Background of the Invention The objective for systems that collect, condense, and couple light into a standard waveguide, such as a single fiber, a fiber bundle, or a homogenizer, is to maximize the brightness of the light at the target (i. e., the input end of the waveguide). Prior art systems using on-axis reflectors and employing spherical, ellipsoidal, and parabolic reflectors have the advantage of being circularly symmetric. On the other hand, such reflectors intrinsically degrade the brightness of the light source due to the variation of the magnification of light emitted from the source at different angles and impinging on different portions of the reflective surface. Off-axis systems which are not circularly symmetric, overcome the variations of magnification to a large extent and also employ spherical, ellipsoidal, and parabolic reflectors.

SUMMARY OF THE INVENTION The invention includes a device for collecting radiation emitted from a source of electromagnetic radiation and condensing the collected radiation into a target. The device comprises a collecting reflector having a concave reflective surface and an opening formed therethrough and a focusing reflector having a concave reflective surface and an opening formed therethrough. The collecting and focusing reflectors are positioned and oriented with their respective concave reflective surfaces in opposed, facing relation.

The focusing reflector is positioned with respect to the collecting reflector so that a source of electromagnetic radiation positioned near the opening formed in the focusing reflector will reflect at least a portion of its electromagnetic radiation through the opening toward the concave reflective surface of the collecting reflector. The collecting reflector

is positioned with respect to the focusing reflector so that electromagnetic radiation reflected by the concave reflective surface of the focusing reflector is transmitted through the opening formed through the collecting reflector toward a target positioned near the opening formed in the collecting reflector.

The collecting reflector reflects at least a portion of the electromagnetic radiation incident thereon toward the concave reflective surface of the focusing reflector, and the focusing reflector reflects at least a portion of the electromagnetic radiation incident on the concave reflective surface thereof through the opening formed in the collecting reflector and toward the target.

The concave reflective surfaces of the collecting and focusing reflectors are preferably parabolic in shape. Moreover, the optical axes of the respective parabolic reflective surfaces are preferably coincident, extending through the openings formed in the collecting and focusing reflectors, and the focal point of the collecting reflector is preferably located proximate the opening formed in the focusing reflector and the focal point of the focusing reflector is preferably located proximate the opening formed in the collecting reflector.

The device may also include a focusing lens disposed between the collecting and focusing reflectors. The focusing lens receives a portion of the electromagnetic radiation transmitted through the opening formed through the focusing reflector and focuses the received electromagnetic radiation through the opening formed in the collecting reflector.

An electromagnetic source, such as a xenon, metal halide, halogen, or mercury arc lamp, may or may not comprise a part of the device. Similarly, a target, e. g., the input portion of a wave guide, such as a single optic fiber, a fiber bundle, or a homogenizer of circular or polygonal shape, may or may not comprise a part of the device Other features and characteristics of the invention will become apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of the specification, and wherein like reference numerals designate corresponding parts in the various figures.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of an ideal paired reflector system for collecting light from a light source and condensing the collected light onto a target with unit magnification.

Figure 2 is a schematic diagram of a practical paired reflector system including an arc lamp, an output fiber, a retro-reflector, and openings formed in the opposed reflectors for receiving light from the arc lamp and passing light to the output fiber.

Figure 3 is a schematic diagram illustrating the loss of radiation energy through openings formed in the opposed reflectors for the light source and the output fiber.

Figure 4 is a schematic diagram illustrating the use of a focusing lens in a paired reflector system for collecting and condensing radiation that would otherwise be lost through openings formed in the reflectors.

Figure 5 is a schematic diagram of a cascaded system where the outputs of multiple sources are added together for increased brightness at the target.

Figs. 6A-6G are schematic views of a plurality of polygonal lightguide (waveguide) targets in cross-sections which may be employed in embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS With reference to the figures, exemplary embodiments of the invention will now be described. These embodiments illustrate principles of the invention and should not be construed as limiting the scope of the invention.

