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EP0452438A1 - Light control devices with liquid crystals - Google Patents

Light control devices with liquid crystals

Info

Publication number
EP0452438A1
EP0452438A1 EP90915402A EP90915402A EP0452438A1 EP 0452438 A1 EP0452438 A1 EP 0452438A1 EP 90915402 A EP90915402 A EP 90915402A EP 90915402 A EP90915402 A EP 90915402A EP 0452438 A1 EP0452438 A1 EP 0452438A1
Authority
EP
European Patent Office
Prior art keywords
liquid crystal
light control
control device
cell
light
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.)
Ceased
Application number
EP90915402A
Other languages
German (de)
French (fr)
Inventor
Jürg FÜNFSCHILLING
Martin Schadt
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.)
Rolic Technologies Ltd
Original Assignee
F Hoffmann La Roche AG
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
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Application filed by F Hoffmann La Roche AG filed Critical F Hoffmann La Roche AG
Publication of EP0452438A1 publication Critical patent/EP0452438A1/en
Ceased legal-status Critical Current

Links

Classifications

    • 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 
    • G02F1/13—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 liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/133382—Heating or cooling of liquid crystal cells other than for activation, e.g. circuits or arrangements for temperature control, stabilisation or uniform distribution over the cell
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/52—Liquid crystal materials characterised by components which are not liquid crystals, e.g. additives with special physical aspect: solvents, solid particles
    • C09K19/58—Dopants or charge transfer agents
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/02—Liquid crystal materials characterised by optical, electrical or physical properties of the components, in general
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3016—Polarising elements involving passive liquid crystal elements
    • 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
    • G02F1/0009—Materials therefor
    • G02F1/0063—Optical properties, e.g. absorption, reflection or birefringence
    • 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 
    • G02F1/13—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 liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—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 liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/139—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 liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
    • G02F1/1396—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 liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
    • H04N9/3141—Constructional details thereof
    • H04N9/315—Modulator illumination systems
    • H04N9/3167—Modulator illumination systems for polarizing the light beam
    • 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 
    • G02F1/13—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 liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133528—Polarisers
    • G02F1/133536—Reflective polarizers
    • 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 
    • G02F1/13—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 liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133528—Polarisers
    • G02F1/133543—Cholesteric polarisers

Definitions

  • the invention relates to light control devices which consist of a combination of liquid crystal cells and polarizers.
  • FIG. 4 shows an arrangement with a parallel-oriented cell in reflection mode with circularly polarized light.
  • Fig. 5 shows an arrangement with a vertically oriented so-called DAP cell in operation with circularly polarized light
  • a linear polarizer with a low degree of polarization can be inserted between the ⁇ / 4 plate and TN cell, which improves the linear polarization without reducing the brightness of the Systems deteriorate significantly.
  • circular polarizers can be used as the circular polarizer 8, e.g. B. also wavelength-selective reflecting cholesteric layers with a small pitch.
  • the light reflected by them is known to be circularly polarized. In color projection systems, this light is controlled by downstream liquid crystal cells. It is advantageous if a previous conversion into linearly polarized light can be dispensed with.
  • FIGS. 1 and 2 provide a positive contrast if display cells are constructed according to this principle. Negative contrast is easily possible in each case, namely in FIG. 1 in a known manner by rotating the linear polarizers on the output side by 90 °. In Fig. 2, this is done by using a right-handed circular polarizer instead of a left-handed one.
  • FIG. 3 The arrangement shown in FIG. 3 is also based on the fact that, as in FIG. 2, circularly polarized light is fed directly to a TN cell 9.
  • the right circularly polarized input light passes through the TN cell.
  • the reflector 10 can also be integrated directly on the inside of the rear substrate of the TN cell.
  • any other liquid crystal cell can be used for this arrangement, which allows the desired optical path difference between the switched-off and switched-on state to be achieved.
  • Other liquid crystal cells with a helical molecular arrangement ie for example the highly twisted so-called supertwist, SBE and STN cells, are particularly suitable. Liquid crystal cells with a non-twisted structure can also be used in this new mode of operation.
  • the reflector 10 can be arranged directly on the substrate or the rear wall of the liquid crystal cell, so that light-absorbing structures, such as e.g. Thin film transistors etc., are located behind the reflector and thus do not reduce the aperture or the brightness of the active area of the picture element.
  • Another significant advantage is that the path of the light behind the liquid crystal to the reflector and back is shorter due to the lack of an intermediate glass substrate, so that when the light is at an angle, i.e. large viewing angle, the parallax error is smaller than in conventional arrangements.

