US20020113923A1 - Polarized light extraction optical element - Google Patents

Polarized light extraction optical element Download PDF

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Publication number
US20020113923A1
US20020113923A1 US10/115,036 US11503602A US2002113923A1 US 20020113923 A1 US20020113923 A1 US 20020113923A1 US 11503602 A US11503602 A US 11503602A US 2002113923 A1 US2002113923 A1 US 2002113923A1
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Prior art keywords
polarized light
liquid crystal
light
polarization separation
separation layer
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Abandoned
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US10/115,036
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English (en)
Inventor
Keiji Kashima
Yukihiro Toyota
Masanori Umeya
Mariko Goto
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Dai Nippon Printing Co Ltd
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Dai Nippon Printing Co Ltd
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Priority claimed from JP11113675A external-priority patent/JP2000304919A/ja
Priority claimed from JP2000066645A external-priority patent/JP2001004842A/ja
Priority claimed from JP2000081444A external-priority patent/JP3705989B2/ja
Application filed by Dai Nippon Printing Co Ltd filed Critical Dai Nippon Printing Co Ltd
Priority to US10/115,036 priority Critical patent/US20020113923A1/en
Assigned to DAI NIPPON PRINTING CO., LTD. reassignment DAI NIPPON PRINTING CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GOTO, MARIKO, UMEYA, MASANORI, KASHIMA, KEIJI, TOYOTA, YUKIHIRO
Publication of US20020113923A1 publication Critical patent/US20020113923A1/en
Abandoned legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • 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
    • G02F1/01—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
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/34—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 reflector
    • G02F2201/343—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 reflector cholesteric liquid crystal reflector

Definitions

  • the present invention relates to an optical element that extracts either circularly polarized light of a prescribed rotation direction or linearly polarized light of a prescribed polarization direction, and more particularly it relates to a polarization extraction optical element that reflects part of one of right and left circularly polarized light or one of two linearly polarized lights, the oscillation planes of which are mutually perpendicular, and passes the remaining light.
  • a polarizing beam splitter or polarizing filter is known as an optical element that reflects either right or left circularly polarized light and passes the other light.
  • linear polarization extraction optical element would be a polarizing beam splitter or a polarizing filter. These have a planar multilayer structure in which a large number of layers of birefringent materials are laminated, arranged so that the difference in refractive indices of layers that are mutually adjacent in the thickness direction with respect to one of two linearly polarized light components that have oscillation directions that are mutually perpendicular within a plane is different than the difference in refractive indices of layers mutually adjacent in the thickness direction with respect to the other linearly polarized light component.
  • An optical element that uses a cholesteric liquid as any of those described above reflects either right or left circularly polarized light in a specific wavelength range and passes the other circularly polarized light component in this wavelength range, and also passes all of the left and right circularly polarized light in other wavelength regions, and light incident from the opposite side is affected in the same manner, either left or right circularly polarized light being reflected and therefore striking the optical element, the result being that, although it is possible extract as reflected light either right or left circularly polarized light in a specific wavelength region, it is not possible to perform extraction from the transmitted light.
  • a reflecting/transmitting optical element using cholesteric liquid crystal has a fixed reflection/transmission ratio of 50/50, and is therefore accompanied by the problem of preventing free changing of this ratio as required.
  • the present invention was made in consideration of the above-described drawbacks of past technology, and has as an object to provide a polarized light extraction optical element that can extract, from both reflected light and transmitted light, either one of right- and left-rotational circularly polarized light of a specific wavelength region, or one of two linearly polarized light components of a specific wavelength region, the oscillation planes of which are mutually perpendicular.
  • the present invention has a polarization separation layer laminated onto a light-transmitting substrate, this polarization separation layer has one of two functions, one to separate at least part of non-polarized incident light into two linearly polarized lights, the polarization directions of which are mutually perpendicular, one being reflected, and another being transmitted, the other to separate at least part of the non-polarized incident light into two circularly polarized lights, the rotation directions of which are mutually opposite, one being reflected and the other being transmitted, the thickness of the polarization separation layer being within the range of 10% to 90% of the thickness required to reflect the one polarized light component with the maximum reflectivity.
