Patent Application
20070139766
This invention generally relates to projection screens and projection systems incorporating same. The invention is particularly applicable to front projection screens with high ambient light rejection.
A front projection screen is generally designed to reflect an image projected by a projector onto the front side of the screen into a viewing space where the projector and the viewing space are both located on the front side of the screen. Typical screen characteristics used to describe a screen's performance include gain, viewing angle, resolution, contrast, color fidelity and the like. It is generally desirable to have a front projection screen that has high resolution, high contrast and a large gain. It is also desirable that the screen spread the light over a large viewing space. Unfortunately, as one screen characteristic is improved, one or more other screen characteristics often degrade. For example, in order to increase the screen gain, one must often decrease the contrast and/or viewing angle of the screen. As a result, certain tradeoffs are made in screen characteristics and performance in order to optimize the screen's overall performance in a desired projection display application.
Front projection screens reflect substantially all of the light incident on them, i.e., they reflect ambient light as well as light from an image projecting source. Because a portion of the ambient light is reflected towards the viewing space, the image contrast or the apparent brightness of the image is often reduced, particularly in areas with relatively high levels of ambient light.
Generally, the present invention relates to projection screens. The present invention also relates to projection screens employed in projection systems.
In one embodiment of the invention, a front projection screen includes a plurality of cholesteric liquid crystal layers and one or more retarder layers. Each cholesteric liquid crystal layer has a reflectance curve characterized by a reflectance peak and a reflectance full width at half maximum. The reflectance peaks of at least two cholesteric liquid crystal layers in the plurality of cholesteric liquid crystal layers are located at different wavelengths. A retardance full width at half maximum of a first retarder layer in the one or more retarder layers encloses the reflectance full width at half maxima of two or more cholesteric liquid crystal layers in the plurality of cholesteric liquid crystal layers.
In another embodiment of the invention, a front projection screen includes a plurality of cholesteric liquid crystal layers and one or more retarder layers. A first cholesteric liquid crystal layer in the plurality of cholesteric liquid crystal layers has a first reflectance peak at an mth order half-wave retardance peak of a retarder layer in the one or more retarder layers. A second cholesteric liquid crystal layer in the plurality of cholesteric liquid crystal layers has a second reflectance peak at an nth order half-wave retardance peak of a retarder layer in the one or more retarder layers. The first reflectance peak is at a different wavelength than the second reflectance peak. n is different than m.
In another embodiment of the invention, a front projection screen includes a plurality of cholesteric liquid crystal layers and one or more retarder layer. Each cholesteric liquid crystal layer has a reflectance curve characterized by a reflectance peak and a reflectance full width at half maximum. At least one of the one or more retarder layers has a plurality of half-wave retardance peaks within the reflectance full width at half maximum of a cholesteric liquid crystal layer in the plurality of cholesteric liquid crystal layers.
In another embodiment of the invention, a front projection screen includes at least three groups of optical layers. Each group includes a retarder layer disposed between two cholesteric liquid crystal layers having a same handed-ness. Each group reflects light in a wavelength region in which the other groups transmit light.
In another embodiment of the invention, a front projection screen includes at least three groups of optical layers. Each group reflects light in a wavelength region in which the other groups transmit light. Each of at least two groups include a retarder layer disposed between two cholesteric liquid crystal layers having a same handed-ness. At least one group includes a multilayer optical film that includes alternating first and second layers. The multilayer optical film reflects light by optical interference.
In another embodiment of the invention, a front projection screen includes a first group of optical layers that substantially reflects light in a first wavelength region in the visible and substantially transmits light elsewhere in the visible. The front projection screen further includes a second group of optical layers that substantially reflects light in a second wavelength region in the visible and substantially transmits light elsewhere in the visible. The second region is different than the first region. Each of the first and second groups includes a retarder layer disposed between two cholesteric liquid crystal layers that have a same handed-ness. The front projection screen further includes a colored reflective layer that substantially reflects light in a third wavelength region in the visible and substantially absorbs light elsewhere in the visible. The third region is different than the first and the second regions.
The invention may be more completely understood and appreciated in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:
The present invention generally relates to front projection screens and front projection systems incorporating a front projection screen. The invention is particularly applicable to a front projection screen where it is desirable to display a projected image with high contrast and brightness.
In the specification, a same reference numeral used in multiple figures refers to the same or similar elements having the same or similar properties and functionalities.
The present invention describes a front projection screen that utilizes highly reflective cholesteric liquid crystal films combined with one or more retarder films. One advantage of the screen of the invention is efficient reflection of light incident onto the screen from a projector which leads to displayed images having high brightness. Another advantage of the invention is substantial absorption of ambient light by the screen leading to displayed images having high contrast.
As used herein, the terms “specular reflection” and “specular reflectance” refer to the reflection of an incident collimated light into a reflected light cone with a relatively narrow cone angle, where the full cone angle is typically about 10 degrees or less, more typically about 5 degrees or less, and even more typically about 2 degrees or less. The terms “diffuse reflection” or “diffuse reflectance” refer to the reflection of an incident collimated light outside the specular full cone angle. The terms “total reflectance” or “total reflection” refer to the combined reflectance of all light from a surface. Thus, for example, total reflection is the sum of specular and diffuse reflections.
