EP1474722A2 - Method and device for modifying the polarisation state of light - Google Patents

Method and device for modifying the polarisation state of light

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Publication number
EP1474722A2
EP1474722A2 EP03704088A EP03704088A EP1474722A2 EP 1474722 A2 EP1474722 A2 EP 1474722A2 EP 03704088 A EP03704088 A EP 03704088A EP 03704088 A EP03704088 A EP 03704088A EP 1474722 A2 EP1474722 A2 EP 1474722A2
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European Patent Office
Prior art keywords
crystal
magnetic field
pulse
light
state
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German (de)
French (fr)
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Yuri S. Didosyan
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/11—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
    • G02F1/092—Operation of the cell; Circuit arrangements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation

Definitions

  • the invention relates to a method for changing the polarization state of light with a magnetically uniaxial crystal which changes into a single-domain state under the action of an external magnetic field pulse, light passing through predetermined regions of the crystal, and to a device for carrying out such a method.
  • the subject of the invention is therefore methods and devices for changing the polarization of light beams and subsequently for changing the direction, the intensity and the like. More of these light beams, as are used in optical communication systems, information processing, displays etc.
  • MEMS microelectromechanical systems
  • acoustic-optical liquid crystalline
  • electronically switchable Bragg gmtings Bragg grids
  • bubblejets bubblejets
  • thermo-optical interferometric
  • thermo-capillary thermo-capillary
  • electro-holographic and magneto-optical systems Numerous types of optical switches have been developed, including microelectromechanical systems (MEMS), acoustic-optical, liquid crystalline, electronically switchable Bragg gmtings (Bragg grids), bubblejets (bubble systems), thermo-optical, interferometric, thermo-capillary, electro-holographic and magneto-optical systems.
  • MEMS microelectromechanical systems
  • acoustic-optical liquid crystalline
  • electronically switchable Bragg gmtings Bragg grids
  • bubblejets bubblejets
  • thermo-optical interferometric
  • thermo-capillary thermo-capillary
  • electro-holographic and magneto-optical systems thermo-opti
  • Electro-optical systems have comparatively much shorter switching times; for example, the switching time of the new electro-holographic switches is only approx. 10 ns. But these circuits need permanent energy supply, at least in one state. In addition, the insertion loss of electroholographic switches is quite high, namely around 4-5 dB.
  • Magneto-optical systems open up the possibility of combining short switching times and low insertion loss with the so-called “latching” mode of operation (see above).
  • a multistable polarization rotator is described. Stable states in this Rotators are predetermined by inhomogeneities on the surfaces of orthoferritic platelets that cover the domain walls (DWs) Hold layers, guaranteed. Transitions between these stable states result from the shifting of the domain walls between these positions and take place without the creation of new domains. The time required for these transitions is approximately 100 ns, which means that they are several thousand times faster than for other optical switches of the "latching" type. However, the aperture of the switch is considerably restricted. The amplitude of the driver magnetic field is fairly small, which is why DWs can only travel at comparatively small distances.
  • the object of the invention is to reduce the restrictions on the aperture of the switch.
  • this is achieved in that a magnetic field pulse with a magnetic field strength (H) is applied to the crystal, in which the crystal does not remain in the signal domain state after the end of the pulse, but in a defined, from the direction of the applied Magnetic field returns certain multi-domain state.
  • H magnetic field strength
  • This increases the aperture of the switch by using higher amplitude magnetic field pulses.
  • the aperture is defined by the zone in which magnetic pulses alternate. In the present invention, this zone represents the domain structure that occurs after the magnetic pulse is turned off. In orthoferrites, relatively large domains occur, which means that large switch apertures can also be reached.
  • Orthoferrites have a rectangular hysteresis function.
  • the coercive force of the Orthoferrite is quite high, it is a few kilo-oersted (kOe).
  • the force required to overcome the coercive force generation 'high magnetic fields requires large energy input (this factor is particularly important for construction of densely packed switch matrices of importance) and can also increase the inductance of the scheme lead to, which increases the switching times.
  • inhomogeneities on the crystal surface are used, which fix the domain walls in predetermined positions. If the distance between the inhomogeneities is small, or if thin orthoferrite flakes are used, the DW's move continuously from one dissimilarity to another.
  • the last refers to the thickness »100 ⁇ m, used for polarization rotation in the visible and near infrared spectrum range. It was found that with thicker patterns, namely at> 1.2 mm thick yttrium orthoferrite crystals, which are responsible for 45 ° polarization rotation on the wavelengths> 1.3 ⁇ m are used, other situation is.
