GB1592234A - Sin2 coated optical fibre - Google Patents
Sin2 coated optical fibre Download PDFInfo
- Publication number
- GB1592234A GB1592234A GB16255/78A GB1625578A GB1592234A GB 1592234 A GB1592234 A GB 1592234A GB 16255/78 A GB16255/78 A GB 16255/78A GB 1625578 A GB1625578 A GB 1625578A GB 1592234 A GB1592234 A GB 1592234A
- Authority
- GB
- United Kingdom
- Prior art keywords
- cladding
- silicon nitride
- silica
- doped
- fiber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000013307 optical fiber Substances 0.000 title claims description 28
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical group O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 83
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 47
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 47
- 238000005253 cladding Methods 0.000 claims description 46
- 239000000835 fiber Substances 0.000 claims description 39
- 239000000377 silicon dioxide Substances 0.000 claims description 37
- 239000011521 glass Substances 0.000 claims description 21
- 239000011162 core material Substances 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 17
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 15
- 239000000463 material Substances 0.000 claims description 15
- 229910052710 silicon Inorganic materials 0.000 claims description 15
- 239000010703 silicon Substances 0.000 claims description 15
- 150000001875 compounds Chemical class 0.000 claims description 12
- 238000000576 coating method Methods 0.000 claims description 11
- 229910017464 nitrogen compound Inorganic materials 0.000 claims description 11
- 150000002830 nitrogen compounds Chemical class 0.000 claims description 11
- 239000011248 coating agent Substances 0.000 claims description 9
- 238000004519 manufacturing process Methods 0.000 claims description 9
- 230000003287 optical effect Effects 0.000 claims description 8
- 239000003365 glass fiber Substances 0.000 claims description 6
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 5
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 5
- 229910052791 calcium Inorganic materials 0.000 claims description 5
- 239000011575 calcium Substances 0.000 claims description 5
- 238000000151 deposition Methods 0.000 claims description 5
- 230000008021 deposition Effects 0.000 claims description 5
- 150000002222 fluorine compounds Chemical class 0.000 claims description 5
- 229910052749 magnesium Inorganic materials 0.000 claims description 5
- 239000011777 magnesium Substances 0.000 claims description 5
- 239000007787 solid Substances 0.000 claims description 4
- 238000002360 preparation method Methods 0.000 claims description 3
- 239000011347 resin Substances 0.000 claims description 3
- 229920005989 resin Polymers 0.000 claims description 3
- 238000005229 chemical vapour deposition Methods 0.000 claims description 2
- 238000001514 detection method Methods 0.000 claims description 2
- 238000010494 dissociation reaction Methods 0.000 claims description 2
- 230000005593 dissociations Effects 0.000 claims description 2
- 150000004820 halides Chemical class 0.000 claims description 2
- 150000004678 hydrides Chemical class 0.000 claims description 2
- 238000006243 chemical reaction Methods 0.000 description 7
- 239000004033 plastic Substances 0.000 description 5
- 229920003023 plastic Polymers 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000002352 surface water Substances 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- 238000007738 vacuum evaporation Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C25/00—Surface treatment of fibres or filaments made from glass, minerals or slags
- C03C25/10—Coating
- C03C25/104—Coating to obtain optical fibres
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02395—Glass optical fibre with a protective coating, e.g. two layer polymer coating deposited directly on a silica cladding surface during fibre manufacture
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Optics & Photonics (AREA)
- General Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Surface Treatment Of Glass Fibres Or Filaments (AREA)
Description
(54) SiN2 COATED OPTICAL FIBRE
(71) We, INTERNATIONAL STAN
DARD ELECTRIC CORPORATION a
Corporation organised and existing under the Laws of the State of Delaware, United
States of America, of 320 Park Avenue,
New York 22, State of New York, United
States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:
This invention relates to glass optical fibers, as used for communications equipment.