  • auxiliary polarization separation layer on the above-noted polarization separation layer, this auxiliary polarization separation layer having a function of transmitting a polarized light component that remained from the reflection by the polarization separation layer and was transmitted therethrough, and reflecting the other polarized light component that remained from the reflection by the polarization separation layer and was transmitted therethrough, the thickness of the auxiliary polarization separation layer being in the range of 10% to 90% of the thickness required to reflect the other polarization component with the maximum reflectivity.
  • the polarization separation layer can be a liquid crystal having cholesteric characteristics, the helical axis of liquid crystal molecules thereof being formed so as to traverse the liquid-crystal layer in the thickness direction, and the thickness of the liquid-crystal layer being thinner than the thickness required to reflect the one of the incident right or left circularly polarized light components with maximum reflectivity, so that this circularly polarized light component is reflected thereby with a reflectivity that is less than the maximum reflectivity, the other left or right circularly polarized light component being transmitted therethrough.
  • the number of molecular helix pitches in the part in which the selective reflection wavelength of the liquid-crystal layer in the polarization separation layer is less than 20, and preferably between 1 and 10 pitches.
  • the thickness of the part in which the selective reflection wavelength of the liquid crystal is in the visible light region in the polarization separation layer is less than 30 ⁇ m, and preferably in the range 5 to 20 ⁇ m.
  • the pitch of the molecular helix of the liquid-crystal layer in the polarization separation layer can be changed in the thickness direction of the liquid crystal layer, and the difference between the maximum pitch and minimum pitch thereof can be made at least 100 nm.
  • the pitch of the molecule helix in the liquid crystal layer is made such that the circularly polarized light reflection wavelength bandwidth is 300 nm or greater, and preferably in the range 400 to 800 nm.
  • the liquid crystal layer has a molecule helix pitch such that it minimally reflects circularly polarized light of the colors red, green, and blue.
  • auxiliary polarization separation layer laminated onto said polarization separation layer, wherein said auxiliary polarization separation layer is a liquid crystal having cholesteric characteristics, a helical axis of liquid crystal molecules thereof being formed so as to traverse said liquid-crystal layer in a thickness direction, and a thickness of said liquid-crystal layer being smaller than a thickness required to reflect said other circularly polarized light components with maximum reflectivity, so that said other circularly polarized light component is reflected thereby with a reflectivity that is less than said maximum reflectivity, said one circularly polarized light component being transmitted therethrough.
  • said auxiliary polarization separation layer is a liquid crystal having cholesteric characteristics, a helical axis of liquid crystal molecules thereof being formed so as to traverse said liquid-crystal layer in a thickness direction, and a thickness of said liquid-crystal layer being smaller than a thickness required to reflect said other circularly polarized light components with maximum reflectivity, so that said other circularly polarized light component is
  • the number of molecular helix pitches in a part in which a selective reflection wavelength of said liquid-crystal layer in said auxiliary polarization separation layer is less than 20, and preferably between 1 and 10 pitches.
  • the thickness of a part in which a selective reflection wavelength of a liquid crystal is in the visible light region in said auxiliary polarization separation layer is less than 30 ⁇ m, and preferably in a range 5 to 20 ⁇ m.
  • the pitch of a molecular helix of said liquid-crystal layer in said auxiliary polarization separation layer is changed in a thickness direction of said liquid crystal layer, and a difference between a maximum pitch and a minimum pitch thereof is made at least 100 nm.
  • the pitch of a molecule helix in said liquid crystal layer is made such that the circularly polarized light reflection wavelength bandwidth is 300 nm greater, and preferably in the range 400 to 800 nm.
  • the liquid crystal layer has a molecule helix pitch such that it minimally reflects circularly polarized light of the colors red, green, and blue.
  • the polarization separation layer can be formed by a plurality of liquid crystal layers exhibiting cholesteric behavior, each of these liquid crystal layers being laminated so that they have the same liquid crystal molecule rotational direction and so that the molecule helix axis traverses the liquid crystal layer in the thickness direction.
  • the liquid crystal layers have mutually different distances per pitch in their molecular helices, and the thicknesses of the liquid crystal layers are thinner than the thickness required to reflect either the right or left circularly polarized light component at the wavelength of the incident light with maximum reflectivity, so that the right or left circularly polarized light is reflected with a reflectivity less than the maximum reflectivity, the other circularly polarized component (left- or right-rotational, respectively) being transmitted.