  • the magnetization directions in certain crystal areas are changed to opposite:
  • the DWs are oriented perpendicular to the direction of the crystallographic ⁇ -axis, see Fig. 1.
  • the magnetizations are positive in the upper and lower domains and negative in the middle domains (Fig. La).
  • a magnetic field pulse of negative polarity now acts on the crystal. If the amplitude of the pulse is approximately H s , the crystal is magnetized to the single domain state, Fig. Ib. After the end of the pulse, the crystal is divided into the domains, Fig. Lc.
  • the polarization of the rays that pass through area 1 is “+” (that is, the direction of polarization has rotated clockwise) and the polarization of the rays that pass through area 2 is “-” "(the direction of polarization has rotated counterclockwise).
  • a magnetic field pulse of negative polarity is applied, the polarization of the two beams will be “minus” during the pulse.
  • the polarization of beams 1 and 2 will accordingly become “-” (for 1) and "+” (for 2
  • the application of a magnetic field pulse of positive polarity leads to the new distribution: "+” and “+” and after the termination of this pulse the state "+” and "-” is created again.
  • the polarity and the duration achieve a desired polarization distribution or combination at selected time intervals.
  • Patent No. 408,700 uses irregularities (such as scratches) on the crystal surface through which the light rays pass to fix the DWs. These inhomogeneities on the surface cause light scattering, which is particularly troublesome when such crystals are used in attenuators.
  • the inhomogeneities are applied to the side surface or the crystal.
  • Fig. 2 shows such inhomogeneities in the form of scratches or scratches on the side surface of a rotator. The direction of the scratches or scratches is perpendicular to the crystallographic ⁇ -axis and parallel to the planes of the DWs.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

A magnetic, single-axis crystal is used to modify the polarisation state of light, whereby light passes through predetermined areas of the crystal. To change the polarisation state of the light, a magnetic field pulse is applied to the crystal with a magnetic field amplitude, at which the crystal no longer remains in the single-domain state at the end of the pulse, but returns to a defined multi-domain state that is determined by the direction of the applied magnetic field, thus achieving large usable apertures of the switching element and extremely short change periods. According to the invention, energy is only required for the change operation and not for maintaining a specific state.

Description

Verfahren und Vorrichtung zur Änderung des Polarisationszustandes von Licht Method and device for changing the polarization state of light
Gegenstand der ErfindungSubject of the invention
Die Erfindung betrifft ein Nerfahren zur Änderung des Polarisationszustandes von Licht mit einem magnetisch einachsigen Kristall, der unter der Einwirkung eines äußeren Magnetfeldimpulses in einen Eindomänen-Zustand übergeht, wobei Licht durch vorgegebene Bereiche des Kristalls hindurchtritt, sowie eine Vorrichtung zur Durchführung eines derartigen Verfahrens. Gegenstände der Erfindung sind also Methoden und Vorrichtungen zur Änderung der Polarisation von Lichtstrahlen und in der Folge zur Änderung der Richtung, der Intensität u dgl. mehr dieser Lichtstrahlen, wie sie in optischen Kommunikationssystemen, Informationsverarbeitung, Displays etc. zur Anwendung kommen.The invention relates to a method for changing the polarization state of light with a magnetically uniaxial crystal which changes into a single-domain state under the action of an external magnetic field pulse, light passing through predetermined regions of the crystal, and to a device for carrying out such a method. The subject of the invention is therefore methods and devices for changing the polarization of light beams and subsequently for changing the direction, the intensity and the like. More of these light beams, as are used in optical communication systems, information processing, displays etc.
Kurze Beschreibung des Standes der TechnikBrief description of the state of the art
Zur Zeit wurden zahlreiche Arten von optischen Schalter entwickelt, inklusive mikroelektro- mechanische Systeme (MEMS), akustisch-optische, flüssige kristalline, elektronisch schaltbare Bragg gmtings (Bragg'sche Gitter) , bubblejets (Blasensysteme), thermo-optische, inter- ferometrische, thermo-kapillarische, elektro-holograpfische und magneto-optische Systeme. Zur Zeit sind MEMS am meisten in Verwendung. Wichtiger Vorteil von MEMS ist, dass diese zu den sogenannten „latching Systemen" gehören, das heisst, dass sie energielose stabile Schaltzustände haben und Energie nur zum Schalten benötigen.Numerous types of optical switches have been developed, including microelectromechanical systems (MEMS), acoustic-optical, liquid crystalline, electronically switchable Bragg gmtings (Bragg grids), bubblejets (bubble systems), thermo-optical, interferometric, thermo-capillary, electro-holographic and magneto-optical systems. MEMS are currently the most widely used. An important advantage of MEMS is that they belong to the so-called "latching systems", which means that they have de-energized, stable switching states and only require energy for switching.