Landscapes

  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Nonlinear Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Mathematical Physics (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Liquid Crystal (AREA)
  • Liquid Crystal Substances (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)

Abstract

Il est proposé un nouveau mode d'exploitation pour des dispositifs de commande d'éclairage comprenant une combinaison de cellules à cristaux liquides et de polariseurs. L'exploitation directe de cellules à cristaux liquides (7) à lumière polarisée circulaire est avantageuse à bien des égards. La lumière polarisée circulaire est produite au moyen, soit de polariseurs circulaires traditionnels (3), soit de cristaux liquides cholestériques monomères ou polymères. Le nouveau mode d'exploitation est rendu possible, dans des conditions déterminées, pour toutes les cellules à cristaux liquides qui devaient être actionnées, jusqu'à présent, par une lumière polarisée linéaire.A new operating mode is proposed for lighting control devices comprising a combination of liquid crystal cells and polarizers. Direct operation of liquid crystal cells (7) with circular polarized light is advantageous in many respects. Circular polarized light is produced using either traditional circular polarizers (3) or monomeric or polymeric cholesteric liquid crystals. The new operating mode is made possible, under determined conditions, for all the liquid crystal cells which have hitherto had to be actuated by linear polarized light.

Description

Lichtsteuereinrichtungen mit Flüssigkristallen Light control devices with liquid crystals

Die Erfindung betrifft Lichtsteuereinrichtungen die aus einer Kombina¬ tion aus Flüssigkristallzellen und Polarisatoren bestehen.The invention relates to light control devices which consist of a combination of liquid crystal cells and polarizers.

In den herkömmlichen Anordnungen mit Flüssigkristallzellen werden diese in der Regel mit einem oder mehreren Linearpolarisator(en) betrieben. Wenn zirkulär polarisiertes Licht zur Verfügimg stand und gesteuert werden musste, wurde es z.B. mit einer λ/4-Platte in linear polarisiertes Licht umge¬ wandelt und ggf. hinter der Flüssigkristallzelle wiederum mit einer λ/4-Platte in zirkulär polarisiertes Licht zurückgewandelt. Vor allem die sog. Drehzelle oder TN (=Twisted Nematic)-Zelle benötigt für ihre Betriebsweise, bei der im ausgeschalteten Zustand die Polarisationsrichtung des einfallenden Lichts mit der Helixstruktur gedreht wird (Wave-Guiding Mode), linear polarisiertes Licht.In the conventional arrangements with liquid crystal cells, these are usually operated with one or more linear polarizers. If circularly polarized light was available and needed to be controlled, e.g. converted into linearly polarized light with a λ / 4 plate and, if necessary, converted back into circularly polarized light with a λ / 4 plate behind the liquid crystal cell. Above all, the so-called rotary cell or TN (= Twisted Nematic) cell requires linearly polarized light for its mode of operation, in which, when switched off, the direction of polarization of the incident light is rotated with the helix structure (wave guiding mode).

