EP2035846A1 - Electrooptic probe for vector measurement of an electromagnetic field - Google Patents

Electrooptic probe for vector measurement of an electromagnetic field

Info

Publication number
EP2035846A1
EP2035846A1 EP07789010A EP07789010A EP2035846A1 EP 2035846 A1 EP2035846 A1 EP 2035846A1 EP 07789010 A EP07789010 A EP 07789010A EP 07789010 A EP07789010 A EP 07789010A EP 2035846 A1 EP2035846 A1 EP 2035846A1
Authority
EP
European Patent Office
Prior art keywords
fiber
phase shift
orientation
wave plate
axes
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Withdrawn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
EP07789010A
Other languages
German (de)
French (fr)
Inventor
Lionel Duvillaret
Gwenaël GABORIT
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.)
Institut Polytechnique de Grenoble
Universite Savoie Mont Blanc
Original Assignee
Institut Polytechnique de Grenoble
Universite Savoie Mont Blanc
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
Application filed by Institut Polytechnique de Grenoble, Universite Savoie Mont Blanc filed Critical Institut Polytechnique de Grenoble
Publication of EP2035846A1 publication Critical patent/EP2035846A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
    • G01R29/08—Measuring electromagnetic field characteristics
    • G01R29/0864—Measuring electromagnetic field characteristics characterised by constructional or functional features
    • G01R29/0878—Sensors; antennas; probes; detectors
    • G01R29/0885—Sensors; antennas; probes; detectors using optical probes, e.g. electro-optical, luminescent, glow discharge, or optical interferometers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
    • G01R29/12—Measuring electrostatic fields or voltage-potential
    • G01R29/14—Measuring field distribution

Definitions

  • the invention relates to measuring electromagnetic fields in small areas analytical dimen ⁇ sions.
  • electromagnetic field or simply "field”
  • an electromagnetic field itself, or a pure magnetic field, or a pure electric field.
  • optical detection systems have been provided in which the field reacts on a light beam passing through an electro-optical crystal. In an electro-optical crystal, the field acts essentially on the polarization of a light beam.
  • optical waves with rectilinear polarization, circular polarization and elliptical polarization In order not to burden this description, we will speak, as is often done in practice, rectilinear waves, circular or elliptical, and it will be understood that each time is optical waves whose polarization is respectively rectilinear, circular or elliptical.
  • An example of a conventional device for optically measuring an electromagnetic field is illustrated in Figure 1.
  • the detec tor ⁇ consists of a crystal electro-optical disc 1, one end 2 comprises a reflecting surface and whose other end is coupled by a coupler 3 at one end of an optical fiber polarization maintaining light 5.
  • pola ⁇ derision is sent by a polarized light source, coherent or not, including for example a light emitting diode 7 and a polarizer 8, with the other end of the optical fiber 5 via a coupler 9.
  • the light returned by the mirror 2 and having thus crossed twice the crystal 1 and twice the fiber 5 is taken up by a separator 11 and sent in a set polarization analysis system comprising, for example, a quarter-wave plate (or ⁇ / 4 plate) 13, a half-wave plate (or ⁇ / 2 plate) 14 and a polarizer 15, each of these elements being individually adjustable in rotation, either manually or under the effect of a control device 17.
  • polarizer an element capable of fixing the polarization of the light that passes through in the direction of a device using this light, and called “analyzer” the same device when it is placed on the side of the detector of a system, and is used to analyze the polarization of the light it receives.
  • the term “polarizer” will always be used, whether it is placed in a position where it fixes the polarization or in a position where it analyzes the polarization of the light that it receives, since it This is the same hardware device.
  • the analyzer term will be reserved to a set of ana ⁇ lysis of the polarization state of a light wave, comprising the blade assembly ⁇ / 4 13, the ⁇ / 2 blade 14 and the polarizer 15.
  • a detector 19 At the output of the polarizer 15 is disposed a detector 19 which provides on a terminal 20 a signal proportional to the intensity of the wave incident on the polarizer 15 in the polarization direction of this polarizer.
  • the optical fiber 5 will transmit to the crystal 1 a linearly polarized wave in the direction of an axis of the polarization-maintaining fiber (If the polarizer 8 is aligned along one of the two axes of the fiber 5). This state of polarization will be modified by the anisotropic crystal which will return in the fiber an elliptical wave.
  • the analyzer 13-15 is set in the absence of a field to set a reference point.
  • This modification is characteristic of the field applied at the sensor and can be detected by the analyzer 13-15. It will be recalled that this type of device only measures a component of the field parallel to a characteristic sensitivity vector of the electro-optical crystal used.
  • the axes of the electro-optical crystal 2 form an angle of 45 ° with the axes of the polarization maintaining fiber.
  • a device of the type described above gives, a priori, good results, in particular because it allows elements requiring the presence of electric currents, comprising the light source 7, the photoreceptor 19 and the unrepresented circuits of analysis of its output signal 20 are remote from the area where the field is measured. Thus, these elements are not disturbed by the field to be measured, nor do they disturb this field.
