GB2228585A - Silica optical fibre having two cladding layers - Google Patents

Silica optical fibre having two cladding layers Download PDF

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Publication number
GB2228585A
GB2228585A GB8904483A GB8904483A GB2228585A GB 2228585 A GB2228585 A GB 2228585A GB 8904483 A GB8904483 A GB 8904483A GB 8904483 A GB8904483 A GB 8904483A GB 2228585 A GB2228585 A GB 2228585A
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United Kingdom
Prior art keywords
fibre
refractive index
cladding layer
optical fibre
optical
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.)
Withdrawn
Application number
GB8904483A
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GB8904483D0 (en
Inventor
Terry Bricheno
Kevin John Warbrick
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
STC PLC
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STC PLC
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Publication date
Application filed by STC PLC filed Critical STC PLC
Priority to GB8904483A priority Critical patent/GB2228585A/en
Publication of GB8904483D0 publication Critical patent/GB8904483D0/en
Publication of GB2228585A publication Critical patent/GB2228585A/en
Withdrawn legal-status Critical Current

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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02Optical fibres with cladding with or without a coating
    • G02B6/036Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03661Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 4 layers only
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02Optical fibres with cladding with or without a coating
    • G02B6/036Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03638Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only
    • G02B6/0365Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only arranged - - +

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Couplings Of Light Guides (AREA)

Abstract

Silica optical fibre, particularly for use in fibre taper structures, includes a core section of refractive index n1, a substantially thick first cladding layer of refractive index n2 surrounding the core and a relatively thin outer cladding layer of refractive index n3 (n1>n2>n3). When such a fibre is tapered the thin outer cladding layers serves to confine a mode to the guide and prevents power loss. Such tapered fibres can be encapsulated directly by material, such as an epoxy resin, which has a higher refractive index than n2, without power loss. <IMAGE>

