EP2100175A2 - Doped optical fibre with broken space symmetry - Google Patents

Doped optical fibre with broken space symmetry

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Publication number
EP2100175A2
EP2100175A2 EP07871847A EP07871847A EP2100175A2 EP 2100175 A2 EP2100175 A2 EP 2100175A2 EP 07871847 A EP07871847 A EP 07871847A EP 07871847 A EP07871847 A EP 07871847A EP 2100175 A2 EP2100175 A2 EP 2100175A2
Authority
EP
European Patent Office
Prior art keywords
symmetry
core
optical fiber
dopant
axis
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Withdrawn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
EP07871847A
Other languages
German (de)
French (fr)
Inventor
Christelle Lesvigne
Vincent Couderc
Philippe Leproux
Jean-Louis Auguste
Guillaume Huss
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.)
Centre National de la Recherche Scientifique CNRS
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Centre National de la Recherche Scientifique CNRS
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Filing date
Publication date
Application filed by Centre National de la Recherche Scientifique CNRS filed Critical Centre National de la Recherche Scientifique CNRS
Publication of EP2100175A2 publication Critical patent/EP2100175A2/en
Withdrawn legal-status Critical Current

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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
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02295—Microstructured optical fibre
    • G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
    • G02B6/02319—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by core or core-cladding interface features
    • G02B6/02338—Structured core, e.g. core contains more than one material, non-constant refractive index distribution in core, asymmetric or non-circular elements in core unit, multiple cores, insertions between core and clad
    • 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
    • G02B6/024—Optical fibres with cladding with or without a coating with polarisation maintaining properties

Definitions

  • the invention relates to a microstructured optical fiber comprising at least one core having a spatial symmetry of shape comprising at least one axis of symmetry.
  • Optical fibers are known and used as a waveguide.
  • the microstructured fibers comprise, in section, a matrix of microscopic air holes. These air holes extend over the entire length of the optical fiber. In the center of the optical fiber, one or more air holes are absent so as to form an area having a higher index constituting a light trap and thus a core for the optical fiber.
  • the heart of a microstructured optical fiber is therefore the place of propagation inducing a minimum of loss to light.
  • the same fiber may have a plurality of cores.
  • the non-linearity of an optical fiber depends solely on the material constituting it. Nevertheless, the threshold of appearance of these effects depends on the power density propagating in the heart and thus the confinement of the power throughout its propagation. Moreover, all the parametric effects at the base of complex spectral enlargements require an agreement of the phase velocities of the waves considered and are then sensitive to the polarization effects and thus to the birefringence of the waveguide considered. Indeed, even if a fiber is manufactured to be in isotropic theory, the presence of impurities and physical stresses in the fiber imposes a so-called local or so-called birefringence therein.
  • the heart thus formed is therefore substantially elliptical. This results in the appearance of a shape birefringence related to the geometry of the core of the fiber.
  • Such a birefringence is independent of the power of the wave propagating in the heart. This birefringence is therefore permanent and is a linear effect.
  • microstructured fibers are known from US-2005/105867 and US-2006/088262.
  • the elliptical core of the fiber described in the aforementioned publication has a birefringence induced by the geometrical dissymmetry of the guide and can not exceed index variations of the order of about 3.10 "3 to 7.10 " 3 .
  • the distribution of the dopant modifies the spatial symmetry of the core, which causes an improved anisotropy of the doped core of the fiber, with respect to the same undoped core.
  • the linear birefringence of the optical fiber thus obtained is modified, permanent and potentially improved.
  • the introduction of the asymmetry according to the invention also has the advantage of making it possible to shift the dispersion zero of the modes propagating in the core towards the low wavelengths.
  • a dopant into the core of a microstructured optical fiber is known per se and makes it possible to amplify an optical signal propagating in the core of the fiber or to exacerbate the non-linear effects.
  • Different dopants have been proposed depending on the signal to be amplified and the desired optical effect.
  • the dopants are positioned in the center of the heart and symmetrically with respect to axes of symmetry of the heart.
  • the dopant is distributed so as to break the symmetry of the core of the fiber.
  • the shape birefringence is reinforced by a birefringence induced by the doping geometry.
  • An increase in the index of the core in a given zone and asymmetrically allows further asymmetrization of the profile of the mode and thus a modification of the birefringence. Phase agreements that are not accessible without this particular doping are then possible.
  • At least one dopant is positioned in a plurality of doping zones of said core, each of the doping zones being distinct, said doping zones being arranged so as to break said spatial symmetry.
  • the non-isotropic distribution of the dopant (s) makes it possible to break the symmetry of the core and thus to increase the birefringence effect.
  • said core comprises a single dopant, said dopant being positioned in each of said doping zones, the concentration of said dopant being different in each of the doping zones.
  • said plurality of doping zones comprises two doping zones.
  • the dopant concentrations are distinct within the heart, the symmetry of the heart is broken.
  • This embodiment has the advantage of allowing the increase of the birefringence of the heart, while using a type of dopant.
  • said core comprises a plurality of dopants, each of the dopants of said plurality of dopants being located in a respective doping zone of said plurality of doping zones.
  • said optical fiber may comprise a plurality of cores, each of the cores of said plurality of cores having a spatial symmetry, each of the cores of the plurality of cores comprising at least one dopant arranged so as to break the spatial symmetry.
  • This embodiment makes it possible to increase the birefringence of the optical fiber, while allowing the generation of several different spectra according to the opto-geometric characteristics of each of the cores.
