U.S. patent application number 11/059160 was filed with the patent office on 2006-08-17 for rear projection screen with spatial varying diffusing angle.
This patent application is currently assigned to K Laser Technology, Inc.. Invention is credited to Wai-Hon Lee.
Application Number | 20060181770 11/059160 |
Document ID | / |
Family ID | 36282737 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060181770 |
Kind Code |
A1 |
Lee; Wai-Hon |
August 17, 2006 |
Rear projection screen with spatial varying diffusing angle
Abstract
A Fresnel lens of the prior art is split into two Fresnel lenses
to allow easier control of the horizontal and vertical viewing
angles. In a second embodiment, the Fresnel lens is entirely
eliminated. Instead, the diffuser contains elliptical
microstructures so that the diffusing cones in orthogonal
directions are different, eliminating the need for a Fresnel lens
to perform this function. To compensate for the absence of the
light collimation provided by the Fresnel lens, a diffuser with
spatially varying diffusing angles is used.
Inventors: |
Lee; Wai-Hon; (Los Altos,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
K Laser Technology, Inc.
Hsin-Chu
TW
|
Family ID: |
36282737 |
Appl. No.: |
11/059160 |
Filed: |
February 15, 2005 |
Current U.S.
Class: |
359/460 |
Current CPC
Class: |
G03B 21/625
20130101 |
Class at
Publication: |
359/460 |
International
Class: |
G03B 21/56 20060101
G03B021/56 |
Claims
1. A projection screen comprising: a first Fresnel lens configured
to diverge light at a first angle; a second Fresnel lens, coupled
to said first Fresnel lens, and configured to diverge light at a
second angle; and a diffuser coupled to said second Fresnel
lens.
2. The screen of claim 1 wherein said first Fresnel lens is a
cylindrical Fresnel phase relief structure derived from a function
y(x)=Mod(D(x), m.lamda.) where D .function. ( x ) = x 2 2 .times. n
.times. .times. F + .lamda..PHI. .function. ( x ) 2 .times. n
.times. .times. .pi. . ##EQU7##
3. The screen of claim 1 wherein said second Fresnel lens has a
focusing axis rotated 90 degrees from said first Fresnel lens.
4. The screen of claim 1 wherein the focal lengths of said Fresnel
lenses are not identical.
5. The screen of claim 1 wherein the structural depths of said
Fresnel lenses are less than 10 .mu.m.
6. The screen of claim 1 wherein a diffusing cone from said
diffuser has aspect ratio larger than 2:1.
7. The screen of claim 1 wherein said diffuser is the only
diffusing layer.
8. The screen of claim 6 wherein the diffusing cone of said
diffuser changes spatially.
9. A system for constructing a cylindrical Fresnel phase relief
structure, comprising: a laser device for producing a laser beam; a
spatial light modulator; a lens; a two axis translator; and a light
sensitive recording material mounted on said two axis translator,
wherein said spatial light modulator is configured to produce on
said recording material, through said lens and in conjunction with
said two axis translator, a phase relief structure derived from a
function y(x)=Mod(D(x), m.lamda.) where D .function. ( x ) = x 2 2
.times. n .times. .times. F + .lamda..PHI. .function. ( x ) 2
.times. n .times. .times. .pi. . ##EQU8##
10. The system of claim 9 wherein said spatial light modulator
controls the shape and brightness of a laser spot on the said
recording surface.
11. A system for constructing a diffuser for a projection screen,
comprising: a laser device for generating a laser beam: a rotating
diffuser mounted to receive said laser beam; a first lens mounted
to receive a diffused laser beam from said rotating diffuser; a
spatial modulator mounted to receive a modified laser beam from
said first lens; a second lens mounted to receive a spatially
modulated laser beam from said spatial modulator; a two axis
translator mounted after said second lens; and a light sensitive
recording material mounted on a two axis translator; wherein said
spatial modulator and said two axis translator are configured to
operate to produce a spatial varying diffuser.
12. The system of claim 11 wherein said first lens produces a
spatial spectrum of said diffuser.
13. The system of claim 11 wherein said spatial light modulator
controls spectral region of the diffuser.
