Note: Descriptions are shown in the official language in which they were submitted.
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LIGHT MULTIPLEXER AND RECYCLER, AND MICRO-PROJECTOR
INCORPORATING THE SAME
TECHNICAL FIELD OF INVENTION
[0001 ] This invention relates to systems and methods for multiplexing output
of
LEDs, particularly increasing the brightness of the multiplexed LED output
through
recycling and incorporating the same in a micro-projector.
BACKGROUND
[0002] Light sources are used in all types of illumination applications.
Typical
light sources include but are not limited to arc lamps, halogens, fluorescent
devices,
microwave lamps, and Light Emitting Diodes (LEDs). Many applications require
an
illumination system with a high level of brightness in a small effective
emitting area.
This high level of brightness can be accomplished conventionally by adding
more light
sources. However, this can be both technologically impossible if there is a
limited space
for integrating light sources and economically unfeasible as it can be
expensive to
integrate and use multiple light sources. Accordingly, the present invention
proceeds
upon the desirability of increasing the brightness of a light source without
increasing the
number of the light source.
[0003] For example, micro-display based television (MDTV) has the potential of
being low cost with large screen size. Traditional MDTVs are usually
illuminated by arc
lamps. Although this light source is the brightest at the lowest cost, the
need to split the
white light into 3 colors and the short lifetime make is less desirable. With
advances in
LED technology, the use of LED as the light source in MDTVs has to be
considered to
capture the long life feature of LEDs and other benefits such as instant ON.
However, at
the present time, LEDs are not bright enough for low cost application using
small
imaging panels or with larger screens. LED recycling scheme has been used to
enhance
the brightness of the light source, see U.S. Patent 6,869,206 issued to
Zimmerman et al.
However, Zimmerman et al. describes enclosing the LEDs in a light-reflecting
cavity with
one light output aperture. Also, U.S. Patent 6,144,536 issued to Zimmerman et
al.
describes a fluorescent lamp having a glass envelope with a phosphor coating
enclosing a
gas filled hollow interior. A portion of the light generated by the phosphor
coating is
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recycled back to the phosphor coating. The present invention proceeds upon the
desirability of providing a recycling device that can be coupled to one or
more LEDs to
increase the useable brightness of the LED by recycling efficiently such that
smaller
panels can be used or large screens can be illuminated with sufficient
brightness.
[0004] For example, LEDs are one type of light source used in many
illumination
applications such as general lighting, architectural lighting, and more
recently in
projection televisions. When used in projection televisions for example, LEDs
must emit
light in a small effective emitting area at a high brightness level in order
to provide the
requisite high light output on the television screen. Specifically, the LEDs
must provide
an intense and bright light as measured in lumens at a small and solid angle
in a small
emitting area to be useful in projection televisions.
[0005] Although there had been tremendous advancement in the light emitting
diode (LED) development, the output brightness of currently available LEDs is
still not
sufficient for most projection applications. Various methods had been proposed
used to
combine LED's with primary colors and recycling of output light to increase
brightness.
However, most of them these methods involve utilizing expensive components
and/or
results in a large, bulky device which greatly limits their applications.
Therefore, the
present invention proceeds upon the desirability of providing low cost LED
multiplexer
with recycling that solves these problems.
[0006] With the advancement in information transfer, displaying of images has
become an important means of communication in the marketplace. For example,
although portable electronic devices, such mp3 players, cell phones, audio
and/or video
players, portable digital assistants (PDAs), keep decreasing in size and
price, the
requirement for large display area in these portable electronic devices
remains unchanged.
Accordingly, the screen size now limits the size of these portable electronic
devices and
incorporating micro-projectors into the portable electronic devices would be
highly
desirable, but their high cost prevent such full-scale incorporation. However,
currently
available micro-projectors have architectures that are simply reduced from
standard
projectors, and as a result, the cost remains too high to be incorporated into
low cost
portable electronic devices. The most important parameters for any component
to be
embedded in these portable electronic devices are size and cost. Accordingly,
the present
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invention proceeds upon the desirability of providing a low cost micro-
projectors with
integrated multiplexer/recycler in accordance with an embodiment of the
present
invention.
[0007] Therefore, the present invention proceeds upon the desirability of
providing a low cost LED multiplexer with recycling to increase the brightness
of LEDs
while maintaining the size of the LED multiplexer small. This permits the LED
multiplexer/recycler of the present invention to be readily incorporated into
low cost
micro-projectors for use in low cost portable electronic devices. That is, the
micro-
projector of the present invention incorporates the LED multiplexer with
recycling to
advantageously provide a small, low cost, versatile, and bright LED based
illumination
system which can be readily integrated with the portable electronic devices.
The LED
based illumination system can also multiplex colors to provide both colored
pixel displays
and time sequential displays.
SUMMARY OF THE INVENTION
[0008] Therefore, it is an object of the present invention to provide a LED
multiplexer with recycling to increase the brightness of the LEDs.
[0009] Another object of the present invention is to provide a small, low cost
LED
multiplexer with recycling, which can be readily incorporated into a micro-
projector
[0010] A further object of the present invention is to provide a light pipe
based
RGB multiplexer with recycling for efficiently combining LED's with Red,
Green, and
Blue outputs and recycling the output to increase the brightness.
[0011] A still another object of the present invention is to provide a wafer
scale
LED illumination system extendible into a wafer scale LED projector system.
That is, a
complete illumination and projection system can be fabricated in a wafer form
and cut
into individual system at the very end.
[0012] A yet another object of the present invention is to provide a low cost
micro-projector for use in portable electronic device, which incorporates the
LED
multiplexer/recycler of the present invention.
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[0013] In accordance with an exemplary embodiment of the present invention, a
light multiplexer and recycler comprises an LED layer which has a plurality of
LEDs,
each emitting a light output. The light multiplexer and recycler further
comprises an
optics layer having an input end and an output end. The input end of the
optics layer is
coupled to the plurality of LEDs for multiplexing light output from the
plurality of LEDs.
