This invention relates to the field of light filters, and more particularly to light filters that exhibit asymmetrical dispersion of light perpendicular to direction of propagation.
Rear projection screens and light diffusers include light filters which provide an optically dispersing medium for transmitting light from an image source on one side of the screen to a viewer on the opposite side of the screen. A basic refractive light filter has been described in U.S. Pat. No. 2,378,252, which includes a refracting lens system as its principal component. The refracting lens system comprises an array of spherical transparent beads embedded in an opaque binder layer and mounted on a transparent support material. Certain known light filters orient the bead layer toward the image source and the transparent support material toward the viewers. (See, for example, U.S. Pat. No. 5,563,738).
The opaque binder layer affixes the beads to the support material, reduces the reflectivity of the filter, and reduces the amount of light transmitted through the interstices between the beads of the lens system. Light from an image is refracted by the beads and dispersed to the viewer through a transmission area of the beads. This transmission area includes an aperture about the point of contact between the bead and support material and the area surrounding this point where the opaque binder layer is too thin to absorb the refracted light.
Rear projection screens and light diffusers are characterized by their ambient light rejection, resolution, gain, and contrast as properties which are determined by the structure and composition of the component materials. For example, the gain which is a measure of the intensity of transmitted light as a function of the viewing angle, is determined primarily by the index of refraction of the spherical beads and the surrounding medium. Similarly, the ambient light rejection and contrast of the light filter are determined largely by the optical absorption of the binder layer. The resolution of the screen is determined by the size of the beads used and how they pack together in the lens system.
However, the interdependence of certain optical properties and their dependence on the properties of component materials, limit optimization of the optical properties of basic refractive light filters. For example, if the optical absorption of the binder layer is increased to enhance the ambient light rejection of the viewing surface, transmission of refracted image light through the binder layer in the transmission area of the bead will be reduced. In addition, the range of indices of refraction of available materials also limits the performance of such filters. Such interdependencies and material limitations hamper the performance of basic refractive filters.
A multi-layer light filter in accordance with the present invention includes a single layer of glass or resin beads supported in an opaque layer and an additional contiguous light-dispersing support or backing layer that exhibits asymmetrical or anisotropic light-dispersing properties along axes perpendicular to the direction of propagation. “Anisotropic” and “asymmetrical” are used interchangeably to have the same meaning for purposes of this disclosure. This structure of optical components enhances the dispersion or scattering of light along one axis, for example the horizontal axis, and without changing the dispersion or scattering of light along an orthogonal axis, for example, the vertical axis. Such a structure promotes wider viewing angles as viewed along one (i.e., the horizontal) axis from the light output side of the support layer. Such structure also leaves unchanged viewing angles, as viewed along the other (i.e., vertical) axis from the light output side of the support layer.
In accordance with another embodiment of the present invention, the gain of the structure that may be altered by the addition of a layer of transparent resin on the incident light side of the structure to cover all or part of the portion of the beads protruding from the opaque layer in substantial surface conformity with the contour of the protruding beads.
The transparent resin layer provides additional gain control by increasing the incident area of light transmitted through a bead and by replacing the air/bead interface with air/resin and resin/bead interfaces at which both the refraction and reflection of image light can be separately adjusted. Selecting the relative indices of refraction, contour, and the thickness of the transparent resin forming the conformal layer as well as the index of refraction of the beads controls refraction and reflection at the resin/bead interface. A thin layer of transparent resin is effective to alter the shape of the protruding surfaces of the beads. Also, a thin transparent layer may be disposed between the contact points of the beads with the support layer and the opaque binder layer to alter the exit apertures of the beads for enhancing transmission therethrough of refracted light.
Additionally, the support layer may exhibit asymmetric dispersion of light by different amounts and angles in one orientation than in an orthogonal orientation. This facilitates expansion of the viewing angle, for example, along the horizontal axis compared with narrower viewing angle along the vertical axis. Such support layer may form the support or backing layer contiguous the single layer of beads, or may supplement a transparent support layer in a more rigid structure to provide substantially the same asymmetrical scattering oflight passing through the light filter assembly.
FIG. 10 and
Referring now to
Light 38 that is approximately collimated from an effectively distant image source (not shown) is incident on filter 10 at back surfaces 36 of beads 14 and back surface 19 of opaque binder layer 16 between the beads. These surfaces define an incident or image side of light filter 10. Outer surface 18 of the support layer 12 defines a front or viewing side of light filter 10 through which viewers observer the transmitted image light. Thus, light incident on beads 14 is refracted, transmitted through the beads 14 and the associated transmission apertures 34, and is asymmetrically dispersed to viewers through the support layer 12. Light 38 incident on the back surface 19 of the opaque binder layer 16 between beads 14 is absorbed to reduce transmission of this light through the filter assembly 10. Therefore. “opaque binder layer.” “optical absorption binder layer,” “light absorbing binder layer.” “absorbing binder,” and “absorbing layer” are used interchangeably to refer to layer 16 in this disclosure.