14. The system of claim 11 wherein said second lens images the
diffuser to the recording surface.
15. A system for constructing a diffuser comprising: a laser device
producing a laser beam: a spatial light modulator mounted to
receive said laser beam; a lens mounted to receive a spatially
modulated beam from said spatial light modulator; a two axis
translator mounted after said lens; and a light sensitive recording
material mounted on said two axis translator; wherein said spatial
modulator and said two axis translator are configured to operate to
produce a spatial varying diffuser.
16. The system of claim 15 wherein said lens performs a Fourier
transform on the pattern displayed on said spatial light
modulator.
17. The system of claim 15 wherein the pattern displayed on said
spatial light modulator is the Fourier transform of a random phase
function.
18. A projector system comprising: a projector; and a screen having
spatially varying diffusion properties; such that the angle of
light rays projected from said screen increase with an increasing
deviation from a center of said screen in at least one
direction.
19. The system of claim 18 wherein said direction is
horizontal.
20. The system of claim 18 wherein said screen comprises a
plurality of diffusing dots.
21. A method for constructing a cylindrical Fresnel phase relief
structure, comprising: producing a laser beam; spatially modulating
said laser beam to produce a spatially modulated laser beam;
focusing said spatially modulated laser beam on a recording
material; and translating said recording material along two axes;
wherein said spatially modulating and said translating produce on
said recording material a phase relief structure derived from a
function y(x)=Mod(D(x),m.lamda.) where D .function. ( x ) = x 2 2
.times. n .times. .times. F + .lamda..PHI. .function. ( x ) 2
.times. n .times. .times. .pi. . ##EQU9##
22. A method for constructing a diffuser for a projection screen,
comprising: generating a laser beam: rotating a diffuser to diffuse
said laser beam to produce a diffused laser beam; collimating said
diffused laser beam to produce a collimated laser beam; spatially
modulating said collimated laser beam to produce a spatially
modulated laser beam; focusing said spatially modulated laser beam
on a recording material; and translating said recording material
along two axes; wherein said spatially modulating and said
translating operate to produce a spatial varying diffuser on said
recording material.
23. A method for constructing a diffuser comprising: providing a
collimated laser beam; spatially modulating said collimated laser
beam to produce a spatially modulated laser beam; focusing said
spatially modulated laser beam on a recording material; and
translating said recording material along two axes; wherein said
spatially modulating and said translating operate to produce a
spatial varying diffuser.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] Not Applicable
REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER PROGRAM
LISTING APPENDIX SUBMITTED ON A COMPACT DISK
[0003] Not Applicable
BACKGROUND OF THE INVENTION
[0004] The present invention relates to rear projection screens for
slide or movie projectors, and in particular to an improved Fresnel
lens and diffuser system for such projectors.
[0005] Images on photographic films can be projected on a screen
with devices such as slide projectors or movie projectors.
Electronic images can also be projected on screens through the use
of high power cathode ray tubes. This is the principle used in most
projection televisions sold today. More recently, with the
advancement of liquid crystal displays (LCD), compact projectors
have been developed and have led to a new generation of low cost
and high performance projection televisions. As a result, there is
an increasing demand for low cost rear projection screens. The
common characteristics of such viewing screens are high light
efficiency, wide viewing angle and uniform brightness.
[0006] There is a tradeoff between wider viewing angles and
brightness of the image at any viewing angle. In particular, it is
desirable to have a wide viewing angle in the horizontal direction
so that people can be seated on either side. However, since most
people's eyes are at similar levels vertically, it is desirable to
have a narrower viewing angle vertically to preserve the brightness
of the image.
[0007] FIG. 1 illustrates the principle of an image projection
system 100. An image projector 101 projects images on a rear
projection screen 102. The light coming out from the projector
subtends an angle 103 and angle 104 depicts the diffusing angle of
the screen. The angle 104 also defines the angle from which a
viewer can see the images on the screen.