  • the adjustment of the device, and in particular the adjustment of the point of reference above drifts considerably over time, especially when the optical fiber is long. It has been noted that this particular maladjustment is related to fluctuations in tempera ⁇ ture. Thus, the same field may be measured as having different values if the temperature has varied without being noticed. It is therefore very often necessary to readjust the setting of the reference point of the analyzer 13-15 if a reliable measurement is to be obtained, and this adjustment, which is empirical, is relatively long and difficult. Summary of the invention
  • the present invention aims to overcome at least some of the disadvantages of optical field measuring devices and in particular to avoid the effects induced by a temperature variation of the fiber.
  • the present invention also aims to provide a particularly simple analysis system to use.
  • the present invention also aims at providing two components of the field at the level of the analysis zone.
  • the present invention provides a device for measuring two components of an electromagnetic field in an analysis zone, comprising: a light source sending in an optical fiber to maintain polarization a light beam polarized along an axis of the fiber; an isotropic electro-optical material disposed in said zone, receiving the beam of the optical fiber via a ⁇ / 4 plate having its axes oriented at an angle of 45 ° to the axes of the optical fiber and returning a beam in this fiber, this blade being slightly ⁇ mentally disordered as to its characteristic or its orientation; beam phase-shifting means returned to the fiber set to impose a phase shift equal to and opposite to that imposed between the two polarizations aligned along the proper dielectric axes of the fiber; means for analyzing the orientation and the ellipticity of the wave coming out of the phase - shift means, the orientation and the ellipticity being linked by non - phase relations. trivial to the orientation and intensity of the field in the analysis area.
  • the analysis means comprise a ⁇ / 4 plate, and polarizers respectively arranged on two distinct paths between the quarter wave plate and intensity detectors.
  • the phase-shift means comprise a ⁇ / 4 blade and a ⁇ / 2 blade. According to one embodiment of the present invention, the phase-shift means comprise a Sun-Babinet compensator.
  • a method of adjusting the phase shift means of the device comprises the following steps: arranging a polarizer behind the phase shift means at 45 ° of the reference polarization defined by an axis of the fiber, and adjusting the phase shift means so that the polarizer transmits half of the light he receives.
  • FIG. device for measuring an electromagnetic field by an electro-optical effect crystal according to the prior art and Figure 2 schematically shows an embodiment of a device for measuring a field Electromagnetic ⁇ tick by an electrooptic effect crystal according to the present invention.
  • FIG. 2 uses a hardware device of which some elements are identical to those shown in Figure 1. These elements are designated by the same references and will not be described again.
  • crystal electrooptic effect crystal 21 isotropic in the absence of a field and which becomes anisotropic in the presence of field, for exam ple ⁇ a crystal of gallium arsenide type tellurium or zinc.
  • a quarter wave plate 22 oriented at 45 ° to the axes of the fiber.
  • This blade must either be exactly quarter-wave or not be oriented exactly 45 ° to the axes of the fiber. Then, the polarization sent into the crystal will be a quasi-circular polarization.
  • the axes of the crystal can be placed at any angle to the axes of the fiber and the quarter wave plate.
  • the beam returned by the crystal 21 in the fiber 5 is deflected by the separator 11 to a phase shifter assembly comprising for example a quarter-wave plate (or ⁇ / 4 blade) 13 and a half-wave plate (or ⁇ / 2 blade) 14.
  • a phase shifter assembly comprising for example a quarter-wave plate (or ⁇ / 4 blade) 13 and a half-wave plate (or ⁇ / 2 blade) 14.
  • the output beam of the phase shifter 13-14 is sent to a polarizer 15 and a detector 19. And the inventor has been able to show that the polarization state at the output of the phase shifter assembly, when an electric field is applied to the crystal
  • ⁇ E phase shift introduced in the presence of a field between the polarizations oriented along the dielectric axes of the crystal by a round trip in the material of the electro-optical crystal, noting that ⁇ ⁇ is always very small in front of 2 ⁇
  • ⁇ phase shift introduced by the phase shifter corresponding to the set of blades ⁇ / 4 13 and ⁇ / 2 14
  • CC angular value depending on the orientation of the electromagnetic field with respect to the axes of the crystal 21.
  • Equations (1) then become:
  • polarization analyzers can be used to determine ⁇ ⁇ and CC.
  • An example is given in FIG. 2 and comprises a ⁇ / 4 blade 32 transforming the flattened elliptical wave into a quasi-circular wave, and this quasi-circular wave is sent via a separator 33 on two channels, to detectors S1 and S2 via polarizers P1 and P2 of orientation ⁇ 1 and ⁇ 2.
  • the present invention is capable of many features or variants, among which may be mentioned, without limitation, the following.
  • any known phase-shifting device for example a Sun-Babinet compensator, may be used. This compensator will be easier to enslave by the control device 23.
  • the field applied to the sensor 21 is an alternating field of given frequency, synchronous detections of the output signal of the sensors S1 and S2 will preferably be carried out. 3. To increase the sensitivity, it will be possible to associate antenna elements with the sensor crystal.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

The invention relates to a device for measuring two components of an electromagnetic field in an analysis zone, said device comprising: a light source (7) sending a polarized light beam into a polarization-maintaining optical fibre (5), said beam being directed along one axis of the fibre; an isotropic electrooptic material (21) placed in said zone, receiving the beam from the optical fibre via a quarter-wave plate (22) having its axes oriented at an angle of 45° to the axes of the optical fibre and sending a beam into this fibre, this plate being slightly detuned as regards is characteristic or its orientation; means (13-14) for phase-shifting the beam sent into the fibre, which means are set so as to impose a phase shift (g) equal and opposite to that (q) imposed by the fibre; and means for analyzing the orientation and the ellipticity of the wave exiting the phase-shifting means.