  • This also makes it possible to produce coupled waveguides by coherently summing several spectra.
  • Each wavelength injected into each of the cores can generate a broad spectrum by nonlinear effect independently of the other wavelengths. This makes it possible to obtain at the output of the fiber a spectrum having different characteristics for each core.
  • said at least one dopant is a rare-earth ion. This makes it possible to amplify in parallel one or more wavelengths.
  • This also makes it possible to obtain a population inversion at different wavelengths to generate a laser effect or a multiple amplification.
  • the Applicant has demonstrated that the birefringence was particularly improved when said core is a silica core surrounded by four small diameter air holes and two large diameter air holes, the four small diameter air holes being distributed. in pairs on both sides of large diameter air holes and especially when the small diameter is 2.2 microns, and the large diameter is 4 microns.
  • te invention relates ⁇ to ⁇ ⁇ equal "ment ⁇ to ⁇ u ⁇ " method of fabricating a doped optical fiber comprising the steps of:
  • microstructured optical fiber having a shape symmetry-shaped core
  • FIG. 1 is a section of an optical fiber according to the invention in an XY plane
  • FIG. 2 is a section of an optical fiber according to a first embodiment of the invention
  • FIG. 3 is a section of a multi-core optical fiber according to the invention
  • FIG. 4 is a detailed view of an optical fiber core according to the invention.
  • FIG. 1 is a section of an optical fiber 1 according to the invention.
  • the optical fiber 1 is a microstructured fiber comprising an array of air holes 2 surrounding intermediate areas of silica 3. This set of holes 2 and silica zones 3 forms a sheath 2, 3 surrounding a fiber core 7.
  • This optical fiber 1 is for example manufactured by the known method known as "stack and draw” in English, in which juxtapose silica tubes.
  • the diameter of the air holes 2 is about 2.2 micrometers, and the various holes ai ⁇ -c ⁇ ⁇ are esp ⁇ ⁇ a "EES" by ⁇ silica areas of about 2.7 micrometers.
  • the core 7 of the fiber 1 is delimited non-symmetrically along the X axis and the Y axis of the reference mark shown in FIG. 1.
  • the core 7 is delimited by two holes 4 of diameters greater than the diameters of the holes of the microstructure 2.
  • the diameter of the holes 4 along the X axis of the core 7 is about 4 micrometers.
  • the core is delimited by holes of the same diameter as the holes 2 of the sheath 2, 3. Due to the presence of the large diameter air holes 4, the core 7 therefore has a shape substantially ellipsoidal.
  • the surface of the heart 7 is about 5 microns square.
  • the arrangement of the holes delimiting the core 7 thus gives a spatial symmetry to the core 7 along the two axes X and Y. In space, this corresponds to two planes of symmetry.
  • the amount of air in the sheath 2, 3 is of the order of 65%.
  • the core 7 of the fiber 1 has a size allowing the guiding of six transverse modes of a wave, corresponding to the fundamental mode LP01 with a polarization according to X, to the fundamental mode LP01 with a polarization along Y, to the first higher order mode
  • LP1 1 with a central zero in the X or Y direction, and a polarization along X or Y.
  • the dispersion zero wavelength is around 770 nanometers for the LP01 mode according to X or Y, and around 560 nanometers for LP1 modes 1.
  • the core 7 is non-symmetrically micro-structured and comprises two distinct zones of doping 5 and 6.
  • the doping zones 5 and 6 comprise two different materials having different refractive indices.
  • the heart 7 is thus separated vertically into two zones ⁇ and 6. This separation can also be vertical.
  • these two doping zones 5 and 6 are doped with a different dopant for each doping zone.
  • the dopants may be germanium, phosphorus, or rare-earth ions. Germanium and Phosphorus can be introduced more importantly in the fiber than rare earth ions and then allow to obtain a higher birefringence.
  • the two doping zones 5 and 6 comprise the same dopant, for example germanium.
  • the concentrations of germanium are distinct in zones 5 and 6.
  • Zone 5 has a low doping of 3% while the other zone 6 has a higher doping of the order of 10% for example.
  • the fiber 1 may comprise a plurality of cores 7, 7A, 7B, 7C, 7D, 7E, 7F, as illustrated in FIG. 3.
  • the cores 7A, 7B, 7D and 7E are substantially circular because they are surrounded by air holes 2 of the same diameter. Because of the X-axis presence of the large-diameter air holes 4, the core 7 is substantially ellipsoidal in shape as before, and the holes 7F and 7C are asymmetrical along the X axis, and symmetrical by relative to the X axis.
  • doping zones of doping arranged to break a spatial symmetry of the heart are doped.
  • At least one spatial symmetry of the core of the fiber is determined, and this core is doped so as to break the spatial symmetry due to the distribution of the fiber. dopant within the heart.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
  • Lasers (AREA)
  • Agricultural Chemicals And Associated Chemicals (AREA)

Abstract

The invention relates to a micro-structured optical fibre (1) including at least one core (7, 7A, 7B, 7C, 7D1 7E, 7F) with a core space symmetry, characterised in that said core contains at least one doping material distributed in said core according to a dissymmetrical implantation relative to said at least one symmetry axis.

Description

FIBRE OPTIQUE DOPÉE A SYMÉTRIE SPATIALE BRISÉE DOPED OPTICAL FIBER WITH BROKEN SPACE SYMMETRY
L'invention se rapporte à une fibre optique microstructurée comprenant au moins un cœur ayant une symétrie spatiale de forme comprenant au moins un axe de symétrie.The invention relates to a microstructured optical fiber comprising at least one core having a spatial symmetry of shape comprising at least one axis of symmetry.