Es wurde nun gefunden, dass eine Betriebsart möglich und in mancher Hinsicht vorteilhaft ist, nämlich der direkte Betrieb von Flüssigkristallzellen mit zirkular polarisiertem Licht, wobei das zirkulär polarisierte Licht entweder mit herkömmlichen Zirkularpolarisatoren oder mit monomeren oder poly¬ meren cholesterischen Flüssigkristallen erzeugt wird.It has now been found that an operating mode is possible and advantageous in some respects, namely the direct operation of liquid crystal cells with circularly polarized light, the circularly polarized light being generated either with conventional circular polarizers or with monomeric or polymeric cholesteric liquid crystals.

Die Erfindung zeichnet sich demnach dadurch aus, dass Lichtsteuerein¬ richtungen der eingangs erwähnten Art mit Mitteln zur Zuführung von zir¬ kulär polarisiertem Licht zu Flüssigkristallzellen versehen sind.The invention is therefore characterized in that light control devices of the type mentioned at the outset are provided with means for supplying circularly polarized light to liquid crystal cells.

Im folgenden wird die Erfindimg anhand der in den Zeichnungen darge¬ stellten Ausführungsbeispiele erläutert. Es zeigen:The invention is explained below on the basis of the exemplary embodiments illustrated in the drawings. Show it:

Fig. 1 eine Anordnung mit einer TN-Zelle in herkömmlicher Betriebs¬ weise Fig. 2 eine Anordnung mit einer TN-Zelle im Betrieb mit zirkulär polari¬ siertem Licht in Transmission1 shows an arrangement with a TN cell in a conventional operating manner 2 shows an arrangement with a TN cell in operation with circularly polarized light in transmission

Fig. 3 eine Anordnung ähnlich wie in Fig. 2 aber in ReflexionFig. 3 shows an arrangement similar to that in Fig. 2 but in reflection

Fig. 4 eine Anordnung mit einer parallel orientierten Zelle im Reflexi¬ onsbetrieb mit zirkulär polarisiertem Licht.4 shows an arrangement with a parallel-oriented cell in reflection mode with circularly polarized light.

Fig. 5 eine Anordnimg mit einer senkrecht orientierten sog. DAP-Zelle im Betrieb mit zirkulär polarisiertem LichtFig. 5 shows an arrangement with a vertically oriented so-called DAP cell in operation with circularly polarized light

Die in Fig. 1 gezeigte Anordnung enthält eine Lichtquelle 1, deren Licht in einem Zirkularpolarisator 3 in rechtsdrehend zirkuläres Licht umgewandelt wird. Hinter dem Zirkularpolarisator 3 ist eine λ/4-Platte 4 angeordnet, die das zirkulär polarisierte Licht in linear polarisiertes umwandelt. Die Polarisations¬ richtung ist durch einen Doppelpfeil angezeigt. Hinter der λ/4-Platte 4 ist eine TN-Zelle 5 angeordnet, welche im ausgeschalteten Zustand die Polarisations¬ richtung des Lichtes in bekannter Weise um 90° dreht. Dieses gedrehte Licht kann einen hinter der TN-Zelle 5 im Winkel von 90° gegenüber der Polarisa¬ tionsrichtung vor der Zelle verdrehten Linearpolarisator 6 ungeschwächt pas¬ sieren. Wenn Spannung an der Zelle 5 anliegt, wird die Drehwirkung aufge¬ hoben und das nicht mehr gedrehte Licht kann den Polarisator 6 nicht passie¬ ren. Die TN-Zelle 5 arbeitet also in der herkömmlichen Betriebsart, in der die Polarisationsrichtung des einfallenden Lichts im ausgeschalteten Zustand ge¬ dreht wird (Wave-Guiding Mode).The arrangement shown in FIG. 1 contains a light source 1, the light of which is converted in a circular polarizer 3 into clockwise circular light. A λ / 4 plate 4 is arranged behind the circular polarizer 3 and converts the circularly polarized light into linearly polarized. The direction of polarization is indicated by a double arrow. A TN cell 5 is arranged behind the λ / 4 plate 4 and, in the switched-off state, rotates the direction of polarization of the light by 90 ° in a known manner. This rotated light can pass a linear polarizer 6 rotated behind the TN cell 5 at an angle of 90 ° with respect to the direction of polarization in front of the cell without weakening. If voltage is applied to the cell 5, the rotational effect is canceled and the light which is no longer rotated cannot pass through the polarizer 6. The TN cell 5 thus operates in the conventional operating mode, in which the direction of polarization of the incident light when switched off State is turned (wave guiding mode).

