Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
2002-07-26
2004-07-27
Dunn, Drew A. (Department: 2872)
Optical: systems and elements
Diffraction
From grating
C359S562000, C359S568000, C359S630000, C345S007000, C345S008000
Reexamination Certificate
active
06768588
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to image display/projection systems, and more particularly to an apparatus such as a virtual retinal display that generates an array of exit-pupil images of uniform brightness.
BACKGROUND OF THE INVENTION
A variety of image-display/image-projection devices and techniques are available for displaying/projecting graphical or video images—often called video frames—to a viewer. A graphical image, i.e., a graphic, typically changes infrequently or not at all. For example, a flight-instrument graphic of cockpit instruments may overlay a pilot's view. This graphic may be projected onto a viewing area such as the windshield, or may be projected directly into the pilot's eyes such that he/she sees the flight instruments regardless of his/her viewing direction. Typically, there is little change in this graphic other than the movement of the instrument pointers or numbers. Conversely, video frames are a series of images that typically change frequently to show movement of an object or the panning of a scene. For example, a television displays video frames.
A cathode-ray-tube (CRT) display, such as used in a television or computer monitor, is a common image-display/image-projection device that, unfortunately, has several limitations. For example, a CRT is typically bulky and consumes a significant amount of power, thus making it undesirable for many portable or head-mounted applications.
Flat-panel displays, such as liquid-crystal displays (LCDs), organic LEDs, plasma displays, and field-emission displays (FEDs), are typically less bulky and consume significantly less power than a CRT having a comparable viewing area. But flat panel displays often lack sufficient luminance and adequate color purity or resolution for many head-mounted applications.
Referring to
FIG. 1
, although a scanned-beam display system
71
often overcomes the limitations of the above-described displays, the viewer may lose sight of the displayed image if he/she moves his/her eye
73
. The display system
71
includes a scanning source
72
, which outputs a scanned beam of light that is coupled to a viewer's eye
73
by a beam combiner
74
. In one embodiment, the scanning source
72
includes a scanner (not shown), such as a scanning mirror or acousto-optic scanner, that scans a modulated light beam through a viewer's pupil
75
and onto a viewer's retina
76
. In another embodiment, the scanning source
72
may include one or more light emitters (not shown) that are rotated through an angular sweep. Because such displays scan or project an image through the pupil of the viewer's eye, the display's “exit pupil”—defined as an area, often a plane, in front of the viewer's eye
73
where the image is located—is limited to the diameter of the viewer's pupil
75
, which typically ranges from about 2 millimeters (mm) in bright light to about 7 mm in dim light. Consequently, the viewer may “lose” the image when he/she moves his/her eye
73
. A display system similar to the display system
71
is further described in U.S. Pat. No. 5,467,104, which is incorporated by reference.
Referring to
FIG. 2
, a scanned-beam display system
82
overcomes the problem of “losing” an image due to eye movement by including a diffraction grating
84
to generate an exit pupil
86
, which includes an array of multiple exit-pupil images
88
. Specifically, a modulated light beam
92
scans an image
93
onto the diffraction grating
84
, where the size of the image is determined by a scanning angle
20
. The grating
84
diffracts the beam
92
into fractional beams
98
a
-
98
c
, which respectively generate exit-pupil images
88
a
-
88
c
as the beam
92
scans the image
93
. Each of the images
88
a
-
88
c
is a replica of, but has a lower intensity than, the image
93
. An eyepiece
95
collimates the images
88
a
-
88
c
to form the exit pupil
86
. When the viewer's pupil
75
is aligned with one or more of the images
88
a
-
88
c
, the aligned image or images
88
converge on an area
100
of the viewer's retina
76
to replicate the image
93
. The intensity of the replicated image is proportional to the number of images
88
that converge to form the replicated image on the retinal area
100
.