Glass optical communication fibers having initially high tensile strengths are found to fail over prolonged periods of stress, the failure mechanism involved being termed "fatigue resistance" failure. Surface imperfections develop along the outer perimeter of the glass to form micro-cracks which cause the fiber to break when subjected to tensile forces substantially lower than the original tensile strength rating of the fiber.
The crack formation fatigue failure mechanism is somehow related to induced OH reactions occurring with the glass when water molecules seep into microcracks existing along the glass outer surface. Overcoating the fiber with various plastics resins retards the fatigue failure formation to some extent, but over a sustained period of operation the plastics material becomes less resistant to water permeation, and, for some plastics, the material itself becomes a source of water.
U.S. Patent No. 3,485,666 teaches a method of forming silicon nitride coatings on the surface of semi-conductor materials to protect the materials from attack by moisture.
According to the present invention there is provided a method of manufacturing glass optical fibres having improved fatigue resistance, which fibres have a doped silica core and a doped silica cladding, the core and the cladding being differently doped, which includes the step of applying to the outer surface of the cladding a layer of a waterimpervious compound whose properties are compatible with those of the doped silica cladding, said water-impervious compound being selected from the group consisting of silicon nitride and the fluorides of calcium, magnesium and silicon which are solid under normal ambient conditions.
According to the present invention there is a method of manufacturing glass optical fibers having improved fatigue resistance, which includes the preparation of a preform consisting of a doped silica core with a doped silica cladding, the core and the cladding being differently doped, drawing said preform down to give the core the diameter needed for the finished fiber, and applying to the outer surface of said cladding a layer of water - impervious layer of silicon nitride whose properties are compatible with those of the doped silica cladding.
According to the present invention there is an optical fiber having improved fatigue resistance, including a silica core material doped with a compound having a higher refraction index than the silica to provide a first index of refraction; a cladding layer of silica doped with a second compound having a lower refractive index than silica to provide a second index of refraction the second index of refraction being lower than the first index of refraction; and a silicon nitride layer on the outer surface of the cladding layer to provide a water impervious coating to said cladding layer.
Embodiments of the invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a graphic representation of the time to failure for silica fibers as a function of the pH chemistry of the fiber surface;
Figure 2 is a cross-section of an optical fiber having a silicon nitride coating according to the invention.
Figure 3 is a cross-section of the optical fiber of Figure 2 after being given an outer plastics jacket;
Figure 4 is a cross-section of a fiber optic preform; and
Figure 5 is a sectional view of the apparatus used to provide the silicon nitride coated fiber according to the invention.
Figure 1 shows the relationship between the effective tensile strength of silica fibers in terms of time to failure under applied stress (500 kg/MM2) as a function of the pH of the fiber surface in a saturated environmental enclosure. The data shows that the loss rate can be substantially reduced when the pH value approaches 0 and becomes negative in value. Point B is the failure time for a silica fiber in air having 50% relative humidity. Point A is the failure time for a silica fiber in water having a pH value equal to 7.0.
Point C is the failure time for a silica fiber under a condition of partial vacuum (2x10-2torr) in order to keep the concentration of water at a very low level. Point D shows the predicted failure time for silica fibers coated with silicon nitride in accordance with this invention. The extended time to failure is an indication that the tensile strength of the fiber under continuing applied stress can be substantially increased when the surface water is effectively eliminated.
Figure 2 shows a glass optical communications fiber 10 having a core l1 consisting essentially of doped silica and having a doped silica cladding 12. Also included on the doped silica optical fiber 10 is a layer of silicon nitride material 13. The purpose of the silicon nitride layer 13 is to keep the outer surface of the optical fiber 10 free of any contact with moisture. Silicon nitride is chosen since its properties are compatible with silica and since very thin layers of silicon nitride have been found to be effectively water impervious. The thickness of the silicon nitride layer 13 is adjusted so that the effective water permeation can be zero.
One mil thickness is satisfactory since only a few hundred angstroms are generally required to provide continuity between the silicon nitride molecules. For the embodiment shown in Figure 2, the silicon nitride thickness is approximately 1,000 angstroms.
Figure 3 shows the silicon nitride coated optical fiber 10 of Figure 2 containing a core 11, cladding 12, silicon nitride layer 13 and an outer plastics jacket 14. The purpose of the jacket 14 is to improve the overall strength properties of the fiber 10.
For manufacturing the glass optical fibers of Figures 2 and 3 a fiber optic preform is conveniently employed. The preform 15 shown in Figure 4 contains a core material 11' and a cladding material 12' which after drawing into an optical fiber form the optical fiber core and cladding (11, 12).
To provide the silicon nitride coating the fiber optic preform 15 of Figure 4 is heated and drawn into an optical fiber and the optical fiber is drawn through an inline silicon nitride coating apparatus so that the silicon nitride layer 13 of Figures 2 and 3 is applied to the optical fiber surface while the fiber is still hot from drawing so that water molecules are not able to condense on the hot fiber surface.
Figure 5 shows a fiber optic preform 15 positioned above a suitable heat source 16 wherein a portion of a drawn optical fiber 15' is drawn through a reaction tube 17. The reaction tube 17 for the purpose of this embodiment consists of a hermetically sealed device containing an inlet 18 for introducing the silicon nitride reagents and an exhaust 19. Surrounding the reaction tube 17 are RF exciting coils 22 to generate the
RF plasma 20 as shown. The silicon nitride deposition by means of the RF plasma discharge 20 is preferred because of the water-tight continuous silicon nitride material generated. The silicon nitride coated fiber 10 is shewn issuing from the bottom of the reaction tube with the silicon nitride layer 13 as indicated.
Although the silicon nitride is shown as deposited from a reaction involving a radio frequency plasma 20 and silicon nitride 21 in molecular form, other methods of applying the silicon nitride coating 13 are equally effective. One method provides a reaction between the surface of the silica outer layer with a suitable nitrogen compound to form a very thin displacement of silicon nitride in situ on the silica surface.
Other materials contemplated for forming the water impervious layer of this invention include certain fluorides of magnesium, calcium and silicon, which are solid: at normal ambient temperature and whose properties are compatible with those of the fibre's cladding. Other methods of application which may be used include vacuum evaporation as well as the use of a glow discharge. One method of generating silicon nitride coatings by a glow discharge is that disclosed within U.S. Patent No. 3,485,666 incorporated herein by reference.
Although the fluorides of magnesium, calcium and silicon are specially effective other water-tight impervious layers can be used providing that the materials chosen are electrically non-conductive. This requirement is important for example when the optical fibers are to be used in a secured area. This is particularly important when the optical communication is to occur in a military environment when detection by radio frequency devices such as radar is to be avoided.
The embodiment of this invention which has been specifically described is directed to water impervious silicon nitride coated fibers for use with optical communication fibers to improve the tensile strength of the fiber in environments containing relatively high concentrations of atmospheric water vapor. This is by way of example only since the coated fibers of this invention readily find application wherever high tensile strength glass fibers may be required.
WHAT WE CLAIM IS:
1. A method of manufacturing glass optical fibres having improved fatigue resistance, which fibres have a doped silica core and a doped silica cladding, the core and the cladding being differently doped, which includes the step of applying to the outer surface of the cladding a layer of waterimpervious compound whose properties are compatible with those of the doped silica cladding, said water-impervious compound being selected from the group consisting of silicon nitride and the fluorides of calcium, magnesium and silicon which are solid under normal ambient conditions.
2. A method of manufacturing glass optical fibers having improved fatigue resistance which includes the preparation of a preform consisting of a doped silica core with a doped silica cladding, the core and the cladding being differently doped, drawing said preform down to give the core the diameter needed for the finished fiber, and applying to the outer surface of said cladding a layer of a water-impervious layer of silicon nitride whose properties are compatible with those of the doped silica cladding.
