Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/02—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the intensity of light
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/001—Optical devices or arrangements for the control of light using movable or deformable optical elements based on interference in an adjustable optical cavity
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/20—Filters
  • G02B5/28—Interference filters
  • G02B5/285—Interference filters comprising deposited thin solid films

Definitions

• Light valve and device provided with a light valve
• the invention relates to a light valve for controlled transmission of light, the light valve comprising a first and a second element, at least one of which two elements is controllably movable into optical contact with the other element, and means for projecting light on the first of the two elements on the side remote from the second of the two elements.
• the invention also relates to a device for displaying signals present in an electronic form, the device comprising a light source and a plurality of light valves for controlling the transmission of light emitted by the light source on the basis of the signals present in an electronic form.
• a light valve and a device of this type are known from international patent application WO 99/28890.
• This document describes a device which is provided with a plurality of light valves, which device comprises a lamp, an optical waveguide and a movable foil.
• the optical waveguide captures the light until the optical waveguide is locally "touched" by the movable foil, so that the conditions for total reflection within the optical waveguide are locally lost.
• the combination of movable foil and optical waveguide constitutes a light valve at each position where the foil and the optical waveguide can be brought into contact with each other.
• the foil is brought into and out of contact with the optical waveguide by means of electrostatic forces which are generated by a modulated electric field generated by a matrix of electrodes on the optical waveguide and a matrix of counter electrodes on a facing transparent plate.
• this object is achieved in a light valve in that each facing side of the elements is provided with an interference filter layer, which interference filter layers, when being in optical contact with each other, have a transmission for light projected onto the light valve in a wavelength range determined by the interference filter layers, which transmission differs from the transmission in the case where the interference filter layers are not in optical contact with each other.
• Interference filter layers are also effective in the case where radiation is perpendicularly incident on the interference filter layers.
• a device according to the invention is characterized in that one or more light valves as described hereinbefore are provided.
• a device according to the invention is capable of controlling the transmission of perpendicularly incident light. It is thereby achieved that the display performance as regards luminance and light efficiency is enhanced by means of rear illumination.
• the transmission and reflection of the stacked layers can be chosen within preselected wavelength ranges of the light, which are understood to be ranges varying from infrared to ultraviolet.
• the subject of reflection and anti-reflection coatings is very well known. The relevant knowledge is used in, but does not form part of, the present invention. Where wavelength ranges are referred to in ' the foregoing, it should also be understood to be a specific wavelength.
• the invention can be most easily understood by considering that a l/4 ⁇ layer provided on a surface ensures that light having the wavelength ⁇ can enter or exit the relevant body.
• the function of this type of filters is based on a reflective stack of dielectric layers having alternately a high and a low refraction index and a thickness of l/4 ⁇ . Such an optical stack reflects light with a wavelength ⁇ .
• the invention is based on the insight that when two of these stacks are placed behind each other and brought in optical contact a single layer of one l/2 ⁇ thickness is created and the two stacks together transmit light with a wavelength ⁇ . By moving the two stacks to and from each other the light can be switched and a controllable light valve is created. In this way, a light valve is formed which can switch for the wavelength ⁇ between full transmission and full reflection, i.e. no transmission at all, for perpendicularly incident radiation.
• light valves can thus be designed which can switch between full transparency and full reflection for a desired wavelength range around a given wavelength or are even limited to one specific wavelength by bringing the relevant layers into contact, or conversely, not into contact with each other.
• a preferred embodiment of a light valve according to the invention is characterized in that at least one of the interference filter layers comprises a self-supporting multilayer interference foil.
• Such multilayer interference foils are known per se and are preferably used in a light valve according to the invention.
• Fig. 1 A is a diagrammatic cross-section of a light valve according to the invention, in a first state
• Fig. IB is a diagrammatic cross-section of a light valve according to the invention, in a second state
• Fig. 2 is a diagrammatic cross-section of a plurality of juxtaposed light valves adapted to different colors of light
• Fig. 3 is a diagrammatic cross-section of a plurality of juxtaposed light valves forming part of a device according to the invention
• Fig. 4 is a diagrammatic cross-section of a multilayer interference foil
• Fig. 5 A is an example of the transmission of a light valve as a function of the wavelength when two specific interference filter layers are not in contact with each other;
• Fig. 5B is an example of the transmission of a light valve as a function of the wavelength when the interference filter layers of Fig. 5 A are in contact with each other.