An aperture layer is coupled to the output end of the optics layer which has a
transmissive
opening for transmitting a portion of the multiplexed light output to provide
a single light
output and a reflective surface for reflecting a remaining portion of the
multiplexed light
toward the input end of the optics layer. Thus, the remaining portion of the
multiplexed
light is recycled back to the plurality of LEDs to increase the brightness of
the light
output of the plurality of LEDs.
[0014] In accordance with an exemplary embodiment of the present invention, a
micro-projector comprises an LED layer which has an LED emitting a light
output. The
micro-projector further comprises a light pipe having an input end and an
output end
where the input end of the light pipe is coupled to the LED. An aperture layer
is coupled
to the output end of the light pipe which has a transmissive opening for
transmitting a
portion of the light output and a reflective surface for reflecting the
remaining portion of
the light output toward the input end of the light pipe. Thus, the remaining
portion of the
light output is recycled back to the LED to increase the brightness of the
light output of
the LED. The micro-projector also comprises a reflective polarizer disposed
between the
light pipe and the aperture layer for transmitting the light output of a
predetermined
polarization and reflecting other polarization of the light output, thereby
recycling unused
polarization of the light output back to the LED to increase the brightness of
the light
output of the LED. The micro-projector further comprises a liquid crystal on
silicon
(LCOS) panel for receiving and reflecting the light output of a predetermined
polarization, wherein the size of the transmissive opening substantially
matches the size
of the LCOS panel such that a face of the PBS coupling the LCOS panel is
larger than the
LCOS panel. In addition, the micro-projector comprises a projection lens for
capturing
the light output of the predetermined polarization from the LCOS panel to
project an
image.
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[0015] In accordance with an exemplary embodiment of the present invention, a
micro-projector comprises an LED layer that has an LED emitting a light output
and also
has a light pipe having an input end and an output end. The input end of the
light pipe is
coupled to the LED. The micro-projector further comprises a polarization beam
splitter
(PBS) with all surfaces polished to provide total internal reflection such
that the PBS acts
as a waveguide.
[0016] Various other objects, advantages and features of the present invention
will become readily apparent from the ensuing detailed description, and the
novel features
will be particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The following detailed description, given by way of example, and not
intended to limit the present invention solely thereto, will best be
understood in
conjunction with the accompanying drawings in which like components or
features in the
various figures are represented by like reference numbers:
[0018] Fig. 1 is a cross-sectional view of a light pipe based light
multiplexer and
recycler in accordance with an exemplary embodiment of the present invention;
[0019] Fig. 2 shows a perspective view of the light pipe based light
multiplexer
and recycler of Fig. 1;
[0020] Fig. 3 is a perspective view of the output end of the light pipe coated
with
reflective coating except the transmissive opening in accordance with an
exemplary
embodiment of the present invention;
[0021] Fig. 4 is a perspective view of light pipe based light multiplexer and
recycler of the present invention with a selectively coated thin glass plate
attached to the
input end of the light pipe in accordance with an exemplary embodiment of the
present
invention;
[0022] Fig. 5 is a cross-sectional view of the light multiplexer and recycler
of the
present invention using a light generating layer excited by external optical
source in
accordance with an exemplary embodiment of the present invention;
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[0023] Fig. 6 is a cross-sectional view of the light multiplexer and recycler
of the
present invention of Fig. 5 where the light generating layer is coated
directly on the
external optical source in accordance with an exemplary embodiment of the
present
invention;
[0024] Figs. 7(a)-(b) are cross-sectional view of a cavity housing the light
generating layer and/or the external excitation light source in accordance
with an
exemplary embodiment of the present invention;
[0025] Fig. 8(a) is a cross-sectional view of the light multiplexer and
recycler of
present invention of Fig. 5 where the light generating layer comprises one or
more
different light generating material excited by a laser in accordance with an
exemplary
embodiment of the present invention;
[0026] Fig. 8(b) is a view of the light generating layer comprising three
different
light generating materials excited by a laser in accordance with an exemplary
embodiment of the present invention;
[0027] Figs. 9(a)-(c) are cross-sectional views of the light multiplexer and
recycler of present invention of Fig. 5 where the light generating layer
comprises one or
more different light generating material excited by one or more lasers in
accordance with
an exemplary embodiment of the present invention;
[0028] Fig. 10 is a cross-sectional view of the light generating layer with a
coating
in accordance with an exemplary embodiment of the present invention;
[0029] Fig. 11 is a cross-sectional view of three cube prisms for multiplexing
three colored lights from three different light generating materials to form a
single output
in accordance with an exemplary embodiment of the present invention;
[0030] Fig. 12 is a schematic diagram of wafer scale illumination systems
and/or
wafer scale projector systems in accordance with an exemplary embodiment of
the
present invention;
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[0031 ] Fig. 13 is a schematic diagram of wafer scale light pipe based
illumination
systems and/or wafer scale light pipe based projector systems in accordance
with an
exemplary embodiment of the present invention;
[0032] Fig. 14 is a schematic diagram of wafer scale illumination systems
and/or
wafer scale projector systems in accordance with another exemplary embodiment
of the
present invention;
[0033] Fig. 15 is a cross-sectional view of the LED package with a cover glass
in
accordance with an exemplary embodiment of the present invention;
[0034] Figs. 16-19 are cross-sectional views of the micro-projector in
accordance
with an exemplary embodiment of the present invention;
[0035] Fig. 20 is view of a face of a PBS which is reflective coated except
for an
opening for coupling the LCOS panel in accordance with an exemplary embodiment
of
the present invention;
[0036] Fig. 21 is a cross-sectional view of the micro-projector incorporating
a
DMD in accordance with an exemplary embodiment of the present invention; and
[0037] Fig. 22-26 are views of the light multiplexer and recycler in
accordance
with an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0038] With reference to the figures, exemplary embodiments of the present
invention are now described. These embodiments illustrate principles of the
invention
and should not be construed as limiting the scope of the invention.