Um die Polarisationsqualität nach der λ/4-Platte in dieser Anordnung noch zu erhöhen, kann zwischen λ/4-Platte und TN-Zelle ein Linearpolarisa¬ tor mit geringem Polarisationsgrad eingefügt werden, der die linear Polarisa¬ tion verbessert, ohne die Helligkeit des Systems wesentlich zu verschlechtern.In order to increase the polarization quality after the λ / 4 plate in this arrangement, a linear polarizer with a low degree of polarization can be inserted between the λ / 4 plate and TN cell, which improves the linear polarization without reducing the brightness of the Systems deteriorate significantly.

Eine andere Betriebsart ist in Fig. 2 dargestellt. Das wie vorhin beschrie¬ ben erzeugte, rechtsdrehend zirkulär polarisierte Licht wird direkt einer TN- Zelle 7 zugeführt. Für diese Betriebsart muss die Zelle einen minimalen opti¬ schen Gangunterschied von δ = Δn.d = λ/2 zwischen ausgeschaltetem und ein¬ geschaltetem Zustand aufweisen. Wenn diese Bedingung erfüllt ist, ändert sich beim Durchgang des zirkulär polarisierten Lichts dessen Drehrichtung, d.h. im vorliegenden Fall von rechtssinnig (+) auf linkssinnig (-). Hinter der TN-Zelle 7 befindet sich ein weiterer Zirkularpolarisator 8, der diesmal für den ersten Zirkularpolarisator 3 entgegengesetzten Drehsinn, d.h. also linksdre¬ hend, durchlässig ist. Wenn die TN-Zelle 7 eingeschaltet und somit optisch uniaxial wird, beeinflusst sie den Polarisationszustand des Lichts nicht, so dass es durch den Zirkularpolarisator 8 blockiert wird.Another operating mode is shown in FIG. 2. The right-handed circularly polarized light generated as described above is fed directly to a TN cell 7. For this operating mode, the cell must have a minimal optical path difference of δ = Δn.d = λ / 2 between the switched-off and switched-on state. If this condition is met, the direction of rotation of the circularly polarized light changes, ie in the present case from right-hand (+) to left-hand (-). Behind the TN cell 7 there is a further circular polarizer 8, which this time is permeable to the first circular polarizer 3 in the opposite direction of rotation, that is to say left-turning. When the TN cell 7 is switched on and thus optically becomes uniaxial, it does not influence the polarization state of the light, so that it is blocked by the circular polarizer 8.

Als Zirkularpolarisator 8 kommt jede bekannte Form von Zirkularpola¬ risatoren in Frage, z. B. auch wellenlängen-selektiv reflektierende cholesteri- sche Schichten mit kleiner Ganghöhe. Das von ihnen reflektierte Licht ist be¬ kanntlich zirkular polarisiert. In Farbprojektionssystemen wird dieses Licht durch nachgeschaltete Flüssigkristallzellen gesteuert Dabei ist es vorteilhaft, wenn auf eine vorgängige Umwandlung in linear polarisiertes Licht verzich¬ tet werden kann.Any known form of circular polarizers can be used as the circular polarizer 8, e.g. B. also wavelength-selective reflecting cholesteric layers with a small pitch. The light reflected by them is known to be circularly polarized. In color projection systems, this light is controlled by downstream liquid crystal cells. It is advantageous if a previous conversion into linearly polarized light can be dispensed with.