An ideal paired reflector collecting and condensing system is schematically shown in Figure 1 and generally identified by reference number 2. The system 2 includes a first reflector 10 (also known as the collecting reflector) having a concave reflective surface 12 and a second reflector 20 (also known as the condensing, or focusing, reflector) also having a concave reflective surface 22. The concave reflective surfaces 12 and 22 are arranged in an opposed-facing relation and are preferably both parabolic in shape. The reflective surfaces 12 and 22 may be coated with any suitable reflective material, such as aluminum, silver, or a single or multi-layer dielectric coating for use in various color

systems, e. g., a cold mirror for visible light. The first reflector 10 has an optical axis 14 on which lies a focal point 16. Similarly, the second reflector 20 has an optical axis 24 on which lies a focal point 26. The first reflector 10 and the second reflector 20 are preferably arranged so that their respective optical axes 14 and 24 are coincident with one another. In the ideal system 2 shown in Figure 1, a source of electromagnetic radiation 30 is placed at the focal point 16 of the first reflector 10 and a target 32 is placed at the focal point 26 of the second reflector 20. Radiation emitted by the source 30 is reflected by the concave reflective surface 12 of the first reflector 10 as collimated rays of radiation toward the concave reflective surface 22 of the second reflector 20. Thereafter, the radiation is again reflected by the concave reflective surface 22 of the second reflector 20 toward the focal point 26 of the second reflector 20 onto target 32 placed at the focal point 26.

Figure 1 is a schematic view of a cross-section of a paired reflector system. In a preferred embodiment, the first and second reflectors 10 and 20 are each a paraboloid of revolution. Moreover, where the first reflective surface 12 and the second reflective surface 22 are continuous solid surfaces as shown in Figure 1, it is impractical to introduce the source radiation into the system, and, as well, it is impractical to extract the focused radiation from the closed system.

Figure 2 shows a practical implementation of the current invention in which the radiation source is an arc lamp 40 placed at the focal point 16 of the first reflector 10, and the target 32 is the input end of a waveguide, such as an output fiber 44, placed at the focal point 26 of the second reflector 20 along the common optical axes 14 and 24 of the reflectors 10 and 20, respectively. An opening 28 is formed in the second reflector 20 through which radiation emitted by the lamp 40 enters the region between the opposed reflective surfaces 12 and 22 and impinges on the reflective surface 12 of the first reflector 10. Opening 28 is preferably generally centered about the optical axes 14,24, which extend through the opening 28. Radiation in the form of light emitted by the arc lamp 40 is collected by the first reflector 10, is collimated, and is directed toward the second reflector 20. The light is then reflected by the second reflector 20 and condensed, or focused, onto the target 32 placed at the focal point 26 of the second reflector 20. An

opening 18 is formed in the first reflector 10 to permit focused light reflected by the reflective surface 22 of the second reflector 20 to escape the region between the reflective surfaces 12,22 and be incident onto the target 32. Opening 18 is preferably generally centered about the optical axes 14,24 which extend through the opening 18. The first and second reflectors 10,20 are preferably constructed and arranged so that their respective focal points 16,26 are located proximate the corresponding opening formed in the opposite reflector.

A spherical retro-reflector 42 may be placed on the other sides of the arc lamp 40 such that the light emitted from this side of the arc lamp 40 is reflected by the retro- reflector 42 back into the arc lamp itself and subsequently is coupled into the paired reflectors 10,20, thereby increasing the overall brightness of the output of the system.

Suitable lamps include xenon, metal halide, halogen, or mercury arc lamps.

While a single output fiber 44 is shown in Figure 3, the target may comprise the input end of an output fiber bundle, a homogenizer used for outputting high power to low temperature plastic fibers, or a homogenizer for a projection television.

A disadvantage of the practical arrangement of Figure 2 is illustrated in Figure 3.

In particular, because the opening 18 formed in the first reflector 10 may, of necessity, be larger than the focal point 26 of the second reflector 20 and the target 32, a portion of the radiation emitted by the source 30 that is within a loss cone 46 that subtends the opening 18 will be lost. As shown, the opening 18 formed in the first reflector 10 effectively takes away the collecting function of the reflector 10 at this area, and the amount of loss can be significant.

