CA2056078A1 - Display device - Google Patents
Display deviceInfo
- Publication number
- CA2056078A1 CA2056078A1 CA002056078A CA2056078A CA2056078A1 CA 2056078 A1 CA2056078 A1 CA 2056078A1 CA 002056078 A CA002056078 A CA 002056078A CA 2056078 A CA2056078 A CA 2056078A CA 2056078 A1 CA2056078 A1 CA 2056078A1
- Authority
- CA
- Canada
- Prior art keywords
- light
- reflector
- light source
- splitter
- plane
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/133553—Reflecting elements
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/0101—Head-up displays characterised by optical features
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B21/00—Projectors or projection-type viewers; Accessories therefor
- G03B21/10—Projectors with built-in or built-on screen
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B21/00—Projectors or projection-type viewers; Accessories therefor
- G03B21/54—Accessories
- G03B21/56—Projection screens
- G03B21/60—Projection screens characterised by the nature of the surface
- G03B21/62—Translucent screens
- G03B21/625—Lenticular translucent screens
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/74—Projection arrangements for image reproduction, e.g. using eidophor
- H04N5/7408—Direct viewing projectors, e.g. an image displayed on a video CRT or LCD display being projected on a screen
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/133524—Light-guides, e.g. fibre-optic bundles, louvered or jalousie light-guides
Abstract
ABSTRACT
DISPLAY DEVICE
A display device in the form of a slim screen projector has a beam-splitter and a reflector co-planar and in contact with each other. Incident light from a light source strikes the beam-splitter and reflector and a portion thereof is directed towards a mirror. Light from the mirror then passes through a louvre-screen via the beam-splitter and strikes a viewing surface on which a viewable image is formed.
DISPLAY DEVICE
A display device in the form of a slim screen projector has a beam-splitter and a reflector co-planar and in contact with each other. Incident light from a light source strikes the beam-splitter and reflector and a portion thereof is directed towards a mirror. Light from the mirror then passes through a louvre-screen via the beam-splitter and strikes a viewing surface on which a viewable image is formed.
Description
7 ~
~ISP~A~ DEVIC~
The present inventlon relate6 to apparatu6 for projectin~
light onto a viewing surface and ha~ particular, though not exclu~ive, relevance to equipment for use in a rear-pro~ection image display, such as a liquid crystal tele~ision display.
Published European Patent Application numbe ~ 333 333~
discloses a display device including equipment for projecting light onto a surface. The equipment include6 a beam-splltter ~ 3 ~
for effecting partial reflect;on and partial transmission of an ~l~/O
incident bea~. On one side of the beam-splitter are a light 10 source for directing light onto the beam-splitter and a mirror ~!
for directing back toward6 the beam-splitter light reflected therefrom. On the other side of the beam-6plitter i6 a lou~re for permitting passage therethrough of llght of incldent angle relative to a normal to the beam--splitter wlthin a predetermined restricted range.
Bowever, whilst the above system achieve~ a substantlally slimmer device than was previously kno~ for the viewing area achieved, it has a relatively low overa!Ll optical efficiency.
It is thus an ob~ect of the present invention to provide a sllm equ~pment for the pro~ection of light onto a viewin~
surface wlth a substantially increased optic~l efficiency as compared wlth the display device detailed in ~PA 0333,333.
Accordingly there is provided apparatu~ for projecting li~ht onto a surface comprising:
a light source for providing polarised light;
beam-splitting means for efectlng part~al reflection and partial tran~mission of light lncident thereon from the l~ght source; reflector means for reflecting light incident thereon from the llght source;
mirror means for directing towards the beam-splittin~ means light reflected from the beam-splitting means and also light rJ ~
: 2 :
reflected from the reflector means;
and louvre means located on a side of the beam-spllttlng means remote from the llght source for allowing the passage of llght therethrough ~n a predetermined range of incident angles relatlve to the beam-splittiDg means.
The prior art device, whlch had no reflector means, wa8 susceptible to a loss of llght at this stage due to only partial reflection from the beam-splitter means. Furthermore, incluslon of the reflector means produces a narrowlng of incident angles for light directly incldent upon the beam-splitting means a~
compaxed with the prior art devlce~ and thus by arranging for linearly polarised light to be incident upon the beam-spllttlng means, a higher component of light reflected therefrom, as opposed to transmitted therethrough, l8 achieved.
Preferably, the polarised light source compr~ses a liquid crystal display. Generally, light passing through a llqu~d crystal display becomefi plane polarised and is thus clearly well suited for employment within the present invention.
Preferably, the llquid crystal display comprises separate di6plays for each of the primary colours; red, ~reen and blue.
In a preferred embodlment of the present invention, the reflector means comprises an optlcal æurface havin~ a non-uniform reflectivlty. This allows for compensation of the image at the lower portion of the viewlng ~urface so that it matche~ the brlghtness on the upper portion of the viewing surface.
Preferably the non-uniform reflect~vity across the opt~cal surface is achieved by way of an arrangement of areas of dots havlng lower reflectivity than the optical surface.
Alternatively, or additionally, the device may include a variable neutral denæity filter in order to compensate for the variation in image intensity across the viewlng surface.
In an embodiment of the present invention comprislng a liquid crystal display, the compensation for varying lntens~ty at the view~ng surface may be achleved by inclufiion of a part~al mask over the display Dr the beam-splitter or any posltion ln 7 ~
between. Such a mask may be applied to each individual pixel of the liquid crystal display.