Similarly, the terms “specular transmission” and “specular transmittance” refer to the transmission of rays into a transmitted light cone with a relatively narrow full cone angle, where the full cone angle is typically about 10 degrees or less, more typically about 5 degrees or less, and even more typically about 2 degrees or less. The terms “diffuse transmission” and “diffuse transmittance” refer to rays that are transmitted outside the specular cone. The terms “total transmission” or “total transmittance” refer to the combined transmission of all light through an optical body. Thus, for example, total transmission is the sum of specular and diffuse transmissions.
The present invention discloses a front projection screen where the reflection spectrum of the screen substantially matches that of the image producing projector. Accordingly, one advantage of the present invention is that a projected image can be displayed with high brightness and color fidelity.
The present invention further discloses a front projection screen that absorbs a substantial amount of the ambient light. In a typical setting, ambient light can include light from various artificial light sources such as a mercury arc light source, an incandescent light source, a fluorescent light source, or a light emitting diode (LED) light source, or a natural light source such as the sun. The present invention discloses a front projection screen that absorbs a substantial amount of the ambient light that lies outside the wavelength ranges emitted by a projector. Thus, another advantage of the present invention is that a projected image can be displayed with high contrast even in the presence of high ambient light.
The present invention discloses a front projection screen that includes cholesteric liquid crystal (CLC) layers. Examples of references discussing CLCs in detail include De Gennes, Prost, “The Physics of Liquid Crystals,” Oxford University Press 1995, ISBN 0198517858 and Collings, Hird, “Introduction to Liquid Crystals: Chemistry and Physics,” Taylor & Francis 1997, ISBN 074840483X. In summary, CLCs have a liquid crystal phase or a mesophase in which the director (that is, the unit vector in the direction of average local molecular alignment) of the liquid crystal rotates in a helical fashion along the dimension perpendicular to the director. Cholesteric liquid crystals are also referred to as chiral nematic liquid crystals. The pitch of a cholesteric liquid crystal compound is the distance (in a direction perpendicular to the director) that it takes for the director to rotate through 360°. This distance is typically 100 nm, although in some cases the pitch can be larger or smaller than 100 nm.
The pitch of a cholesteric liquid crystal compound can typically be altered by mixing or otherwise combining (e.g., by copolymerization) a chiral compound (e.g., a cholesteric liquid crystal compound) with a nematic liquid crystal compound, where a chiral compound refers to a compound that does not possess an internal plane of symmetry. In other words, a chiral compound or object is one that is not superimposable on its mirror image. An example of a chiral object is a coiled spring. An achiral compound, on the other hand, is a compound that has at least one internal plane of symmetry and, therefore, can be superimposed on its mirror image.
The pitch of a cholesteric liquid crystal compound generally depends on a number of factors such as the relative weight ratio of the chiral compound and the nematic liquid crystal compound. The pitch is generally selected to be on the order of the wavelength of light of interest. The helical twist of the director results in a spatially periodic variation in the dielectric tensor, which in turn gives rise to wavelength selective reflection of light by a CLC. In some applications such as display systems, the pitch can be chosen such that the selective reflection is peaked in the visible, such as in the red, green, or blue regions of the electromagnetic spectrum.
One characteristic of CLCs is that they circularly polarize an incident light beam upon reflection. If a light beam has two orthogonal polarization directions which vary in phase by 90°, the beam is said to be elliptically or circularly polarized. Circular polarization occurs when the magnitude of the two oscillations are equal (i.e., the tip of the electric field vector moves in a circle). In general, a right-handed CLC reflects right-handed circularly polarized light within a reflection band and a left-handed CLC reflects left-handed circularly polarized light within a reflection band. The peak of the reflection band, λp, is given by:
λp=nP (1)
where n and P are the average index and pitch of the CLC, respectively. The reflectance full width at half maximum (FWHM) or the bandwidth, Δλ, of the CLC is approximately given by:
Δλ=ΔnP (2)
where Δn is the birefringence of the CLC.
The present invention also discloses front projection screens that include one or more retarder films. A retarder film is generally made of a birefringent material that can change the phase of an incident polarized light beam as it travels through the thickness of the retarder. Accordingly, a retarder film can shift the phase of light polarized in one direction relative to the phase of light polarized in a perpendicular direction. By controlling the magnitude of birefringence in a retarder film a desired phase shift (or retardance) can be introduced in a light beam that is transmitted by the retarder film.
A retarder film can change the polarization of an incident light beam. For example, a quarter-wave retarder can convert linearly polarized light to circularly polarized light by virtue of introducing a 90° phase shift. As another example, a half-wave retarder can introduce a phase shift of 180°. Thus, a half-wave retarder can be used to, for example, convert a right-handed circularly polarized light to a left-handed circularly polarized light.
The retardance or retardation angle, δ, of a retarder film is given by:
where t is the film thickness, Δnr is the film birefringence and λ is wavelength.
In general, a retarder has a fast axis which is the direction with the smaller index of refraction, and a slow axis which is the direction with the larger index of refraction. The fast axis is normal to the slow axis.
One way to determine the orientations of axes 110 and 120 is to rotate retarder 100 in the xy-plane about the z-axis until optical detector 170 measures a minimum optical intensity, in which case, one of the two angles α and β is zero and the other angle is 90°. Alternatively, retarder 100 may be rotated in the xy-plane about the z-axis until optical detector 170 measures a maximum optical intensity, in which case, angles α and β are both 45°.
The half-wave peaks of retarder film 100 may be determined by using a spectrophotometer to measure the optical transmission of the assembly of linear polarizer 130, retarder 100, and linear polzarizer 140 for incident unpolarized light as a function of wavelength. In the assembly, polarizers 130 and 140 are crossed and retarder film 100 is oriented so that its fast axis 110 makes a 45° angle with polarization axes 135 and 145.