[0039] In accordance with an exemplary embodiment of the present invention, a
light multiplexer and recycler 1000 comprises a LED layer 1100 comprising a
plurality of
LEDs 1140. Each LED 1140 emits a light output to an optics layer 1200, such as
a light
pipe 1200. The optics layer 1200 has an input end 1210 and an output end 1220.
The
input end 1210 of the optics layer 1200 being coupled to the plurality of LEDs
1140 for
multiplexing light output from the plurality of LEDs 1140. Additionally, the
light
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multiplexer and recycler 1000 comprises an aperture layer 1500, such as a
reflective
coating 1500, coupled to the output end 1220 of the optics layer 1200. The
aperture layer
1500 has a transmissive opening 1510 for transmitting a portion of the
multiplexed light
output to provide a single light output 1600 and a reflective surface for
reflecting
remaining portion of the multiplexed light toward the input end 1210 of the
optics layer
1200, thereby recycling the remaining portion of the multiplexed light back to
the
plurality of LEDs 1140 to increase the brightness of the light output of the
plurality of
LEDs 1140. Preferably, a reflective layer 1400 covers the input end 1210 of
the light
pipe 1200 except areas 1410, 1420, 1430 of the input end 1210 of the light
pipe where the
plurality of LEDs 1140 are coupled such that the input end 1210 is reflective
for all colors
of light except areas 1410, 1420, 1430.
[0040] In accordance with an exemplary embodiment of the present invention,
Fig. 1 shows a light pipe based light multiplexer and recycler 1000 comprising
a LED
layer 1110 comprising a plurality of LED chips 1140 mounted on a heat sink
1150 and an
optics layer or light pipe 1200. The LED multiplexer and recycler 1000
multiplexes or
combines the outputs of Red, Green, and Blue LED chips 1110, 1120, 1130 using
the
light pipe 1200 to produce a single output 1600. In accordance with an aspect
of the
present invention, the reflective layer 1400 is a reflective coating 1400 on
the input end or
surface 1210 of the light pipe 1200 such that the input end 1210 is reflective
for all colors
of light except areas of the input end or surface 1210 above or corresponding
to the LED
chips 1140. Additionally, the area 1410 of the input end 1210 of the light
pipe 1200
above or corresponding to the red LED chip 1110 is coated with transmissive
red coating
that transmits the red light but reflects other colored lights, such as green
and blue light.
Similarly, the area 1420 of the input end 1210 of the light pipe 1200 above or
corresponding to the green LED chip 1120 is coated with transmissive green
coating that
transmits green light but reflects other colored lights, such as red and blue
light. The area
1430 of the input end 1210 above or corresponding to the blue LED chip 1130 is
coated
with transmissive blue coating that transmits blue light but reflects other
colored lights,
such as red and green light. Although only one red LED chip 1110, one green
LED chip
1120, and one blue LED chip 1130 are shown in Fig. 1, it is understand that a
plurality of
red LED chips 1110, a plurality of green LED chips 1120, and a plurality of
blued LED
chips 1130 can be mounted on the heat sink 1150. Preferably, the output end or
surface
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1220 of the light pipe 1200 has reflective coating 1500 except in the area or
transmissive
opening 1510 of the output end or surface 1220 where the output 1600 is
coupled.
[0041 ] When the red light from the red LED chips 1110 enters into the light
pipe
1200, a portion or part of the red light will exit the light pipe through the
transmissive
opening 1510. The remaining portion or rest of the red light will be reflected
back to the
input end 1210 of the light pipe 1200 and be recycled. Similarly, when green
light from
green LED chips 1120 and blue light from blue LED chips 1130 enter into the
light pipe
1200, portions of the green and red light exit the light pipe 1200 through the
transmissive
opening 1510 and the remaining portions of the green and red light are
recycled.
[0042] Fig. 2 shows a perspective view of the light multiplexer and recycler
with
nine LED chips 1140 of three different colors (red, green and blue) in
accordance with an
exemplary embodiment of the present invention. In practical applications, the
number of
LED chips 1140 and the colors emitted by the LED chips 1140 can be optimized
to
produce the desired outputs. The LED chips 1140 can be arranged in any MxN
array
(where M and N are both positive integers), such 3x3 array as shown in Fig. 2.
[0043] Fig. 3 shows two examples of the aperture layer 1500 comprising the
transmissive or output opening 1510 at the output end 1220 of the light pipe
1200
surrounded by reflective coating 1510. The transmissive opening 1510 is
smaller than the
output end 1220 of the light pipe 1200. Also, the transmissive opening 1510
can have
aspect ratios of 16:9 (Fig. 3(a)), 4:3 (Fig. 3(b)), or any other acceptable
aspect ratios.
[0044] In accordance with an exemplary embodiment of the present invention,
the
transmissive opening 1510 is coated with a reflective coating 1530 that
transmits a
predetermined color of light, such as red light, and reflects all other color
of light toward
the input end 1210 of the light pipe 1200 for recycling. Preferably, the
transmissive
opening 1510 can be additionally coated with a reflective polarization coating
1540 or
cover with a reflective polarization layer 1540 for transmitting the light
output of a
predetermined polarization, such as s-polarization or p-polarization, and
reflecting the
light output of all other polarization (i.e., unused polarization of light)
for recycling.
Alternatively, the transmissive opening 1510 is coated with the reflective
polarization
coating or covered with a reflective polarization layer 1540 without the
reflective coating
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1530. In accordance with an aspect of the present invention, the light
multiplexer and
recycler 1000 additionally includes a wave plate 1550 disposed between the
reflective
polarization layer 1540 and reflective coating 1530 or between the reflective
polarization
layer 1540 and the transmissive opening 1510. The wave plate 1550 rotates the
polarization state of the light output and converts the unused polarization of
light into the
useful, predetermined polarization of light.