Durch den Betrieb von TN-Zellen mit zirkular polarisiertem Licht ergibt sich, wie erwähnt, eine deutliche Verschiebung der erforderlichen Steuer¬ spannungen zu niedrigeren Werten. Ferner können steilere Spannungs- Transmissions-Kennlinien, wie sie z.B. für den Multiplexbetrieb erforderlich sind, erzeugt werden.As mentioned, the operation of TN cells with circularly polarized light results in a significant shift in the required control voltages to lower values. Furthermore, steeper voltage transmission characteristic curves, such as e.g. are required for the multiplex operation.

Die Anordnungen gemäss Fig. 1 und 2 liefern einen positiven Kontrast, wenn nach diesem Prinzip Anzeigezellen aufgebaut werden. Negativer Kon¬ trast ist jeweils ohne weiteres möglich und zwar in Fig. 1 in bekannter Weise durch Drehen der Linearpolarisatoren an der Ausgangsseite um 90°. In Fig. 2 erfolgt dies durch Verwendung eines rechtsdrehenden Zirkularpolarisators statt eines linksdrehenden.The arrangements according to FIGS. 1 and 2 provide a positive contrast if display cells are constructed according to this principle. Negative contrast is easily possible in each case, namely in FIG. 1 in a known manner by rotating the linear polarizers on the output side by 90 °. In Fig. 2, this is done by using a right-handed circular polarizer instead of a left-handed one.

Die in Fig. 3 gezeigte Anordnung beruht ebenfalls darauf, dass wie in Fig. 2 zirkular polarisiertes Licht direkt einer TN-Zelle 9 zugeführt wird. Die TN- Zelle 9 weist im Unterschied zu der TN-Zelle 7 gemäss Fig. 2 jedoch einen mi¬ nimalen optischen Gangunterschied zwischen aus- und eingeschaltetem Zu¬ stand von δ = λ/4 auf. Sie wirkt im ausgeschalteten Zustand somit als λ/4- Platte, die zirkular polarisiertes Licht in linear polarisiertes umwandelt Hinter der Zelle 9 ist ein Reflektor 10 angeordnet, der das linear polarisierte Licht zur Zelle 9 zurück reflektiert. Diese wandelt - aus Symmetriegründen - das linear polarisierte Licht in zirkular polarisiertes zurück, das den Zirkularpolarisator 3 passieren kann. Im eingeschalteten Zustand passiert das rechts zirkular polari¬ sierte Eingangslicht die TN-Zelle. Dieses ändert bei der Reflexion am Spiegel 10 den Drehsinn, so dass der nun links zirkular polarisierte, reflektierte Strahl den Zirkularpolarisator 3 nicht mehr passieren kann. Der Reflektor 10 kann auch direkt auf der Innenseite des rückwärtigen Substrats der TN-Zelle inte¬ griert werden. Anstelle einer TN-Zelle kann für diese Anordnung auch jede andere Flüssigkristallzelle verwendet werden, die es erlaubt, den gewünschten opti¬ schen Gangunterschied zwischen aus- und eingeschaltetem Zustand zu erzie¬ len. Speziell kommen andere Flüssigkristallzellen mit helixförmiger Mole¬ külanordnung, d.h. beispielsweise die hochverdrillten sog. Supertwist-, SBE- und STN-Zellen in Frage. Auch Flüssigkristallzellen mit nicht verdrillter Struktur können in dieser neuern Betriebsweise eingesetzt werden.The arrangement shown in FIG. 3 is also based on the fact that, as in FIG. 2, circularly polarized light is fed directly to a TN cell 9. In contrast to the TN cell 7 according to FIG. 2, however, the TN cell 9 has a minimal optical path difference between the off and on state of δ = λ / 4. In the switched-off state, it thus acts as a λ / 4 plate which converts circularly polarized light into linearly polarized. Behind the cell 9 there is a reflector 10 which reflects the linearly polarized light back to the cell 9. For symmetry reasons, this converts the linearly polarized light back into circularly polarized light, which can pass through the circular polarizer 3. In the switched-on state, the right circularly polarized input light passes through the TN cell. This changes the direction of rotation when the mirror 10 is reflected, so that the reflected beam, which is now circularly polarized on the left, can no longer pass the circular polarizer 3. The reflector 10 can also be integrated directly on the inside of the rear substrate of the TN cell. Instead of a TN cell, any other liquid crystal cell can be used for this arrangement, which allows the desired optical path difference between the switched-off and switched-on state to be achieved. Other liquid crystal cells with a helical molecular arrangement, ie for example the highly twisted so-called supertwist, SBE and STN cells, are particularly suitable. Liquid crystal cells with a non-twisted structure can also be used in this new mode of operation.