[0008] FIG. 2 illustrates a basic structure of a rear projection
screen 200. Element 202 is a field lens. Its function is to
collimate the diverging cone of light 203 into a parallel beam of
light. Element 202 can be a glass lens. But, more commonly, it is a
plastic Fresnel lens. Element 205 is a diffuser which causes the
incident light falling on its surface to spread over an angular
cone. Angle 204 depicts the diffusing angle on the plane of the
paper and angle 206 depicts the diffusing angle on a plane out of
the paper.
[0009] FIG. 3 shows a rear projection screen according to U.S. Pat.
No. 4,773,731. In this prior art, the Fresnel lenses are recorded
on both surfaces of a first element 302. Element 302 is bonded to a
second element 320 which contains scattering particles 318 and
surface structure 322 to increase the viewing angle. The refractive
index of 302 is different from the refractive index of 320.
[0010] FIG. 4 shows another construction of the field lens
according to U.S. Pat. No. 6,046,847. The alternating zones of the
Fresnel lens have different focal lengths f1 and f2. As a result,
the light beam from the projector can be made parallel in one
direction and converging in a direction orthogonal to the first
direction.
[0011] FIG. 5 shows another embodiment of rear projection screen
where special structures and Fresnel lens are molded into a single
plastic element (U.S. Pat. No. 6,304,378).
[0012] FIG. 6 shows a diffusing element consisting of micro-lenses
and light blocking elements according to U.S. Pat. No. 5,870,224.
The light blocking elements enhance the contrast in the projected
image. A Fresnel lens is made by first mechanically cutting
circular grooves with different slopes on a metal blank. After
machining, this blank is used in a plastic injection molding
equipment to replicate the structure onto a plastic sheet. The
depth of the grooves in a mechanically engraved Fresnel lens is
typically more than 100 .mu.m and is not suitable for use in
surface embossing equipment.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention provides methods and apparatus for
improving the manufacturability of a Fresnel lens and diffuser
system for a projector, and for enabling finer control of viewing
angles.
[0014] In a first embodiment of the present invention, the Fresnel
lens of the prior art is split into two Fresnel lenses. This allows
easier control of the viewing angle in horizontal and vertical
directions by physically separating, and manufacturing separately,
the lens structure for each.
[0015] Additionally, separating the Fresnel lens into two lenses
eliminates the circular structure of the single lens of the prior
art. In particular, the field lens of the invention consists of two
orthogonal cylindrical Fresnel lenses and a diffuser. The focal
length of each cylindrical lens can be selected independently. In
addition, the two structures can be thinner in combination than the
single structure of the prior art, further improving
manufacturability.
[0016] In a second embodiment of the invention, the Fresnel lens is
entirely eliminated. Instead, the rear projection screen contains
only the diffusing element. The diffuser contains elliptical
microstructures so that the diffusing cones in orthogonal
directions are different, eliminating the need for a Fresnel lens
to perform this function. To compensate for the absence of the
light collimation provided by the Fresnel lens, a diffuser with
spatially varying diffusing angles is used.
[0017] The present invention also sets forth methods for producing
the cylindrical Fresnel lens of the first embodiment and the
diffusing element with elliptical microstructures and spatially
varying diffusing angles of the second embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a diagram of a prior art rear projection
system.
[0019] FIG. 2 is a diagram of the structure of a prior art rear
projection screen.
[0020] FIG. 3 is a cross-sectional diagram of a prior art rear
projection screen according to U.S. Pat. No. 4,773,731.
[0021] FIG. 4 is a cross-sectional diagram of a prior art rear
projection screen according to U.S. Pat. No. 6,046,847.
[0022] FIG. 5 is a cross-sectional diagram of a prior art rear
projection screen according to U.S. Pat. No. 6,304,378.
[0023] FIG. 6 is a cross-sectional diagram of a prior art rear
projection screen according to U.S. Pat. No. 5,870,224.
[0024] FIG. 7 is a cross-sectional diagram of a rear projection
screen system according to the present invention.
[0025] FIGS. 8(a) and (b) are cross-sectional views of negative and
positive thin Fresnel lenses with a resulting fine spatial
structure
[0026] FIGS. 8(c) and (d) are cross-sectional views of negative and
positive thick Fresnel lenses with a resulting coarse spatial
structure.
