Abstract:
An illumination system having a concave minor for imaging a light source. The illumination system includes a light source, a first concave minor for imaging the light source and a second concave minor for reimaging the imaged light source at another location. The system timber includes a light collecting element passing through the surface of one of the concave mirrors enabling light removal without reimaging the light source outside the radii of curvature of the concave mirrors.

Description:
This is a continuation of application Ser. No. 07/901,885 filed Jun. 22, 1992, abandoned. 
    
    
     The present invention is concerned with an illumination system for a light source including a plurality of concave mirrors for reimaging of the light source at a selected location. More particularly, the invention is directed to a light source illumination system having a plurality of concave minors which reimage the light source and includes a light collecting means for removing the reimaged light source from the confines of the concave mirrors. 
     A number of optical applications require the production of a controlled light image which is as bright as possible, while achieving efficient use of the light produced. Typical problems encountered include: (1) the presence of a nonuniform light distribution arising from the filament shape of the light source, (2) collection of the light in an efficient manner, (3) controlled directional output of the collected light without loss of brightness, and (4) performance of the above described functions with compact imaging optics but without introduction of excessive aberrations. 
     OBJECTS OF THE INVENTION 
     It is therefore an object of the invention to provide a novel optical illumination system having a plurality of concave mirrors for controlling the reimaging of a light source for output and use. 
     it is yet another object of the invention to provide an improved optical illumination system having at least two mirrors enclosing a light source and reimaging the light source within the mirror enclosure for controlled output and use. 
     It is a further object of the invention to provide a novel optical illumination system having minors enclosing a light source and an optical collection element entering the mirror enclosure for extracting the light source image for illumination purposes. 
     It is still another object of the invention to provide an improved optical illumination device including a mirror system for reimaging a light source and a tight collection means passing through the mirror system for removing the light from the mirror system for exterior usage. 
     Other objects and advantages of the invention will be apparent from the detailed description and drawings described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an optical illumination system including two spherical concave mirrors and a light pipe; 
     FIG. 2A illustrates an optical illumination system having a plurality of spherical segment mirrors completely enclosing a light source and FIG. 2B shows a top view of FIG. 2A illustrating a plurality of light pipes to remove light for external uses; 
     FIG. 3 illustrates a cross sectional view of a portion of one of the mirrors shown in FIGS. 1 and 2; and 
     FIG. 4 illustrates a two dimensional type of illumination system having at least one concave semi-circular cylindrical mirror and a light sheet for removal of the light source image. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An optical illumination system constructed in accordance with the invention is shown in the figures generally at 10. As shown in FIG. 1, the optical illumination system 10 (hereinafter, the &#34;system 10&#34;) includes a light source 12, such as a filament or arc source, and a mirror system 13 having a first concave mirror 14 and a second concave mirror 16. In the system 10 the first concave minor 14 images the light source 12 at a first selected location to form an image 18. The second concave mirror 16 reimages the image 18 (the imaged source) at a second selected location, such as on face 32 of light pipe 19. The light pipe thus functions to collect the light from the light source 12 and the image 18 and remove the light for use outside the system 10. The image 18 can therefore be extracted by the light pipe 19 passing through the minor 14, or extracted by other such means, and then output to optical means, such as a compound parabolic concentrator 23 which has a reflector mirrored surface 25, for various optical applications. In other embodiments the concentrator 23 can include an elliptically-shaped mirror surface 27 (in phantom in FIG. 2A) and a nonimaging mirror 29 in FIG. 1 in phantom. 
     In the preferred form of the invention the light source 12 is displaced from a first center of curvature 20 and second center of curvature 21 for the first and second concave minors 14 and 16, respectively. These mirrors 14 and 16 operate to position the image 18 for removal from the system 10. However, in order to minimize brightness loss and optimize efficiency, the mirror system 13 exhibits certain spacing relationships between (a) the light source 12 and the first center of curvature 20 and (b) between the image 18 and the second center of curvature 21. Preferably, the light source 12 is displaced a distance D 1  from the center of curvature 20 with D 1  being less than about one-fourth the radius of curvature of the first concave mirror 14. In addition, the image 18 is displaced a distance D 2  from the center of curvature 21 with D 2  being less than about one-fourth the radius of curvature of the second concave mirror 16. Alternatively, one can express this preferred arrangement as requiring the light source 12 to be within the above-stated distance D 1  of the center of curvature 20 and the image 18 is within the above-stated D 2  distance of the center of curvature 21. 
     As shown in FIG. 3, one or more of the mirrors 14 and 16 can also include a front surface 24 and a back surface 26 and an absorbing medium 28 for selectively removing unwanted portions of the light spectrum from the light source 12. In addition, the minor system 13 can include a dielectric layer 30 (the outer boundary is shown in phantom in FIG. 3 ). This dielectric layer 30 allows selective transmission or reflection of parts of the light spectrum from the light source 12. 
     In other forms of the invention the mirror system 13 and the position of the light source 12 can be constructed to enable reimaging of the light source in substantial coincidence with the light source 12 itself. This can be particularly useful for a filamentary source having substantial light level nonuniformities. For example, one can reimage the light source 12 such that intensity lows of the image 18 are matched with intensity highs from the light source 12. This methodology is also useful for optically thin sources in order to improve brightness. 
     The mirror system 13 can include a plurality of mirrors, such as the two mirrors 14 and 16 in FIG. 1 or the spherically segmented mirror 32 in FIG. 2. The system 13 can even be a single mirror having regions of varying curvature (see FIG. 1 with phantom lines 33 forming a continuous surface mirror. The spherical segments 32 in the embodiment of FIG. 2 have the advantage of requiring only a single reflection to form an image 3a from light source 36. Also note planer light source 36 (in phantom in FIG. 2A) for an alternative embodiment. Such a geometry also can ensure collecting virtually all the light emitted from the light source 36. 
     As noted hereinbefore the image 18 in FIG. 1 is removed by the light pipe 19 for various optical uses. The system 10 in FIG. 2 also includes means for collecting the light from the reimaged light source (the image 18). The collecting means is a light pipe 38, which passes through a surface 40 of one of the mirrors. The light pipe 38 thus enables light to be removed for use without reimaging the light source 12 outside the radius of curvature described by the concave mirrors. If such a substantial displacement were used, it would result in loss of brightness due to substantial aberrations. In the most preferred embodiment at least one of the concave mirrors comprises a spherical mirror in order to minimize aberration effects. In order to remove all the light associated with the image 34, one can use a plurality of the light pipes 38 as shown in FIG. 2B. 
     The above described embodiments can also be applied to two dimensional optical illumination systems. In such a system (see FIG. 4) at least one of the concave mirrors 50 and 52 comprises a concave semi-circular cylinder 53, and the light pipe can take the form of a light sheet 54 passing through an opening in one of the concave mirrors 50 and 52. 
     Further advantages and features of the invention will be appreciated by reference to the figures and to the claims set forth hereinafter. Therefore, while preferred embodiments of the invention have been described, it will be clear to those of ordinary skill in the art that changes and modifications can be made without departing from the invention in its broader aspects.