Display system

A laser scanned, flat panel display system is disclosed. In one embodiment, the display system comprises a display panel (54), a plurality of first mirrors (30), a plurality of second mirrors (50), a source of light (10), means for modulating the intensity of the light (12), and deflection means (14). The display panel includes a display surface that extends along X and Y axes. Each first mirror is located at a different position along the X axis, and has an elongated dimension normal to the X axis. Each second mirror is located at a different position along the Y axis, and includes an elongated dimension normal to the Y axis. The deflection means directs the light as a first beam (17) to a selected first reflection point (32) on one of the first mirrors, such that the first beam is reflected from the first reflection point as a second beam (18). The second beam strikes one of the second mirrors at a second reflection point (52) and is reflected as a third beam (19) to a display point (53) on the display surface. The first and second mirrors are positioned such that varying the location of the first reflection point along the elongated dimension of a particular first mirror causes the Y coordinate of the display point to change, and varying the location of the first reflection point from one first mirror to another first mirror causes the X coordinate of the display point to change.

FIELD OF THE INVENTION 
The present invention relates to flat panel display systems. 
BACKGROUND OF THE INVENTION 
Currently available display systems include cathode ray tubes and a variety 
of flat panel displays such as LED arrays, liquid crystal arrays, thin 
film electroluminescent displays, and gas discharge displays. The flat 
panel display systems incorporate an X-Y grid of contacts to address and 
drive the individual display pixels. 
Cathode ray tubes are bulky, relatively heavy, and susceptible to image 
distortion caused by magnetic field variations. For large area displays, 
the bulk and weight of cathode ray tubes increases rapidly, resulting in 
the use of projection systems for most large television systems. For flat 
panel displays, the large number of drivers and addressing lines becomes a 
limitation for large display sizes. As a result of these limitations, 
there is a need for a display system that combines the low volumes of flat 
panel displays with the relatively simple scanning techniques of cathode 
ray tubes. 
Several efforts have been under way to provide such an enhanced system that 
would be particularly suitable for large displays. One approach has been 
the reformatting of the cathode ray tube envelope and electron gun 
geometry. This approach is a variation of the standard cathode ray tube 
electromagnetic or electrostatic deflection scheme, and seeks to direct 
the electron beam or beams within the confines of a less bulky vacuum 
envelope. The need to direct the electron beam within the vacuum envelope, 
however, requires that the envelope be sufficiently massive or contain 
sufficient internal supports to withstand the high force generated by 
atmospheric pressure over large areas. A second approach has been a 
reduction in the number of drivers required in a flat panel display 
system. This approach eliminates the need for a scanned beam, but may 
still require internal supports, particulary for the gas discharge 
displays and liquid crystal displays. 
SUMMARY OF THE INVENTION 
The present invention provides a laser scanned flat panel display system 
that uses an optical scanning technique that permits the laser beam to be 
folded to fit within a flat panel, low volume configuration. 
In one preferred embodiment, the display system of the present invention 
comprises a display panel, a plurality of first mirrors, a plurality of 
second mirrors, a source of light, means for modulating the intensity of 
the light, and deflection means. The display panel includes a display 
surface that extends along X and Y axes. Each first mirror is located at a 
different position along the X-axis, and has an elongated dimension normal 
to the X-axis. Each second mirror is located at a different position along 
the Y-axis, and includes an elongated dimension normal to the Y-axis. The 
deflection means directs the light as a first beam to a selected first 
point on one of the first mirrors, such that the first beam is reflected 
from the first reflection point as a second beam. The second beam strikes 
one of the second mirrors at a second reflection point, and is reflected 
as a third beam to a display point on the display surface. The first and 
second mirrors are positioned such that varying the location of the first 
reflection point along the elongated dimension of a particular first 
mirror causes the Y coordinate of the display point to change, and varying 
the location of the first reflection point from one first mirror to 
another first mirror causes the X coordinate of the display point to 
change. 