  • the present invention it is possible to use a laminate made of a plurality of liquid crystal layers exhibiting cholesteric characteristics, the distance per pitch of the molecular helices in each liquid crystal layer being mutually different, enabling extraction of right or left circularly polarized light having a broad wavelength region as reflected light with respect to light incident to thereto from one side, and extraction of circularly polarized light having the same rotational direction and in the same wavelength region as the reflected light on the same side as the reflected light.
  • the number of molecular helix pitches in said each liquid-crystal layers is less than 20, and preferably between 1 and 10 pitches.
  • the thickness of a part in which a selective reflection wavelength of a liquid crystal is in the visible light region in said each polarization separation layer is less than 5 ⁇ m, and preferably in a range 1 to 4 ⁇ m.
  • the liquid crystal layer has three kind of helical pitch molecular such that it minimally reflects circularly polarized light of the colors red, green, and blue, and each kind of the helical pitch molecule consists of at least one liquid crystal layer.
  • auxiliary polarization separation layer laminated onto said polarization separation layer, wherein said auxiliary polarization separation layer is a liquid crystal having cholesteric characteristics, a helical axis of liquid crystal molecules thereof being formed so as to traverse said liquid-crystal layer in a thickness direction, and a thickness of said liquid-crystal layer being smaller than a thickness required to reflect said other circularly polarized light components with maximum reflectivity, so that said other circularly polarized light component is reflected thereby with a reflectivity that is less than said maximum reflectivity, said one circularly polarized light component being transmitted therethrough.
  • said auxiliary polarization separation layer is a liquid crystal having cholesteric characteristics, a helical axis of liquid crystal molecules thereof being formed so as to traverse said liquid-crystal layer in a thickness direction, and a thickness of said liquid-crystal layer being smaller than a thickness required to reflect said other circularly polarized light components with maximum reflectivity, so that said other circularly polarized light component is
  • the number of molecular helix pitches in a part in which a selective reflection wavelength of said liquid-crystal layer in said auxiliary polarization separation layer is less than 20, and preferably between 1 and 10 pitches.
  • the thickness of a part in which a selective reflection wavelength of a liquid crystal is in the visible light region in said auxiliary polarization separation layer is less than 30 ⁇ m, and preferably in a range 5 to 20 ⁇ m.
  • the pitch of a molecular helix of said liquid-crystal layer in said auxiliary polarization separation layer is changed in a thickness direction of said liquid crystal layer, and a difference between a maximum pitch and a minimum pitch thereof is made at least 100 nm.
  • the pitch of a molecule helix in said liquid crystal layer is made such that the circularly polarized light reflection wavelength bandwidth is 300 nm greater, and preferably in the range 400 to 800 nm.
  • the liquid crystal layer has a molecule helix pitch such that it minimally reflects circularly polarized light of the colors red, green, and blue.
  • the configuration can be one in which the polarization separation layer is a birefringent layer is provided on a light-transmitting material, this birefringent layer being of multilayer planar construction made of at least three laminated layers of birefringent material such that the difference in refractive indices of layers that are mutually adjacent in the thickness direction with respect to one of two linearly polarized light components that have oscillation directions that are mutually perpendicular within the plane of each layer is different than the difference in refractive indices of layers mutually adjacent thereto in the thickness direction with respect to the other linearly polarized light component.
  • the number of laminated layers of birefringent material can be made smaller than the number required to reflect one of the linearly polarized light components with maximum reflectivity, so that the one linearly polarized light component is reflected with reflectivity smaller than the maximum reflectivity, the other linearly polarized light component being transmitted.
  • auxiliary polarization separation layer on the above-noted polarization separation layer, this auxiliary polarization separation layer being of planar laminated construction of three or more layers of birefringent material, and being such that the difference in refractive indices of layers that are mutually adjacent in the thickness direction with respect to one of two linearly polarized light components that have oscillation directions that are mutually perpendicular within the plane of each layer is different than the difference in refractive indices of layers mutually adjacent thereto in the thickness direction with respect to the other linearly polarized light component.