Les fibres optiques sont connues et utilisées en tant que guide d'onde. Les fibres microstructurées comprennent, en coupe, une matrice de trous d'air microscopiques. Ces trous d'air s'étendent sur toute la longueur de la fibre optique. Au centre de la fibre optique, un ou plusieurs trous d'air sont absents de sorte à former une zone possédant un indice plus élevé constituant un piège à lumière et donc un cœur pour la fibre optique. Le cœur d'une fibre optique microstructurée est donc le lieu de propagation induisant un minimum de perte à la lumière. Une même fibre peut avoir une pluralité de cœurs.Optical fibers are known and used as a waveguide. The microstructured fibers comprise, in section, a matrix of microscopic air holes. These air holes extend over the entire length of the optical fiber. In the center of the optical fiber, one or more air holes are absent so as to form an area having a higher index constituting a light trap and thus a core for the optical fiber. The heart of a microstructured optical fiber is therefore the place of propagation inducing a minimum of loss to light. The same fiber may have a plurality of cores.
La non-linéarité d'une fibre optique dépend uniquement du matériau la constituant. Néanmoins, le seuil d'apparition de ces effets dépend de la densité de puissance se propageant dans le cœur et donc du confinement de la puissance tout au long de sa propagation. De plus, tous les effets paramétriques à la base d'élargissements spectraux complexes nécessitent un accord des vitesses de phase des ondes considérées et sont alors sensibles aux effets de polarisation et donc à la biréfringence du guide considéré. En effet, même si une fibre est fabriquée pour être en théorie isotrope, la présence d'impuretés et de contraintes physiques dans la fibre impose une biréfringence dite locale ou dite de forme dans celle-ci. Il est également connu que l'apparition d'une biréfringence dans une fibre optique modifie sa courbe de dispersion et rend la propagation du champ sensible à la polarisation. Ainsi les conditions de propagation en régime non linéaire des ondes dans le cœur du guide sont largement affectées par la présence d'une biréfringence locale ou de forme. La publication « Highly biréfringent photonic crystal fibers », deThe non-linearity of an optical fiber depends solely on the material constituting it. Nevertheless, the threshold of appearance of these effects depends on the power density propagating in the heart and thus the confinement of the power throughout its propagation. Moreover, all the parametric effects at the base of complex spectral enlargements require an agreement of the phase velocities of the waves considered and are then sensitive to the polarization effects and thus to the birefringence of the waveguide considered. Indeed, even if a fiber is manufactured to be in isotropic theory, the presence of impurities and physical stresses in the fiber imposes a so-called local or so-called birefringence therein. It is also known that the appearance of a birefringence in an optical fiber modifies its dispersion curve and makes the propagation of the field sensitive to polarization. Thus, the nonlinear wave propagation conditions in the guide core are largely affected by the presence of a local birefringence or shape. The publication "Highly Birefringent Photonic Crystal Fibers",
Ortigosa-Blanch et al., Optics letter, Vol. 25, 2000, décrit par exemple une fibre optique microstructurée dont le cœur est formé au sein de trous formant deux axes de symétrie. Le cœur ainsi formé est donc sensiblement elliptique. Ceci se traduit par l'apparition d'une biréfringence de forme liée à la géométrie du cœur de la fibre. Une telle biréfringence est indépendante de la puissance de l'onde se propageant dans le cœur. Cette biréfringence est donc permanente et est un effet linéaire.Ortigosa-Blanch et al., Optics letter, Vol. 25, 2000, describes for example a microstructured optical fiber whose core is formed within holes forming two axes of symmetry. The heart thus formed is therefore substantially elliptical. This results in the appearance of a shape birefringence related to the geometry of the core of the fiber. Such a birefringence is independent of the power of the wave propagating in the heart. This birefringence is therefore permanent and is a linear effect.
D'autres fibres microstructurées sont connues des documents US- 2005/105867 et US-2006/088262.Other microstructured fibers are known from US-2005/105867 and US-2006/088262.
Toutefois, le cœur elliptique de la fibre décrite dans la publication susmentionnée possède une biréfringence induite par la dissymétrie géométrique du guide et ne peut dépasser des variations d'indice de l'ordre environ de 3.10"3 à 7.10"3.However, the elliptical core of the fiber described in the aforementioned publication has a birefringence induced by the geometrical dissymmetry of the guide and can not exceed index variations of the order of about 3.10 "3 to 7.10 " 3 .
On connaît également, du document US-2004/086213, un système permettant l'ajustement de la biréfringence grâce à une amplification dissymétrique au sein de la fibre. Ce contrôle de la biréfringence est permis par l'introduction d'une zone de dopage par ion actif dans le cœur d'une fibre standard et par le couplage d'une seconde onde de pompe de forte puissance afin d'induire par effet non linéaire une modification de l'indice dans cette zone dopée et donc de jouer sur les paramètres de biréfringence. Dans ce système, la biréfringence est dite "non linéaire" car elle n'est pas permanente, elle dépend de la puissance de l'onde incidente et est présente uniquement lorsqu'un pompage annexe est effectué afin d'amplifier localement le signal. Un tel système présente le désavantage de requérir une pompe externe et de ne pas fournir de biréfringence améliorée en utilisation statique (sans pompe). Le problème que se propose de résoudre l'invention est d'augmenter davantage les effets de biréfringence linéaire dans une fibre optique microstructurée.Also known from US-2004/086213, a system for adjusting the birefringence through asymmetric amplification within the fiber. This control of the birefringence is enabled by the introduction of an active ion doping zone in the core of a standard fiber and the coupling of a second high power pump wave to induce by nonlinear effect a modification of the index in this doped zone and thus to play on the birefringence parameters. In this system, the birefringence is said to be "non-linear" because it is not permanent, it depends on the power of the incident wave and is present only when an auxiliary pumping is performed in order to locally amplify the signal. Such a system has the disadvantage of requiring an external pump and not providing improved birefringence in static use (without pump). The problem to be solved by the invention is to further increase the effects of linear birefringence in a microstructured optical fiber.
