Optically addressed liquid crystal display device having a matrix array of photocells

A display mechanism is featured which incorporates a scanning laser which is used to address a two dimensional photocell matrix array. This array is coupled directly to a liquid crystal display (LCD) and is used to address pixels on the LCD thus creating a display as addressed by the laser. The image created is on the far side of the scanning laser and remains on the LCD until the charge from the photocells dissipate. A new display is created once again as the scanning laser addresses and illuminates desired photocells. Additional illumination is provided at the front of the display on the same side as the observer, or at the rear on the same side as the laser.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus and a method for producing a display 
mechanism utilizing a scanning laser which addresses pixels on the device. 
In particular, the apparatus employs a liquid crystal display panel which 
interfaces with a two dimensional photocell matrix array. These photocells 
are individually addressed by a scanning laser and when addressed, the 
photocells utilizing the energy given by the laser beam send a charge to 
the liquid crystal display panel thus activating a pixel on the display 
screen. By selectively addressing photocells in the matrix formation, the 
desired display is formed on the liquid crystal display panel. A single 
laser or multiple lasers can be used to scan the photocell array which is 
similar to the functioning of an electron gun in a Cathode Ray Tube (CRT) 
to form an image. Unlike applications that use laser beams to reflect off 
a display screen, this device is capable of brighter outputs as the laser 
beam is used only to activate the liquid crystal display and uses other 
brighter lights that can be used to illuminate the display screen. 
Prior art would involve passive liquid crystal displays which require I.C. 
drivers to address each pixel. These drivers are placed around the display 
screen increasing the overall size and also making it difficult to place 
two or more screens adjacent to each other without a space between them. 
Active liquid crystal displays require a transistor at each pixel's 
location increasing the complexity and cost with a limited yield in 
production. The advantages of this device are that unlike prior art, 
addressing the device does not require active electronics and hence the 
display screen can be made quite large, in addition to which pixels can be 
located at the extreme edge, as no electronics are required there. This 
enables screens to be placed adjacent to each other in a matrix fashion to 
create extremely large displays utilizing a multitude of smaller screens, 
with continuity across screens as no gaps are present. Conventional CRT's 
require a vacuum in the tube increasing the cost of manufacturing, and 
when in operation, the electron beam is susceptible to distortion by the 
earth's magnetic field. The power requirement for a CRT is considerably 
more than that required for the scanning laser in the present invention. 
The device has potential applications from Computer Aided Design (CAD) work 
stations to cinema screens. Large screen implementation could also involve 
street displays and highway information displays. High definition 
television applications of the device are particularly advantageous in 
situations where conventional liquid crystal displays do not permit high 
resolution screens of large dimensions. 
SUMMARY OF THE INVENTION 
Generally speaking, in accordance with the present invention, a display 
device utilizing a scanning laser to address pixels on a liquid crystal 
display is constructed, having properties of high resolution and large 
screen capability with a relatively low cost of manufacturing. 
A scanning laser is used to address pixels on a liquid crystal display in 
which the pixels are composed of photocells arranged in a large two 
dimensional matrix array. The photocells are mounted on a reflective layer 
which are then attached to a first transparent panel at the back of the 
device. This panel sandwiches liquid crystals with a second transparent 
panel lined with a transparent conductive layer on the inside located at 
the front of the device. Each pixel or photocell is laser addressed at the 
back of the device by illuminating, and produces a low voltage at their 
specific location on the panel to which they are attached. The transparent 
conductive layer on the inside of the second transparent panel is kept at 
ground or a different voltage than the photocell thus orienting the liquid 
crystal layer such that light is polarized across it, as an electric field 
occurs between the addressed photocells and the second transparent panel. 
Addition of a polarizing filter to the front of the display device makes 
these spots or pixels appear black or other colors where the electric 
field is influencing the liquid crystals, and external light sources can 
be added at the front to illuminate the device, for this particular 
embodiment. By varying the laser's intensity of illumination on each 
pixel, the amount of charge accumulated at the photocell site also varies, 
thus changing the darkness of each pixel. This produces a grey scale 
effect on the display screen. 
In another embodiment, it is possible to have the device back lit by 
mounting the photocells on a transparent conductive layer in the assembly 
previously described as opposed to a reflective layer. When addressed by 
illuminating, each photocell produces a localized low voltage at the 
panel. A filter to allow only the passage light of a specific wavelength 
band identical to the laser's is deposited over each photocell in the two 
dimensional array. As a photocell is illuminated by the laser, it 
accumulates a charge where it touches the first transparent panel. This 
produces a voltage difference across the transparent panels and orients 
the liquid crystals in such a manner that light is polarized across it. 
Further effects of a polarizing filter across the front of the display 
makes these pixels appear black or other colors. An external light source 
is now used to illuminate the display at the back of the screen. This is 
accomplished as light from a source travels through a special filter that 
removes only the specific wavelengths allowed through the photocells' 
filter and illuminates a transparent conductive layer affixed to each 
photocell. As individual photocells are addressed, corresponding pixels on 
the LCD become active when charges are directed to them by the photocells, 
thus creating a display. When this charge dissipates, the laser would 
address a new selection of photocells for the next display. 
For both embodiments, the photocell stores an electrical charge over a 
preset duration after which this charge leaks or dissipates. This memory 
effect keeps the pixel dark (or active) over a predetermined duration, 
which is a fraction of the time the laser takes to get back to the pixel 
after scanning the rest of the display producing a grey scale effect.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
For a better understanding of the invention, reference is first made to the 
block diagram of FIG. 1 which illustrates the three main components of the 
device as they function to create a display. A scanning laser 1 is used to 
address and illuminate selected pixels on a photocell matrix array 2. 