The invention will now be described, by way of ~xample only, with reference to the following drawlngs, of which:
Figure 1 represent~ a schematic illustration of a prior art di~pl~y device;
Figure 2 representa a schematic illustration of a display device according to the present inv~ntion9 Figure 3 repreæents a variation of re1ectlon coefficients wlth incident angle for plane polarised light associated with the beam--splitter of the present invention;
Figure 4 show6 a schematic representation of the reflector means with a non-uniform reflectivity distribution; and Figure 5 show~ the vari~tion of overall efflciency of the equipment ~ersus the position of the image on the v~e~ing surface.
Referrin~ f~rstly to Figure 1, the prior art devlce compri6es a diffuser plate 2 effective as a ~iewing ~urface, which is illumlnated from the rear by a light source 3.
The light ~ource directs a beam of llght onto a beam splitter 4 which produces a reflected portion rl ~nd a transmitted portion tl, the transmitted portion tl of this beam pass~ng on to a louvred plate 6 where it is absorbed as its direction i~
at a substantial angle to the transmisæion directlon of the louvre, ie, that direction at which the louvre permit6 p~ssage of light by virtue of the orientation of the lou~re 6 to that ~ncident light. The portlon rl of this beam, which ~s flr~t reflected by the beam-splitter 4, passes to a mirror 8 di~posed at an angle ~ to the beam-splitter 4, the mirror 8 directing reflected portion rl back towards the beam-~plltter 4. This time, a portion t2 is transmitted by the beam-splitter 4 and is subseyuently incident on the louvred plate 6 at an angle within a predetermined restricted range such that lt passes therethrough and onto the diffuser plate 2; the portion r2 whlch is reflected is subse~uently d~rected back by ~irror 8 towards the beam-splitter 4. Any portlonæ subsequently v ~
: 4 -tran~mitted through the beam-splitter 4 are either at an angle at which passage through the lou~re 6 i8 inhlbited, or of very low lntensity, thereby having no or min-1mal effect on the ill~n~natlon of diffuser plate 2.
Referring now to Yigure 2, thls embodiment of the present lnvention ~llu~trates how a greater proportlon of the llght transmitted from the light source may be incident on a viewing surface 103 which view1ng ~urface was ln ~he fo~m of a d~ffuser plate 2 in the prior art device. Similar components are similarly numbered.
Light incident from a l~ght source 3 ls arranged to be polarised before being incident upon a reflector mPans 12 and the beam-Rpl~tting means 4. This may be achleved by passing ll~ht ~hrou~h a polari6ing plate. The orientation of the plane of polar1sed light may be altered by passing the llght through a liquid crystal material such as i8 com~only used in liquid cryætal displays. It will be apparent to those skilled in the art that such plane polarised light may be arranged to have the electric vector either paralle~l or perpendicular to the plane of lncidence, and such polarisation states are referred to respectively as p and 8 polarised l~ght. These terms are well known by persons skilledl in thi~ art nnd will not, therefore, be described further im the present appllcation.
By reference to Figure 2, it will be seen that by including a reflector means 12 immed~ately below and ~n contact with the beam-splitting means 4, all ~ncident light thereupon i8 reflected to mirror mean6 8 and 6ubsequently onto the beam-~plitter means 4 at very low incidence angles, whereby the proportion of light from the reflector 12 passing through the beam-splitter 4 and louvre 6 and onto the viewing surface 10 i8 ~aximised. It will be seen that such light ls incident only upon the lower portion of the bea~-splitter 4 and thus an observer of the viewing surface 10 would see an ~mage havin~ a step function of intensity, the lmage being much brighter at the bottom portion of the viewing ~urface lO than at the top portion not influenced by the reflector 120 ti ~i : 5 :
In order to correct for this enhanced brightneæs at the bottom port~on of viewing ~urface 10, the reflector 12 may be arran8ed to have a variation in reflectl~ity across its opt~cal surface. Thi8 i~ achieved by arrangin~ for the optical 6urface of the reflector 12 to have a non-uniform reflectivity.
There are several alternative~ avallable for gultable choice of reflector 12 and for the compen~ation which may be requlred tc be applied thereto in order to correct for the step function mentioned above.
A prefered form of reflector 12 is that of the 6ubstrate coated with, for example, a layer of aluminium. The compensation may be in the form of areas of dots 14 of lower reflectivity than the optlcal surface of the reflector 12 a6 for ex~mple shown in Figure 3. Such dots do not necessarily need to be of particularly 6ms~1 dimens~ons, they could for example be of up to about O.lmm diameter in order to function effectively.
The 6pacing and pattern of the dots will be dependent upon the extent to which the brightness mu3t be compensated.
~ISP~A~ DEVIC~
The present inventlon relate6 to apparatu6 for projectin~
light onto a viewing surface and ha~ particular, though not exclu~ive, relevance to equipment for use in a rear-pro~ection image display, such as a liquid crystal tele~ision display.
Published European Patent Application numbe ~ 333 333~
discloses a display device including equipment for projecting light onto a surface. The equipment include6 a beam-splltter ~ 3 ~
for effecting partial reflect;on and partial transmission of an ~l~/O
incident bea~. On one side of the beam-splitter are a light 10 source for directing light onto the beam-splitter and a mirror ~!
for directing back toward6 the beam-splitter light reflected therefrom. On the other side of the beam-6plitter i6 a lou~re for permitting passage therethrough of llght of incldent angle relative to a normal to the beam--splitter wlthin a predetermined restricted range.