Ce problème est résolu selon l'invention grâce à une fibre telle que précédemment décrite, dans laquelle ledit cœur comprend au moins un dopant réparti au sein dudit cœur selon une implantation dissymétrique par rapport audit au moins un axe de symétrie.This problem is solved according to the invention by means of a fiber as described above, wherein said core comprises at least one dopant distributed within said heart according to an asymmetric implantation with respect to said at least one axis of symmetry.
Selon l'invention, la répartition du dopant modifie la symétrie spatiale du cœur, ce qui provoque une anisotropie améliorée du cœur dopé de la fibre, par rapport au même cœur non dopé. De la sorte, la biréfringence linéaire de la fibre optique ainsi obtenue est modifiée, permanente et potentiellement améliorée.According to the invention, the distribution of the dopant modifies the spatial symmetry of the core, which causes an improved anisotropy of the doped core of the fiber, with respect to the same undoped core. In this way, the linear birefringence of the optical fiber thus obtained is modified, permanent and potentially improved.
L'introduction d'une dissymétrie spatiale des modes transverses se propageant dans^re^cœuF^peut^etre^réalisée par l'introduction d'un dopage qui modifie directement l'indice d'une partie du cœur. Cette dissymétrie du mode induit alors une biréfringence équivalente qui rend la propagation sensible à la polarisation.The introduction of spatial asymmetry of transverse modes propagating in re ^ ^ ^ cœuF can be ^ ^ carried out by introducing a doping which directly modifies the index of part of the heart. This asymmetry of the mode then induces an equivalent birefringence which makes the propagation sensitive to polarization.
L'introduction de la dissymétrie selon l'invention a également l'avantage de permettre de décaler le zéro de dispersion des modes se propageant dans le cœur vers les basses longueurs d'onde.The introduction of the asymmetry according to the invention also has the advantage of making it possible to shift the dispersion zero of the modes propagating in the core towards the low wavelengths.
L'introduction d'un dopant dans le cœur d'une fibre optique microstructurée est connue en soi et permet d'amplifier un signal optique se propageant dans le cœur de la fibre ou d'exacerber les effets non linéaires. Différents dopants ont été proposés en fonction du signal à amplifier et de l'effet optique désiré. Dans les fibres optiques connues, les dopants sont positionnés au centre du cœur et de manière symétrique par rapport à des axes de symétrie du cœur. Au contraire, selon l'invention, le dopant est réparti de sorte à rompre la symétrie du cœur de la fibre.The introduction of a dopant into the core of a microstructured optical fiber is known per se and makes it possible to amplify an optical signal propagating in the core of the fiber or to exacerbate the non-linear effects. Different dopants have been proposed depending on the signal to be amplified and the desired optical effect. In known optical fibers, the dopants are positioned in the center of the heart and symmetrically with respect to axes of symmetry of the heart. In contrast, according to the invention, the dopant is distributed so as to break the symmetry of the core of the fiber.
Du fait de l'implantation dissymétrique d'un dopage dans le cœur de la fibre, la biréfringence de forme est renforcée par une biréfringence induite par la géométrie du dopage. Une augmentation de l'indice du cœur dans une zone donnée et de manière dissymétrique permet une dissymétrisation supplémentaire du profil du mode et donc une modification de la biréfringence. Des accords de phase non accessibles sans ce dopage particulier sont alors possibles.Due to the dissymmetrical implantation of a doping in the fiber core, the shape birefringence is reinforced by a birefringence induced by the doping geometry. An increase in the index of the core in a given zone and asymmetrically allows further asymmetrization of the profile of the mode and thus a modification of the birefringence. Phase agreements that are not accessible without this particular doping are then possible.
Par exemple, pour un cœur possédant initialement un profil centrosymétrique, ayant donc une infinité d'axes de symétrie se coupant en son centre, peut être modifié par l'introduction d'un dopage non homogène sur la totalité de la surface du cœur. Une seule zone dopée placée sur le bord du cœur permet également de rompre la centrosymétrie-du^cœur:For example, for a core initially having a centrosymmetric profile, thus having an infinity of axes of symmetry intersecting at its center, can be modified by the introduction of inhomogeneous doping on the entire surface of the heart. One doped region placed on the edge of the heart also helps to break the centrosymmetry-the ^ heart:
Selon l'invention, au moins un dopant est positionné dans une pluralité de zones de dopage dudit cœur, chacune des zones de dopage étant distincte, lesdites zones de dopage étant agencées de sorte à rompre ladite symétrie spatiale.According to the invention, at least one dopant is positioned in a plurality of doping zones of said core, each of the doping zones being distinct, said doping zones being arranged so as to break said spatial symmetry.