By including multiple exit-pupil images
88
, the exit pupil
86
effectively increases the viewer's field of view with respect to the image
93
. That is, as long as at least one of the exit-pupil images
88
a
-
88
c
is within the viewer's field of view, he/she can see the image
93
. For example, if the viewer looks down slightly, the exit-pupil image
88
b
moves out of his/her view, but the image
88
a
remains in view and the image
88
c
enters his/her view. Therefore, even though the viewer has moved his/her eye
73
, he/she still views the image
93
via the exit-pupil images
88
a
and
88
c
. A scanned-beam display system that is similar to the display system
82
is further described in U.S. Pat. No. 5,701,132, which is incorporated by reference.
Unfortunately, the exit-pupil images
88
generated by the scanned-beam display
82
often have non-uniform intensities, which may annoy or distract the viewer. Specifically, the diffraction grating
84
is typically designed for a single wavelength of light, but the image beam
92
typically includes other wavelengths in addition to this single wavelength. These other wavelengths often cause the exit-pupil images
88
to have different intensities. Therefore, one typically limits the intensity of the beam
92
so that the brighter exit-pupil images
88
are not too bright for the viewer. But this may cause some of the dimmer images
88
to be too dim for the viewer to see, thus causing “holes” in the exit pupil
86
. Furthermore, even if none of the images
88
are too dim for the viewer to see, the differences in intensity among the images
88
may annoy or distract the viewer as he/she shifts his/her gaze.
SUMMARY OF THE INVENTION
In one aspect of the invention, a display system includes a diffraction grating that generates exit-pupil images from a light source, where one of the exit-pupil images has a first intensity and the remaining exit-pupil images each have or approximately have a second intensity that is less than the first intensity. The system also includes a filter that attenuates the intensity of the one exit-pupil image. In one example, the filter attenuates the 0
th
-order exit-pupil image so that all of the exit-pupil images have the same or approximately the same intensities.
REFERENCES:
patent: 3453035 (1969-07-01), Walther
patent: 4099829 (1978-07-01), Straayer
patent: 4105289 (1978-08-01), Hershel
patent: 4828392 (1989-05-01), Nomura
patent: 4947413 (1990-08-01), Jewell
patent: 5016950 (1991-05-01), Smith
patent: 5164848 (1992-11-01), Firth et al.
patent: 5414551 (1995-05-01), Okazaki et al.
patent: 5467104 (1995-11-01), Furness, III et al.
patent: 5482801 (1996-01-01), Smith
patent: 5555476 (1996-09-01), Suzuki et al.
patent: 5587836 (1996-12-01), Takahashi et al.
patent: 5606458 (1997-02-01), Fergason
patent: 5625489 (1997-04-01), Glenn
patent: 5629801 (1997-05-01), Staker
patent: 5701132 (1997-12-01), Kollin
patent: 5726793 (1998-03-01), Boardman et al.
patent: 5742262 (1998-04-01), Tabata et al.
patent: 5886760 (1999-03-01), Ueda et al.
patent: 6140979 (2000-10-01), Gerhard et al.
patent: 2001/0000124 (2001-04-01), Kollin et al.
patent: 2 406 168 (1974-08-01), None
patent: WO 94/27177 (1994-11-01), None
A.J. Stevens et al., “Diffractive optical elements for numerical aperture expansion in retinal scanning displays”, OSA Trends in Optics and Photonics, Jun. 2000, vol. 41, pp. 316-318.*
Hakan Urey, “Diffractive Exit-pupil Expander for Display Applications”, Applied Optics, vol. 40, No. 32, Nov. 10, 2002, pp. 5840-5851.
A. Stevens, et al., “Diffractive optical elements for numerical aperture expansion in retinal scanning displays”, OSA Trends in Optics and Photonics: Diffractive Optics and Micro-optics, vol. 41, 2000, pp. 316-318, SP009004678.
Ta
Boutsikaris Leo
Dunn Drew A.
Graybeal Jackson Haley LLP
Microvision Inc.
Wiklof Christopher A.
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