EP1702240A1 - Overhead projection screen - Google Patents

Overhead projection screen

Info

Publication number
EP1702240A1
EP1702240A1 EP05707748A EP05707748A EP1702240A1 EP 1702240 A1 EP1702240 A1 EP 1702240A1 EP 05707748 A EP05707748 A EP 05707748A EP 05707748 A EP05707748 A EP 05707748A EP 1702240 A1 EP1702240 A1 EP 1702240A1
Authority
EP
European Patent Office
Prior art keywords
face
optical
optical plate
main axis
rays
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05707748A
Other languages
German (de)
French (fr)
Inventor
Arno Schubert
Pascal Benoit
Khaled Sarayeddine
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.)
Thomson Licensing SAS
Original Assignee
Thomson Licensing SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson Licensing SAS filed Critical Thomson Licensing SAS
Publication of EP1702240A1 publication Critical patent/EP1702240A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00—Projectors or projection-type viewers; Accessories therefor
    • G03B21/54—Accessories
    • G03B21/56—Projection screens
    • G03B21/60—Projection screens characterised by the nature of the surface
    • G03B21/62—Translucent screens
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/04—Prisms
    • G02B5/045—Prism arrays

Definitions

  • the lens comprises prismatic elements which straighten the rays received from the source into a beam of parallel rays.
  • the prismatic elements are designed to straighten the incident rays either by refraction (low angle of incidence) or by reflection (high angle of incidence) .
  • Such lenses are for example used in a projection display device.
  • a reduced size imager is projected onto a display screen by a projection system, with angles of incidence on the screen which extend over a determined range of values, for example of 30 ° to 60 °.
  • the flux received from the projection system must therefore be globally collimated by a Fresnel lens, that is to say rectified in a horizontal direction, before being generally micro-focused through a dark matrix and then diffused in the field d observation desired.
  • the optical efficiency (or yield) of the prismatic elements of the Fresnel lens is however poor under certain incidences, and in particular for angles of incidence of 20 ° to 40 °. Indeed, such angles do not allow a good yield either by reflection or by refraction for prismatic structures located on the incident face. 3.
  • the invention proposes using an optical plate in place of the Fresnel lens, comprising on a first face a first set of at least two optical elements capable of straightening rays received from a light source into a beam of rays essentially parallel to a first direction in a plane containing a main axis, with means on the second face for straightening said beam in a second direction different from the first direction.
  • the second face carries at least a first optical element for straightening the beam in the second direction.
  • the first optical element preferably comprises at least one face having an orientation such that the rays in the first direction are refracted in the second direction.
  • the second face can then carry a second optical element having a face essentially parallel to said face of the first optical element in said plane.
  • the second face includes a holographic device for straightening the beam in the second direction.
  • the optical elements are preferably symmetrical in revolution around the main axis and the second direction is directed essentially along the main axis.
  • the optical elements are able to straighten the rays from the source by refraction.
  • the optical elements each have a face capable of reflecting the rays coming from the source in the first direction.
  • the essentially parallel rays make an angle less than or equal to 3 ° with the first direction.
  • said first direction makes an angle greater than or equal to 10 ° with said second direction.
  • the invention proposes to use the optical plate in a screen of a projection display device also comprising means for generation of an image and means of projecting the image onto the screen.
  • the screen can also include optical focusing and / or scattering elements.
  • the projection means are such that the rays are received by the optical plate with angles of incidence relative to the general direction of the optical plate varying over a continuous range of non-zero orientations relative to Principal tax and the first direction corresponds to one of the orientations of said continuous range. 4. List of figures.
  • FIG. 1 shows an example of a display device to which the invention applies;
  • - Figure 2 shows the screen of Figure 1 using a first embodiment of the invention;
  • - Figure 3 shows a detail of Figure 2;
  • - Figure 4 shows the screen of Figure 1 using a second embodiment of the invention;
  • - Figure 5 shows a detail of Figure 4. 5.
  • the display device schematically represented in FIG. 1 comprises an illumination system 2 which generates a primary light beam B received by an imager (or valve) 4.
  • the imager 4 determines which parts of the primary beam Bm must be transmitted to an imaging system, thus creating a secondary light beam B img which represents the image to be displayed.
  • the imager 4 is for example produced in the form of a matrix of pixels. Each pixel acts on the incident ray (part of the beam primary Bm) as a function of the intensity at which the corresponding pixel in the image to be displayed must be lit.
  • the light from the imager 4 is projected by an imaging system 6 towards a display screen 10.
  • the rays incident on the screen 10 have an angle d incidence which varies by an angle ⁇ i (of the order of
  • FIG. 2 A first embodiment of the screen 10 according to the invention is shown in FIG. 2.
  • the screen 10 comprises an optical plate 12 whose function is to collimate the incident beam Ri into a beam Rc essentially parallel to a main axis AA .
  • the main axis AA ′ is horizontal and perpendicular to the plane defined by the optical plate 12.
  • the optical plate 12 comprises on its first face (face which receives light from the source, this is i.e. optical motor here) of first prismatic elements 14 and, on its second face
  • the optical plate 12 is symmetrical in revolution around the main axis AA ′ (output axis of the optical engine) and FIG. 2 represents a section along a plane containing the main axis AA ′, here the vertical plane containing l 'main axis AA'.
  • the first prismatic elements 14 straighten the incident beam Ri into a beam generally parallel to a different first direction Rmt from the direction of the main axis AA '.
  • the direction Rj nt therefore depends on the plane containing the main axis considered.
  • the incident ray Ri is refracted into a radius Rjnt which forms with the main axis AA ′ a fixed angle ⁇ in t, as will be explained in detail below with reference to FIG. 3.
  • the angle ⁇ mt can vary according to an amplitude of 3 ° ( ⁇ in is equal to a fixed value plus or minus 3 °).