[0045] In accordance with exemplary embodiment of the present invention, the
light multiplexer and recycler 1000 comprises a color wheel comprising a
plurality of
colored filters for transmitting colored light corresponding to the color
filter and
reflecting light of all other colors. That is, the reflective coating 1530 is
replaced with a
color wheel which covers the transmissive opening 1510 for selectively
transmitting a
different colors of light depending on which colored filter of the color wheel
is covering
the transmissive opening 1510.
[0046] The exemplary embodiment of the present invention, as shown in Figs. 1,
2, has the reflective coatings 1400, 1500 coated directly on the input and
output ends
1210, 1220 of the light pipe 1200. This is highly efficient, but can be
costly.
Accordingly, in a low cost application, the reflective coatings 1400, 1500 can
be done
separately, such as using a selectively, reflectively coated thin glass plate
1400. A large
glass plate can be selectively or patterned coated with a reflective coating
and then cut to
appropriate size to match the input end 1210 or output end 1220 of the light
pipe 1200, as
shown in Fig. 4. The patterned or selectively coated glass plate 1400 is
attached to the
light pipe 1200.
[0047] In accordance with an exemplary embodiment of the present invention,
the
light pipe 1200 can be one of the following: hollow light pipe, solid light
pipe, straight
light pipe, increasingly tapered light pipe, decreasingly tapered light pipe,
compound
parabolic concentrator, free form light pipe with its shape defined by
equations, or totally
free-form light pipe determined numerically or other means, or any suitable
combination,
such as straight hollow light pipe, a increasingly tapered solid light pipe.
All of these
various light pipes will be collectively referred to herein as the light pipe.
Any reference
to a light pipe includes any of the light pipes or combination of various
light pipes set
forth herein.
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[0048] In accordance with an exemplary embodiment of the present invention, as
shown in Fig. 5, the light multiplexer and recycler 1000, at the input side,
comprises a
light generating layer 1700 for emitting rays of light when excited by a light
source 1750
and having a reflective surface. The input end 1210 of the light pipe 1120
being coupled
to the light generating layer 1700 for multiplexing the rays of light from the
light
generating layer 1700 to provide a light output. As shown in Fig. 1, the light
multiplexer
and recycler 1000 at the output side, comprises the aperture layer 1500
coupled to the
output end 1220 of the light pipe 1200 and having a transmissive opening 1510
for
transmitting a portion of the light output and a reflective surface for
reflecting remaining
portion of the light output toward the light generating layer 1700 which
reflects and
recycles the remaining portion of light output back towards the transmissive
opening
1510.
[0049] As noted herein, although not shown in Fig. 5, the light multiplexer
and
recycler 1000 comprising the light generating layer 1700, also comprises a
light pipe
1200 with the output end 1220 partially or totally covered with the reflective
coating
1530 and/or the reflective polarization layer 1540, and/or the wave plate 1550
to transmit
light of predetermined color and/or polarization, and reflect/recycle all
other unused color
and/or polarization of light, as shown in Fig. 1. The input end 1210 of the
light pipe 1200
is disposed in proximity to the light generating layer 1700 which is excited
by external
optical light sources 1750, such that the light emitted by the light
generating layer 1700 is
coupled into the light pipe 1200. Preferably, the light generating layer 1700
is also
reflective such that light reflected from the output end 1220 of the light
pipe 1200 is
totally or partially reflected back to the output end 1220 of the light pipe
1200 from the
reflective light generating layer 1700.
[0050] In accordance with an exemplary embodiment of the present invention,
the
light generating layer 1700 in proximity to the input end 1210 of the light
pipe 1200
comprises one or more type of material compositions to emit rays of light
having a
plurality of wavelengths or colors. That is, the light generating layer 1700
can emit only
one color of light or multiple colors of light depending on the material
composition of the
light generating layer 1700. Preferably, the various material compositions of
the light
generating layer 1700 are spatially distributed such that each area of the
light generating
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layer 1700 emits rays of light of different color. The external excitation
light source 1750
can be arc lamps, LEDs, lasers and the like, emitting light of single
wavelength or
multiple wavelengths (i.e., a single color or multiple colors). In accordance
with an
aspect of the present invention, the excitation wavelength(s) (i.e., the
wavelengths of light
emitted by the external excitation light source 1750 can be shorter than the
wavelength(s)
emitted by the light generating layer 1700. For example, a blue or UV light
can be used
to generate red, green, blue, or other colored light. Preferably, the light
generating layer
1700 can be made of phosphor or other materials with the same properties as
phosphor.
Alternatively, the excitation wavelength(s) can also be longer than the
wavelength(s) of
the light generating layer 1700. For example, infrared light can be used to
generate red,
green, blue, or other colored light using non-linear crystals.
[0051 ] In accordance with an exemplary embodiment of the present invention,
the
light generating layer 1700 can be coated on the input end 1210 of the light
pipe similar
to the reflective coating 1400 in Fig. 1. Alternatively, the light generating
layer 1700 can
be coated on a sheet of transparent material, e.g. a glass plate, similar to
the thin glass
plate 1400 in Fig. 4, and placed in close proximity to the input end 1210 of
the light pipe
1220, or coated directly on the excitation light source 1750 as shown in Fig.
6. For
example, the phosphor materials can be coated directly on a blue or UV LED
1750, and
the non-linear crystal materials can be coated directly on an infrared LED
1750. An
example of a blue or UV LED 1750 is a light-emitting junction fabricated on
GaN. An
example of an infrared LED 1750 is light-emitting junction fabricated on GaAs.
[0052] In accordance with an exemplary embodiment of the present invention, as
shown in Fig. 7(b), the light generating layer 1700 is placed between total or
partially
reflecting layers 1810 in opposite sides of the light generating layer 1700 to
form a cavity
1800, thereby enabling a smaller output angular distribution or reducing
angular
distribution of the light emitted by the light generating layer 1700. In
accordance with an
aspect of the present invention, both the excitation light source 1750 and the
light
generating layer 1700 are inside the cavity 1800, as shown in Fig. 7(a).