Description

SONDE ELECTRO-OPTIQUE DE MESURE VECTORIELLE D'UN CHAMP ELECTRO-OPTICAL PROBE OF VECTOR MEASUREMENT OF A FIELD
ELECTROMAGNETIQUEELECTROMAGNETIC
Domaine de l' inventionField of the invention
La présente invention concerne la mesure de champs électromagnétiques dans des zones d'analyse de petites dimen¬ sions. Dans la présente demande, on désigne par "champ électromagnétique", ou tout simplement par "champ", un champ électromagnétique proprement dit, ou bien un champ magnétique pur, ou bien un champ électrique pur. Exposé de l'art antérieur L'une des difficultés quand on veut mesurer un champ électromagnétique est que ce champ est susceptible de réagir directement sur les circuits des instruments de mesure utilisés pour le mesurer ou d'être influencé par ceux-ci. Pour éviter cet inconvénient, on a prévu des systèmes de détection optiques dans lesquels le champ réagit sur un faisceau lumineux traversant un cristal électro-optique. Dans un cristal électro-optique, le champ agit essentiellement sur la polarisation d'un faisceau lumineux. On sera amené ici à mentionner des ondes optiques à polarisation rectiligne, à polarisation circulaire et à polari- sation elliptique. Pour ne pas alourdir la présente description, on parlera, comme cela est souvent effectué dans la pratique, d'ondes rectilignes, circulaires ou elliptiques, et on comprendra qu'il s'agit chaque fois d'ondes optiques dont la polarisation est respectivement rectiligne, circulaire ou elliptique. Un exemple de dispositif classique de mesure optique d'un champ électromagnétique est illustré en figure 1. Le détec¬ teur est constitué d'un cristal électro-optique 1 dont une extrémité 2 comporte une surface réflectrice et dont l ' autre extrémité est couplée par un coupleur 3 à une extrémité d'une fibre optique à maintien de polarisation 5. De la lumière pola¬ risée est envoyée par une source lumineuse polarisée, cohérente ou non, comprenant par exemple une diode photoémettrice 7 et un polariseur 8, à l'autre extrémité de la fibre optique 5 par l'intermédiaire d'un coupleur 9. La lumière renvoyée par le miroir 2 et ayant donc traversé deux fois le cristal 1 et deux fois la fibre 5 est reprise par une séparatrice 11 et envoyée dans un ensemble d'analyse de polarisation comprenant par exemple une lame quart d'onde (ou lame λ/4) 13, une lame demi onde (ou lame λ/2) 14 et un polariseur 15, chacun de ces éléments étant individuellement réglable en rotation, soit manuellement soit sous l'effet d'un dispositif de commande 17. On notera que, habituellement, dans le domaine de l'optique anisotrope, on appelle "polariseur" un élément susceptible de fixer la polarisation de la lumière qui le traverse en direction d'un dispositif utilisant cette lumière, et on appelle "analyseur" ce même dispositif quand il est placé du côté du détecteur d'un système, et sert à l'analyse de la polarisation de la lumière qu'il reçoit. Dans la présente description, on utilisera toujours le terme "polariseur", que celui-ci soit placé dans une position où il fixe la polarisation ou dans une position où il analyse la polarisation de la lumière qu'il reçoit, étant donné qu'il s'agit bien du même dispositif matériel. On réservera le terme analyseur à un ensemble d'ana¬ lyse de l'état de polarisation d'une onde lumineuse, comprenant l'ensemble de la lame λ/4 13, de la lame λ/2 14 et du polariseur 15.The invention relates to measuring electromagnetic fields in small areas analytical dimen ¬ sions. In the present application, the term "electromagnetic field" or simply "field", an electromagnetic field itself, or a pure magnetic field, or a pure electric field. DISCUSSION OF THE PRIOR ART One of the difficulties when measuring an electromagnetic field is that this field is likely to react directly on the circuits of the measuring instruments used to measure or be influenced by them. To avoid this drawback, optical detection systems have been provided in which the field reacts on a light beam passing through an electro-optical crystal. In an electro-optical crystal, the field acts essentially on the polarization of a light beam. We shall mention here optical waves with rectilinear polarization, circular polarization and elliptical polarization. In order not to burden this description, we will speak, as is often done in practice, rectilinear waves, circular or elliptical, and it will be understood that each time is optical waves whose polarization is respectively rectilinear, circular or elliptical. An example of a conventional device for optically measuring an electromagnetic field is illustrated in Figure 1. The detec tor ¬ consists of a crystal electro-optical disc 1, one end 2 comprises a reflecting surface and whose other end is coupled by a coupler 3 at one end of an optical fiber polarization maintaining light 5. pola ¬ derision is sent by a polarized light source, coherent or not, including for example a light emitting diode 7 and a polarizer 8, with the other end of the optical fiber 5 via a coupler 9. The light returned by the mirror 2 and having thus crossed twice the crystal 1 and twice the fiber 5 is taken up by a separator 11 and sent in a set polarization analysis system comprising, for example, a quarter-wave plate (or λ / 4 plate) 13, a half-wave plate (or λ / 2 plate) 14 and a polarizer 15, each of these elements being individually adjustable in rotation, either manually or under the effect of a control device 17. Note that, usually in the field of anisotropic optics, is called "polarizer" an element capable of fixing the polarization of the light that passes through in the direction of a device using this light, and called "analyzer" the same device when it is placed on the side of the detector of a system, and is used to analyze the polarization of the light it receives. In the present description, the term "polarizer" will always be used, whether it is placed in a position where it fixes the polarization or in a position where it analyzes the polarization of the light that it receives, since it This is the same hardware device. The analyzer term will be reserved to a set of ana ¬ lysis of the polarization state of a light wave, comprising the blade assembly λ / 4 13, the λ / 2 blade 14 and the polarizer 15.