Associated with each peak is a retardance full width at half maximum (FWHM). For example, retardance FWHM 230 is associated with peak 220 and retardance FWHM 231 is associated with peak 221. Generally, the size of FWHM decreases as the order of the peak increases. In other words, a half-wave peak at a shorter wavelength generally has a smaller FWHM than a half-wave peak at a longer wavelength.
The local shape of retardance profile 210 at a given peak is generally asymmetric. For example, the local shape of retardance profile 210 at peak 220 is asymmetric with respect to line 240 that passes through peak 220, meaning that, for example, midpoint 232 of FWHM 230 does not lie on line 240. Similarly, the local shape of retardance profile 210 at peak 221 is asymmetric with respect to line 241 that passes through peak 221. The degree of local asymmetry may vary depending on the type of retarder used. Some retarders can have symmetric or almost symmetric local shapes.
The separation between adjacent peaks generally decreases with decreasing wavelength. For example, separation 252 which is λ2-λ3 is generally smaller than separation 250 which is λo-λ1. The separation between adjacent peaks at sufficiently high order half-wave peaks can become small enough that a measuring instrument such as a spectrophotometer may not be able to resolve the separation.
CLC layers 1110A and 1110B substantially reflect right-handed circularly polarized light at a wavelength λ1 and substantially transmit left-handed circularly polarized light at the same wavelength. Retarder layer 1150 is a half-wave retarder at λ1 and as such, can change the handedness of a circularly polarized light on transmission. Optical stack 1100 is capable of substantially reflecting an incident light at wavelength λ1 as described below.
An incident light ray 1105 at wavelength λ1 can be decomposed into a right-handed circularly polarized light ray 1101 and a left-handed circularly polarized light ray 1102 where the two polarization states are orthogonal to each other. Light ray 1101 is substantially reflected by CLC layer 1110A producing a right-handed circularly polarized reflected light ray 1101E. Light ray 1102, on the other hand, is substantially transmitted by CLC layer 1110A producing a left-handed circularly polarized transmitted light ray 1102A. Retarder film 1150 shifts the phase of light ray 1102A on transmission and produces a right-handed circularly polarized light ray 1102B. Light ray 1102B is substantially reflected by CLC layer 1110B producing a right-handed circularly polarized reflected light ray 1102C. Retarder film 1150 shifts the phase of light ray 1102C on transmission and produces a left-handed circularly polarized light ray 1102D. Light ray 1102D is substantially transmitted by CLC layer 1110A producing a left-handed circularly polarized light ray 1102E. Accordingly, optical stack 1100 substantially reflects incident light ray 1105.
Wavelength λ1 can be any wavelength that may be desirable in an application. In one embodiment of the invention, wavelength λ1 is in the visible region of the electromagnetic spectrum. For example, wavelength λ1 can be a primary color such as red, green, or blue. In some applications, optical stack 1100 is illuminated by light projected by a projector or a projection system, in which case, λ1 can be the wavelength of a light ray emitted by the projector or the projection system.
Optical stack 1100 has been described as being capable of reflecting light at a single wavelength λ1. In general, optical stack 1100 can be capable of reflecting light at a plurality of wavelengths such as a plurality of discrete wavelengths. In some embodiments of the invention, optical stack 1100 is capable of reflecting light at a range of wavelengths Δλ1 where Δλ1 can, for example, be a range of wavelengths in the visible such as a range in the blue, green, or red region of the electromagnetic spectrum.
In optical stack 1200, each of CLC layers 1210A and 1210B substantially reflects right-handed circularly polarized light at a wavelength λ1a and substantially transmits left-handed circularly polarized light at λ1a; each of CLC layers 1220A and 1220B substantially reflects right-handed circularly polarized light at a wavelength λ2a and substantially transmits left-handed circularly polarized light at λ2a where λ2a is different from λ1a; and each of CLC layers 1230A and 1230B substantially reflects right-handed circularly polarized light at a wavelength λ3a and substantially transmits left-handed circularly polarized light at λ3a where λ3a is different from λ1a and λ2a.
Furthermore, each of CLC layers 1210A and 1210B substantially transmits light at wavelengths λ2a and λ3a, each of CLC layers 1220A and 1220B substantially transmits light at wavelengths λ1a and λ3a, and each of CLC layers 1230A and 1230B substantially transmits light at wavelengths λ1a and λ2a.
Retarder layer 1250 is substantially a half-wave retarder at all three wavelengths λ1a, λ2a, and λ3a and, therefore, can change the handedness of a circularly polarized light on transmission at any of the three wavelengths. Optical stack 1200 functions similarly to optical stack 1100 except that optical stack 1200 is capable of substantially reflecting an incident light at three wavelengths λ1a, λ2a, and λ3a. In particular, the combination of CLC layers 1210A and 1210B and retarder layer 1250 (the first combination) is capable of substantially reflecting light at wavelength λ1a; the combination of CLC layers 1220A and 1220B and retarder layer 1250 (the second combination) is capable of substantially reflecting light at wavelength λ2a; and the combination of CLC layers 1230A and 1230B and retarder layer 1250 (the third combination) is capable of substantially reflecting light at wavelength λ3a.
