Micro-lens array based light transmission screen

Description of equivalent WO 2004111915 A2

MICRO-LENS ARRAY BASED LIGHT TRANSMISSION SCREEN

CROSS-REFERENCE TO RELATED APPLICATIONS

[1] This application is a continuation-in-part of U.S. Patent Application Serial No.

10/120,785 filed on April 12, 2002, which is a continuation-in-part of U.S. Patent Application

Serial No. 09/521,236, filed April 5, 2000, now U.S. Patent No. 6,483,612, which is a

continuation of U.S. Patent Application Serial No. 08/060,906, filed April 15, 1998, now

abandoned. The contents of the above prior applications are hereby incorporated by

reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

[2] This invention relates to generating images, and more particularly to a light-

transmission screen for projecting images in televisions, computers, and/ or other display

devices. The invention also relates to a method for making a Eght-transmission screen of the

aforementioned type.

2. Description of the Related Art.

[3] Light-projection systems are used to generate images in computer monitors,

televisions, and other forms of display devices. Two types of light-projection systems are

available in the market today: rear-projection systems and front-projection systems. In a rear- projection system, a beam of light is projected onto the rear side of an angle-transforming

screen. The screen transmits an image corresponding to the beam to a front side of the

screen, where it can be seen by a viewer. Conversely, in a front-projection system a light beam

is directed onto the front side of a screen where it is then reflected towards a viewer. Because

of their optical properties, screens in rear-projection systems are often referred to as

transmission- type screens.

[4] Screens in conventional rear-projection displays perform a number of

functions. First, these screens distribute light from an image engine into a viewing space. An

example of such a viewing space is shown in Figs. 1(a) and 1(b). In these figures, angles φv

and ΦH define the range of viewing angles measured in vertical and horizontal directions

relative to a normal (dotted line) of the screen. The viewing angles are delimited by beams 1

and 2, which correspond to places where the intensity of the projected image falls to half the

value it has in the normal direction. In conventional screens, angles φv and ΦH are small

values, typically 15° and 35° respectively. As a result, the images generated by these screens is

projected into a small viewing area.

[5] Second, rear-projection screens must generate images have a certain minimum

resolution.

[6] Third, rear-projection screens must provide the viewer with a high contrast

image.

[7] Fourth, rear-projection screens must provide sufficient gain to enable

comfortable viewing in normal ambient light conditions. [8] Fifth, rear-projection screens must minimize artifacts, such as aliasing, which

tends to degrade image quality. The exact parameters and specifications for each of these

requirements will vary with each application.

[9] Fig. 2a shows one type of conventional rear-projection screen which performs

the aforementioned functions. These screens are formed from an array of lenticular lenses 3

separated by stripes 4 of black material. Current lenticular lens arrays generate insufficient

resolution and contrast for purposes of displaying high-quality digital images.

[10] Fig. 2b shows another type of conventional rear-projection screen. This screen

includes a plurality of glass beads 5 embedded in a black matrix 6. Screens of this type are

often niche-type devices and have proven unsuitable for many reasons. This is mainly

attributable to their use of beads as optical elements for projecting light. For example, it is

difficult to produce different angular light-distribution patterns in both vertical and horizontal

directions using beads because they all have the same spherical shape and curvature. As a

result, light is directed to unwanted areas, for example, towards the ceiling where there are no

viewers. In addition, manufacture difficulties associated with this type of screen result in

inhomogeneous placement of the beads, including areas with no beads ("drop outs").

[11] In view of the foregoing considerations, it is clear that there is a need for a

light-transmission screen which overcomes the drawbacks of conventional screens, and more

specifically one which generates images of improved quality using a light-diffusing element

which enhances control of the projected light at less cost and with substantially fewer

manufacturing steps compared with conventional screens. SUMMARY OF THE INVENTION

[12] An object of the present invention is to provide a light-transmission screen

which overcomes the drawbacks of conventional screens.

[13] Another object of the present invention is to provide a light-transmission

screen which generates images of improved quality compared with those produced by

conventional screens.

[14] Another object of the present invention is to provide a light-transmission

screen which improves image quality by providing independent control of viewing angles in

vertical and horizontal directions,

[15] Another object of the present invention is to provide a Kght-ttansmission

screen which improves image quality by achieving higher resolution than is attainable by

conventional screens.

