1998) by Shukunami et.al., 'Doped optical fibre having core and clad structure are used for increasing the amplification band of an optical amplifier using the optical fibre' wherein the porous core layer is deposited after developing the cladding inside a quartz tube by MCVD process and solution doping method is employed to impregnate Er as the active ion into the porous core to be followed by vitrification and collapsing for making the preform. The solution also contains compound of Al, say chlorides, for codoping of the core with Al in order to expand the amplification band. The Er and Al doped glass constitutes first region of the core.
Surrounding this are the second and third regions of the core. The third region contains Ge to increase the refractive index. The second region has an impurity concentration lower 2o than both those of first and third regions and consequently low RI also.
The second region acts as a barrier to prevent diffusion of the active dopant.
Reference may also be made to US Patent No. 5474588 (1995) by Tanaka, D. et.
al., 'Solution doping of a silica with erbium, aluminium and phosphorus to form an optical fibre' wherein a manufacturing method for Er doped silica is described in which silica glass soot is deposited on a seed rod ( VAD apparatus ) to form a porous soot preform, dipping the said preform into an ethanol solution containing an erbium compound, an aluminium compound and a phosphoric ester, and desiccating said preform to form Er, Al and P containing soot preform. The desiccation is carried out for a period ofe24 -240 hours at a temperature of 60° - 70°C in an atmosphere of nitrogen gas or inert gas. This desiccated soot preform is heated and dehydrated for a period of 2.5 - 3.5 hours at a temperature of 950° - 1050°C in an atmosphere of helium gas containing 0.25 to 0.35%
chlorine gas and further heated for a period of 3-5 hours at a temperature of 1400 ° -1600°C to render it transparent, thereby forming an erbium doped glass preform. The segregation of AlCl3 in the preform formation process is suppressed due to the presence of phosphorus and as a result the doping concentration of A1 ions can be set to a high level >3 wt%). The dopant concentration and component ratio of Er, A1 and P ions are claimed to be extremely accurate and homogeneous in the radial as well as in longitudinal directions.
A few of the drawbacks of the above mentioned processes are as follows:
1. Step like RE distribution profile is obtained in the core resulting to poor overlap between the pump signal and the RE ions which lowers the pump efficiency.
2., Step like RE distribution requires high numerical aperture (NA) of the core or confinement of the RE in the central region (say 50% of the total core area) for increase to in pump efficiency which in turn leads to the following disadvantages:
i) Doping of RE 'only in selected portion of the core is extremely difficult and affects the repeatability of the process due to the sensitivity of the method to process parameters during various stages of processing such as deposition, solution doping, drying and sintering.
ii) Increasing the NA of the fibre with simultaneously reducing the core area requires high germania concentration in a small core which enhances the possibility of formation of the dip at the centre due to evaporation during sintering &
collapsing.
iii) For preforms with high NA (>0.20) high germania concentration in the core lowers 2o the viscosity of the glass and makes the process very sensitive to temperature especially during the stages of porous soot layer deposition and sintering.
iv) Increase in temperature sensitivity during porous soot deposition leads to variation in composition and soot density along the length of the tube.
v) High germania concentration in the core results to generation of residual stress at the core-clad interface due to difference in viscosity and thermal expansion coefficient. Residual stress produces tmdesirable increase in background loss of the fibre.
vi) Residual stress is believed to introduce polarisation mode dispersion (PMD) which results in serious capacity impairments including pulse broadening. Since the 3o magnitude of PMD at a given wavelength is not stable passive compensation becomes impossible.
3. Dehydration and sintering of the RE chloride containing soot layer is critical because it alters the composition by vaporisation and also diffusion of the dopant salt as well as Ge02 present in the core.
Objects of the invention The main obj ect of the present invention is to provide a process for making Rare Earth doped optical fibre, which obviates the drawbacks as detailed above.
Another object of the present invention is to provide fibres possessing controlled 5 distribution of RE, more particularly Erbium in the doped region similar to the pump beam intensity distribution in the fibre with maximum concentration at the centre so that the overlapping between the two is considerably improved.
Still another object of the present invention is to provide fibres in which the pump beam has a radius of distribution equal to or greater than the radius of distribution of RE ions in 1o the core to increase the chances of all the active ions getting exposed to the pump light, consequently increasing the pump conversion efficiency in the fibre.
Yet another object of the present invention is to provide a method of controlling the Gaussian RE distribution profile along the radial direction in the core.
Still another object of the present invention is to achieve high optical gain in the fibres for NA value close to 0.20 only thus avoiding wide variation in composition between the core and cladding glass to eliminate problems like residual stress and PMD.
Yet another object of the present invention is to develop erbium doped fibres suitable for amplification of the input signal with NA and mode field diameter not widely different from signal transmitting fibre for ease of splice.
2o Still another object of the present invention is to reduce the possibility of change in composition of the particulate core layer due to evaporation of the RE salt during drying and sintering .
Yet another object of the present invention is to reduce the quantity of germanium halide required to achieve the desired NA in the fibre.
One more object of the present invention is to provide a process where the numerical aperture of the fibre is varied from 0.10 to 0.30 maintaining RE concentration in the core between 50 to 6000 ppm along with variation in RE distribution profile in the doped region to produce fibres suitable for application as amplifiers, fibre lasers and sensors for different purposes.
3o Summary of the invention The novelty of the present invention lies in controlling the concentration profile of RE ion in the collapsed preform by minimising evaporation of the RE salt and also preventing diffusion of the rare earth ion due to subsequent heat treatment. The optimum soot density to achieve this objective is estimated to lie between 0.3 to 0.5 after deposition. The inventive step lies in transformation of the RE salts to oxides by gradually heating the tube to a higher temperature maintaining an oxidising atmosphere inside, thereby minimising the possibility of evaporation of RE during subsequent processing as the oxide has a very high melting temperature compared to halide/nitrate salts. This step also helps to remove the solvent trapped within the porous layer. The inventive step also includes increasing the temperature of the RE containing porous layer gradually in steps of 50 to 200°C up to the sintering temperature and above for sintering and further fixing of the RE
ions in their desired sites. The steps will depend on the host glass composition and Er/Al concentration of the core layer. The incorporation efficiency of the RE from the solution to the core l0 layer thus increases appreciably making the process more efficient and economic. The RE
distribution along the transverse direction in the core will depend on the density of the porous soot layer, dipping period and the processing conditions during oxidation, sintering and collapsing.
The sintering of the porous core layer in Ge02 rich atmosphere along with the addition of oxygen and helium is another inventive step of the process which reduces the quantity of GeCl4 required to achieve the desired NA and adds to the economy of the process. At temperatures between 200° to 1400° C during the sintering step pure GeCl4 is supplied with the input oxygen, the quantity of which depends on the NA desired in the fibre. The sintering is continued by gradually raising the temperature till a clear glassy layer is formed.
Detailed Description of the Invention Accordingly the present invention provides an improved process for making rare earth doped optical fibre which comprises (a) providing deposition of P205 and F
doped synthetic cladding within a silica glass substrate tube to obtain matched or depressed clad type structure, (b) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of 1200-1400°C, (c) maintaining Pa05 and Ge02 concentrations from 0.5 to 5.0 mol% and 3.0 to 25.0 mol% in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, (d) immersing the tube containing the porous soot layer into a solution containing RE salt in 3o the concentration range of 0.002M to 0.25 M with or without aluminium salt of the concentration range 0.05 M to 1.25 M for a period of 1 to 2 hours, (e) draining the solution out at a rate in the range of 10-50 cc/min, (f) drying the porous layer by flowing dry nitrogen or any other inert gas through the tube, (g) heating the tube gradually in the presence of oxygen at a temperature in the range of 600-1100°C, (h) dehydrating the core layer of the tube at a temperature in the range of 800-1200°C and in presence of excess C12, (i) sintering the core layer in the presence of a mixture of oxygen and helium in the temperature range of 1400 to 1900°C, (j) collapsing the tube at a temperature in the range of 2000-2300°C to obtain a preform, (k) overcladding the preform with silica tube, (1) drawing fibres from the preform.