Ihre Schaltzeiten sind jedoch ziemlich lang - ca. 1 ms. Elektro-optische Systeme haben vergleichsweise viel kürzere Schaltzeiten; zum Beispiel beträgt die Schaltzeit der neuen elektro- holographischen Schalter nur ca. 10 ns. Aber diese Schaltungen brauchen permanente Energieversorgung, zumindest in einem Zustand. Außerdem ist der „insertion loss" (Eingangsverlust) von elektroholographischen Schalter ziemlich hoch, nämlich etwa 4-5 dB.However, their switching times are quite long - approx. 1 ms. Electro-optical systems have comparatively much shorter switching times; for example, the switching time of the new electro-holographic switches is only approx. 10 ns. But these circuits need permanent energy supply, at least in one state. In addition, the insertion loss of electroholographic switches is quite high, namely around 4-5 dB.
Mit magneto-optischen Systemen eröffnet sich die Möglichkeit, kurze Schaltzeit und geringen insertion loss mit der sogenannten „latching" Funktionsweise (siehe oben) zu kombinieren. In der Erfindung gemäß Österr. Patent r. 408.700 wird ein multistabiler Polarisationsrotator beschrieben. Stabile Zustände bei diesem Rotator werden durch Inhomogenitäten auf den Oberflächen von orthoferritischen Plättchen, die die Domänenwände (DWs) in vorgegebenen Lagen halten, gewährleistet. Übergänge zwischen diesen stabilen Zuständen kommen durch Verschiebung der Domänenwände zwischen diesen Lagen zustande und finden ohne Erzeugung von neuen Domänen statt. Die für diese Übergänge benötigte Dauer beträgt ca. 100 ns, das heisst, dass sie um etliche 1000 Male schneller sind als für andere optischen Schalter der „latching" Art. Die Apertur des Schalters ist aber wesentlich eingeschränkt. Die Amplitude des Treiber-Magnetfeldes ist ziemlich gering, weswegen sich DWs nur auf vergleichbar kleinen Distanzen fortbewegen können.Magneto-optical systems open up the possibility of combining short switching times and low insertion loss with the so-called “latching” mode of operation (see above). In the invention according to Austrian patent r. 408.700, a multistable polarization rotator is described. Stable states in this Rotators are predetermined by inhomogeneities on the surfaces of orthoferritic platelets that cover the domain walls (DWs) Hold layers, guaranteed. Transitions between these stable states result from the shifting of the domain walls between these positions and take place without the creation of new domains. The time required for these transitions is approximately 100 ns, which means that they are several thousand times faster than for other optical switches of the "latching" type. However, the aperture of the switch is considerably restricted. The amplitude of the driver magnetic field is fairly small, which is why DWs can only travel at comparatively small distances.
Aufgabe der Erfindung ist es, die Beschränkungen der Apertur des Schalters zu reduzieren.The object of the invention is to reduce the restrictions on the aperture of the switch.
Gemäß der gegenständlichen Erfindung wird dies dadurch gelöst, daß an den Kristall ein Magnetfeldimpuls mit einer Magnetfeldstärke (H) angelegt wird, bei der der Kristall nach dem Ende des Impulses nicht im Signaldomänen-Zustand verbleibt, sondern in einen definierten, von der Richtung des angelegten Magnetfeldes bestimmten Multidomänen-Zustand zurückkehrt. Damit wird die Apertur des Schalters durch Anwendung von Magnetfeldimpulsen von höherer Amplitude vergrößert. Die Apertur ist dabei definiert durch die Zone, in der abwechselnd Magnetpulse einwirken. Bei der vorliegenden Erfindung repräsentiert diese Zone die Domänenstruktur, die nach dem Abschalten des Magnetimpulses auftritt. In Orthoferriten treten relativ große Domänen auf, womit entsprechend auch große Aperturen des Schalters erreichbar sind.According to the present invention, this is achieved in that a magnetic field pulse with a magnetic field strength (H) is applied to the crystal, in which the crystal does not remain in the signal domain state after the end of the pulse, but in a defined, from the direction of the applied Magnetic field returns certain multi-domain state. This increases the aperture of the switch by using higher amplitude magnetic field pulses. The aperture is defined by the zone in which magnetic pulses alternate. In the present invention, this zone represents the domain structure that occurs after the magnetic pulse is turned off. In orthoferrites, relatively large domains occur, which means that large switch apertures can also be reached.