Figure 4 shows the use of a focusing lens 50 disposed between the first and second reflectors 10,20 and covering the loss cone 46 of light that would have been lost due to the openings 28,18 of the parabolic reflectors 20,10, respectively. The lens 50 is preferably configured to produce a 1: 1 magnification of radiation onto the target located at the focal point 26. In the embodiment shown in Figure 4, the target is the input end of a fiber bundle 54. The combination of the reflectors 10,20, and 42 and the focusing lens 50 effectively couples substantially all of the light emitted from the arc lamp 40 onto the target located at the focal point 26. The focusing lens 50 may be a conventional, bi-

convex lens and can be made from any suitable material, such as plastic, glass, or quartz.

Furthermore, an anti-reflective coating may be applied to the external surfaces of the focusing lens 50.

Figure 4 shows the preferred embodiment including an arc lamp 40 positioned at the opening 28 of the second reflector 20, which is preferably parabolic, a retro-reflector 42, a focusing lens 50, and an output fiber bundle 54 having an input end positioned within the opening 18 formed in the first reflector 10, which is also preferably a parabolic reflector. The light emitted from the arc lamp 40 that is within the lost cone 46 that subtends the opening 18 is collected and condensed by the lens 50 and focused onto the input end of the fiber bundle 54 at the focal point 26 with unit magnification. The focusing lens 50 has an optical axis that preferably coincides with the optical axes 14 and 24 of the first and second reflectors 10,20, respectively, and images the focal points 16 and 26 of the first and second reflectors 10 and 20, respectively, in a 1: 1 manner. The remainder of the light emitted by the arc lamp 40 is collected by the first reflector 10 and the retro-reflector 42, is collimated by the first reflector 10 toward the second reflector 20.

The light is then refocused onto the input end of the output fiber bundle 54 by the second reflector 20. The arc lamp 40 and the input end of the output fiber bundle 54 are placed at the focal points 16,26, respectively, of the first and second reflectors 10,20, respectively.

To increase the intensity of light incident upon an optical target, multiple sources and reflectors can be cascaded such that the output of the various sources are combined and focused onto a single target. Such a system is shown in Figure 5. Figure 5 shows three first, or collecting, reflectors 10a, 10b, and 10c having respective focal points 16a, 16b, 16c, and respective openings 18a, 18b, 18c formed therein. Similarly, the system includes three second, or focusing, reflectors 20a, 20b, 20c having respective focal points 26a, 26b, 26c and respective openings 28a, 28b, 28c formed therein. Three sources 30a, 30b, 30c are positioned at the focal points 16a, 16b, 16c, respectively. The retro-reflector 42 may be employed in conjunction with the first source 30a. The second and third sources 30b and 30c are located at the focal points 16b and 16c of the reflectors 10b and l Oc, respectively. These focal points substantially coincide with the focal points 26a and 26b of the reflectors 20a and 20b, respectively. Accordingly, the outputs of the sources

30a, 30b, 30c located on the common optical axes, are combined and ultimately focused by the third reflector 20c onto the target 60, which, in the illustrated embodiment, comprises a homogenizer, having an input end located at the focal point 26c. To minimize losses and further increase intensity at the third focal point 26c, focusing lenses 50a, 50b, 50c are positioned along the common optical axes between the reflectors 10a and 20a, 10b and 20b, and 10c and 20c, respectively.

Figure 5 shows a cascaded arrangement including three paired reflector sets and three focusing lenses. A cascaded system can comprise only two paired reflector sets or more than three paired reflector sets.

As shown in Figures 6A-6G, the homogenizer can be circular (Figure 6A) or be in the shape of a polygon, such as square (Figure 6B), a rectangle (Figure 6C), a triangle (Figure 6D), a pentagon (Figure 6E), a hexagon (Figure 6F), an octagon (Figure 6G) or any other multi-sided shape. Moreover, the homogenizer can be made of any suitable material, such as plastic, glass, or quartz.

While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but, on the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Thus, it is to be understood that variations in the particular parameters used in defining the invention can be made without departing from the novel aspects of this invention as defined in the following claims.