The present invention further provides an process for making erbium doped optical fibre which comprises (a) providing deposition of P205 and F doped synthetic cladding within a silica glass substrate tube to obtain matched or depressed clad type structure, (b) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of l0 1200-1350°C, (c) maintaining P205 and Ge02 concentrations from 0.5 to 3.5 mol% and 3.0 to 20.0 mol% in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, (d) immersing the tube containing the porous soot layer into a solution containing Er salt in the concentration range of 0.004M to 0.20 M with or without aluminium salt at the concentration range of 0.05 M to 1.0 M for a period of 1 to 2 hours, (e) draining the solution out at a rate in the range of 10-30 cc/min, (f) drying the porous layer by flowing dry nitrogen through or any other inert gas the tube, (g) heating the tube gradually in the presence of oxygen in the temperature range of 700-1000°C , (h) dehydrating the core layer of the tube at a temperature in the range of 800-1200 °C and in presence of excess Cla, (i) sintering the core layer in the presence of a mixture of oxygen and helium in the temperature range of 1400 to 1800°C, (j) collapsing the tube at a temperature in the range of 2000-2300°C to obtain a preform, (k) overcladding the preform with silica tube, and (1) drawing fibres from the preform.
The present invention also provides an process for making rare earth doped optical fibre wherein the RE distribution along the transverse direction in the core is varied by controlling the density of the porous soot layer, dipping period and the processing conditions during oxidation, sintering and collapsing depending on the host glass composition and RE/Al concentration of the core layer. The numerical aperture of the fibre is varied from 0.10 to 0.30 maintaining RE concentration in the core between 50 to 6000 ppm along with variation in RE distribution profile along the radial direction in the doped region to produce fibres suitable for application as amplifiers, fibre lasers and sensors for different purposes.
In an embodiment of the present invention, theoretically estimated relative density of the porous soot ranges between 0.30 to 0.50 to avoid core-clad interface defect.
8 ~ ~, , , In another embodiment of the present invention GeCl4 supplied during soot deposition is to 30% less than that required for achieving the desired NA numerical aperture.
In another embodiment of the invention, the pump beam has a radius of distribution equal to or greater than the radius of distribution of Er ions in the core, which enhances the 5 chance of all the active ions getting exposed to the pump light.
In another embodiment of the invention, relatively high gain is achieved in the fibres for NA (Numerical aperture) value close to 0.20.
In yet another embodiment of the present invention RE salt used is selected from chloride, nitrate or any other salt soluble in solvent used in the process.
to In still another embodiment of the present invention aluminium salt used is selected from chloride, nitrate or any other salt soluble in solvent used in the process.
In yet another embodiment of the present invention solution for aluminium and RE salts is prepared using solvent selected from alcohol and water.
In still another embodiment of the present invention the temperature of the core layer is increased in steps of 50 to 200°C during oxidation and sintering depending on the composition and Al/RE concentration of the core layer.
In yet another embodiment of the present invention the mixture of 02 and He is in the range of 3:1 to 9:1.
In still another embodiment of the present invention source of chlorine is selected from 2o CC14 where Helium is used as carrier gas.
In yet another embodiment of the present invention the proportion of Clz: 02 varies from 1.5: 1 to 3.5: 1 while the dehydration period lies between 1 to 2 hours.
In yet another embodiment of the present invention the porous core is sintered in presence of germania by supplying GeCl4 with the input oxygen at a temperature of 1200°C to 1400°C during sintering to facilitate germania incorporation and obtain appropriate numerical aperture.
In yet another embodiment, the process provides variation in the numerical aperture of the fibre from 0.10 to 0.30 maintaining RE concentration in the core between 50 to 6000 ppm along with variation in RE distribution profile along the transverse direction in the doped 3o region to produce fibres suitable for application in any devices.
In yet another embodiment, the devices are amplifiers, fibre lasers and sensors for different purposes where optical fibre is used. .
Another embodiment of the invention is a method of controlling the Gaussian RE
distribution profile along the radial direction in a core used in the process of making rare earth doped optical fibre wherein, said process comprising the steps of a) Depositing P205 and F within a high silica glass substrate tube to make matched clad or depressed clad type structure.
b) Depositing predefined composition of unsintered particulate Iayer at a temperature of 1200 to 1400°C for the forming a core, wherein P205 and Ge02 levels in the core vary from 0.5 to 5.0 mol% and 3.0 to 25.0 mol%
respectively, and GeCl4 concentration in the gas phase is kept 10 to 30% lower than that required for achieving the desired NA of 0.20.
c) The deposition temperature is dependent on the composition and desired porosity l0 of the soot. A theoretically estimated porosity of 0.3 to 0.5 is found suitable to avoid core-clad interface defect and clustering after dipping and to control the RE
distribution in the core with maximum concentration at the centre.
d) Immersing the tube containing the porous soot layer into an alcoholic/aqueous solution of RECl3 / RE(NO3)3 Of strength varying between 0.002 M and 0.25 M
with or without the addition of AlCl3 / Al(N03)3 in the concentration range 0.05 M to 1.25 M for a period of one to two hours.
e) Draining out the solution slowly at a rate of 10 to 50 cc/min. to avoid imperfection in the porous soot material, particularly at the lower end of the tube.
f) Passing dry nitrogen through the tube for sufficient drying of the porous layer and 2o the tube is remounted on lathe.
g) Repeatedly heating the RE/Al containing particulate layer in the range from to 1100°C (tube surface temperature), in presence of 02+He wherein the temperature is increased in steps of 50 to 200°C thus oxidising the RE/Al chloride or nitrate present in the layer to corresponding oxides, wherein the ratio of 02 &
He is varied between 3:1 to 9:1.
h) The particulate core layer containing RE is dehydrated at a temperature between 800° to 1200°C in presence of excess chlorine. CC14 is used as the source material for C12 and supplied by using Helium as a carrier gas which being a lighter gas diffuses through the small pores and assists in the drying process. The proportion of C12: 02 varies from 1.5: 1 to 3.5: 1 while the dehydration period lies between 1 to 2 hours.
i) The porous core layer is then sintered in presence of 02 and He by heating the tube to a temperature as high as 1900°C. The temperature is gradually increased in steps of 50 to 200°C depending on the composition and RE/Al concentration of j) the core layer from the drying temperature between 800 to 1200°C
mentioned above.
k) At temperatures between 1200° to 1400°C during sintering pure GeCl4 is supplied with the input oxygen to carry out the sintering of the porous layer in germania 5 rich atmosphere which facilitates germania incorporation. The flow rate of GeCl4 and the no. of pass depend on the NA desired in the fibre. The supply of GeCl4 is then stopped and the sintering is continued by gradually raising the temperature till a clear glassy layer is formed.
1) The collapsing is carned out at a high temperature (>2000°C) in 3 to 4 passes of l0 the burner to produce a solid glass rod called preform.
m) The preform is overcladded with silica tubes of suitable dimensions to achieve the appropriate core - clad dimensions in the ultimate preform/fibre.
n) Fibres are drawn from the preform.