Ainsi, la répartition non isotrope du ou des dopants permet de briser la symétrie du cœur et donc d'augmenter l'effet de biréfringence.Thus, the non-isotropic distribution of the dopant (s) makes it possible to break the symmetry of the core and thus to increase the birefringence effect.
Selon un mode de réalisation, ledit cœur comprend un unique dopant, ledit dopant étant positionné dans chacune desdites zones de dopage, la concentration dudit dopant étant différente dans chacune des zones de dopage.According to one embodiment, said core comprises a single dopant, said dopant being positioned in each of said doping zones, the concentration of said dopant being different in each of the doping zones.
Par exemple, ladite pluralité de zones de dopage comprend deux zones de dopage. Selon ce mode de réalisation, puisque les concentrations en dopant sont distinctes au sein du cœur, la symétrie du cœur est rompue. Ce mode de réalisation a l'avantage de permettre l'augmentation de la biréfringence du cœur, tout en utilisant qu'un type de dopant.For example, said plurality of doping zones comprises two doping zones. According to this embodiment, since the dopant concentrations are distinct within the heart, the symmetry of the heart is broken. This embodiment has the advantage of allowing the increase of the birefringence of the heart, while using a type of dopant.
Selon un autre mode de réalisation de l'invention, ledit cœur comprend une pluralité de dopants, chacun des dopants de ladite pluralité de dopants étant situé dans une zone de dopage respective de ladite pluralité des zones de dopage.According to another embodiment of the invention, said core comprises a plurality of dopants, each of the dopants of said plurality of dopants being located in a respective doping zone of said plurality of doping zones.
Cette fois, c'est l'agencement des différentes zones de dopage comprenant chacune un dopant différent qui permet de briser la symétrie du cœur. Comme précédemment, l'effet de biréfringence est alors amélioré.This time, it is the arrangement of the different doping zones each comprising a different dopant which makes it possible to break the symmetry of the heart. As before, the birefringence effect is then improved.
Selon l'invention, ladite fibre optique peut comprendre une pluralité de cœurs, chacun des cœurs de ladite pluralité de cœurs ayant une symétrie spatiale, chacun des cœurs de la pluralité de cœur comprenant au moins un dopant agencé de sorte à briser la symétrie spatiale.According to the invention, said optical fiber may comprise a plurality of cores, each of the cores of said plurality of cores having a spatial symmetry, each of the cores of the plurality of cores comprising at least one dopant arranged so as to break the spatial symmetry.
Ce mode de réalisation permet d'augmenter la biréfringence de la fibre optique, tout en permettant la génération de plusieurs spectres différents en fonction des caractéristiques opto-géométriques de chacun des cœurs. Ceci permet également de réaliser des guides d'onde couplés en faisant la somme cohérente de plusieurs spectres. Chaque longueur d'onde injectée dans chacun des cœurs peut engendrer un spectre large par effet non linéaire indépendamment des autres longueurs d'onde. Ceci permet d'obtenir en sortie de la fibre un spectre possédant des caractéristiques différentes pour chaque cœur. Selon un mode de réalisation de l'invention, ledit au moins un dopant est un ion terre-rare. Ceci permet d'amplifier en parallèle une ou plusieurs longueurs d'onde.This embodiment makes it possible to increase the birefringence of the optical fiber, while allowing the generation of several different spectra according to the opto-geometric characteristics of each of the cores. This also makes it possible to produce coupled waveguides by coherently summing several spectra. Each wavelength injected into each of the cores can generate a broad spectrum by nonlinear effect independently of the other wavelengths. This makes it possible to obtain at the output of the fiber a spectrum having different characteristics for each core. According to one embodiment of the invention, said at least one dopant is a rare-earth ion. This makes it possible to amplify in parallel one or more wavelengths.
Ceci permet également d'obtenir une inversion de population à différentes longueurs d'onde pour engendrer un effet laser ou une amplification multiple.This also makes it possible to obtain a population inversion at different wavelengths to generate a laser effect or a multiple amplification.
La Demanderesse a démontré que la biréfringence était particulièrement amélioré lorsque ledit cœur est un cœur de silice entouré de quatre trous d'air de petit diamètre et de deux trous d'air de grand diamètre, les quatre trous d'air de petit diamètre étant répartis par paire de part et d'autre des trous d'air de grand diamètre et notamment lorsque le petit diamètre est de 2,2 micromètres, et le grand diamètre est de 4 micromètres.The Applicant has demonstrated that the birefringence was particularly improved when said core is a silica core surrounded by four small diameter air holes and two large diameter air holes, the four small diameter air holes being distributed. in pairs on both sides of large diameter air holes and especially when the small diameter is 2.2 microns, and the large diameter is 4 microns.
t'invention~se~rapporte~egale"ment ~à~u ^"procédé de fabrication d'une fibre optique dopée comprenant des étapes consistant à :te invention relates ~ to ~ ~ equal "ment ~ to ~ u ^" method of fabricating a doped optical fiber comprising the steps of:
- fournir une fibre optique microstructurée ayant un cœur à symétrie spatiale de forme;providing a microstructured optical fiber having a shape symmetry-shaped core;
- déterminer au moins un axe de symétrie de ladite symétrie spatiale de forme ;determining at least one axis of symmetry of said spatial symmetry of shape;
- répartir au moins un dopant au sein dudit cœur selon une implantation dissymétrique par rapport audit au moins un axe de symétrie.distributing at least one dopant within said heart according to an asymmetrical implantation with respect to said at least one axis of symmetry.