Orthoferrite besitzen eine rechteckige Hysterese-Funktion. Die Koerzitivkraft der Orthoferrite ist ziemlich hoch, sie beträgt einige kilo-Oersted (kOe). Die zur Überwindung der Koerzitivkraft erforderliche Erzeugung' großer magnetischer Felder verlangt großen Energieinput (dieser Faktor ist besonders bei Konstruktion von dichtgepackten Schaltermatrizen von Bedeutung) und kann auch erhöhte Induktivität des Schemas nach sich ziehen, was die Schaltzeiten vergrößert. Um die erforderliche Intensität des Treiber-Feldes zu verringern, werden Inhomogenitäten auf der Kristalloberfläche verwendet, die die Domänenwände in vorgegebenen Positionen fixieren. Wenn die Entfernung zwischen den Inhomogenitäten gering ist, oder wenn man dünn Orthoferritplätchen verwendet, bewegen sich die DW's kontinuierlich von einer Ungleichartigkeit zu der anderen. Im Falle des Orthoferrite Kristalles bezieht sich das Letzte auf die Dicke » 100 μm, verwendet bei Polarisationsdrehung in sichtbaren und nahe infraroten Spektrumbereich. Es wurde gefunden, dass bei dickeren Muster und zwar bei > 1,2 mm dick Yttrium Orthoferrite Kristalle, die für 45° Polarisationsdrehung auf der Wellenlängen > 1,3 μm verwendet werden, andere Situation ist. Anwendung bei diesen Kristallen der Magnetfelder, die ziemlich stark sind, um die Magnetisierung der großen Bereichen zu ändern verursacht nun die Erzeugung neuer Domänen und deren Ausbreitung, Kollaps von Domänen mit ungünstigen Magnetisierungsrichtung und in der Folge eine Magnetisierung des Kristalls. Falls die Amplitude des Magnetfeldimpulses ziemlich hoch ist (einige kOe), bleibt nach dem Ende dieses Impulses der Kristall im monodomänen Zustand und Änderungen der Magnetisierungsrichtung verlangen wieder die Anwendung von Impulsen mit gleichen oder sogar höheren Amplituden.Orthoferrites have a rectangular hysteresis function. The coercive force of the Orthoferrite is quite high, it is a few kilo-oersted (kOe). The force required to overcome the coercive force generation 'high magnetic fields requires large energy input (this factor is particularly important for construction of densely packed switch matrices of importance) and can also increase the inductance of the scheme lead to, which increases the switching times. In order to reduce the required intensity of the driver field, inhomogeneities on the crystal surface are used, which fix the domain walls in predetermined positions. If the distance between the inhomogeneities is small, or if thin orthoferrite flakes are used, the DW's move continuously from one dissimilarity to another. In the case of the Orthoferrite crystal, the last refers to the thickness »100 μm, used for polarization rotation in the visible and near infrared spectrum range. It was found that with thicker patterns, namely at> 1.2 mm thick yttrium orthoferrite crystals, which are responsible for 45 ° polarization rotation on the wavelengths> 1.3 μm are used, other situation is. Application to these crystals of magnetic fields, which are quite strong to change the magnetization of the large areas, now causes the creation and propagation of new domains, collapse of domains with an unfavorable direction of magnetization and subsequently magnetization of the crystal. If the amplitude of the magnetic field pulse is quite high (a few kOe), after the end of this pulse the crystal remains in the monodomain state and changes in the direction of magnetization again require the use of pulses with the same or even higher amplitudes.
Wenn jedoch die Amplitude H der Impulse nicht sehr hoch ist und gerade dazu reicht, Sättigungsmagnetisierung des Kristalls (H=HS) zu erreichen, so kehrt nach der Beendung des Impulses der Kristall wieder in den multidomänen Zustand zurück ( Keime der entgegengesetzt magnetisierten Domänen werden nämlich nicht völlig unterdrückt, und nach Beendung des Impulses wachsen diese zu neuen Domänen).However, if the amplitude H of the pulses is not very high and is just sufficient to achieve saturation magnetization of the crystal (H = H S ), the crystal returns to the multidomain state after the pulse has ended (nuclei of the oppositely magnetized domains become namely not completely suppressed, and after the impulse ends, they grow into new domains).