A la sortie du polariseur 15 est disposé un détecteur 19 qui fournit sur une borne 20 un signal proportionnel à l'intensité de l'onde incidente sur le polariseur 15 dans la direction de polarisation de ce polariseur. L'homme de l'art comprendra que, en l'absence de champ au niveau du capteur 1, la fibre optique 5 transmettra vers le cristal 1 une onde à polarisation rectiligne selon la direction d'un axe de la fibre à maintien de polarisation (si le polariseur 8 est aligné selon l'un des deux axes de la fibre 5) . Cet état de polarisation sera modifié par le cristal anisotrope qui renverra dans la fibre une onde elliptique. L'analyseur 13-15 est réglé en l'absence de champ pour fixer un point de référence. Ensuite, quand un champ est appliqué sur le cristal 1, ceci modifie les indices du cristal et la polarisation de l'onde reçue au niveau de l'analyseur 13-15 se modifie. Cette modification est caractéristique du champ appliqué au niveau du capteur et pourra être détectée par l'analyseur 13-15. On rappellera que l'on ne mesure en fait par ce type de dispositif qu'une composante du champ, parallèle à un vecteur sensibilité caractéristique du cristal électro-optique utilisé.At the output of the polarizer 15 is disposed a detector 19 which provides on a terminal 20 a signal proportional to the intensity of the wave incident on the polarizer 15 in the polarization direction of this polarizer. Those skilled in the art will understand that, in the absence of a field at the sensor 1, the optical fiber 5 will transmit to the crystal 1 a linearly polarized wave in the direction of an axis of the polarization-maintaining fiber (If the polarizer 8 is aligned along one of the two axes of the fiber 5). This state of polarization will be modified by the anisotropic crystal which will return in the fiber an elliptical wave. The analyzer 13-15 is set in the absence of a field to set a reference point. Then, when a field is applied to the crystal 1, this modifies the crystal indices and the polarization of the wave received at the analyzer 13-15 changes. This modification is characteristic of the field applied at the sensor and can be detected by the analyzer 13-15. It will be recalled that this type of device only measures a component of the field parallel to a characteristic sensitivity vector of the electro-optical crystal used.
Divers moyens ont été proposés pour optimiser la mesure. Par exemple, on préférera que les axes du cristal électro-optique 2 forment un angle de 45° avec les axes de la fibre à maintien de polarisation.Various means have been proposed to optimize the measurement. For example, it will be preferred that the axes of the electro-optical crystal 2 form an angle of 45 ° with the axes of the polarization maintaining fiber.
Un dispositif du type décrit ci-dessus donne a priori de bons résultats, notamment du fait qu'il permet que les éléments nécessitant la présence de courants électriques, comprenant la source lumineuse 7, le photorécepteur 19 et les circuits non représentés d'analyse de son signal de sortie 20 soient à distance de la zone où l'on mesure le champ. Ainsi, ces éléments ne sont pas perturbés par le champ à mesurer, pas plus qu'ils ne perturbent ce champ. Toutefois, on s'aperçoit que le réglage du dispositif, et notamment le réglage du point de référence susmentionné, dérive considérablement au cours du temps, surtout quand la fibre optique est longue. On a pu noter que ce déréglage est notamment lié aux fluctuations de tempéra¬ ture. Ainsi, un même champ risque d'être mesuré comme ayant des valeurs différentes si la température a varié sans que l'on s'en aperçoive. Il faut donc effectuer très souvent un réajustement du réglage du point de référence de l'analyseur 13-15 si l'on veut obtenir une mesure fiable, et ce réglage, empirique, est relativement long et difficile. Résumé de l'inventionA device of the type described above gives, a priori, good results, in particular because it allows elements requiring the presence of electric currents, comprising the light source 7, the photoreceptor 19 and the unrepresented circuits of analysis of its output signal 20 are remote from the area where the field is measured. Thus, these elements are not disturbed by the field to be measured, nor do they disturb this field. However, it can be seen that the adjustment of the device, and in particular the adjustment of the point of reference above, drifts considerably over time, especially when the optical fiber is long. It has been noted that this particular maladjustment is related to fluctuations in tempera ¬ ture. Thus, the same field may be measured as having different values if the temperature has varied without being noticed. It is therefore very often necessary to readjust the setting of the reference point of the analyzer 13-15 if a reliable measurement is to be obtained, and this adjustment, which is empirical, is relatively long and difficult. Summary of the invention
La présente invention vise à pallier au moins certains des inconvénients des dispositifs optiques de mesure de champ et notamment à s ' abstraire des effets induits par une variation de température de la fibre. La présente invention vise en outre à prévoir un système d'analyse particulièrement simple à utiliser.The present invention aims to overcome at least some of the disadvantages of optical field measuring devices and in particular to avoid the effects induced by a temperature variation of the fiber. The present invention also aims to provide a particularly simple analysis system to use.