[16] Another object of the present invention is to provide a light-transmission

screen which improves image quality by achieving higher gain than is attainable by

conventional screens.

[17] Another object of the present invention is to provide a light-transmission

screen which improves image quality by more effectively eliminating aliasing and other image

artifacts compared with conventional screens. [18] Another object of the present invention is to achieve one or more of the

aforementioned object using a diffusing element which projects Hght into a viewing area with

greater control than conventional screens.

[19] Another object of the present invention is to achieve this greater control using

a diffusing element which includes a micro-lens array, where structural features of individual

lenses in the array are varied so that some lenses project Hght in different directions and/or

with different optical properties than others.

[20] Another object of the present invention is to provide a method of making a

Hght-transmission screen which satisfies one or more of the aforementioned objects.

[21] Another object of the present invention is to provide a method for making a

Hght-transmission screen which has substantially fewer manufacturing steps and is more

economical to implement compared with conventional screens.

[22] The foregoing and other objects and advantages of the present invention are

achieved by providing a Hght-transmission screen, including a transparent substrate, a mask

layer having a pluraHty of apertures, and an array of lenses for projecting Hght through the

substrate and said apertures, wherein at least one of the lenses in said array has an aspherical

shape.

[23] In accordance with another embodiment, the present invention provides a

Hght-transmission screen which includes a transparent substrate, a mask layer having a

pluraHty of apertures, and an array of lenses projecting Hght through the substrate and the

apertures, wherein first and second lenses in the array project Hght in different directions. [24] In accordance with another embodiment, the present invention provides a

Hght-transmission screen, including a transparent substrate, a mask layer having a pluraHty of

apertures, and an array of lenses for projecting Hght through the substrate and said apertures,

wherein first and second lenses in said array project Hght in different directions.

[25] In accordance with another embodiment, the present invention provides a

Hght-transmission screen, including a transparent substrate, a mask layer having a pluraHty of

apertures, and an array of lenses for projecting Hght through the substrate and said apertures,

wherein at least a portion of the lenses in said array overlap one another.

[26] In accordance with another embodiment, the present invention provides a

Hght-transmission screen, including a transparent substrate, a mask layer having a pluraHty of

apertures, and an array of lenses for projecting Hght through the substrate and said apertures,

wherein at least two lenses in said array have different surface figures.

[27] In accordance with another embodiment, the present invention provides a

Hght-transmission screen, including a transparent substrate, a mask layer having a pluraHty of

apertures, and an array of lenses for projecting Hght through the substrate and said apertures,

wherein sizes of at least two of the lenses in said array are different.

[28] In accordance with another embodiment, the present invention provides a

Hght-transmission screen, including a first region which includes a first group of lenses, and a

second region which includes a second group of lenses, wherein the lenses in said first group

are structuraHy different from the lenses in said second group. [29] In accordance with another embodiment, the present invention provides a

Hght-transmission screen, including a transparent substrate, a mask layer having a pluraHty of

apertures, and an array of lenses, wherein at least two of the lenses in the array are configured

to project Hght through the substrate and through a corresponding aperture, and wherein at

least two of the lenses in the array have different shapes, sizes and/or are spaced differently

than the other lenses in the array so as to obtain a desired screen directionaHty, viewing angle,

gain, resolution and/ or contrast.

[30] The present invention also provides a Hght-transmission screen which

combines one or more of the embodiments previously mentioned. For example, the screen

may include a micro-lens array wherein the spacing and shape of the lenses are varied relative

to one another in order to achieve a desired viewing range and screen resolution. Other

combinations are also possible. Furthermore, the lenses at different regions of the screen may

be coUectively varied relative to one another. For example, the lenses situated along the

perimeter of the screen may have shapes and thus may project Hght in different directions

compared with lenses in a central portion of the screen. The same may be true on other

regions of the screen.

[31] The present invention is also a method for making a Hght-transmission screen

having any one or more of the aforementioned features. In accordance with one

embodiment, the method includes providing a transparent substrate, coating a surface of the

substrate with a mask layer, forrning a micro-lens array over the mask, and forming apertures

in the mask, each of which are aHgned to receive Hght from one or more lenses in the array. The micro-lens array is preferably formed based on a stamping operation using a master. An

optional step includes forming an anti-reflective coating on an opposing surface of the

substrate.