Referring now to
Refracted rays 22, 24, 26, 28 diverge after passing through the transmission aperture 34 of bead 14 and disperse through the support layer 12 over a larger range of horizontal viewing angles and a narrower range of vertical viewing angles. The collective action of beads 14 and support layer 12 in dispersing transmitted light intensity at various horizontal and vertical viewing angles relative to a normal axis 11 of filter output surface 18 results in the gain profile of the filter. High gain light filters generally transmit image light in a narrow angular distribution about a normal viewing axis, whereas low gain filters generally transmit image light in broad distributions about the normal viewing axis. The optimum gain for such light filters depends upon its intended use, and is selected in part by choosing the optical material for beads 14 having an appropriate index of refraction, as later discussed herein.
Referring to the graph of
In addition to gain, light filters 10 are characterized by their resolution, contrast, and ambient light rejection. For these filters, it is generally desirable to have both high resolution and high ambient light rejection. The resolution of light filter 10 is determined by the size of beads 14, since the packing density of beads 14 on support layer 12 determines the density of transmission apertures 34 on this surface. This property can generally be maximized by constructing filters 10 using the smallest diameter beads 14 available, typically of approximately 25-100 microns in diameter. The minimum practical size of beads 14 selected may be dictated by variations in the quality and properties of available beads 14.
Ambient light rejection measures how well ambient light incident on the viewing surface of a light filter is absorbed or transmitted relative to the amount redispersed back toward the viewer. This property depends primarily on the reflectivity of the front surface of the support layer 18, the optical absorption of binder layer 16 and the index of refraction of beads 14. Ambient light reflected into viewers' eyes from filter 10 can significantly impair the quality of an image by reducing the contrast.
In the filter assembly 10 illustrated in
Referring now to
Referring now to the graph of
Referring now to
The conformal layer 128 defines a plurality of lenses 131 for controlling dispersion of incident light and increasing the transmittance of the light filter 120. Each such lens 131 is disposed on the protruding surface 36 of a bead 14 and has a substantially spherical or curved incident surface 129 with a radius of curvature about 1.1 to 2 times the radius of the bead 14 or an average thickness around the beads of about 0.1 to 1 times the radius of the beads 14.
The conformal layer 128 presents increased incident surface to incoming light 220 and functions as a preliminary stage of convergent refraction of light 220 from the image source (not shown) into the beads 14. This allows a greater portion of incident light to enter into the beads 14, and such light 220 so converged is incident on the protruding surfaces 36 of the beads 14 above the absorbing layer 16 at angles that allow a greater percentage of the light 220 to enter the beads 14 and propagate into the transmission apertures 34 of the beads 14. Light emanating from the transmission apertures 34 is then asymmetrically or anisotropically dispersed by the support layer 12 for viewing through different horizontal and vertical viewing angles relative to the axis 11 that is normal to the viewing surface 18. Thus, a greater percentage of the light 220 striking the back surfaces 36 of the beads 14 is transmitted through the filter surface 18 than is typically feasible with conventional single-layer light filters, which have a typical transmittance of about 35 percent.
The conformal layer 128 also reduces the index of refraction mis-match (nbeads/nmedium) at the rear surface of the screen. Reducing this index mis-match reduces reflection of the light 220 off the surfaces 36 of the beads 14, and increases the transmittance of the light filter 120. Typical index of refraction of the bead material is about 1.4 to 1.9.
The gain of light filter 120 can further be controlled by the degree of curvature of the incident surface 129 of the conformal layer 128. These properties of the present invention beneficially prevent excessive loss of image light intensity caused by reflection, as in conventional single-layer light filters. Adjustment of the dispersion of light through various angles Φ relative to the axis 11 that is normal to the viewing surface 18 of the support layer 12 in light filter 120 can also be achieved by appropriately selecting the index of refraction of the light-transmissive material of the conformal layer 128. Heat and pressure can be applied to selectively shape the incident surface 129 of the conformal layer 128 for improved operation of the light filter 120. For example, the transmittance of the light filter 120 can be increased by reducing the radius of curvature of the incident surface 129 of this layer 128, as illustrated and described in greater detail later herein with reference to FIG. 8.
Referring to the graph of
Referring now to
The light filter 122 also includes a conformal layer 128 of light transmissive material disposed on the incident surfaces 36 of the beads 14 and surface 19 of an absorbing binder layer 16. The additional conformal layer 128 defines a substantially spherical or parabolic lens 131 behind each bead 14, with local points or centers of curvature 342 disposed forward in the direction toward the source of incident light relative to the centers of curvature 340 of the beads 14. The layer 128 thus has a non-uniform thickness as measured normally to the spherical protruding surfaces 36 of the beads 14.
The conformal layer 128 provides a preliminary stage of convergent refraction of the incident light 320, 322 into the beads 14. Further, it is believed that displacing the centers of curvature 342 or the focal points of the incident surface 129 of layer 128 in the direction toward the source of incident light relative to the centers of curvature 340 of the beads 14 increases convergence of such light 320, 322 into the beads 14, and converges such light into the beads 14 nearer to the ideal angles for refraction of such light 320, 322 through the transmission apertures 34. This filter assembly exhibits transmittance of up to about 60 percent.