  • the number of layers of birefringent material in the auxiliary polarization separation layer can be made smaller than the number required to reflect light other linear polarization direction with the maximum reflectivity, so that the other linearly polarized light component is reflected with a reflectivity that is smaller than the maximum reflectivity, with light of the opposing linear polarization direction being transmitted.
  • the number of birefringent material layers in at least one of the polarization separation layer and the auxiliary polarization separation layer can be made 30 to 150.
  • a prescribed linearly polarized light component is extracted as reflected light with respect to light incident from one side of the polarization separation layer, and light of the same linear polarization direction as the reflected light is extracted as transmitted light in the opposite direction.
  • a polarized light extraction optical element it is possible, for example, when using a cholesteric color liquid crystal or birefringent layer to inspect the validity of such items as certificates and credit cards that have been patterned with information that cannot be seen with visible light, to extract circularly polarized or linearly polarized light from natural light and shine the extracted light onto the credit card or the like, causing light from a illumination lamp to be reflected by a polarized light extraction optical element of the present invention, the extracted circularly or linearly polarized light being then shone onto the item to be validated.
  • FIG. 1 is a simplified cross-section view showing a polarized light extraction optical element according to a first embodiment of the present invention.
  • FIG. 2 is an enlarged perspective view showing the relationship between the pitch and the directors cholesteric liquid crystal molecules.
  • FIG. 3 is a simplified cross-section view showing a polarized light extraction optical element according a second embodiment of the present invention.
  • FIG. 4 is a simplified cross-section view illustrating the manufacturing process for a polarized light extraction optical element according to the present invention.
  • FIG. 5 is a simplified cross-section view showing a polarized light extraction optical element according to a third embodiment of the present invention.
  • FIG. 6 is a simplified cross-section view showing a polarized light extraction optical element according to a fourth embodiment of the present invention.
  • FIG. 7 is a simplified cross-section view showing the manufacturing process for a polarized light extraction optical element according to the present invention.
  • FIG. 8 is a simplified cross-section view showing a polarized light extraction optical element according to a fifth embodiment of the present invention.
  • FIG. 9 is a simplified cross-section view showing a polarized light extraction optical element according to a sixth embodiment of the present invention.
  • a polarized light extraction optical element 10 is formed by a light-transmitting base material 12 and a liquid crystal layer 14 laminated onto the light-transmitting base material 12 as a polarization separation layer.
  • the liquid crystal layer 14 is made by aligning a liquid crystal exhibiting cholesteric characteristics so that molecular helix thereof transverses the liquid crystal in the thickness direction, the thickness thereof being made thinner than the thickness required to achieve the maximum reflectivity (usually 95 to 99%) with respect to either right or left circularly polarized incident light, thereby causing reflection of that direction of circularly polarized light with a reflectivity that is smaller than the maximum reflectivity, and transmission of the other direction of circularly polarized light (left- or right-rotational, respectively).
  • the above-noted cholesteric liquid crystal usually has selective circular polarization characteristics that separate light of one circular polarization from light of circular polarization of the oppositely rotated direction, with light incident to the planarly oriented helix axis being split into two circularly polarized components, left- and right-rotational, one of which is transmitted, and the other of which is reflected.
  • This phenomenon is known as circular dichroism, and if the rotation direction of the circularly polarized light is selected appropriately with respect to the incident light, there is selective diffuse reflection of circularly polarized light having the same rotation direction as the helical axis direction in the cholesteric liquid crystal.
  • p is the helical pitch
  • nav is the average refractive index within the plane perpendicular to the helical axis.
  • helical pitch (p) refers to the distance p in the thickness direction required for one rotation of the director D of the liquid crystal molecules in the liquid crystal layer.
  • ⁇ n is the value of birefringence.
  • Methods of broadening the wavelength bandwidth ⁇ include that of changing the helical pitch (disclosed, for example, in Japanese Unexamined Patent Application publication H6-281814) and that of overlapping several layers of cholesteric liquid crystal for which p differs (disclosed, for example, in Japanese Unexamined Patent Application publication H9-304770).