Brief description of the accompanying drawings Figure 1 ~ 2 represents Er fluorescence distribution across the fibre core The invention is further explained with the help of following examples, which should not be construed to limit the scope of the invention:
EXAMPLE.1 ~ Deposition of F-doped cladding within a silica tube by MCVD process at a temperature of1855°C.
~ Unsintered core deposition at a temperature of 1290°C. The carrier gas flows through the reagent liquids were adjusted to obtain a composition of SiOa= 90.2 mol%, PZOs=
1.3 mol% and GeOa= 8.5 mol% in the deposited soot layer.
~ Dipping the tube with the deposited layer in a solution containing 0.025 (M) ErCl3 and 0.1 S (M) Al(N03)3 9H20 for 1 hour and draining out the solution slowly.
~ Drying by maintaining nitrogen gas flow through the tube for 10 min.
~ Oxidation at temperatures of 725°C, 825°Cand 950°C with 2 passes of the burner at each temperature maintaining a constant He/OZ ratio of 1:5.
~ Dehydration was carried out at a temperature of 1010°C with a C12: OZ
ratio of 2.5: 1 for a period of 1 hour 15 mins.
~ The temperature was increased in 4 steps up to 1400°C. GeCI4 was added from this stage with input oxygen with 3 passes between 1200° 1400°C. The tube was further heated to increase the temperature stepwise to 1650°C for complete sintering of the Er & A1 containing porous soot layer. During sintering Oa and He flow was in the ratio of 4.5:1.
~ The collapsing was done in 3 steps in the usual manner.
~ Overcladding was done to reduce the core:clad ratio to 3.6:125. The NA
measured in the fibre was 0.204 ~ 0.01.
~ The Er3+ ion concentration in the fibre was 950 ppm with maximum concentration at the core centre and distribution as shown in fig.l accompanying this specification. The Er distribution in the core was measured from the fibre section by fluorescence spectroscopy by Photonics Resource Facility, 60 St. George Street, Suite No.
331, to Toronto, Ontario, Canada MSS 1A7.
~ The fibre recorded a gain of 35.4 dB. The gain was measured at C-DOT, 39 Main Pusa Road, New Delhi - 110 005 using their measurement set-up.
~ Deposition of F-doped cladding inside a silica glass tube by MCVD process at a temperature of 1840°C.
~ Unsintered core deposition at a temperature of 1310°C. The carrier gas flows through the reagent liquids were adjusted to obtain a composition of SiO2= 9I.6 mol%, P205=
1.1 mol% and Ge02= 7.3 mol% in the deposited soot layer.
~ Dipping the tube with the deposited layer in a solution containing 0.015 (M) ErCl3, 6H20 and 0.15 (M) Al(N03)3 9Ha0 for 1.5 hours and draining out the solution slowly.
~ Drying by maintaining nitrogen gas flow through the tube for 10 min.
~ Oxidation at temperatures of 750°, 800° and 900°C with 2 passes of the burner at each temperature maintaining a constant He/02 ratio of 1:5.
~ Dehydration was carried out at a temperature of 915°C with a C12: 02 ratio of 2.3: 1 for a period of one hour.
~ The temperature was increased in 3 steps up to1200°C. GeCl4 was added from this stage with input oxygen with one pass each at 1200°, 1300° and 1400°C. The tube was further heated to increase the temperature stepwise to I6I0°C for complete sintering of the Er & AI containing porous soot layer. During sintering 02 and He flow was in the ratio of 5:1.
~ The collapsing was done in 3 steps in the usual manner.
~ Overcladding was done to reduce the core:clad ratio to 3.6:125.
~ The NA measured in the fibre was 0.201 ~ 0 .O1.
~ The Er3+ ion concentration in the fibre was 460 ppm with peak at the core centre and similar distribution as shown in accompanying drawings as figure 1.
~ The fibre recorded a gain up to 37 dB as measured from C-DOT, 39 Main Pusa Road, New Delhi -110 005 using their measurement set-up.
~ Deposition of F-doped cladding within a silica tube by MCVD process at a temperature of 1870°C.
~ Unsintered core deposition at a temperature of 1250°C. The carrier gas flows through l0 the reagent liquids were adjusted to obtain a composition of SiOa= 89.1 mol%, P205=
2.3 mol% and Ge02= 8.6 mol% in the deposited soot layer.
~ Dipping the tube with the deposited layer in a aqueous solution containing 0.07 (M) ErCl3 and 0.25 (M) Al(N03)3 9H20 for 1 hour and draining out the solution slowly.
~ Drying by maintaining nitrogen gas flow through the tube for 10 min.
~ Oxidation at temperatures of 730°, 820° and 925°C with 2 passes of the burner at each temperature maintaining at constant He/OZ ratio of 1:6.
~ Dehydration was carried out at a temperature of 925°C with a C12: 02 ratio is 2.3 : 1 for a period of 1.5 hour.
~ The temperature was increased in 4 steps up to1400°C. GeCl4 was added with the input oxygen with 2 passes at 1200°C and one pass each at 1300°C and 1400°C. The tube was further heated to increase the temperature stepwise to 1725°C for complete sintering of the Er & A1 containing porous soot layer. During sintering 02 and He flow was in the ratio of 4:1.
~ The collapsing was done in 3 steps in the usual manner.
~ Overcladding was done to reduce the core:clad ratio to 6.5:125. The NA
measured in the fibre was 0.22~.O1 .
~ The Er3+ ion concentration in the fibre was 3020 ppm with peak concentration at the core centre and Er distribution in the core as shown in accompanying drawing as figure -2 measured from the fibre section by fluorescence spectroscopy by Photonics 3o Resource Facility, 60 St. George Street, Suite No. 331, Toronto, Ontario, Canada MSS-1 A7.
The main advantages of the present invention are:
1. The developed fibres have a RE distribution in the doped region similar to the Gaussian pump beam intensity distribution in the fibre so that the overlapping between the two is considerably improved consequently increasing the pump conversion efficiency in the fibre.
2. The pump beam has a radius of distribution equal to or greater than the radius of distribution of RE ions in the core, which enhances the chance of all the active ions getting exposed to the pump light.
3. The RE distribution along the transverse direction in the core is varied by controlling the density of the porous soot layer, dipping period and the processing conditions during oxidation, sintering and collapsing depending on the host glass composition and RE/Al concentration of the core layer.
l0 4. The compositions of the core and cladding glass are varied to achieve NA
close to 0.20 for Er3+ ion concentration in the range of 100 to 1500 ppm in order to provide erbium doped fibre suitable for pumping for amplification of the input signal with gain in the range 10 to 37 dB for optical amplifier application.
Objects of the invention The main obj ect of the present invention is to provide a process for making Rare Earth doped optical fibre, which obviates the drawbacks as detailed above.
Another object of the present invention is to provide fibres possessing controlled 5 distribution of RE, more particularly Erbium in the doped region similar to the pump beam intensity distribution in the fibre with maximum concentration at the centre so that the overlapping between the two is considerably improved.
Still another object of the present invention is to provide fibres in which the pump beam has a radius of distribution equal to or greater than the radius of distribution of RE ions in 1o the core to increase the chances of all the active ions getting exposed to the pump light, consequently increasing the pump conversion efficiency in the fibre.
Yet another object of the present invention is to provide a method of controlling the Gaussian RE distribution profile along the radial direction in the core.
Still another object of the present invention is to achieve high optical gain in the fibres for NA value close to 0.20 only thus avoiding wide variation in composition between the core and cladding glass to eliminate problems like residual stress and PMD.