[0027] FIG. 9 is a diagram of a system for producing cylindrical
Fresnel lenses.
[0028] FIG. 10 is a diagram of a second embodiment of a rear
projection system according to the present invention, eliminating
the Fresnel lens with a spatially varying diffuser.
[0029] FIG. 11 is a diagram of a first system for producing the
spatial varying diffuser of FIG. 10.
[0030] FIG. 12 is a diagram of a speckle pattern for a spatial
varying diffuser with a 4:1 aspect ratio produced using the system
of FIG. 11.
[0031] FIG. 13 is a diagram of a second system for producing the
spatial varying diffuser of FIG. 10.
DETAILED DESCRIPTION OF THE INVENTION
[0032] In FIG. 7, element 700 is the first embodiment of a rear
projection screen of the present invention. An image projector 701
projects images on a rear projection screen 700, which consists of
three planar optical elements 702, 703 and 704 laminated together.
Element 704 is a diffuser that scatters incident light over an
elliptical cone with angle 705 and 706. Angle 705 depicts the
diffusing angle on the plane of the paper and angle 706 depicts the
diffusing angle on a plane out of the paper. Optical elements 702
and 703 are cylindrical Fresnel lenses with surface structure as
illustrated in FIGS. 8(a)-(d). Optical element 704 is a diffuser.
The phase variation of a cylindrical lens is approximately given by
.theta. .function. ( x ) = .pi. .times. .times. x 2 .lamda. .times.
.times. F + .PHI. .function. ( x ) ( 1 ) ##EQU1## where x is the
spatial variable, .lamda. is the wavelength of light, F is the
focal length and .psi.(x) is either phase aberration or phase
correction. The phase of a Fresnel lens is determined by taking the
modulo 2m.pi. of the phase function .THETA. (x) as shown below:
.THETA..sub.F(x)=Mod(.THETA.(x),2m.pi.), (2) where Mod means
modulo, and m is a non-zero integer. The thickness d(x) of a
Fresnel lens having the same phase is given by F .function. ( x ) =
2 .times. .pi. .function. ( n - 1 ) .times. d .function. ( x )
.lamda. , ( 3 ) ##EQU2## where n is the refractive index of the
substrate. Therefore, d .function. ( x ) = .lamda. 2 .times. .pi.
.function. ( n - 1 ) .times. F .function. ( x ) = ( .lamda. ( n - 1
) ) .times. Mod .function. [ ( .function. ( x ) 2 .times. .pi. ) ,
m ] . ( 4 ) ##EQU3## The structural depth of the Fresnel lens is m
.times. .times. .lamda. n - 1 ##EQU4## with minimum structural
depth of .lamda. n - 1 . ##EQU5##
[0033] FIG. 8(a) and FIG. 8(b) show respectively the phase of a
negative and a positive Fresnel lens m=1. FIG. 8(c) and FIG. 8(d)
show respectively the phase of a negative and a positive Fresnel
lens with m=2. As can be seen, when the structural depth increases,
the spatial structure becomes coarser. Most of the Fresnel lenses
made by injection molding have a structural depth of more than 100
.mu.m. The spatial structure is sufficiently coarse so that the
structure can be cut into a metal blank by mechanical means. In
this present invention an optical method is used to produce a
structural depth of less than 10 .mu.m on a plate coated with
photoresist.
[0034] One embodiment of an optical system for recording the
Fresnel lens on a photoresist plate is shown in FIG. 9. Laser beam
901 is incident on a spatial light modulator 902. After passing
through the spatial modulator 902, the laser beam is focused by
lens 903 to a spot on the surface of a photoresist plate 904, which
is mounted on a two axis translator stage 906. The spatial light
modulator 901 controls the brightness and the shape of the spot in
accordance to the function y(x). After the photoresist is exposed
and developed, the surface profile thus recorded is identical to
y(x). The surface relief pattern on the photoresist is then
transferred to a nickel blank by electroplating. The nickel shim
with the Fresnel lens pattern is then used as master to emboss the
Fresnel lens structure on a substrate coated with UV curable
polymer.