Bowever, whilst the above system achieve~ a substantlally slimmer device than was previously kno~ for the viewing area achieved, it has a relatively low overa!Ll optical efficiency.
It is thus an ob~ect of the present invention to provide a sllm equ~pment for the pro~ection of light onto a viewin~
surface wlth a substantially increased optic~l efficiency as compared wlth the display device detailed in ~PA 0333,333.
Accordingly there is provided apparatu~ for projecting li~ht onto a surface comprising:
a light source for providing polarised light;
beam-splitting means for efectlng part~al reflection and partial tran~mission of light lncident thereon from the l~ght source; reflector means for reflecting light incident thereon from the llght source;
mirror means for directing towards the beam-splittin~ means light reflected from the beam-splitting means and also light rJ ~
: 2 :
reflected from the reflector means;
and louvre means located on a side of the beam-spllttlng means remote from the llght source for allowing the passage of llght therethrough ~n a predetermined range of incident angles relatlve to the beam-splittiDg means.
The prior art device, whlch had no reflector means, wa8 susceptible to a loss of llght at this stage due to only partial reflection from the beam-splitter means. Furthermore, incluslon of the reflector means produces a narrowlng of incident angles for light directly incldent upon the beam-splitting means a~
compaxed with the prior art devlce~ and thus by arranging for linearly polarised light to be incident upon the beam-spllttlng means, a higher component of light reflected therefrom, as opposed to transmitted therethrough, l8 achieved.
Preferably, the polarised light source compr~ses a liquid crystal display. Generally, light passing through a llqu~d crystal display becomefi plane polarised and is thus clearly well suited for employment within the present invention.
Preferably, the llquid crystal display comprises separate di6plays for each of the primary colours; red, ~reen and blue.
In a preferred embodlment of the present invention, the reflector means comprises an optlcal æurface havin~ a non-uniform reflectivlty. This allows for compensation of the image at the lower portion of the viewlng ~urface so that it matche~ the brlghtness on the upper portion of the viewing surface.
Preferably the non-uniform reflect~vity across the opt~cal surface is achieved by way of an arrangement of areas of dots havlng lower reflectivity than the optical surface.
Alternatively, or additionally, the device may include a variable neutral denæity filter in order to compensate for the variation in image intensity across the viewlng surface.
In an embodiment of the present invention comprislng a liquid crystal display, the compensation for varying lntens~ty at the view~ng surface may be achleved by inclufiion of a part~al mask over the display Dr the beam-splitter or any posltion ln 7 ~
between. Such a mask may be applied to each individual pixel of the liquid crystal display.
The invention will now be described, by way of ~xample only, with reference to the following drawlngs, of which:
Figure 1 represent~ a schematic illustration of a prior art di~pl~y device;
Figure 2 representa a schematic illustration of a display device according to the present inv~ntion9 Figure 3 repreæents a variation of re1ectlon coefficients wlth incident angle for plane polarised light associated with the beam--splitter of the present invention;
Figure 4 show6 a schematic representation of the reflector means with a non-uniform reflectivity distribution; and Figure 5 show~ the vari~tion of overall efflciency of the equipment ~ersus the position of the image on the v~e~ing surface.
Referrin~ f~rstly to Figure 1, the prior art devlce compri6es a diffuser plate 2 effective as a ~iewing ~urface, which is illumlnated from the rear by a light source 3.
The light ~ource directs a beam of llght onto a beam splitter 4 which produces a reflected portion rl ~nd a transmitted portion tl, the transmitted portion tl of this beam pass~ng on to a louvred plate 6 where it is absorbed as its direction i~
at a substantial angle to the transmisæion directlon of the louvre, ie, that direction at which the louvre permit6 p~ssage of light by virtue of the orientation of the lou~re 6 to that ~ncident light. The portlon rl of this beam, which ~s flr~t reflected by the beam-splitter 4, passes to a mirror 8 di~posed at an angle ~ to the beam-splitter 4, the mirror 8 directing reflected portion rl back towards the beam-~plltter 4. This time, a portion t2 is transmitted by the beam-splitter 4 and is subseyuently incident on the louvred plate 6 at an angle within a predetermined restricted range such that lt passes therethrough and onto the diffuser plate 2; the portion r2 whlch is reflected is subse~uently d~rected back by ~irror 8 towards the beam-splitter 4. Any portlonæ subsequently v ~
: 4 -tran~mitted through the beam-splitter 4 are either at an angle at which passage through the lou~re 6 i8 inhlbited, or of very low lntensity, thereby having no or min-1mal effect on the ill~n~natlon of diffuser plate 2.
Referring now to Yigure 2, thls embodiment of the present lnvention ~llu~trates how a greater proportlon of the llght transmitted from the light source may be incident on a viewing surface 103 which view1ng ~urface was ln ~he fo~m of a d~ffuser plate 2 in the prior art device. Similar components are similarly numbered.
Light incident from a l~ght source 3 ls arranged to be polarised before being incident upon a reflector mPans 12 and the beam-Rpl~tting means 4. This may be achleved by passing ll~ht ~hrou~h a polari6ing plate. The orientation of the plane of polar1sed light may be altered by passing the llght through a liquid crystal material such as i8 com~only used in liquid cryætal displays. It will be apparent to those skilled in the art that such plane polarised light may be arranged to have the electric vector either paralle~l or perpendicular to the plane of lncidence, and such polarisation states are referred to respectively as p and 8 polarised l~ght. These terms are well known by persons skilledl in thi~ art nnd will not, therefore, be described further im the present appllcation.