Yet another object of the present invention is to develop erbium doped fibres suitable for amplification of the input signal with NA and mode field diameter not widely different from signal transmitting fibre for ease of splice.
2o Still another object of the present invention is to reduce the possibility of change in composition of the particulate core layer due to evaporation of the RE salt during drying and sintering .
Yet another object of the present invention is to reduce the quantity of germanium halide required to achieve the desired NA in the fibre.
One more object of the present invention is to provide a process where the numerical aperture of the fibre is varied from 0.10 to 0.30 maintaining RE concentration in the core between 50 to 6000 ppm along with variation in RE distribution profile in the doped region to produce fibres suitable for application as amplifiers, fibre lasers and sensors for different purposes.
3o Summary of the invention The novelty of the present invention lies in controlling the concentration profile of RE ion in the collapsed preform by minimising evaporation of the RE salt and also preventing diffusion of the rare earth ion due to subsequent heat treatment. The optimum soot density to achieve this objective is estimated to lie between 0.3 to 0.5 after deposition. The inventive step lies in transformation of the RE salts to oxides by gradually heating the tube to a higher temperature maintaining an oxidising atmosphere inside, thereby minimising the possibility of evaporation of RE during subsequent processing as the oxide has a very high melting temperature compared to halide/nitrate salts. This step also helps to remove the solvent trapped within the porous layer. The inventive step also includes increasing the temperature of the RE containing porous layer gradually in steps of 50 to 200°C up to the sintering temperature and above for sintering and further fixing of the RE
ions in their desired sites. The steps will depend on the host glass composition and Er/Al concentration of the core layer. The incorporation efficiency of the RE from the solution to the core l0 layer thus increases appreciably making the process more efficient and economic. The RE
distribution along the transverse direction in the core will depend on the density of the porous soot layer, dipping period and the processing conditions during oxidation, sintering and collapsing.
The sintering of the porous core layer in Ge02 rich atmosphere along with the addition of oxygen and helium is another inventive step of the process which reduces the quantity of GeCl4 required to achieve the desired NA and adds to the economy of the process. At temperatures between 200° to 1400° C during the sintering step pure GeCl4 is supplied with the input oxygen, the quantity of which depends on the NA desired in the fibre. The sintering is continued by gradually raising the temperature till a clear glassy layer is formed.
Detailed Description of the Invention Accordingly the present invention provides an improved process for making rare earth doped optical fibre which comprises (a) providing deposition of P205 and F
doped synthetic cladding within a silica glass substrate tube to obtain matched or depressed clad type structure, (b) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of 1200-1400°C, (c) maintaining Pa05 and Ge02 concentrations from 0.5 to 5.0 mol% and 3.0 to 25.0 mol% in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, (d) immersing the tube containing the porous soot layer into a solution containing RE salt in 3o the concentration range of 0.002M to 0.25 M with or without aluminium salt of the concentration range 0.05 M to 1.25 M for a period of 1 to 2 hours, (e) draining the solution out at a rate in the range of 10-50 cc/min, (f) drying the porous layer by flowing dry nitrogen or any other inert gas through the tube, (g) heating the tube gradually in the presence of oxygen at a temperature in the range of 600-1100°C, (h) dehydrating the core layer of the tube at a temperature in the range of 800-1200°C and in presence of excess C12, (i) sintering the core layer in the presence of a mixture of oxygen and helium in the temperature range of 1400 to 1900°C, (j) collapsing the tube at a temperature in the range of 2000-2300°C to obtain a preform, (k) overcladding the preform with silica tube, (1) drawing fibres from the preform.
The present invention further provides an process for making erbium doped optical fibre which comprises (a) providing deposition of P205 and F doped synthetic cladding within a silica glass substrate tube to obtain matched or depressed clad type structure, (b) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of l0 1200-1350°C, (c) maintaining P205 and Ge02 concentrations from 0.5 to 3.5 mol% and 3.0 to 20.0 mol% in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, (d) immersing the tube containing the porous soot layer into a solution containing Er salt in the concentration range of 0.004M to 0.20 M with or without aluminium salt at the concentration range of 0.05 M to 1.0 M for a period of 1 to 2 hours, (e) draining the solution out at a rate in the range of 10-30 cc/min, (f) drying the porous layer by flowing dry nitrogen through or any other inert gas the tube, (g) heating the tube gradually in the presence of oxygen in the temperature range of 700-1000°C , (h) dehydrating the core layer of the tube at a temperature in the range of 800-1200 °C and in presence of excess Cla, (i) sintering the core layer in the presence of a mixture of oxygen and helium in the temperature range of 1400 to 1800°C, (j) collapsing the tube at a temperature in the range of 2000-2300°C to obtain a preform, (k) overcladding the preform with silica tube, and (1) drawing fibres from the preform.
The present invention also provides an process for making rare earth doped optical fibre wherein the RE distribution along the transverse direction in the core is varied by controlling the density of the porous soot layer, dipping period and the processing conditions during oxidation, sintering and collapsing depending on the host glass composition and RE/Al concentration of the core layer. The numerical aperture of the fibre is varied from 0.10 to 0.30 maintaining RE concentration in the core between 50 to 6000 ppm along with variation in RE distribution profile along the radial direction in the doped region to produce fibres suitable for application as amplifiers, fibre lasers and sensors for different purposes.
In an embodiment of the present invention, theoretically estimated relative density of the porous soot ranges between 0.30 to 0.50 to avoid core-clad interface defect.
8 ~ ~, , , In another embodiment of the present invention GeCl4 supplied during soot deposition is to 30% less than that required for achieving the desired NA numerical aperture.
In another embodiment of the invention, the pump beam has a radius of distribution equal to or greater than the radius of distribution of Er ions in the core, which enhances the 5 chance of all the active ions getting exposed to the pump light.
In another embodiment of the invention, relatively high gain is achieved in the fibres for NA (Numerical aperture) value close to 0.20.
In yet another embodiment of the present invention RE salt used is selected from chloride, nitrate or any other salt soluble in solvent used in the process.
to In still another embodiment of the present invention aluminium salt used is selected from chloride, nitrate or any other salt soluble in solvent used in the process.
In yet another embodiment of the present invention solution for aluminium and RE salts is prepared using solvent selected from alcohol and water.
In still another embodiment of the present invention the temperature of the core layer is increased in steps of 50 to 200°C during oxidation and sintering depending on the composition and Al/RE concentration of the core layer.
In yet another embodiment of the present invention the mixture of 02 and He is in the range of 3:1 to 9:1.
In still another embodiment of the present invention source of chlorine is selected from 2o CC14 where Helium is used as carrier gas.
In yet another embodiment of the present invention the proportion of Clz: 02 varies from 1.5: 1 to 3.5: 1 while the dehydration period lies between 1 to 2 hours.
In yet another embodiment of the present invention the porous core is sintered in presence of germania by supplying GeCl4 with the input oxygen at a temperature of 1200°C to 1400°C during sintering to facilitate germania incorporation and obtain appropriate numerical aperture.
In yet another embodiment, the process provides variation in the numerical aperture of the fibre from 0.10 to 0.30 maintaining RE concentration in the core between 50 to 6000 ppm along with variation in RE distribution profile along the transverse direction in the doped 3o region to produce fibres suitable for application in any devices.
In yet another embodiment, the devices are amplifiers, fibre lasers and sensors for different purposes where optical fibre is used. .
