WO1987003676A1 - Fibre optic devices - Google Patents

Fibre optic devices Download PDF

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Publication number
WO1987003676A1
WO1987003676A1 PCT/GB1986/000738 GB8600738W WO8703676A1 WO 1987003676 A1 WO1987003676 A1 WO 1987003676A1 GB 8600738 W GB8600738 W GB 8600738W WO 8703676 A1 WO8703676 A1 WO 8703676A1
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WO
WIPO (PCT)
Prior art keywords
fibre
refractive index
medium
wavelengths
surrounding
Prior art date
Application number
PCT/GB1986/000738
Other languages
French (fr)
Inventor
George Antony Georgiou
Anthony Christos Boucouvalas
Original Assignee
The General Electric Company, P.L.C.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from GB858529862A external-priority patent/GB8529862D0/en
Priority claimed from GB858529863A external-priority patent/GB8529863D0/en
Application filed by The General Electric Company, P.L.C. filed Critical The General Electric Company, P.L.C.
Publication of WO1987003676A1 publication Critical patent/WO1987003676A1/en

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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
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
    • G01D5/3538—Optical fibre sensor using a particular arrangement of the optical fibre itself using a particular type of fiber, e.g. fibre with several cores, PANDA fiber, fiber with an elliptic core or the like
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
    • G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
    • G01N21/43—Refractivity; Phase-affecting properties, e.g. optical path length by measuring critical angle
    • G01N21/431—Dip refractometers, e.g. using 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
    • G02B6/02052—Optical fibres with cladding with or without a coating comprising optical elements other than gratings, e.g. filters
    • 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
    • G02B6/255—Splicing of light guides, e.g. by fusion or bonding
    • 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
    • G02B6/264—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting
    • G02B6/266—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting the optical element being an attenuator
    • 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
    • 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
    • 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 
    • G02F1/011—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  in optical waveguides, not otherwise provided for in this subclass
    • 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 
    • G02F1/011—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  in optical waveguides, not otherwise provided for in this subclass
    • G02F1/0115—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  in optical waveguides, not otherwise provided for in this subclass in optical fibres
    • G02F1/0118—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  in optical waveguides, not otherwise provided for in this subclass in optical fibres by controlling the evanescent coupling of light from a fibre into an active, e.g. electro-optic, overlay