The first, second, and third combinations in optical stack 1200 have been described as being capable of reflecting light at discrete wavelengths λ1a, λ2a, and λ3a, respectively. In general, each of the first, second, and third combinations can be capable of reflecting light at a plurality of wavelengths such as a plurality of discrete wavelengths. In some embodiments of the invention, the first combination in optical stack 1200 is capable of reflecting light at a range of wavelengths Δλ1a where Δλ1a can, for example, be a range of wavelengths in the visible such as a range in the blue region of the electromagnetic spectrum. Similarly, in some embodiments of the invention, the second combination in optical stack 1200 is capable of reflecting light at a range of wavelengths Δλ2a where Δλ2a can, for example, be a range of wavelengths in the visible such as a range in the green region of the electromagnetic spectrum. Furthermore, in some embodiments of the invention, the third combination in optical stack 1200 is capable of reflecting light at a range of wavelengths Δλ3a where Δλ3a can, for example, be a range of wavelengths in the visible such as a range in the red region of the electromagnetic spectrum.
In one embodiment of the invention, a combination substantially transmits light in wavelength regions where the other combinations substantially reflect light. For example, the first combination substantially transmits light in ranges Δλ2a and Δλ3a; the second combination substantially transmits light in ranges Δλ1a and Δλ3a; and the third combination substantially transmits light in ranges Δλ1a and Δλ2a.
In one embodiment of the invention, there is no overlap between wavelength ranges Δλ1a, Δλ2a, and Δλ3a. In some applications, there may be an overlap between two or more of the wavelength ranges. In some applications, the combination of the wavelength ranges may include a fraction of the visible region. In some other applications, the combination of the wavelength ranges may extend the entire visible region of the electromagnetic spectrum.
According to one embodiment of the invention, each optical stack in screen 300 reflects light at a wavelength and transmits light at other wavelengths. For example, optical stack A1 reflects light at a wavelength λA1 and transmits light at other wavelengths; optical stack B1 reflects light at a wavelength λB1, where λB1 is different from wavelength ΔA1, and transmits light at other wavelengths; optical stack C1 reflects light at a wavelength λC1, where λC1 is different from wavelengths λA1 and λB1, and transmits light at other wavelengths, and optical stack X1 reflects light at a wavelength λX1, where λX1 is different from wavelengths λA1, λB1, and λC1, and transmits light at other wavelengths. Similar to the discussion in reference to optical stack 1100, each of the wavelengths λA1, λB1, λC1, and λX1 can be a wavelength in the visible region of the spectrum.
Although each optical stack in screen 300 is described as being capable of reflecting light at a single wavelength, in general, each optical stack can be capable of reflecting light at a plurality of wavelengths such as a plurality of discrete wavelengths. In some embodiments of the invention, optical stack A1 is capable of reflecting light at a range of wavelengths ΔλA1, optical stack B1 is capable of reflecting light at a range of wavelengths ΔλB1, optical stack C1 is capable of reflecting light at a range of wavelengths ΔλC1, and optical stack X1 is capable of reflecting light at a range of wavelengths ΔλX1, where one or more of the wavelength ranges ΔλA1, ΔλB1, ΔλC1, and ΔλA1 can, for example, be a range of wavelengths in the visible region of the electromagnetic spectrum.
According to one embodiment of the invention, each optical stack in screen 300 is substantially reflective in a wavelength region and substantially transmissive in each wavelength region in which another stack is substantially reflective.
Although screen 300 is shown to have four optical stacks, in general, screen 300 can have more or fewer number of optical stacks. In particular, according to one embodiment of the invention, screen 300 includes three optical stacks A1, B1, and C1, where optical stack A1 substantially reflects light within the wavelength range ΔλA1 and substantially transmits light within a different wavelength range ΔλA2; optical stack B1 substantially reflects light within the wavelength range ΔλB1 and substantially transmits light within a different wavelength range ΔλB2; and optical stack C1 substantially reflects light within the wavelength range ΔλC1 and substantially transmits light within a different wavelength range ΔλC2. Ranges ΔλA1, ΔλB1, and ΔλC1 can be different wavelength ranges, although there can be one or more overlapping regions between the ranges.
According to one embodiment of the invention, ΔλA2 includes ranges ΔλB1 and ΔλC1, ΔλB2 includes ranges ΔλA1 and ΔλC1, and ΔλC2 includes ranges ΔλA1 and ΔλB1.
In one embodiment of the invention, ΔλA1 is a wavelength range in the visible region of the spectrum that includes a first primary color such a blue color, ΔλB1 is a wavelength range in the visible region of the spectrum that includes a second primary color such a green color, and ΔλC1 is a wavelength range in the visible region of the spectrum that includes a third primary color such a red color. Furthermore, optical stack A1 substantially reflects light within ΔλA1 and substantially transmits light elsewhere in the visible; optical stack B1 substantially reflects light within ΔλB1 and substantially transmits light elsewhere in the visible; and optical stack C1 substantially reflects light within ΔλC1 and substantially transmits light elsewhere in the visible.
Each cholesteric liquid crystal layer in screen 300 has a reflectance curve that is characterized by a reflectance peak and a reflectance full width at half maximum (FWHM). Furthermore, each retarder layer in screen 300 has a retardance profile characterized by a plurality of half-wave peaks where each half-wave peak has an associated retardance full width at half maximum (FWHM).