  • a cholesteric liquid crystal material it is desirable to use a chiral nematic liquid crystal with a Shiff's base, an azo compound, an ester, or a biphenyl nematic liquid crystal compound, with an optically activated 2-methyl butyl group, a 2-methyl butoxy group, a 4-methyl hexyl group joined to an end group thereof, or a chiral reactive liquid crystal compound such as disclosed in the Japanese Unexamined Patent Application publication H7-258638, a ring organo-polysiloxane compound having a cholesteric phase as disclosed in the Japanese Unexamined Patent Application publication S57-165480, or a polymerizable monomer and chiral compound such as disclosed in the Japanese Unexamined Patent Application publication S10-508882.
  • a general high-polymer liquid crystal is a high polymer in which a mesogen group is introduced in the main chain, the side chain, or the main and side chain positions
  • a high-polymer cholesteric liquid crystal is obtained by introducing a cholesteryl group, for example, into the side chain.
  • a liquid crystal high polymer such as disclosed in the Japanese Unexamined Patent Application publication H9-133810, or a liquid crystal high polymer such as disclosed in the Japanese Unexamined Patent Application publication H11-293252 or the like be used as a cholesteric liquid crystal material.
  • the light-transmitting base material 12 is made of a single or a copolymer of an acrylic ester such as polymethyl metacrylate or metacrylate ester, a polyester such as polyethylene teraphthalate, a transparent resin such as polycarbonate or polyethylene, transparent glass, or a transparent ceramic or the like, formed into a planar sheet or plate.
  • an acrylic ester such as polymethyl metacrylate or metacrylate ester
  • a polyester such as polyethylene teraphthalate
  • a transparent resin such as polycarbonate or polyethylene, transparent glass, or a transparent ceramic or the like
  • the polarization separation action of the cholesteric liquid crystal causes passes of either the right or the left circularly polarized light, and reflection of the circularly polarized light of the other rotational direction. When reflection occurs, the right or left circularly polarized light is reflected without change, as right or left circularly polarized light.
  • the amount of reflection of either right or left circularly polarized light can be made 80%, with the amount of transmitted light being 20%.
  • the transmissivity is improved to nearly 100%.
  • the reference symbols R and L refer to right and left circularly polarized light, respectively.
  • the number of pitches of in the liquid crystal layer 14 is made, for example, 5.6 pitches, it is possible to make the reflectivity for either right or left circularly polarized light in the liquid crystal layer be 70%, with the transmitted proportion of light being 30%. That is, depending upon the thickness of the liquid crystal layer 14 , it is possible to obtain an arbitrary reflectivity and transmissivity with respect to the maximum reflectivity.
  • the thickness of the liquid crystal layer made of the above-noted cholesteric liquid crystal is made, for example, 10 ⁇ m, which is thinner than the above-noted 30 ⁇ m.
  • the thickness of the liquid crystal layer 14 is made 15 ⁇ m, it is possible to make the reflectivity for either right or left circularly polarized light in the liquid crystal layer be 80%, with the transmitted proportion of light being 20%. That is, depending upon the thickness of the liquid crystal layer 14 , it is possible to obtain an arbitrary reflectivity and transmissivity with respect to the maximum reflectivity.
  • the polarized light extraction optical element 20 uses a liquid crystal layer 14 as a polarization separation layer, over which a second liquid crystal layer 22 is laminated as an auxiliary polarization separation layer.
  • the second liquid crystal layer 22 is made of a cholesteric liquid crystal, the alignment and thickness thereof, also similar to the liquid crystal layer 14 , are such that a circularly polarized light of one rotational direction is reflected with a reflectivity that is less than the maximum reflectivity.
  • the direction of the helical axis of the molecules of this auxiliary polarization separation layer is such that a part of the circularly polarized light of either right or left polarization that is 100% transmitted by the liquid crystal layer 14 is reflected, and the remaining light is transmitted, so that part of the light is reflected by at the liquid crystal layer 14 and one circularly polarized component of the remaining light is transmitted.
  • the reflecting/transmitting optical element 20 by establishing the thicknesses of the liquid crystal layer 14 and the liquid crystal layer 22 appropriately, it is possible to arbitrarily adjust the proportion of right or left circularly polarized light that is transmitted by the second liquid crystal layer 22 so that, for example, these are equal.