Definitions

  • optical fibre couplers can be fabricated by imparting a biconical taper to a monomode optical fibre. With the aid of such tapering the core HE-., mode can couple into the HE-- mode of the tube waveguide, which is formed due to the cladding, in an efficient manner.
  • the present invention has for an object to utilise optical fibres having such biconical tapers to form devices, including sensing devices and tuneable attenuators, which are simple to manufacture and which incorporate low cost electronics.
  • the present invention consists in an optical fibre device comprising a monomode optical fibre having an optical coupler fabricated therein in the form of a biconical tapered portion, means for modifying the refractive index of a medium surrounding the tapered portion so that for a specified wavelength travelling along the fibre the power transmitted will vary in accordance with variation in the refractive index of the medium, and means for detecting light transmitted by the core of the optical fibre.
  • Figure 1 shows various refractive index profiles taken across the diameter of optical fibres suitable for use in sensors according to the present invention
  • Figure 2 is a plot of transmitted power against extension of an optical fibre dum ' ng the process of producing a biconical taper in the fibre
  • Figure 3 is a plot similar to Figure 2 showing the effect of stopping extension at a selected point
  • Figure 4 is a plot showing the refractive index response of the taper, the refractive index varying in response to temperature variations
  • Figure 5 is a diagram showing how a temperature-linked refractive index variation can be applied to a tapered fibre to make a fuseable attenuator
  • Figure 6 is a plot of the refractive index response of a tapered fibre at a second wavelength
  • Figure 7 is a diagram of a sensing device
  • Figures 8 to 10 are vaious plots again showing the responses obtained to varying degrees of taper and surrounding refractive indices.
  • the refractive index profiles shown in Figure 1 show some of the types of single mode optical fibres which can be utilised in carrying out the present invention.
  • the profiles a, b, c, d, e and f respectively relate to Matched, Depressed, Quadruple Clad, Segmented Core and Raised Cladding optical fibres.
  • All these types of fibre can be formed into coaxial couplers by the process described in our co-pending U.K. Application No. 8519086 entitled "Coaxial Couplers".
  • laser light is launched into one end of an optical fibre and the transmitted power detected at the other end. Whilst the light is being transmitted a portion of the fibre is simultaneously heated and elongated, generating a biconical taper in the fibre.
  • the light guided in the core of the single mode fibre is directed into the tapered section.
  • the tapering being applied causes the tapered portion to become a multi-mode section, and interference of thelocal HE.. and HE-- modes causespower transfer along the taper.
  • a tapered optical coupler produced by this procedure can be incorporated in a range of sensing devices by utilising the refractive index response of the tapers. Then if the tapered portion is immersed in a liquid such as silicone oil, which has a higher refractive index than silica, and the liquid is heated so that its refractive index varies the response of the taper to light of a particular wavelength will vary. This variation is shown in the plot of Figure 4. From this plot it can be seen that there is maximum power transmission at point A. This is at a temperature of 29 C. At higher temperatures the power throughput decreases almost linearly as temperature rises. Thus point B shows power transmission at 55 C.
  • the section A-B of the plot can be used to provide a sensor with relatively low sensitivity and good dynamic range in which a change of refractive index of the order of 10 corresponds to a change in temperature of approximately 30 C, and requiring a detection sensit- ivity range of ⁇ " ⁇ 20 dB.
  • These figures provide the basis for an intensity sensor for the measurement of temperature, refractive index, acoustic, biological and other sensors which directly or indirectly use this refractive index and intensity relation.
  • FIG. 6 is a plot of the refractive index response of the same taper at a second wavelength when subjected to the same changes in refractive index as caused the plot of Figure 4. It will be seen here that the linear slope A-B of Figure 4 has been replaced by a substantially constant plateau. It is the ability of a single fibre to give two such separate results which enables a compensating factor to be built in to a sensor.
  • Such a compensated sensor is shown" in Figure 7.
  • Laser light at two differing wavelengths , A- is launched down a single monomode optical fibre 10 which has a biconical taper imparted to it at 11 and which is surrounded by a sensor area generally indicated at 12.
  • This sensor area could, for example, be a capillary tube filled with silicone oil as in the embodiment shown in Figure 5.
  • the tapered portion 11 will give power transmission plots of the kind shown in Figures 4 and 6 in response to changes in the refractive index of the surrounding sensor area, and in response to light of wavelengths r and respectively.
  • the two wavelengths can be launched into the fibre by means of a coupler.
  • FIG. 5 shows a tuneable attenuator.
  • a monomode optical fibre 1 has a biconical taper fabricated in it in the region generally indicated at 2. This region is housed in a capillary glass tube 3 filled with a liquid such as silicone oil the refractive index of which varies with temperature over the required ranges. The ends of capillary 3 are sealed with UV-cured epoxy resin. The tube is coated with resistive material and provided with electrodes 4 and 5. The application of a voltage across the electrodes causes the heat released to heat the liquid and lower its refractive index, hence varying the transmission through the fibre 1. In this manner a tuneability of >30 dB can be achieved.
  • an optical modulator can be constructed using this fact.
  • a monomode fibre is surrounded with a material having a refractive index which has.a value selected to provide maximum power transmission.
  • the transmission power is rapidly reduced to a minimum, a loss of approximately 30 dB.
  • Figure 4 shows a plot which has been derived using a tapered biconical fibre the elongation of which has been stopped after l ⁇ power oscillations. If instead the fabrications of the taper had been extended to two complete power oscillations, as shown in Figure 8, then using this biconiclly tapered fibre to produce a plot in response to changes of refractive index results in the plot of Figure 9. Similarly extending the number of oscillations to 12 produces the equivalent plots of Figures 7 and 8.
  • variable refractive index surrounding medium various types of material can be used for the variable refractive index surrounding medium.
  • the monomode fibre could be fabricated from a material having a high enough refractive index to match an electro-optic crystal such as KDP. The electro-optic effect could then be used so that the tapered fibre portion and the crystal together act as a modulator. If an electro-optic crystal is used as a cladding medium surrounding the taper it must be grown carefully around the taper. It is possible to grow single KDP crystals long enough to clad the taper region and also to enclose the modulating electrodes.
  • low refractive index liquid crystals are used with Si ⁇ 2 guides or with high refractive index glass fibre tapers.
  • the necessary change of refractive index of the surrounding medium is 10 "3 .