By reference to Figure 2, it will be seen that by including a reflector means 12 immed~ately below and ~n contact with the beam-splitting means 4, all ~ncident light thereupon i8 reflected to mirror mean6 8 and 6ubsequently onto the beam-~plitter means 4 at very low incidence angles, whereby the proportion of light from the reflector 12 passing through the beam-splitter 4 and louvre 6 and onto the viewing surface 10 i8 ~aximised. It will be seen that such light ls incident only upon the lower portion of the bea~-splitter 4 and thus an observer of the viewing surface 10 would see an ~mage havin~ a step function of intensity, the lmage being much brighter at the bottom portion of the viewing ~urface lO than at the top portion not influenced by the reflector 120 ti ~i : 5 :
In order to correct for this enhanced brightneæs at the bottom port~on of viewing ~urface 10, the reflector 12 may be arran8ed to have a variation in reflectl~ity across its opt~cal surface. Thi8 i~ achieved by arrangin~ for the optical 6urface of the reflector 12 to have a non-uniform reflectivity.
There are several alternative~ avallable for gultable choice of reflector 12 and for the compen~ation which may be requlred tc be applied thereto in order to correct for the step function mentioned above.
A prefered form of reflector 12 is that of the 6ubstrate coated with, for example, a layer of aluminium. The compensation may be in the form of areas of dots 14 of lower reflectivity than the optlcal surface of the reflector 12 a6 for ex~mple shown in Figure 3. Such dots do not necessarily need to be of particularly 6ms~1 dimens~ons, they could for example be of up to about O.lmm diameter in order to function effectively.
The 6pacing and pattern of the dots will be dependent upon the extent to which the brightness mu3t be compensated.
2~ Alternatively the reflector 12 may it~elf be formed from a material of non unifonm reflectivity, thu~ negating the need for dots 14 to be formed on the optical surPace of the reflector 12.
Alternatlvely, a variable neutral density filter could be employed to cover the reflector 12 or, alternatively, the v~ewlng surface 10. If the neutral density filter i~ arranged on the vlewing 6urface 10, it may be applied to either She front or the rear of the v~ewing ~urface. Thl~ will adequately compensate for intensity variations acros~ the viewing ~urface 10, but is not effective for correcting any chromatic abberations which mar occur.
It will be ~een by referring agaln to Figure 2 that incluslon of reflector 12 enable6 a narrowing of the angle6 of incidence ~ from the llght source onto the beam-~plitter 4. Figure 4 6hows, for the beam-splitter 4, the variation of reflection coefficient against angle~ of incidence for plane polari6ed light. It will be seen that the greater the ~, . .
G3 ~ r~ $
: 6 s angle of incidence of light upon beam-splitting means 4 the greater the s-component of polarisation ln the reflected portion rl ~up to the limit of grazlng incldence).
The converee also holds; ie, as the angle of lncidence decrea~es the p-component of polari~ation in the light reflected f rom the beam splitter 4 increases.
Furthermore, as can be 6een from Flgure 4 9 the greater the ~-component of the incident light, the greater the coefficlent of reflectivity of the beam-splitter 4 and therefore the less the coeffic~ent of transmittivity.
Thus, by predetermlning the plane of polarisation of light incldent upon the beam-splitter 4 and by re6tricting the range of angle~ of ~ncidence of this l~ght on the beam-spltter 4, the energy in re1ected portion rl may be enhanced and that in the tran~mitted portion tl reduced.
As previously stated, the provision of the reflector means 12 restrict~ the range of incldent angle~ of the light incident on the beam-splitter 4. In a preferrecl form of the inventlon~
the pro~ection system geometry i8 arranged to provide a rectangular image on the viewing surface 10 with the horizontal edges of the lmage belng of longer len~th than the vertical edges of the image; that is the image i.8 of 'l~ndscape' format.
To provide maximum efficiency for the optical system the plane of polar~satlon of the light source 3 18 chosen to be parallel to a longer edge of the final image. In ~o doing, all rays from the light source 3 whlch ult~mately fo~m an image on a vertlcsl axi~ or line running through the centre of the flnal lmage will be 8 component polarised light during the first and second interactlons with the beam-splitter 4. Ray~ from the light ~ource 3 which for~ image points off this axis will compr~se of polarised llght ha~ing a mix of s and p components, the proport~on of these components being determined by the plane of lncidence of the6e rays relative to the beam-splitter 4 during thelr interaction with the beam-splitter 4, which in turn determines the 6a~d p-components in the reflected light. If the plane of polarlsation of the light from the light r~
: 7:
source 3 ia not carefully cho3en to provide a pure component of polarisation alone the central axi8 of the final ima~e, which can be elther pure ~ or pure p component but i~ chosen to be pure s-component to provlde maximum intensity in the final image, there would be an imbalance in the perceived brightnes6 from 6ide to ~ide of the final lmage.
The effect of the reflector 12 i8, therefore, two fold.