In a further aspect of the invention, the first and second mirrors are 
positioned such that varying the location of the first reflection point 
along the elongated dimension of a particular first mirror causes the 
second beam to strike different second mirrors, and such that varying the 
location of the first reflection point from one first mirror to another 
first mirror causes the second reflection point to move along the 
elongated dimension of a particular second mirror.

DETAILED DESCRIPTION OF THE INVENTION 
Referring initially to FIG. 1, a preferred embodiment of the present 
invention is shown comprising laser 10, modulator 12, deflection unit 14, 
deflection mirror 16, first mirror assembly 20, second mirror assembly 40, 
and display panel 54. Laser 10 produces light beam 11 that is modulated in 
intensity by modulator 12 to produce modulated beam 13. Modulated beam 13 
is input into deflection unit 14, and the deflection unit produces small 
deflections in the modulated beam in two independent directions normal to 
the modulated beam to produce output beam 15. The light of output beam 15 
is then reflected by deflection mirror 16, first mirror assembly 20 and 
second mirror assembly 40 to point 53 on display panel 54. The laser light 
striking the display panel at point 53 causes illumination at that point, 
the intensity of the illumination corresponding to the intensity of 
modulated beam 13. Modulator 12 therefore controls the intensity of 
illumination at point 53. As described below, the position of point 53 on 
the display panel is controlled by deflection unit 14. 
The entire display system of FIG. 1 can be contained within a volume having 
a comparatively small extent in the direction normal to display panel 54. 
For ease of discussion, display panel 54 will be assumed to lie in the X-Y 
plane (FIG. 1), with the X-axis coinciding with the elongated dimension of 
first mirror assembly 20, and the Y-axis coinciding with the elongated 
dimension of second mirror assembly 40. The Z-axis is normal to the 
display panel, and the edges of the display panel are aligned with the X 
and Y axes. The positive directions along the X, Y and Z axes are 
indicated by arrows in FIG. 1. 
In one preferred embodiment, the display system of FIG. 1 is provided with 
signals identical to those used in a black and white raster scanned 
display such as a television receiver. In particular, modulator 12 is 
controlled by a conventional video intensity signal, and deflection unit 
14 is controlled by conventional horizontal and vertical scanning signals. 
Deflection unit 14 is oriented such that the horizontal scanning signal 
causes deflection along the Z-axis, with the slowly changing (scanning) 
portion of the horizontal deflection signal causing output beam 15 to 
change its deflection in the negative Z direction, and the rapid return 
portion of the horizontal deflection signal causing output beam 15 to 
change its deflection in the positive Z direction. The deflection unit is 
also oriented such that the vertical deflection signal causes deflection 
along the X-axis, with the slowly changing (scanning) portion of the 
vertical deflection signal causing output beam 15 to change its deflection 
in the positive X direction, and the rapid return portion of the vertical 
deflection signal causing output beam 15 to change its deflection in the 
negative X direction. As described below, the result of deflecting the 
laser beam in such a manner will be that point 53 will be scanned across 
and down display panel 54 in a manner identical to the scanning of a 
conventional CRT display. 
Laser 10 may comprise any suitable commercially available laser. The width 
and divergence of the laser beam should be selected based upon the desired 
size for point 53 on display panel 54, i.e., on the required resolution of 
the display system. In general, a laser that produces a beam having a 
divergence less than or equal to one milliradian is preferred. The power 
of laser 10 should be selected based upon the required brightness of the 
display, and upon the type of display panel, as described below. Different 
types of lasers may be selected to produce displays of different colors. 
Modulator 12 may be any well-known type of electro-optic or acousto-optic 
device having a suitable bandwidth. Deflection unit 14 is preferably a 
two-axis, acousto-optic deflector that has sufficient resolution to 
produce a 400-500 line display on display panel 54. 
Deflection mirror 16 is preferably a front surfaced mirror having a planar, 
spherical or cylindrical reflecting surface that may either be smooth or 
stepped as described below. The function of deflection mirror 16 is to 
reflect output beam 15 to beam 17 traveling toward first mirror assembly 
20. The deflection mirror thereby permits a more compact arrangement of 
the components of the display system. In the embodiment shown in FIG. 1, 
deflection mirror 16 is a smooth surfaced planar mirror positioned 
directly below the first mirror assembly and oriented at an angle of 
45.degree. with respect to the undeflected output beam 15. 