  • the second prismatic elements 16 are therefore designed such that they straighten the beam Rjn t essentially parallel (that is to say preferably parallel to a determined direction with an uncertainty of more or less 3 °, the beam Rjn t being at l 'interior of the material of the optical plate) (in each plane containing the main axis AA') in a beam Rc in a second direction essentially parallel to the main axis AA '(that is to say preferably parallel to l main axis with an uncertainty of plus or minus 5 °, the beam Rc being outside the material of the optical plate).
  • the second prismatic elements are therefore identical whatever the height on the plate 12 (that is to say whatever the distance from the main axis AA ′ of the second prismatic element 16 considered).
  • the angle between the first direction and the second direction is greater than or equal to 10 ° and even more preferably 15 °.
  • the collimated beam R c at the outlet of the optical plate 12 falls on a set 18 of focusing elements 20 which allow the passage of the beam through a dark matrix 22, which allows an improvement of the contrast.
  • the focusing elements 20 generally also allow vertical and horizontal diffusion of the beam in order to project the images in a sufficient solid angle.
  • Other optical elements can naturally be provided to modify the optical characteristics of the beam, for example at the level of the dark matrix 22.
  • first and a second prismatic element 14, 16 The detail of a first and a second prismatic element 14, 16 is given in FIG. 3 in section in the vertical plane containing the main axis AA '.
  • the first prismatic element 14 has a first optically active face 24 which forms an angle ⁇ with the general direction of the plate 18, that is to say here with the vertical.
  • a ray Ri incident on the optical plate 12 with an angle ⁇ (angle formed with the main axis AA ') will be refracted by the first face 24 inside the optical plate 12 in the form of a ray R in t in a first direction which forms with the main axis a fixed angle ⁇ mt, and therefore in particular independent of ⁇ .
  • the angle between the first direction and the second direction is greater than or equal to 10 °.
  • the second direction R c is directed along the main axis AA' and therefore constant in all the planes containing this axis, that is to say on the whole plate.
  • the second face 30 of the second prismatic element 16 is not optically active and is therefore determined so as to obtain the least sharp prisms possible to facilitate their realization, for example by forming an angle ⁇ with the main axis AA 'close to , or even equal to, ⁇ in t.
  • a second embodiment of the screen 10 is shown in Figure 4.
  • the screen 10 here also includes an optical plate 32 whose function is to collimate the incident beam Ri into a beam Rc essentially parallel to the main axis AA '.
  • the optical plate 32 for this purpose comprises on its first face of first prismatic elements 34 and on its second face of second prismatic elements 36.
  • the optical plate 32 is also symmetrical of revolution around the 'main axis AA' (optical motor output axis) and Figure 4 shows a section along a plane containing the main axis AA ', here the vertical plane containing the main axis AA'.
  • the first prismatic elements 34 straighten in each plane containing the main axis AA ′ the incident beam Ri into a beam generally parallel to a first direction Rj n t (that is to say preferably parallel at a determined direction with an uncertainty of plus or minus 3 °, the beam Rj n t being inside the material of the optical plate) different from the direction of the main axis AA '.
  • the direction Rint therefore depends on the plane containing the main axis considered.
  • the angle between the first direction and the direction of the main axis is greater than or equal to 10 °.
  • the incident ray Ri is refracted then reflected in a radius R int which forms with the main axis AA ′ a fixed angle ⁇ in t , here negative, as will be explained in detail below with reference to FIG. 5.
  • the second prismatic elements 36 are therefore designed as they straighten the beam R in t essentially parallel (in each plane containing the main axis AA ') in a beam R c in a second direction essentially parallel to the main axis AA' (that is to say preferably parallel to l main axis with an uncertainty of more or less 5 °, the beam Rc being outside the material of the optical plate).
  • the second prismatic elements are therefore identical whatever the height on the plate 32 (that is to say whatever the distance from the main axis AA ′ of the second prismatic element 36 considered).
  • the detail of a first and a second prismatic element 34, 36 is given in FIG. 5 in section in the vertical plane containing the main axis AA ′.
  • the first prismatic element 34 has a first face 38 and a second face 40.
  • a ray Ri incident on the optical plate 12 with an angle ⁇ (angle formed with the main axis AA ') is refracted by the second face 40 to the interior of the optical plate 12 in the form of a radius R R directed towards the first face 38; the first face 38 reflects this radius R R into a radius Rjnt in a first direction which forms with the main axis a fixed angle ⁇ in t non-zero, and therefore in particular independent of ⁇ .
  • the second prismatic element 36 has a first optically active face 42 which forms a non-zero angle with the general direction of the plate 12 (here with the vertical).
  • the second prismatic element 36 straightens by refraction the beam Rjnt internal to the plate directed in the first direction into a collimated beam R c in a second direction essentially parallel to the main axis AA '.
  • the second face 44 of the second prismatic element 36 is not optically active and is therefore determined so as to obtain the least sharp prisms possible to facilitate their production.
  • the second face 44 is therefore preferably oriented parallel to the main axis AA '.
  • the invention is naturally not limited to the embodiments described above.
  • the means for straightening the internal beam Rjnt into a collimated beam along the main axis can for example be produced by a holographic surface on the second face of the optical plate.
  • the holographic structure notably comprises a structure with pseudo-periodic variation of the optical index. This solution is also particularly advantageous thanks to the parallelism of the internal rays Rj n t in the plate in each plane containing the main axis.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Overhead Projectors And Projection Screens (AREA)

Abstract

The invention relates to an optical plate (12), in particular in a screen for a projection displaying device comprising on the first face thereof, optical elements (14) for erecting rays received from a light source in the form of a beam of rays in a first direction on the plane of a main axis (AA'). A second face (16) is embodied in such a way that it erects the beam in a second direction which differs from the first direction, preferably along the main axis (AA').