On décrit maintenant un mode de réalisation de l'invention en référence aux figures annexées dans lesquelles :An embodiment of the invention will now be described with reference to the appended figures in which:
- FIG. 1 est une coupe d'une fibre optique selon l'invention dans un plan XY ;FIG. 1 is a section of an optical fiber according to the invention in an XY plane;
- FIG. 2 est une coupe d'une fibre optique selon un premier mode de réalisation de l'invention ; - FIG. 3 est une coupe d'une fibre optique multicoeur selon l'invention ;FIG. 2 is a section of an optical fiber according to a first embodiment of the invention; FIG. 3 is a section of a multi-core optical fiber according to the invention;
- FIG. 4 est une vue détaillée d'un cœur de fibre optique selon l'invention.FIG. 4 is a detailed view of an optical fiber core according to the invention.
FIG. 1 est une coupe d'une fibre optique 1 selon l'invention. La fibre optique 1 est une fibre microstructurée comprend un réseau de trous d'air 2 entourant des zones intermédiaires de silice 3. Cet ensemble de trous 2 et de zones de silice 3 forme une gaine 2, 3 entourant un cœur de fibre 7.FIG. 1 is a section of an optical fiber 1 according to the invention. The optical fiber 1 is a microstructured fiber comprising an array of air holes 2 surrounding intermediate areas of silica 3. This set of holes 2 and silica zones 3 forms a sheath 2, 3 surrounding a fiber core 7.
Cette fibre optique 1 est par exemple fabriquée par la méthode connue dite « stack and draw » en langue anglaise, dans laquelle on juxtapose des tubes de silice.This optical fiber 1 is for example manufactured by the known method known as "stack and draw" in English, in which juxtapose silica tubes.
Le diamètre des trous d'air 2 est d'environ 2,2 micromètres, et les différënts-trous-c^aiι^sOnt~esp~a"eeS"par~des zones de silice d'environ 2,7 micromètres.The diameter of the air holes 2 is about 2.2 micrometers, and the various holes aiι-c ^ ^ are esp ~ ~ a "EES" by ~ silica areas of about 2.7 micrometers.
Le cœur 7 de la fibre 1 est délimité de manière non symétrique suivant l'axe des X et l'axe des Y du repère illustré sur la FIG. 1 . Dans la direction des X, le cœur 7 est délimité par deux trous 4 de diamètres supérieurs aux diamètres des trous de la microstructure 2. Le diamètre des trous 4 selon l'axe des X du cœur 7 est d'environ 4 micromètres. Dans la direction des Y, le cœur est délimité par des trous de même diamètre que les trous 2 de la gaine 2, 3. Du fait de la présence des trous d'air 4 de grand diamètre, le cœur 7 a donc une forme sensiblement ellipsoïdale. La surface du cœur 7 est environ de 5 micromètres carré.The core 7 of the fiber 1 is delimited non-symmetrically along the X axis and the Y axis of the reference mark shown in FIG. 1. In the X direction, the core 7 is delimited by two holes 4 of diameters greater than the diameters of the holes of the microstructure 2. The diameter of the holes 4 along the X axis of the core 7 is about 4 micrometers. In the Y direction, the core is delimited by holes of the same diameter as the holes 2 of the sheath 2, 3. Due to the presence of the large diameter air holes 4, the core 7 therefore has a shape substantially ellipsoidal. The surface of the heart 7 is about 5 microns square.
L'agencement des trous délimitant le cœur 7 donne donc une symétrie spatiale au cœur 7 suivant les deux axes X et Y. Dans l'espace, ceci correspond à deux plans de symétrie. La quantité d'air dans la gaine 2, 3 est de l'ordre de 65 %.The arrangement of the holes delimiting the core 7 thus gives a spatial symmetry to the core 7 along the two axes X and Y. In space, this corresponds to two planes of symmetry. The amount of air in the sheath 2, 3 is of the order of 65%.
Le cœur 7 de la fibre 1 a une taille permettant le guidage de six modes transverses d'une onde, correspondant au mode fondamental LP01 avec une polarisation suivant X, au mode fondamental LP01 avec une polarisation suivant Y, au premier mode d'ordre supérieurThe core 7 of the fiber 1 has a size allowing the guiding of six transverse modes of a wave, corresponding to the fundamental mode LP01 with a polarization according to X, to the fundamental mode LP01 with a polarization along Y, to the first higher order mode
LP1 1 avec un zéro central dans la direction X ou Y, et une polarisation selon X ou Y. La longueur d'onde de zéro de dispersion se situe autour de 770 nanomètres pour le mode LP01 selon X ou Y, et autour de 560 nanomètres pour les modes LP1 1.LP1 1 with a central zero in the X or Y direction, and a polarization along X or Y. The dispersion zero wavelength is around 770 nanometers for the LP01 mode according to X or Y, and around 560 nanometers for LP1 modes 1.
Selon l'invention, le cœur 7 est micro-structuré de façon non symétrique et comprend deux zones distinctes de dopage 5 et 6.According to the invention, the core 7 is non-symmetrically micro-structured and comprises two distinct zones of doping 5 and 6.
Les zones de dopage 5 et 6 comprennent deux matériaux différents présentant des indices de réfraction différents. Le cœur 7 est donc séparé-verticalement^en^deux- zones^δ et 6. Cette séparation peut également être verticale.The doping zones 5 and 6 comprise two different materials having different refractive indices. The heart 7 is thus separated vertically into two zones δ and 6. This separation can also be vertical.
