Note: Descriptions are shown in the official language in which they were submitted.
CA 02555375 2009-11-04
TILED OPTICAL FIBER DISPLAY
FIELD OF THE INVENTION
The present invention relates to a tiled optical fiber display.
BACKGROUND OF THE INVENTION
Liquid crystal (LC), light emitting diode (LED) and plastic optical fibre
(POF) technologies are combined in a unique way to form full colour displays.
Remarkable progress in LED technology has recently enabled high efficiency
red, green and blue light sources with lifetimes of 100,000 hours. These are
in current use for very large outdoor video displays (diagonal size of 20 ft,
for
example) with pixel spacings >2 cm, where the high cost of assembling from
-100,000 to -1,000,000 LEDs is warranted. (Cost from $50,000 to
$1,000,000or more.)
In many applications, this is not affordable, particularly where a large
number of pixels is desired. One approach is to use a bright white light
source and then to use a LCD (liquid crystal display) light modulator to
control
the brightness of each pixel. This approach has a lower cost structure and
has been demonstrated:
The publication "Case Study: Building the Market for a Tiled-
Display Solution", Needham, B., Information Display 10, pages 20-24, 2003,
discloses an optical fiber-based display technology and application in public
information displays and advertising.
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A major issue with this approach is the loss of light associated with the
LCD device. Typically only 5% of the light is used, and the remaining 95% is
absorbed by components of the LCD.
Another issue is the strict requirement for exact alignment of the LCD
units where an array of LCD units is tiled together to produce the desired
display size. This generally requires that the image size of each LCD unit be
expanded, allowing seamless tiling of the LCD units.
The publication "Psychophysical Requirements for Seamless Tiled
Large-Screen Displays" Alphonse G A; Lubin J., Society for Information
Display (SID) Digest, 49.1, pages 941-944,1992, discusses the optical
requirements of a tiled display system to achieve a seamless appearance to
the human observer. The publication entitled "Optical Tiled AM LCD for Very
Large Display Applications"; Abileah A; Yaniv Z, Society for Information
Display (SID) Digest, 49.2, pages 945-949, 1992, describes an optical fiber
module that may be used to enlarge the image size of a LC display enabling a
tiled display.
The largest single light absorbing component of the LCD device is the
colour filter array, used to separate the white light source into colour
components. Typically, about 75% of the white light is absorbed by colour
filters.
Other related references of general relevance include:
WO/03/067318 discloses a Tiled Display with Filter for Uniform Pixel
Brightness which comprises an image display device having an array of
electrically driven picture elements which are viewable at a viewing surface.
Luminance corrections are arranged with respect to the image display device
so as to apply a spatial luminance filter to the output of the image display
device, the spatial luminance filter attenuating the light output by each
picture
element of the image display device in substantially inverse relation to the
luminance response characteristics of the picture element so that each picture
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element exhibits substantially the same luminance for a given input electrical
driving signal.
WO/03/067563 discloses a Display with Optical Fibre Face Plate which
comprises an array of pixel elements; and an image guide having an array of
light transmission guides, input ends of the light transmission guides being
arranged to receive light from pixel elements of the image display device.
Output ends of the light transmission guides provide an image output surface.
Each light transmission guide includes a light-guiding region to promote light
propagation by total internal reflection and a reflective. coating on the
light
guiding region to promote specular reflection at the region-coating interface.
Therefore, it would be very advantageous to provide a tiled optical fiber
display device structure in which the image size of a LCD display is
expanded, enabling any desired number of LCD displays to be tiled together
without gaps between them, so as to create a seamless picture, with superior
display brightness and colour quality achieved due to backlighting with LED
lamps and eliminating the need for light absorbing colour filters.
SUMMARY OF THE INVENTION
The present invention provides a tiled optical fiber display device
structure which includes a light emitting diode (LED) backlit liquid crystal
display (LCD). Light from the LCD enters an array of optical fibers that
directs
the light to a viewing screen. The optical fibers are arranged so as to
eliminate the use of energy absorbing colour filters in conventional LCD's,
and
also to enable the seamless tiling of display modules.
