Fresnel lens for use with rear projection display

Details Fresnel lens for use with rear projection display Fresnel lens for use with rear projection display

2003-08-12

2004-10-12

Fuller, Rodney (Department: 2851)

Optical: systems and elements

Projection screen

Unitary sheet comprising plural refracting areas

C359S454000, C359S459000

Reexamination Certificate

active

06804055

ABSTRACT:

FIELD
The invention relates to display devices. More specifically, the invention relates to a thin rear projection display device.
BACKGROUND
In order to provide a television with a screen size greater than approximately 40 inches a display device other than a direct view cathode ray tube (CRT) is typically used. As the screen size of a CRT increases, so too does the depth. It is generally accepted that for screen sizes greater than 40 inches direct view CRTs are no longer practical. Two alternatives exist for large screen (>40 inch screen size) displays: projection displays and plasma displays.
Current plasma displays are much more expensive than projection displays. Plasma displays are generally thin enough to mount on a wall, but can be heavy enough that mounting can be difficult. For example, current 42 inch plasma displays can weigh 80 pounds or more and 60 inch plasma displays can weigh 150 pounds or more. One advantage of plasma displays over current projection displays is that plasma displays are typically much thinner than current projection displays having the same screen size.
Projection displays, specifically rear projection displays, are typically more cost-effective then plasma displays. Projection displays may also consume too much space in a room to provide a practical solution for large screen needs. For example, typical 60 inch rear projection displays are 24 inches thick and can weigh 200 to 300 pounds.
FIG. 1
illustrates a prior art rear projection display device. In general, display device
100
includes optical engine
140
, projection lens
130
, back plate mirror
120
and screen
110
. Optical engine
140
generates an image to be projected on screen
110
. projection lens
130
projects the image from optical engine
140
on to back plate mirror
120
, which reflects the image to screen
110
. The size of display device
100
is proportional to the size of the image to be displayed on screen
110
. Thus, for large screen sizes (e.g., >60 inches), the overall size of display device
100
can be very large.
Thin rear projection display devices have been developed that are less than 12 inches thick. However, these thinner rear projection display devices typically rely on an aspherical mirror, which is difficult to manufacture and difficult to align. The difficulties associated with the aspherical mirror results in current thin rear projection displays being expensive, which restricts the availability of rear projection displays in desirable packages.
FIG. 2
illustrates a prior art thin rear projection display device with an aspherical mirror. An image from optical engine
260
is projected on reflective mirror
240
by projection lens
250
. Reflective mirror
240
reflects the image to aspherical mirror
230
, which magnifies the projected image and extends the field ray angle. Aspherical mirror
230
reflects the image to back plate mirror
220
, which then reflects the image to screen
210
. While rear projection display device
200
provides a thinner package for the same size screen as compared to display device
100
of
FIG. 1
, the manufacturing and alignment issues associated with use of aspherical mirror
230
greatly increases the cost of display device
200
.
Another shortcoming of display device
200
is the angle of optical engine
260
with respect to mirrors
220
,
230
and
240
and to screen
210
. Without compensation, the angle of optical engine
260
results in a trapezoidal, or keystone, shaped image. The compensation associated with the angle to provide a square image further increases the cost and complexity of display device
200
.
SUMMARY
A display device includes a screen, a wide angle lens system that projects an image using a portion of a lens field of the wide angle lens system, and a substantially planar back plate mirror to reflect the image to the screen. The back plate mirror is substantially perpendicular to the optic axis of the wide angle lens system and substantially parallel to the screen. In one embodiment, the display device also includes a substantially planar intermediate mirror that reflects the image projected by the wide angle lens system to the back plate mirror. The intermediate mirror being parallel to the back plate mirror. In one embodiment, the screen has a first region and a second region, the first region having a first groove angle and the second region having a second groove angle.


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