These individually addressed pixels on the photocell matrix array direct a 
charge to the liquid crystal display (LCD) device 3, which has the same 
matrix configuration as the photocell array, such that the selected pixels 
addressed by the scanning laser appear on the LCD. 
Referring now to FIG. 2, which illustrates the composition of the two 
dimensional photocell matrix array in FIG. 1, the scanning laser 1 
addresses and illuminates pixels which collectively compose the desired 
display. Each of these pixels consists of a photocell 4 which when 
addressed by illuminating produces a low voltage at the transparent panel 
5. The liquid crystals 6 are sandwiched between two transparent panels 8 & 
5. The panel 8 also has a conductive transparent layer 7 deposited on its 
inner surface which could have the option of being patterned depending on 
the image quality desired. Layer 7 is kept at ground or at a different 
voltage than that to be achieved for the photocells at the other 
transparent panel 5. As a photocell 4 is illuminated by the laser, it 
accumulates a charge where it touches the panel 5. This produces a voltage 
difference across these pixels on panel 5 and layer 7 and orients the 
liquid crystal layer 6 in such a manner that light is polarized across it. 
Further effects of a polarizing filter 9 across the front of the display 
makes these pixels appear black or another color. An external light source 
10 can be implemented to illuminate the display at the front of the 
display screen where the observer 10A is situated. This is accomplished as 
light travels through the polarizing filter 9, the transparent panel 8, 
and the liquid crystal layer 6 after which it is reflected off layer 11 
passing back through the liquid crystal layer, transparent panel and 
polarizing filter directly to the observer 10A. The reflective surface 11 
can be an integral part of the photocell 4 or a separate layer deposited 
on the outer side of panel 5. The photocell 4 could also be deposited on 
the inner side of panel 5. As individual photocells are addressed, 
corresponding pixels on the LCD become active when charges are directed to 
them by the photocells, thus creating a display. When this charge 
dissipates, the laser would address a new selection of photocells for the 
next display. The photocells store charges for a preset duration acting as 
a memory for the device. Variable illumination intensities on the 
photocell by the laser would result in variable amounts of charge stored 
producing a variable darkness display or grey scale display for the 
device. 
A typical representation of the photocell matrix array as obtained from 
view AA of FIG. 2 is clearly illustrated in FIG. 3. For example, the 
entire array 12 is composed of individual photocells or pixels 13 in a two 
dimensional matrix formation. 
Referring now to FIG. 4, which illustrates the implementation of multiple 
laser beams 14 to scan separate allotted portions of the display screen 
15. This allows more time for the lasers to address each pixel with 
varying intensity in fast changing displays assisting in contrast control 
of the displayed image. 
Referring to FIG. 5, which illustrates multiple lasers 16 scanning the 
entire display screen 17', whereby the lasers overlap in scanned areas to 
allow more than one laser to address the same pixel if required, yielding 
a higher contrast than neighboring pixels for an enhanced grey scale 
display, in this particular embodiment. 
Referring now to FIG. 6, which illustrates an alternate composition of the 
two dimensional photocell matrix array in FIG. 1, the scanning laser 1 of 
a particular wavelength band addresses and illuminates pixels which 
collectively compose the desired display. Each of these pixels consists of 
a photocell 19 which when addressed by illuminating produces a low voltage 
at the transparent panel 20. A filter 21 to allow the passage light of the 
laser's wavelength only, is deposited over each photocell in the array. 
The liquid crystals 22 are sandwiched between two transparent panels 20 & 
23. The panel 23 also has a conductive transparent layer 24 deposited on 
its inner surface which could have the option of being patterned depending 
on the image quality desired. Layer 24 is kept at ground or at a different 
voltage than that to be achieved for the photocells at the other panel 20. 
As a photocell 19 is illuminated by the laser, it accumulates a charge 
where it touches the panel 20. This produces a voltage difference across 
these pixels on the panel 20 and layer 24 and orients the liquid crystals 
22 in such a manner that light is polarized across it. Further effects of 
a polarizing filter 25 across the front of the display makes these pixels 
appear black or another color. An external light source 26 can be 
implemented to illuminate the display at the back of the display screen 
with the observer 26A to the front of the display. This is accomplished as 
light from source 26 travels through a special filter 27 that removes only 
the laser's wavelength and illuminates the transparent conductive surface 
28 which can be an integral part of the photocell 19 or a separate layer 
deposited on the transparent panel 20. The photocells 19 can also be 
deposited on the inner side of panel 20 with the transparent layer 28 
deposited on the exposed surface of the photocell. As individual 
photocells are addressed, corresponding pixels on the LCD become active 
when charges are directed to them by the photocells, thus creating a 
display. When this charge dissipates, the laser would address a new 
selection of photocells for the next display 
Referring to FIG. 7, which illustrates the scanning sequence of the laser 
for a matrix array of photocells or pixels 29, whereby the laser commences 
scanning the designated array block at the top left traversing 
horizontally to the right delivering varied illumination intensities on 
individual pixels. At the end of each horizontal path, the laser acquires 
its location on the next row below extreme left, and commences scanning to 
the right as demonstrated by the traversing path lines 30. When the last 
pixel in the array is illuminated, the laser is targeted back to the first 
pixel scanned by which time the charge can no longer be held by addressed 
photocells. Should any photocell require addressing before the laser has 
scanned the last in the array, multiple lasers would have to be 
implemented to speed up the scanning process. 
It is also understood that the following claims are intended to cover all 
of the general and specific features of the invention herein described, 
and all statements of the scope of the invention which, as a matter of 
language, might be said to fall therebetween.