Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-10-18
2003-11-18
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S224200, C359S298000, C348S755000
Reexamination Certificate
active
06650460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection type display apparatus and, more particularly, to a projection type display apparatus for displaying a full-color image on a display surface such as a screen using a mirror array device as optical modulation means.
2. Related Background Art
Along with the advent of the age of multimedia, image display apparatuses are used in every scene. Generally, display apparatuses for forming an image by modulating light are roughly classified into two types. One type is a direct viewing image type display apparatus such as a direct viewing CRT (Cathode Ray Tube) and direct viewing LCD, and the other type is a projection type display apparatus, including a LCD (Liquid Crystal Display), and a mirror device such as a DMD (Deformable Mirror Device), or AMA (Actuated Mirror Array). Since projection type display apparatuses can easily increase the screen size, front projectors for presentation or the like and rear projectors for a home theater or the like are becoming widely used. In such a projection type display apparatus using a liquid crystal panel or mirror device, the liquid crystal panel or mirror device serving as an optical modulation device is illuminated with light from a light source, and transmitted or reflected light is made incident on a screen or the like through a projecting optical system, thereby forming an image.
Although a direct viewing CRT is excellent in image quality, the weight and volume of the apparatus increase, and the manufacturing cost increases as the screen size increases. To the contrary, a projecting liquid crystal display apparatus can be made relatively thin, and the weight and volume can be reduced because its optical structure is simple. However, since an LCD normally uses linearly polarized light, the light utilization efficiency is as low as 1% to 5%. In addition, liquid crystal molecules respond slowly, and the liquid crystal layer is readily heated.
To solve the above problems, projection type display apparatuses using a mirror device such as a DMD or AMA have been developed. Currently, such projection type display apparatuses can obtain a light utilization efficiency of 5% to 10%. In addition, optical modulation is not affected by the polarization state of incident light and does not affect the polarization state of reflected light.
AMAs serving as mirror devices are roughly classified into a bulk type and a thin-film type. A bulk AMA is disclosed in U.S. Pat. No. 5,469,302 by Dae-Young Lim. To obtain the bulk AMA, a ceramic layer having a multilayered structure is cut into a thin ceramic wafer with a metal electrode formed inside, the ceramic wafer is mounted on an active matrix incorporating a transistor, the resultant structure is fabricated by sawing, and a mirror is formed on it.
A thin-film AMA is disclosed in U.S. Pat. No. 5,815,305. Referring to
FIG. 4
, the thin-film AMA has an active matrix
31
, an actuator
33
formed on the active matrix
31
, and a mirror
35
formed on the actuator
33
.
The active matrix
31
has a substrate
37
, and M×N (M and N are positive integers) transistors (not shown) formed on the substrate
37
, and M×N connection terminals
39
formed on the respective transistors.
The actuator
33
has a support portion
41
formed on the active matrix
31
and having the connection terminal
39
, a first electrode
43
whose lower end on one side is attached to the support portion
41
and other side is formed in parallel to the active matrix
31
, an interconnection or conductive tube
49
formed in the support portion
41
to connect the connection terminal
39
and first electrode
43
, a deformable layer
45
formed on the first electrode
43
, a second electrode
47
formed on the deformable layer
45
, a spacing member
51
formed on one side of the second electrode
47
, and a support layer
53
whose lower end on one side is attached to the spacing member
51
and other side is formed in parallel to the second electrode
47
. The second electrode
47
is connected to the active matrix
31
by an interconnection (not shown). The mirror
35
is formed on the support layer
53
.
When a predetermined electrical signal (voltage) corresponding to an image signal is applied to the first electrode
43
of each pixel through the active matrix
31
, each pixel actuator
33
tilts by a predetermined angle, and accordingly, each pixel mirror
35
tilts.
FIG. 3
shows this state. The pixel mirror
35
tilts by a predetermined amount in accordance with the voltage applied to the first electrode
43
, as indicated by an arrow A. The reflecting direction of reflected light of a light beam L incident on the mirror
35
changes in accordance with the tilt amount, as indicated by an arrow B.
Such a thin-film AMA is manufactured using semiconductor manufacturing processes. For this reason, the mirror array has a perfect quality so that light enough to display digital image with a high-luminance and high-contrast under normal indoor illumination conditions can be transmitted to the screen. In other words, a thin-film AMA is a reflection-type optical modulator using a thin-film piezoelectric actuator in relation to a microscopic mirror and has been developed to obtain a tilt angle enough to provide high contrast and a light utilization efficiency enough to provide high luminance. A thin-film AMA has also been developed to ensure uniformity in a large scale integration across 300,000 pixels of mirrors formed from a single pattern.
As for forming a projection type display apparatus using a mirror device such as a thin-film AMA or DMD, a typical arrangement is disclosed in, e.g., Japanese Patent Application Laid-open No. 8-21977. That is, white illumination light is time-divisionally color-separated by a rotary color filter, a mirror device is illuminated with each color light component, and reflected light is guided into or outside the aperture of a projecting lens in accordance with tilt drive of each pixel mirror, thereby obtaining a predetermined full-color projected image.
In the prior art disclosed in Japanese Patent Application Laid-open No. 8-21977, however, in projecting a full-color image, the illumination system has at least a rotary filter, a rotary filter drive motor, and a rotary syndronized signal processing system for color separation, resulting in complex structure. Additionally, since the rotary filter, i.e., a section rotatably driven at a high speed of up to 10,000 rpm is present, the system has problems in vibration noise and reliability.
SUMMARY OF THE INVENTION
One aspect of the present invention is to provide a projection type display apparatus comprising:
a mirror array device for performing optical modulation by a plurality of tiltable pixel mirrors;
an illumination optical system for illuminating the mirror array device with a plurality of color light components of different colors from different directions; and a projecting optical system for projecting reflected light components from the mirror array device onto a projected surface, wherein tilt angles of the pixel mirrors have a plurality of angle ranges that do not overlap each other, and one of the plurality of color light components is projected onto the projected surface for each angle range.
An apparatus described above preferably has a feature that each pixel mirror is not tilted to display black on the projected surface.
An apparatus described above preferably has a feature that the tilt angle of each pixel mirror is maximized to display black on the projected surface.
An apparatus described above preferably has a feature that each pixel mirror is tilted by a predetermined angle to display black on the projected surface.
An apparatus described above preferably has a feature that the projecting optical system has an aperture which shields, of the reflected light components from the mirror array device, a light component which is not to be projected onto the projected surface.
An apparatus described above preferably has a feature that the pl
Choi William
Epps Georgia
Morgan & Finnegan , LLP
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