Description

OPTICAL FIBRE.
This invention relates to optical fibre and in particular to fibre for optical fibre tapers and optical devices and structures including optical fibre tapers.
Single mode optical fibre (1 - Fig. 1) is frequently provided with an adiabatic taper 2 adjacent its end which is to be coupled to other fibres or devices, and a reduced diameter parallel-sided section 3. Such tapering is performed in order to reduce coupling losses between, for example, spatially separated fibres, which fibres are separated to allow for the inclusion of a device or other material, for example, in the optical path therebetween. The effect of tapering is to increase the field radius of the transmitted mode together with increased collimation of the unguided light (in the optical path between the fibre ends, for example).For typical single mode telecommunication fibre of 125jim OD the mode spot size diameter is 10cm. By adiabatically tapering the fibre down to 5(m OD, the spot size is increased to 25cm.
Adiabatic tapering may be achieved using the basic progressive stretching (differential pulling) technique of GB 2150703B.
One limitation of this tapering approach is that the larger propagating mode has a significant power density external to the taper which makes it sensitive to changes in the refractive index external to the taper. In particular power can be lost as a result of encapsulation using epoxy resins since they have a higher refractive index than silica.
According to one aspect of the present invention there is provided a silica optical fibre including a core section of refractive index nl, a substantially thick first cladding layer of refractive index n2 surrounding the core and a relatively thin outer cladding layer of refractive index n3, and wherein n1n2n3.
According to another aspect of the present invention there is provided an optical fibre element comprising a length of optical fibre according to the preceding paragraph and which has an adiabatic taper whereby one length section of the fibre is of a reduced diameter in comparison with another length section, the outer cladding layer of the fibre serving to increase the confinement of a guided mode in the reduced diameter length section in comparison with a tapered fibre without such an outer cladding layer.
Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 illustrates a fibre taper as referred to above; Fig. 2 illustrates for a conventional fibre the mode field amplitude between the centre of a tapered fibre and the edge of the fibre as well the portion thereof which extends outside of the fibre; Fig. 3 is similar to Fig. 2 but for a fibre having a depressed external glass cladding, and Fig. 4 illustrates an encapsulated fibre taper.
In Fig. 2, is shown the mode field amplitude 5 of a conventional single-mode fibre whose outer protective plastics coating, e.g. of acrylate, has been stripped and the fibre tapered by the differential pulling technique referred to above. As can be seen there is significant power (shaded area 6) in the region outside of the fibre, which power will be lost if the taper is encapsulated in a material having a higher refractive index than the material of the fibre (silica). To overcome this a previous suggestion involved encapsulating (coating) the taper at least over the length from which the acrylate was removed with a thin layer of a low index polymer prior to use of an epoxy encapsulant.In one previous arrangement the tapered fibre end coated with the low index polymer is inserted in a length of tube of glass or metal, for example, and then the space between the tube and the polymer filled with an epoxy, thus providing a handleable structure. Whilst this approach should reduce power losses as a result of the low index polymer confining the mode more tightly to the fibre guide, in practice there are a number of difficulties. The polymer is very soft and its adhesion to the silica fibre is poor. Furthermore the optical properties of the polymer are variable depending on how it was treated/applied and contaminents thereof.
The mode may be more tightly confined to the guide by an alternative approach which is that proposed by the present invention, namely that the optical fibre itself is provided with a thin depressed refractive index silica cladding which confines the power to the guide after tapering. Fig. 3 illustrates the effect of an extra cladding 10 which is only some 5Jum thick prior to tapering and 2.5,utn thick after tapering and is depressed in refractive index relative to the normal silica cladding by an amount of the order of 0.05. As can be seen this depressed external silica cladding has the effect of confining the power 7 within the guide (fibre).Thus the silica fibre has a core section of refractive index n1, a substantially thick first index n, and a relatively cladding layer of refractive index n2 and a relatively thin outer cladding layer 10 of refractive index n3 (n1 > n2n3). Typically for single-mode fibre the core diameter is in the range 9-lOpm, the first cladding layer outer diameter is in the range 1l5-120,um and the outer cladding layer is of the order of 5-lOpm. thick.
The thin depressed refractive index cladding approach may also be applicable to large cored multimode fibres in which case the core diameter will be larger than that quoted.
Such a depressed external silica cladding can be achieved in various ways. For example it can be achieved at the fibre preform stage by the deposition of doped silica, fluorine being a suitable dopant, either directly on the preform or on the internal bore of a silica support tube which is then collapsed around the preform, before having the support tube removed in a reducing flame. The refractive index profile in Figure 3 relates to the latter method of manufacture, the step at the edge of the fibre being due to incomplete removal of the support tube. Alternatively a predepressed support tube of a suitable thickness may be used. What ever method is used to produce the preform, fibre will be drawn therefrom as normal to a size compatible with, for example, the standard single-mode telecommunications fibre.
Tapers can be provided in such optical fibre with a depressed refractive index silica cladding in the conventional manner referred to above. Instead of having first to coat them with polymer as described above, the fibre taper and end 12 (Fig. 4) can inserted directly into a reinstatement tube 13 and the space therebetween filled with epoxy resin 14. Thus the epoxy is applied directly to the fibre, i.e. to the low refractive index cladding thereof. This obviates the problems associated with the use of low refractive index polymers. Thus the fibre taper end is easily reinstated using a standard epoxy technique. Whereas reinstatement of a single fibre taper has so far been described, the principle is also applicable to arrays of tapers such as in 1 x N couplers. See for example our GB Applications Nos.
8718055 (Serial No. 2207525) (T. Bricheno 18-3-1) and 8816896.8 (Serial No. ) (T. Bricheno 23-62).
The removal of the low refractive index polymer for the epoxy encapsulation process, simplifies the manufacture of arrays of tapers, in particular. By providing optical fibre with a thin depressed refractive index silica cladding, fibre tapers which are insensitive to the refractive index of the surrounding medium are achieved.
One use for reinstated fibre tapers is in optical isolators, which are optical "one-way valves" used to protect laser diodes from back reflected light.
Tapered optical fibres are used to feed light to and from the Faraday rotator (active component) in the isolator.

Claims (8)

CLAIMS.
1. A silica optical fibre including a core section of refractive index nl, a substantially thick first cladding layer of refractive index n2 surrounding the core and a relatively thin outer cladding layer of refractive index n3, and wherein n1n2 > n3.
2. A fibre as claimed in claim 1, wherein for single-mode fibre the core diameter is in the range 9-lOpm, the first cladding layer outer diameter is in the range 115-120Fm and the outer cladding layer is of the order of 5-lOpm thick.
3. An optical fibre element comprising a length of fibre as claimed in claim 1 or claim 2 and which has an adiabatic taper whereby one length section of the fibre is of a reduced diameter in comparison with another length section, the outer cladding layer of the fibre serving to increase the confinement of a guided mode in the reduced diameter length section in comparison with a tapered fibre without such an outer cladding layer.
4. An optical fibre element as claimed in claim 3 wherein the taper and at least a portion of the fibre on either side thereof is disposed within a tube, the space between the tube and the fibre being filled with an encapsulant.
5. An element as claimed in claim 4 wherein the encapsulant is an epoxy resin.
6. An optical device including at least one optical fibre element as claimed in any one of claims 3 to 5.
7. An optical fibre for optical fibre tapers substantially as herein described with reference to the accompanying drawings.
8. An optical device including an optical fibre taper substantially as herein described with reference to the accompanying drawings.
GB8904483A 1989-02-28 1989-02-28 Silica optical fibre having two cladding layers Withdrawn GB2228585A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8904483A GB2228585A (en) 1989-02-28 1989-02-28 Silica optical fibre having two cladding layers