  • the reflected component from the second liquid crystal layer 22 passes therethrough without being reflected by the liquid crystal layer 14 , there is interference that is set up between the reflected component from the second liquid crystal layer 22 and the light reflected by the liquid crystal layer 14 , so that, similar to the case of the second liquid crystal layer 22 , it is possible to arbitrarily adjust the proportion of right- and left-rotational circularly polarized light.
  • both the light that passes through the polarized light extraction optical element 20 and the light reflected thereby can be made to approach the condition of natural light.
  • At least one liquid crystal side of the above-noted substrates 24 A and 24 B has formed on it an alignment film (not shown in the drawing), whereby the molecular helix axis in the liquid crystal injected between the substrates is aligned so as to traverse the liquid crystal in the thickness direction thereof.
  • a method of achieving alignment of the liquid crystal molecules is to use extended PET (polyethylene terephthalate) in place of the alignment film.
  • the second liquid crystal layer 22 it is also possible for the second liquid crystal layer 22 , to use side of the cured liquid crystal layer 14 as a substrate, or to use this as a substrate on the opposite side of the light-transmitting base material 12 from the side on which is formed the liquid crystal layer 14 .
  • the polarized light extraction optical element 30 uses a liquid crystal layer 32 having cholesteric characteristics as a polarization separation layer, this liquid crystal layer 32 , in contrast to the above-noted liquid crystal layer, having a helical pitch in the molecules of the cholesteric liquid crystal that is changed in the thickness direction thereof, so that it is possible to obtain reflected and transmitted light over a broad wavelength region, for example over the entire visible light region.
  • the structure of a cholesteric liquid crystal in which the helical pitch is changed in this manner can be formed by a method that is disclosed, for example, in the Japanese Unexamined Patent Application publication H6-281814.
  • the liquid crystal layer 32 in the polarized light extraction optical element 30 as well has a thickness that is smaller than the thickness for maximum reflectivity, as is the case with the above-described liquid crystal layer 14 and second liquid crystal layer 22 .
  • the pitch of the molecular helix in the liquid crystal layer 32 is changed in the thickness direction of the liquid crystal layer, and the difference between the maximum pitch and the minimum patch is made at least 100-nm.
  • the pitch of the molecular helix in the liquid crystal layer 32 is made so that the circularly polarized light reflection wavelength bandwidth is 300 nm or greater, and preferably so that it is 400 to 800 n.
  • any of the above-described polarized light extraction optical elements 10 , 20 , and 30 can be used as either a beam splitter or a polarizing filter.
  • a polarized light extraction optical element 40 is formed by a light-transmitting base material 12 and a laminate 44 formed as a polarization separation layer on the light-transmitting base material 12 .
  • the laminate 44 is formed by a plurality of liquid crystal layers 45 A, 45 B, 45 C, and so on, which have cholesteric characteristics, the rotational direction of the molecules in each liquid crystal layer being the same, and the lamination being done so that the molecular helix axes thereof traverse the liquid crystal in the thickness direction.
  • the distances per pitch of the molecular helix i.e., the helical pitches
  • the thicknesses of the liquid crystal layers 45 A, 45 B, 45 C, and so on are smaller than the thickness required for reflection of either right or left circularly polarized light at the wavelength of light to strike the layers at the maximum reflectivity, so that this one circularly polarized light component (right or left) is reflected therefrom with a reflectivity that is less than the maximum reflectivity, the other circularly polarized light of the right and left circularly polarized light being transmitted therethrough.
  • the number of pitches in the liquid crystal layers 45 A, 45 B, 45 C, and so on is made 6.4, this being less than the required number of pitches.
  • the amount of reflection of either right or left circularly polarized light can be made 80%, with the amount of transmitted light being 20%.
  • the transmissivity is improved to nearly 100%.
  • the number of pitches of in the liquid crystal layers 45 A, 45 B, 45 C, and so on is made, for example, 5.6 pitches, it is possible to make the reflectivity for either right or left circularly polarized light in the liquid crystal layers be 70%, with the transmitted proportion of light being 30%. That is, depending upon the thickness of the liquid crystal layers, it is possible to obtain an arbitrary reflectivity and transmissivity with respect to the maximum reflectivity.