Firstly, the intensity or brlghtnesa of the final image on that portion of the viewing ~urface having its image formed by light reflected from the reflector 12 is increased, when compared to the known device. Secondly, the reflector 12 reduces the range of angle~ of incidence of the light from the llght source falling on the beam-splitter 4, which in thi~ preferred e~bodiment of the lnvention allows the lowest value of image intensity of the final image to be maximised and the spread or range in ima8e intenæity from one part of the image to another due to the initial reflection of the ~ncident light from the beam-aplitter, to be reduced. For example, confiiderlng the s-component of polarlsed llght forming the central vertical axi~
of the final ima~e formed on the ~iewing surface 10, the lowest in~tial angle of incldence of any incidlent llght ray on the beam-splitter 4 i8 increa6ed, thereby incresing the intensity of the portion rl. On the second lnteraction of theæe rays with the beam-splitter 4 the reflection coefficient ia ~lmilar for 8~ and p-component6 due to the low angle of incidence, a~ can be ~een from Figure 4. Hence the lowest value of i~age brightne~s along this axis i~ increa~ed and, therefore, the varlstion6 ln ~mage br~ghtne~s alon~ this axis is reduced.
The beam-splitter 4 i8, in one form of the invention a single layer d~electric type beam-splitter and haa an anti-reflection co~ting of magne~i~m fluoride on one 8~ de thereof remote from the mirror 8.
However, multi layer beam-splitters may also be used in the present invention. Both ~ingle and multi layer beam-splitter~
introduce chromatic aberration~ slnce their reflectivity is a function of wavelength; these aberrations will generally be : 8 :
most notlceable at the boundary between the lower portion of the image fQrmed by rays which are ~n~tially lncident on the reflector, and the upper portion which is produced by rays reflected from the beam-6plitter.
The var~ation of reflectivity with wavelength in dielectric beam-splitters lncreases with the total optical path length in the thin films which produce the beam-splitting effect; thu~ ~t is possible to produce a single layer beam-splitter whlch ~ive~
minimal chromatic aberration in this application, wherea6 a multi layer design will ln general produce chromatic aberrations which must be corrected by some method.
A preferred method of correct~ng such chrGmatic aberratlon~, and simultaneously correcting more gross brightness varlations~ may be understood with reference to a typical LCD
pro~ector in whlch the final image is formed by combining three separate primary coloured images of red, green and blue. By introducing a partial masking plate (whlch ha6 dlfferent transmlssions ln different regions; ie, effectively a variable neutral den~ity f~lter) into each colour channel of the projector prior to the point at which the colours are combined, it will be apparent that it is possible to selectively modify the intenaity of each of the primary colours at each polnt of the final image, and hence, the colour and brightness at each point of the final image. Active matrix displays provlde a part~cularly convenient means of introduc~ng such ~ partial ma~k~ng plate since they already include a small llght masking area ln each p~xel to prevent photo-acti~ation of the translstor used to dr~ve a respective pixel of the display. A modif~cation to the mas~ design would increase the size of this mask ~electively on a pixel by pixel basis so that the partial masking plate may be built into the LCD and no additional manufacturing costs would be incurred. However, it should be stres6ed that there i~ no absolute requirement to bu~ld thi~
effect into the LCD. Those skilled in the art will see how a partial ma~kin8 plate could be introduced into the colour channels of any suitable pro~ector.
.~
h ~ d : 9:
An additlonal alternative would be to electrically control the transmi6s~0n of each pixel.
Thoi~e skilled in the art will appreciste that t~o or more of these techniques may be used ~imultaneouslyO For example, electrical co~pensatlon of pixels alone might prove not to be the best choice since it could suppres~ the contrast and range of grey levels in the final image. A partial masking plate ~olution might suffer due to quality control problemOE on the bei~m-splltter, requlring masking plates to be customised for each beam-splitter. However, the two techniquefi might be combined wlth almost all the correctlon being achieved with a standard set of masking plates and the remaining correction achieved with programmable electrical compensation.
Figure 5 lllustrates the overall efficiency ~hich the present device aims to achieve. It will be seen that the optical efficlency Yaries acros6 the viewing surface from the centre to the edges (top and bottom). This occurs because of the variation of angles of incidence o~ the light from the light source which strikes the beam-splltting means 4, and hence the variation in reflectivity and thus in imten~ity of llght ~ncident upon the vlewing screen lO. Im normal circumstances9 these variations wlll not be discernable by a viewer of th~
final ~mage on the viewlng surface 10. I~owever, if necessary the variations can be compen~ated by approprlate deslgn of the neutral density filter and or the partial mask~ng plate referred to above.
It wlll be apparent that the present ~nvention achieve~ a substantial increase in optical efficiency as compared with the pr~or art device by employing a beam-splitter and reflector arranged such that incident polarised llght has a greater reflected (and subsequently) viewed component thaD the pr~or art.
Alternatlvely, a variable neutral density filter could be employed to cover the reflector 12 or, alternatively, the v~ewlng surface 10. If the neutral density filter i~ arranged on the vlewing 6urface 10, it may be applied to either She front or the rear of the v~ewing ~urface. Thl~ will adequately compensate for intensity variations acros~ the viewing ~urface 10, but is not effective for correcting any chromatic abberations which mar occur.
It will be ~een by referring agaln to Figure 2 that incluslon of reflector 12 enable6 a narrowing of the angle6 of incidence ~ from the llght source onto the beam-~plitter 4. Figure 4 6hows, for the beam-splitter 4, the variation of reflection coefficient against angle~ of incidence for plane polari6ed light. It will be seen that the greater the ~, . .
