Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1999-10-22
2001-03-20
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S477000, C359S479000, C353S010000
Reexamination Certificate
active
06204973
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to apparatus for displaying an image suspended in space, comprising: an object for display; a retroreflector being arranged to receive light from the object; a beamsplitter in a path for light from the object to the retroreflector, the beamsplitter being arranged at an oblique angle to the direction of propagation of the light such that it transmits part of the light and reflects part of the light, the light being either transmitted or reflected by the beamsplitter is received by the retroreflector and is reflected by it back to the beamsplitter, which either reflects or transmits part of this retroreflected light to form a real image suspended in space.
A known display apparatus of this type is described in EP-A-0460873.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided apparatus for displaying an image suspended in space, comprising: an object for display, a retroreflector which is arranged to receive light from the object, and a beamsplitter in a path for light from the object to the retroreflector. The beamsplitter is arranged at an oblique angle to the direction of propagation of the light such that it transmits part of the light and reflects part of the light. The light, which is either transmitted or reflected by the beamsplitter, is received by the retroreflector and is reflected by it back to the beamsplitter, which either reflects or transmits part of this retroreflected light, to form a real image suspended in space, characterized by the apparatus further comprising a converging optical element which is arranged between the beamsplitter and the retroreflector such that in use light from the beamsplitter passes through the converging optical element to the retroreflector, which reflects it back through the optical element towards the beamsplitter. The presence of a converging optical element between the beamsplitter and the retroreflector can improve the viewing angle, or reduce the area of retroreflector required to provide a given viewing angle for a real image suspended in space, or both.
Preferably a first retroreflector is provided to receive light being transmitted by the beamsplitter from the object and a further retroreflector is provided to receive light being reflected by the beamsplitter from the object, such that light being reflected from both retroreflectors forms the real image suspended in space, thereby increasing the brightness of the real image.
Very preferably, the converging optical element is located such that it forms an image of the given object or image in the plane of the retroreflector. This can improve the resolution of the real image suspended in space significantly, and for example allows low cost bead retroreflectors to be used in high resolution displays.
If the object is three dimensional, then the real image appears as a three dimensional image projected into or suspended in space.
According to a second aspect of the invention there is provided an apparatus in which the retroreflector is replaced by a specularly reflective surface which forms a real or virtual image suspended in space.
REFERENCES:
patent: 4550978 (1985-11-01), Friedle
patent: 5477385 (1995-12-01), Freeman
patent: 5583695 (1996-12-01), Dobrusskin
patent: 5764411 (1998-06-01), Shanks
patent: 5861993 (1999-01-01), Shanks et al.
patent: 0 460 873 A1 (1991-05-01), None
patent: WO 96/29677 A1 (1996-09-01), None
Bollman William H.
Central Research Labs, Ltd.
Epps Georgia
Spector David N.
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