Another embodiment of the invention is a method of controlling the Gaussian RE
distribution profile along the radial direction in a core used in the process of making rare earth doped optical fibre wherein, said process comprising the steps of a) Depositing P205 and F within a high silica glass substrate tube to make matched clad or depressed clad type structure.
b) Depositing predefined composition of unsintered particulate Iayer at a temperature of 1200 to 1400°C for the forming a core, wherein P205 and Ge02 levels in the core vary from 0.5 to 5.0 mol% and 3.0 to 25.0 mol%
respectively, and GeCl4 concentration in the gas phase is kept 10 to 30% lower than that required for achieving the desired NA of 0.20.
c) The deposition temperature is dependent on the composition and desired porosity l0 of the soot. A theoretically estimated porosity of 0.3 to 0.5 is found suitable to avoid core-clad interface defect and clustering after dipping and to control the RE
distribution in the core with maximum concentration at the centre.
d) Immersing the tube containing the porous soot layer into an alcoholic/aqueous solution of RECl3 / RE(NO3)3 Of strength varying between 0.002 M and 0.25 M
with or without the addition of AlCl3 / Al(N03)3 in the concentration range 0.05 M to 1.25 M for a period of one to two hours.
e) Draining out the solution slowly at a rate of 10 to 50 cc/min. to avoid imperfection in the porous soot material, particularly at the lower end of the tube.
f) Passing dry nitrogen through the tube for sufficient drying of the porous layer and 2o the tube is remounted on lathe.
g) Repeatedly heating the RE/Al containing particulate layer in the range from to 1100°C (tube surface temperature), in presence of 02+He wherein the temperature is increased in steps of 50 to 200°C thus oxidising the RE/Al chloride or nitrate present in the layer to corresponding oxides, wherein the ratio of 02 &
He is varied between 3:1 to 9:1.
h) The particulate core layer containing RE is dehydrated at a temperature between 800° to 1200°C in presence of excess chlorine. CC14 is used as the source material for C12 and supplied by using Helium as a carrier gas which being a lighter gas diffuses through the small pores and assists in the drying process. The proportion of C12: 02 varies from 1.5: 1 to 3.5: 1 while the dehydration period lies between 1 to 2 hours.
i) The porous core layer is then sintered in presence of 02 and He by heating the tube to a temperature as high as 1900°C. The temperature is gradually increased in steps of 50 to 200°C depending on the composition and RE/Al concentration of j) the core layer from the drying temperature between 800 to 1200°C
mentioned above.
k) At temperatures between 1200° to 1400°C during sintering pure GeCl4 is supplied with the input oxygen to carry out the sintering of the porous layer in germania 5 rich atmosphere which facilitates germania incorporation. The flow rate of GeCl4 and the no. of pass depend on the NA desired in the fibre. The supply of GeCl4 is then stopped and the sintering is continued by gradually raising the temperature till a clear glassy layer is formed.
1) The collapsing is carned out at a high temperature (>2000°C) in 3 to 4 passes of l0 the burner to produce a solid glass rod called preform.
m) The preform is overcladded with silica tubes of suitable dimensions to achieve the appropriate core - clad dimensions in the ultimate preform/fibre.
n) Fibres are drawn from the preform.
Brief description of the accompanying drawings Figure 1 ~ 2 represents Er fluorescence distribution across the fibre core The invention is further explained with the help of following examples, which should not be construed to limit the scope of the invention:
EXAMPLE.1 ~ Deposition of F-doped cladding within a silica tube by MCVD process at a temperature of1855°C.
~ Unsintered core deposition at a temperature of 1290°C. The carrier gas flows through the reagent liquids were adjusted to obtain a composition of SiOa= 90.2 mol%, PZOs=
1.3 mol% and GeOa= 8.5 mol% in the deposited soot layer.
~ Dipping the tube with the deposited layer in a solution containing 0.025 (M) ErCl3 and 0.1 S (M) Al(N03)3 9H20 for 1 hour and draining out the solution slowly.
~ Drying by maintaining nitrogen gas flow through the tube for 10 min.
~ Oxidation at temperatures of 725°C, 825°Cand 950°C with 2 passes of the burner at each temperature maintaining a constant He/OZ ratio of 1:5.
~ Dehydration was carried out at a temperature of 1010°C with a C12: OZ
ratio of 2.5: 1 for a period of 1 hour 15 mins.
~ The temperature was increased in 4 steps up to 1400°C. GeCI4 was added from this stage with input oxygen with 3 passes between 1200° 1400°C. The tube was further heated to increase the temperature stepwise to 1650°C for complete sintering of the Er & A1 containing porous soot layer. During sintering Oa and He flow was in the ratio of 4.5:1.
~ The collapsing was done in 3 steps in the usual manner.
~ Overcladding was done to reduce the core:clad ratio to 3.6:125. The NA
measured in the fibre was 0.204 ~ 0.01.
~ The Er3+ ion concentration in the fibre was 950 ppm with maximum concentration at the core centre and distribution as shown in fig.l accompanying this specification. The Er distribution in the core was measured from the fibre section by fluorescence spectroscopy by Photonics Resource Facility, 60 St. George Street, Suite No.
331, to Toronto, Ontario, Canada MSS 1A7.
~ The fibre recorded a gain of 35.4 dB. The gain was measured at C-DOT, 39 Main Pusa Road, New Delhi - 110 005 using their measurement set-up.
~ Deposition of F-doped cladding inside a silica glass tube by MCVD process at a temperature of 1840°C.
~ Unsintered core deposition at a temperature of 1310°C. The carrier gas flows through the reagent liquids were adjusted to obtain a composition of SiO2= 9I.6 mol%, P205=
1.1 mol% and Ge02= 7.3 mol% in the deposited soot layer.
~ Dipping the tube with the deposited layer in a solution containing 0.015 (M) ErCl3, 6H20 and 0.15 (M) Al(N03)3 9Ha0 for 1.5 hours and draining out the solution slowly.
~ Drying by maintaining nitrogen gas flow through the tube for 10 min.
~ Oxidation at temperatures of 750°, 800° and 900°C with 2 passes of the burner at each temperature maintaining a constant He/02 ratio of 1:5.
~ Dehydration was carried out at a temperature of 915°C with a C12: 02 ratio of 2.3: 1 for a period of one hour.
~ The temperature was increased in 3 steps up to1200°C. GeCl4 was added from this stage with input oxygen with one pass each at 1200°, 1300° and 1400°C. The tube was further heated to increase the temperature stepwise to I6I0°C for complete sintering of the Er & AI containing porous soot layer. During sintering 02 and He flow was in the ratio of 5:1.
~ The collapsing was done in 3 steps in the usual manner.
~ Overcladding was done to reduce the core:clad ratio to 3.6:125.
~ The NA measured in the fibre was 0.201 ~ 0 .O1.
~ The Er3+ ion concentration in the fibre was 460 ppm with peak at the core centre and similar distribution as shown in accompanying drawings as figure 1.
~ The fibre recorded a gain up to 37 dB as measured from C-DOT, 39 Main Pusa Road, New Delhi -110 005 using their measurement set-up.
~ Deposition of F-doped cladding within a silica tube by MCVD process at a temperature of 1870°C.
~ Unsintered core deposition at a temperature of 1250°C. The carrier gas flows through l0 the reagent liquids were adjusted to obtain a composition of SiOa= 89.1 mol%, P205=
2.3 mol% and Ge02= 8.6 mol% in the deposited soot layer.
~ Dipping the tube with the deposited layer in a aqueous solution containing 0.07 (M) ErCl3 and 0.25 (M) Al(N03)3 9H20 for 1 hour and draining out the solution slowly.
~ Drying by maintaining nitrogen gas flow through the tube for 10 min.
