Title of Invention: Image projection system with light reflector
Abstract: In an image projection system, light emitted by a point source is reflected off the concave surface of a reflector to a fly-eye-lens system where the incident light is distributed to uniformly irradiate multiple optical elements. Each optical element splits incident light into a first polarized component and a second orthogonally polarized component parallel to the first component and converting the second component to polarization identical to the first component. Light from the enhancer is imagewise-modulated by an image formed in a display panel and projected onto a screen. The reflector is configured so that any point on the reflector is defined by an equation containing a term of parabola and at least one term of a series of aspheric coefficients of order of even number which is equal to or greater than two.
Detailed Description: Part PAC: DETAILED DESCRIPTION
Part PAR: In FIG. 2, there is shown an image projection system embodying the present invention. The system includes a light reflector 1 and a point-source lamp 2 located at the focal point of the light reflector 1. Along the optical axis of the light reflector 1 are arranged a fly-eye-lens system comprising a pair of first and second plates 3 and 4, an optical enhancer 5, and a condenser lens 6.
Part PAR_2: Each of the fly-eye-lens plates 3 and 4 has a matrix array of cells of microscopic lenses with the center of the array being aligned with the optical axis of the light reflector 1. In order to uniformly distribute flux densities of light from the light reflector 1, the first and second plates 3 and 4 are spaced at such a distance apart so that rays leaving each cell 30 of the first plate 3 are focused to a corresponding cell 31 of the second plate 4 as shown in detail in FIG. 3. Optical enhancer 5 is located behind the second fly-eye-lens plate 4 to be uniformly illuminated by incident light.
Part PAR_3: As shown in detail in FIG. 4, the light enhancer 5 is composed of an array of horizontal light shields 40 where rays from the second flyeye-lens plate 4 are masked and the unmasked portions of the light are allowed to enter an array of polarization beam splitters 41 where they are split into a first component 42 and a second component 43, the first component 42 being the useful component and the second component 43 being the otherwise useless component. Light enhancer 5 is further provided with an array of reflectors 44 and associated phase shifters 45. The second component 43 of light from the corresponding beam splitter 41 is reflected off the reflector 44 to the associated phase shifter 45 which causes the polarization plane of the incident light to be aligned to that of the first component 42 and both components are emitted in parallel. Light emitted from the light enhancer 5 is focused by the condenser lens 6 onto a liquid crystal display panel (see FIG. 3).
Part PAR_4: A dichroic mirror 7 is located behind the condenser lens 6 to split the incident light into a first primary color component and the other two color components. The first primary color component is directed to a mirror 8 where it is reflected off to a first LCD panel 10 via a condenser lens 9. The other primary color components are reflected off the dichroic mirror 7 to a second dichroic mirror 11, where they are split so that the second primary color component is directed to a second LCD panel 13 via a condenser lens 12. The third primary color component passes through the dichroic mirror 11 and its optical path is deflected by mirrors 14 and 15 to a third LCD panel 17 via a condenser lens 16. The primary color components incident on each of the LCD panels 10, 13 and 17 are imagewise-modulated by respective video images and combined into a single color image by a dichroic prism 18 and projected by a projection lens system 21 onto a screen, not shown, located at a distance which is conjugate with respect to each of the LCD panels. Condenser lens 6 is used to form a sharp focus on each of the LCD panels. Release lenses 19 and 20 are provided for adjusting the focal point of the third primary component on the LCD panel 17.
Part PAR_5: According to the present invention, the light reflector 1 has a concave surface and any point on the concave surface is defined by the following equation: ##EQU1##
Part PA1: where, x is a distance from the vertex of the parabolic reflector along its optical axis, y is a distance from the optical axis on a plane normal to the optical axis x, R is the radius of curvature, K is an aspheric constant, A.sub.2i is an aspheric coefficient of order 2i, and i and N are an integer equal to or greater than 1 (for further information see Japanese-laguage publications titled "Introduction to Optics", Toshio Kishikawa, Oputoronikus-sha, and "Guides to the Design of Lenses", Eiichi Takano, Shashin Kougaku Shuppan). Note that the aspheric constant K is smaller than -1 for hyperbolic surfaces, equal to -1 for parabolic surfaces, larger than -1 and smaller than 0 for elliptical surfaces, and equal to 0 for spherical surfaces.
Part PAR_6: In the case of a normal parabolic surface, the curvature K is equal to -1 and the high-order aspheric coefficients A.sub.2i are all zero, giving the relation x=(1/2R)y.sup.2. Whereas, in the present invention, K=-1, A.sub.4 =1.5.times.10.sup.-6, A.sub.6 =1.5.times.10.sup.-9, A.sub.8 =1.5.times.10.sup.-16, and A.sub.10 =4.0.times.10.sup.-18. As a result, the light reflector 1 has a lower rate of increase in section toward its aperture as indicated by a thick-line curve of FIG. 5 than the rate of similar increase in the case of a pure parabolic reflector indicated by the dotted-line curve. In other words, the light reflector 1 takes the shape of a paraboloid of revolution (with K=-1) and a spheroid of revolution. he length of the reflector 1 along its optical axis is thus greater than that of a paraboloidal reflector. Therefore, a larger amount of luminous flux can be exploited from the optical energy emitted from the point source 2 for imagewise-modulation than is possible with parabolic reflectors.
Part PAR_7: As shown in FIG. 6, the reflector 1 produces a near-parallel beam of light in the outer portion of the reflector near its edge as indicated by a bundle of rays A and a parallel beam of light in the inner portion of the reflector near its optical axis as indicated by a bundle of rays B. Therefore, the reflector 1 suffers from smaller aberrations than spheroidal reflectors, and hence the loss of luminous flux at the fly-eye-lens plates 3 and 4 and the light enhancer 5 is decreased.
Part PAR_8: It is seen from the foregoing that high utilization efficiency of available optical energy is achieved by the combined effects of increased luminous flux and decreased aberrations.


{'bibliographic_information': "{'Patent Number': '063025442', 'Series Code': '9', 'Application Number': '5228220', 'Application Type': '1', 'Art unit': '281', 'Application Filing Date': '20000310', 'Title of Invention': 'Image projection system with light reflector', 'Issue Date': '20011016', 'Number of Claims': '3', 'Exemplary Claim Number(s)': '1', 'Primary Examiner': 'Dowling; William', 'Number of Drawing Sheets': '5', 'Number of figures': '7'}", 'source_file': './grant/2001/pftaps20011016_wk42.txt', 'source_data': 'USPTO-Grant'}