First mirror assembly 20 comprises a body 22 that is wedge shaped in cross 
section, and that has a comparatively long dimension along the X-axis and 
a comparatively short dimension along the Y-axis. Referring now to FIGS. 2 
and 2a, body 22 includes rear surface 26 aligned with the X-axis, and 
front surface 24 slightly inclined with respect to the X-axis. Front 
surface 24 is formed into a series of steps comprising mirrors 30a, 30b 
and 30c and spacing surfaces 28. Each mirror 30 is generally rectangular 
in shape, and is elongated across the width of the first mirror assembly 
in the Z direction. Mirrors 30 are inclined at an angle of approximately 
45.degree. with respect to the X-axis, such that when beam 17 strikes 
first reflection point 32 on one of such mirrors, it is reflected to the 
left normal to the X-axis as beam 18, as shown in FIG. 2a. The short 
dimension of each mirror is preferably on the order of the diameter of 
beam 17. Each spacing surface 28 is oriented substantially parallel to the 
X-axis, such that beam 17 cannot strike the spacing surfaces. 
The function of first mirror assembly 20 is to determine the vertical 
position of point 53, i.e., the position of point 53 along the X-axis. 
Referring to FIG. 2a, beam 17 from deflection mirror 16 is shown striking 
first reflection point 32 on mirror 30b and being reflected to the left as 
beam 18. It is evident from FIG. 2a that if beam 17 were to be deflected a 
small distance either to the left or to the right, then the first 
reflection point would be on mirror 30a or mirror 30c respectively, and as 
a result the vertical position of beam 18 would be modified. As described 
below, second mirror assembly 40 does not modify the vertical position of 
the laser beam, and the vertical position of beam 18 therefore specifies 
the vertical position of point 53. thus by modifying the position of beam 
17 in the Y direction, the height of point 53 can be controlled. The 
position of beam 17 in the Y direction can be controlled by deflection 
unit 14 by varying the orientation of output beam 15 in the X direction. 
The vertical deflection signal applied to deflection unit 14 therefore 
controls the vertical position of point 53. As illustrated in FIG. 2a, the 
projections of spacing surfaces 28 onto the X-Y plane have a considerably 
greater extent than do the projection of mirrors 30. As a result, a 
comparatively small deflection of beam 17 along the Y direction (and of 
output beam 15 in the X direction) results in a comparatively large change 
in the height of point 53. 
Referring now to FIGS. 1, 3 and 3a, second mirror assembly 40 comprises 
body 42 that is wedge shaped in cross section, and that has a 
comparatively long dimension along the Y-axis and a comparatively short 
dimension along the Z-axis. The cross section of body 42 is constant along 
the X-axis, and body 42 is coextensive with first mirror assembly 20 in 
the X direction. Body 42 includes rear surface 46 aligned with the Y-axis 
and front surface 44 slightly inclined with respect to the Y-axis. Front 
surface 44 is formed into a series of steps comprising mirrors 50a, 50b 
and 50c and spacing surfaces 48. Each mirror 50 is generally rectangular 
in shape, and is elongated across the width of the second mirror assembly 
in the X direction. Mirrors 50 are inclined at an angle of approximately 
45.degree. with respect to the Y-axis, such that when beam 18 strikes a 
second reflection point 52 on one of mirrors 50, it is reflected in the 
forward (Z) direction as beam 19 towards display panel 54. The short 
dimension of each mirror is preferably on the order of the diameter of 
beam 18. Each spacing surface 48 is oriented substantially parallel to the 
Y-axis, such that beam 18 cannot strike the spacing surfaces. 
The function of second mirror assembly 40 is to control the horizontal 
position of point 53, i.e., the position of point 53 along the Y-axis. 