G3 ~ r~ $
: 6 s angle of incidence of light upon beam-splitting means 4 the greater the s-component of polarisation ln the reflected portion rl ~up to the limit of grazlng incldence).
The converee also holds; ie, as the angle of lncidence decrea~es the p-component of polari~ation in the light reflected f rom the beam splitter 4 increases.
Furthermore, as can be 6een from Flgure 4 9 the greater the ~-component of the incident light, the greater the coefficlent of reflectivity of the beam-splitter 4 and therefore the less the coeffic~ent of transmittivity.
Thus, by predetermlning the plane of polarisation of light incldent upon the beam-splitter 4 and by re6tricting the range of angle~ of ~ncidence of this l~ght on the beam-spltter 4, the energy in re1ected portion rl may be enhanced and that in the tran~mitted portion tl reduced.
As previously stated, the provision of the reflector means 12 restrict~ the range of incldent angle~ of the light incident on the beam-splitter 4. In a preferrecl form of the inventlon~
the pro~ection system geometry i8 arranged to provide a rectangular image on the viewing surface 10 with the horizontal edges of the lmage belng of longer len~th than the vertical edges of the image; that is the image i.8 of 'l~ndscape' format.
To provide maximum efficiency for the optical system the plane of polar~satlon of the light source 3 18 chosen to be parallel to a longer edge of the final image. In ~o doing, all rays from the light source 3 whlch ult~mately fo~m an image on a vertlcsl axi~ or line running through the centre of the flnal lmage will be 8 component polarised light during the first and second interactlons with the beam-splitter 4. Ray~ from the light ~ource 3 which for~ image points off this axis will compr~se of polarised llght ha~ing a mix of s and p components, the proport~on of these components being determined by the plane of lncidence of the6e rays relative to the beam-splitter 4 during thelr interaction with the beam-splitter 4, which in turn determines the 6a~d p-components in the reflected light. If the plane of polarlsation of the light from the light r~
: 7:
source 3 ia not carefully cho3en to provide a pure component of polarisation alone the central axi8 of the final ima~e, which can be elther pure ~ or pure p component but i~ chosen to be pure s-component to provlde maximum intensity in the final image, there would be an imbalance in the perceived brightnes6 from 6ide to ~ide of the final lmage.
The effect of the reflector 12 i8, therefore, two fold.
Firstly, the intensity or brlghtnesa of the final image on that portion of the viewing ~urface having its image formed by light reflected from the reflector 12 is increased, when compared to the known device. Secondly, the reflector 12 reduces the range of angle~ of incidence of the light from the llght source falling on the beam-splitter 4, which in thi~ preferred e~bodiment of the lnvention allows the lowest value of image intensity of the final image to be maximised and the spread or range in ima8e intenæity from one part of the image to another due to the initial reflection of the ~ncident light from the beam-aplitter, to be reduced. For example, confiiderlng the s-component of polarlsed llght forming the central vertical axi~
of the final ima~e formed on the ~iewing surface 10, the lowest in~tial angle of incldence of any incidlent llght ray on the beam-splitter 4 i8 increa6ed, thereby incresing the intensity of the portion rl. On the second lnteraction of theæe rays with the beam-splitter 4 the reflection coefficient ia ~lmilar for 8~ and p-component6 due to the low angle of incidence, a~ can be ~een from Figure 4. Hence the lowest value of i~age brightne~s along this axis i~ increa~ed and, therefore, the varlstion6 ln ~mage br~ghtne~s alon~ this axis is reduced.
The beam-splitter 4 i8, in one form of the invention a single layer d~electric type beam-splitter and haa an anti-reflection co~ting of magne~i~m fluoride on one 8~ de thereof remote from the mirror 8.
However, multi layer beam-splitters may also be used in the present invention. Both ~ingle and multi layer beam-splitter~
introduce chromatic aberration~ slnce their reflectivity is a function of wavelength; these aberrations will generally be : 8 :
most notlceable at the boundary between the lower portion of the image fQrmed by rays which are ~n~tially lncident on the reflector, and the upper portion which is produced by rays reflected from the beam-6plitter.
The var~ation of reflectivity with wavelength in dielectric beam-splitters lncreases with the total optical path length in the thin films which produce the beam-splitting effect; thu~ ~t is possible to produce a single layer beam-splitter whlch ~ive~
minimal chromatic aberration in this application, wherea6 a multi layer design will ln general produce chromatic aberrations which must be corrected by some method.
A preferred method of correct~ng such chrGmatic aberratlon~, and simultaneously correcting more gross brightness varlations~ may be understood with reference to a typical LCD
pro~ector in whlch the final image is formed by combining three separate primary coloured images of red, green and blue. By introducing a partial masking plate (whlch ha6 dlfferent transmlssions ln different regions; ie, effectively a variable neutral den~ity f~lter) into each colour channel of the projector prior to the point at which the colours are combined, it will be apparent that it is possible to selectively modify the intenaity of each of the primary colours at each polnt of the final image, and hence, the colour and brightness at each point of the final image. Active matrix displays provlde a part~cularly convenient means of introduc~ng such ~ partial ma~k~ng plate since they already include a small llght masking area ln each p~xel to prevent photo-acti~ation of the translstor used to dr~ve a respective pixel of the display. A modif~cation to the mas~ design would increase the size of this mask ~electively on a pixel by pixel basis so that the partial masking plate may be built into the LCD and no additional manufacturing costs would be incurred. However, it should be stres6ed that there i~ no absolute requirement to bu~ld thi~
effect into the LCD. Those skilled in the art will see how a partial ma~kin8 plate could be introduced into the colour channels of any suitable pro~ector.