[32] In accordance with another embodiment, the present invention provides a

method for making a Hght-transmission apparatus, which is similar to the above method

except that the mask layer and lens array are formed on different sides of the substrate.

[33] In accordance with another embodiment, the present invention provides a

method for making a Hght-transmission apparatus which includes forming a micro-lens array

on a transparent substrate, coating a surface of the substrate opposing the lens array with an

adhesive, curing the adhesive, for example with UV Hght, and then forming a mask layer over

the adhesive. The portions of the adhesive struck by UV Hght are removed but those portions

not exposed to the Hght remain. As a result, the mask layer forms only over the unexposed

portions of the adhesive layer leaving apertures.

BRIEF DESCRIPTION OF THE DRAWINGS

[34] Figs. 1(a) is a diagram of a viewing space produced in a vertical direction by a

conventional Hght-transmission screen, and Fig. 1(b) is a diagram of a viewing space

produced in a horizontal direction by a conventional Hght-transmission screen;

[35] Fig. 2a is a diagram of a conventional Hght-transmission apparatus including a

lenticular lens array; [36] Fig. 2b is a diagram of a conventional Hght-transmission apparatus including

glass beads embedded in a black matrix;

[37] Fig. 3 is a diagram of a Hght-transmission screen that may include a micro-lens

array in accordance with any of the embodiments of the present invention;

[38] Fig. 4 is n gra showing the formation of lenses in a micro-lens array in

accordance with one embodiment of the invention;

[39] Fig. 5 is a diagram showing the formation of lenses in a micro-lens array in

accordance with another embodiment of the invention;

[40] Fig. 6 is a diagram showing the formation of lenses in a micro-lens array in

accordance with another embodiment of the invention;

[41] Fig. 7 is a diagram showing the formation of lenses in a micro-lens array in

accordance with another embodiment of the invention;

[42] Fig. 8 is a diagram showing the formation of lenses in a micro-lens array in

accordance with another embodiment of the invention;

[43] Fig. 9 is a diagram showing the formation of lenses in a micro-lens array in

accordance with another embodiment of the invention;

[44] Fig. 10 is a diagram showing the formation of lenses in a micro-lens array in

accordance with another embodiment of the invention;

[45] Fig. 11 is a diagram showing the formation of lenses in a micro-lens array in

accordance with another embodiment of the invention; [46] Fig. 12 is a diagram showing the formation of lenses in a micro-lens array in

accordance with another embodiment of the invention;

[47] Fig. 13 is a graph showing a profile curve which may be used as a basis for

forming a micro-lens array in accordance with the present invention;

[48] Fig. 14 is a diagram showing one example of a viewing range in the horizontal

direction achieved by the light- transmission screen of the present invention;

[49] Fig. 15 is a diagram showing one example of a viewing range in the vertical

direction achieved by the Hght-transmission screen of the present invention;

[50] Fig. 16 is a diagram of an embodiment of a Hght-transmission screen in

accordance with the present invention;

[51] Fig. 17 is a diagram showing an aperture-to-pixel arrangement in accordance

with one embodiment of the present invention;

[52] Fig. 18 is a flow diagram showing steps included in one embodiment of the

method of the present invention for making a Hght-transmission screen;

[53] Figs. 19a-e are diagrams showing results obtained at various steps of the

method in Fig. 18;

[54] Fig. 20 is a diagram of another embodiment of a Hght-transmission screen in

accordance with the present invention;

[55] Fig. 21 is a flow diagram showing steps included in another embodiment of the

method of the present invention for making a Hght-transmission screen; [56] Figs. 22a-d are diagrams showing results obtained at various steps of the

method in Fig. 21;

[57] Fig. 23 is a flow diagram showing steps included in another embodiment of a

method of the present invention for making a Hght-transmission screen; and

[58] Figs. 24a-d are diagrams showing results obtained at various ^' steps of the

method of Fig. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[59] The present invention is a Hght-transmission screen which generates images of

improved quaHty compared with conventional screens of this type. The screen is particularly

suitable for generating images in rear-projection systems, such as televisions and computer

monitors, and will be described below in that context for illustrative purposes. However, the

screen of the present invention may be used in other appHcations including, but not limited

to, diffusers and other diffractivε optical systems which evenly diffuse Hght over large areas

and solar panels.