3. A method as claimed in claim 2, wherein the silicon nitride is applied to the glass surface by the deposition of the silicon nitride on the outer cladding glass surface of the fiber immediately after drawing into a fiber.
4. A method as claimed in claim 2, wherein the silicon nitride is applied to the outer cladding glass surface by the thermal dissociation of a silicon and a nitrogen compound in the presence of the glass fiber.
5. A method as claimed in claim 4, modified in that the silicon and nitrogen compound comprises halides.
6. A method as claimed in claim 4, modified in that the silicon and nitrogen compound comprises hydrides.
7. A method as claimed in claim 4, wherein the silicon and nitrogen compound is applied to the glass fiber surface by chemical vapor deposition.
8. A method as claimed in claim 4 wherein the deposition of the silicon and nitrogen compound is by an electrodeless glow discharge.
9. An optical fiber having improved fatigue resistance, which has a core of high purity silica material so doped as to have a first index of refraction with a doped silica cladding having a second index of refraction overlaying the core, a coating of silicon nitride material on the outer surface of said cladding and a layer of resin material on the outer surface of the silicon nitride layer.
10. An optical fiber having improved fatigue resistance, including a silica core material doped with a compound having a higher refraction index than the silica to provide a first index of refraction; a cladding layer of silica doped with a second compound having a lower refractive index than silica to provide a second index of refraction the second index of refraction being lower than the first index of refraction; and a silicon nitride layer on the outer surface of the cladding layer to provide a water impervious coating to said cladding layer.
11. A method of manufacturing glass optical fibers substantially as described with reference to the accompanying drawing.
12. An optical fiber made by the method of any one of claims 1 to 8, or 11.
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (12)
1. A method of manufacturing glass optical fibres having improved fatigue resistance, which fibres have a doped silica core and a doped silica cladding, the core and the cladding being differently doped, which includes the step of applying to the outer surface of the cladding a layer of waterimpervious compound whose properties are compatible with those of the doped silica cladding, said water-impervious compound being selected from the group consisting of silicon nitride and the fluorides of calcium, magnesium and silicon which are solid under normal ambient conditions.
2. A method of manufacturing glass optical fibers having improved fatigue resistance which includes the preparation of a preform consisting of a doped silica core with a doped silica cladding, the core and the cladding being differently doped, drawing said preform down to give the core the diameter needed for the finished fiber, and applying to the outer surface of said cladding a layer of a water-impervious layer of silicon nitride whose properties are compatible with those of the doped silica cladding.
3. A method as claimed in claim 2, wherein the silicon nitride is applied to the glass surface by the deposition of the silicon nitride on the outer cladding glass surface of the fiber immediately after drawing into a fiber.
4. A method as claimed in claim 2, wherein the silicon nitride is applied to the outer cladding glass surface by the thermal dissociation of a silicon and a nitrogen compound in the presence of the glass fiber.
5. A method as claimed in claim 4, modified in that the silicon and nitrogen compound comprises halides.
6. A method as claimed in claim 4, modified in that the silicon and nitrogen compound comprises hydrides.
7. A method as claimed in claim 4, wherein the silicon and nitrogen compound is applied to the glass fiber surface by chemical vapor deposition.
8. A method as claimed in claim 4 wherein the deposition of the silicon and nitrogen compound is by an electrodeless glow discharge.
9. An optical fiber having improved fatigue resistance, which has a core of high purity silica material so doped as to have a first index of refraction with a doped silica cladding having a second index of refraction overlaying the core, a coating of silicon nitride material on the outer surface of said cladding and a layer of resin material on the outer surface of the silicon nitride layer.
10. An optical fiber having improved fatigue resistance, including a silica core material doped with a compound having a higher refraction index than the silica to provide a first index of refraction; a cladding layer of silica doped with a second compound having a lower refractive index than silica to provide a second index of refraction the second index of refraction being lower than the first index of refraction; and a silicon nitride layer on the outer surface of the cladding layer to provide a water impervious coating to said cladding layer.