Screen 300 further includes optional optical buffer layers, such as layers 330A and 330B placed between adjacent cholesteric liquid crystal layers. For example, buffer layer 330A is placed between cholesteric liquid crystal layers 310A and 300B. The buffer layers can be advantageous in, for example, preventing a layer from adversely affecting the performance of an adjacent layer by, for example, partially diffusing into the adjacent layer during the manufacturing of the screen. As another example, the buffer layers may have alignment properties to assist in orienting liquid crystal molecules in the cholesteric liquid crystal layers. The buffer layers may have adhesive properties for attaching adjacent optical stacks.
One or more of the buffer layers and/or CLC layers can be optically diffusive by, for example, dispersing small particles in a host material where the index of refraction of the particles is different than the index of refraction of the host material. Furthermore, one or more of the buffer layers may function as a color filter to, for example, improve color purity of an image displayed by the screen.
Screen 300 further includes one or more diffuser layers such as diffuser layer 340. Diffuser layer 340 can assist in scattering light into a viewing space 370 which may include one or more viewers such as a viewer 395. Diffuser layer 340 can include structures (not shown in
Screen 300 further includes a light absorbing layer 350 for increasing screen contrast by absorbing non-imaging or otherwise undesirable light such as ambient light.
Screen 300 may further include other layers not explicitly shown in
In one embodiment of the invention, a projection system illuminates screen 300 with light 399 from the viewing side of the screen. The screen includes optical stacks A1, B1, and C1 and light absorbing layer 350. Light 399 includes wavelengths that are substantially limited to ranges ΔλA1, ΔλB1, and ΔλC1. Screen 300 substantially reflects light 399 while absorbing layer 350 substantially absorbs any ambient light 364 that falls outside the three wavelength ranges.
Optical stack 401 is capable of substantially reflecting light at wavelengths λY1, λY2, and λY3. In particular, the combination of CLC layers 400A and 410A and retarder layer 420 (the Y1 combination) is capable of substantially reflecting light at wavelength λY1, the combination of CLC layers 400B and 410B and retarder layer 420 (the Y2 combination) is capable of substantially reflecting light at wavelength λY2, and the combination of CLC layers 400C and 410C and retarder layer 420 (the Y3 combination) is capable of substantially reflecting light at wavelength λY3.
Wavelengths λY1, λY2, and λY3 can be any wavelengths that may be desirable in an application. In one embodiment of the invention, wavelengths λY1, λY2, and λY3 are located in the visible region of the electromagnetic spectrum. For example, wavelengths λY1, λY2, and λY3 can be primary colors blue, red, and green, respectively.
The Y1, Y2, and Y3 combinations in optical stack 401 have been described as being capable of reflecting light at discrete wavelengths λY1, λY2, and λY3, respectively. In general, each of the Y1, Y2, and Y3 combinations can be capable of reflecting light at a plurality of wavelengths such as a plurality of discrete wavelengths. In some embodiments of the invention, the Y1 combination in screen 400 is capable of substantially reflecting light in a wavelength range ΔλY1 and substantially transmitting light in a different wavelength range ΔλZ1, the Y2 combination is capable of substantially reflecting light in a wavelength range ΔλY2 and substantially transmitting light in a different wavelength range ΔλZ2, and the Y3 combination is capable of substantially reflecting light in a wavelength range ΔλY3 and substantially transmitting light in a different wavelength range ΔλZ3. Furthermore, wavelength range ΔλZ1 preferably includes ranges ΔλY2 and ΔλY3, wavelength range ΔλZ2 preferably includes ranges ΔλY1 and ΔλY3, and wavelength range ΔλZ3 preferably includes ranges ΔλY1 and ΔλY2.
In one embodiment of the invention, ΔλY1, ΔλY2, and ΔλY3 are ranges of wavelength in the visible such as ranges in the blue, green, and red regions of the electromagnetic spectrum, respectively. Furthermore, optical stack 401 substantially reflects light within ranges ΔλY1, ΔλY2, and ΔλY3 and substantially transmits light elsewhere in the visible.
In one embodiment of the invention, ΔλY1 is a wavelength range in the visible region of the spectrum that includes a first primary color such as a blue color, ΔλY2 is a wavelength range in the visible region of the spectrum that includes a second primary color such as a green color, and ΔλY3 is a wavelength range in the visible region of the spectrum that includes a third primary color such as a red color. Furthermore, combination Y1 substantially reflects light within ΔλY1 and substantially transmits light elsewhere in the visible, combination Y2 substantially reflects light within ΔλY2 and substantially transmits light elsewhere in the visible, and combination Y3 substantially reflects light within ΔλY3 and substantially transmits light elsewhere in the visible.
In some embodiments of the invention, the order of CLC layers 400A-400C and/or CLC layers 410A-410C may be reversed or otherwise changed.
Each cholesteric liquid crystal layer in screen 400 has a reflectance curve that is characterized by a reflectance peak and a reflectance full width at half maximum. Furthermore, each retarder layer in screen 400 has a retardance profile characterized by a plurality of half-wave peaks where each half-wave peak has an associated retardance full width at half maximum.
Screen 400 further includes one or more diffuser layers such as diffuser layer 440. Diffuser layer 440 may be used to assist in scattering light in a viewing space 470 which may include one or more viewers such as a viewer 495.
Screen 400 further includes a light absorbing layer 450 for increasing screen contrast by absorbing all or a substantial fraction of ambient light that is not reflected by optical stack 401.
Screen 400 may further include other layers not explicitly shown in
The combination of optical stacks 501 and 502 is capable of substantially reflecting light at preferably distinct wavelengths λW1, λW2, and λW3. In particular, optical stack 501 (combination W1) is capable of substantially reflecting light at wavelength λW1. Furthermore, optical stack 502 is capable of substantially reflecting light at wavelengths λW2 and λW3.