.~
h ~ d : 9:
An additlonal alternative would be to electrically control the transmi6s~0n of each pixel.
Thoi~e skilled in the art will appreciste that t~o or more of these techniques may be used ~imultaneouslyO For example, electrical co~pensatlon of pixels alone might prove not to be the best choice since it could suppres~ the contrast and range of grey levels in the final image. A partial masking plate ~olution might suffer due to quality control problemOE on the bei~m-splltter, requlring masking plates to be customised for each beam-splitter. However, the two techniquefi might be combined wlth almost all the correctlon being achieved with a standard set of masking plates and the remaining correction achieved with programmable electrical compensation.
Figure 5 lllustrates the overall efficiency ~hich the present device aims to achieve. It will be seen that the optical efficlency Yaries acros6 the viewing surface from the centre to the edges (top and bottom). This occurs because of the variation of angles of incidence o~ the light from the light source which strikes the beam-splltting means 4, and hence the variation in reflectivity and thus in imten~ity of llght ~ncident upon the vlewing screen lO. Im normal circumstances9 these variations wlll not be discernable by a viewer of th~
final ~mage on the viewlng surface 10. I~owever, if necessary the variations can be compen~ated by approprlate deslgn of the neutral density filter and or the partial mask~ng plate referred to above.
It wlll be apparent that the present ~nvention achieve~ a substantial increase in optical efficiency as compared with the pr~or art device by employing a beam-splitter and reflector arranged such that incident polarised llght has a greater reflected (and subsequently) viewed component thaD the pr~or art.
Claims (8)
1. Apparatus for projecting light onto a surface comprising:
a light source for providing polarised lights;
beam-splitting means for effecting partial reflection and partial transmission of light incident thereon from the light source; reflector means for reflecting light incident thereon from the light source;
mirror means for directing towards the beam-splitting means light reflected from the beam-splitting means and also light reflected from the reflector means;
and louvre means located on a side of the beam-splitting means remote from the light source for allowing the passage of light therethrough in a predetermined range of incident angles relative to the beam-splitting means.
a light source for providing polarised lights;
beam-splitting means for effecting partial reflection and partial transmission of light incident thereon from the light source; reflector means for reflecting light incident thereon from the light source;
mirror means for directing towards the beam-splitting means light reflected from the beam-splitting means and also light reflected from the reflector means;
and louvre means located on a side of the beam-splitting means remote from the light source for allowing the passage of light therethrough in a predetermined range of incident angles relative to the beam-splitting means.
2. Apparatus according to claim 1 wherein the reflector means is arranged to possess a non-uniform optical reflectivity across the optical surface thereof.
3. Apparatus according to claim 2 wherein the non-uniform reflectivity is achieved by an arrangement of areas of dots having lower reflectivity than the optical surface.
4. Apparatus according to claim 1 wherein the light source comprises a liquid crystal display.
5. Apparatus according to claim 4 wherein the liquid crystal display comprises separate displays for each of the the primary colours; red, green and blue.
6. Apparatus according to claim 1 wherein the beam-splitting means and the reflector means are arranged to lie in the same, first plane, and the mirror means is arranged to lie in a second plane at an acute angle with the first plane.
7. Apparatus according to claim 6 wherein the surface onto which the light is projected is located adjacent to the louvre : 11 :
means on a side remote from the light source enabling viewing of the light transmitted via the louvre means.
means on a side remote from the light source enabling viewing of the light transmitted via the louvre means.
8. Apparatus according to claim 1 further including a neutral density filter to compensate for any variation in image intensity across the viewing surface onto which the light is projected.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB909026151A GB9026151D0 (en) | 1990-11-30 | 1990-11-30 | Display device |
| GB9026515.2 | 1990-11-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2056078A1 true CA2056078A1 (en) | 1992-05-31 |
Family
ID=10686317
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002056078A Abandoned CA2056078A1 (en) | 1990-11-30 | 1991-11-22 | Display device |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5184238A (en) |
| EP (1) | EP0488590B1 (en) |
| JP (1) | JPH04293031A (en) |
| AT (1) | ATE120017T1 (en) |
| CA (1) | CA2056078A1 (en) |
| DE (1) | DE69108186T2 (en) |