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Nonlinear Science (AREA)
  • Biochemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Measuring Temperature Or Quantity Of Heat (AREA)

Abstract

A fibre optic device which can be used as an attenuator or a sensor. The fiber has a biconical taper which can be immersed in a medium having a higher refractive index so that light transmission through the fibre can be used as a sensor in measuring temperature, refractive index. When used as a tuneable attenuator electrodes are mounted in contact with the medium so that it can be heated to vary transmissivity through the fibre.

Description

Fibre Optic Devices
The present invention concerns optical fibre devices. It has been discovered that optical fibre couplers can be fabricated by imparting a biconical taper to a monomode optical fibre. With the aid of such tapering the core HE-., mode can couple into the HE-- mode of the tube waveguide, which is formed due to the cladding, in an efficient manner.
The present invention has for an object to utilise optical fibres having such biconical tapers to form devices, including sensing devices and tuneable attenuators, which are simple to manufacture and which incorporate low cost electronics.
Accordingly from one aspect the present invention consists in an optical fibre device comprising a monomode optical fibre having an optical coupler fabricated therein in the form of a biconical tapered portion, means for modifying the refractive index of a medium surrounding the tapered portion so that for a specified wavelength travelling along the fibre the power transmitted will vary in accordance with variation in the refractive index of the medium, and means for detecting light transmitted by the core of the optical fibre.
In order that the present invention may be more readily understood, two embodiments of devices constructed in accordance with the invention will now be described by way of example and with reference to the accompanying drawings, in which:
Figure 1 shows various refractive index profiles taken across the diameter of optical fibres suitable for use in sensors according to the present invention,
Figure 2 is a plot of transmitted power against extension of an optical fibre dum'ng the process of producing a biconical taper in the fibre,
Figure 3 is a plot similar to Figure 2 showing the effect of stopping extension at a selected point,
Figure 4 is a plot showing the refractive index response of the taper, the refractive index varying in response to temperature variations,
Figure 5 is a diagram showing how a temperature-linked refractive index variation can be applied to a tapered fibre to make a fuseable attenuator,
Figure 6 is a plot of the refractive index response of a tapered fibre at a second wavelength,
Figure 7 is a diagram of a sensing device, and
Figures 8 to 10 are vaious plots again showing the responses obtained to varying degrees of taper and surrounding refractive indices.
Referring now to the drawings, the refractive index profiles shown in Figure 1 show some of the types of single mode optical fibres which can be utilised in carrying out the present invention. The profiles a, b, c, d, e and f respectively relate to Matched, Depressed, Quadruple Clad, Segmented Core and Raised Cladding optical fibres.
All these types of fibre can be formed into coaxial couplers by the process described in our co-pending U.K. Application No. 8519086 entitled "Coaxial Couplers". In this process laser light is launched into one end of an optical fibre and the transmitted power detected at the other end. Whilst the light is being transmitted a portion of the fibre is simultaneously heated and elongated, generating a biconical taper in the fibre. The light guided in the core of the single mode fibre is directed into the tapered section. The tapering being applied causes the tapered portion to become a multi-mode section, and interference of thelocal HE.. and HE-- modes causespower transfer along the taper. If the taper length is such that for the particular taper shape power emerges at the taper end in the core of the fibre, then the light will be transmitted. If, however, it emerges in the cladding it will be lost. This can be seen from the plot shown in Figure 2 which consists of power oscillations induced by the tapering process. Figure 2 shows the result if the taper is elongated until it breaks. However, the tapering process can be stopped at will. Figure 3 shows the power transmission response when extension of a fibre portion to produce a biconical taper has been stopped just after I5 detected power oscillations.
A tapered optical coupler produced by this procedure can be incorporated in a range of sensing devices by utilising the refractive index response of the tapers. Then if the tapered portion is immersed in a liquid such as silicone oil, which has a higher refractive index than silica, and the liquid is heated so that its refractive index varies the response of the taper to light of a particular wavelength will vary. This variation is shown in the plot of Figure 4. From this plot it can be seen that there is maximum power transmission at point A. This is at a temperature of 29 C. At higher temperatures the power throughput decreases almost linearly as temperature rises. Thus point B shows power transmission at 55 C. The section A-B of the plot can be used to provide a sensor with relatively low sensitivity and good dynamic range in which a change of refractive index of the order of 10 corresponds to a change in temperature of approximately 30 C, and requiring a detection sensit- ivity range of <"^20 dB. These figures provide the basis for an intensity sensor for the measurement of temperature, refractive index, acoustic, biological and other sensors which directly or indirectly use this refractive index and intensity relation.