In one embodiment of the invention, the combination of CLC layers 500B and 510B and retarder layer 520B (the W2 combination) is capable of substantially reflecting light at wavelength λW2, and the combination of CLC layers 500C and 510C and retarder layer 520B (the W3 combination) is capable of substantially reflecting light at wavelength λW3.
Wavelengths λW1, λW2, and λW3 can be any wavelengths that may be desirable in an application. In one embodiment of the invention, wavelengths λW1, λW2, and λW3 are located in the visible region of the electromagnetic spectrum. For example, wavelengths λW1, λW2, and λW3 can be primary colors blue, red, and green, respectively.
The W1, W2, and W3 combinations have been described as being capable of reflecting light at discrete wavelengths λW1, λW2, and λW3, respectively. In general, each of the W1, W2, and W3 combinations can be capable of reflecting light at a plurality of wavelengths such as a plurality of discrete wavelengths. In some embodiments of the invention, the W1 combination is capable of substantially reflecting light in a wavelength range ΔλW1 and substantially transmitting light in a different wavelength range ΔλU1, the W2 combination is capable of substantially reflecting light in a wavelength range ΔλW2 and substantially transmitting light in a different wavelength range ΔλU2, and the W3 combination is capable of substantially reflecting light in a wavelength range ΔλW3 and substantially transmitting light in a different wavelength range ΔλU3. Furthermore, wavelength range ΔλU1 preferably includes ranges ΔλW2 and ΔλW3, wavelength range ΔλU2 preferably includes ranges ΔλW1 and ΔλW3, and wavelength range ΔλU3 preferably includes ranges ΔλW1 and ΔλW2.
In one embodiment of the invention, ΔλW1, ΔλW2, and ΔλW3 are ranges of wavelength in the visible such as ranges in the blue, green, and red regions of the electromagnetic spectrum, respectively. Furthermore, the combination of optical stacks 501 and 502 substantially reflects light within ΔλW1, ΔλW2, and ΔλW3 and substantially transmits light elsewhere in the visible.
In one embodiment of the invention, ΔλW1 is a wavelength range in the visible region of the spectrum that includes a first primary color such as a blue color, ΔλW2 is a wavelength range in the visible region of the spectrum that includes a second primary color such as a green color, and ΔλW3 is a wavelength range in the visible region of the spectrum that includes a third primary color such as a red color. Furthermore, combination W1 substantially reflects light within ΔλW1 and substantially transmits light elsewhere in the visible, combination W2 substantially reflects light within ΔλW2 and substantially transmits light elsewhere in the visible, and combination W3 substantially reflects light within ΔλW3 and substantially transmits light elsewhere in the visible.
In some embodiments of the invention, the order of CLC layers 500B and 500C, and/or layers 510B and 510C may be reversed or otherwise changed. Furthermore, the order of optical stacks 501 and 502 may be reversed or otherwise changed.
Each cholesteric liquid crystal layer in screen 500 has a reflectance curve that is characterized by a reflectance peak and a reflectance full width at half maximum. Furthermore, each retarder layer in screen 500 has a retardance profile characterized by a plurality of half-wave peaks where each half-wave peak has an associated retardance full width at half maximum.
Screen 500 further includes optional optical buffer layers, such as buffer layer 530 placed between adjacent cholesteric liquid crystal layers 510A and 500B. The buffer layers can be advantageous in, for example, preventing a layer from adversely affecting the performance of an adjacent layer by, for example, partially diffusing into the adjacent layer during the manufacturing of the screen. As another example, the buffer layers may have alignment properties to assist in orienting liquid crystal molecules in cholesteric liquid crystal layers. In some embodiments of the invention, screen 500 includes one or more buffer layers disposed between adjacent CLC layers in optical stack 502, such as between CLC layers 500B and 500C.
One or more of the buffer layers and/or CLC layers in screen 500 can be optically diffusive by, for example, dispersing small particles in a host material where the index of refraction of the particles is different than the index of refraction of the host material. Furthermore, one or more of the buffer layers may function as a color filter to, for example, improve color purity of an image displayed by the screen.
Screen 500 further includes one or more diffuser layers such as diffuser layer 540. Diffuser layer 540 can assist in scattering light into a viewing space 570 which may include one or more viewers such as a viewer 595. Diffuser layer 540 can include structures (not shown in
Screen 500 further includes a light absorbing layer 550 for increasing screen contrast by absorbing non-imaging or otherwise undesirable light such as ambient light.
Screen 500 may further include other layers not explicitly shown in
Plot 600 has a vertical transmittance axis 601, a vertical reflectance axis 602, and a horizontal wavelength axis 603. Reflectance curves 610, 620, and 630 illustrate reflectance of the cholesteric liquid crystal layers in the screen. Each reflectance curve is characterized by a reflectance peak and a reflectance full width at half maximum. In particular, curves 610, 620, and 630 have reflectance peaks 611 (located at wavelength λc), 621 (located at wavelength λb), and 631 (located at wavelength λa), where the peaks are located at different wavelengths. Curves 610, 620, and 630 further have reflectance full width at half maxima (FWHM) 612, 622, and 632, respectively.