Description

ECRAN DE RETROPROJECTION BACK PROJECTION SCREEN
1. Domaine de l'invention. L'invention concerne une plaque optique et un dispositif d'affichage à projection utilisant une telle plaque. 2. Etat de l'art. Il est bien connu d'utiliser en optique une lentille de Fresnel pour obtenir un effet général de collimation avec une épaisseur de lentille réduite. Ainsi, afin de collimater un faisceau incident émis par une source de lumière, la lentille comporte des éléments prismatiques qui redressent les rayons reçus de la source en un faisceau de rayons parallèles. Comme cela est décrit dans la demande de brevet publiée sous la référence JP 2002-221 605, les éléments prismatiques sont conçus pour redresser les rayons incidents soit par réfraction (angle d'incidence faible), soit par réflexion (angle d'incidence élevé). De telles lentilles sont par exemple utilisées dans un dispositif d'affichage à projection. En effet, dans un tel dispositif, un imageur de taille réduite est projeté sur un écran de visualisation par un système de projection, avec des angles d'incidence sur l'écran qui s'étendent sur une plage déterminée de valeurs, par exemple de 30° à 60°. Le flux reçu du système de projection doit donc être globalement collimaté par une lentille de Fresnel, c'est-à-dire redressé selon une direction horizontale, avant d'être généralement micro-focalisé à travers une matrice sombre puis diffusé dans le champ d'observation souhaité. L'efficacité optique (ou rendement) des éléments prismatiques de la lentille de Fresnel est toutefois médiocre sous certaines incidences, et notamment pour des angles d'incidence de 20° à 40°. En effet, de tels angles ne permettent un bon rendement ni par réflexion ni par réfraction pour des structures prismatiques situées sur la face incidente. 3. Résumé de l'invention. Afin notamment de résoudre ce problème, l'invention propose d'utiliser à la place de la lentille de Fresnel une plaque optique comportant sur une première face un premier ensemble d'au moins deux éléments optiques apte à redresser des rayons reçus d'une source lumineuse en un faisceau de rayons essentiellement parallèles à une première direction dans un plan contenant un axe principal, avec des moyens sur la seconde face pour redresser ledit faisceau selon une seconde direction différente de la première direction. Selon une solution possible, la seconde face porte au moins un premier élément optique pour redresser le faisceau selon la seconde direction. Dans ce cas, le premier élément optique comporte de manière préférée au moins une face ayant une orientation telle que les rayons selon la première direction sont réfractés selon la seconde direction. De façon avantageuse, la seconde face peut alors porter un second élément optique ayant une face essentiellement parallèle à ladite face du premier élément optique dans ledit plan. Selon une autre solution possible, la seconde face comporte un dispositif holographique pour redresser le faisceau selon la seconde direction. De manière générale, les éléments optiques sont de préférence symétriques de révolution autour de l'axe principal et la seconde direction est dirigée essentiellement selon l'axe principal. Dans un premier mode de réalisation, les éléments optiques sont aptes à redresser les rayons issus de la source par réfraction. Dans un second mode de réalisation, les éléments optiques comportent chacun une face apte à réfléchir les rayons issus de la source selon la première direction. Selon une caractéristique préférée, les rayons essentiellement parallèles, font un angle inférieur ou égal à 3° avec la première direction. Avantageusement, ladite première direction fait un angle supérieur ou égal à 10°avec ladite seconde direction. L'invention propose d'utiliser la plaque optique dans un écran d'un dispositif d'affichage à projection comprenant également des moyens de génération d'une image et des moyens de projection de l'image sur l'écran. L'écran peut également comporter des éléments optiques de focalisation et/ou de diffusion. Selon une construction particulièrement avantageuse, les moyens de projection sont tels que les rayons sont reçus par la plaque optique avec des angles d'incidence par rapport à la direction générale de la plaque optique variant sur une plage continue d'orientations non nulles par rapport à Taxe principal et la première direction correspond à l'une des orientations de ladite plage continue. 4. Liste des figures. D'autres caractéristiques de l'invention apparaîtront à la lumière de la description suivante faite en référence aux dessins annexés dans lesquels : - la figure 1 représente un exemple de dispositif d'affichage auquel s'applique l'invention ; - la figure 2 représente l'écran de la figure 1 utilisant un premier mode de réalisation de l'invention ; - la figure 3 représente un détail de la figure 2 ; - la figure 4 représente l'écran de la figure 1 utilisant un second mode de réalisation de l'invention ; - la figure 5 représente un détail de la figure 4. 5. Description détaillée de l'invention. Le dispositif d'affichage schématiquement représenté à la figure 1 comprend un système d'éclairement 2 qui génère un faisceau de lumière primaire B reçu par un imageur (ou valve) 4. L'imageur 4 détermine quelles parties du faisceau primaire Bm doivent être transmises à un système d'imagerie, créant ainsi un faisceau de lumière secondaire Bimg qui représente l'image à afficher. L'imageur 4 est par exemple réalisé sous forme d'une matrice de pixels. Chaque pixel agit sur le rayon incident (partie du faisceau primaire Bm) en fonction de l'intensité à laquelle le pixel correspondant dans l'image à afficher doit être éclairé. La lumière issue de l'imageur 4 est projetée par un système d'imagerie 6 en direction d'un écran d'affichage 10. Dans l'exemple représenté sur la figure 1, les rayons incidents sur l'écran 10 ont un angle d'incidence qui varie d'un angle Θi (de l'ordre de1. Field of the invention. The invention relates to an optical plate and a projection display device using such a plate. 