So zeigt Fig. 4 eine in Reflexion arbeitende Anordnung mit einer planar ' orientierten nematischen Zelle 11 mit positiver dielektrischer Anisotropie des Flüssigkristalls, d.h. Δε>0. Diese Anordnung entspricht der vorstehend be¬ schriebenen Alternative mit einer TN-Zelle, deren optischer Gangunterschied zwischen ausgeschaltetem und eingeschaltetem Zustand δ = λ/4 beträgt. Im ausgeschalteten Zustand wirkt die Zelle also wie eine λ/4-Platte, d.h. das zirku¬ lär polarisierte Licht wird in linear polarisiertes umgewandelt. Nach Reflexion an einem Spiegel 10 läuft der umgekehrte Vorgang ab, d.h. das linear polari¬ sierte Licht wird in der λ/4-Zelle wieder in zirkular polarisiertes umgewandelt, passiert den Zirkularpolarisator 3 ungehindert und ist mit voller Intensität am Ausgang verfügbar. Wenn Spannung an der Zelle 11 anliegt und diese somit optisch uniaxial wird, beeinflusst sie den Polarisationszustand des Lichts nicht. Hinter der Zelle gelangt also rechtszirkular polarisiertes Licht zum Reflektor 12, das wie schon erwähnt bei der Reflexion seinen Drehsinn ändert. Dieses nach Reflexion linkszirkulare Licht gelangt, durch die planare Zelle 11 unbe- einflusst zum Zirkularpolarisator 3 und wird von diesem blockiert.Thus, Fig. 4 shows an operating in reflection arrangement with a planar 'oriented nematic cell 11 having positive dielectric anisotropy of the liquid crystal, that is, Δε> 0,. This arrangement corresponds to the alternative described above with a TN cell whose optical path difference between the switched-off and switched-on state is δ = λ / 4. In the switched-off state, the cell thus acts like a λ / 4 plate, ie the circularly polarized light is converted into linearly polarized. After reflection from a mirror 10, the reverse process takes place, ie the linearly polarized light is converted back to circularly polarized in the λ / 4 cell, passes through the circular polarizer 3 unhindered and is available at the output with full intensity. If voltage is present at the cell 11 and it thus becomes optically uniaxial, it does not affect the polarization state of the light. Behind the cell, right-hand circularly polarized light reaches reflector 12, which, as already mentioned, changes its direction of rotation during reflection. This left circular light after reflection reaches the circular polarizer 3 unaffected by the planar cell 11 and is blocked by it.