In the exemplary embodiment of
Plot 600 also shows retardance profile 640 of a retarder layer employed in the screen. Profile 640 has a plurality of half-wave peaks such as a zeroth order half-wave peak 655, a 1st order half-wave peak 660, a 2nd order half-wave peak 670, and a 3rd order half-wave peak 680. In the exemplary retardance profile 640, each half-wave peak has a height Tmax and a half-peak height Tmax/2. In general, the height of a half-wave peak in retardance profile 640 may be different for different peaks, for example, due to wavelength dependent absorption losses and/or measurement errors. Furthermore, in general, Rmax may be less than, equal to, or greater than Tmax. In general, the height of a reflectance peak of a CLC layer can be less than, equal to, or greater than the height of a half-wave peak of a retarder layer.
Retardance profile 640 has an extended half-wave peak area 650, meaning that a retarder layer having retardance profile 640 is substantially a half-wave retarder in extended peak area 650. Area 650 includes reflectance peaks 611, 621, and 631. Accordingly, a retarder layer having a retardance profile similar to profile 640 is substantially a half-wave retarder at reflectance peaks 611, 621, and 631.
Retardance profile 640 further has a retardance full width at half maximum 645 corresponding to peak 655 that encloses the reflectance full width at half maxima 612, 622, and 632.
In plot 600, the reflectance peaks of the cholesteric liquid crystal layers are located substantially at the zeroth order half-wave retardance peak of the retardance profile. In general, the reflectance peak of the CLC layers can be located at a higher order half-wave peak of the retardance profile.
According to one embodiment of the invention, retarder layers in a front projection screen may or may not have the same retardance profile. For example, two or more retarder layers in a front projection screen can have the same retardance profile that is, for example, similar to retardance profile 640. As another example, the retarder layers in a front projection screen can have different retardance profiles, although each retardance profile may have a half-wave retardance peak at the reflectance peak of one or more cholesteric liquid crystal layers in the screen.
In plot 700, reflectance peaks 611 and 621 of respective reflectance curves 610 and 620 are located substantially at the zeroth order half-wave peak 655 of the retardance profile and reflectance peak 631 of reflectance curve 630 is located at a higher order, such as a 1st order, half-wave peak of the retardance profile. According to one embodiment of the invention, retardance FWHM 645 encloses the reflectance full width at half maxima 612 and 622 of respective reflectance curves 610 and 620. Furthermore, retardance FWHM 661 of 1st order half-wave peak 660 encloses the reflectance full width at half maxima 632 of reflectance curve 630.
In plot 800, reflectance peaks of the CLC layers are located at higher order half-wave peaks of the retardance profiles of one or more retarder layers in the front projection screen. In the exemplary embodiment shown in
In general, the reflectance FWHM 612, 622, and 632, and retardance FWHM 661, 662, and 663 are so designed that the screen reflects one or more desired ranges of wavelengths that may, for example, exclude some of the wavelengths projected by a projector onto the screen. The exclusion my be desirable to improve, for example, the overall color of a projected image. According to one embodiment of the invention, the retardance FWHM of a half-wave peak located at a reflectance peak of a CLC layer encloses the reflectance full width at half maximum of the reflectance peak. For example, in plot 800, retardance FWHM 661 of 1st order half-wave peak 660 encloses the reflectance full width at half maximum 612 of reflectance curve 610, retardance FWHM 662 of 2nd order half-wave peak 670 encloses the reflectance full width at half maximum 622 of reflectance curve 620, and retardance FWHM 663 of 3rd order half-wave peak 680 encloses the reflectance full width at half maximum 632 of reflectance curve 630.
In another embodiment of the invention, the reflectance full width at half maximum 612 of reflectance curve 610 encloses retardance FWHM 661 of 1st order half-wave peak 660, the reflectance full width at half maximum 622 of reflectance curve 620 encloses retardance FWHM 662 of 2nd order half-wave peak 670, and the reflectance full width at half maximum 632 of reflectance curve 630 encloses retardance FWHM 663 of 3rd order half-wave peak 680.
In general, the reflectance peaks can occur at different order half-wave peaks. In one embodiment of the invention, a first reflectance peak occurs at a k1th order half-wave peak, a second reflectance peak occurs at a k2th order half-wave peak where k2 is different than k1, and a third reflectance peak occurs at a k3th order half-wave peak where k3 is different than k1 and k2.
In general, reflectance curves 610, 620, and 630 can be located in one or more desired regions of the electromagnetic spectrum. In one embodiment of the invention, the reflectance curves are located in the visible region of the spectrum.
In plot 900, retardance profile 640 has a plurality of half-wave retardance peaks enclosed within the reflectance full width at half maximum of a CLC layer. For example, half-wave retardance peaks 673, 674, and 675 of retardance profile 640 are enclosed within reflectance full width at half maximum 632 of reflectance curve 630. According to one embodiment of the invention, the reflectance FWHM of each CLC layer in the screen encloses a plurality of retardance half-wave peaks of one or more retarder layers in the screen.
In one embodiment of the invention, the reflectance peak of a first CLC layer may be located at or near a low order half-wave retardance peak of retardance profile 640 such that the reflectance full width at half maximum of the first CLC layer encloses a single half-wave retardance peak (e.g., reflectance curve 620A), and the reflectance peak of a second CLC layer may be located at or near a high order half-wave retardance peak of retardance profile 640 such that the reflectance full width at half maximum of the second CLC layer encloses a plurality of half-wave retardance peaks (e.g., reflectance curve 630).