2. State of the art. It is well known to use a Fresnel lens in optics to obtain a general collimation effect with a reduced lens thickness. Thus, in order to collimate an incident beam emitted by a light source, the lens comprises prismatic elements which straighten the rays received from the source into a beam of parallel rays. As described in the patent application published under the reference JP 2002-221 605, the prismatic elements are designed to straighten the incident rays either by refraction (low angle of incidence) or by reflection (high angle of incidence) . Such lenses are for example used in a projection display device. In fact, in such a device, a reduced size imager is projected onto a display screen by a projection system, with angles of incidence on the screen which extend over a determined range of values, for example of 30 ° to 60 °. The flux received from the projection system must therefore be globally collimated by a Fresnel lens, that is to say rectified in a horizontal direction, before being generally micro-focused through a dark matrix and then diffused in the field d observation desired. The optical efficiency (or yield) of the prismatic elements of the Fresnel lens is however poor under certain incidences, and in particular for angles of incidence of 20 ° to 40 °. Indeed, such angles do not allow a good yield either by reflection or by refraction for prismatic structures located on the incident face. 3. Summary of the invention. In particular in order to solve this problem, the invention proposes using an optical plate in place of the Fresnel lens, comprising on a first face a first set of at least two optical elements capable of straightening rays received from a light source into a beam of rays essentially parallel to a first direction in a plane containing a main axis, with means on the second face for straightening said beam in a second direction different from the first direction. According to a possible solution, the second face carries at least a first optical element for straightening the beam in the second direction. In this case, the first optical element preferably comprises at least one face having an orientation such that the rays in the first direction are refracted in the second direction. Advantageously, the second face can then carry a second optical element having a face essentially parallel to said face of the first optical element in said plane. According to another possible solution, the second face includes a holographic device for straightening the beam in the second direction. In general, the optical elements are preferably symmetrical in revolution around the main axis and the second direction is directed essentially along the main axis. In a first embodiment, the optical elements are able to straighten the rays from the source by refraction. In a second embodiment, the optical elements each have a face capable of reflecting the rays coming from the source in the first direction. According to a preferred characteristic, the essentially parallel rays, make an angle less than or equal to 3 ° with the first direction. Advantageously, said first direction makes an angle greater than or equal to 10 ° with said second direction. The invention proposes to use the optical plate in a screen of a projection display device also comprising means for generation of an image and means of projecting the image onto the screen. The screen can also include optical focusing and / or scattering elements. According to a particularly advantageous construction, the projection means are such that the rays are received by the optical plate with angles of incidence relative to the general direction of the optical plate varying over a continuous range of non-zero orientations relative to Principal tax and the first direction corresponds to one of the orientations of said continuous range. 4. List of figures. Other characteristics of the invention will appear in the light of the following description made with reference to the appended drawings in which: - Figure 1 shows an example of a display device to which the invention applies; - Figure 2 shows the screen of Figure 1 using a first embodiment of the invention; - Figure 3 shows a detail of Figure 2; - Figure 4 shows the screen of Figure 1 using a second embodiment of the invention; - Figure 5 shows a detail of Figure 4. 5. Detailed description of the invention. The display device schematically represented in FIG. 1 comprises an illumination system 2 which generates a primary light beam B received by an imager (or valve) 4. The imager 4 determines which parts of the primary beam Bm must be transmitted to an imaging system, thus creating a secondary light beam B img which represents the image to be displayed. The imager 4 is for example produced in the form of a matrix of pixels. Each pixel acts on the incident ray (part of the beam primary Bm) as a function of the intensity at which the corresponding pixel in the image to be displayed must be lit. The light from the imager 4 is projected by an imaging system 6 towards a display screen 10. In the example shown in FIG. 1, the rays incident on the screen 10 have an angle d incidence which varies by an angle Θi (of the order of
10°) dans sa partie inférieure à un angle Θ2 (de l'ordre de 60°) dans sa partie supérieure. Dans la suite, on dénommera moteur optique l'ensemble des éléments qui génère le faisceau destiné à l'écran 10, à savoir ici l'ensemble comprenant le système d'éclairement 2, l'imageur 4 et le système d'imagerie 6. Un premier mode de réalisation de l'écran 10 selon l'invention est représenté en figure 2. L'écran 10 comprend une plaque optique 12 dont la fonction est de collimater le faisceau incident Ri en un faisceau Rc essentiellement parallèle à un axe principal AA'. (En général, l'axe principal AA' est horizontal et perpendiculaire au plan défini par la plaque optique 12.) Pour ce faire, la plaque optique 12 comprend sur sa première face (face qui reçoit la lumière de la source, c'est-à-dire ici du moteur optique) de premiers éléments prismatiques 14 et, sur sa seconde face10 °) in its lower part at an angle Θ 2 (of the order of 60 °) in its upper part. In the following, an optical engine will be called the set of elements which generate the beam intended for the screen 10, namely here the set comprising the illumination system 2, the imager 4 and the imaging system 6. A first embodiment of the screen 10 according to the invention is shown in FIG. 2. The screen 10 comprises an optical plate 12 whose function is to collimate the incident beam Ri into a beam Rc essentially parallel to a main axis AA . (In general, the main axis AA ′ is horizontal and perpendicular to the plane defined by the optical plate 12.) To do this, the optical plate 12 comprises on its first face (face which receives light from the source, this is i.e. optical motor here) of first prismatic elements 14 and, on its second face
(face de sortie de la lumière, donc dirigée vers les éléments de focalisation mentionnés ci-dessous), de seconds éléments prismatiques(light exit face, therefore directed towards the focusing elements mentioned below), second prismatic elements
16. La plaque optique 12 est symétrique de révolution autour de l'axe principal AA' (axe de sortie du moteur optique) et la figure 2 représente une section selon un plan contenant l'axe principal AA', ici le plan vertical contenant l'axe principal AA'. Dans chaque plan contenant l'axe principal AA', les premiers éléments prismatiques 14 redressent le faisceau incident Ri en un faisceau globalement parallèle à une première direction Rmt différente de la direction de l'axe principal AA'. (La direction Rjnt dépend donc du plan contenant l'axe principal considéré.) Ainsi, quel que soit l'angle d'incidence θ sur le premier élément prismatique 14 (c'est-à-dire quelle que soit la hauteur du premier élément prismatique 14 sur la plaque 12), le rayon incident Ri est réfracté en un rayon Rjnt qui forme avec l'axe principal AA' un angle θint fixe, comme cela sera expliqué en détail plus loin en référence à la figure 3. Selon une variante de réalisation, compte-tenu des incertitudes de réalisation, l'angle θmt peut varier suivant une amplitude de 3° (θin est égal à une valeur fixe plus ou moins 3°). Les seconds éléments prismatiques 16 sont donc conçus tels qu'ils redressent le faisceau Rjnt essentiellement parallèle (c'est-à-dire préférentiellement parallèle à une direction déterminée avec une incertitude de plus ou moins 3°, le faisceau Rjnt étant à l'intérieur du matériau de la plaque optique) (dans chaque plan contenant l'axe principal AA') en un faisceau Rc selon une seconde direction essentiellement parallèle à l'axe principal AA' (c'est-à-dire préférentiellement parallèle à l'axe principal avec une incertitude de plus ou moins 5°, le faisceau Rc étant à l'extérieur du matériau de la plaque optique). Les seconds éléments prismatiques sont donc identiques quelle que soit la hauteur sur la plaque 12 (c'est-à-dire quel que soit l'éloignement de l'axe principal AA' du second élément prismatique 16 considéré). Préférentiellement, l'angle entre la première direction et la seconde direction est supérieur ou égal à 10°et encore plus préférentiellement à 15°. Le faisceau collimaté Rc en sortie de la plaque optique 12 tombe sur un ensemble 18 d'éléments de focalisation 20 qui permettent le passage du faisceau à travers une matrice sombre 22, ce qui permet une amélioration du contraste. Les éléments de focalisation 20 permettent en général également une diffusion verticale et horizontale du faisceau afin de projeter les images dans un angle solide suffisant. D'autres éléments optiques peuvent naturellement être prévus pour modifier les caractéristiques optiques du faisceau, par exemple au niveau de la matrice sombre 22. Le détail d'un premier et d'un second éléments prismatiques 14, 16 est donné en figure 3 en section dans le plan vertical contenant l'axe principal AA'. Le premier élément prismatique 14 comporte une première face 24 optiquement active qui forme un angle α avec la direction générale de la plaque 18, c'est-à-dire ici avec la verticale. Comme précédemment décrit, un rayon Ri incident sur la plaque optique 12 avec un angle θ (angle formé avec l'axe principal AA') sera réfracté par la première face 24 à l'intérieur de la plaque optique 12 sous forme d'un rayon Rint selon une première direction qui forme avec l'axe principal un angle θmt fixe, et donc notamment indépendant de θ. D'après les lois de la réfraction, on a donc pour une plaque optique d'indice n : sin(θ - α) = n.sin(θint - α) ce qui donne en développant : α = atan( n-sinθ^ - sinθ ) . n.cosθint - cosθ On choisit de préférence θin de telle sorte que l'angle d'incidence effectif (θ - α) sur la première face 24 reste faible sur l'ensemble de la plaque pour obtenir un bon rendement en réfraction des premiers éléments 14. C'est notamment le cas lorsque l'on choisi θin dans la plage des angles d'incidence, soit entre Θi et Θ2, par exemple La seconde face 28 du premier élément prismatique 14, qui forme un angle β avec la direction de l'axe principal AA', n'est pas optiquement active et devra donc intercepter le moins de rayons lumineux possibles. Dans la partie où θ est inférieur à θint/ on prendra donc de préférence β proche de θ et/ou θint (pour éviter l'interception de rayons par la face 28 à l'intérieur ou à l'extérieur de la plaque optique 12). Naturellement, β n'est pas nécessairement constant sur la plaque 12 ; on peut prendre par exemple pour chaque premier élément prismatique 14 : β = θ. Une solution alternative est d'utiliser pour l'ensemble des prismes considérés précisément β = θint. Ces solutions sont notamment intéressantes dans le cas mentionné ci-dessus (θιnt entre Θi et Θ2) où θ est proche de θjn sur toute la hauteur de la plaque 12. Pour la partie où θ est supérieur à Q-mtf on prendra par exemple la face 28 suivant AA' (β=3°). Le second élément prismatique 16 comporte une première face 26 optiquement active qui forme un angle γ avec la direction générale de la plaque 12 (ici avec la verticale). Comme vu précédemment, le second élément prismatique 16, et donc sa première face 26, redresse par réfraction le faisceau Rint interne à la plaque dirigé selon la première direction en un faisceau collimate Rc selon une seconde direction essentiellement parallèle à l'axe principal AA' (c'est-à-dire préférentiellement parallèle à l'axe principal avec une incertitude de plus ou moins 5°, le faisceau Rc étant à l'extérieur du matériau de la plaque optique). Préférentiellement, l'angle entre la première direction et la seconde direction est supérieur ou égal à 10°. D'après les lois de la réfraction on a donc : sin γ = n.sin(γ - θint) et γ est ainsi défini par : . , n.sinθin). γ = atan( ^ — ) . n.cosθint -1 On peut remarquer que, bien que la première direction Rjnt ne soit constante que dans chaque plan contenant l'axe principal AA', la seconde direction Rc est dirigée selon l'axe principal AA' et donc constante dans tous les plans contenant cet axe, c'est-à-dire sur toute la plaque. La seconde face 30 du second élément prismatique 16 n'est pas optiquement active et est donc déterminée de manière à obtenir des prismes le moins aigus possibles pour faciliter leur réalisation, par exemple en formant un angle δ avec l'axe principal AA' proche de, voire égal à, θint. Un seconde mode de réalisation de l'écran 10 est représenté en figure 4. Sur cette figure, les éléments qui sont identiques à ceux présents dans le premier mode de réalisation (figure 2) portent les mêmes références et ne seront pas décrits à nouveau. L'écran 10 comprend ici également une plaque optique 32 dont la fonction est de collimater le faisceau incident Ri en un faisceau Rc essentiellement parallèle à l'axe principal AA'. Comme dans le premier mode de réalisation, la plaque optique 32 comprend à cet effet sur sa première face de premiers éléments prismatiques 34 et sur sa seconde face de seconds éléments prismatiques 36. La plaque optique 32 est elle-aussi symétrique de révolution autour de l'axe principal AA' (axe de sortie du moteur optique) et la figure 4 représente une section selon un plan contenant l'axe principal AA', ici le plan vertical contenant l'axe principal AA'. Comme pour le premier mode de réalisation, les premiers éléments prismatiques 34 redressent dans chaque plan contenant l'axe principal AA' le faisceau incident Ri en un faisceau globalement