Classifications

• • 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
  • G02B6/24—Coupling light guides
  • G02B6/42—Coupling light guides with opto-electronic elements
  • G02B6/4201—Packages, e.g. shape, construction, internal or external details
  • G02B6/4246—Bidirectionally operating package structures
• • 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
  • G02B6/24—Coupling light guides
  • G02B6/26—Optical coupling means
  • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
  • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
  • G02B6/29331—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by evanescent wave coupling
  • G02B6/29332—Wavelength selective couplers, i.e. based on evanescent coupling between light guides, e.g. fused fibre couplers with transverse coupling between fibres having different propagation constant wavelength dependency

Definitions

• Optical fiber coupler used as WDM.
• the present invention concerns single mode couplers and in particular, though not exclusively, Wavelength Division Multiplex (WDM) couplers.
• WDM Wavelength Division Multiplex
• Such a coupler can be manufactured by fusing together two single mode optical fibres, this being done by placing two portions of the fibres in contact, and subjecting the contiguous portions to both heat and elongation.
• This biconical fusion technique produces couplers with natural wavelength dependence.
• Such couplers should be highly suitable for low loss and cheap wavelength division in multiplexing/demultiplexing.
• the present invention has for an object to provide a coupler which affords high isolation, is capable of maintaining this through a wide temperature range and which is relatively insensitive to the polarisation of input light.
• the present invention consists in a coupler for use in wavelength division multiplex, the coupler comprising a pair of monomode optical fibres having had adjacent portions fused together, and a biconical taper fabricated in the fused portion, the fused portion having a near-circular cross-section such that it has substantially zero birefringence.
• Figure 1 is a refractive index profile across a monomode optical fibre
• Figure 2 is a diagrammatic view of a wave coupler utilising two fused monomode fibres
• Figure 3 shows some cross-sections of fused monomode optical fibres.
• FIG. 1 of the drawings shows the refractive index profile of a matched, monomode optical fibre.
• two lengths of optical fibre profiles are placed and held in juxtaposition.
• One fibre may be twisted around the other but this is- not normal.
• the juxtaposed portions are then heated, for example by an oxy-butane flame.
• the heating causes fusion between the two fibres.
• the fused fibres are subjected to extrusion so as to generate a biconical taper.
• the heating period determines the degree of fusion between the two fibres. Whilst the fused fibres are being extended light at selected wavelength is launched down one of the fibres and the power transmitted through the fibre monitored.
• the extension of the fibre causes a biconical taper to be formed in the extended portion, and this taper becomes a multi-mode section.
• this taper becomes a multi-mode section.
• interference of the local LP 01 and LP 11 modes causes power transfer along the taper.
• the taper length could be such that for a particular taper shape all power emerges at the taper end in one fibre or the other. produced during the fabrication of the taper, the actual tapering process can be controlled to give a desired degree of taper.
• the extension of the coupled fibres is stopped after 2 power oscillations have been detected.
• the resultant pair of fused fibres are shown in Figure 2 at 10 and 11.
• the fibres are fused together at the portion generally indicated at 12 which also includes a biconical taper which, as mentioned, has been stopped at two power oscillations during the fabrication process.
• FIG. 3 a-c this shows some possible fusion cross-sectional geometries obtainable with fused couplers of the kind shown in Figure 2.
• fusion between fibres 10 and 11 is far from total and the contours of the two fibres are easily discernible.
• This structure has poor field confinement so that the coupling ratio is very sensitive to the outside index of the potting material. This in turn makes the coupler very sensitive to temperature variations and these change the refractive index of the potting material.
• the other two structures, 3b and 3c show successively greater degrees of fusion between the two fibres. The amount of fusion is dependent on the intensit and duration of the heat applied. In fact, the circular nature of Figure 3c shows that total fusion has occurred.
• the formed birefringence has the same value as that of the stress birefringence and therefore gives a total birefringence of zero. Since the coupler is well fused it is not very sensitive to the index change of its surrounding potting material and therefore can be operated over a broad temperature range. Its birefringence of zero also means that it can be operated with all possible polarisation input states. It will be appreciated that the wavelength period of WDM couplers is also related to the fusion crosssection so that if a zero birefringence structure does not exactly have the required channel wavelengths at the maxima and minima of its period, fehen it has to be adjusted very slightly to make them fall on the maxima and minima. This minor adjustment to more than zero birefringence only sacrifices an equally small degree of insensitivity to polarisation. It is thus possible to compromise between the three major requirements of high isolation, and maintaining high isolation over a broad temperature range and for all polarisation input states.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Couplings Of Light Guides (AREA)
• Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=10589233

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Family Cites Families (8)

• 1985
  • 1985-12-04 GB GB858529864A patent/GB8529864D0/en active Pending
• 1986
  • 1986-12-04 GB GB08629039A patent/GB2184258A/en not_active Withdrawn
  • 1986-12-04 JP JP50026586A patent/JPS63501985A/ja active Pending
  • 1986-12-04 EP EP19870900182 patent/EP0248065A1/de not_active Withdrawn
  • 1986-12-04 WO PCT/GB1986/000739 patent/WO1987003702A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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