Weitere Merkmale und Vorteile des erfindungsgemäßen Verfahrens sowie der entsprechenden Vorrichtung werden im folgenden anhand der Tabelle 1 sowie der Zeichnungen näher erläutert.Further features and advantages of the method according to the invention and the corresponding device are explained in more detail below with reference to Table 1 and the drawings.
In manchen Fällen werden nach der Anwendung der Impulse (H≤ Hs) die Magnetisierungsrichtungen in bestimmten Kristallenbereichen zu entgegengesetzten geändert: Betrachtet sei nun ein Orthoferrite-Kristall, der senkrecht zur optischen Achse geschnitten ist. In solchem Kristall sind die DWs senkrecht zur Richtung der kristallographischen α-Achse ausgerichtet, siehe Fig. 1. Die Magnetisierungen seien in der oberen und unteren Domäne positiv und in der mittleren Domänen negativ (Fig. la). Ein Magnetfeldimpuls von negativer Polarität wirke nun auf den Kristall. Wenn die Amplitude des Impulses ungefähr Hs beträgt, wird der Kristall bis in den Eindomänen-Zustand magnetisiert, Fig. Ib. Nach dem Ende des Impulses unterteilt sich der Kristall in die Domänen, Fig. lc. Im unteren und oberen Bereich des Kristalls sind die Kupplungskräfte ziemlich hoch und die Magnetisierungsrichtung bleibt genau so wie während des Impulses. Im mittleren Bereich, wo die Kupplungskräfte schwächer sind, wird die Magnetisierungsrichtung allerdings entgegengesetzt. Für die Stabilisierung der Domänen kann man wieder Inhomogenitäten (Nichtuniformitäten), wie sie in der Erfindung Nr. 408.700 beschrieben werden, verwenden. Werden nun Lichtstrahlen in verschiedene Kristallbereiche gelenkt, so werden sich die Polarisationen der verschiedenen Strahlen in Abhängigkeit vom magnetischen Treiberfeld und der Positionen der Strahlen verändern. Bei dem Bespiel in der Tabelle 1 ist die Polarisation der Strahlen, die durch Bereich 1 durchgehen, mit „+" (d. h. dass die Polarisationsrichtung hat sich im Uhrzeigersinn gedreht ), und die Polarisation der Strahlen, die durch Bereich 2 durchgehen, mit „-" (die Polarisationsrichtung hat sich gegen den Uhrzeigersinn gedreht) charakterisiert. Wird ein Magnetfeldimpuls negativer Polarität appliziert, so wird während des Impulses die Polarisation der beiden Strahlen „minus" betragen. Nach der Beendung des Impulses wird die Polarisation der Strahlen 1 und 2 dementsprechend "-" (für 1) und "+" (für 2) betragen. Die Applikation eines Magnetfeldimpulses positiver Polarität führt zur neuen Verteilung: „+" und „+" und nach der Beendung dieses Impulses entsteht wieder der Zustand "+" und "-". Somit kann man durch die Wahl der Polarität und die Dauer der Impulse in ausgewählten Zeitabständen eine erwünschte Polarisationsverteilung bzw. -kombination erreichen.In some cases, after applying the pulses (H≤ H s ), the magnetization directions in certain crystal areas are changed to opposite: Now consider an orthoferrite crystal that is cut perpendicular to the optical axis. In such a crystal the DWs are oriented perpendicular to the direction of the crystallographic α-axis, see Fig. 1. The magnetizations are positive in the upper and lower domains and negative in the middle domains (Fig. La). A magnetic field pulse of negative polarity now acts on the crystal. If the amplitude of the pulse is approximately H s , the crystal is magnetized to the single domain state, Fig. Ib. After the end of the pulse, the crystal is divided into the domains, Fig. Lc. In the lower and upper area of the crystal, the coupling forces are quite high and the direction of magnetization remains the same as during the pulse. In the middle area, where the coupling forces are weaker, the magnetization direction is reversed. Inhomogeneities (non-uniformities), as described in the invention No. 408.700, can again be used for the stabilization of the domains. If light beams are now directed into different crystal areas, the polarizations of the different beams will change depending on the magnetic driver field and the positions of the beams. In the example in Table 1, the polarization of the rays that pass through area 1 is “+” (that is, the direction of polarization has rotated clockwise) and the polarization of the rays that pass through area 2 is “-” "(the direction of polarization has rotated counterclockwise). If a magnetic field pulse of negative polarity is applied, the polarization of the two beams will be "minus" during the pulse. After the pulse has ended, the polarization of beams 1 and 2 will accordingly become "-" (for 1) and "+" (for 2 The application of a magnetic field pulse of positive polarity leads to the new distribution: "+" and "+" and after the termination of this pulse the state "+" and "-" is created again. Thus, by choosing the polarity and the duration the pulses achieve a desired polarization distribution or combination at selected time intervals.