Ein Vorteil auch bei dieser reflektiven Konfiguration besteht darin, dass der Reflektor 10 direkt auf dem Substrat bzw. der Rückwand der Flüssigkri¬ stallzelle angeordnet sein kann, so dass lichtabsorbierende Strukturen, wie z.B. Dünnfilmtransistoren etc., hinter dem Reflektor liegen und damit die Apertur bzw. die Helligkeit der aktiven Fläche des Bildelements nicht verringern. Ein weiterer wesentlicher Vorteil besteht darin, dass der Weg des Lichtes hinter dem Flüssigkristall zum Reflektor und zurück infolge des Fehlens eines da¬ zwischenliegenden Glassubstrates kürzer ist, so dass bei schrägem Lichteinfall, d.h. grossem Blickwinkel der Parallaxenfehler kleiner ist als bei herkömmli¬ chen Anordnungen.An advantage with this reflective configuration is that the reflector 10 can be arranged directly on the substrate or the rear wall of the liquid crystal cell, so that light-absorbing structures, such as e.g. Thin film transistors etc., are located behind the reflector and thus do not reduce the aperture or the brightness of the active area of the picture element. Another significant advantage is that the path of the light behind the liquid crystal to the reflector and back is shorter due to the lack of an intermediate glass substrate, so that when the light is at an angle, i.e. large viewing angle, the parallax error is smaller than in conventional arrangements.

In der in Fig. 5 gezeigten Anordnung gelangt das zirkular polarisierte Licht auf eine DAP-Zelle 13, die sich dadurch auszeichnet, dass sie im ausgeschalteten Zustand uniaxial is*t und somit also das Licht unbeeinflusst durchlässt Die Po¬ larisation ist also vor und hinter der Zelle gleich. Hinter der Zelle 13 ist ein zweiter Zirkularpolarisator 14 angeordnet, der je nach seinem Drehsinn das transmittierte Licht durchlässt oder blockiert. Im eingeschalteten Zustand ver¬ ändert die Zelle 13 den Polarisationszustand des Lichts so, dass der Zirkularpo¬ larisator 14 nun das vorher durchgelassene Licht sperrt bzw. das vorher ge¬ sperrte Licht durchlässt. In the arrangement shown in Fig. 5, the circularly polarized light reaches a DAP-cell 13, which is characterized in that it uniaxially t in the off state is * and thus so the light unaffected by leaves larisa tion The polyvinyl is therefore front of and behind equal to the cell. Behind the cell 13, a second circular polarizer 14 is arranged, which depending on its direction of rotation transmitted light transmits or blocks. In the switched-on state, the cell 13 changes the polarization state of the light such that the circular polarizer 14 now blocks the previously transmitted light or transmits the previously blocked light.

