Optical: systems and elements – Mirror – Plural mirrors or reflecting surfaces
Reexamination Certificate
1995-05-15
2001-12-25
Dzierzynski, Paul M. (Department: 2507)
Optical: systems and elements
Mirror
Plural mirrors or reflecting surfaces
C359S850000, C359S856000, C359S364000, C359S365000, C359S869000, C359S726000, C359S727000, C362S297000, C362S298000, C362S302000
Reexamination Certificate
active
06332688
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to optical apparatus for uniformizing light from a light source and delivering the light to a light valve. In particular, the inventive apparatus makes use of an optical system, including a light transmitting tunnel, to receive non-homogeneous light from an extended light source and deliver uniform illumination onto a light valve.
Recently, considerable interest has arisen in applying liquid crystal display technology as well as the technology of deformable mirror devices to implementation of projection systems. Such applications usually require a uniform illumination of the light valve, viz., the liquid crystal display or the deformable mirror device, in order to provide a uniform, stable projection image. In most applications, the projection system design specification includes space limitations, viz., the distance between the light source and the light valve. The light valve and its illumination system must fit into a restricted space. For light valves which are sensitive to infrared or ultraviolet light, such as the liquid crystal or deformable mirror device, the space restriction leads to a requirement for efficient removal ot these wavelengths from the light beam.
Thus, a need exists for a compact light valve illumination system which provides for uniformity of light across the active area of the valve. Furthermore, there is a need for a light valve illumination system which makes efficient use of light power and which provides a means for directing infrared and ultraviolet light away from the valve. In addition, low cost and light weight are required for the projection system to be commercially competitive.
A light transmitting tunnel is described in U.S. Pat. No. 3,170,980, Pritchard. However, in this patent the tunnel specifications are rigorous to an extent that the tunnel could not readily be incorporated into a light valve illumination system. “. . . manufacturers of high precision optical equipment state that the glass used in making the optical tunnel should have no dimension ratios greater than roughly 5:1.” (Col.2, II. 19-22) “This limitation means that the weight of the optical tunnel increases enormously as its length increases.” (Col.2, II. 26-28).
In U.S. Pat. No. 5,059,013, Jain, there is a system described relating to, “. . . method and apparatus for providing a light beam of selected cross section shape and uniform intensity, and which emits self luminously into a selected numerical aperture.” (Col. 1, II. 11-14) However, the system is complicated and expensive in that it makes use of a polygon aperture, a light expanding and trimming sub-system, a laser, a second light source and a number of other components as set forth in the method section. (Col.4, I. 48 to Col.5, I. 32.).
SUMMARY OF THE INVENTION
The present invention meets the need for a simple, low cost light uniformizing or homogenizing transmission system which is cost effective, can efficiently operate using light from sources having a wide variety of sizes and shapes and can function properly within the spatial restrictions usually associated with projection or display systems.
A first aspect of the invention is an apparatus for uniformly illuminating a light valve. Light from a light source is focused into a light tunnel. In one embodiment of the invention the light tunnel is shaped as a right parallelepiped. The focusing means may be one or more lenses or mirrors. For example, the source may be located at one focus of a truncated ellipsoid mirror. An additional mirror, in the shape of an annulus taken from the surface of a sphere, may be positioned adjacent the opening in the truncated ellipsoid. The concave surface of the annulus reflects light back into the ellipsoid mirror, thereby capturing additional light from the source for delivery into the tunnel. The focus of the spherical segment is coincident with the one focus of the ellipsoidal mirror.
A preferred mirror system includes a first annular paraboloid mirror positioned in edge to edge contact with the ellipsoidal mirror, the reflective surface of the paraboloid mirror forming a continuation of the reflective surface of the ellipsoid. The focus of the paraboloid annulus coincides with the one ellipsoidal focus. A second annular paraboloid mirror, having its reflective surface facing the reflective ellipsoid surface and having its focus coincident with the first paraboloid focus, is positioned in edge to edge contact with the first paraboloid mirror annulus. The final mirror element is the spherical element formed as described above and positioned in space apart and symetrical relation to the second annular paraboloid mirror. The annular openings in the paraboloid and spherical mirrors is chosen to permit passage of the cone of light reflected from the ellipsoidal mirror to the target.
The spot of light focused on the plane of the tunnel entrance is generally circular in shape, having a diameter D. The spot may have a more general shape, e.g., an ellipse or an area with irregular boundaries. In these latter cases, D is the maximum linear dimension of the spot in the plane of the tunnel entrance. The maximum angle between a line perpendicular to the tunnel cross section and any light ray of the spot is u. The angle u is the angular aperture of the focusing means. The light tunnel has walls, which form a rectangular cross section, a length L and a smaller inside dimension N. The relationship between N, D, L and u is given by the equation,
L=
k
*N/tan (u),
where k is a constant in the range of about 1.5 to 3. This relationship essentially provides for multiple reflections of the input light from the walls of the tunnel. The multiple reflections serve to uniformize the transmitted beam across the tunnel exit end. A light valve is positioned at the exit end of the tunnel to receive the light emerging from the tunnel. The maximum angle of any light ray exiting the tunnel, where the angle is defined analogously to angle u, is generally less than or equal to angle u.
An embodiment of the invention further comprises an exit optical system, located between the tunnel exit and the light valve, which produces an image of the tunnel exit light on the light valve. The exit optical system may be one or more lenses to magnify or reduce the image of the tunnel exit so that the image essentially coincides with the entire active area of the light valve. The active area of a light valve is the area of the valve which is capable of varying, in a controllable way, the direction or intensity of light incident thereon or passing therethrough. This exit optical system is designed to have an aperture capable of collecting essentially all light exiting the tunnel. That is, the entrance angular aperture of the exit optical system is greater than or equal to u.
The light tunnel may be a hollow tube having an interior surface which reflects light from the source. The tube cross section shape in general matches the shape of the active area of the light valve. For a rectangular light valve, the tunnel is a right parallelepiped having a cross sectional aspect ratio essentially equal to the aspect ratio of the active area of the light valve.
In another aspect of the invention, the tunnel may be filled with a material transparent to light from the source. Total internal reflection of the light within the transparent material occurs because the refractive index of the fill material is higher than the refractive index of the material immediately adjacent the sides of the fill material and because the maximum angle between the fill material wall and essentially any ray in the light traversing the tunnel fill material is less than or equal to the critical angle for total internal reflection. The fill material may be any of a number glass or plastic compositions such as BK 7 glass, available from Bourns Optical Glass, Inc. or acrylic plastic, e.g., V825 from Rohm & HAAS Co., Inc.
In yet another aspect of the invention, the walls of the tunnel are uniformly tapered so that the cross section changes uniformly from entr
Chervenak William J.
Corning Incorporated
Dzierzynski Paul M.
Sikd-er Mohammad Y.
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