| GB (1) | GB9026151D0 (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5594561A (en) * | 1993-03-31 | 1997-01-14 | Palomar Technologies Corporation | Flat panel display with elliptical diffuser and fiber optic plate |
| EP0618476A1 (en) * | 1993-03-31 | 1994-10-05 | Hughes Aircraft Company | Rear projection screen with off-axis sunlight rejection |
| US6483612B2 (en) | 1998-04-15 | 2002-11-19 | Duke University | Projection screen apparatus including holographic optical element |
| BE1007864A3 (en) * | 1993-12-10 | 1995-11-07 | Philips Electronics Nv | Image projection system. |
| US5808704A (en) * | 1994-01-17 | 1998-09-15 | Hitachi, Ltd. | Rear projection type image display apparatus |
| GB2316262B (en) * | 1994-01-17 | 1998-06-24 | Hitachi Ltd | Rear projection type image display apparatus |
| US5879067A (en) * | 1994-05-25 | 1999-03-09 | De Vaan; Adrianus J. S. M. | Image projection system |
| FR2732783B1 (en) * | 1995-04-07 | 1997-05-16 | Thomson Csf | COMPACT BACK PROJECTION DEVICE |
| US6181386B1 (en) | 1995-12-29 | 2001-01-30 | Duke University | Projecting images |
| CA2193790C (en) | 1995-12-29 | 2001-03-13 | Duke University | Projecting images |
| US5771321A (en) * | 1996-01-04 | 1998-06-23 | Massachusetts Institute Of Technology | Micromechanical optical switch and flat panel display |
| US5975703A (en) * | 1996-09-30 | 1999-11-02 | Digital Optics International | Image projection system |
| US6390626B2 (en) | 1996-10-17 | 2002-05-21 | Duke University | Image projection system engine assembly |
| US5844722A (en) * | 1997-06-05 | 1998-12-01 | Hughes-Jvc Technology Corporation | Internal aperture mask for embedded optics |
| FR2764462A1 (en) * | 1997-06-10 | 1998-12-11 | Thomson Multimedia Sa | IMPROVEMENT IN PROJECTION SYSTEMS |
| US6204901B1 (en) | 1997-07-31 | 2001-03-20 | Duke University | Liquid crystal color shutters that include reflective polarizers that pass color components of light of a first polarization and that reflect a majority of color components of light of a second polarization |
| US6967779B2 (en) | 1998-04-15 | 2005-11-22 | Bright View Technologies, Inc. | Micro-lens array with precisely aligned aperture mask and methods of producing same |
| US6185041B1 (en) | 1998-10-23 | 2001-02-06 | Duke University | Projection lens and system |
| US6172816B1 (en) | 1998-10-23 | 2001-01-09 | Duke University | Optical component adjustment for mitigating tolerance sensitivities |
| US6907183B1 (en) * | 1999-06-30 | 2005-06-14 | Kabushiki Kaisha Toshiba | Display device and display method |
| JP2011512006A (en) | 2008-01-30 | 2011-04-14 | デジタル オプティクス インターナショナル，リミティド ライアビリティ カンパニー | Thin lighting system |
| US8721149B2 (en) | 2008-01-30 | 2014-05-13 | Qualcomm Mems Technologies, Inc. | Illumination device having a tapered light guide |
| JP2020013037A (en) * | 2018-07-19 | 2020-01-23 | Ｇａｔｅｂｏｘ株式会社 | Projection device |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE136899C (en) * | ||||
| US4033672A (en) * | 1971-11-24 | 1977-07-05 | Ing. C. Olivetti & C., S.P.A. Ufficio Brevetti | Liquid crystal devices |
| US3947091A (en) * | 1974-09-19 | 1976-03-30 | Rockwell International Corporation | Reflective display apparatus |
| US3941467A (en) * | 1974-10-29 | 1976-03-02 | Kaptron, Inc. | Optical projector/reader |
| CH591705A5 (en) * | 1975-10-28 | 1977-09-30 | Bbc Brown Boveri & Cie | |
| JPS5383498A (en) * | 1976-12-28 | 1978-07-22 | Seiko Epson Corp | Liquid crystal display device |
| DE3102626A1 (en) * | 1981-01-27 | 1982-08-19 | Siemens AG, 1000 Berlin und 8000 München | "PASSIVE ELECTROOPTICAL DISPLAY DEVICE" |
| JPS60117215A (en) * | 1983-11-29 | 1985-06-24 | Sharp Corp | Liquid crystal display device |
| NL8600684A (en) * | 1986-03-18 | 1987-10-16 | Philips Nv | COMPLETE TRANSPARENT PROJECTION SYSTEM WITH INCREASED LIGHT BEAM. |
| US4822145A (en) * | 1986-05-14 | 1989-04-18 | Massachusetts Institute Of Technology | Method and apparatus utilizing waveguide and polarized light for display of dynamic images |
| US4913528A (en) * | 1987-05-30 | 1990-04-03 | Pioneer Electronic Corporation | Optical prism, and projection television set using same |
| JP2569632B2 (en) * | 1987-11-26 | 1997-01-08 | カシオ計算機株式会社 | Rear projection display |
| GB8804402D0 (en) * | 1988-02-25 | 1988-03-23 | Emi Plc Thorn | Display device |
-
1990
- 1990-11-30 GB GB909026151A patent/GB9026151D0/en active Pending
-
1991
- 1991-11-21 EP EP91310749A patent/EP0488590B1/en not_active Expired - Lifetime
- 1991-11-21 DE DE69108186T patent/DE69108186T2/en not_active Expired - Fee Related
- 1991-11-21 AT AT91310749T patent/ATE120017T1/en not_active IP Right Cessation
- 1991-11-22 CA CA002056078A patent/CA2056078A1/en not_active Abandoned
- 1991-11-25 US US07/797,036 patent/US5184238A/en not_active Expired - Fee Related
- 1991-11-29 JP JP3356084A patent/JPH04293031A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| US5184238A (en) | 1993-02-02 |
| DE69108186D1 (en) | 1995-04-20 |
| ATE120017T1 (en) | 1995-04-15 |
| DE69108186T2 (en) | 1995-09-28 |
| JPH04293031A (en) | 1992-10-16 |
| EP0488590A1 (en) | 1992-06-03 |
| EP0488590B1 (en) | 1995-03-15 |
| GB9026151D0 (en) | 1991-01-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |