Illumination – Light source and modifier – Including reflector
Reexamination Certificate
1998-10-13
2001-02-13
Cariaso, Alan (Department: 2875)
Illumination
Light source and modifier
Including reflector
C362S551000, C362S347000, C362S346000, C359S858000
Reexamination Certificate
active
06186648
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems for collecting and condensing electromagnetic radiation, particularly a system for providing a high radiance to a small target such as an optical fiber.
BACKGROUND OF THE INVENTION
Conventional collecting and condensing designs for electromagnetic radiation emphasize collecting and redirecting the maximum amount of light from a source of radiation, approximated by a point source. To produce a small spot size based on these designs results in a decrease in radiation flux because conventional designs (i.e., the collection and redirection of the maximum amount of light) inherently conflict with the goal of concentrating the radiation flux into the smallest possible spot size when the radiation originates from conventional incoherent sources. Thus, images of small spot size may be obtained only by a corresponding decrease in flux density.
There are two basic optical designs in common use for collecting and condensing radiation. The first is a system of condenser lenses such as illustrated in FIG.
1
. Condenser lenses have several problems which include creation of chromatic and spherical aberrations, relatively high cost, inherently difficult alignment, and large amount of space. Ellipsoidal reflectors as shown in
FIG. 2
are also used in prior art systems. Their problems also include high cost and an unavoidable magnification of the image (i.e. a reduction in the flux density). Both of these systems tend to emphasize redirection of the maximum amount of flux from a point source at the expense of the flux density, as discussed above.
U.S. Pat. No. 4,757,431, the embodiment of which is incorporated herein by reference (FIG.
3
), describes an improved condensing and collecting system employing an off-axis spherical concave reflector which enhances the maximum flux illuminating a small target and the amount of collectable flux density by a small target. The off-axis spherical concave reflector described in this patent has certain disadvantages, namely, astigmatism parallel to the direction of the off-axis displacement and the physical limitations inherent in the requirement to minimize this distance. The effect of astigmatism is to decrease the concentrating efficiency of the system and thereby reduce the flux collected at a target. The requirement to minimize the off-axis distance between the source and the target (i.e. minimize astigmatic distortion), imposes limitations on the physical dimensions of a source and target of the described embodiment. The teachings of the use of a deformable spherical concave reflector does not lead to the use of a toroidal reflector having two perpendicular and unequal radii of curvature.
SUMMARY OF THE INVENTION
The present invention represents an improvement over the system disclosed in U.S. Pat. No. 4,757,431 in three ways: (i) it enhances the concentration and collection of radiation emitted by a point-like source of electromagnetic radiation into a small target; (ii) it increases the collectable flux into a small target, and (iii) it improves the collection and coupling efficiency between a source of electromagnetic radiation and a small target for any “off-axis optical system” as described in U.S. Pat. No. 4,757,431, particularly in the reduction of the preferred embodiment into practical systems.
To achieve these and other objectives, the present invention employs as the primary optical element a concave reflecting surface having different radii of curvature along two orthogonal axes (i.e. a toroidal reflector), a source of electromagnetic radiation and a target (i.e. an optical fiber). The source and target are located at similar distances on opposite sides of the optical axis of the system which is defined as the optical axis of the concave toroidal reflector (the “off-axis reflector”). For concentrating maximum flux density at the target, a retro-reflector, preferably of toroidal design or alternatively of spherical design, is located behind the source to reflect and re-focus radiation from and back through the source onto the toroidal reflector. The retro-reflector together with the off-axis toroidal reflector act as a system for maximizing the collectable flux density of radiation concentrated at the target. The system substantially improves the collectable radiance at the target in two ways: (i) the toroidal design of the reflectors substantially corrects for astigmatism caused both by the off-axis geometry and glass-envelope of typical electromagnetic radiation sources such as an arc lamp and (ii) the retro reflector increases the effective brightness of the radiation source. The maximum optical efficiency of the system is obtained by optically matching the reflectors and target, while the maximum flux density at the target and, in particular, collectable by an optical fiber as the target, is obtained both by maximizing the system efficiency and optically matching the source, reflectors, and target. Whereas prior art teaches the use of ellipsoidal reflectors “on-axis” or deformable spherical concave reflectors “off-axis,” in practice the use of aspheric mirrors is expensive. A significant advantage of the present system is the use of very inexpensive aspheric mirrors, toroids, to concentrate light at a target in which the collectable flux density at the target is insensitive to the surface quality of the mirror.
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Mertz, L., “Configuration for a Large Light Collector,” Journal of the Optical Society of America, Feb. 1965.
Baker Glenn
Brenner Douglas M.
Fischer Robert
Piccioni Robert L.
Strobl Karlheinz
Cariaso Alan
Cogent Light Technologies Inc.
Rothwell Figg Ernst & Manbeck p.c.
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