Reflectance curves 610, 620, and 630 can, for example, correspond to CLC layers 300A, 300B, and 300C and/or CLC layers 310A, 310B, and 310C of screen 300 shown in
Retardance profile 640 can, for example, correspond to one or more of retarder layers 320A, 320B, 320C, and 320X in screen 300. As another example, profile 640 can correspond to retarder layer 420 in screen 400. As yet another example, profile 640 can correspond to one or more of retarder layers 520A and 520B in screen 500.
In one embodiment of the invention, in screen 300, CLC layers 300A and 310A have reflectance curves similar to curve 610, CLC layers 300B and 310B have reflectance curves similar to curve 620, and CLC layers 300C and 310C have reflectance curves similar to curve 630. Furthermore, retarder layers 320A, 320B, 320C, and 320X have retardance profiles similar to profile 640.
In another embodiment of the invention, in screen 400, CLC layers 400A and 410A have reflectance curves similar to curve 610, CLC layers 400B and 410B have reflectance curves similar to curve 620, and CLC layers 400C and 410C have reflectance curves similar to curve 630. Furthermore, retarder layer 420 has a retardance profile similar to profile 640.
In another embodiment of the invention, in screen 500, CLC layers 500A and 510A have reflectance curves similar to curve 610, CLC layers 500B and 510B have reflectance curves similar to curve 620, and CLC layers 500C and 510C have reflectance curves similar to curve 630. Furthermore, retarder layers 520A and 520B have retardance profiles similar to profile 640.
Projector 1010 has light sources 1001, 1002, and 1003 where the emission spectrum of each light source may include a range of wavelengths in the visible region of the electromagnetic spectrum. In one embodiment of the invention, light source 1001 emits light at a blue primary color, light source 1002 emits light at a green primary color, and light source 1003 emits light at a red primary color.
Screen 1020 has a plurality of cholesteric liquid crystal layers, one or more retarder layers, and a light absorbing layer. The retardance profile of the retarder layers and the reflectance curves of the cholesteric liquid crystal layers are so located along the electromagnetic spectrum that screen 1020 substantially reflects all light projected by projector 1010 and substantially absorbs all light that lies outside the FWHM of the CLC reflectance curves.
Screen 1020 scatters light that is incident on the screen from projector 1010 into a viewing space 1040 that can include one or more viewers such as viewers 1095 and 1096. Furthermore, screen 1020 absorbs a substantial fraction of ambient light 1030 that lies outside the reflectance curves of the cholesteric liquid crystal layers in the screen resulting in a displayed image having high contrast.
In one embodiment of the invention, the emission spectrum of light projected by projector 1010 substantially matches the reflectance curves of the CLC layers in screen 1020 as shown schematically in
In the exemplary embodiment shown in
MOF 1510 includes alternating layers 1530 and 1540 where the alternating layers have different indices of refraction. MOF 1510 reflects light by optical interference. The term optical interference, as used herein, means that an incoherent analysis is generally not adequate to sufficiently predict or describe all the reflective properties of a layer that reflects light by optical interference in a desired region of the spectrum. In one embodiment of the invention each of alternating layers 1530 and 1540 reflects light by optical interference. Multilayer optical films have been discussed in, for example, U.S. Pat. Nos. 3,610,729; 4,446,305; 4,540,623; 5,448,404; and 5,882,774.
Colored reflective layer 1610 can be any reflective layer that reflects light in one wavelength region and absorbs light in other regions. For example, colored reflective layer 1610 can be made by dispersing a colorant such as a pigment and/or a dye in a binder. The light absorbing properties of colored reflective layer 1610 eliminates or reduces the need for a separate light absorbing layer in screen 1600. Colored reflective layer 1610 is preferably disposed in back side 390 of screen 1600.
In one embodiment of the invention, ΔλA1 is a wavelength range that includes a first primary color such a blue color, ΔλB1 is a wavelength range that includes a second primary color such a green color, and ΔλC1 is a wavelength range that includes a third primary color such a red color.
Advantages and embodiments of the present invention are further illustrated by the following example. The particular materials, amounts and dimensions recited in this example, as well as other conditions and details, should not be construed to unduly limit the present invention. A front projection screen similar to screen 300 of
Optical stack A1 was prepared by coating both sides of a Scotchpak film with a solution containing a nematic liquid crystalline monomer LC756 commercially available from BASF AG, Ludwigshafen, Germany, a chiral dopant LC242 also commercially available from BASF AG, and a photoinitiator (Irgacure 819 commercially available from Ciba Specialty Chemicals, Tarrytown, N.Y.) where the weight ratio of LC242 to LC756 was approximately 23.6 resulting in a reflectance curve located in the red region of the spectrum with a reflectance peak at about 654 nm. The coated assembly was cured and cross-linked by exposure to UV radiation. Optical stacks B1 and C1 were similarly prepared except that in the case of optical stack B1, the weight ratio was approximately 20.8 resulting in a reflectance curve located in the green region of the spectrum with a reflectance peak at about 575 nm, and in the case of optical stack C1, the weight ratio was approximately 16.9 resulting in a reflectance curve located in the blue region of the spectrum with a reflectance peak at about 479 nm.
Next, the three optical stacks were arranged similar to the arrangement shown in
All patents, patent applications, and other publications cited above are incorporated by reference into this document as if reproduced in full. While specific examples of the invention are described in detail above to facilitate explanation of various aspects of the invention, it should be understood that the intention is not to limit the invention to the specifics of the examples. Rather, the intention is to cover all modifications, embodiments, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