~ Oxidation at temperatures of 730°, 820° and 925°C with 2 passes of the burner at each temperature maintaining at constant He/OZ ratio of 1:6.
~ Dehydration was carried out at a temperature of 925°C with a C12: 02 ratio is 2.3 : 1 for a period of 1.5 hour.
~ The temperature was increased in 4 steps up to1400°C. GeCl4 was added with the input oxygen with 2 passes at 1200°C and one pass each at 1300°C and 1400°C. The tube was further heated to increase the temperature stepwise to 1725°C for complete sintering of the Er & A1 containing porous soot layer. During sintering 02 and He flow was in the ratio of 4:1.
~ The collapsing was done in 3 steps in the usual manner.
~ Overcladding was done to reduce the core:clad ratio to 6.5:125. The NA
measured in the fibre was 0.22~.O1 .
~ The Er3+ ion concentration in the fibre was 3020 ppm with peak concentration at the core centre and Er distribution in the core as shown in accompanying drawing as figure -2 measured from the fibre section by fluorescence spectroscopy by Photonics 3o Resource Facility, 60 St. George Street, Suite No. 331, Toronto, Ontario, Canada MSS-1 A7.
The main advantages of the present invention are:
1. The developed fibres have a RE distribution in the doped region similar to the Gaussian pump beam intensity distribution in the fibre so that the overlapping between the two is considerably improved consequently increasing the pump conversion efficiency in the fibre.
2. The pump beam has a radius of distribution equal to or greater than the radius of distribution of RE ions in the core, which enhances the chance of all the active ions getting exposed to the pump light.
3. The RE distribution along the transverse direction in the core is varied by controlling the density of the porous soot layer, dipping period and the processing conditions during oxidation, sintering and collapsing depending on the host glass composition and RE/Al concentration of the core layer.
l0 4. The compositions of the core and cladding glass are varied to achieve NA
close to 0.20 for Er3+ ion concentration in the range of 100 to 1500 ppm in order to provide erbium doped fibre suitable for pumping for amplification of the input signal with gain in the range 10 to 37 dB for optical amplifier application.
5. Wide variation in composition between the core and cladding glass is avoided due to relatively low NA in the RE doped fibres mentioned under 4 above eliminating problems like residual stress and PMD which may substantially degrade the performance of the fibres.
6. The developed fibres mentioned under 4 and 5 above have NA and mode field diameter not widely different from signal transmitting fibre for ease of splice. This miumises the optical loss of the signal travelling through the fibres.
7. Sintering in germania rich atmosphere facilitates incorporation of germania in the core and reduces the quantity of germanium halide necessary during deposition to achieve the desired NA making the process efficient and economic.
8. The oxidation step before drying and sintering of the particulate layer reduces the possibility of change in composition due to evaporation of RE salts during subsequent processing.
9. The stepwise increase in temperature during oxidation and sintering stages prevents diffusion of RE and the codopants minimising the probability of a change in composition.
10. The incorporation efficiency of RE in the doped region is increased due to the reason stated in 8 and 9 above, which adds to the economy of the process.
11. The improvement in process efficiency due to the reasons mentioned in 8 -10 above enhances the yield and repeatability of the process.
12. The concentration of RE in the core is varied between 50 to 6000 ppm along with variation in RE distribution profile in the doped region and NA between 0.10 to 0.30 to produce fibres suitable for application as amplifiers, microlasers and sensors for different purposes.
Claims (44)
1. A process for making rare earth doped optical fibre, said process comprising the steps of:
a) providing deposition of P2O5 and F doped synthetic cladding within a silica glass substrate tube to obtain matched or depressed clad type structure, b) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of 1200-1400°C, c) maintaining P2O5 and GeO2 concentrations from 0.5 to 5.0 mol% and 3.0 to 25.0 mol%
in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, d) immersing the tube containing the porous soot layer into a solution containing RE salt in the concentration range of 0.002 M to 0.25 M
for a period of 1 to 2 hours, e) draining the solution out at a rate in the range of 10-50 cc/min, f) drying the porous layer by flowing dry nitrogen or any other inert gas through the tube, g) heating the tube gradually in presence of oxygen at a temperature ranging between 600 - 1100°C, h) dehydrating the core layer of the tube at a temperature in the range of about 800-1200°C
and in presence of excess Cl2, i) sintering the core layer in germanium chloride rich atmosphere and in presence of a mixture of oxygen and helium in the temperature range between 1400 to 1900°C, collapsing the tube by usual method at a temperature ranging from 2000-2300°C to obtain a preform, k) overcladding the preform with silica tube, and l) drawing fibres from the preform by the conventional methods.
a) providing deposition of P2O5 and F doped synthetic cladding within a silica glass substrate tube to obtain matched or depressed clad type structure, b) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of 1200-1400°C, c) maintaining P2O5 and GeO2 concentrations from 0.5 to 5.0 mol% and 3.0 to 25.0 mol%
in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, d) immersing the tube containing the porous soot layer into a solution containing RE salt in the concentration range of 0.002 M to 0.25 M
for a period of 1 to 2 hours, e) draining the solution out at a rate in the range of 10-50 cc/min, f) drying the porous layer by flowing dry nitrogen or any other inert gas through the tube, g) heating the tube gradually in presence of oxygen at a temperature ranging between 600 - 1100°C, h) dehydrating the core layer of the tube at a temperature in the range of about 800-1200°C
and in presence of excess Cl2, i) sintering the core layer in germanium chloride rich atmosphere and in presence of a mixture of oxygen and helium in the temperature range between 1400 to 1900°C, collapsing the tube by usual method at a temperature ranging from 2000-2300°C to obtain a preform, k) overcladding the preform with silica tube, and l) drawing fibres from the preform by the conventional methods.
2. A process as claimed in claim 1 wherein, the theoretically estimated relative density of the porous soot ranges between 0.30 to 0.50 to avoid core-clad interface defect.
3. A process as claimed in claim 1 wherein, the RE salt used is selected from chloride and nitrate.
4. A process as claimed in claim 1 wherein, the aluminium salt used is selected from chloride and nitrate.
5. A process as claimed in claim 1 wherein, the solution for aluminium and erbium salt is prepared using solvent selected from alcohol and water.
6. A process as claimed in claim 1 wherein, the source of chlorine is CCl4 where He is used as carrier gas.
7. A process as claimed in claim 1 wherein, the.proportion of Cl2: O2 is ranging from 1.5: 1 to 3.5: 1 while the dehydration period lies between 1 to 2 hours.
8. A process as claimed in claim 1 wherein, the mixture of O2 and He is in the range of 3:1 to 9:1.
9. A process as claimed in claim 1 wherein, sintering in germania rich atmosphere facilitates higher germania incorporation and reduces the quantity of germanium halide necessary during deposition.
10. A process as claimed in claim 1 wherein, during sintering of porous core layer GeCl4 is supplied with the input oxygen maintaining a temperature of 1200°C to 1400°C.
11. A process as claimed in claim 1 wherein, the increase in temperature in steps of 50 to 200°C
during oxidation and sintering stages prevents diffusion of RE and the codopants from the doped region resulting to minimum change in composition.
during oxidation and sintering stages prevents diffusion of RE and the codopants from the doped region resulting to minimum change in composition.