La présente invention vise également à fournir deux composantes du champ au niveau de la zone d'analyse.The present invention also aims at providing two components of the field at the level of the analysis zone.
Pour atteindre tout ou partie de ces objets ainsi que d'autres, la présente invention prévoit un dispositif de mesure de deux composantes d'un champ électromagnétique dans une zone d'analyse, comprenant : une source lumineuse envoyant dans une fibre optique à maintien de polarisation un faisceau lumineux polarisé selon un axe de la fibre ; un matériau électro-optique isotrope disposé dans ladite zone, recevant le faisceau de la fibre optique par l'intermédiaire d'une lame λ/4 ayant ses axes orientés à un angle de 45° des axes de la fibre optique et renvoyant un faisceau dans cette fibre, cette lame étant légère¬ ment déréglée quant à sa caractéristique ou à son orientation ; des moyens de déphasage du faisceau renvoyé dans la fibre réglés pour imposer un déphasage égal et opposé à celui imposé entre les deux polarisations alignées selon les axes diélectriques propres de la fibre ; des moyens d'analyse de l'orientation et de l 'ellipticité de l'onde sortant des moyens de déphasage, l'orientation et l 'ellipticité étant liées par des relations non triviales à l'orientation et à l'intensité du champ dans la zone d' analyse.To achieve all or part of these objects as well as others, the present invention provides a device for measuring two components of an electromagnetic field in an analysis zone, comprising: a light source sending in an optical fiber to maintain polarization a light beam polarized along an axis of the fiber; an isotropic electro-optical material disposed in said zone, receiving the beam of the optical fiber via a λ / 4 plate having its axes oriented at an angle of 45 ° to the axes of the optical fiber and returning a beam in this fiber, this blade being slightly ¬ mentally disordered as to its characteristic or its orientation; beam phase-shifting means returned to the fiber set to impose a phase shift equal to and opposite to that imposed between the two polarizations aligned along the proper dielectric axes of the fiber; means for analyzing the orientation and the ellipticity of the wave coming out of the phase - shift means, the orientation and the ellipticity being linked by non - phase relations. trivial to the orientation and intensity of the field in the analysis area.
Selon un mode de réalisation de la présente invention, les moyens d'analyse comprennent une lame λ/4, et des polari- seurs respectivement disposés sur deux voies distinctes entre la lame quart d'onde et des détecteurs d'intensité.According to one embodiment of the present invention, the analysis means comprise a λ / 4 plate, and polarizers respectively arranged on two distinct paths between the quarter wave plate and intensity detectors.
Selon un mode de réalisation de la présente invention, les moyens de déphasage comprennent une lame λ/4 et une lame λ/2. Selon un mode de réalisation de la présente invention, les moyens de déphasage comprennent un compensateur de Soleil- Babinet .According to one embodiment of the present invention, the phase-shift means comprise a λ / 4 blade and a λ / 2 blade. According to one embodiment of the present invention, the phase-shift means comprise a Sun-Babinet compensator.
Un procédé de réglage des moyens de déphasage du dispositif comprend les étapes suivantes : disposer un polariseur derrière les moyens de déphasage à 45° de la polarisation de référence définie par un axe de la fibre, et régler les moyens de déphasage pour que le polariseur transmette la moitié de la lumière qu'il reçoit. Brève description des dessinsA method of adjusting the phase shift means of the device comprises the following steps: arranging a polarizer behind the phase shift means at 45 ° of the reference polarization defined by an axis of the fiber, and adjusting the phase shift means so that the polarizer transmits half of the light he receives. Brief description of the drawings
Ces objets, caractéristiques et avantages, ainsi que d'autres de la présente invention seront exposés en détail dans la description suivante de modes de réalisation particuliers faite à titre non-limitatif en relation avec les figures jointes parmi lesquelles : la figure 1 représente schématiquement un dispositif de mesure d'un champ électromagnétique par un cristal à effet électro-optique selon l'art antérieur ; et la figure 2 représente schématiquement un mode de réalisation d'un dispositif de mesure d'un champ électromagné¬ tique par un cristal à effet électro-optique selon la présente invention.These and other objects, features, and advantages of the present invention will be set forth in detail in the following description of particular embodiments, given in a non-limiting manner, with reference to the accompanying drawings in which: FIG. device for measuring an electromagnetic field by an electro-optical effect crystal according to the prior art; and Figure 2 schematically shows an embodiment of a device for measuring a field Electromagnetic ¬ tick by an electrooptic effect crystal according to the present invention.
Description détailléedetailed description
La présente invention, dont un mode de réalisation est illustré en figure 2, utilise un dispositif matériel dont certains éléments sont identiques à ceux représentés en figure 1. Ces éléments sont désignés par de mêmes références et ne seront pas décrits à nouveau.The present invention, an embodiment of which is illustrated in FIG. 2, uses a hardware device of which some elements are identical to those shown in Figure 1. These elements are designated by the same references and will not be described again.