11. A method of manufacturing glass optical fibers substantially as described with reference to the accompanying drawing.
12. An optical fiber made by the method of any one of claims 1 to 8, or 11.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79242977A | 1977-04-29 | 1977-04-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1592234A true GB1592234A (en) | 1981-07-01 |
Family
ID=25156860
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB16255/78A Expired GB1592234A (en) | 1977-04-29 | 1978-04-25 | Sin2 coated optical fibre |
Country Status (5)
| Country | Link |
|---|---|
| AU (1) | AU3539878A (en) |
| DE (1) | DE2818036A1 (en) |
| FR (1) | FR2389147A1 (en) |
| GB (1) | GB1592234A (en) |
| NL (1) | NL7804449A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2138167A (en) * | 1981-03-24 | 1984-10-17 | Consiglio Nazionale Ricerche | Connector for optic fibre laser radiation conveying device |
| GB2151369A (en) * | 1983-10-24 | 1985-07-17 | British Telecomm | Optical fibres |
| EP0177206A1 (en) * | 1984-09-29 | 1986-04-09 | Stc Plc | Optical fibres |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4249925A (en) * | 1978-05-12 | 1981-02-10 | Fujitsu Limited | Method of manufacturing an optical fiber |
| US4319803A (en) * | 1978-11-24 | 1982-03-16 | Hewlett-Packard Company | Optical fiber coating |
| US4306897A (en) * | 1980-04-16 | 1981-12-22 | International Telephone And Telegraph Corporation | Method of fabricating fatigue resistant optical fibers |
| DE3035879A1 (en) * | 1980-09-23 | 1982-04-29 | Siemens AG, 1000 Berlin und 8000 München | Core and sheath glass optical fibre of lead glass - of specified size is made simply and cheaply and has required damping, coupling and strength |
| ZA833150B (en) * | 1982-05-28 | 1984-01-25 | Int Standard Electric Corp | Coating an optical fibre |
| US4696543A (en) * | 1984-05-22 | 1987-09-29 | Standard Telephone And Cables, Plc | Optical fiber cable having a low permeability to hydrogen |
| GB2159290B (en) * | 1984-05-22 | 1987-11-18 | Stc Plc | Cables containing amorphous metals |
-
1978
- 1978-04-24 AU AU35398/78A patent/AU3539878A/en active Pending
- 1978-04-25 GB GB16255/78A patent/GB1592234A/en not_active Expired
- 1978-04-25 DE DE19782818036 patent/DE2818036A1/en active Pending
- 1978-04-26 FR FR7812277A patent/FR2389147A1/en not_active Withdrawn
- 1978-04-26 NL NL7804449A patent/NL7804449A/en not_active Application Discontinuation
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2138167A (en) * | 1981-03-24 | 1984-10-17 | Consiglio Nazionale Ricerche | Connector for optic fibre laser radiation conveying device |
| GB2151369A (en) * | 1983-10-24 | 1985-07-17 | British Telecomm | Optical fibres |
| EP0177206A1 (en) * | 1984-09-29 | 1986-04-09 | Stc Plc | Optical fibres |
| AU574225B2 (en) * | 1984-09-29 | 1988-06-30 | Northern Telecom Limited | Optical fibre surface modification |
| AU584009B2 (en) * | 1984-09-29 | 1989-05-11 | Stc Plc | Optical fibres |
| US4911742A (en) * | 1984-09-29 | 1990-03-27 | Stc, Plc | Method of manufacturing optical fibers |
| US5102438A (en) * | 1984-09-29 | 1992-04-07 | Stc, Plc | Method of manufacturing silicon optical fiber having a compressive surface layer |
Also Published As
| Publication number | Publication date |
|---|---|
| NL7804449A (en) | 1978-10-31 |
| FR2389147A1 (en) | 1978-11-24 |
| DE2818036A1 (en) | 1978-11-09 |
| AU3539878A (en) | 1979-11-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |