WO2005069059A1 - Procede pour reduire le contraste de chatoiement dans une projection laser sur un ecran et ecran approprie pour une projection laser - Google Patents

Procede pour reduire le contraste de chatoiement dans une projection laser sur un ecran et ecran approprie pour une projection laser Download PDF

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Publication number
WO2005069059A1
WO2005069059A1 PCT/EP2004/014349 EP2004014349W WO2005069059A1 WO 2005069059 A1 WO2005069059 A1 WO 2005069059A1 EP 2004014349 W EP2004014349 W EP 2004014349W WO 2005069059 A1 WO2005069059 A1 WO 2005069059A1
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WO
WIPO (PCT)
Prior art keywords
layer
reflective layer
laser light
screen
transparent
Prior art date
Application number
PCT/EP2004/014349
Other languages
German (de)
English (en)
Inventor
Matthias Fahland
Nicolas Schiller
Christoph Rickers
Michael Vergöhl
Christian Von Kopylow
Original Assignee
Fraunhofer Gesellschaft zur Förderung der angewandten Forschung e.V.
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 Fraunhofer Gesellschaft zur Förderung der angewandten Forschung e.V. filed Critical Fraunhofer Gesellschaft zur Förderung der angewandten Forschung e.V.
Publication of WO2005069059A1 publication Critical patent/WO2005069059A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/48—Laser speckle optics