The support layer 12 diffuses light emanating through transmission apertures 34 through different vertical and horizontal viewing angles relative to axis 30 normal to the viewing surface 18, as previously described with reference to FIG. 3. Alternatively, the support layer 12 may comprise a thin film of such anisotropical dispersing material, as previously described with reference to
The index of refraction of the beads 14 is preferably selected to be from 1× to 1.3×index of refraction of the conformal layer 128 for increasing transmission of image light into the beads 14. Suitable materials for the conformal layer 128 include polymethylmethacrylate and thermoplastic polyurethane (TPU), and similar clear thermoplastic materials. For example, a conformal layer 128 with an index of refraction of about 1.5 can be fabricated for either of these two materials, and the beads 14 can be fabricated from glass or resinous material selected with an index of refraction in a range between about 1.5 and 1.94. The conformal layer 128 beneficially reduces the difference, or mis-match in indices of refraction encountered by light 320, 322 at the interface with the incident surface 36 of the beads 14. This increases the transmittance of the filter. Gain control can also be provided, by controlling the thickness and/or selectively shaping the incident surface 129 of the conformal layer 128 in the manner described above. In an alternative embodiment of the present invention, a layer of anisotropic or asymmetrical light diffusing material of the type previously described herein with reference to layer 12 may be use to asymmetrically disperse the incident light over a greater angle along the horizontal axis than along the vertical axis.
One process of the present invention for making light filter 122 of the embodiment illustrated in
In another embodiment of the present invention, the asymmetrical gain of the filter may be enhanced along one axis relative to another orthogonal axis using a structure as partially illustrated in FIG. 9. Specifically, the sectional view of the filter illustrated in this figure (i.e., as a top sectional view) shows a layer 399 of prismatic ‘lenses’ 400 having planar or plateau faces 402 and faceted or angular sloped faces 404, 406 in iterative, contiguous orientations along, for example, the horizontal axis of the filter. In this embodiment, the layer 399 of prismatic ‘lenses’ is disposed to receive incident collimated light rays A, B from a light source (not shown). Rays A impinging upon the plateau faces 402 are transmitted through the layer without deviation, and the dispersion of light via the successive segments of the filter including a beaded layer proceeds as previously described. However, collimated light rays B impinging upon the sloped faces 404, 406 are deviated from the incident orientation to provide additional dispersion through the successive segments of the filter including a beaded layer as previously described, with resultant wider viewing angle θ2 along the horizontal axis. The horizontal angle may be adjusted by changing the size of the plateau faces 402 and the angles of the sloping faces 404, 406. It should be noted that enhanced viewing angle, for example, along the horizontal axis may be so enhanced with the prismatic layer 399 disposed before or after a beaded segment of the filter, and with the prismatic surfaces 402, 404, 406 facing in either direction relative to the axis of incident light. Also, the spacing shown between the prismatic layer 399 and beaded segment of filter on support layer 12 is illustrative only, and such spacing may be zero for a contiguous, layered structure.
Thus, a flat-surface filter structure may be achieved that is conducive to receiving anti-reflective coatings, and the like, using a prismatic layer 399 at the incident or input side of the filter with the prismatic surfaces oriented inwardly. A support layer of the transparent material may be disposed at the output side of the filter, with beaded segments according to previously-described embodiments interposed between such input and output surfaces. Alternatively, the prismatic layer 399 may also be disposed to receive light ou tput from a beaded segment as previously described, with the sloping faces oriented toward the direction of light output or toward the incident light.
Variations of the prismatic layer 399 in accordance with alternative embodiments of the present invention are illustrated in the top sectional views of
The various configurations of prismatic lenses, for example, as illustrated in
Therefore, asymmetrical viewing angles may be established using filter structures according to the present invention which promote a larger viewing angle along one axis (e.g., the horizontal axis) in comparison with the viewing angle along an orthogonal (e.g. vertical) viewing axis.
Number | Name | Date | Kind |
---|---|---|---|
2378252 | Staehle et al. | Jun 1945 | A |
5563738 | Vance | Oct 1996 | A |
5781344 | Vance | Jul 1998 | A |
5932342 | Zeira et al. | Aug 1999 | A |
6076933 | DiLoreto et al. | Jun 2000 | A |
6310722 | Baek | Oct 2001 | B1 |
6417966 | Moshrefzadeh et al. | Jul 2002 | B1 |
6468378 | Hannington | Oct 2002 | B1 |
6600599 | Hannington | Jul 2003 | B2 |
6695453 | Hannington | Feb 2004 | B2 |
Number | Date | Country |
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03-002855 | Jan 1991 | JP |
03002855 | Jan 1991 | JP |
05-216121 | Aug 1993 | JP |
05216121 | Aug 1993 | JP |