In der Erfindung gemäß Österr. Patent Nr. 408.700 werden Ungleichmäßigkeiten (wie z.B. Ritzen bzw. Kratzer), auf der Kristalloberfläche, durch die die Lichtstrahlen durchgehen, zur Fixierung der DWs verwendet. Diese Inhomogenitäten auf der Oberfläche verursachen Lichtstreuung, was besonders beim Einsatz solcher Kristalle in Attenuatoren störend ist.In the invention according to Austria. Patent No. 408,700 uses irregularities (such as scratches) on the crystal surface through which the light rays pass to fix the DWs. These inhomogeneities on the surface cause light scattering, which is particularly troublesome when such crystals are used in attenuators.
Abweichend von den Anordnungen gemäß Österr. Patent Nr. 408.700 werden bei der gegenständlichen Erfindung die Inhomogenitäten (wie Ritzen) auf der bzw. den Seitenflächen des Kristalls angebracht.. Fig. 2 zeigt solche Inhomogenitäten in Form von Ritzen bzw. Kratzern auf der Seitenfläche eines Rotators. Die Richtung der Ritzen bzw. Kratzer ist senkrecht zur kristallographischen α-Achse und parallel zu den Ebenen der DWs.Deviating from the arrangements according to Österr. Patent No. 408,700 in the subject invention, the inhomogeneities (such as scratches) are applied to the side surface or the crystal. Fig. 2 shows such inhomogeneities in the form of scratches or scratches on the side surface of a rotator. The direction of the scratches or scratches is perpendicular to the crystallographic α-axis and parallel to the planes of the DWs.
Um eine kontinuierliche Bewegung der DWs über große Distanzen zu gewährleisten, sollen relativ dünne Plättchen verwendet werden (im Falle der Orthoferite gelten „als relativ dünn" einige hundert Micrometer dicke Plättchen). In einem sehr breiten Bereich der Magnetfeldstärke besteht die Wirkung des Magnetfeldes auf diese Plättchen in der Verbreiterung der existierenden Domänen mit passender Polarität und nicht in der Erzeugung neuer Domänen. Die Inhomogenitäten halten die DWs in gewünschten Positionen, wodurch ein multistabiler Betrieb des Rotators ermöglicht wird. Stapel von einigen solchen Plättchen können zur Konstruktion eines Rotators mit erwünschter Dicke verwendet werden. Man kann weiters die Inhomogenitäten, die die DWs fixieren, mit den Quellen permanenter Magnetfelder kombinieren. In der Erfindung gemäß Österr. Patent Nr. 408.700 wird vorgeschlagen, das inhomogene Magnetfeld eines Paares von Magneten zu verwenden. Jedoch erhöht die Verwendung von zwei Magneten die Dimensionen der Elemente bzw. Systeme.In order to ensure continuous movement of the DWs over large distances, relatively thin platelets should be used (in the case of orthoferite, "platelets are considered to be relatively thin", a few hundred micrometer thick platelets). The effect of the magnetic field on these is in a very wide range of the magnetic field strength Platelets in the widening of existing domains with appropriate polarity and not in the creation of new domains. The inhomogeneities hold the DWs in desired positions, which enables multistable operation of the rotator. Stacks of some such platelets can be used to construct a rotator of a desired thickness become. You can also combine the inhomogeneities that fix the DWs with the sources of permanent magnetic fields. In the invention according to Austria. Patent No. 408,700 proposes to use the inhomogeneous magnetic field of a pair of magnets. However, the use of two magnets increases the dimensions of the elements or systems.