Selon un mode de réalisation, ces deux zones de dopage 5 et 6 sont dopées avec un dopant différent pour chaque zone de dopage. Selon les propriétés désirées, les dopants peuvent être du germanium, du phosphore, ou des ions terre-rare. Le Germanium et le Phosphore peuvent être introduits de manière plus importante dans la fibre que les ions terres rares et permettent alors d'obtenir une biréfringence plus élevée.According to one embodiment, these two doping zones 5 and 6 are doped with a different dopant for each doping zone. Depending on the desired properties, the dopants may be germanium, phosphorus, or rare-earth ions. Germanium and Phosphorus can be introduced more importantly in the fiber than rare earth ions and then allow to obtain a higher birefringence.
Selon un mode de réalisation illustré FIG. 2, dans le cœur 7, les deux zones de dopage 5 et 6 comprennent un même dopant, par exemple du germanium. Les concentrations du germanium sont distinctes dans les zones 5 et 6. La zone 5 possède un dopage faible de 3% tandis que l'autre zone 6 possède un dopage plus élevé de l'ordre de 10% par exemple. Du fait de la présence d'un dopant à deux concentrations différentes de part et d'autre de l'axe des X dans le cœur 7, la symétrie du cœur est rompue dans la direction de l'axe des Y. De la sorte, la biréfringence de la fibre optique 1 augmente.According to an embodiment illustrated FIG. 2, in the heart 7, the two doping zones 5 and 6 comprise the same dopant, for example germanium. The concentrations of germanium are distinct in zones 5 and 6. Zone 5 has a low doping of 3% while the other zone 6 has a higher doping of the order of 10% for example. Due to the presence of a dopant at two different concentrations on either side of the X axis in the heart 7, the symmetry of the heart is broken in the direction of the Y axis. In this way, the birefringence of the optical fiber 1 increases.
Selon l'invention, la fibre 1 peut comprendre une pluralité de cœurs 7, 7A, 7B, 7C, 7D, 7E, 7F, comme illustré FIG. 3. Les cœurs 7A, 7B, 7D et 7E sont sensiblement circulaires car ils sont entourés de trous d'air 2 de même diamètre. Du fait de la présence selon l'axe des X des trous d'air 4 de grand diamètre, le cœur 7 est sensiblement de forme ellipsoïdale comme précédemment, et les trous 7F et 7C sont asymétriques selon l'axe des X, et symétriques par rapport à l'axe des X.According to the invention, the fiber 1 may comprise a plurality of cores 7, 7A, 7B, 7C, 7D, 7E, 7F, as illustrated in FIG. 3. The cores 7A, 7B, 7D and 7E are substantially circular because they are surrounded by air holes 2 of the same diameter. Because of the X-axis presence of the large-diameter air holes 4, the core 7 is substantially ellipsoidal in shape as before, and the holes 7F and 7C are asymmetrical along the X axis, and symmetrical by relative to the X axis.
Selon l'invention, dans chacun de ces cœurs, on dope des zones de dopages agencées pour rompre une symétrie spatiale du cœur.According to the invention, in each of these cores doping zones of doping arranged to break a spatial symmetry of the heart are doped.
Ces différentes cœurs peuvent être couplés de sorte à briser une symétrie de propagation et ainsi augmenter les effets de biréfringence.These different cores can be coupled so as to break a propagation symmetry and thus increase the effects of birefringence.
Illustré par exemple en FIG. 4, pour les cœurs 7F et 7C, qui ont une symétrie selon l'axe des Y, on positionne deux zones de dopage 5 et 6 de part et d'autre de l'axe des X séparant le cœur 7F, avec soit des dopants identiques à des concentrations différentes, soit des dopants différents. De la sorte, la symétrie spatiale du cœur 7F est rompue, ce qui augmente la biréfringence de la fibre pour un flux lumineux se propageant dans le cœur 7F.Illustrated for example in FIG. 4, for the cores 7F and 7C, which have a symmetry along the Y axis, two doping zones 5 and 6 are positioned on either side of the X axis separating the core 7F, with either dopants identical at different concentrations, different dopants. In this way, the spatial symmetry of the core 7F is broken, which increases the birefringence of the fiber for a light flux propagating in the heart 7F.
De façon générale, selon l'invention, pour améliorer la biréfringence d'une fibre optique, on détermine au moins une symétrie spatiale du cœur de la fibre, et on dope ce cœur de sorte à briser la symétrie spatiale du fait de la répartition du dopant au sein du cœur. In general, according to the invention, in order to improve the birefringence of an optical fiber, at least one spatial symmetry of the core of the fiber is determined, and this core is doped so as to break the spatial symmetry due to the distribution of the fiber. dopant within the heart.

Claims

REVENDICATIONS
1. Fibre optique microstructurée (1 ) comprenant au moins un cœur (7, 7A, 7B, 7C, 7D, 7E, 7F) ayant une symétrie spatiale de forme comprenant au moins un axe de symétrie, caractérisé en ce que ledit cœur comprend au moins un dopant réparti au sein dudit cœur selon une implantation dissymétrique par rapport audit au moins un axe de symétrie.A microstructured optical fiber (1) comprising at least one core (7, 7A, 7B, 7C, 7D, 7E, 7F) having a spatial symmetry of shape comprising at least one axis of symmetry, characterized in that said core comprises at least one less a dopant distributed within said heart according to an asymmetrical implantation with respect to said at least one axis of symmetry.
