Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-04-10
2003-09-02
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S237000, C359S298000
Reexamination Certificate
active
06614580
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of image projectors. More particularly, this invention relates to the field of modulation of light out of the focal plan in a grating light valve based projection system.
BACKGROUND OF THE INVENTION
In recent years, light modulators have been developed using MEMS (micro-electro-mechanical systems) technology in which moveable elements are configurable to direct light. An example of such light modulators is a grating light valve type device (GLV type device) taught in U.S. Pat. No. 5,311,360 to Bloom et al., in which the GLV type device is configurable in a reflecting mode and a diffracting mode. The GLV type device taught by Bloom et al. is isometrically illustrated in FIG.
1
. The GLV type device
10
includes moveable elongated elements
12
suspended over a substrate
14
.
A first side view of the GLV type device
10
of the prior art is illustrated in
FIG. 2A
, which shows the GLV type device
10
in the reflecting mode. The moveable elongated elements
12
each include a first reflective coating
16
. Interspersed between the moveable elongated elements
12
are second reflective coatings
18
. In the reflecting mode, upper surfaces of the first and second reflective coatings,
16
and
18
, are separated by a height difference of a half wavelength &lgr;/2 of incident light I. The incident light I reflecting from the second reflecting coatings
18
travels a full wavelength further than the incident light I reflecting form the first reflecting coatings
16
. So the incident light I, reflecting from the first and second reflecting coatings,
16
and
18
, constructively combines to form reflected light R. Thus, in the reflecting mode the GLV type device
10
produces the reflected light R.
A second side view of the GLV type device
10
of the prior art is illustrated in
FIG. 2B
, which shows the GLV type device in the diffracting mode. To transition from the reflecting mode to the diffracting mode, an electrostatic potential between the moveable elongated elements
12
and the substrate
14
moves the moveable elongated elements
12
to contact the substrate
14
. To maintain the diffracting mode, the electrostatic potential holds the moveable elongated elements
12
against the substrate
14
. In the diffracting mode, the upper surfaces of the first and second reflective coatings,
16
and
18
, are separated by a quarter wavelength &lgr;/4 of the incident light I. The incident light I reflecting from the second reflecting surfaces
18
travels a half wavelength further than the incident light I reflecting from the first reflective coatings
16
. So the incident light I, reflecting from the first and second reflecting coatings,
16
and
18
, destructively interferes to produce diffraction. The diffraction includes a plus one diffraction order D
+1
and a minus one diffraction order D
−1
. Thus, in the diffracting mode, the GLV type device
10
produces the plus one and minus one diffraction orders, D
+1
and D
−1
.
A first alternative GLV type device of the prior art is illustrated in
FIGS. 3A and 3B
. The first alternative GLV type device
10
A includes first elongated elements
22
interdigitated with second elongated elements
23
. The first elongated elements
22
include third reflective coatings
26
; the second elongated elements
23
include fourth reflective coating
28
. In the reflecting mode, illustrated in
FIG. 3A
, the third and fourth reflective coatings,
26
and
28
, are maintained at the same height to produce the reflected light R. In the diffracting mode, illustrated in
FIG. 3B
, the first and second reflected coatings,
26
and
28
, are separated by the second height difference of the quarter wavelength &lgr;/4 of the incident light Ito produce the diffraction including the plus one and minus one diffraction orders, D
+1
and D
−1
.
A display system utilizing a GLV type device is taught in U.S. Pat. No. 5,982,553 to Bloom et al. The display system includes red, green, and blue lasers, a dichroic filter group, illumination optics, the GLV type device, Schlieren optics, projection optics, a scanning mirror, and display electronics, which project a color image onto a display screen. The red, green, and blue lasers, driven by the display electronics and coupled to the GLV type device (via the dichroic filter group and the illumination optics) sequentially illuminate the GLV type device with red, green, and blue illuminations. The GLV type device, driven by the display electronics, produces a linear array of pixels which changes with time in response to a signal from the display electronics, each pixel configured in the reflecting mode or the diffracting mode at a given instant in time. Thus, the GLV type device produces sequential linear arrays of red, green, and blue pixels with each of the red, green, and blue pixels in the reflecting mode or the diffracting mode.
The red, green, and blue pixels are then coupled to the Schlieren optics which blocks the reflecting mode and allows at least the plus one and minus one diffraction order, D
+1
and D
−1
, to pass the Schlieren optics. Thus, after passing the Schlieren optics, the linear arrays of the red, green, and blue pixels have light pixels corresponding to the pixels at the GLV type device in the diffracting mode and dark pixels corresponding to pixels at the GLV type device in the reflecting mode. The projection optics (via the scanning mirror) project the linear arrays of the red, green, and blue pixels onto the display screen while the scanning mirror, driven by the display electronics, scans the linear arrays of the red, green, and blue pixels across the display screen. Thus, the display system produces a two dimensional color image on the display screen.
A graphical top cross sectional view of a GLV type device is illustrated in
FIG. 4. A
scale in millimeters is provided to show an approximate layout of the system. In a system such as this, the GLV type device
10
is positioned such that the focal point
36
of the incident light I is located on the surface of the GLV type device
10
. A seal glass
34
is positioned over the GLV type device
10
forming an air gap
32
between the GLV type device
10
and the seal glass
34
. In this prior art embodiment, the seal glass
34
permits the incident light I to pass to the air gap
32
and then to the GLV type device
10
. The reflected light R travels through the air gap
32
and the seal glass
34
before a portion of the reflected light R is reflected by an outer surface
38
of the seal glass. As depicted in
FIG. 4
, this second reflected light R
2
eventually leaves the seal glass at a different point than the reflected light R. This second reflected light R
2
, as well as additional reflected light derivative of R
2
, creates undesirable background light in the final display.
An alternative display system utilizing the GLV type device includes the red, green, and blue lasers, red, green, and blue illumination optics; first, second, and third GLV type devices; the dichroic filter group; the projection optics; the scanning mirror; and the display electronics. The red, green, and blue lasers, via the red, green, and blue illumination optics, illuminate the first, second, and third GLV type devices, respectively. The first, second, and third GLV type devices produce the linear arrays of the red, green, and blue pixels, respcetively, in response to signals from the display electronics. The dichroic filter group directs the light from the linear arrays of the red, green, and blue pixels to the Schlieren optics, which allows at least the plus one and minus one diffraction order, D
+1
and D
−1
, to pass the Schlieren optics. The projection optics, via the scanning mirror, project the linear arrays of the red, green, and blue pixels onto the display screen while the scanning mirror, driven by the display electronics, scans the linear arrays of the red, green, and blue pixels across the display screen. Thus, the alternative displ
Epps Georgia
Haverstock & Owens LLP
O'Neill Gary
Silicon Light Machines
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