[60] Fig. 3 shows a Hght-transmission screen which includes a pluraHty of lenses 100

for projecting an image within a predetermined viewing area. These lenses are formed in a

micro-lens array, the structure of which will be explained in greater detail below. For

Hlustrative purposes, the lenses are grouped into five regions: regions 101 and 102 are located

along lateral sides of the screen, two regions 103 and 104 are located along top and bottom

portions of the screen, and one region 105 is located at a central portion of the screen. While only five regions are shown, those skilled in the art can appreciate that the entire screen may

be populated with lenses in order to provide a complete image to the viewer.

[61] In accordance with the present invention, the screen lenses may be structuraHy

varied to improve the quaHty of the projected image, expand the effective viewing range of

the screen, reduce image artifacts, and/ or achieve any one of a number of other objectives.

The structural variances may exist between or among the lenses in one region of the screen or

in different regions. Each structural variance may be individually taken to correspond to a

different embodiment of the screen of the present invention. AdditionaUy, these variances

may be combined to achieve one or more of the quaHty, range, or anti-artifact objectives

previously mentioned.

[62] Fig. 4 shows how lenses may be structuraHy varied in accordance with one

embodiment of the Hght-transmission screen of the present invention. In this embodiment, at

least two lenses have an aspherical shape. In the example shown, lenses 120 and 122 are

substantiaUy elHptical, however the lenses may have other aspherical shapes or curvatures if

desired. Also, the aspherical lenses may be adjacent one another or separated by one or more

lenses having the same or different shapes.

[63] Fig. 5 shows how lenses may be structuraHy varied in accordance with another

embodiment of the screen of the present invention. In this embodiment, at least two lenses

not only have an aspherical shape, but are also asymmetrical. The asymmetry may exist along

one or more axes or the lenses may be completely asymmetrical so as to be irregular in shape.

In the example shown, lenses 130 and 132 are substantially egg-shaped and thus are asymmetrical with respect to a horizontal axis passing through the lens. Also, the

asymmetrical lenses may be adjacent one another or separated by one or more lenses having

the same or different shapes.

[64] Fig. 6 shows how lenses may be structuraHy varied in accordance with another

embodiment of the screen of the present invention. In this embodiment, at least one lens has

a spherical or hemispherical shape and at least another lens has an aspherical shape or

aspherical and asymmetrical shape. In the example shown, lens 140 has a hemispherical shape

and lens 142 a shape which is asymmetrical along only one axis. Alternatively, the lenses may

be completely asymmetrical so as to be irregular. The lenses may be adjacent one another or

separated by one or more lenses having the same or different shapes.

[65] Fig. 7 shows how lenses may be structuraHy varied in accordance with another

embodiment of the screen of the present invention. In this embodiment, aU lenses are

sphericaUy or hemispherically shaped, however their radiuses of curvature are different. In the

example shown, lenses 145 and 149 have a radius Ri which is greater than a radius R₂ of

lenses 146 and 147. These lenses may be adjacent one another or separated by lenses which

have the same or different curvatures. Hemispherical lens 148 is provided to show that lenses

with varying radiuses of curvature may also be varied in terms of their spacing within a single

micro-lens array.

[66] Fig. 8 shows how lenses may be structuraHy varied in accordance with another

embodiment of the screen of the present invention. In this embodiment, at least two lenses

have different sizes and/or shapes. The size differences may, for example, be in terms of diameter, height, and/ or thickness. In the example shown, lenses 150, 151, and 152 differ in

aU three of these dimensions. Lenses 153, 154 and 155 show examples of how the shape of

the lenses may differ. Lenses 153, 154 and 155 are square-shaped, triangular-shaped and

polygonal-shaped, respectively. The lenses may be adjacent one another or separated by one

or more lenses having the same or different shapes.

[67] Fig. 9 shows how lenses may be structuraHy varied in accordance with another

embodiment of the screen of the present invention. In this embodiment, the packing

arrangement is chosen to achieve a desired effect. For example, the spacing may be varied in

one or more directions in order to achieve a desired effect. In the example shown, lenses 161-

163 are in an abutting relationship to one another and lenses 163 and 164 are separated by a

distance D. If desired, the lenses may be varied in horizontal and vertical directions to achieve

a desired packing arrangement. A hexagonal arrangement has been found to be preferable,

but other arrangements, such as a square or pentagonal packing arrangement, are possible.