However use of such a device as an intensity sensor raises a number of problems. For example, external variations such as bending, microbending, etc. could affect the intensity transmitted. To overcome these drawbacks some form of compensation is required. This can be achieved by a dual wavelength transmission. Figure 6 is a plot of the refractive index response of the same taper at a second wavelength when subjected to the same changes in refractive index as caused the plot of Figure 4. It will be seen here that the linear slope A-B of Figure 4 has been replaced by a substantially constant plateau. It is the ability of a single fibre to give two such separate results which enables a compensating factor to be built in to a sensor.
Such a compensated sensor is shown" in Figure 7. Laser light at two differing wavelengths , A-, is launched down a single monomode optical fibre 10 which has a biconical taper imparted to it at 11 and which is surrounded by a sensor area generally indicated at 12. This sensor area could, for example, be a capillary tube filled with silicone oil as in the embodiment shown in Figure 5. In any case it will be such that the tapered portion 11 will give power transmission plots of the kind shown in Figures 4 and 6 in response to changes in the refractive index of the surrounding sensor area, and in response to light of wavelengths r and respectively. The two wavelengths can be launched into the fibre by means of a coupler. It will be appreciated that with a device of the characteristics just described measurement will only occur at wavelength λ- . At the output end of fibre 10 the two wavelengths A., and Λ~ are separated, for example, by another coupler and the power transmitted by each of the wavelengths detected by detectors D1 and D2 The outputs of the detectors are connected to logarithmic amplifiers 16, 17 the outputs of which are divided by a divider 18. The result is a linear output as a function of temperature, or of refractive index of the substance surrounding the biconical taper. Thus .temperature, refractive index and acoustic sensors can be made with this arrangement.
Such sensors would be simple to make with low cost electronics. Another application involving this relationship, and in particular part A-B of the refractive index response is that of a tuneable attenuator. By changing the refractive index surrounding the taper the throughput attenuation is changed linearly in dB. Thus Figure 5 shows a tuneable attenuator. A monomode optical fibre 1 has a biconical taper fabricated in it in the region generally indicated at 2. This region is housed in a capillary glass tube 3 filled with a liquid such as silicone oil the refractive index of which varies with temperature over the required ranges. The ends of capillary 3 are sealed with UV-cured epoxy resin. The tube is coated with resistive material and provided with electrodes 4 and 5. The application of a voltage across the electrodes causes the heat released to heat the liquid and lower its refractive index, hence varying the transmission through the fibre 1. In this manner a tuneability of >30 dB can be achieved.
Referring again to the plot of Figure 4, it can be -seen that there is maximum power transmission at point A. Thus an optical modulator can be constructed using this fact. To manufacture an optical modulator a monomode fibre is surrounded with a material having a refractive index which has.a value selected to provide maximum power transmission. By shifting refractive index of the surrounding material higher (to the left of Figure 4) the transmission power is rapidly reduced to a minimum, a loss of approximately 30 dB.
Variations are possible on this basic concept. Figure 4 shows a plot which has been derived using a tapered biconical fibre the elongation of which has been stopped after l± power oscillations. If instead the fabrications of the taper had been extended to two complete power oscillations, as shown in Figure 8, then using this biconiclly tapered fibre to produce a plot in response to changes of refractive index results in the plot of Figure 9. Similarly extending the number of oscillations to 12 produces the equivalent plots of Figures 7 and 8.
One advantage afforded by the effect of the increased taper as illustrated in Figures 8 and 9 is that the range of shift required in the refractive index to produce modulation is narrower. This is even more apparent when examining the plots of Figures 10 and 11 where the effective bandwidth of changes in the refractive index along the central peak (between power points -45 and -38.3 dB) is very small. Here also the refractive index can be varied in either direction to obtain modulation. This latter arrangement does have a potential disadvantage in that very accurate control of temperature may be required.
Whatever the nature of the tapering various types of material can be used for the variable refractive index surrounding medium. One possibility is to use an electro-optic material having a sufficiently low refractive index tp match Siθ£ fibres. Alternatively the monomode fibre could be fabricated from a material having a high enough refractive index to match an electro-optic crystal such as KDP. The electro-optic effect could then be used so that the tapered fibre portion and the crystal together act as a modulator. If an electro-optic crystal is used as a cladding medium surrounding the taper it must be grown carefully around the taper. It is possible to grow single KDP crystals long enough to clad the taper region and also to enclose the modulating electrodes.
As an alternative, low refractive index liquid crystals are used with Siθ2 guides or with high refractive index glass fibre tapers.
For modulators of the kind just described the necessary change of refractive index of the surrounding medium is 10"3.
Such a modulator would find ready application in digital transmission systems. The actual structure of a modulator employing the principles just discussed is similar to that shown in Figure 5 of the drawings.