Definitions

  • the invention relates to a method for reducing the speckle contrast in a laser projection onto a screen and a screen for a laser projection.
  • speckle A major disadvantage of laser light with regard to its use as a light source for projectors, however, is the occurrence of so-called speckle. Speckle always occur when coherent radiation diffusely reflects from a surface and is then recorded by a detector with a finite aperture. In particular, the human eye can be understood as such a detector. The speckles overlap with the image information and impair the perceived image quality to a considerable extent. The impression of a granularity of an object illuminated with laser light is created. Speckle contrast is the ratio between the difference between brightness maxima and brightness minima and the average brightness value of a uniformly illuminated surface. The speckle contrast depends on various factors.
  • the parameters of a light source used such as wavelength and coherence length, play just as much a role as the structure of a reflecting screen and the aperture of a detector, for example a human eye. There are therefore several starting points for eliminating or reducing the speckle contrast in laser projection processes.
  • the speckle contrast can be adjusted both by adjustments to the light source, i.e. the laser, as well as adjustments to the projection surface and the detector. Since the eye serves as a detector in many cases, the last path is omitted.
  • a method is known from US 5,272,473 A in which a sound source is arranged on a screen.
  • the acoustic waves generated by the sound source pass through the screen, which is thus excited to vibrate.
  • the speckled laser light beams generate different speckle patterns which are averaged during the integration time of a detector and thus reduce the speckle contrast.
  • a disadvantage of this method has been found that, depending on the sound frequency and screen dimension, wave bellies and
  • JP 2000081602 A An alternative solution for preventing speckle effects is known from JP 2000081602 A.
  • a screen is used which comprises a liquid crystal material. If a high-frequency low-voltage signal is applied to this liquid crystal material, the liquid crystal molecules on which the laser light rays are reflected vibrate slightly at a frequency of over 60 Hz. The vibrating liquid crystal molecules in turn cause very quickly varying speckle patterns, which, by averaging them, reduce the speckle contrast.
  • a disadvantage of this solution is the rigidity of such screens. In applications where a flexible screen is required, liquid crystal screens cannot be used. Another disadvantage arises from the technologically related limited dimensions of liquid crystal picture walls. A contrast-enhancing coating of such picture walls, as described above, is also difficult to achieve.
  • an image wall which comprises at least one layer which is transparent to laser light and at least one layer which reflects the laser light, the reflective layer being designed to be flexible and the transparent layer having a higher rigidity than the reflective layer, so that laser light hitting the screen penetrates the transparent layer and is reflected on the surface of the at least one reflective layer of the screen, at least the surface structure of the reflective layer being changed over time during the projection process in such a way that a laser light beam hitting a point on the reflective layer is dependent on a time function is reflected in different directions.
  • the change in the surface structure of the reflective layer is to be understood in such a way that individual surface elements, which are each so small that they cannot be resolved as individual dots by a detector, are tilted in their alignment with the incident laser light. This tilting means that the angular distribution of the light beam reflected by a surface element is changed over time. Since the speckle phenomenon is due to the interference of wave trains of adjacent points on a screen, this locally limited, but distributed over the entire surface also changes the respective speckle pattern. The impression of a speckle when looking at the projection image is reduced if a sufficient number of different speckle patterns arise during the integration time of the detector. As a result, the detector, which can also be a human eye, perceives only an averaged brightness value and the disturbing granular brightness appearance disappears. In the case of a human eye, a sufficient number of speckle patterns must be generated within 50 ms, since the integration time for a human eye is of this order of magnitude.
  • the transparent layer can be rigid or, like the reflective layer, can be flexible, but in any case has a higher rigidity than the reflective layer.
  • the transparent layer can be designed as a substrate to which the flexible layer is applied.
  • the reflective layer also includes, for example, a flexible substrate with a reflective coating or a layer system consisting of different individual layers.
  • the reflective layer can also have a surface roughness that leads to a diffuse reflection of the light, similar to a conventional screen.
  • the surface structure of the reflective layer is changed with a suitable frequency in the range from 1 Hz to 100 Hz.
  • the frequency of change during a projection process is not necessarily to be kept constant but can vary in this range. Since a laser projection is created on an image wall by repeatedly scanning a surface element from a laser light beam within a unit of time (hereinafter referred to as scanning), it should be noted that there is no interference between the scanning frequency of the laser light beam and the frequency of change in the surface structure of the reflective layer. If both frequencies interfere, it is not possible to reduce the speckle effects.
  • the surface structure of the reflective layer is changed over the entire surface of the reflective layer in surface sections that are smaller than the resolution of a detector of the reflected laser light.
  • the surface structure of the reflective layer is changed by bending the reflective layer.
  • the reflective layer can be bent periodically, with a regular bending structure distributed over the surface of the reflecting layer, or with an irregular bending structure. It is only important that the entire surface area of the reflective layer, which is used for laser projection, is captured by the bending.
  • the reflective layer can be bent, for example, by exerting pressure or tension on the reflective layer at least.
  • spacer elements are arranged between the transparent layer and the reflecting layer.
  • the spacer elements create the space that a reflective layer needs over a transparent layer in order to bend the reflective layer Layer. Spacer elements are, however, not absolutely necessary if the transparent layer is also flexible and the reflective layer can be bent together with the transparent layer.
  • the reflective layer can be bent, for example, by pressing in the spacer elements.
  • spacer elements can also be rigid.
  • the bending of the reflective layer can be realized, for example, by exerting pressure on the reflective layer in areas between the spacer elements.
  • the deformation can also be caused by electrostatic forces.
  • the reflective layer is preferably coated on the back with a conductive material which serves as an electrode. When a voltage is applied between this and another electrode, a force can be exerted on the reflective layer. This also causes the reflective layer to bend as described above.
  • An additional possibility for reducing the speckle contrast is to arrange at least one partially transparent layer between the transparent layer and the reflecting layer of an image wall. Due to the resulting reflections of part of the laser light between the partially transparent layer and the reflecting layer, an additional tilting of the laser light rays ultimately reflected back through the transparent layer can be realized. Thereby arise within the integration period additional speckle patterns of a detector, which contribute to averaging the speckle brightness values within the integration time of the detector.
  • the reflective layer of a projection screen according to the invention is formed according to a known procedure as a layer system consisting of several individual layers in such a way that preferably the discrete wavelengths of the three primary colors red, green and blue emitted by laser remit to a detector, light rays originating from extraneous light however, are not remitted to the detector. This can increase the contrast of a laser projection.
  • FIG. 1 shows a schematic sectional view through a screen according to the invention in the idle state
  • FIG. 2 shows a schematic sectional view through the screen according to FIG. 1 in a working state
  • FIG. 3 shows a schematic sectional view through an alternative screen according to the invention.
  • FIG. 1 An advantageous embodiment of a screen 1 according to the invention is shown schematically in FIG. 1 as a section.
  • the image wall 1 comprises a layer 2 which is transparent to laser light, a layer 3 which reflects the laser light and a piezoelectric layer 4 which is in direct contact with the reflecting layer 3.
  • the transparent layer 2, which, like the reflective layer 3, is flexible, has a higher rigidity than the reflective layer 3 and fulfills the function of a holding plate.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Overhead Projectors And Projection Screens (AREA)

Abstract

L'invention concerne un procédé permettant de réduire le contraste de chatoiement lors de la projection de lumière laser sur un écran, ainsi qu'un écran approprié pour une projection laser, qui comprend au moins une couche transparente à la lumière laser (2) et au moins une couche réfléchissant la lumière laser (3). La couche réfléchissante (3) est conçue de manière souple et la couche transparente (2) présente une plus grande rigidité que la couche réfléchissante (3), de sorte que la lumière laser qui arrive sur l'écran traverse la couche transparente (2) et soit réfléchie sur la surface de la couche réfléchissante (3) (au moins au nombre de une) de l'écran (1). Au moins la structure superficielle de la couche réfléchissante (3) est modifiée temporairement pendant le processus de projection, de sorte qu'un faisceau de lumière laser arrivant sur un point de la couche réfléchissante (3) soit réfléchi en fonction d'une fonction temporelle dans différentes directions.
PCT/EP2004/014349 2004-01-19 2004-12-16 Procede pour reduire le contraste de chatoiement dans une projection laser sur un ecran et ecran approprie pour une projection laser WO2005069059A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102004002685 2004-01-19
DE102004002685.8 2004-01-19

Publications (1)

Publication Number Publication Date
WO2005069059A1 true WO2005069059A1 (fr) 2005-07-28

Family

ID=34778087

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2004/014349 WO2005069059A1 (fr) 2004-01-19 2004-12-16 Procede pour reduire le contraste de chatoiement dans une projection laser sur un ecran et ecran approprie pour une projection laser

Country Status (1)

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WO (1) WO2005069059A1 (fr)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4143943A (en) * 1977-02-17 1979-03-13 Xerox Corporation Rear projection screen system
JPS5565940A (en) * 1978-11-13 1980-05-17 Matsushita Electric Ind Co Ltd Laser image display device
US5272473A (en) * 1989-02-27 1993-12-21 Texas Instruments Incorporated Reduced-speckle display system
EP1260850A1 (fr) * 2001-05-25 2002-11-27 EADS Deutschland Gmbh Méthode et dispositif pour éliminer des perturbations stationnaires d'images pendant la projection d'images avec la lumière cohérente en temps ou dans l'espace et système de projection d'images
WO2003054624A1 (fr) * 2001-12-12 2003-07-03 Rheinmetall Defence Electronics Gmbh Ecran de projection destine a la projection d'images
JP2003262920A (ja) * 2002-03-07 2003-09-19 Seiko Epson Corp 背面投写型表示装置

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4143943A (en) * 1977-02-17 1979-03-13 Xerox Corporation Rear projection screen system
JPS5565940A (en) * 1978-11-13 1980-05-17 Matsushita Electric Ind Co Ltd Laser image display device
US5272473A (en) * 1989-02-27 1993-12-21 Texas Instruments Incorporated Reduced-speckle display system
EP1260850A1 (fr) * 2001-05-25 2002-11-27 EADS Deutschland Gmbh Méthode et dispositif pour éliminer des perturbations stationnaires d'images pendant la projection d'images avec la lumière cohérente en temps ou dans l'espace et système de projection d'images
WO2003054624A1 (fr) * 2001-12-12 2003-07-03 Rheinmetall Defence Electronics Gmbh Ecran de projection destine a la projection d'images
JP2003262920A (ja) * 2002-03-07 2003-09-19 Seiko Epson Corp 背面投写型表示装置

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 004, no. 107 (P - 021) 31 July 1980 (1980-07-31) *
PATENT ABSTRACTS OF JAPAN vol. 2003, no. 12 5 December 2003 (2003-12-05) *

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