Optical: systems and elements – Polarization without modulation
Reexamination Certificate
1999-10-26
2001-11-27
Epps, Georgia (Department: 2873)
Optical: systems and elements
Polarization without modulation
C359S493010
Reexamination Certificate
active
06324002
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical imaging systems, and more particularly, to an optical imaging element that transmits light of one polarization while focusing light of a second polarization.
BACKGROUND OF THE INVENTION
To simplify the following discussion, the present invention will be discussed in terms of displays utilized in head mounted computer displays; however, it will be apparent to those skilled in the art from the following discussion that the present invention may be applied to other types of displays. Head-mounted computer displays may be viewed as “eye glasses” that are worn by the user to view images created by a computer or other image source. The image seen by each eye is generated on a display screen having a two dimensional array of pixels.
It is advantageous to minimize the distance between the display and the eye of the viewer to minimize the portion of the display that extends from the viewer's face. Large overhanging displays are uncomfortable to wear. In addition, it is advantageous to be able to see around the display so the folded optical system and display should not occlude the user's vision of the surrounding view.
Prior art systems that combine reflective optics with short display to eye distances are known to the art. These systems typically utilize partially reflecting optical surfaces to fold the optical path so that the distance from the viewer's eye to the display is minimized. Such a system is described in U.S. Pat. No. 5,644,436. For such systems to operate, the direct light emitted by the display must be blocked. In addition, these systems depend on polarization filters to block light from the display from reaching the viewer's eye via direct paths.
The prior art system described above relies on partially reflecting mirrors to fold the light path. Unfortunately, such optical systems are very inefficient in terms of the fraction of the light leaving the display that actually reaches the viewer. For example, the system taught in the '436 patent only transmits {fraction (1/16)}
th
of the light that leaves the display.
In principle, an optical element having a polarization-dependent coating on a curved surface could be utilized in such displays. However, constructing a polarization-dependent coating by depositing various layers on glass is not feasible. Coatings deposited on glass are isotropic, and hence, a polarization-dependent coating that operates at normal incidence cannot be made.
In addition, any such coating must reflect over a broad band of wavelengths. The preferred coatings from an efficiency point of view are multilayer dielectric coatings. However, such coating systems are too expensive. Hence, broad band reflectors are constructed from metallic coatings, which are not as efficient.
Broadly, it is the object of the present invention to provide an improved polarization-dependent reflector with optical power (curvature), which reflects light of one polarization while transmitting light of the orthogonal polarization.
It is a further object of the present invention to provide a broadband polarization-dependent curved reflector that operates at normal incidence.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is an optical element constructed from a transparent support having a curved surface and a layer of a polarization-dependent film that is affixed to the curved surface. The polarization-dependent film passes linearly polarized light of a predetermined polarization while reflecting linearly polarized light having a polarization orthogonal to the predetermined polarization. The element is constructed by applying a layer of a transparent adhesive either to the layer of polarization-dependent film or the curved surface. The support and layer of polarization-dependent film are then heated to a temperature above the temperature at which the polarization film can be deformed. The support and layer of polarization-dependent film are then pressed together so as to deform the layer of polarization-dependent film to cause the layer of polarization-dependent film to conform to the curved surface.
REFERENCES:
patent: 5286419 (1994-02-01), Van Ligten et al.
patent: 5851328 (1998-12-01), Kohan
Mertz Pierre H.
Robrish Peter R.
Agilent Technologie,s Inc.
Epps Georgia
Magee John J.
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