• Light valves and devices for displaying signals which are present in an electronic form comprising a light source and a plurality of light valves for controlling the transmission of light emitted by the light source on the basis of the signals present in an electronic form are known per se from, inter alia, United States patent 4,113,360, international application WO 97/31288, international application WO 98/19201 and the afore mentioned international application WO 99/28890. The details of such devices will not be further described, and the operation of the light valves as described in the above-mentioned state of the art is assumed to be known.
• Fig. 1 A shows a light valve 1 in a diagrammatic cross-section. The light valve 1 forms part of a device 2 for displaying signals which are present in an electronic form.
• the device 2 comprises a light source 3 which emits light towards the light valve 1, which light is incident substantially perpendicularly or only at small angles, for example maximally 30° different therefrom, as indicated by arrow A, on a transparent support 4 which forms part of the light valve 1.
• a transparent electrode of, for example, ITO, 5 is provided on the transparent support 4 in known manner.
• An interference filter layer 6 is provided on the electrode 5.
• the interference filter layer 6 may comprise in known manner a plurality of dielectric layers, which is diagrammatically indicated by means of the lines 7.
• a second interference filter layer 8 is provided on a transparent support 9.
• a foil having a thickness of not more than 5 micrometers is preferably used as a transparent support 9.
• the interference filter layer 8 may also be built up of a plurality of dielectric layers, which is indicated diagrammatically by means of lines 10.
• the support 9 with the interference filter layer 8 is flexible. Separated or not separated by a space 11 from the transparent support 9, an electrode 13 is provided on a transparent support 12.
• the electrode 13 may also be made of ITO.
• the side 14 of the transparent support 12 constitutes an exit of the light valve 1 and of the device 2. It is to be noted that the positioning shown for the electrode layers 5 and 13 between the transparent support 4 and the interference filter layer 6 on the side 15 of the support 12 is not crucial. As is known from the above-mentioned state of the art, the electrode layers 5 and 13 may be provided at different positions.
• the interference filter layers 6 and 8 face each other and can assume at least two positions, a first position in which they are not in contact with each other, as is shown in Fig. 1 A, and a second position in which they are in contact with each other, as is shown in Fig. IB.
• Interference filter layer 8 also comprises an alternating succession of layers of TiO and SiO .
• the layers 6 and 8 whose details are shown in Table 1 are not transparent to visible light if they are not in contact with each other, as is shown in Fig. 5 A, whereas they have a narrow transmission band for green light if they are in contact with each other, as is shown in Fig. 5B.
• the single arrow A indicates that no light is transmitted in the interference filter layers 6 and 8 when they are not in contact with each other.
• Fig. IB the succession of arrows A, B, C and D indicates that the light valve is transparent in the interference filter layers 6 and 8.
• the interference filter layers 6 and 8 In order to realize a satisfactory optical contact between the interference filter layers 6 and 8, it is recommendable to provide at least one of the interference filter layers 6 and 8 with a thin polymer film 21.
• the advantage of this polymer film 21 is that it is easily deformable.
• the thickness of the polymer film 21 is preferably chosen to be such that it forms part of the optical system, i.e. forming one of the layers which is decisive for the transmission characteristic of the layers 6 and 8.
• Fig. 2 shows an example of a device 2 in which it is possible to visualize a multi-color image to an observer 17 by means of a strong light source 3 and by making use of the present invention.
• Fig. 2 only shows the support 4, interference filter layers 6B, 6G and 6R, interference filter layer 8, transparent support 9 and color filters 16B, 16G and l6R.
• Light source 3 emits a plurality of colors of light, for example, red R, green G and blue B.
• Fig. 2 further shows three different light valves, a light valve IB, a light valve IG and a light valve 1R.
• interference filter layer 8 is a layer having a wide transmission band which passes all the visible light.
• an interference filter layer 6B is chosen which specifically passes blue light
• an interference filter layer 6G is chosen which passes green light only
• an interference filter layer 6R is chosen which passes red light only.
• the interference filter layers 6B, 6G and 6R are structured in known manner such that there is no transmission of light, when they are not in optical contact with the interference filter layer 8.
• the light valve IB, IG and 1R are regularly distributed in known manner on the surface of the device 2, of which Fig. 2 is a diagrammatic cross-section. If the color rendition of the device shown in Fig. 2 is to be enhanced, each light valve IB, IG and 1R is associated with a known color filter 16B, 16G and 16R, respectively. By using color filters 16B, 16G and 16R, it is prevented that stray light of other colors coming from light valves IB and IG around the light valve 1R does not mix with the red light R required at the location of a pixel associated with filter 16R.
• the color filters 16B, 16G and 16R may be provided at any arbitrary location in the light path between the light source 3 and the observer 17, provided that they are associated with a relevant light valve IB, IG and 1R, respectively.
• the interference filter layers ensuring the color selection are provided on the transparent support 4, and an interference filter layer 8 co-operating with each interference layer on the transparent support 4 and ensuring the transmission is provided on the movable transparent support 9. It is of course also possible to provide the interference filter layer 8 on the transparent support 4 and to provide the color-selective interference filter layers on the transparent support 9. It is also possible to use narrow-band interference filter layers 8B, 8G and 8R, as is shown between brackets in Fig. 2, instead of a single interference filter layer 8. Then, a situation as described for green light in Figs. 1 A and IB is created for each color of blue light B, green light G and red light R in each light valve IB, IG and 1R, respectively. Due to the narrow-band property of the combined interference filter layers 6 and 8 and the color filters 16B, 16G and 16R, a considerable color saturation is achieved.
• Fig. 3 shows a further embodiment of a device according to the invention, in which the light source 3 emits ultraviolet light.
• a collimator 19 is provided and the interference filter layers 6 and 8 have a uniform composition throughout the surface of the device 2.
• the interference filter layers 6 and 8 have a narrow band and are adapted to a peak in the ultraviolet spectrum of the light source 3.
• phosphors 18B, 18G and 18R are provided in a known, regular manner on the right-hand side of the interference filter layer 8. Under the influence of the ultraviolet light emitted by the light source 3 and transmitted by the light valves IB, IG and 1R, the phosphors 18B, 18G and 18R luminesce in the colors blue B, green G and red R, respectively.
• collimator 19 is shown in Fig. 3 on the left-hand side of the transparent support 4, it is alternatively possible to position the collimator 19 in Fig. 3 on the right-hand side of the interference filter layer 8 but on the left- hand side of the phosphors 18B, 18G and 18R.
• color filters 16B, 16G and 16R are arranged in known manner between the light source 3 and an exit of the device 2.
• the interference filter layers 6 and 8 are dimensioned in known manner so that they pass light of a first color when they are not in contact with each other and pass light of a second color when they are in contact with each other.
• the first color is blue and the second color is red for light valve IB
• the first color is green and the second color is blue for light valve IG
• the first color is red and the second color is blue for light valve 1R. It is important that the second color is different from the first color.
• a further embodiment of an interference filter layer is constituted by a layer consisting of an array of cholesteric liquid crystals. These crystals constitute a layered structure which gives rise to interference of light waves incident on this structure. The mutual distance between the layers in the layered structure may be modified under the influence of an applied electric field.
• a light valve which, as an interference filter layer, comprises at least a cholesteric liquid crystal layer which may have a ' transmission peak at a desired location in the spectrum under the influence of an electric field. Dependent on the choice and the location of the transmission peak, there is transmission or no transmission of light with a specific wavelength.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Devices For Indicating Variable Information By Combining Individual Elements (AREA)
• Optical Filters (AREA)
• Mechanical Light Control Or Optical Switches (AREA)
• Push-Button Switches (AREA)
• Indication Of The Valve Opening Or Closing Status (AREA)
• Liquid Crystal (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (2)

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• 2001
  • 2001-09-06 TW TW090122099A patent/TW556002B/zh not_active IP Right Cessation
  • 2001-09-10 US US09/950,475 patent/US6864933B2/en not_active Expired - Fee Related
  • 2001-10-05 DE DE60109186T patent/DE60109186T2/de not_active Expired - Fee Related
  • 2001-10-05 AT AT01969809T patent/ATE290231T1/de not_active IP Right Cessation
  • 2001-10-05 JP JP2002536460A patent/JP2004511827A/ja not_active Abandoned
  • 2001-10-05 WO PCT/EP2001/011601 patent/WO2002033313A2/en not_active Ceased
  • 2001-10-05 EP EP01969809A patent/EP1327173B1/en not_active Expired - Lifetime
  • 2001-10-05 KR KR1020027007530A patent/KR20020064935A/ko not_active Ceased
  • 2001-10-05 CN CNB018031811A patent/CN1252507C/zh not_active Expired - Fee Related

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