Referring to FIG. 3a, beam 18 from first mirror assembly 20 is shown 
striking second reflection point 52 on mirror 50b and being reflected 
forward as beam 19. It is evident from FIG. 3a that if beam 18 were to be 
deflected a small distance either forward or rearward in the Z direction, 
then the second reflection point would be on mirror 50a or mirror 50c 
respectively, and as a result the horizontal position of beam 19 and of 
point 53 would be modified. Since neither deflection mirror 16 nor first 
mirror assembly 20 changes the orientation of the laser beam in the Z 
direction, the horizontal position of point 53 is controlled by the amount 
of deflection of output beam 15 along the Z-axis. The horizontal 
deflection signal applied to deflection unit 14 therefore controls the 
horizontal position of point 53. As illustrated in FIG. 3a, the 
projections of spacing surfaces 48 onto the Y-Z plane have a considerably 
greater extent than do the projections of mirrors 50. As a result, a 
comparatively small deflection of beam 18 along the Z direction results in 
a comparatively large change in the horizontal position of point 53. 
In summary, movement of point 53 from left to right across display panel 54 
results when deflection unit 14 causes output beam 15 to move in the 
negative Z direction. Such motion of output beam 15 causes beam 17 to move 
in the same direction, causing first reflection point 32 to move in the 
negative Z direction along the length of a given first mirror. As a 
result, beam 18 moves in the negative Z direction, and second reflection 
point 52 moves in the negative Y direction, such that the second 
reflection point is successively located on different second mirrors. Each 
second mirror reflects the light in the Z direction towards display panel 
54, and movement of second reflection point 52 from left to right 
therefore causes point 53 to move from left to right across the display 
panel. Vertical scanning of point 53 results when deflection unit 14 
causes output beam 15 to be deflected in the positive X direction. Such 
deflection of output beam 15 causes beam 17 to increase its deflection in 
the negative Y direction, causing first reflection point 32 to move down 
the length of first mirror assembly 20, successively striking different 
first mirrors. Each first mirror causes beam 18 to be produced traveling 
towards the second mirror assembly in the Y direction. The second mirror 
assembly does not change the X position of the light beam, and the X 
position of point 53 is therefore the same as the X position of first 
reflection point 32. Motion of first reflection point 32 down the length 
of first mirror assembly 20 therefore causes point 53 to move down the 
display panel. 
Display panel 54 may comprise a ground glass plate upon which beam 19 is 
incident to produce a visible spot of light having a color determined by 
the color of beam 11 produced by laser 10. A color display on display 
panel 54 can be created using a superposition of laser beams at different 
wavelengths (e.g., red, green and blue) to create the desired colors. For 
comparatively large displays, or for displays intended for use in a high 
ambient light environment, display panel 54 can be coated with an 
appropriate phosphor adapted to be excited by the laser beam. In the case 
of a phosphor coated panel, a color display could be achieved through the 
use of multiple color phosphors on the display panel. A third embodiment 
for display panel 54 is illustrated in FIG. 6. In this embodiment, the 
display panel is enclosed between transparent rear plate 58 and 
transparent front plate 59. The display panel of FIG. 6 further includes 
photocathode 55, channel electron multiplier 56 and phosphor layer 57. 
Beam 19 causes the emission of photoelectrons from photocathode 55. The 
electrons are then multiplied in channel electron multiplier 56 and 
accelerated by an electrostatic potential to excite phosphor layer 57. The 
display panel of FIG. 6 can be used in connection with a lower power base, 
because of the amplification provided by the electrostatic potential power 
supply. Operation of the electron multiplier layer generally requires a 
sealed, evacuated area between rear plate 58 and front plate 59. However, 
the proper construction can allow the electron multiplier to operate at 
atmospheric pressure. 
FIGS. 4 and 5 illustrate a second embodiment of the present invention in 
which the mirrors are positioned and oriented in a nonrectilinear fashion. 
Referring initially to FIG. 4, the second embodiment comprises laser 60, 
modulator 62 and deflection unit 64 that are fully analogous to the 
corresponding components of the FIG. 1 embodiment. The embodiment of FIG. 