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8904483A GB2228585A (en) 1989-02-28 1989-02-28 Silica optical fibre having two cladding layers

Publications (2)

Publication Number Publication Date
GB8904483D0 GB8904483D0 (en) 1989-04-12
GB2228585A true GB2228585A (en) 1990-08-29

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7844155B2 (en) * 2007-05-07 2010-11-30 Corning Incorporated Optical fiber containing alkali metal oxide
US7889960B2 (en) 2008-05-06 2011-02-15 Draka Comteq B.V. Bend-insensitive single-mode optical fiber
US7899293B2 (en) 2006-04-10 2011-03-01 Draka Comteq, B.V. Single-mode optical fiber
US7995889B2 (en) 2005-11-10 2011-08-09 Draka Comteq, B.V. Single mode optical fiber
US8145027B2 (en) 2007-11-09 2012-03-27 Draka Comteq, B.V. Microbend-resistant optical fiber

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3784386A (en) * 1971-02-16 1974-01-08 Corning Glass Works Cladding glasses for photochromic optical fibers
US3806224A (en) * 1972-10-06 1974-04-23 Bell Telephone Labor Inc Optical transmission line
GB1436605A (en) * 1972-10-06 1976-05-19 Western Electric Co Glass transmission line
GB2035601A (en) * 1978-11-13 1980-06-18 Furukawa Electric Co Ltd Single-mode optical fibre
GB1574355A (en) * 1976-03-08 1980-09-03 American Optical Corp Optical fibres
GB2071351A (en) * 1979-08-27 1981-09-16 Northern Telecom Ltd Manufacture of monomode fibers
US4436368A (en) * 1977-06-06 1984-03-13 Corning Glass Works Multiple core optical waveguide for secure transmission
GB2136239A (en) * 1983-03-03 1984-09-12 British Telecomm Optical fibre transmission systems
GB2185331A (en) * 1985-09-02 1987-07-15 Nippon Telegraph & Telephone Single mode optical fibre
EP0260795A2 (en) * 1986-08-08 1988-03-23 AT&T Corp. Optical fiber

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3784386A (en) * 1971-02-16 1974-01-08 Corning Glass Works Cladding glasses for photochromic optical fibers
US3806224A (en) * 1972-10-06 1974-04-23 Bell Telephone Labor Inc Optical transmission line
GB1436605A (en) * 1972-10-06 1976-05-19 Western Electric Co Glass transmission line
GB1574355A (en) * 1976-03-08 1980-09-03 American Optical Corp Optical fibres
US4436368A (en) * 1977-06-06 1984-03-13 Corning Glass Works Multiple core optical waveguide for secure transmission
GB2035601A (en) * 1978-11-13 1980-06-18 Furukawa Electric Co Ltd Single-mode optical fibre
GB2071351A (en) * 1979-08-27 1981-09-16 Northern Telecom Ltd Manufacture of monomode fibers
GB2136239A (en) * 1983-03-03 1984-09-12 British Telecomm Optical fibre transmission systems
GB2185331A (en) * 1985-09-02 1987-07-15 Nippon Telegraph & Telephone Single mode optical fibre
EP0260795A2 (en) * 1986-08-08 1988-03-23 AT&T Corp. Optical fiber

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7995889B2 (en) 2005-11-10 2011-08-09 Draka Comteq, B.V. Single mode optical fiber
US8837889B2 (en) 2005-11-10 2014-09-16 Draka Comteq, B.V. Single mode optical fiber
US7899293B2 (en) 2006-04-10 2011-03-01 Draka Comteq, B.V. Single-mode optical fiber
US8103143B2 (en) 2006-04-10 2012-01-24 Draka Comteq, B.V. Single-mode optical fiber
US7844155B2 (en) * 2007-05-07 2010-11-30 Corning Incorporated Optical fiber containing alkali metal oxide
US8145027B2 (en) 2007-11-09 2012-03-27 Draka Comteq, B.V. Microbend-resistant optical fiber
US8385705B2 (en) 2007-11-09 2013-02-26 Draka Comteq, B.V. Microbend-resistant optical fiber
US7889960B2 (en) 2008-05-06 2011-02-15 Draka Comteq B.V. Bend-insensitive single-mode optical fiber
US8131125B2 (en) 2008-05-06 2012-03-06 Draka Comteq, B.V. Bend-insensitive single-mode optical fiber
US8145025B2 (en) 2008-05-06 2012-03-27 Draka Comteq, B.V. Single-mode optical fiber having reduced bending losses
US8428414B2 (en) 2008-05-06 2013-04-23 Draka Comteq, B.V. Single-mode optical fiber having reduced bending losses

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Publication number Publication date
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