Claims

1. An optical fibre device comprising a monomode optical fibre having an optical coupler fabricated therein in the form of a biconical tapered portion, a medium surrounding the biconical tapered portion of the fibre, the refractive index of the medium being capable of variation whereby for a specified wavelength travelling along the fibre the power transmitted will vary in accordance with variations of the refractive index of the medium, and means for detecting light transmitted by the core of the fibre.
2. A device as claimed in Claim 1, and including means for launching light at two different wavelengths into said fibre, means for separating the two wavelengths at the output end of the fibre, means for detecting the respective powers of the transmitted wavelengths, and means for generating a compensation factor for one of the wavelengths from the two detected outputs.
3. A device as claimed in Claim 1 or Claim 2, and including means for varying the refractive index of the medium.
4. A device as claimed in Claim 3, wherein the medium surrounding the fibre is chosen so that at a specified condition the fibre offers maximum power transmission to a selected wavelength, and wherein the means for altering the refractive index of the medium do so in such a manner that transmission power is substantially reduced whereby the device can function as a modulator.
5. A device as claimed in any one of the preceding claims wherein the medium is a liquid surrounding the tapered portion.
6. A device as claimed in Claim 5 wherein the liquid is silicone oil.
7. A device as claimed in Claim 6 wherein the means for varying the refractive inded of the silicone oil comprise heating means.
PCT/GB1986/000738 1985-12-04 1986-12-04 Fibre optic devices WO1987003676A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB8529863 1985-12-04
GB858529862A GB8529862D0 (en) 1985-12-04 1985-12-04 Fibre optic devices
GB8529862 1985-12-04
GB858529863A GB8529863D0 (en) 1985-12-04 1985-12-04 Fibre optic modulator

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US6205280B1 (en) * 1998-08-25 2001-03-20 Molecular Optoelectronics Corporation Blockless fiber optic attenuators and attenuation systems employing dispersion controlled polymers
US6301426B1 (en) 1999-03-16 2001-10-09 Molecular Optoelectronics Corporation Mechanically adjustable fiber optic attenuator and method employing same
US6370312B1 (en) 1998-02-20 2002-04-09 Molecular Optoelectronics Corporation Fiber optic attenuation systems, methods of fabrication thereof and methods of attenuation using the same
US6459526B1 (en) 1999-08-09 2002-10-01 Corning Incorporated L band amplifier with distributed filtering
US6483981B1 (en) 2000-06-28 2002-11-19 Molecular Optoelectronics Corp. Single-channel attenuators
US6489399B1 (en) 2000-07-31 2002-12-03 Molecular Optoelectronics Corp. Dye-appended polymers for broadband fiber optic devices
US6490391B1 (en) 2000-07-12 2002-12-03 Oluma, Inc. Devices based on fibers engaged to substrates with grooves
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US6542663B1 (en) 2000-09-07 2003-04-01 Oluma, Inc. Coupling control in side-polished fiber devices
US6571035B1 (en) 2000-08-10 2003-05-27 Oluma, Inc. Fiber optical switches based on optical evanescent coupling between two fibers
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US6611649B2 (en) 2001-03-19 2003-08-26 Molecular Optoelectronics Corporation Variable optical attenuator with polarization maintaining fiber
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US6370312B1 (en) 1998-02-20 2002-04-09 Molecular Optoelectronics Corporation Fiber optic attenuation systems, methods of fabrication thereof and methods of attenuation using the same
US6191224B1 (en) 1998-08-25 2001-02-20 Molecular Optoelectronics Corporation Dispersion-controlled polymers for broadband fiber optic devices
US6205280B1 (en) * 1998-08-25 2001-03-20 Molecular Optoelectronics Corporation Blockless fiber optic attenuators and attenuation systems employing dispersion controlled polymers
US6268435B1 (en) 1998-08-25 2001-07-31 Molecular Optoelectronics Corporation Dispersion-controlled polymers for broadband fiber optic devices
US6303695B1 (en) 1998-08-25 2001-10-16 Molecular Optoelectronics Corporation Dispersion-controlled polymers for broadband fiber optic devices
US6444756B2 (en) 1998-08-25 2002-09-03 Molecular Optoelectronics Corporation Dispersion-controlled polymers for broad band fiber optic devices
US6785461B2 (en) 1998-08-25 2004-08-31 Molecular Optoelectronics Corp. Blockless fiber optic attenuators and attenuation systems employing dispersion tailored polymers
US6301426B1 (en) 1999-03-16 2001-10-09 Molecular Optoelectronics Corporation Mechanically adjustable fiber optic attenuator and method employing same
US6459526B1 (en) 1999-08-09 2002-10-01 Corning Incorporated L band amplifier with distributed filtering
US6516114B2 (en) 2000-06-27 2003-02-04 Oluma, Inc. Integration of fibers on substrates fabricated with grooves
US6625349B2 (en) 2000-06-27 2003-09-23 Oluma, Inc. Evanescent optical coupling between a waveguide formed on a substrate and a side-polished fiber
US6501875B2 (en) 2000-06-27 2002-12-31 Oluma, Inc. Mach-Zehnder inteferometers and applications based on evanescent coupling through side-polished fiber coupling ports
US6621951B1 (en) 2000-06-27 2003-09-16 Oluma, Inc. Thin film structures in devices with a fiber on a substrate
US6597833B1 (en) 2000-06-27 2003-07-22 Oluma, Inc. Wavelength-division multiplexers and demultiplexers based on mach-zehnder interferometers and evanescent coupling
US6556746B1 (en) 2000-06-27 2003-04-29 Oluma, Inc. Integrated fiber devices based on Mach-Zehnder interferometers and evanescent optical coupling
US6483981B1 (en) 2000-06-28 2002-11-19 Molecular Optoelectronics Corp. Single-channel attenuators
US6490391B1 (en) 2000-07-12 2002-12-03 Oluma, Inc. Devices based on fibers engaged to substrates with grooves
US6690857B2 (en) 2000-07-12 2004-02-10 Oluma, Inc. Fiber devices having side evanescent coupling port
US6489399B1 (en) 2000-07-31 2002-12-03 Molecular Optoelectronics Corp. Dye-appended polymers for broadband fiber optic devices
US6621952B1 (en) 2000-08-10 2003-09-16 Oluma, Inc. In-fiber variable optical attenuators and modulators using index-changing liquid media
US6571035B1 (en) 2000-08-10 2003-05-27 Oluma, Inc. Fiber optical switches based on optical evanescent coupling between two fibers
US6542663B1 (en) 2000-09-07 2003-04-01 Oluma, Inc. Coupling control in side-polished fiber devices
US6611649B2 (en) 2001-03-19 2003-08-26 Molecular Optoelectronics Corporation Variable optical attenuator with polarization maintaining fiber
US6681073B2 (en) 2001-03-19 2004-01-20 Molecular Optoelectronics Corporation Fiber optic power control systems and methods
WO2003005081A1 (en) * 2001-07-02 2003-01-16 Acreo Ab Method and device for controlling the refractive index in an optical fiber
WO2003005082A1 (en) * 2001-07-02 2003-01-16 Acreo Ab Method and device for tuning bragg gratings
US6973247B2 (en) 2001-07-02 2005-12-06 Acreo Ab Method and device for controlling the refractive index in an optical fiber
CN107390318A (en) * 2017-08-21 2017-11-24 中国工程物理研究院上海激光等离子体研究所 A kind of new optical waveguide filter and its application

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EP0248052A1 (en) 1987-12-09
GB2184859A (en) 1987-07-01
GB2184859B (en) 1989-10-11
GB8629038D0 (en) 1987-01-14

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