Selon la présente invention, on utilise comme cristal à effet électro-optique un cristal 21, isotrope en l'absence de champ et qui devient anisotrope en présence de champ, par exem¬ ple un cristal du type arséniure de gallium ou tellure de zinc.According to the present invention is used as crystal electrooptic effect crystal 21, isotropic in the absence of a field and which becomes anisotropic in the presence of field, for exam ple ¬ a crystal of gallium arsenide type tellurium or zinc.
Entre le cristal 21 et la fibre 5 est insérée une lame quart d'onde 22 orientée à 45° des axes de la fibre. Cette lame doit ou bien n'être pas exactement quart d'onde ou bien ne pas être orientée exactement à 45° des axes de la fibre. Alors, la polarisation envoyée dans le cristal sera une polarisation quasi circulaire. Les axes du cristal peuvent être mis à un angle quelconque par rapport aux axes de la fibre et de la lame quart d ' onde .Between the crystal 21 and the fiber 5 is inserted a quarter wave plate 22 oriented at 45 ° to the axes of the fiber. This blade must either be exactly quarter-wave or not be oriented exactly 45 ° to the axes of the fiber. Then, the polarization sent into the crystal will be a quasi-circular polarization. The axes of the crystal can be placed at any angle to the axes of the fiber and the quarter wave plate.
Le faisceau renvoyé par le cristal 21 dans la fibre 5 est dévié par la séparatrice 11 vers un ensemble déphaseur comprenant par exemple une lame quart d'onde (ou lame λ/4) 13 et une lame demi onde (ou lame λ/2) 14. On notera que, en l'absence de champ, le cristal 21 étant isotrope, l'onde sortant de la séparatrice 11 serait rectiligne si la lame 22 était parfaite¬ ment quart d'onde et exactement à 45°. En raison du caractère volontairement imparfait de la lame λ/4 22, cette onde est légè¬ rement elliptique, présentant par exemple une composante orthogonale ayant une intensité de quelques pourcents de sa composante principale.The beam returned by the crystal 21 in the fiber 5 is deflected by the separator 11 to a phase shifter assembly comprising for example a quarter-wave plate (or λ / 4 blade) 13 and a half-wave plate (or λ / 2 blade) 14. It will be noted that, in the absence of a field, the crystal 21 being isotropic, the wave emerging from the separator 11 would be rectilinear if the blade 22 was perfectly ¬ quarter-wave and exactly 45 °. Due to the imperfect nature voluntarily blade λ / 4 22 this wave is surely lege ¬ elliptical, having for example an orthogonal component having an intensity a few percent of its main component.
Le faisceau de sortie du déphaseur 13-14 est envoyé vers un polariseur 15 et un détecteur 19. Et l'inventeur a pu montrer que l'état de polarisation en sortie de l'ensemble déphaseur, quand un champ électrique est appliqué sur le cristalThe output beam of the phase shifter 13-14 is sent to a polarizer 15 and a detector 19. And the inventor has been able to show that the polarization state at the output of the phase shifter assembly, when an electric field is applied to the crystal
21, est donné par les expressions suivantes :21, is given by the following expressions:
-j(a+±—)-j (a + ± -)
Ex = (\-eJ^E).e Ex = ( \ -e J ^ E). e
:D en utilisant les notations suivantes : j : le nombre dont le carré est égal à -1, Ex, Ey : composantes orthogonales de polarisation, θ : déphasage introduit par la fibre à maintien de polarisa- tion 5 entre les polarisations alignées selon ses axes diélectriques propres (ce déphasage varie avec la température de la fibre) , : D using the following notations: j: the number whose square is equal to -1, Ex, Ey: orthogonal polarization components, θ: phase shift introduced by the polarization maintaining fiber 5 between the polarizations aligned along its dielectric axes clean (this phase shift varies with the temperature of the fiber),
ΨE : déphasage introduit en présence d'un champ entre les polarisations orientées selon les axes diélectriques du cristal par un aller et retour dans le matériau du cristal électro-optique, en notant que φ^ est toujours très petit devant 2π, γ : déphasage introduit par le déphaseur correspondant à l'ensemble des lames λ/4 13 et λ/2 14, et CC : valeur angulaire dépendant de l'orientation du champ électromagnétique par rapport aux axes du cristal 21.ΨE: phase shift introduced in the presence of a field between the polarizations oriented along the dielectric axes of the crystal by a round trip in the material of the electro-optical crystal, noting that φ ^ is always very small in front of 2π, γ: phase shift introduced by the phase shifter corresponding to the set of blades λ / 4 13 and λ / 2 14, and CC: angular value depending on the orientation of the electromagnetic field with respect to the axes of the crystal 21.
On voit que, si on règle γ égal à -θ, l'état de polari¬ sation à la sortie de l'analyseur 13-14 devient indépendant de θ, c'est-à-dire des paramètres de la fibre optique, et notamment des variations θ, c'est-à-dire de la température de la fibre. Les équations (1) deviennent alors :It can be seen that, if one adjusts γ equal to -θ, the state of polari ¬ tion at the output of the analyzer 13-14 becomes independent of θ, that is to say the parameters of the optical fiber, and in particular variations θ, that is to say the temperature of the fiber. Equations (1) then become:
Ey = (\+eJ(S?E)eJa (2)Ey = (\ + eJ (S? E ) eJ a (2)
On notera en outre que, comme φ^ est toujours très petit devant 1, l'onde obtenue est pratiquement rectiligne.Note further that, since φ ^ is always very small in front of 1, the wave obtained is substantially rectilinear.