[68] Fig. 10 shows how lenses may be structuraHy varied in accordance with another

embodiment of the screen of the present invention. In this embodiment, the lenses overlap

either uniformly or randomly. In the example shown, lenses 171-173 overlap by a uniform

amount, e.g., by 10 %.

[69] Fig. 11 shows another overlapping pattern of lenses. This pattern includes

three rows of lenses. The first and second rows of lenses 180 and 181 include sphericaHy or

hemispheficaUy shaped lenses which are adjacent one another but do not overlap. Centers of

the lenses in the first and second rows may be spaced by an amount X_p. The third row of lenses 182 overlap the first and second rows by predetermined amounts. Preferably, each of

the lenses in the second row overlaps two lenses in the first row and two lenses in the second

row by a same amount The degree, uniformity, and pattern of overlap may be altered to

produce any desired effect. While the use of spherical or hemispherical lenses is preferable,

aspherical and/or asymmetrical lenses may be used in an overlapping pattern if desired. Also,

the lenses may be arranged according to a hexagonal packing scheme with fill factors from

95% and above.

[70] Fig. 12 shows another overlapping pattern of lenses. In this example,

overlapping lenses are arranged in the form of a matrix 190. In the matrix, the lenses

randomly overlap one another in at least one direction and in some cases in two directions.

This may be achieved by aHowing the centers of the lenses to travel up to a predetermined

amount (e.g., 20%) of the inter-lens spacing along one or more axes. The foHowing steps may

be taken to generate such a randomized lens pattern.

[71]^" First, initial parameters are selected including the size and initial spacing of each

lens in the array, as well as the number of lenses therein. For example, each of the lenses may

be 60 microns in diameter and may be spaced from one another so that their centers are 50

microns apart in the horizontal direction and 30 microns apart in the vertical direction. Also,

the lenses may be arranged, for example, in a 20 x 20 matrix.

[72] Second, a vector is computed for the center of each lens. The horizontal

component of the vector may be a random number in the range of -10 microns to + 10

microns and the vertical component may be a random number in the range of - 6 microns to + 6 microns. The center of each lens may then be displaced from its original position based

on the computed vector.

[73] Third, the newly computed centers of the lenses are used as a basis for

patterning a master. The master is then used to generate a micro-lens array, in a manner that

will be discussed in more detail below, which array includes one or more repHcations of the

20 x 20 pattern of overlapping lenses. The initial parameters may be varied to produce

virtuaHy any pattern of lenses desired, including ones which overlap in a different manner or

which do not overlap at all. In addition, the size of the pattern is not limited to the 20 x 20

pattern described above. This pattern may then be formed on the master roHer so that, for

example, the micro-lens array may be mass-produced in the quantity desired in order to meet

consumer demands.

[74] Fig. 13 is a graph which provides a profile curve may be used as a guide for

constructing an aspherical lens design for a 25-micron radius lens in accordance with the

present invention. In this graph, lens height is plotted against lens radius of curvature and the

foHowing table sets forth values that He along the curve. Only profile information is given

since the lens is radially symmetric. To image the fuH lens, the profile curve may be rotated

about the y-axis. By using the profile curve in the graph, a micro-lens array may be

constructed in the form of a matrix which, for example, has a lens spacing of 35 microns in

the x-direction and 22 microns in the y-direction. Such a matrix may also have a modified

hexagonal packing arrangement, where the centers of lenses have a randomized factor of plus or minus 20%. Such a factor may produce a matrix where the lenses overlap in one or more directions.