parallèle à une première direction Rjnt (c'est -à-dire préférentiellement parallèle à une direction déterminée avec une incertitude de plus ou moins 3°, le faisceau Rjnt étant à l'intérieur du matériau de la plaque optique) différente de la direction de l'axe principal AA'. (La direction Rint dépend donc du plan contenant l'axe principal considéré.) Préférentiellement, l'angle entre la première direction et la direction de l'axe principal est supérieur ou égal à 10°. Ainsi, quel que soit l'angle d'incidence θ sur le premier élément prismatique 34 (c'est-à-dire quelle que soit la hauteur du premier élément prismatique 34 sur la plaque 32), le rayon incident Ri est réfracté puis réfléchi en un rayon Rint qui forme avec l'axe principal AA' un angle θint fixe, ici négatif, comme cela sera expliqué en détail plus loin en référence à la figure 5. Les seconds éléments prismatiques 36 sont donc conçus tels qu'ils redressent le faisceau Rint essentiellement parallèle (dans chaque plan contenant l'axe principal AA') en un faisceau Rc selon une seconde direction essentiellement parallèle à l'axe principal AA' (c'est-à-dire préférentiellement parallèle à l'axe principal avec une incertitude de plus ou moins 5°, le faisceau Rc étant à l'extérieur du matériau de la plaque optique). Les seconds éléments prismatiques sont donc identiques quelle que soit la hauteur sur la plaque 32 (c'est-à-dire quel que soit l'éloignement de l'axe principal AA' du second élément prismatique 36 considéré). Le détail d'un premier et d'un second éléments prismatiques 34, 36 est donné en figure 5 en section dans le plan vertical contenant l'axe principal AA'. Le premier élément prismatique 34 comporte une première face 38 et une seconde face 40. Un rayon Ri incident sur la plaque optique 12 avec un angle θ (angle formé avec l'axe principal AA') est réfracté par la seconde face 40 à l'intérieur de la plaque optique 12 sous forme d'un rayon RR dirigé vers la première face 38 ; la première face 38 réfléchit ce rayon RR en un rayon Rjnt selon une première direction qui forme avec l'axe principal un angle θint non nul fixe, et donc notamment indépendant de θ. Le second élément prismatique 36 comporte une première face 42 optiquement active qui forme un angle non nul avec la direction générale de la plaque 12 (ici avec la verticale). Comme vu précédemment, le second élément prismatique 36, et donc sa première face 42, redresse par réfraction le faisceau Rjnt interne à la plaque dirigé selon la première direction en un faisceau collimate Rc selon une seconde direction essentiellement parallèle à l'axe principal AA'. La seconde face 44 du second élément prismatique 36 n'est pas optiquement active et est donc déterminée de manière à obtenir des prismes le moins aigus possible pour faciliter leur réalisation. La seconde face 44 est donc de préférence orientée parallèlement à l'axe principal AA'. L'invention n'est naturellement pas limitée aux modes de réalisation décrits ci-dessus. Notamment, les moyens de redressement du faisceau interne Rjnt en un faisceau collimate selon l'axe principal peuvent par exemple être réalisés par une surface holographique sur la seconde face de la plaque optique. La structure holographique comprend notamment une structure avec variation pseudo périodique de l'indice optique. Cette solution est d'ailleurs particulièrement avantageuse grâce au parallélisme des rayons internes Rjnt dans la plaque dans chaque plan contenant l'axe principal. 16. The optical plate 12 is symmetrical in revolution around the main axis AA ′ (output axis of the optical engine) and FIG. 2 represents a section along a plane containing the main axis AA ′, here the vertical plane containing l 'main axis AA'. In each plane containing the main axis AA ′, the first prismatic elements 14 straighten the incident beam Ri into a beam generally parallel to a different first direction Rmt from the direction of the main axis AA '. (The direction Rj nt therefore depends on the plane containing the main axis considered.) Thus, whatever the angle of incidence θ on the first prismatic element 14 (that is to say whatever the height of the first prismatic element 14 on the plate 12), the incident ray Ri is refracted into a radius Rjnt which forms with the main axis AA ′ a fixed angle θ in t, as will be explained in detail below with reference to FIG. 3. According to an alternative embodiment, taking into account the uncertainties of implementation, the angle θmt can vary according to an amplitude of 3 ° (θin is equal to a fixed value plus or minus 3 °). The second prismatic elements 16 are therefore designed such that they straighten the beam Rjn t essentially parallel (that is to say preferably parallel to a determined direction with an uncertainty of more or less 3 °, the beam Rjn t being at l 'interior of the material of the optical plate) (in each plane containing the main axis AA') in a beam Rc in a second direction essentially parallel to the main axis AA '(that is to say preferably parallel to l main axis with an uncertainty of plus or minus 5 °, the beam Rc being outside the material of the optical plate). The second prismatic elements are therefore identical whatever the height on the plate 12 (that is to say whatever the distance from the main axis AA ′ of the second prismatic element 16 considered). Preferably, the angle between the first direction and the second direction is greater than or equal to 10 ° and even more preferably 15 °. The collimated beam R c at the outlet of the optical plate 12 falls on a set 18 of focusing elements 20 which allow the passage of the beam through a dark matrix 22, which allows an improvement of the contrast. The focusing elements 20 generally also allow vertical and horizontal diffusion of the beam in order to project the images in a sufficient solid angle. Other optical elements can naturally be provided to modify the optical characteristics of the beam, for example at the level of the dark matrix 22. The detail of a first and a second prismatic element 14, 16 is given in FIG. 3 in section in the vertical plane containing the main axis AA '. The first prismatic element 14 has a first optically active face 24 which forms an angle α with the general direction of the plate 18, that is to say here with the vertical. As previously described, a ray Ri incident on the optical plate 12 with an angle θ (angle formed with the main axis AA ') will be refracted by the first face 24 inside the optical plate 12 in the form of a ray R in t in a first direction which forms with the main axis a fixed angle θmt, and therefore in particular independent of θ. According to the laws of refraction, we therefore have for an optical plate of index n: sin (θ - α) = n.sin (θint - α) which gives by developing: α = atan ( n - sinθ ^ - sinθ ). n.cosθ int - cosθ We preferably choose θin in such a way that the effective angle of incidence (θ - α) on the first face 24 remains small on the whole of the plate to obtain a good refractive efficiency of the first elements 14. This is particularly the case when we choose θin in the range of angles of incidence, ie between entrei and Θ 2 , for example The second face 28 of the first prismatic element 14, which forms an angle β with the direction of the main axis AA ', is not optically active and must therefore intercept the fewest light rays possible. In the part where θ is less than θ in t / we will therefore preferably take β close to θ and / or θ int (to avoid interception of rays by the face 28 inside or outside of the optical plate 12). Naturally, β is not necessarily constant on the plate 12; one can take for example for each first prismatic element 14: β = θ. An alternative solution is to use for the set of prisms considered precisely β = θint. These solutions are particularly interesting in the case mentioned above (θ ιn t between Θi and Θ 2 ) where θ is close to θj n over the entire height of the plate 12. For the part where θ is greater than Q- m t f we will take for example the face 28 along AA '(β = 3 °). The second prismatic element 16 has a first optically active face 26 which forms an angle γ with the general direction of the plate 12 (here with the vertical). As seen previously, the second prismatic element 16, and thus its first face 26, rectified by the refraction beam R int internal to the plate directed along the first direction in a collimates Rc beam in a second direction substantially parallel to the main axis AA '(that is to say preferably parallel to the main axis with an uncertainty of more or less 5 °, the beam Rc being outside the material of the optical plate). Preferably, the angle between the first direction and the second direction is greater than or equal to 10 °. According to the laws of refraction we therefore have: sin γ = n.sin (γ - θ in t) and γ is thus defined by:. , n.sinθ in) . γ = atan (^ -). n.cosθ int -1 We can notice that, although the first direction Rjnt is constant only in each plane containing the main axis AA ', the second direction R c is directed along the main axis AA' and therefore constant in all the planes containing this axis, that is to say on the whole plate. The second face 30 of the second prismatic element 16 is not optically active and is therefore determined so as to obtain the least sharp prisms possible to facilitate their realization, for example by forming an angle δ with the main axis AA 'close to , or even equal to, θ in t. A second embodiment of the screen 10 is shown in Figure 4. In this figure, the elements which are identical to those present in the first embodiment (Figure 2) have the same references and will not be described again. The screen 10 here also includes an optical plate 32 whose function is to collimate the incident beam Ri into a beam Rc essentially parallel to the main axis AA '. As in the first embodiment, the optical plate 32 for this purpose comprises on its first face of first prismatic elements 34 and on its second face of second prismatic elements 36. The optical plate 32 is also symmetrical of revolution around the 'main axis AA' (optical motor output axis) and Figure 4 shows a section along a plane containing the main axis AA ', here the vertical plane containing the main axis AA'. As for the first embodiment, the first prismatic elements 34 straighten in each plane containing the main axis AA ′ the incident beam Ri into a beam generally parallel to a first direction Rj n t (that is to say preferably parallel at a determined direction with an uncertainty of plus or minus 3 °, the beam Rj n t being inside the material of the optical plate) different from the direction of the main axis AA '. (The direction Rint therefore depends on the plane containing the main axis considered.) Preferably, the angle between the first direction and the direction of the main axis is greater than or equal to 10 °. Thus, whatever the angle of incidence θ on the first prismatic element 34 (that is to say whatever the height of the first prismatic element 34 on the plate 32), the incident ray Ri is refracted then reflected in a radius R int which forms with the main axis AA ′ a fixed angle θin t , here negative, as will be explained in detail below with reference to FIG. 5. The second prismatic elements 36 are therefore designed as they straighten the beam R in t essentially parallel (in each plane containing the main axis AA ') in a beam R c in a second direction essentially parallel to the main axis AA' (that is to say preferably parallel to l main axis with an uncertainty of more or less 5 °, the beam Rc being outside the material of the optical plate). The second prismatic elements are therefore identical whatever the height on the plate 32 (that is to say whatever the distance from the main axis AA ′ of the second prismatic element 36 considered). The detail of a first and a second prismatic element 34, 36 is given in FIG. 5 in section in the vertical plane containing the main axis AA ′. The first prismatic element 34 has a first face 38 and a second face 40. A ray Ri incident on the optical plate 12 with an angle θ (angle formed with the main axis AA ') is refracted by the second face 40 to the interior of the optical plate 12 in the form of a radius R R directed towards the first face 38; the first face 38 reflects this radius R R into a radius Rjnt in a first direction which forms with the main axis a fixed angle θin t non-zero, and therefore in particular independent of θ. The second prismatic element 36 has a first optically active face 42 which forms a non-zero angle with the general direction of the plate 12 (here with the vertical). As seen above, the second prismatic element 36, and therefore its first face 42, straightens by refraction the beam Rjnt internal to the plate directed in the first direction into a collimated beam R c in a second direction essentially parallel to the main axis AA '. The second face 44 of the second prismatic element 36 is not optically active and is therefore determined so as to obtain the least sharp prisms possible to facilitate their production. The second face 44 is therefore preferably oriented parallel to the main axis AA '. The invention is naturally not limited to the embodiments described above. In particular, the means for straightening the internal beam Rjnt into a collimated beam along the main axis can for example be produced by a holographic surface on the second face of the optical plate. The holographic structure notably comprises a structure with pseudo-periodic variation of the optical index. This solution is also particularly advantageous thanks to the parallelism of the internal rays Rj n t in the plate in each plane containing the main axis.

Claims

REVENDICATIONS
1. Plaque optique (12 ; 32) comportant sur une première face un premier ensemble d'au moins deux éléments optiques (14 ; 34) apte à redresser des rayons (Ri) reçus d'une source lumineuse en un faisceau de rayons (Rint) essentiellement parallèles à une première direction dans un plan contenant un axe principal (AA'), caractérisée par des moyens (16 ; 36) sur la seconde face pour redresser ledit faisceau selon une seconde direction (Rc) différente de la première direction (Rint)-1. Optical plate (12; 32) comprising on a first face a first set of at least two optical elements (14; 34) capable of straightening rays (Ri) received from a light source into a beam of rays (Rint ) essentially parallel to a first direction in a plane containing a main axis (AA '), characterized by means (16; 36) on the second face for straightening said beam in a second direction (R c ) different from the first direction ( Rint) -
2. Plaque optique selon la revendication 1, dans laquelle la seconde face porte au moins un premier élément optique (16 ; 36) pour redresser le faisceau selon la seconde direction (Rc).2. Optical plate according to claim 1, in which the second face carries at least a first optical element (16; 36) for straightening the beam in the second direction (Rc).
3. Plaque optique selon la revendication 2, dans laquelle le premier élément optique (16 ; 36) comporte au moins une face (26 ; 42) ayant une orientation telle que les rayons selon la première direction (Rjnt) sont réfractés selon la seconde direction (Rc).3. Optical plate according to claim 2, in which the first optical element (16; 36) comprises at least one face (26; 42) having an orientation such that the rays in the first direction (Rj n t) are refracted according to the second direction (Rc).
4. Plaque optique selon la revendication 3, dans laquelle la seconde face porte un second élément optique ayant une face essentiellement parallèle à ladite face du premier élément optique dans ledit plan.4. Optical plate according to claim 3, in which the second face carries a second optical element having a face essentially parallel to said face of the first optical element in said plane.
5. Plaque optique selon la revendication 1, dans laquelle la seconde face comporte un dispositif holographique pour redresser le faisceau selon la seconde direction (Rc).5. Optical plate according to claim 1, in which the second face comprises a holographic device for straightening the beam in the second direction (R c ).
6. Plaque optique selon l'une des revendications 1 à 5, dans laquelle les éléments optiques (14 ; 34) sont symétriques de révolution autour de l'axe principal (AA') et dans laquelle la seconde direction (Rc) est dirigée essentiellement selon l'axe principal (AA').6. Optical plate according to one of claims 1 to 5, in which the optical elements (14; 34) are symmetrical in revolution around the main axis (AA ') and in which the second direction (R c ) is directed essentially along the main axis (AA').
7. Plaque optique selon l'une des revendications 1 à 6, dans laquelle les éléments optiques (14) sont aptes à redresser les rayons issus de la source par réfraction.7. Optical plate according to one of claims 1 to 6, wherein the optical elements (14) are able to straighten the rays from the source by refraction.
8. Plaque optique selon l'une des revendications 1 à 6, dans laquelle les éléments optiques (34) comportent chacun une face (38) apte à réfléchir les rayons (Ri) issus de la source selon la première direction8. Optical plate according to one of claims 1 to 6, in which the optical elements (34) each comprise a face (38) capable of reflecting the rays (Ri) coming from the source in the first direction
(Rint).(Rint).
9. Plaque optique selon l'une quelconque des revendications 1 à 8, caractérisé en ce que le premier ensemble d'au moins deux éléments optiques est apte à redresser des rayons reçus d'une source lumineuse en un faisceau de rayons faisant un angle inférieur ou égal à 3° avec la première direction.9. Optical plate according to any one of claims 1 to 8, characterized in that the first set of at least two optical elements is capable of straightening rays received from a light source into a beam of rays making a lower angle or equal to 3 ° with the first direction.
10. Plaque optique selon l'une quelconque des revendications 1 à 9, caractérisé en ce que la seconde direction fait un angle supérieur ou égal à 10° avec la première direction.10. Optical plate according to any one of claims 1 to 9, characterized in that the second direction makes an angle greater than or equal to 10 ° with the first direction.
11. Dispositif d'affichage à projection comprenant :11. Projection display device comprising:
- des moyens de génération d'une image (2, 4) ; - des moyens de projection (6) de l'image sur un écran (10) ;- means for generating an image (2, 4); - means for projecting (6) the image onto a screen (10);
- l'écran (10) comportant au moins une plaque optique (12 ; 32), dans lequel la plaque optique (12 ; 32) est conforme à l'une des revendications 1 à 8.- the screen (10) comprising at least one optical plate (12; 32), in which the optical plate (12; 32) conforms to one of claims 1 to 8.
12. Dispositif d'affichage selon la revendication 11, dans lequel les moyens de projection (6) sont tels que les rayons (Ri) sont reçus par la plaque optique (12) avec des orientations (θ) par rapport à la direction générale de la plaque optique (12) variant sur une plage continue d'orientations non nulles par rapport à l'axe principal (AA') et dans lequel la première direction (Rint) correspond à l'une (θint) des orientations de ladite plage continue. 12. Display device according to claim 11, in which the projection means (6) are such that the rays (Ri) are received by the optical plate (12) with orientations (θ) relative to the general direction of the optical plate (12) varying over a continuous range of non-zero orientations relative to the main axis (AA ') and in which the first direction (R in t) corresponds to one (θ in t) of the orientations of said continuous range.
EP05707748A 2004-01-07 2005-01-07 Overhead projection screen Withdrawn EP1702240A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR0450025A FR2864853A1 (en) 2004-01-07 2004-01-07 OPTICAL PLATE AND PROJECTION DISPLAY DEVICE USING SUCH PLATE
PCT/EP2005/050053 WO2005066711A1 (en) 2004-01-07 2005-01-07 Overhead projection screen

Publications (1)

Publication Number Publication Date
EP1702240A1 true EP1702240A1 (en) 2006-09-20

Family

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EP05707748A Withdrawn EP1702240A1 (en) 2004-01-07 2005-01-07 Overhead projection screen

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Country Link
US (1) US20090268169A1 (en)
EP (1) EP1702240A1 (en)
JP (1) JP2007518127A (en)
CN (1) CN1910514A (en)
FR (1) FR2864853A1 (en)
WO (1) WO2005066711A1 (en)

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4482206A (en) * 1983-04-21 1984-11-13 Rca Corporation Rear projection television screen having a multi-surface Fresnel lens
US4512631A (en) * 1983-04-21 1985-04-23 Rca Corporation Rear projection television screen incorporating a prism lens
JPS6333736A (en) * 1986-07-29 1988-02-13 Matsushita Electric Ind Co Ltd Transmission type screen
US5208620A (en) * 1988-10-04 1993-05-04 Canon Kabushiki Kaisha Display apparatus
JPH02153338A (en) * 1988-12-05 1990-06-13 Canon Inc Backproject type screen and backproject type image display device using it
US6483612B2 (en) * 1998-04-15 2002-11-19 Duke University Projection screen apparatus including holographic optical element
JP2002207254A (en) * 2001-01-09 2002-07-26 Nec Viewtechnology Ltd Back projection type image display device

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2005066711A1 *

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US20090268169A1 (en) 2009-10-29
FR2864853A1 (en) 2005-07-08
CN1910514A (en) 2007-02-07
JP2007518127A (en) 2007-07-05
WO2005066711A1 (en) 2005-07-21

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