Pour s'assurer que γ = -θ, selon un exemple de réalisa¬ tion de la présente invention, on mesure l'intensité reçue par le détecteur 19 situé derrière le polariseur 15. Cette intensité I est donnée par : I = cos2ψ + δsin(γ + θ) sin2ψ (3) où : ψ définit l'orientation du polariseur 15, δ définit le déphasage lié à l ' imperfection de la lame 22. Si on règle le polariseur 15 à 45° de la direction de polarisation imposée par le polariseur d'entrée 8, l'équation (3) devient :To ensure that γ = -θ, according to an exemplary realized ¬ of the present invention, measuring the intensity received by the detector 19 located behind the polarizer 15. The intensity I is given by: I = cos 2 ψ + δsin (γ + θ) sin2ψ (3) where: ψ defines the orientation of the polarizer 15, δ defines the phase shift related to the imperfection of the blade 22. If the polarizer 15 is set at 45 ° to the polarization direction imposed by the input polarizer 8, equation (3) becomes:
1 = 1/2 + δsin(γ + θ) (4) Ainsi on vérifie que la condition γ = -θ est satisfaite quand, à la suite du réglage de l'analyseur 13-14, la puissance à la sortie du polariseur 15 (réglé à 45°) est égale à la moitié de ce qu'elle serait en l'absence de ce polariseur. La sortie du détecteur 19 peut être utilisée par un contrôleur 23 agissant sur l'analyseur 13-14 pour que cette condition soit en permanence satisfaite. Alors, comme on l'a indiqué précédemment, le signal analysé sera indépendant des variations de température de la fibre 5.1 = 1/2 + δsin (γ + θ) (4) Thus it is verified that the condition γ = -θ is satisfied when, following the adjustment of the analyzer 13-14, the power at the output of the polarizer 15 (set at 45 °) is half of what it would be in the absence of this polarizer. The output of the detector 19 can be used by a controller 23 acting on the analyzer 13-14 so that this condition is permanently satisfied. Then, as indicated previously, the analyzed signal will be independent of the temperature variations of the fiber 5.
En outre, l'onde de sortie de l'analyseur 13-14, qui est donnée par :In addition, the output wave of analyzer 13-14, which is given by:
Ey = (\+eJ(S?E)eJa (2) est déviée par une séparatrice 31 vers un dispositif d'analyse de cette ellipticité. Rappelons que φ^ caractérise l'intensité du champ sur le capteur 21 et que CC caractérise l'orientation du champ par rapport aux axes du cristal 21. φ^ et CC sont reliés par des relations non triviales à l 'ellipticité et à l'orientation par rapport à la direction de référence de polarisation de l'onde sortie du déphaseurEy = (\ + eJ (S? E ) eJ a (2) is deflected by a separator 31 to a device for analyzing this ellipticity Let us recall that φ ^ characterizes the intensity of the field on the sensor 21 and that CC characterizes the orientation of the field with respect to the axes of the crystal 21. φ ^ and CC are connected by non-trivial relations to the ellipticity and to the orientation with respect to the polarization reference direction of the output wave of the phase-shifter
De nombreux types d'analyseurs de polarisation pourront être utilisés pour déterminer φ^ et CC. Un exemple en est donné en figure 2 et comprend une lame λ/4 32 transformant l'onde elliptique aplatie en une onde quasi circulaire, et cette onde quasi circulaire est envoyée par l'intermédiaire d'une séparatrice 33 sur deux voies, vers des détecteurs Sl et S2 par l'intermédiaire de polariseurs Pl et P2 d'orientation ψl et ψ2.Many types of polarization analyzers can be used to determine φ ^ and CC. An example is given in FIG. 2 and comprises a λ / 4 blade 32 transforming the flattened elliptical wave into a quasi-circular wave, and this quasi-circular wave is sent via a separator 33 on two channels, to detectors S1 and S2 via polarizers P1 and P2 of orientation ψ1 and ψ2.
Sur les détecteurs Sl et S2, on obtient des signaux respectifs Pl et P2 tels que : Pi = [1 - sinφE.cos2 (ψi+CC) ] /2, avec i = 1 ou 2. Alors, en prenant par exemple ψl=0 et ψ2=π/4, on obtient : sinφE = [(2Pl - I)2 + (2P2 - I)2]1/2, et tan2α = -(2P2 - I)/ (2Pl - 1)On detectors S1 and S2, respective signals P1 and P2 are obtained such that: Pi = [1 - sinφ E .cos2 (ψi + CC)] / 2, with i = 1 or 2. Then, taking e.g. ψl = 0 and ψ2 = π / 4, one obtains: sinφ E = [(2PL - I) 2 + (2P2 - I) 2] 1/2, and tan2α = - (2P2 - I) / (2Pl - 1)
Par ailleurs, la présente invention est susceptible de nombreuses particularités ou variantes, parmi lesquelles on peut mentionner, sans caractère limitatif, les suivantes.Furthermore, the present invention is capable of many features or variants, among which may be mentioned, without limitation, the following.