[0053] In accordance with an exemplary embodiment of the present invention, as
shown in Fig. 8(a), the light generating layer 1700 comprises one or more
different light
generating materials 1710 (e.g., containing different colored phosphors) for
emitting one
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or more colors of light when excited by a laser. The light generating
materials can be
arranged in a row, column, array or some predetermined pattern. For example,
Fig. 8(b)
shows a light generating layer 1700 with three different light generating
materials 1710
(green, red and blue light generating materials 1710). Preferably, the laser
is a diode
laser. An example of a blue or UV laser is a laser fabricated using GaN
materials. An
example of an infrared laser is a laser fabricated using GaAs.
[0054] In accordance with an exemplary embodiment of the present invention, as
shown in Fig. 9(a), one or more lasers 1750 can be used to excite one or more
different
light generating materials 1710 of the light generating layer 1700. For
example in Fig.
9(b), three different lasers 1750 can be used, each laser 1750 exciting a
different light
generating material 1710, thereby enabling light multiplexer and recycler 1000
to
independently control the emission of three different colors from the light
generating
layer 1700. In accordance with an aspect of the present invention, more than
one laser
1750 can be used to excite the same light generating material 1710, thereby
producing a
higher light output from that light generating material. For example, in Fig.
9(c), the red
and blue light generating materials 1710 are each excited by one laser 1750,
but the green
light generating material 1710 is excited by two laser, thereby producing more
green light
than either blue or red light by the light generating layer 1700.
[0055] In accordance with an exemplary embodiment of the present invention, as
shown in Fig. 10, the light generating layer 1700 is coated such that the
coating 1760
transmits the light from the excitation light source 1750, but reflects the
light generated
by the light generating layer 1700 such that the generated light is emitted in
only one
direction, thereby increasing the efficiency of the light generating layer
1700 and the light
multiplexer and recycler 1000 of the present invention. Preferably, the
surface of the
light generating layer 1700 near the excitation light source 1750 is coated.
[0056] In accordance with an exemplary embodiment of the present invention,
laser beams from three different lasers 1750 are used to excite three
different light
generating materials 1710 (red, green and blue light generating materials
1710). The light
emitted from the three light generating materials 1710 are multiplexed into a
single output
using three total internal reflection (TIR) prisms or cubes 1900, as shown in
Fig. 11.
Since laser beams have a very narrow emission angle, each colored light
generating
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material 1710 can be excited by more than one laser beam, thereby producing
higher light
output. For example, if a higher output of green light is needed for white
balance, then
two laser beams can be directed to the green light generating material 1710
while directed
only one laser beam each to the blue and red light generating material,
thereby producing
higher output of green light.
[0057] In accordance with an aspect of the present invention, the TIR cube
prism
cube 1900 comprises two triangular prisms. All surfaces or faces of the two
triangular
prisms are polished such that the TIR cube prism 1900 act as a waveguide. The
faces of
the triangular prisms at the interface between the two triangular prisms are
coated with
dichoric coating 1910 to transmit a predetermined wavelength or color of light
and reflect
all other wavelengths or colors of light. Preferably, the interface is filled
with air gap or
low index glue.
[0058] Turning now to Figs. 12-14, there is illustrated a schematic diagram of
the
wafer scale illumination systems 2000 and/or wafer scale projector systems
3000 in
accordance with an exemplary embodiment of the present invention. The wafer
scale
illumination systems 2000 comprises a heat sink layer 2100 for mounting the
LED wafer
or layer 2200, an optional filter layer 2300, preferably a colored filter
layer 2300, an
optics layer 2400, and an aperture layer 2500. The wafer scale projector
systems 3000
additionally includes a reflective polarization layer 2600, an imaging or
display panel
layer 2700, such as liquid crystal display (LCD) panel layer or transmissive
imaging
panel layer, and a projections lens layer 2800. Current technology allows the
LEDs to be
made with the same color, but different colored LEDs 2210 can be made on the
same
wafer using colored phosphors in accordance with an exemplary embodiment of
the
present invention. Emissions from the same colored LEDs 2210 can be
transformed into
several other colors using colored phosphors. For example, a blue or UV LED
wafer can
be used to provide a plurality of LEDs 2210 of single color. Different colored
phosphors
can be deposited on the LED wafer, thereby producing different colored LEDs
2210.
That is, three primary colors (red, green and blue) emitting LEDs 2210 can be
produced
using red, green, and blue phosphors.
[0059] Preferably, the colored filter layer 2300 is placed on the LED layer
2200
comprising a colored LEDs 2210 to improve the recycling efficiency of the
wafer scale
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illumination system 2000. The colored filter on top of a colored LED 2210
transmits
only the color of light emitted by the LED 2210 and reflects all other color
of light. For
example, the colored filter on top of the blue LED 2210 will transmit only
blue light and
will reflect all other color of light. For white or single color LED
applications, the filter
layer 2300 is not necessary and can be removed.
[0060] The optics layer 2400 transforms or images the light onto the
subsequent
layers. In accordance with exemplary embodiment of the present invention, as
shown in
Fig. 12, the optics layer 2400 comprises a reflector layer 2420 and a lens
layer 2440.
Depending on the application, the optics layer 2400 can comprise an array of
light pipes
2450, as shown in Fig. 13, or spherical reflector layer 2460 and a collimating
lens layer
2480. It is appreciated that depending on the application, the wafer scale
illumination
systems 2000 and the wafer scale projector systems 3000 can have multiple
optics layers
2400.
[0061 ] In accordance with an exemplary embodiment of the present invention,
the
light pipe 2450 can be one of the following: hollow light pipe, solid light
pipe, straight
light pipe, increasingly tapered light pipe, decreasingly tapered light pipe,
compound
parabolic concentrator, free form light pipe with its shape defined by
equations, or totally
free-form light pipe determined numerically or other means, or any suitable
combination,
such as straight hollow light pipe, a increasingly tapered solid light pipe.
All of these
various light pipes will be collectively referred to herein as the light pipe.
Any reference
to a light pipe includes any of the light pipes or combination of various
light pipes set
forth herein.