4 also includes deflection mirror 66, first mirror assembly 70, second 
mirror assembly 90 (FIG. 5), and display panel 104. As in the embodiment 
of FIG. 1, deflection unit 64 produces output beam 65 that can be 
independently deflected along the X and Z axes. Output beam 65 is 
reflected by deflection mirror 66, first mirror assembly 70 and second 
mirror assembly 90 to point 106 on display panel 104. 
Deflection mirror 64 includes a stepped spherical reflecting surface that 
is convex in the direction facing output beam 65. Mirror 66 therefore 
causes output beam 65 to be reflected towards first mirror assembly 70 as 
beam 67. The convex, spherical shape of mirror 66 causes a given angular 
deflection of output beam 65 to be amplified into a larger angular 
deflection of beam 67, with the degree of amplification being controlled 
by the radius of curvature of mirror 66. The steps on the reflecting 
surface of mirror 66 extend substantially in the Z direction and 
correspond in number to the number of horizontal scanning lines used in 
the display system. In particular, each step of mirror 66 is positioned to 
intercept output beam 65 during one complete horizontal scanning line. 
First mirror assembly 70, shown in cross section in FIG. 4, comprises a 
body 72 that is generally wedge shaped in cross section, and that has a 
comparatively long dimension along the X-axis and a comparatively short 
dimension along the Y-axis. body 72 includes rear surface 76 aligned with 
the X-axis, and front surface 74 that is variably inclined with respect to 
the X-axis. Front surface 74 is formed into a series of steps comprising 
spacing surfaces 78 and mirrors 80. The sizes of mirrors 80 and spacing 
surfaces 78 have been exaggerated in FIGS. 4 and 5 for purposes of 
illustration. Each mirror 80 is generally rectangular in shape, and has an 
elongated dimension that extends in the Z and Y directions and that is 
slightly convex, as indicated schematically in FIG. 5. Each mirror 80 is 
positioned and inclined such that when it intercepts beam 67 emerging from 
mirror 66, it will cause beam 67 to be reflected as beam 68 traveling in 
the Y and Z directions towards second mirror assembly 90. Each spacing 
surface 78 is oriented such that it is parallel to beam 67 when beam 67 
strikes an adjacent mirror 80, and beam 67 therefore cannot strike the 
spacing surfaces. 
Each mirror 80 is associated on a one-to-one basis with a single step of 
mirror 66. For each horizontal scanning line of the display system, 
deflection unit 64 deflects output beam 65 in the X direction such that 
the output beam strikes a particular step of mirror 66 associated with 
that horizontal line. The resulting reflected beam 67 then proceeds to 
strike a particular mirror 80 that is also associated with that horizontal 
scanning line. 
Referring now to FIG. 5, second mirror assembly 90 comprises a body 92 that 
is generally wedge shaped in cross section, and that has a comparatively 
long dimension along the Y-axis and a comparatively short dimension along 
the Z-axis. The second mirror assembly is coextensive with the display 
panel in the X direction. Body 92 includes rear surface 96 aligned with 
the Y-axis, and front surface 94 that is variably inclined with respect to 
the Y-axis. Front surface 94 is formed into a series of steps comprising 
mirrors 90 and spacing surfaces 98. Each mirror 90 is generally 
rectangular in shape, and is elongated across the width of the second 
mirror assembly in the X direction. Each mirror 90 is positioned and 
inclined such that when it intercepts beam 68 reflected from first mirror 
assembly 70, it will cause beam 68 to be reflected as beam 69 traveling in 
the Z direction toward display panel 104. Each spacing surface 98 is 
oriented such that it is parallel to beam 68 when beam 68 strikes an 
adjacent mirror 90, and beam 68 therefore cannot strike the spacing 
surfaces. 
While the preferred embodiments of the invention have been illustrated and 
described, it should be understood that variations will be apparent to 
those skilled in the art. Accordingly, the invention is not to be limited 
to the specific embodiments illustrated and described, and the true scope 
of and spirit of the invention should be determined by reference to the 
following claims.