12. A process as claimed in claim 1 wherein, the incorporation efficiency of RE in the doped region is increased.
13. An improved process for producing Er doped fibre in particular characterised by Er ion distribution in the core similar to the Gaussian pump beam intensity distribution wherein, the said process comprising steps of (a) providing deposition of P2O5 and F doped synthetic cladding within a silica glass substrate tube to obtain matched or depressed clad type structure, (b) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of 1200-1350°C, (c) maintaining P2O5 and GeO2 concentrations from 0.5 to 3.5 mol% and 3.0 to 20.0 mol%
in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, (d) immersing the tube containing the porous soot layer into a solution containing Er salt in the concentration range of 0.004 M to 0.20 M
for a period of 1 to 2 hours, (e) draining the solution out at a rate in the range of 10-30 cc/min, (f) drying the porous layer by flowing dry nitrogen or any other inert gas through the tube, (g) heating the tube gradually in presence of oxygen in the temperature range 1000°C, (h) dehydrating the core layer of the tube at a temperature in the range of 800-1200°C and in presence of excess Cl2, (i) sintering the core layer in germanium chloride rich atmosphere and in presence of a mixture of oxygen and helium in the temperature range of 1400 to 1800°C, (j) collapsing the tube by usual method at a temperature in the range of 2000-2300°C to obtain a preform, (k) overcladding the preform with silica tube, and (l) drawing fibres from the preform by the conventional methods.
in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, (d) immersing the tube containing the porous soot layer into a solution containing Er salt in the concentration range of 0.004 M to 0.20 M
for a period of 1 to 2 hours, (e) draining the solution out at a rate in the range of 10-30 cc/min, (f) drying the porous layer by flowing dry nitrogen or any other inert gas through the tube, (g) heating the tube gradually in presence of oxygen in the temperature range 1000°C, (h) dehydrating the core layer of the tube at a temperature in the range of 800-1200°C and in presence of excess Cl2, (i) sintering the core layer in germanium chloride rich atmosphere and in presence of a mixture of oxygen and helium in the temperature range of 1400 to 1800°C, (j) collapsing the tube by usual method at a temperature in the range of 2000-2300°C to obtain a preform, (k) overcladding the preform with silica tube, and (l) drawing fibres from the preform by the conventional methods.
14. A process as claimed in claim 13 wherein, the theoretically estimated relative density of the porous soot ranges between 0.30 to 0.50 to avoid core-clad interface defect.
15. A process as claimed in claim 13 wherein, the erbium salt used is selected from chloride and nitrate.
16. A process as claimed in claim 13 wherein, the aluminium salt used is selected from chloride and nitrate.
17. A process as claimed in claim 13 wherein, the solutions for aluminium and erbium salts are prepared using solvent selected from alcohol and water.
18. A process as claimed in claim 13 wherein, the source of chlorine is CCl4 where He is used as carrier gas.
19. A process as claimed in claim 13 the proportion of Cl2: O2 is varying from 1.5:1 to 3.5: 1 while the dehydration period lies between 1 to 2 hours.
20. A process as claimed in claim 13 wherein, during sintering of porous core layer GeCl4 is supplied with the input oxygen maintaining a temperature of 1200°C to 1400°C.
21. A process as claimed in claim 13 wherein, sintering in germania rich atmosphere reduces the quantity of germanium halide necessary during deposition to achieve the desired NA.
22. A process as claimed in claim 13 wherein, the increase in temperature in steps of 50 to 200°C
during oxidation and sintering stages prevents diffusion of RE and the codopants minimising the possibility of change in composition.
during oxidation and sintering stages prevents diffusion of RE and the codopants minimising the possibility of change in composition.
23. A process as claimed in claim 13 wherein, the mixture of 02 and He is in the range of 4:1 to 9:1.
24. A process as claimed in claim 13 wherein, the developed fibres have a controlled distribution of RE ion in the doped region with maximum concentration at the centre similar to the Gaussian pump beam intensity distribution in the fibre so that the overlapping between the two is considerably improved, consequently increasing the pump conversion efficiency in the fibre.
25. A process as claimed in claim 13 wherein, the pump beam has a radius of distribution equal to or greater than the radius of distribution of Er ions in the core, which enhances the chance of all the active ions getting exposed to the pump light.
26. A process as claimed in claim 22 wherein, relatively high gain is achieved in the fibres for NA
value close to 0.20.
value close to 0.20.
27. A process as claimed in claim 13 wherein, the fibre has relatively low NA.
28. A process as claimed in claim 13 wherein, the compositions of the core and cladding glass are suitable to achieve NA of 0.20 and Er3+ ion concentration in the range of 100 to 1500 ppm without clustering in order to provide EDF suitable for pumping at 980 nm for amplification of the input signal with gain in the range 10 to 37 dB for optical amplifier application.
29. A process as claimed in claim 13 wherein, the developed fibres have NA and mode field diameter not widely different from signal transmitting fibre.
30. A process as claimed in claim 13 wherein, the numerical aperture of the fibre is varied from 0.10 to 0.30 maintaining Er concentration in the core between 50 to 6000 ppm along with variation in Er distribution profile in the doped region to produce fibres suitable for application as amplifiers, fibre lasers and sensors for different purposes.
31. A method of controlling the Gaussian RE distribution profile along the radial direction in a core used in a process for making rare earth doped optical fibre wherein, the said method comprises the steps of:
a) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of 1200-1400°C, b) maintaining P2O5 and GeO2 concentrations from 0.5 to 5.0 mol% and 3.0 to 25.0 mol%
in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, c) immersing the tube containing the porous soot layer into a solution containing RE salt in the concentration range of 0.002 M to 0.25 M for a period of 1 to 2 hours, d) draining the solution out at a rate in the range of 10-50 cc/min, e) drying the porous layer by flowing dry nitrogen or any other inert gas through the tube, f) heating the tube gradually in presence of oxygen in the temperature range 700 - 1100°C
and increasing the temperature in steps of 50 to 200°C, g) dehydrating the core layer of the tube at a temperature in the range of 800-1200°C and in presence of excess Cl2, h) sintering the core layer in germanium chloride rich atmosphere and in presence of a mixture of oxygen and in the temperature range of 1400 to 1900°C
increasing the temperature in steps of 50 to 200°C, i) collapsing the tube by usual method at a temperature in the range of 2000-2300°C to obtain a preform, and j) drawing fibres from the preform by the conventional methods.
a) forming a core by depositing unsintered particulate layer at a tube surface temperature in the range of 1200-1400°C, b) maintaining P2O5 and GeO2 concentrations from 0.5 to 5.0 mol% and 3.0 to 25.0 mol%
in the said particulate layer respectively to obtain a tube containing F-doped cladding and porous soot layer, c) immersing the tube containing the porous soot layer into a solution containing RE salt in the concentration range of 0.002 M to 0.25 M for a period of 1 to 2 hours, d) draining the solution out at a rate in the range of 10-50 cc/min, e) drying the porous layer by flowing dry nitrogen or any other inert gas through the tube, f) heating the tube gradually in presence of oxygen in the temperature range 700 - 1100°C
and increasing the temperature in steps of 50 to 200°C, g) dehydrating the core layer of the tube at a temperature in the range of 800-1200°C and in presence of excess Cl2, h) sintering the core layer in germanium chloride rich atmosphere and in presence of a mixture of oxygen and in the temperature range of 1400 to 1900°C
increasing the temperature in steps of 50 to 200°C, i) collapsing the tube by usual method at a temperature in the range of 2000-2300°C to obtain a preform, and j) drawing fibres from the preform by the conventional methods.
32. A process as claimed in claim 31 wherein, the theoretically estimated relative density of the porous soot ranges between 0.30 to 0.50 to avoid core-clad interface defect.
33. A process as claimed in claim 31 wherein, the RE salt used is chloride and nitrate.
34. A process as claimed in claim 31 wherein, the aluminium salt used is selected from chloride and nitrate.
35. A process as claimed in claim 31 wherein, the solutions for aluminium and erbium salts are prepared using solvent selected from alcohol and water.
36. A process as claimed in claim 31 wherein, the source of chlorine is CCl4 where He is used as carrier gas.
37. A process as claimed in claim 31 wherein, the proportion of Cl2:O2 is varying from 1.5:1 to 3.5:1 while the dehydration period is between 1 to 2 hours.
38. A process as claimed in claim 31 wherein, during sintering of porous core layer GeCl4 is supplied with the input oxygen maintaining at a temperature hanging from 1200°C to 1400°C.
39. A process as claimed in claim 31 wherein, the mixture of O2 and He is in the range of 3:1 to 9:1.
40. A process as claimed in claim 31 wherein, the numerical aperture of the fibre is varied from 0.10 to 0.30 maintaining RE concentration in the core between 50 to 6000 ppm along with variation in the Gaussian RE distribution profile in the dopes region to produce fibres suitable for any devices.
41. A process as claimed in claim 40, wherein the devices are amplifiers, fibre lasers, sensors for different purposes and other devices where optical fibre is used.
42. A process as claimed in claim 1, wherein the solution of step d) further comprises aluminum salt in the concentration range 0.05M to 1.25M.
43. A process as claimed in claim 13, wherein the solution of step d) further comprises aluminum salt in the concentration range 0.05M to 1.0M.
44. A process as claimed in claim 31, wherein the solution of step c) further comprises aluminum salt in the concentration range 0.05M to 1.25M.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/IN2001/000014 WO2002060830A1 (en) | 2001-02-02 | 2001-02-02 | A process for making rare earth doped optical fibre |
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| Publication Number | Publication Date |
|---|---|
| CA2436579A1 CA2436579A1 (en) | 2002-08-08 |
| CA2436579C true CA2436579C (en) | 2006-09-26 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002436579A Expired - Lifetime CA2436579C (en) | 2001-02-02 | 2001-02-02 | A process for making rare earth doped optical fibre |
Country Status (6)
| Country | Link |
|---|---|
| KR (1) | KR100655480B1 (en) |
| CN (1) | CN1274618C (en) |
| AU (1) | AU2001242728B2 (en) |
| CA (1) | CA2436579C (en) |
| GB (1) | GB2388367B (en) |
| WO (1) | WO2002060830A1 (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20040112089A1 (en) * | 2002-12-16 | 2004-06-17 | Digiovanni David J. | Manufacture of optical fibers using enhanced doping |
| CA2454896A1 (en) * | 2003-01-16 | 2004-07-16 | Sumitomo Electric Industries, Ltd. | Method of producing optical fiber preform, and optical fiber preform and optical fiber produced with the method |
| CN101479205B (en) * | 2006-06-26 | 2013-02-20 | 住友电气工业株式会社 | Process for producing optical fiber base, process for producing optical fiber, and optical fiber |
| JP5018492B2 (en) * | 2008-01-15 | 2012-09-05 | 住友電気工業株式会社 | Preform manufacturing method |
| FR2939522B1 (en) * | 2008-12-08 | 2011-02-11 | Draka Comteq France | OPTICAL FIBER AMPLIFIER RESISTANT TO IONIZING RADIATION |
| CN102086089A (en) * | 2010-12-27 | 2011-06-08 | 富通集团有限公司 | Method for manufacturing rare-earth-doped fiber precast rod |
| CN102515501B (en) * | 2011-11-29 | 2014-04-30 | 富通集团有限公司 | Method for manufacturing doped optical fibre preform by MCVD (modified chemical vapour deposition) |
| CN104058587B (en) * | 2014-07-14 | 2016-06-22 | 富通集团有限公司 | A kind of rare earth doped optical fibre prefabricated rods and preparation method thereof |
| CN106966581A (en) * | 2017-05-18 | 2017-07-21 | 江苏亨通光导新材料有限公司 | A kind of preform and preparation method thereof |
| CN110467342A (en) * | 2019-08-15 | 2019-11-19 | 武汉长进激光技术有限公司 | A kind of ultra wide band gain Er-doped fiber and preparation method thereof |
| CN110467343A (en) * | 2019-08-23 | 2019-11-19 | 武汉长进激光技术有限公司 | A kind of nano-porous glass material hydroxyl-removal sintering method |
| CN110510864A (en) * | 2019-09-11 | 2019-11-29 | 烽火通信科技股份有限公司 | The preparation method and preform of highly doped rare-earth-doped fiber precast rod |
| US11673831B2 (en) * | 2019-10-01 | 2023-06-13 | The Hong Kong University Of Science And Technology | Method for preparing optical fibers with high-particle-coated porous polymeric outer coating layers |
| CN111847864A (en) * | 2020-06-16 | 2020-10-30 | 武汉长进激光技术有限公司 | C-band expanded broadband gain erbium-doped optical fiber and preparation method thereof |
| CN115448590A (en) * | 2022-08-31 | 2022-12-09 | 长飞光纤光缆股份有限公司 | Method for preparing rare earth doped optical fiber preform by in-tube method |
| CN118026517A (en) * | 2024-01-31 | 2024-05-14 | 武汉长进光子技术股份有限公司 | Solution doping device and doping method for preparing optical fiber preform |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE69030736T2 (en) * | 1989-10-31 | 1997-10-23 | Fujitsu Ltd | Method of making an optical fiber preform |
| US5005175A (en) | 1989-11-27 | 1991-04-02 | At&T Bell Laboratories | Erbium-doped fiber amplifier |
| ES2069877T3 (en) * | 1990-02-05 | 1995-05-16 | Furukawa Electric Co Ltd | QUARTZ GLASS DOPED WITH RARE EARTH ELEMENT AND ITS PRODUCTION. |
| JP2766420B2 (en) | 1992-04-07 | 1998-06-18 | 株式会社フジクラ | Method for producing erbium-doped quartz |
| GB2273389B (en) | 1992-12-14 | 1996-07-17 | Pirelli Cavi Spa | Rare earth doped optical fibre amplifiers |
| JP3773575B2 (en) | 1996-01-12 | 2006-05-10 | 富士通株式会社 | Doped fiber, splicing method thereof, and optical amplifier |
| US6578387B2 (en) * | 1999-04-09 | 2003-06-17 | Fitel Usa Corp. | Method of fabrication of rare earth doped preforms for optical fibers |
-
2001
- 2001-02-02 GB GB0318455A patent/GB2388367B/en not_active Expired - Lifetime
- 2001-02-02 KR KR1020037010252A patent/KR100655480B1/en active IP Right Grant
- 2001-02-02 CA CA002436579A patent/CA2436579C/en not_active Expired - Lifetime
- 2001-02-02 AU AU2001242728A patent/AU2001242728B2/en not_active Expired
- 2001-02-02 WO PCT/IN2001/000014 patent/WO2002060830A1/en active IP Right Grant
- 2001-02-02 CN CNB018230083A patent/CN1274618C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| WO2002060830A1 (en) | 2002-08-08 |
| GB2388367B (en) | 2005-05-18 |
| KR100655480B1 (en) | 2006-12-08 |
| KR20040034595A (en) | 2004-04-28 |
| CA2436579A1 (en) | 2002-08-08 |
| CN1274618C (en) | 2006-09-13 |
| WO2002060830A8 (en) | 2003-11-20 |
| CN1500069A (en) | 2004-05-26 |
| GB0318455D0 (en) | 2003-09-10 |
| GB2388367A (en) | 2003-11-12 |
| AU2001242728B2 (en) | 2007-05-10 |
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