[0062] The light exiting the optical layer 2400 is then incident on the
aperture
layer 2500 comprising a plurality of apertures or transmissive openings 2510
where part
of the light is reflected and part of the light passes through the aperture
2510. The
reflected light is recycled back in the LEDs 2210. The light exiting through
the aperture
2510 is unpolarized light output which can be utilized for unpolarized
applications, such
as to provide a wafer scale illumination systems 2000.
[0063] For LCD, liquid crystal on silicon (LCOS), and other polarized light
applications, such as to provide a wafer scale projection systems 3000, an
optional
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reflective polarization layer 2600 is utilized. Preferably, the reflective
polarization layer
2600 includes a wave plate layer (not shown) similar to the wave plate 1550 in
Fig. 1.
The reflective polarization layer or reflective polarizer 2600 transmits a
predetermined
polarization and reflects all other polarization of light (i.e., the unused
polarization of
light) back into the LED layer 2200, thereby increasing the effect of
recycling. The
optional wave plate layer rotates the polarization state of the light output
and converts the
unused polarization of light into the useful, predetermined polarization of
light. At this
stage, the composite wafer comprising illumination layers 2100-2600 (with or
without the
optional filter layer 2300, optional reflective polarization layer 2600, or
the optional wave
plate layer) forms an array of LED illumination systems 2000. The array of LED
illumination systems 2000 can be cut on the saw cut lines 2900 into individual
pieces to
provide a plurality of separate LED illumination system 2000.
[0064] In accordance with an exemplary embodiment of the present invention,
the
wafer scale illumination systems 2000 can be further integrated with other
layers to
provide wafer scale projector systems 3000. The wafer scale projector systems
3000
further comprises a display or imaging panel layer 2700 which is placed on the
top of the
illumination layers 2100-2600 followed by one or more the projection lens
layer 2800.
Fig. 12 shows wafer scale projector systems 2000 where the imaging panel layer
comprises transmissive LCD panels 2710 in accordance with an exemplary
embodiment
of the present invention. For a colored pixel LCD panel 2710, the LED 2210 can
be
white LEDs 2210 with white phosphor, or can be red/green/blue (RGB) LEDs 2210
combined together with the capability of adjusting the color in real time. For
a fast
switching LCD panel 2700, the wafer scale projector systems 3000 can utilize
known
time color multiplexing to -turn on one or more of the red, green, blue LEDs
2210 at a
time. Again, the completed projector units/systems 3000 in the wafer can be
cut on the
saw cut lines 2900 into individual projector units/systems 3000.
[0065] The implementation of the wafer scale projection systems using light
pipes
is shown in Fig. 13 and similarly, the imaging panel layer 2700 and a
projections lens
layer 2800 can be added to the illumination layers 2100-2600 in Fig. 14 to
provide the
wafer scale projection systems.
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[0066] For embedded micro-projectors as used in portable electronic devices,
such as the cell phones, MP3 players, portable digital assistants (PDAs), and
the like, the
most important parameters are size and cost. Accordingly, it is important to
minimize the
number of components in these embedded micro-projectors to reduce their size
and cost.
In accordance with an exemplary embodiment of the present invention, the micro-
projector utilizes multiple LEDs, namely red, green, and blue LEDs on a single
package.
The light output from the multiple LEDs are multiplexed to combine the colors,
recycled
to increased brightness of the LEDs, and coupled to the LCOS panel without
lenses,
thereby minimizing the number of components.
[0067] Turning now to Fig. 15, there is illustrated a structure of the LED
package
4000 comprising a plurality of LEDs 4100. Preferably, the LED package 4000
consists of
one red, one blue, and two green LEDs 4100, commonly supplied by LED
manufacturers
like Osram. In accordance with an exemplary embodiment of the present
invention, the
LED package 4000 has a cover window or glass 4200, which is preferably coated
with
dichroic coating 4400, and a substrate 4300 for mounting the plurality of LEDs
4100. For
example, on top of the red LED 4100, the coating 4400 transmits red light and
reflects all
other colors of light, as shown in Fig. 15. On top of the green LED 4100, the
coating
4400 transmits green light and reflects all other colors of light, as shown in
Fig. 15. On
top of the blue LED 4100, the coating 4400 transmits blue light and reflects
other colors
of light (not shown). In accordance with an exemplary embodiment of the
present
invention, each colored LED 4100 is driven independently. Optionally, the two
green
LEDs 4100 can be driven together or separately.
[0068] Fig. 16 shows a micro-projector 5000 incorporating the LED structure
4000 in accordance with an exemplary embodiment of the present invention. The
micro-
projector 5000 in accordance with an exemplary embodiment of the present
invention
comprises the LED package 4000, a light pipe 5100, a PBS 5200, a projection
lens 5600,
a LCOS panel 5500, an optional reflective polarizer 5300, and an optional wave
plate
5400. The light pipe 5100 with input end or face 5110 substantially covers all
the LEDs
4100 of the LED package 4000, is placed on the cover window 4200 package
window
and is used to coupled light emitted from the LEDs 4100. In accordance with an
exemplary embodiment of the present invention, the light pipe 5100 can be one
of the
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following: hollow light pipe, solid light pipe, straight light pipe,
increasingly tapered light
pipe, decreasingly tapered light pipe, compound parabolic concentrator, free
form light
pipe with its shape defined by equations, or totally free-form light pipe
determined
numerically or other means, or any suitable combination, such as straight
hollow light
pipe, a increasingly tapered solid light pipe. All of these various light
pipes will be
collectively referred to herein as the light pipe 1200. Any reference to a
light pipe
includes any of the light pipes or combination of various light pipes set
forth herein.
[0069] The output end 5120 of the light pipe 5100 has substantially the same
size
as the polarization beam splitter (PBS) 5200, couples light into the PBS 5200.
The PBS
5200 has all surfaces polished so that it acts as a waveguide. Between the
light pipe 5100
and the PBS 5200, a reflective polarizer 5300 is placed so that only the a
predetermined
polarization of light is transmitted into the PBS 5200. Between the light pipe
5100 and
the reflective polarizer 5300, an optional wave plate 5400, preferably a
quarter wave
plate, can used to increase the recycling efficiency of the system. As shown
in Fig. 16,
the LCOS panel 5500 is placed directly opposite the light pipe 5100. Depending
on the
orientation of the PBS 5200, the LCOS panel 5500 can be placed on the
perpendicular
face as shown in Fig. 17. The projection lens 5600 can be placed perpendicular
to the
light pipe as shown in Fig. 16 or Fig. 17. Since the light incidence on the
LCOS panel
5500 has a certain divergence, commonly at F/2.4, the PBS 5200 is larger than
the LCOS
panel 5500 so that the light is captured by the projection lens 5600 without
blocking by
the PBS 5200. The LCOS panel 5500 is placed as close to the PBS 5200 as
possible so as
to minimize losses. The surface of the PBS 5200 facing the LCOS panel 5500 is
coated
with reflective coating 5210 with an opening 5215 such that the size of the
opening 5215
matches with the size of the LCOS panel 5500. As a result, a portion or part
of the light
will be illuminating the LCOS panel 5500, and the remaining portion or rest of
the light
incident on the reflective coating 5210 is reflected back into the light pipe
5100 and
recycled back into LED package 4000.
[0070] In accordance with an exemplary embodiment of the present invention, as
shown in Figs. 18, 19, the reflective polarizer 5300 in Figs. 16, 17 can be
eliminated and
its function can be replaced by the combination of the PBS 5200 and the added
reflective
coating 5210 on the PBS as shown in Figs. 18, 19. This advantageously
eliminates one
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more component from the micro-projector, thereby reducing the cost of the
micro-
projector.
[0071 ] In accordance with an exemplary embodiment of the present invention,
the
output end 5120 of the light pipe 5100 can be made convex for improved
coupling of
light. Preferably, the convex surface of the output end 5120 of the light pipe
5100 forms
an integrated lens. In accordance with an aspect of the present invention, the
function of
the integrated lens can be performed by an optional Fresnel lens 5700 disposed
between
the light pipe 5100 and the PBS 5200. The advantage of a Fresnel lens 5700 is
that it is
very thin and highly suitable for the integrated micro-projector of present
invention. The
focal length of the Fresnel lens 5700 or integrated lens is preferably
adjusted for
maximum performance.
[0072] In accordance with an exemplary embodiment of the present invention,
the
micro-projector 5000 can additionally comprise the color filter as described
herein, which
is placed on the cover glass 4200 of the LED package 4000. Alternatively, as
described
herein with the light multiplexer and recycler 1000, the color filter 4400 can
be coated on
the input face or end 5110 of the light pipe 5100. This preferably makes the
cover glass
4200 optional, thereby eliminating another component from the micro-projector
5000.
[0073] Although the LED package 4000 described herein is a RGGB LED
package, the LED package 4000 can comprise a plurality of LEDs 4100 or any MxN
array of colored LEDs 4100, both M and N being a positive integer. In
accordance with
an exemplary embodiment of the present invention, each color LED 4100 can
comprise
one or more LEDs places strategically so that the color filters can be made
easily. That
is, each color can be made from several small LEDs place next to each other.
Thus, in
accordance with an exemplary embodiment of the present invention, each cluster
of LEDs
of the same color can be treated as a single LED.
[0074] It is appreciated that number of colors is not limited to three (red,
green
and blue) as discussed herein. The micro-projector of the present invention
can be
implemented using a LED package comprising LEDs of a single color, two colors,
three
colors, or more than three colors.
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[0075] In accordance with an exemplary embodiment of the present invention,
all
surfaces of the PBS 5200 are polished. Certain surfaces of the PBS 5200 are
for
transmission and total internal reflection (TIR) and other surfaces are used
only for TIR.
Preferably, these TIR only surfaces of the PBS 5200 can optionally be coated
with
reflective coatings for ease of assembly.
[0076] Turning now to Fig. 20, there is illustrated a view of the PBS 5200
from
the direction of the LCOS panel 5500 showing that the LCOS panel 5500 only
uses part
of the PBS face. The rest of the PBS face is made reflective or has a
reflective coating
5210 for recycling purposes.
[0077] In accordance with an exemplary embodiment of the present invention,
the
micro-projector 5000 utilizes the LED package 4000 comprising only white LEDs
4100
instead of the RGGB LED 4100. As a result, the coating 4400 on the LED package
can
be eliminated. The micro-projector 5000 comprises a white LED 4100, a light
pipe 5100,
a PBS 5200. If a standard LCOS panel 5500 is used as shown in the Figs. 16-19,
the
output will be a black and white picture projected onto a screen (not shown).
Preferable,
a color pixel LCOS can be used instead of stand LCOS panel for producing color
pictures. The color pixel LCOS can be made with transparent color filtered
placed on top
of the pixels such that part of the pixels are red, part of the pixels are
green, and part of
the pixels are blue. In accordance with an aspect of the present invention,
the part of the
pixels are not colored and are considered to be white pixels, thereby
enhancing the
brightness of the display. Although the color pixel LCOS simplifies the
construction, the
resolution can be smaller. For certain applications, lower resolution made be
acceptable
if it lowers the complexity of the micro-projector, thereby lowering the cost
of the micro-
projector.
[0078] In accordance with an exemplary embodiment of the present invention,
the
micro-projector 5000 incorporates a digital mirror device (DMD) 5910, similar
to the
digital light processing (DLP ) device made by Texas Instruments. The DMD 5910
is
preferably mounted on a DMD package 5900. The DMD 5910 has many small mirrors
(pixels), which can be tilted. When the light ray (a) is incident onto the DMD
5910 with
the pixel turned off, the light is reflected away from the incident direction
and away from
the projection lens 5600 and will not be projected onto the screen (not
shown). When the
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pixel is turned on, the mirrors of the DMD 5910 tilts towards the incident
beam and the
reflected light is directed towards the projection lens 5600 and is projected
onto the
screen. The TIR cube prism 5800 comprises two triangular prisms 5810, 5820 in
which
the first triangular prism 5810 provides the incident beam to the DMD 5910 in
which the
incident beam is reflected by total internal reflection. The reflected beam
from the DMD
5910 is not reflected, but transmitted through the interface, and to the
second triangular
prism 5820. The two triangular prisms 5810, 5820 forms parallel interfaces
such that the
image from the DMD 5910 will not be distorted.