1. Pour déphaser l'onde reçue, au lieu d'utiliser une lame λ/4 13 et une lame λ/2 14, on pourra utiliser tout dispositif de déphasage connu, par exemple un compensateur de Soleil- Babinet. Ce compensateur sera plus facile à asservir par le dispositif de contrôle 23.1. In order to phase shift the received wave, instead of using a λ / 4 blade 13 and a λ / 2 blade 14, any known phase-shifting device, for example a Sun-Babinet compensator, may be used. This compensator will be easier to enslave by the control device 23.
2. Si le champ appliqué au capteur 21 est un champ alternatif de fréquence donnée, on réalisera de préférence des détections synchrones du signal de sortie des capteurs Sl et S2. 3. Pour augmenter la sensibilité, on pourra associer au cristal capteur des éléments formant antenne.2. If the field applied to the sensor 21 is an alternating field of given frequency, synchronous detections of the output signal of the sensors S1 and S2 will preferably be carried out. 3. To increase the sensitivity, it will be possible to associate antenna elements with the sensor crystal.
L'homme de l'art aura compris qu'il est équivalent de parler de mesure de deux composantes d'un champ, ou de mesure de l'intensité d'un champ et de son orientation, ou de mesure vectorielle d'un champ.Those skilled in the art will have understood that it is equivalent to speak of measurement of two components of a field, or of measuring the intensity of a field and its orientation, or vectorial measurement of a field .
Bien entendu, la présente invention est susceptible de toutes autres variantes et modifications qui apparaîtront à l'homme de l'art. Of course, the present invention is susceptible to all other variations and modifications which will be apparent to those skilled in the art.

Claims

REVENDICATIONS
1. Dispositif de mesure de deux composantes d'un champ électromagnétique dans une zone d'analyse, comprenant : une source lumineuse (7) envoyant dans une fibre opti¬ que à maintien de polarisation (5) un faisceau lumineux polarisé selon un axe de la fibre ; un matériau électro-optique isotrope (21) disposé dans ladite zone, recevant le faisceau de la fibre optique par l'intermédiaire d'une lame quart d'onde (22) ayant ses axes orientés à un angle de 45° des axes de la fibre optique et renvoyant un faisceau dans cette fibre, cette lame étant légèrement déréglée quant à sa caractéristique ou à son orientation ; des moyens (13-14) de déphasage du faisceau renvoyé dans la fibre réglés pour imposer un déphasage (γ) égal et opposé à celui (θ) imposé entre les deux polarisations alignées selon les axes diélectriques propres de la fibre ; et des moyens d'analyse de l'orientation et de l'ellipti- cité de l'onde sortant des moyens de déphasage, l'orientation et 1 'ellipticité étant respectivement liées à l'orientation et à l'intensité du champ dans la zone d'analyse.1. Device for measuring two components of an electromagnetic field in a scanning area, comprising: a light source (7) in a sending fiber opti ¬ polarization maintaining (5) a polarized light beam along an axis of the fiber ; an isotropic electro-optical material (21) disposed in said area, receiving the beam of the optical fiber via a quarter-wave plate (22) having its axes oriented at an angle of 45 ° to the axes of the fiber optic and returning a beam in this fiber, this blade being slightly out of adjustment as to its characteristic or its orientation; means (13-14) of phase shift of the beam returned in the fiber set to impose a phase shift (γ) equal to and opposite to that (θ) imposed between the two polarizations aligned along the proper dielectric axes of the fiber; and means for analyzing the orientation and the ellipticity of the wave emerging from the phase shift means, the orientation and the ellipticity being respectively related to the orientation and to the intensity of the field in the analysis area.
2. Dispositif selon la revendication 1, dans lequel les moyens d'analyse comprennent une lame quart d'onde (32) et des polariseurs (Pl, P2) respectivement disposés sur deux voies distinctes entre la lame quart d'onde et des détecteurs d'intensité (Sl, S2) .2. Device according to claim 1, wherein the analysis means comprise a quarter wave plate (32) and polarizers (P1, P2) respectively arranged on two separate paths between the quarter wave plate and detectors d intensity (Sl, S2).
3. Dispositif selon la revendication 1, dans lequel les moyens de déphasage comprennent une lame quart d'onde (13) et une lame demi-onde (14) .3. Device according to claim 1, wherein the phase shift means comprise a quarter wave plate (13) and a half wave plate (14).
4. Dispositif selon la revendication 1, dans lequel les moyens de déphasage comprennent un compensateur de Soleil-4. Device according to claim 1, wherein the phase shift means comprise a solar compensator.
Babinet .Babinet.
5. Procédé de réglage des moyens de déphasage d'un dispositif selon la revendication 1, caractérisé en ce qu'il comprend les étapes suivantes : disposer un polariseur (15) derrière les moyens de déphasage à 45° de la polarisation de référence définie par un axe de la fibre, et régler les moyens de déphasage pour que le polariseur transmette la moitié de la lumière qu'il reçoit. 5. A method of adjusting the phase shift means of a device according to claim 1, characterized in that it comprises the following steps: arranging a polarizer (15) behind the phase shift means at 45 ° to the reference polarization defined by an axis of the fiber, and adjusting the phase shift means so that the polarizer transmits half of the light it receives.
EP07789010A 2006-06-16 2007-06-15 Electrooptic probe for vector measurement of an electromagnetic field Withdrawn EP2035846A1 (en)

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