Erfindungsgemäß wird nun lediglich ein Permanentmagnet verwendet. Dieser hält die Magnetisierung des angrenzenden Teils des Rotators aufrecht; die Lage der Grenze dieser Domäne (seine DW) ändert sich unter der Einwirkung des Magnetfeldimpulses und kann durch Inhomogenitäten, wie sie oben erwähnt wurden, fixiert werden. According to the invention, only a permanent magnet is now used. This maintains the magnetization of the adjacent part of the rotator; the position of the boundary of this domain (its DW) changes under the influence of the magnetic field pulse and can be fixed by inhomogeneities as mentioned above.

Claims

Patentansprüche: claims:
1. Verfahren zur Änderung des Polarisationszustandes von Licht mit einem magnetisch einachsigen Kristall, der unter der Einwirkung eines äußeren Magnetfeldes in einen Eindomänen-Zustand übergeht, wobei Licht durch vorgegebene Bereiche des Kristalls hindurchtritt, d a d u r c h g e k e n n z e i c h n e t, dass an den Kristall ein Magnetfeldimpuls mit einer Magnetfeldstärke (H) angelegt wird, bei der der Kristall nach dem Ende des Impulses nicht im Singledomänen-Zustand verbleibt, sondern in einen definierten, von der Richtung des angelegten Magnetfeldes bestimmten Multidomä- nen-Zustand zurückkehrt.1.Method for changing the polarization state of light with a magnetically uniaxial crystal, which changes into a single-domain state under the action of an external magnetic field, light passing through predetermined regions of the crystal, characterized in that a magnetic field pulse with a magnetic field strength ( H) is applied, in which the crystal does not remain in the single-domain state after the end of the pulse, but rather returns to a defined multidomain state which is determined by the direction of the applied magnetic field.
2. Verfaliren nach Anspruch 1, dadurch gekennzeichnet, dass die Domänenwände durch Inhomogenitäten, die im Kristall erzeugt werden, in vorgegebenen Positionen gehalten werden.2. Verfaliren according to claim 1, characterized in that the domain walls are held in predetermined positions by inhomogeneities that are generated in the crystal.
3. Verfaliren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Lichtstrahlen durch solche Bereiche des Kristalls geleitet werden, die nach Abschalten des äußeren Magnetfeldimpulses mit dem selben Vorzeichen wie der äußere Magnetfeldimpuls magnetisiert bleiben.3. Verfaliren according to claim 1 or 2, characterized in that the light rays are guided through those areas of the crystal that remain magnetized after switching off the external magnetic field pulse with the same sign as the external magnetic field pulse.
4. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Lichtstrahlen durch solche Bereiche des Kristalls geleitet werden, die nach Abschalten des äußeren Magnetfeldimpulses mit entgegengesetztem Vorzeichen wie der äußere Magnetfeldimpuls magnetisiert bleiben.4. The method according to claim 1 or 2, characterized in that the light rays are guided through those areas of the crystal that remain magnetized after switching off the outer magnetic field pulse with opposite sign as the outer magnetic field pulse.
5. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Lichtstrahlen durch solche Bereiche des Kristalls geleitet werden, die während der Einwirkung des äußeren Magnetfeldimpulses mit gleichem Vorzeichen magnetisiert sind und nach dem Abschalten des äußeren Magnetfeldimpulses mit entgegengesetztem Vorzeichen magnetisiert werden.5. The method according to claim 1 or 2, characterized in that the light beams are guided through those regions of the crystal which are magnetized with the same sign during the action of the external magnetic field pulse and are magnetized with the opposite sign after the external magnetic field pulse has been switched off.
6. Vorrichtung zur Veränderung des Polarisationszustandes von Lichtstrahlen nach dem Verfahren gemäß einem der Ansprüche 1 bis 5, mit einem magneto-optischen Rotator gebildet aus einem magnetisch einachsigen Kristall, der Inhomogenitäten aufweist, welche die Domänen in vorgegebenen Positionen fixieren, dadurch gekennzeichnet, dass diese Inhomogenitäten sich auf den Seitenflächen des Kristalls befinden. 6. Device for changing the polarization state of light beams by the method according to one of claims 1 to 5, with a magneto-optical rotator formed from a magnetically uniaxial crystal which has inhomogeneities which fix the domains in predetermined positions, characterized in that these Inhomogeneities are on the side faces of the crystal.
EP03704088A 2002-02-12 2003-02-12 Method and device for modifying the polarisation state of light Withdrawn EP1474722A2 (en)

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AT411852B (en) 2004-06-25
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