Optical waveguides – Directional optical modulation within an optical waveguide
Reexamination Certificate
2000-05-18
2002-11-12
Bovernick, Rodney (Department: 2874)
Optical waveguides
Directional optical modulation within an optical waveguide
C385S031000, C385S116000, C359S618000
Reexamination Certificate
active
06480634
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of image projectors. More particularly, this invention relates to the field of image projectors in which a laser illuminated light modulator produces an array of pixels and in which the array of pixels is projected onto a display screen.
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 (GLV) taught in U.S. Pat. No. 5,311,360 to Bloom et al., in which the GLV is configurable in a reflecting mode and a diffracting mode. The GLV taught by Bloom et al. is isometrically illustrated in FIG.
1
. The GLV
10
includes moveable elongated elements
12
suspended over a substrate
14
.
A first side view of the GLV
10
of the prior art is illustrated in
FIG. 2A
, which shows the GLV
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
10
produces the reflected light R.
A second side view of the GLV
10
of the prior art is illustrated in
FIG. 2B
, which shows the GLV 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
10
produces the plus one and minus one diffraction orders, D
+1
and D
−1
.
A first alternative GLV of the prior art is illustrated in
FIGS. 3A and 3B
. The first alternative GLV
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 I to produce the diffraction including the plus one and minus one diffraction orders, D
+1
and D
−1
.
A display system utilizing a GLV 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, 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 (via the dichroic filter group and the illumination optics) sequentially illuminate the GLV with red, green, and blue illuminations. The GLV, 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 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 in the diffracting mode and dark pixels corresponding to pixels at the GLV 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.
An alternative display system utilizing the GLV includes the red, green, and blue lasers; red, green, and blue illumination optics; first, second, and third GLVs; 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 GLVs, respectively. The first, second, and third GLVs produce the linear arrays of the red, green, and blue pixels, respectively, in response to signals from the display electronics. The dichroic filter group directs 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 display system produces the two dimensional color image on the display screen.
Examples of applications for a GLV based display system include a home entertainment system, a boardroom application, and a cinema application among others. In the home entertainment system or the boardroom application, the GLV based display system projects the two dimensional color image onto the display screen located on a wall. In the cinema application, the GLV based display system projects the two dimensional color image from a display booth onto a cinema screen.
In the home entertainment system, the boardroom application, and the cinema application, the red, green, and blue lasers are bulky and, thus, take up space. Further, the red, green, and blue lasers generate heat and, thus, require cooling by a cooling apparatus. Moreover, power supplies for the red, green, and blue lasers as well as the cooling apparatus generates noise and vibration. Additionally, precise coming and control are required between laser electronics and projection electronics in such systems.
It is theorized that as a cinema house transitions from a film based projector to the GLV based display system, the cinema house will want to maintain the film based projector in the projection booth while adding the GLV based display system. Thus, in the cinema application the problem
Bovernick Rodney
Haverstock & Owens LLP
Kang Juliana K.
Silicon Light Machines
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