WO1996003670A1 - An apparatus for displaying an image - Google Patents

An apparatus for displaying an image Download PDF

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Publication number
WO1996003670A1
WO1996003670A1 PCT/GB1995/001658 GB9501658W WO9603670A1 WO 1996003670 A1 WO1996003670 A1 WO 1996003670A1 GB 9501658 W GB9501658 W GB 9501658W WO 9603670 A1 WO9603670 A1 WO 9603670A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical element
image
reflective surface
mirror
converging
Prior art date
Application number
PCT/GB1995/001658
Other languages
French (fr)
Inventor
Ian Alexander Shanks
Christoph Dobrusskin
Original Assignee
Central Research Laboratories Limited
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 Central Research Laboratories Limited filed Critical Central Research Laboratories Limited
Publication of WO1996003670A1 publication Critical patent/WO1996003670A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G02B17/02—Catoptric systems, e.g. image erecting and reversing system
    • G02B17/06—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror
    • G02B17/0605—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror using two curved mirrors
    • G02B17/0621—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror using two curved mirrors off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B30/00—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images
    • G02B30/50—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images the image being built up from image elements distributed over a 3D volume, e.g. voxels
    • G02B30/56—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images the image being built up from image elements distributed over a 3D volume, e.g. voxels by projecting aerial or floating images
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G02B5/09—Multifaceted or polygonal mirrors, e.g. polygonal scanning mirrors; Fresnel mirrors

Definitions

  • This invention relates to an apparatus for displaying an image, comprising a converging first optical element and a further optical element, each optical element comprising a reflective surface facing the other optical element and being arranged such that light rays from an object or first image are reflected from a reflective surface of a given optical element towards a reflective surface of the other optical element, and from the reflective surface of the other optical element towards the reflective surface of the given optical element, thereby forming a real second image being suspended in space, the reflective surface of the further optical element being at least a portion of a surface of revolution of a straight line about an axis.
  • a first object of the present invention is to provide an apparatus as defined in the first paragraph above, characterized in that at least one reflective surface is partly light transmissive. This can give the advantage of allowing the use of reflective surfaces which lie on both sides of the optical axis therefore increasing the light collection efficiency of the apparatus and allowing the image to be viewed through a wide angle.
  • the converging first optical element substantially surrounds the object or first image when both are viewed from the position of the real second image. It is advantageous for the further optical element to be substantially parallel to the focal plane of the converging first optical element.
  • the apparatus may advantageously be provided with light blocking means preventing light rays direct from the object or first image being observable from the area outside the apparatus. This can reduce distraction from the first object or image, and increase the visual contrast of the real second image making it more striking.
  • a second object of the present invention is to provide an apparatus as defined in the first paragraph above, characterized in that at least one reflective surface defines an aperture through which the light rays pass to from the second image.
  • Figure 4 shows a fourth embodiment
  • Figure 5 shows a further example according to the invention.
  • Figure 6 shows yet another example according to the invention.
  • an apparatus for displaying an image comprises a reflective converging first optical element 1 and a reflective further optical element 2 facing the first element.
  • the elements are constructed such that light rays from an object 3 (or first image) are reflected from the first optical element towards the further optical element, and from the further optical element back in the direction of the first optical element to form a real second image 4 viewable from an area remote from the optical elements by an observer 5.
  • the reflective converging first optical element is constituted by a part of a fully silvered spherical mirror 1.
  • the object 3 is a backlit liquid crystal display, and the reflective further element is a part silvered plane mirror, the two mirrors are arranged such that the plane mirror is near the plane of symmetry which is parallel to the focal plane of the spherical mirror, but is tilted with respect to this plane.
  • Figure 1 also shows the position of the centre of curvature 20 of the spherical mirror, and the position of a virtual image 21 of the object 3.
  • the portion of a spherical mirror may be replaced by a parabolic mirror which is a complete surface of revolution of a finite length curved line about an axis.
  • the plane mirror may be replaced by a conical fully silvered mirror with an aperture in the centre close to the position of the real image.
  • the conical mirror may also be replaced by two or more plane mirrors, or a multi-faceted mirror such as for example a pyramidal mirror with a number of facets, each facet similar to the plane mirror described above.
  • a plane mirror 7 lies in a plane parallel to the focal plane of a converging mirror 6.
  • the plane mirror is in the form of a ring defining a central optical aperture 8, through which light rays from an image or object 3 (placed adjacent the converging mirror) pass to form a real image 4, which is viewed from an area outside the apparatus by an observer 5.
  • the planar mirror In order for the light rays to emerge through the optical aperture 8, the planar mirror must be closer to the curved mirror than a distance which is half the focal length of the curved mirror. If the plane mirror 7 is spaced a distance equal to half the focal length of the converging mirror 6, then the object must be closer to the plane mirror than the surface of the converging mirror for the rays to emerge. If these criteria are not met, the rays will travel back along the same path and form an image at the position of the object 3.
  • the plane mirror is replaced by a half silvered plane mirror 9, which has no aperture, the light rays passing through the half- silvered mirror to form a real image 4 of lower apparent brightness.
  • the other component parts of the figure are similar to those described in the previous embodiment and are therefore given the same numbers in Figure 3 as in Figure 2.
  • FIG. 4 A fourth embodiment of the invention is shown in Figure 4.
  • the converging mirror 6 defines a central aperture 10, through which light rays pass from the object 3 to form the real image 4 adjacent the aperture.
  • the further mirror is constituted by a non-polarizing beam-splitter 11 which is placed between the object 3 and the converging mirror 6, and which is parallel to the focal plane of the converging mirror.
  • means 12 is provided to prevent light rays from the object' being directly observable from the area outside the apparatus by an observer 5.
  • this means comprises a louvre film (Light control louvre film obtainable from 3M Inc.) carried on one surface of the polarizing beam-splitter 11.
  • the converging mirror need not be concave as similar effects are produced by means of a Fresnel mirror.
  • one or more of the mirrors may be partially transparent, in which case an aperture to allow the light rays to pass through one mirror is not required.
  • the aperture in a fully silvered mirror need not by a physical void, it could be constituted by a portion of the mirror which is transparent or partially transparent.
  • one or more mirrors are partially transparent and the observer observes the second real image against the outer surface of a given partially transparent mirror it is advantageous to coat the parts of the outer surface of the given mirror through which the light rays do not pass with a material which does not reflect (preferably absorbs) incident light. In this way the real image has greater contrast against an apparently less bright background.
  • Figure 5 shows a modification of the apparatus of Figure 2 in which the parabolic mirror has been replaced by a Fresnel mirror 15 and the plane mirror with an aperture in has been placed by a half silvered mirror 16.
  • the real second image formed in such a system is more distorted when using a Fresnel mirror than when using a concave mirror.
  • an optical element is partially light transmissive, it is preferable to arrange that the element is more light transmissive close to the second real image than further from the second real image.
  • the further optical element comprises an outer region which is substantially reflective and an inner area, closer to the second image, which comprises a polarizing beam splitter.
  • the reflective further optical element need not be parallel to the focal plane of the reflecting converging first optical element.
  • the apparent size of the real second image may be altered by altering the distance between the first optical element and the second optical element.
  • Figure 6 shows yet another example according to the invention in which a part of the reflective further optical element comprises a retroreflective layer 14.
  • This retroreflective layer may also be partially light transmissive.
  • a parabolic mirror or spherical mirror or Fresnel mirror has been used to give the converging reflective optical element
  • a combination of a plane or curved mirror and a converging lens may be used as an alternative.
  • miirors with different types of curvature may be used as an alternative.
  • the reflective converging optical element may also operate by means of diffractive optics, for example by using a hologram. In the above examples it does not matter whether the light rays which form the real image strike the first optical element then the further optical element, or the further optical element then the first optical element.
  • the image formed is a real image which appears in a specific spatial region, and which therefore is not focused at infinity.

Abstract

An apparatus for displaying an image of an illuminated object or a first image comprises a converging mirror and a further planar or conical mirror facing the first. At least one mirror is partially light transmissive, and may comprise a polarizing beam-splitter or normal beam-splitter. Means such as, for example, a louvre film may be provided to prevent light rays from the original object or image from being directly observable from an area remote from the mirrors. The first mirror may be a concave mirror (such as a parabolic mirror) or a Fresnel mirror. The invention can give the advantage of a wide viewing angle, and can give a more visually striking real image which floats in space displaced from the mirrors.

Description

AN APPARATUS FOR DISPLAYING AN IMAGE
This invention relates to an apparatus for displaying an image, comprising a converging first optical element and a further optical element, each optical element comprising a reflective surface facing the other optical element and being arranged such that light rays from an object or first image are reflected from a reflective surface of a given optical element towards a reflective surface of the other optical element, and from the reflective surface of the other optical element towards the reflective surface of the given optical element, thereby forming a real second image being suspended in space, the reflective surface of the further optical element being at least a portion of a surface of revolution of a straight line about an axis.
A known apparatus of this general type is disclosed in US 4,802,750. In this image projection system two parabolic mirrors or one parabolic mirror and a plane mirror are mounted on a skeletal frame and arranged to face one another. Both reflective surfaces are spaced from the optical axis of the system and must be located on only one side of the optical axis of the system to enable a floating three dimensional image to be projected out into the space in front of the apparatus.
Although th s known system works well, because the mirrors and the floating image are in the same plane it is not possible to view the floating image from a wide angle as the mirrors and frame can obstruct the view. As the mirrors of the known system must be located only on one side of the optical axis the light collection efficiency is difficult to optimize. It also appears that a rigid frame or housing is necessary to maintain the relative positions of the mirrors. A first object of the present invention is to provide an apparatus as defined in the first paragraph above, characterized in that at least one reflective surface is partly light transmissive. This can give the advantage of allowing the use of reflective surfaces which lie on both sides of the optical axis therefore increasing the light collection efficiency of the apparatus and allowing the image to be viewed through a wide angle. Preferably the converging first optical element substantially surrounds the object or first image when both are viewed from the position of the real second image. It is advantageous for the further optical element to be substantially parallel to the focal plane of the converging first optical element.
The apparatus may advantageously be provided with light blocking means preventing light rays direct from the object or first image being observable from the area outside the apparatus. This can reduce distraction from the first object or image, and increase the visual contrast of the real second image making it more striking.
A second object of the present invention is to provide an apparatus as defined in the first paragraph above, characterized in that at least one reflective surface defines an aperture through which the light rays pass to from the second image. Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a first embodiment, Figure 2 shows a second embodiment, Figure 3 shows a third embodiment,
Figure 4 shows a fourth embodiment,
Figure 5 shows a further example according to the invention, and
Figure 6 shows yet another example according to the invention.
In the drawings, like elements are given like numerals where possible. In Figure 1, an apparatus for displaying an image comprises a reflective converging first optical element 1 and a reflective further optical element 2 facing the first element. The elements are constructed such that light rays from an object 3 (or first image) are reflected from the first optical element towards the further optical element, and from the further optical element back in the direction of the first optical element to form a real second image 4 viewable from an area remote from the optical elements by an observer 5. In this embodiment the reflective converging first optical element is constituted by a part of a fully silvered spherical mirror 1. The object 3 is a backlit liquid crystal display, and the reflective further element is a part silvered plane mirror, the two mirrors are arranged such that the plane mirror is near the plane of symmetry which is parallel to the focal plane of the spherical mirror, but is tilted with respect to this plane.
The plane mirror is placed so that it does not obscure the view of the real second image 4 from the observer 5. Figure 1 also shows the position of the centre of curvature 20 of the spherical mirror, and the position of a virtual image 21 of the object 3. The virtual image
21 formed by the plane mirror 3, the centre of curvature 20 of the spherical mirror and the real image 4 all lie in a straight line, and for 1: 1 image to object sizing the virtual and real images 21 and 4 are equidistant from the centre of curvature 20.
As an alternative to the above embodiment, the portion of a spherical mirror may be replaced by a parabolic mirror which is a complete surface of revolution of a finite length curved line about an axis. As a further alternative the plane mirror may be replaced by a conical fully silvered mirror with an aperture in the centre close to the position of the real image. The conical mirror may also be replaced by two or more plane mirrors, or a multi-faceted mirror such as for example a pyramidal mirror with a number of facets, each facet similar to the plane mirror described above.
In a second embodiment shown in Figure 2, a plane mirror 7 lies in a plane parallel to the focal plane of a converging mirror 6. The plane mirror is in the form of a ring defining a central optical aperture 8, through which light rays from an image or object 3 (placed adjacent the converging mirror) pass to form a real image 4, which is viewed from an area outside the apparatus by an observer 5. In order for the light rays to emerge through the optical aperture 8, the planar mirror must be closer to the curved mirror than a distance which is half the focal length of the curved mirror. If the plane mirror 7 is spaced a distance equal to half the focal length of the converging mirror 6, then the object must be closer to the plane mirror than the surface of the converging mirror for the rays to emerge. If these criteria are not met, the rays will travel back along the same path and form an image at the position of the object 3.
In a third embodiment shown in Figure 3, the plane mirror is replaced by a half silvered plane mirror 9, which has no aperture, the light rays passing through the half- silvered mirror to form a real image 4 of lower apparent brightness. The other component parts of the figure are similar to those described in the previous embodiment and are therefore given the same numbers in Figure 3 as in Figure 2.
A fourth embodiment of the invention is shown in Figure 4. In this embodiment the converging mirror 6 defines a central aperture 10, through which light rays pass from the object 3 to form the real image 4 adjacent the aperture. The further mirror is constituted by a non-polarizing beam-splitter 11 which is placed between the object 3 and the converging mirror 6, and which is parallel to the focal plane of the converging mirror. In this embodiment means 12 is provided to prevent light rays from the object' being directly observable from the area outside the apparatus by an observer 5. In the present embodiment this means comprises a louvre film (Light control louvre film obtainable from 3M Inc.) carried on one surface of the polarizing beam-splitter 11.
In all the above embodiments, the converging mirror need not be concave as similar effects are produced by means of a Fresnel mirror. Alternatively or in addition, one or more of the mirrors may be partially transparent, in which case an aperture to allow the light rays to pass through one mirror is not required. The aperture in a fully silvered mirror need not by a physical void, it could be constituted by a portion of the mirror which is transparent or partially transparent. In examples in which one or more mirrors are partially transparent and the observer observes the second real image against the outer surface of a given partially transparent mirror it is advantageous to coat the parts of the outer surface of the given mirror through which the light rays do not pass with a material which does not reflect (preferably absorbs) incident light. In this way the real image has greater contrast against an apparently less bright background.
Figure 5 shows a modification of the apparatus of Figure 2 in which the parabolic mirror has been replaced by a Fresnel mirror 15 and the plane mirror with an aperture in has been placed by a half silvered mirror 16. In general the real second image formed in such a system is more distorted when using a Fresnel mirror than when using a concave mirror. In examples in which an optical element is partially light transmissive, it is preferable to arrange that the element is more light transmissive close to the second real image than further from the second real image.
In a further example the further optical element comprises an outer region which is substantially reflective and an inner area, closer to the second image, which comprises a polarizing beam splitter.
In the above examples arid embodiments the reflective further optical element need not be parallel to the focal plane of the reflecting converging first optical element. The apparent size of the real second image may be altered by altering the distance between the first optical element and the second optical element.
Figure 6 shows yet another example according to the invention in which a part of the reflective further optical element comprises a retroreflective layer 14. This retroreflective layer may also be partially light transmissive.
Although in the above example a parabolic mirror or spherical mirror or Fresnel mirror has been used to give the converging reflective optical element, a combination of a plane or curved mirror and a converging lens may be used as an alternative. In the above examples miirors with different types of curvature may be used as an alternative. The reflective converging optical element may also operate by means of diffractive optics, for example by using a hologram. In the above examples it does not matter whether the light rays which form the real image strike the first optical element then the further optical element, or the further optical element then the first optical element.
In all the above embodiments, the image formed is a real image which appears in a specific spatial region, and which therefore is not focused at infinity.

Claims

1. An apparatus for displaying an image, comprising a converging first optical element and a further optical element, each optical element comprising a reflective surface facing the other optical element and being arranged such that light rays from an object or first image are reflected from a reflective surface of a given optical element towards a reflective surface of the other optical element, and from the reflective surface of the other optical element towards the reflective surface of the given optical element, thereby forming a real second image being suspended in space, the reflective surface of the further optical element being at least a portion of a surface of revolution of a straight line about an axis, characterized in that at least one reflective surface is partly light transmissive.
2. An apparatus for displaying an image, comprising a converging first optical element and a further optical element, each optical element comprising a reflective surface facing the other optical element and being arranged such that light rays from an object or first image are reflected from a reflective surface of a given optical element towards a reflective surface of the other optical element, and from the reflective surface of the other optical element towards the reflective surface of the given optical element, thereby forming a real second image being suspended in space, the reflective surface of the further optical element being at least a portion of a surface of revolution of a straight line about an axis, characterized in that at least one reflective surface defines an aperture through which the light rays pass to form the second image.
3. An apparatus as claimed in claim 1 or claim 2 in which the converging first optical element appears to substantially surround the object or first image when both are viewed from the position of the real second image.
4. An apparatus as claimed in claim 1 or claim 2 in which the real second image is spaced from the apparatus.
5. An apparatus as claimed in claim 1 or claim 2 in which the reflective surface of the further optical element comprises a substantially planar surface.
6. An apparatus as claimed in claim 1 in which the at least one reflective surface is more light transmissive close to the second image than further from the second image.
7. An apparatus as claimed in claim 1 in which the at least one reflective surface is light transmissive adjacent the optical axis of the converging first optical element.
8. An apparatus as claimed in claim 1 in which at least a portion of a reflective surface comprises a polarizing beam-splitter.
9. An apparatus as claimed in claim 1 or claim 2 in which a reflective surface comprises substantially transparent and substantially non-transparent regions, the substantially non-transparent regions appearing reflective when viewed from the position of the object or first image and appearing substantially non-reflective when viewed from the area outside the apparatus.
10. An apparatus as claimed* in claim 1 or claim 2 in which the further optical element is in the form of a conical surface.
11. An apparatus as claimed in claim 1 or claim 2 in which the further optical element comprises a plurality of planar surfaces in respective planes.
12. An apparatus as claimed^ in claim 1 or claim 2 in which light blocking means is provided to prevent light rays direct from the object or first image being observable from the area outside the apparatus.
13. An apparatus as claimed in claim 1 or claim 2 in which the reflective surface of the further optical element includes a retroreflective portion.
14. An apparatus as claimed in claim 1 or claim 2 in which the converging first optical element is not light transmissive.
PCT/GB1995/001658 1994-07-21 1995-07-13 An apparatus for displaying an image WO1996003670A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9414723.8 1994-07-21
GB9414723A GB9414723D0 (en) 1994-07-21 1994-07-21 An apparatus for displaying an image

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WO1996003670A1 true WO1996003670A1 (en) 1996-02-08

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999014624A1 (en) * 1997-09-12 1999-03-25 Stn Atlas Elektronik Gmbh Optical transmitter for emitting light signals
WO1999053359A1 (en) * 1998-04-09 1999-10-21 Central Research Laboratories Limited Apparatus for displaying an image suspended in space
EP0994374A1 (en) * 1998-10-16 2000-04-19 Juan Dominguez Montes Optical system capable to create the three-dimensional image of an object in space without image inversion
GB2378499A (en) * 2001-08-10 2003-02-12 Central Research Lab Ltd A lamp for a projection system
WO2004099853A2 (en) * 2003-05-09 2004-11-18 Koninklijke Philips Electronics N.V. Virtual display
US7562985B2 (en) 2003-05-09 2009-07-21 Koninklijke Philips Electronics N.V. Mirror assembly with integrated display device

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989001172A1 (en) * 1987-08-03 1989-02-09 Grand Mirage Real image projection system
EP0324326A1 (en) * 1988-01-11 1989-07-19 Dialectica Ab A display device
DE4202303A1 (en) * 1992-01-28 1993-07-29 Burkhard Katz DEVICE FOR THE PRODUCTION OF THREE-DIMENSIONAL, VIRTUAL IMAGES
DE4228451A1 (en) * 1992-08-26 1994-03-03 Burkhard Katz Three=dimensional image representation device - uses two angled concave mirrors to provide real image of illuminated object at viewing opening in device housing

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989001172A1 (en) * 1987-08-03 1989-02-09 Grand Mirage Real image projection system
EP0324326A1 (en) * 1988-01-11 1989-07-19 Dialectica Ab A display device
DE4202303A1 (en) * 1992-01-28 1993-07-29 Burkhard Katz DEVICE FOR THE PRODUCTION OF THREE-DIMENSIONAL, VIRTUAL IMAGES
DE4228451A1 (en) * 1992-08-26 1994-03-03 Burkhard Katz Three=dimensional image representation device - uses two angled concave mirrors to provide real image of illuminated object at viewing opening in device housing

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999014624A1 (en) * 1997-09-12 1999-03-25 Stn Atlas Elektronik Gmbh Optical transmitter for emitting light signals
WO1999053359A1 (en) * 1998-04-09 1999-10-21 Central Research Laboratories Limited Apparatus for displaying an image suspended in space
EP0994374A1 (en) * 1998-10-16 2000-04-19 Juan Dominguez Montes Optical system capable to create the three-dimensional image of an object in space without image inversion
GB2378499A (en) * 2001-08-10 2003-02-12 Central Research Lab Ltd A lamp for a projection system
WO2004099853A2 (en) * 2003-05-09 2004-11-18 Koninklijke Philips Electronics N.V. Virtual display
WO2004099853A3 (en) * 2003-05-09 2005-04-14 Koninkl Philips Electronics Nv Virtual display
US7562985B2 (en) 2003-05-09 2009-07-21 Koninklijke Philips Electronics N.V. Mirror assembly with integrated display device

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