[0079] All the faces of the first triangular prism 5810 (and preferably, all
the faces
of the second triangular prism 5820) are polished such that it forms a
waveguide. The
angle theta (0) is adjusted for maximum efficiency. Since the light incidence
onto the
DMD 5910 has a certain numerical aperture, the size of the TIR prism 5800 is
larger than
the imaging area of the DMD, as shown in Fig. 21. The light guided onto the
TIR prism
5800 at the DMD surface is larger, and if the light is not collected, then the
light will be
normally lost. Accordingly, in accordance with an exemplary embodiment of the
present
invention, the area outside the imaging area on the TIR prism 5800 is covered
with a
reflecting structure 5920. Preferably, the reflecting structure 5920 is an
angled mirror
array, angled reflector array, angled array of mirrors, gratings, or retro-
reflector array,
such that the light incident on the angled mirror array 5920 is reflected back
into the
incident direction as shown as a ray (b) in Fig. 21. The angled mirror array
5920 can be
made with spacing that is determined by how thick it can be. The limitation is
usually
due to the space between the TIR prism 5800 and the DMD package 5900. The
reflected
light eventually travels back through the light pipe 5100 and back into the
LEDs 4100.
[0080] Turning now to Figs. 22(a)-(b), there is illustrated a light
multiplexer and
recycler 6000 in accordance with an exemplary embodiment of the present
invention.
The light multiplexer and recycler 6000 comprises a light pipe 6100. The cross-
section of
the light pipe 6100 can be rectangular, square, circular, etc. In accordance
with an
exemplary embodiment of the present invention, the light pipe 6100 can be one
of the
following: hollow light pipe, solid light pipe, straight light pipe,
increasingly tapered light
pipe, decreasingly tapered light pipe, compound parabolic concentrator, free
form light
pipe with its shape defined by equations, or totally free-form light pipe
determined
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numerically or other means, or any suitable combination, such as straight
hollow light
pipe, a increasingly tapered solid light pipe. All of these various light
pipes will be
collectively referred to herein as the light pipe 1200. Any reference to a
light pipe
includes any of the light pipes or combination of various light pipes set
forth herein.
[0081] The top, bottom, and left surfaces of the light pipe 6100 are
reflective
coated with the output end 6120 to the right. As shown in Fig. 22(a), the
bottom surface
6130 facing up has three openings for the LED chips 6200. The red chip 6200 is
placed
at the red window 6310 with CR coating, which transmits red light and reflects
green and
blue light. The green chip 6200 is placed at the green window 6320 with CG
coating,
which transmits green light and reflects red and blue light. The blue chip
6200 is place at
the blue window 6330 with CB coating, which transmits blue light and reflects
red and
green light. The sidewalls of the light pipe can be optionally coated as total
internal
reflection can be used intrinsically. As a result, the light from the red chip
6200 does not
see the green or the blue chips 6200 due to the red reflecting window 6310.
The same is
true for the light from the green and blue chips 6200.
[0082] Accordingly, each color forms its own recycling system and all the
colors
are mixed in the same light pipe 6100 and produces a multiplexed output 6400.
[0083] Although Figs. 22(a)-(b), shows the configuration using red, green, and
blue LED chips 6200, the general arrangement can consists of two or more chips
with one
or more colors as shown in Fig. 23. Corresponding coatings are used that
matches each
color of the LED chips 6200. For example, two or more chips 6200 of the same
color can
be used with the coated windows 6310, 6320, 6330 of the same type. Depending
on the
relative intensity of the different colors required in a particular
application, an appropriate
number of chips can be utilized. The LED chips 6200 are shown as single LED
chips
6200 in Figs. 22-23, can also be made up of multiple chips of the same color
with several
chips clustered together in an array form. Minimum spaces between these chips
are
preferred.
[0084] In accordance with an exemplary embodiment of the present invention, as
shown in Fig. 24, the light multiplexer and recycler 6000 additionally
comprises an
output reflective aperture with an opening appropriate for a particular
application at the
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output end 6120 of the light pipe 6100, thereby providing additional
recycling. For
polarized light applications, a reflective polarizer 6500 and an optional wave
plate 6600
can be added. Descriptions of the reflective coating or aperture, reflective
polarizer and
optional wave plate as set forth herein in connection with other exemplary
embodiments
of the present invention are equally applicable and will not set forth again
herein.
[0085] In accordance with an exemplary embodiment of the present invention, as
shown in Fig. 25, the light multiplexer and recycler 6000 comprises a tapered
light pipe
6700 either integrated with the recycling/multiplexing light pipe 6100, or as
a separate
light pipe 6700 for transforming the output to the desired size and angle.
[0086] In accordance with an exemplary embodiment of the present invention, as
shown in Fig. 26(a), the light multiplexer and recycler or system 6000 using
white LEDs
6200 in which the window 6340 has no coating. When singled colored LEDs 6200
are
used, clear windows 6200 with no coating can also be used, as shown in Fig.
26(a).
[0087] In accordance with an embodiment of the present invention, as shown in
Fig. 26(b), two LEDs with wavelengths very closed to each other can be used to
increase
the brightness of the system 6000 as they can be multiplexed together using
coating
windows 6350, 6360. For example, this embodiment can be used with two or more
green
chips 6200 where their wavelengths are close enough to be considered as green.
[0088] The invention, having been described, it will be apparent to those
skilled in
the art that the same may be varied in many ways without departing from the
spirit and
scope of the invention. Any and all such modifications are intended to be
included within
the scope of the following claims.
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