  • the thicknesses of the liquid crystal layers 45 A, 45 B, 45 C, and so on made of cholesteric liquid crystal are, for example, in the range 1.2 ⁇ m (380 nm light) to 2.6 ⁇ m (780 nm light) for the visible light region, the thicknesses of each layer being varied linearly with respect to the selective reflection wavelength of the cholesteric liquid crystal layer, and all of them being thinner than the thickness required to achieve maximum reflectivity.
  • the thicknesses of the liquid crystal layers 45 A, 45 B, 45 C, and so on in the range from 1.1 ⁇ mm (380 nm light) to 2.3 ⁇ m (780 nm light)
  • the thicknesses of each layer is varied linearly with respect to the selective reflection wavelength of each cholesteric liquid crystal layer, it is possible to make the reflectivity of each of the liquid crystal layers 45 A, 45 B, 45 C, and so on be 70% with respect to one of the right and left circularly polarized light, the 30% of circularly polarized light of the other rotational direction being transmitted therethrough. That is, it is possible obtain arbitrary reflectivities and transmissivities with respect to the maximum reflectivity, according to the thicknesses of each liquid crystal layer.
  • the polarized light extraction optical element 40 also enables the reading of information that is written by circularly polarized light such as noted above.
  • At least one liquid crystal side of the above-noted substrates 24 A and 24 B has formed on it an alignment film (not shown in the drawing), whereby the molecular helix axis in the liquid crystal injected between the substrates is aligned so as to traverse the liquid crystal in the thickness direction thereof.
  • a method of achieving alignment of the liquid crystal molecules is to use extended PET (polyethylene terephthalate) in place of the alignment film.
  • the second liquid crystal layer, 45 B is formed by the same procedure as described above, using the cured liquid crystal layer 45 A as one substrate, this process being successively repeated so as to laminate the liquid crystal layers 45 A, 45 B, 45 C, and so on, thereby completing the laminate 44 . If necessary, the exposed laminate 44 is covered by a protective film (not shown in the drawing).
  • liquid crystal layers 14 , 22 , 45 A, 45 B, 45 C, and soon are made of cholesteric liquid crystals
  • the present invention does not impose this as a restriction, and can use any liquid crystal with cholesteric characteristics and having a helical molecular structure.
  • the present invention has superior effectiveness in obtaining circularly polarized light of a prescribed rotational direction, by either reflected light or transmitted light.
  • a polarized light extraction optical element 50 in the fifth embodiment of the present invention is obtained by forming a birefringent layer 54 as a polarization separation layer on a light-transmitting base material 12 , so as to transmit one of two linearly polarized light components that have mutually perpendicular oscillation directions and reflect the other linearly polarized light component.
  • the birefringent layer 54 has a planar multilayer structure in which at least three layers of birefringent materials are laminated, arranged so that the difference in refractive indices of layers that are mutually adjacent in the thickness direction with respect to one of two linearly polarized light components that have oscillation directions that are mutually perpendicular within a plane is different than the difference in refractive indices of layers mutually adjacent in the thickness direction with respect to the other linearly polarized light component.
  • a birefringent film such as noted above is disclosed, for example, in Japanese Unexamined Patent Application publication H3-75705, in which drawing or the like is used to obtain a substance such as a polycarbonate resin, a polyester resin, a polyvinyl alcohol resin, and an acetyl cellulose resin or other substance that exhibits intraplanar birefringence (refractive index anisotropy).
  • the refractive index with respect to a light beam which oscillates in the X-axis direction of adjacent birefringent layers (films) is nx
  • the reflection of light oscillating in a direction (Y-axis direction) in which the refractive index difference is large is greater than the reflection of light oscillating in a direction in which the refractive index is small (X-axis direction), and the transmission of X-axis direction light is greater than the transmission of Y-axis direction light.
  • the birefringent layer 54 is laminated of approximately 200 layers in order to obtain the maximum reflectivity, in the case of the present invention, this number is reduced to, for example, approximately 20 to 170 layers.
  • a polarized light extraction optical element 60 according to the sixth embodiment of the present invention is described below, with reference being made to FIG. 6.
  • the polarized light extraction optical element 60 is formed by a birefringent layer 54 , onto which is laminated a second birefringent layer 56 as an auxiliary polarization separation layer, this second birefringent layer 56 , similar to the birefringent layer 54 , having fewer laminations that the number of laminations for achieving the maximum reflectivity.
  • the linearly polarized light component reflected by the second birefringent layer 56 is the same as the linearly polarized light component transmitted through the birefringent layer 54 .
  • Both the above-described polarized light extraction optical elements 50 and 60 can be used as either a beam splitter or a polarizing filter.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Polarising Elements (AREA)
US10/115,036 1999-04-20 2002-04-04 Polarized light extraction optical element Abandoned US20020113923A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US10/115,036 US20020113923A1 (en) 1999-04-20 2002-04-04 Polarized light extraction optical element

Applications Claiming Priority (12)

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JP11199899 1999-04-20
JP11-111998 1999-04-20
JP11367699 1999-04-21
JP11113675A JP2000304919A (ja) 1999-04-21 1999-04-21 直線偏光抽出光学素子
JP11-113675 1999-04-21
JP11-113676 1999-04-21
JP2000066645A JP2001004842A (ja) 1999-04-21 2000-03-10 円偏光抽出光学素子
JP2000-066645 2000-03-10
JP2000081444A JP3705989B2 (ja) 1999-04-20 2000-03-23 円偏光抽出光学素子
JP2000-081444 2000-03-23
US54961500A 2000-04-14 2000-04-14
US10/115,036 US20020113923A1 (en) 1999-04-20 2002-04-04 Polarized light extraction optical element

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US10/277,868 Expired - Lifetime US6906764B2 (en) 1999-04-20 2002-10-23 Reflective cholesteric filter

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US (2) US20020113923A1 (de)
EP (2) EP1826592A3 (de)
KR (1) KR100452608B1 (de)

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US6747715B2 (en) * 2000-12-04 2004-06-08 Kabushiki Kaisha Toshiba Polarized light reflecting element, liquid crystal display element using the same, and method of manufacturing polarized light reflecting element
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US9562999B2 (en) 2013-10-30 2017-02-07 Samsung Display Co., Ltd. Optical film comprising first and second semi-transmissive films configured to transmit a linearly polarized light component and reflect a circularly polarized light component and display apparatus including the optical film
CN109856881A (zh) * 2019-04-12 2019-06-07 广州林登科技有限公司 一种高亮度液晶书写装置
US11493677B2 (en) 2017-03-06 2022-11-08 3M Innovative Properties Company High contrast optical film having specified transmittance and reflectance of polarized light

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US6747715B2 (en) * 2000-12-04 2004-06-08 Kabushiki Kaisha Toshiba Polarized light reflecting element, liquid crystal display element using the same, and method of manufacturing polarized light reflecting element
US20040056991A1 (en) * 2001-11-09 2004-03-25 Keiji Kashima Optical device manufacturing method
US20090091685A1 (en) * 2002-10-29 2009-04-09 Casio Computer Co., Ltd. Liquid crystal display device viewable from both surfaces and portable apparatus using same
US7800715B2 (en) * 2002-10-29 2010-09-21 Casio Computer Co., Ltd. Liquid crystal display device viewable from both surfaces and portable apparatus using same
US9562999B2 (en) 2013-10-30 2017-02-07 Samsung Display Co., Ltd. Optical film comprising first and second semi-transmissive films configured to transmit a linearly polarized light component and reflect a circularly polarized light component and display apparatus including the optical film
US11493677B2 (en) 2017-03-06 2022-11-08 3M Innovative Properties Company High contrast optical film having specified transmittance and reflectance of polarized light
US11846792B2 (en) 2017-03-06 2023-12-19 3M Innovative Properties Company High contrast optical film and devices including the same
CN109856881A (zh) * 2019-04-12 2019-06-07 广州林登科技有限公司 一种高亮度液晶书写装置

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US20030038918A1 (en) 2003-02-27
US6906764B2 (en) 2005-06-14
KR100452608B1 (ko) 2004-10-14
EP1826592A3 (de) 2007-09-19
KR20000071719A (ko) 2000-11-25
EP1826592A2 (de) 2007-08-29
EP1046934A1 (de) 2000-10-25

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