Height (μm)

25.0 1.0

24.9 2.0

24.7 3.0

24.5 4.0

24.2 5.0

23.7 6.0

23.1 7.0

22.4 8.0

21.4 9.0

20.2 10.0

18.6 11.0

16.7 12.0

14.3 13.0

11.4 14.0

7.9 15.0

3.5 16.0

0.0 17.0

[75] The aforementioned embodiments of the screen of the present invention may

be combined in any manner desired. For example, varying the shape, curvature, spacing,

and/ or size of the lenses may be used as a basis for improving image quaHty, expanding

viewing angle, independendy controlHng the viewing angles in two or more directions (e.g.,

vertical and horizontal directions), and controUing or reducing or eHminating aHasing or other

unwanted image artifacts. Some specific examples will now be provided. [76] Fig. 14 shows an example of a Hght-transmission screen where the curvatures

of the lenses are decreased from the center of the screen to its edges in a horizontal direction.

Through this lens pattern, a wide viewing angle ΘH may be achieved in the horizontal

direction. This angle may, for example, extend ±70° from a normal perpendicular to the

screen, which is substantially wider than viewing ranges that can be achieved by conventional

transmission screens. If desired, the curvatures of the lenses may be varied less in the vertical

direction, e.g., a viewing angle of ΘH extending ±15 from normal may be achieved. (See Fig.

15). Alternatively, instead of a progressive change in lens curvature from a center to a

perimeter of the screen, lenses located in a central region of the screen may all have the same

structural design. In this case, outer lenses (e.g., lenses along the edges) may be varied in

curvature in order to produce the enhanced viewing angle.

[77] Structural variations to achieve other improvements are also possible. For

example, the structure of the screen lenses may be varied to achieve a predetermined gain

within a viewing area. The term gain refers to a ratio of intensities of Hght based on an effect

known as the Lambertian screen. Lambertian screen effect occurs when an intensity of Hght

at a smaH area in the screen is uniformly distributed in every angle. Screen gain refers to a

ratio of the intensity of Hght at an arbitrary point where a viewer is located and the

Lambertian screen at that point. As those skilled in the art can appreciate, the gain may be

greater or less than unity.

[78] In accordance with another embodiment of the present invention, the lenses at

one or more regions of the screen may therefore be structuraHy varied to project beams in a manner and/or in directions that wiU achieve a desired gain in a viewing area. This may be

accompHshed, for example, by forming the lenses so that a greater intensity of Hght is directed

at one particular direction of the screen than at another. Through these structural variations, a

Hght-transmission screen included, for example, in a rear-projection system may be designed

to have a gain sufficient to provide comfortable viewing of projected images from digital

image engines in a wide variety of ambient Hght conditions.

[79] In accordance with another embodiment of the present invention, lenses in

one or more regions of the screen may be varied to distribute Hght to appropriate half-power

half-angles in horizontal and/ or vertical directions. This may be accompHshed, for example,

using aspherical and/ or asymmetrical lenses which generate an angular distribution of Hght

from an image engine in the direction(s) desired. By using lenses of this type, Hght can be

distributed differently in different directions.

[80] Fig. 16 shows a cross-sectional view of a transmission screen including a micro-

lens array having any of the aforementioned structural variations. This screen includes first

and second optical layers 200 and 202 which are at least substantiaHy parallel and spaced by

an air gap 204. The first optical layer includes a coHimator in the form of a Fresnel lens 201.

This lens converts incident Hght 206 from an image engine 208 into collimated beams 210.

Other types of Hght coHimators, such as holographic optical elements, may be used in place

of the Fresnel lens 201.

[81] The second optical layer is a diffuser 212 which includes a pluraHty of lenses

221-227 situated along an incident surface. The lenses may be made from any one of a variety of transparent materials. A mask layer 250 containing a pluraHty of apertures 255 is formed

on a Hght-exiting side of the substrate. The mask layer may be a black mask and the apertures

are preferably aHgned precisely with exit pupils of corresponding ones of the lenses. AHgning

the apertures in this manner is beneficial because it increases contrast, reduces reflected Hght,

and prevents transmission of stray Hght from within the projection system to the viewer.

Also, as shown, the micro-lens array may be formed from combinations of

spherical/hemispherical, aspherical, and asymmetrical lenses as desired, as weH has ones have

varying radiuses of curvature, diameters, spacings, and other size differences.

