Optical: systems and elements – Projection screen
Reexamination Certificate
2000-09-19
2003-03-25
Mahoney, Christopher (Department: 2851)
Optical: systems and elements
Projection screen
C359S460000, C385S901000
Reexamination Certificate
active
06538813
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of display devices and in particular to screens that can enhance the viewing angle, especially for liquid crystal displays (LCD).
BACKGROUND OF THE INVENTION
Display devices as for example projection display devices, off screen display devices and direct view displays are known. See for example, Zimmerman et al U.S. Pat. No. 5,481,385. Such displays are used in a wide range of applications which include computer terminals, airplane cockpit displays, automotive instrument panels, televisions and other devices that provide text, graphics or video information. Conventional direct view displays as for example liquid crystal displays suffer from a number of inherent disadvantages. For example, at high viewing angles (large angles from the direction normal to the surface of the display), such displays suffer from low contrast and changes in visual chromaticity as the viewing angle changes.
For most display devices it is important that the operator can view the display at various off-axis angles. For example, in an aircraft with right and left crew seats (pilot/copilot), the pilot may need to look across the cockpit to read the copilot's displays. In this situation, it is desirable to have a large (>60 degree) off-axis viewing angle. Certain types of displays (e.g. LCDs) have a limited off-axis (<20 degrees) unless external compensation is provided.
In Zimmerman, U.S. Pat. No. 5,481,385, issued Jan. 2, 1996, a viewing screen is placed between a liquid crystal display (LCD) and a person viewing the display. It is desirable in the art to pass collimated light through a LCD display in order to produce an image. Such collimated light has a fairly low scatter angle (approximately 5 to 10 degrees) which results in undesirable off-axis viewing for the display. The viewing screen of Zimmerman, which includes a plurality cone-shaped optical waveguides on the viewer's side of the screen, is shown in FIG.
1
. The viewing screen comprises a plurality of tapered waveguides
11
that are disposed on a transparent planar substrate
12
, such as glass. Each tapered waveguide has a light input surface
13
(not seen in
FIG. 1
) through the substrate
12
, a light output surface
14
and tapered sidewalls
15
. These optical waveguides are constructed from a photopolymeric material such as acrylic.
FIG. 2
illustrates the internal light reflections (i.e. light path) through such a tapered waveguide. Light rays
101
enter a tapered waveguide
11
at the light input surface
13
and propagate through the tapered waveguide
11
via a number of reflections off the tapered sidewalls. At the first reflection, the scatter angle of the light ray
101
is increased from A to A+B, where B is the taper angle of the sidewall. At the second reflection
22
the scatter angle is increase to A+2B. In general the scatter angle of the light output from a tapered waveguide can be expressed as A+(n*B), where ‘n’ is the number of reflections from the tapered sidewalls before the light ray
101
exits the tapered waveguide
12
. Note that the angle of incidence is equal to the angle of reflection for each light ray
101
.
A transparent waveguide, such as shown by Zimmerman, propagates light though total internal reflection (TIR) in the same manner as a fiber optic cable. TIR requires that the incident angle of the light is less than a critical value determined by materiel properties of the optical medium (e.g. acrylic).
FIG. 3
illustrates a plurality of light rays
101
propagating through a tapered waveguide, as taught by Zimmerman, to a output light spread angle
31
. After a limiting number of reflections, the scatter angle of the light ray
101
will exceed a critical incident angle for the waveguide optical medium and the light rays will exit at side points
32
on the tapered waveguide
11
instead of reflecting from the tapered surface
15
. Zimmerman teaches that it is desirable to absorb light that escapes the waveguide
11
by filling the interstitial region between the waveguides with a light absorbing material, such as lampblack.
Typically a tapered cone waveguide is constructed of an optical medium such as glass or a photopolymeric material such as acrylic. Zimmerman teaches a photopolymerization process, using ultraviolet (UV) light from a mercury (Hg) or xenon (Xe) source that is especially suitable for manufacture of a tapered cone waveguide. The exposure sandwich used mask/methanol/PET/photopolymer/clear glass top plate. The exposure sandwich was developed and then hard UV baked. A mask with 50 micron holes and 5 micron lines produces tapered cones that are 200 microns high and have tips (light exit area) that are 20 micron wide. The cones are typically fused to each other at a depth of 160 microns and have a 12-degree sidewall taper.
Light rays
101
enter the tapered cone waveguide
11
at the light input surface
13
and exit through the light output surface
14
. As the light ray
101
propagates through the optical medium
12
, it is reflected from the sidewalls
15
. Geometry for light rays
101
at the left and right extremes of the input spread angle are illustrated. After a certain number of reflections, the light ray incidence angle exceeds the refraction index for the optical material and escapes from the waveguide as shown at
32
. This results in a limited output light spread angle
31
.
Certain improvements to the Zimmerman concept are known including filling the interstitial regions between the waveguides
11
with an optical medium that has a lower refractive index than the refractive index of the waveguides. However this approach will cause undesirable reflections of external light as seen by the viewer. Desired features for avionics displays include high ambient light reflection, high transmission, and asymmetrical output luminance distribution about the display normal.
SUMMARY OF THE INVENTION
Our invention provides an array of tapered cones on the viewing side of a display to increase the off-axis viewing angle. Our invention teaches metallic reflective coating is placed on the exterior of the tapered optical waveguides. In addition, the surface of the resultant metallic cone facing away from the waveguide can be processed to form a black light absorbing area facing the viewer. This black area is useful in reducing reflections as seen by the viewer.
Typical use of the invention would be a viewing angle enhancement screen for use with a conventional liquid crystal display (LCD). These LCD displays typically output collimated light (spreads approximately 5 degrees).
An asymmetrical tapered optical waveguide helps promote wider horizontal versus vertical viewing distribution. A tilted cone provides asymmetrical viewing about one axis (vertical). The metallic coated cone provides higher viewing angle.
The hollow metallic cone is a variation of the previous concept with the photopolymer removed. Preferably an overcoat would be placed on the interior metallic surface to prevent corrosion/oxidation.
The direct view display device of this invention exhibits several advantages over known devices. For example, the device of this invention has an asymmetric viewing angle that can be adjusted to match the characteristics of a liquid crystal display to the cross-cockpit viewing requirements of an aircraft.
REFERENCES:
patent: 3279314 (1966-10-01), Miller
patent: 5481385 (1996-01-01), Zimmerman et al.
patent: 5521726 (1996-05-01), Zimmerman et al.
patent: 5657408 (1997-08-01), Ferm et al.
patent: 5696865 (1997-12-01), Beeson et al.
patent: 5889612 (1999-03-01), Van De Ven
Magno John
Papanestor Paul A.
Honeywell International , Inc.
Mahoney Christopher
LandOfFree
Display screen with metallized tapered waveguides does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Display screen with metallized tapered waveguides, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Display screen with metallized tapered waveguides will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3020019