The present invention provides a tiled optical display, comprising:
at least one display module including
i) a liquid crystal display and an array of light emitting diodes positioned
to backlight the liquid crystal display, the array of light emitting diodes
including at least one each of red, green and blue wavelength emitting light
emitting diodes with a beam of light from each light emitting diode being
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focussed onto a pre-selected region of the liquid crystal display spaced from
the light emitted by the other light emitting diodes, each pre-selected region
of
the liquid crystal display including an array of optical modulation
elements such that light from each beam of light passes through one set of
corresponding optical modulation elements, control means connected to each
individual modulation element of each set of optical modulation elements for
controlling a desired amount of light from each beam to pass through each
individual optical modulation element of the liquid crystal modulator; and
ii) a planar viewing plane having a pre-selected number of pixels, each
individual optical modulation element having a first end of an optical fiber
optically coupled thereto, and a second end of one optical fiber from each pre-
selected region of the liquid crystal modulator optically coupled to one of
the
pre-selected number of pixels so each pixel is optically coupled to a red,
green and blue light emitting diode mediated by the liquid crystal modulator.
BRIEF DESCRIPTION OF, THE DRAWINGS
The invention will now be described, by way of example only, reference
being had to the accompanying drawings, in which:
Figure 1 is schematic diagram of a tiled optical fiber display produced
in accordance with the present invention.
Figure 2 is a LED placement diagram, showing layout of 72 LEDs each
having two leads (all dimensions in mm), each LED only emits light having
one of three possible colours, namely red, green or blue, each triangle formed
by three neighbouring LEDs is comprised of a red, a green and a blue-
emitting LED.
Figure 3 shows hole locations in a first optical fiber retaining plate
through which the optical fibers are inserted.
Figure 4 shows hole locations in a second optical fiber retaining plate
through which the optical fibers are inserted.
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Figure 5 shows an example of correspondence of holes in the first
optical fiber retaining plate of Figure 3 with the holes in second optical
fiber
retaining plate. The left side of the Figure shows fiber locations of the
first
plate, and a right portion showing fiber locations of the second plate. For
example, the three (3) fibers that end in the 3 locations of the second plate
shown generally at 1 form a triangular pattern, and originate from the three
locations, each shown as I in the first plate. Of the said three fibers, one
is
illuminated with green light, one with red and the other with blue.
DETAILED DESCRIPTION OF THE INVENTION
The structure and operation of the display will now be described with
reference to Figure 1, which shows an example of a display 10 constructed in
accordance with the present invention. A red, a green and a blue-emitting
light
emitting diode (LED) at 12, 14 and 16 respectively are supplied with a steady
direct electric current (DC) to provide steady illumination. Focused LED's are
preferred from which a light beam is emitted in a cone 18 of a particular
colour
from each LED with a typical divergence angle of -15 . Light from each LED
12, 14, and 16 illuminates only a desired portion 24, 26 and 28 respectively
of
a liquid crystal display (LCD) modulator 20 so that light of only one colour
from only one LED illuminates each associated portion of LCD modulator 20.
The LCD modulator 20 is comprised of both polarizers and polarization-
rotating LC material capable of allowing varying amounts of light to pass
through the LCD modulator 20 from substantially no light to a significant
amount of light according to control voltages applied to the LCD modulator 20.
These beamlets of light pass through a two dimensional array of
modulator elements 30, with a corresponding set of optical modulation
elements 30 situated to coincide with the intensely illuminated regions 24, 26
and 28 within LCD modulator 20 such that light from each beamlet passes
through one corresponding modulation element 30 and then exits. from the
LCD modulator 20 and enters an optical fiber element 34. Each modulator
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element may be individually controlled to allow a desired amount of light from
each beamlet to pass through the LCD modulator. One optical fiber element
34 is situated in front of each LCD modulation element 30 such that it may
collect one beamlet of light. The optical fiber elements 34 guide the light
from
the individual optical fibers and terminate at a flat viewing plane 40. Three
fiber elements 34, 34' and 34" carrying light from one blue, one green and
one red beamlet, respectively, are grouped together at plane 40 to form one
pixel shown at 42.Another pixel shown at 42' is formed from fiber elements
35, 35' and 35". In the example of Figure 1, there are other pixels and
optical
fiber elements (e.g. fibers 60 and pixel 42") that are not fully shown,
however,
each pixel is formed from three optical fibers that are unique to the
particular
pixel, such that the three, optical fibers are illuminated with red, green and
blue
light, respectively, obtained from corresponding LCD modulator elements with
the three LCD modulation elements being illuminated with light from the red-,
green- and blue-emitting LED's, respectively.
The viewer at 50 observes the light exiting from the pixels 42, 42' and
so on which are formed by the ends of the optical fiber elements 34, 34' and
so on located at plane 40, and the viewer sees a pattern of light and dark
pixels, depending upon the state of each modulator element 30 of modulator
20. Control of LCD modulator elements 30, forms the desired displayed
information in colour. Note that only three LED's have been necessary in total
to illuminate a number of pixels, in the example of Figure 1, twelve (12)
pixels.
Yet more pixels may be provided as indicated in Figure 1 on viewing
plane 40 by additional optical fibers 60 which are lit by beamlets from other
optical modulators, and other red, green and blue LED's. In this manner, as
many pixels as desired may be formed on viewing plane 40, provided that a
suitable number of LCD modulators, LED's, and optical fibers are provided.
An arbitrary number of units may therefore be tiled together from a number of
LCD modulators and LED's to create as many pixels as desired.
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A display module has been constructed comprising seventy-two (72)
LEDs (24 red, 24 green, 24 blue) arranged as shown in Figure 2 to illuminate
an active matrix LCD modulator that contains no colour filters obtained from
Sharp. Although only one modulator element for each fiber is necessary, this
LCD has many closely spaced light modulation elements, such that each
modulator element 30 in display module 10 actually consists of a group of
light modulator elements within the Sharp LCD modulator.
Each cluster of three neighbouring LEDs in a triangular configuration
includes one LED of each of the three colours. The LEDs have a 15 degree
divergence of light.
The LCD is placed directly up against the LEDs and therefore light of
one colour from a given LED does not mix with light from neighbouring LEDs,
but passes through the LCD and enters a first end of twelve (12) optical
fibers
that are arranged in a group in a circular pattern to efficiently utilize the
light
given off by the LED. Since each of the twelve (12) optical fibers is arranged
in a symmetrical manner relative to the LED, it is illuminated with
substantially
the same intensity as the other eleven (11) fibers which access light from the
same pre-selected region of the LCD 20. The arrangement of the optical
fibers where light enters them at the first end is shown in Figure 3.
Each optical fiber now extends away from the LCD 20 and being
bendable, is routed to a series of locations from which light emerges from the
second end as shown in Figure 4. Note that each fiber shown in Figure,4
corresponds to one fiber shown in Figure 3. There are 864 fibers. The two
ends of each fiber are held in position by rigid plates about 2 mm in
thickness.
A first of the plates with holes located as in Figure 3 is at the first end of
the
optical fibers and a second of the plates with holes located as in Figure 4 is
at
the second end of the fibers. The fibers are orthogonal to the first and
second
plates where they pass through the plates, being guided by holes drilled
normal to the plane of each plate, and the fibers are suitably bent as they
pass between the plates which are about 3 cm apart. In plate 4, a 16 x 18
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array of full colour pixels is realized, yielding a display area of dimensions
6.4
cm x 7.2.cm. It will be appreciated by those skilled in the art that the
numbers of pixels, numbers of optical modulators, number of tiles, and
dimensions of the various components making up the tiles disclosed herein
are purely exemplary and are not intended to limit the invention in any way.
The correspondence between the holes in the two plates is partially
shown, by way of example, in Figure 5. Figure 5 has two portions, a left
portion showing fiber locations in the first plate, and a right portion
showing
fiber locations in the second plate. For example, the three (3) fibers that
end
in the three (3) locations of the second plate shown generally at 1 form a
triangular pattern, and originate from the three locations, each shown as
numeral 1 in the first plate. Of the three fibers, one is illuminated with
green
light, one with red and the other with blue.
In the present tiled optical fiber display which uses LEDs to backlight
the LC modulator 20, light from modulator 29 is passed through the optical
fibres to form the pixels seen by the viewer. This structure permits the
number of pixels to be much larger than the number of LEDs.