Claims

Patentansprüche Claims 1. Lichtsteuereinrichtung aus einer Kombination aus Flüssigkristallzelle und Polarisator, gekennzeichnet durch Mittel (3) zur Zuführung von zirkular polarisiertem Licht zur Flüssigkristallzelle (5).1. Light control device from a combination of liquid crystal cell and polarizer, characterized by means (3) for supplying circularly polarized light to the liquid crystal cell (5). 2. Lichtsteuereinrichtung nach Anspruch 1, dadurch gekennzeichnet, dass die Mittel zur Zuführung von zirkular polarisiertem Licht einen Zirkularpo¬ larisator (3) enthalten.2. Light control device according to claim 1, characterized in that the means for supplying circularly polarized light contain a Zirkularpo¬ larizer (3). 3. Lichtsteuereinrichtung nach Anspruch 1, dadurch gekennzeichnet, dass die Mittel zur Zuführung von zirkular polarisiertem Licht eine wellen- längen-selektiv reflektierende cholesterische Flüssigkristallschicht enthalten.3. Light control device according to claim 1, characterized in that the means for supplying circularly polarized light contain a wavelength-selective reflecting cholesteric liquid crystal layer. 4. Lichtsteuereinrichtung nach Anspruch 3, dadurch gekennzeichnet, dass die Flüssigkristallschicht aus monomeren oder polymeren cholesteri- schen Flüssigkristallen besteht.4. Light control device according to claim 3, characterized in that the liquid crystal layer consists of monomeric or polymeric cholesteric liquid crystals. 5. Lichtsteuereinrichtung nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die Flüssigkristallzelle eine TN-Drehzelle (7) ist und die Bedingimg δjj^ = Δn.d = λ/2 für den optischen Gangunterschied zwi¬ schen aus- und eingeschaltetem Zustand gilt.5. Light control device according to one of the preceding claims, characterized in that the liquid crystal cell is a TN rotary cell (7) and the condition δ jj ^ = Δn.d = λ / 2 applies to the optical path difference between the switched on and off state . 6. Lichtsteuereinrichtung nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die Flüssigkristallzelle eine TN-Drehzelle (9) ist und die Bedingung δmjn = Δn.d = λ/4 für den optischen Gangunterschied zwischen aus- und eingeschaltetem Zustand gilt.6. Light control device according to one of the preceding claims, characterized in that the liquid crystal cell is a TN rotary cell (9) and the condition δ mjn = Δn.d = λ / 4 applies to the optical path difference between the switched-off and switched-on state. 7. Lichtsteuereinrichtung nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die Flüssigkristallzelle einen hochverdrillten Flüssigkristall enthält.7. Light control device according to one of the preceding claims, characterized in that the liquid crystal cell contains a highly twisted liquid crystal. 8. Lichtsteuereinrichtung nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die Flüssigkristallzelle (11) einen planaren Flüs¬ sigkristall mit paralleler Molekülausrichtung enthält.8. Light control device according to one of the preceding claims, characterized in that the liquid crystal cell (11) contains a planar liquid crystal with parallel molecular alignment. 9. Lichtsteuereinrichtung nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die Hüssigkristallzelle eine sog. DAP-Zelle (13) mit homöotroper Molekülausrichtung ist. 9. Light control device according to one of the preceding claims, characterized in that the Hüssig crystal cell is a so-called. DAP cell (13) with homeotropic molecular alignment. 10. Lichtsteuereinrichtung nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass auf dem Substrat der Fl ssigkristallzelle ein Re¬ flektor (10) angeordnet ist10. Light control device according to one of the preceding claims, characterized in that a reflector (10) is arranged on the substrate of the liquid crystal cell 11. Lichtsteuereinrichtung nach einem der vorangehenden Ansprüche, ge¬ kennzeichnet durch einen Linearpolarisator mit geringem Polarisationsgrad im Strahlengang des nach der Umwandlung aus zirkular polarisiertem Licht gegebenenfalls unvollständig linear polarisierten Lichts. 11. Light control device according to one of the preceding claims, characterized by a linear polarizer with a low degree of polarization in the beam path of the light which may be incompletely linearly polarized after conversion from circularly polarized light.
EP90915402A 1989-11-01 1990-10-26 Light control devices with liquid crystals Ceased EP0452438A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH3948/89 1989-11-01
CH394889 1989-11-01

Publications (1)

Publication Number Publication Date
EP0452438A1 true EP0452438A1 (en) 1991-10-23

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EP90915402A Ceased EP0452438A1 (en) 1989-11-01 1990-10-26 Light control devices with liquid crystals

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EP (2) EP0450025B1 (en)
JP (2) JP2831463B2 (en)
KR (2) KR920701862A (en)
DE (1) DE59008313D1 (en)
HK (1) HK17897A (en)
SG (1) SG50560A1 (en)
WO (2) WO1991006613A1 (en)

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JPH04502486A (en) 1992-05-07
SG50560A1 (en) 2000-10-24
JP2831463B2 (en) 1998-12-02
JPH04502524A (en) 1992-05-07
JP2809877B2 (en) 1998-10-15
EP0450025A1 (en) 1991-10-09
US5319478A (en) 1994-06-07
WO1991006613A1 (en) 1991-05-16
EP0450025B1 (en) 1995-01-18
KR920701393A (en) 1992-08-11
DE59008313D1 (en) 1995-03-02
KR920701862A (en) 1992-08-12
HK17897A (en) 1997-02-13
WO1991006889A1 (en) 1991-05-16
KR100203549B1 (en) 1999-06-15

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