2. Fibre optique selon la revendication 1 , dans laquelle ledit au moins un dopant est positionné dans une pluralité de zones de dopage (5, 6) dudit cœur, chacune des zones de dopage étant distincte.2. Optical fiber according to claim 1, wherein said at least one dopant is positioned in a plurality of doping zones (5, 6) of said core, each of the doping zones being distinct.
3. Fibre optique selon la revendication 2, dans laquelle ledit cœur comprend un unique dopant, ledit dopant étant positionné dans chacune desdites zones de dopage, la concentration dudit dopant étant différente dans chacune des zones de dopage.An optical fiber according to claim 2, wherein said core comprises a single dopant, said dopant being positioned in each of said doping zones, the concentration of said dopant being different in each of the doping zones.
4. Fibre optique selon l'une des revendications 1 ou 2, dans laquelle ledit cœur comprend une pluralité de dopants distincts, chacun des dopants de ladite pluralité de dopants étant situé dans une zone de dopage distincte de ladite pluralité de zones de dopage.An optical fiber according to claim 1 or 2, wherein said core comprises a plurality of distinct dopants, each of said dopants of said plurality of dopants being located in a doping zone distinct from said plurality of doping zones.
5. Fibre optique selon l'une des revendications 2 à 4, dans laquelle ledit cœur est symétrique par rapport à un axe de symétrie, et dans lequel ledit cœur comprend deux zones de dopage, lesdites zones de dopage étant positionnées de part et d'autre dudit axe de symétrie.5. Optical fiber according to one of claims 2 to 4, wherein said core is symmetrical with respect to an axis of symmetry, and wherein said core comprises two doping zones, said doping zones being positioned on both sides. other of said axis of symmetry.
6. Fibre optique selon l'une des revendications précédentes, comprenant une pluralité de cœurs, chacun des cœurs de ladite pluralité de cœur ayant respectivement une symétrie spatiale selon au moins un axe de symétrie, chacun des cœurs de la pluralité de cœur comprenant respectivement au moins un dopant réparti au sein dudit cœur correspondant selon une implantation dissymétrique par rapport audit au moins un axe de symétrie respectif.Optical fiber according to one of the preceding claims, comprising a plurality of cores, each of the cores of said plurality of cores respectively having a spatial symmetry according to at least one axis of symmetry, each of the cores of the plurality of cores including respectively at less a dopant distributed within said corresponding heart according to an asymmetrical implantation with respect to said at least one respective axis of symmetry.
7. Fibre optique selon l'une des revendications précédentes, dans laquelle ledit dopant est choisi dans le groupe composé d'un ion terre-rare, du germanium et du phosphore.7. Optical fiber according to one of the preceding claims, wherein said dopant is selected from the group consisting of a rare-earth ion, germanium and phosphorus.
8. Fibre optique selon l'une des revendications précédentes, dans laquelle ledit cœur est un cœur de silice entouré de quatre trous d'air (2) de petit diamètre et de deux trous d'air de grand diamètre (4), les quatre trous d'air de petit diamètre étant répartis par paire de part et d'autre des trous d'air de grand diamètre.Optical fiber according to one of the preceding claims, wherein said core is a silica core surrounded by four air holes (2) of small diameter and two air holes of large diameter (4), the four air holes of small diameter being distributed in pairs on both sides of the air holes of large diameter.
9. Fibre optique selon la revendication 8, dans laquelle le petit diamètre est de 2,2 micromètres, et le grand diamètre est de 4 micromètres.The optical fiber of claim 8, wherein the small diameter is 2.2 microns, and the large diameter is 4 microns.
10. Fibre optique selon l'une des revendications précédentes, dans laquelle ladite symétrie spatiale est un plan de symétrie.10. Optical fiber according to one of the preceding claims, wherein said spatial symmetry is a plane of symmetry.
1 1 . Procédé de fabrication d'une fibre optique dopée comprenant des étapes consistant à :1 1. A method of manufacturing a doped optical fiber comprising steps of:
- fournir une fibre optique microstructurée ayant un cœur à symétrie spatiale de forme; - déterminer au moins un axe de symétrie de ladite symétrie spatiale de forme ;providing a microstructured optical fiber having a shape symmetry-shaped core; determining at least one axis of symmetry of said spatial symmetry of shape;
- répartir au moins un dopant au sein dudit cœur selon une implantation dissymétrique par rapport audit au moins un axe de symétrie. distributing at least one dopant within said heart according to an asymmetrical implantation with respect to said at least one axis of symmetry.
EP07871847A 2006-12-12 2007-12-12 Doped optical fibre with broken space symmetry Withdrawn EP2100175A2 (en)

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FR0610837A FR2909776B1 (en) 2006-12-12 2006-12-12 DOPED OPTICAL FIBER WITH BROKEN SPACE SYMMETRY
PCT/FR2007/002054 WO2008090279A2 (en) 2006-12-12 2007-12-12 Doped optical fibre with broken space symmetry

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JP3734733B2 (en) * 2001-09-27 2006-01-11 日本電信電話株式会社 Polarization-maintaining optical fiber and absolute single-polarization optical fiber
JP3825381B2 (en) * 2002-09-10 2006-09-27 三菱電線工業株式会社 Polarization-maintaining photonic crystal fiber
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FR2909776A1 (en) 2008-06-13
FR2909776B1 (en) 2009-06-05

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