[82] In order to achieve a desired resolution, Fig. 17 shows that the screen may be

fabricated so that Hght passing through a pluraHty of apertures 255 in the mask layer

corresponds to one pixel in the screen. By altering the number of lenses per pixel, a desired

screen resolution may be achieved which produces images of improved quaHty compared

with conventional screens. Moreover, the number of lenses or apertures per pixel may be

selected to achieve oversampHng of the digital image being projected. This oversampHng is

preferably performed at or above the Nyquist rate so as to prevent aHasing effects in the

resulting image. In accordance with one exemplary embodiment, oversampHng is performed

at 2 or 3 times the Nyquist rate. In a 10 times oversampHng screen, 100 lenses would be

provided per pixel.

[83] In addition to or as an alternative to the aforementioned control techniques,

screen resolution may be controUed by the size of the lenses. For digital image engines,

spherical or hemispherical lenses with racHi on the order of 20 microns may be used. Also, lens size may be chosen to remove aHasing effects, and the lens array may be randomized to

remove other types of image artifacts.

[84] In rear-projection television or monitor appHcations, it may be desirable to-

direct some Hght at angles wider than the designed viewing angle of the screen. For example,

although the rear projection screen may be designed to have a horizontal viewing angle of ±

70 degrees, it may be desirable for the screen to direct some amount of Hght at angles greater

than ± 70 degrees, so that a viewer will be able to tell if the television or monitor is on when

the viewer is positioned at angles greater than ± 70 degrees. The amount of Hght directed at

angles greater than the designed viewing angle only needs to be as much as is required to alert

a viewer that the television or monitor is on. The individual lenses of the screen of the

present invention may be configured, using the techniques described above, to achieve this

result.

[85] Fig. 18 is a flow diagram showing steps included in a method for making a

transmission screen as shown, for example, in Fig. 16. Accordingly, like reference numerals

are used where appHcable. Also, various stages of the method are shown in Figs. 19a-e. The

method includes as an initial step providing a substrate 240 made of, for example, a

polycarbonate or acryHc plastic thick enough to provide a desired level of mechanical stability.

(Block 380 and Fig. 19a).

[86] A second step includes coating a first surface 310 of the substrate with a thin

layer 320 of black masking material. (Block 381 and Fig. 19b). The thickness of this layer may

vary with the material employed but an order of magnitude of 250 nm has been found to be preferable. Coating techniques include e-beam vacuum deposition, sputtering, chemical vapor

deposition, as weH as other film-deposition techniques.

[87] A third step includes applying a material 360 from which the micro-lens array is

to be repHcated over the mask layer. (Block 382). This material may be, for example, a

photopolymer epoxy, a polycarbonate, or PMMA or other resin. Material_, layer 360 is then

patterned to form the individual lenses in the array. (Block 383 and Fig. 19c). This patterning

step may be performed by any one of a variety of methods. For example, the patterning step

may be performed in accordance with a stamping operation performed by a master which

contains the lens pattern thereon. A stamping operation of this type is described in U.S.

Patent AppHcation Serial Number 10/ (Attorney Docket No. BVT-0010C1P4), the

contents of which is incorporated herein by reference. Other methods, including embossing,

may also be employed to pattern the material layer 360. By forming a pattern in this manner,

two or more lenses in the array may be structuraHy varied in accordance with any of the

techniques described herein in order to achieve a desired screen resolution or image quaHty,

prevent aHasing, define a desired viewing range, etc.

[88] A fourth step includes forming apertures 370 in the mask layer. (Block 384 Fig.

19e). This may be performed by directing pulsed laser radiation 375 (Fig. 19d) through the

curved surface of the lens. The laser radiation is pulsed with an energy sufficient to form a

hole of a desired width in the masking layer without damaging the other features of the lens

or supporting substrate. Preferably, the laser is pulsed with an energy which is an order of

magnitude of 10 mj. [89] An optional fifth step includes forming an anti-reflective coating 390 on the

opposing surface 395 of the substrate. (Block 385 and Fig. 19e).

[90] Fig. 20 shows a cross-sectional view of another transmission screen including a

micro-lens array having any of the aforementioned structural variations. This screen is similar

to the screen shown in Fig. 15 except that the mask layer 400 and lens array 410 are provided

on opposite sides of the transparent substrate 420. Apertures 430 in the mask layer may be

aHgned as previously described to project Hght from one or more of the lenses.