[0035] FIG. 10 shows the second embodiment of the rear projection
screen 1005. Projector 1001 projects an image on a screen 1005. The
light ray from the projector 1001 at any horizontal location x of
the screen 1002 subtends an angle .omega.(x) with respect to the
surface normal of the screen. We assume that the diffusing cone
needed for the horizontal direction is equal to .+-..omega..sub.d
at the center location. In order for a viewer sitting at a position
creating an angle of .omega..sub.d to see the image at location x,
the diffusing cone at location x must equal to
.+-.(.omega..sub.d+.omega.(x)). Since the angle of the projected
rays increases as it deviates from the center of the screen, the
diffusing cone 1004 in the center of the screen is smaller than the
diffusing cone 1006 and 1007 at the edge of the screen.
[0036] There are at least two methods for making such a spatial
varying diffusing screen according to this present invention. A
first method is illustrated in FIG. 11. A light diffusing element
1102 is mounted on a rotating shaft 1103. Light beam 1101 is
incident on the diffusing element 1102. Lens 1004 produces a
spectrum of the diffusing element on plane 1105 where spatial light
modulator 1106 is located. The spatial light modulator has a
rectangular opening to control the spectrum of the speckles
recorded on the photoresist plate at plane 1108, which is also the
image plane of the diffusing element 1102. An objective lens 1107
focuses the light on photoresist plate 1108.
[0037] The diffusing angle of the speckles recorded is given by sin
.times. .times. .omega. d = W 2 .times. F , ##EQU6## where W is the
width of the rectangular aperture on the spatial light modulator.
After recording one diffusing dot at location x, the translator
moves the photoresist plate to a new location, x+.delta.. At the
same time the diffusing element 1102 is now rotated to a new
location to record the next diffusing dot on the photoresist plate.
This process is repeated for both spatial directions until
diffusing dots completely fill the photoresist plate. As the
translator moves to a new location, a controller will input the
appropriate aperture on the spatial modulator so that the new
diffusing dot will have the required diffusing angle for that
location. FIG. 12 shows a spatially varying diffuser with a
simulated speckle pattern with aspect ratio of 4:1 produced
according to this method of the present invention.
[0038] FIG. 13 shows a second method of this present invention for
producing the diffusing element. A collimated beam 1301 illuminates
a spatial modulator 1302 which has a rectangular opening as shown
in the view 1303 of the spatial modulator. The pattern displayed by
spatial modulator 1302 is a computer generated Fourier transform of
a random phase pattern f(x,y)=e.sup.i2.pi..THETA.(x,y)), (4) where
.THETA. (x,y) is a random function with values between 0 and 1.
F(u,v) is the Fourier transform of f(x,y):
F(u,v)=.intg.f(x,y)e.sup.i(ux+vy)dxdy. (5) The pattern displayed on
the spatial modulator is proportional to
I(u,v)=e.sup.i2.pi.{overscore (.omega.)}.sup.u+F(u,v)|.sup.2, (6)
where {overscore (.omega.)} causes a shift in the speckle pattern
away from the optical axis in the reconstruction process. Lens 1304
performs inverse Fourier transform and reproduces a speckle pattern
on the recording plane 1305 similar to those shown in FIG. 12. The
aspect ratio of the speckles is controlled by the width and height
of the computer generated hologram as shown in 1303. As in the
previous system, after recording one diffusing dot, the translator
will move the recording plate to a new position and the pattern on
the spatial light modulator is replaced by a computer generated
hologram with a new random phase structure. This process is
repeated until the recording plate is completely filled with
diffusing dots. The advantage of this second system is that other
than the translator there is no other mechanical motion in the
recording system.
[0039] It will be understood that modifications and variations may
be effected without departing from the scope of the novel concepts
of the present invention. For example, other methods could be used
to produce the split Fresnel lenses or spatially varying diffuser.
Another method for producing a Fresnel lens that can be used to
create the structure of the present invention is set forth in U.S.
Pat. No. 4,737,447. Accordingly, the foregoing description is
intended to be illustrative, but not limiting, of the scope of the
invention which is set forth in the following claims.
* * * * *