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
  • G02B6/26—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
• • 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
  • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
  • G02B6/2821—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals
  • G02B6/2826—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals using mechanical machining means for shaping of the couplers, e.g. grinding or polishing
  • G02B6/283—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals using mechanical machining means for shaping of the couplers, e.g. grinding or polishing couplers being tunable or adjustable
• • 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
  • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
  • G02B6/2821—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals
  • G02B6/2835—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals formed or shaped by thermal treatment, e.g. couplers
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/0147—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on thermo-optic effects

Definitions

• This invention relates to Fused Tapered Fibre-optic couplers and in particular to directional couplers of this type such as beam splitters and combiners.
• Polished directional couplers are made by polishing away the cladding of two single mode fibres to within about one micron of their respective cores. The coupler is then formed by placing the two polished half couplers together with an index-inatching oil or UV curable epoxy resin between them. The optical characteristics of the resulting directional coupler can be tuned by sliding the two polished halves relative to each other and then fixing them, if desired, by curing the epoxy resin.
• the fused tapered single mode directional coupler is made by a quite different technique and a section through a typical fused directional coupler is shown in figure 1.
• two single-mode fibres are intertwined at the coupling location and then held by two movable supports on either side of the intertwined section.
• a small oxy-butane flame is applied to the fibres so that they fuse together at the intertwined section.
• the two supports are moved apart such that an elongate fused section 1 is formed between two fused tapered sections 3 from which the two separate fibres 5 emerge at both ends of the coupler. It is important to move the supports apart in a straight line so that a low-loss coupler will be produced.
• the speed of separation of the supports is also .Important since this determines the shape of the resulting taper which has a significant effect on any losses in the coupler.
• both types of directional coupler can be made with losses less than 0.05dB
• the fused directional coupler can be made much more quickly and cheaply and its power splitting ratio can be monitored during fabrication.
• the polished coupler's power splitting ratio can be measured after fabrication but it can then be tuned to a desired ratio by sliding the two halves over each other.
• Figure 1 is a longitudinal section through a typical fused tapered directional coupler as described above;
• Figure 2 is a longitudinal section through an adjustable fused tapered directional coupler assembly in accordance with the invention
• Figure 3 is a graph showing the variation of power-splitting ratio for the coupler shown in Figure 2 as a function of the axial twist angle
• Figure 4 is a graph of the spectral power splitting ratio for increasing amounts of twist angle.
• a twistable optic fibre directional coupler assembly is shown in figure 2 and comprises a silica tube 2 cont ⁇ _ining a fused directional coupler 4.
• the tube has two rotatable plastic end caps 6 each having a hole therein, through which the optic fibres 8, leading to and from the coupler pass.
• the holes in this case are 1mm diameter to make threading of the fibres t ⁇ irough the end caps relatively simple.
• the fibres are secured to the end caps with epoxy resin 10 whilst the coupler is kept taut between them.
• the relatively rotatable end caps thus provide a means for twisting the coupler 4.
• the end caps may have a graduated scale upon them to indicate the power splitting ratio available at any angular position.
• the coupler assembly was also struck vigourously and dropped onto a bench from a height of 20mm. This caused a momentary coupled power variation of typically 0.4% and at no stage greater than 0.9%
• the reason twisting induces a change in the power splitting ratio of the coupler is that the effective refractive index across the transverse cross section of the coupling region 1 of Figure 1 changes with twisting.
• This accounts for the decoupling observed in twisted directional couplers since the effective index induced by the twist increases with distance from the longitudinal axis of the coupler.
• the relative increase in the effective index at the edges of the coupler causes a redistribution of the modal fields in the coupler away from the axis. This reduces the field overlap between the two sides of the coupler and hence causes a degree of decoupling. It can be shown by calculation that although this change in the effective index is small it is sufficient to account for the halving of the coupling strength observed in twisted couplers.
• the coupler was twisted and untwisted through 480° many times without suffering any degradation in performance.
• the coupler was finally destroyed after eight consecutive revolutions in the same direction.
• the twisting of fused tapered directional couplers provides a method of tuning them across all splitting ratios with low losses.
• the process is reversible and repeatable and does not degrade the coupler performance.

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

Applications Claiming Priority (2)

Publications (1)

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• 1988
  • 1988-06-09 GB GB888813624A patent/GB8813624D0/en active Pending
• 1989
  • 1989-06-09 WO PCT/GB1989/000644 patent/WO1989012243A1/en not_active Application Discontinuation
  • 1989-06-09 EP EP19890906411 patent/EP0418286A1/de not_active Withdrawn

Non-Patent Citations (1)

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