[91] Fig. 21 is a flow diagram showing steps included in a method for making a

transmission screen as shown in Fig. 20. In this method, the mask layer 400 and lenses 410

are formed on opposing sides of the substrate 420. Figs. 22a-d show results obtained at ^■

various stages of this method. An initial step of the method includes providing a substrate

420 made of, for example, a polycarbonate or acryHc plastic thick enough to provide a desired

level of mechanical stability. (Block 500 and Fig. 22a).

[92] A second step includes applying a material 440 from which the micro-lens array

is to be repHcated on a surface 430 of the transparent substrate. (Block 510). This material

may be, for example, a photopolymer epoxy, a polycarbonate, or PMMA resin. Material layer

440 is then patterned to form the individual lenses in the array. (Block 520 and Fig. 22a). This

patterning step may be performed by any one of a variety of methods. Preferably, the

patterning step is performed in accordance with a stamping operation performed by a master

which contains the lens pattern thereon. A stamping operation of this type is described in

U.S. Patent AppHcation Serial Number 10/ , , (Attorney Docket No. BVT-0010C1P4), the contents of which is incorporated herein by reference. By forming a pattern in this

manner, two or more lenses in the array may be structuraHy varied in accordance with any of

the techniques described herein in order to achieve a desired screen resolution or image

quaHty, prevent aHasing, define a desired viewing range, etc.

[93] A third step includes coating a second surface 450 of the substrate with a thin

layer 460 of black masking material. (Block 530 and Fig. 22b). The thickness of this layer may

vary with the material employed but an order of magnitude of 250 nm has been found to be

preferable. Coating techniques include e-beam vacuum deposition, sputtering, chemical vapor

deposition, as weU as other film-deposition techniques.

[94] A fourth step includes forming apertures 470 in the mask layer. (Block 540 and

Fig. 22d). This may be performed by directing pulsed laser radiation 480 (Fig. 22c) through

the curved surface of the lens. The laser radiation is pulsed with an energy sufficient to form a

hole of a desired width in the masking layer without damaging the other features of the lens

or supporting substrate. Preferably, the laser is pulsed with an energy which is an order of

magnitude of 10 mj.

[95] An optional fifth step includes attaching a transparent layer 490 of

polycarbonate or other material to the mask layer to provide mechanical stabiHty to the lens

screen. (Block 550 and Fig. 22d).

[96] Fig. 23 is 'a flow diagram showing steps included in another method for making

a transmission screen as shown in Fig. 20, and Figs. 24a-d show results obtained at various

stages of this method. The method includes as an initial step forming a lens array 610 using a stamping operation of the type described in U.S. Patent AppHcation Serial Number

10/ ^' . , (Attorney Docket No. BVT-0010C1P4), the contents of which is incorporated

by reference. (Block 700 and Fig. 24a).

[97] A second step includes coating an opposing surface 620 of the array with a

photocurable adhesive 630 which, for example, may be UV curable. (Block 610 and Fig. 24b).

The photocurable adhesive is preferably one whose adhesive properties are affected by

exposure to UV Hght, suitably a photocurable adhesive that becomes non-adhesive when

exposed to UV Hght.

[98] A third step includes directing a beam of Hght 630 through the lens array. If a

photocurable adhesive 630 is used that becomes non-adhesive upon exposure to Hght of a

predetermined frequency and intensity, then the Hght beam has a frequency (e.g., UV Hght)

and intensity sufficient to cause the portions of the adhesive layer which are exposed to the

beam to become non-adhesive. (Block 620 and Fig. 24c).

[99] A fourth step includes applying a layer 650 of black mask material over the

adhesive layer. As a result of the third step, the mask material wiU adhere only to those places

which have not been irradiated, thereby leaving apertures in the mask layer. (Block 630 and

Fig. 24d).

[100] In aH the foregoing embodiments of the method of the present invention, a

one-to-one correspondence has been shown between the lenses and apertures, i.e., each

aperture is shown to emit a beam from only one of the respective lenses. In order to achieve

enhanced screen resolution and/ or to diminish the effects of aHasing or other image artifacts, the lenses and apertures may be formed so that each aperture emits Hght from multiple

lenses.

[101] Other modifications and variations to the invention will be apparent to those

skilled in the art from the foregoing disclosure. Thus, while only certain embodiments of the

invention have been specificaHy described herein, it will be apparent that numerous

modifications may be made thereto without departing from the spirit and scope of the

invention.