In the non-limiting tiled optical fiber display example constructed
according to the present invention, four (4) full colour pixels are obtained
for
each LED. This represents a twelve (12) times reduction in LEDs, since
twelve (12) full colour pixels require thirty-six (36) LEDs in conventional
LED
displays. Up to about one hundred (100) pixels can be achieved per LED for
high resolution tiled optical fiber displays disclosed herein.
It should be noted that the optical light-guiding components in this
invention may consist of optical fibers 34, 34', 34" as described above,
however other optical light guides may also be used, such as those made
from moulded or extruded, substantially transparent polymers. In addition, the
overall light guide may be composed of two or more connected light guide
components such as a moulded portion from which light is coupled to a
further, extruded component. These various configurations do not alter the
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inventive concept, but have a bearing on the manufacturing cost of the light
guides.
In a conventional LED display, high cost, high current drive electronics
are required to turn LEDs on and off. In the present tiled optical fiber
display,
LED's are not modulated, and only low cost, low power LCD drivers are
needed. The present tiled optical fiber displays, unlike other LCD's, are not
limited in viewing angle by the LED or the LCD. This is due to the optical
design of the display, since optional, optical elements such as diffusers may
be placed at viewing plane 40 to control the viewing angle. Viewing angles
from small (30 ) to large (160 ) are-possible for the present tiled optical
fiber
displays. Excellent contrast is achieved due to the black display screen. This
is due to the use of a light-absorbing optical fiber retaining plate at
viewing
plane 40 and the-high contrast available from the LCD modulator.
The present tiled optical fiber display system is also very advantageous
in that it enables full colour with outstanding colour saturation, long life
(-100,000 hours), high efficiency (6 lumens/watt), high brightness (400
cd/m2), excellent contrast (sunlight viewing), shock-resistant screen (not
glass), EMI compatible without shielding, pixel pitch from about 2 mm to about
mm and a wide range of display sizes including, for example, displays of
20 10 or 20 feet diagonal.
The present tiled optical fiber display system is applicable to those
areas of display technology which currently use LED and projection displays.
Projection displays are not flat panels and are therefore restricted to
applications that permit space for a screen and projector. Lamp life is
limited,
and regularly scheduled lamp replacement is necessary. Contrast is only
acceptable in low ambient light applications. A summary of key
characteristics of LED, projection and technology of the present invention is
shown in Table 1.
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Table I
Attribute LED Present tiled Projection
device
Size, feet diagonal 3-50 3-20 5-50
Resolution 10-40 mm pixel 1-20 mm pixel 1-10 mm
spacing spacing
Flat Yes Yes No
Cost/pixel $1.00 $0Ø10 $0.01
Sunlight-viewable Yes Yes No
Life 100,000 hours 100,000 hours 5,000 hours for
lamp replacement
Brightness 300 t0 5000cd/m2 300 to 2000cd/m2 100cd/m2typical
Seamlessly Yes Yes No
tileable*
The present tiled optical fiber display system is modular. This means
that small blocks (for example 30 cm x 30 cm) may be tiled together in a
seamless manner to create the required display size. LED displays are also
modular, however, projection displays show black lines where they are tiled
together. The present tiled optical fiber display system therefore achieves a
uniform appearance regardless of the number of modules used, and is
therefore suitable for unusual size formats, for example, long, narrow banners
(1' x 20') for overhead signage or architect- specified custom installations.
Glass-based technologies such as plasma, LCD, EL and CRT are not
successful in formats over about 4-8 feet due to their high weight, high cost
and fragile nature. These technologies are targeted at TV and smaller, public
information displays only. They also suffer from lower operating lifetimes
(10,000-60,000 hours) and lower power efficiencies (1-3 lumens/watt) which
limits their suitability for high brightness, large size displays.
As used herein, the terms "comprises" and "comprising" are to be
construed as being inclusive and open ended, and not exclusive. Specifically,
when used in this specification including claims, the terms "comprises" and
"comprising" and variations thereof mean the specified features, steps or
components are included. These terms are not to be interpreted to exclude
the presence of other features, steps or components.
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The foregoing description of the preferred embodiments of the
invention has been presented to illustrate the principles of the invention and
not to limit the invention to the particular embodiment illustrated. It is
intended
that the scope of the invention be defined by all of the embodiments
encompassed within the following claims.
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