Illumination – Light source and modifier – Including reflector
Reexamination Certificate
2000-03-21
2001-11-06
O'Shea, Sandra (Department: 2875)
Illumination
Light source and modifier
Including reflector
C362S551000, C362S560000, C362S298000, C362S301000, C362S302000
Reexamination Certificate
active
06312144
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and systems for increasing the flux density of light exiting a source of electromagnetic radiation by retro-reflection.
BACKGROUND OF THE INVENTION
One of the major goals when collecting and condensing radiation, particularly visible light, from a source onto a target surface is the maximization of the flux density, or brightness, of the light at the target surface. Various configurations using on-axis elliptical and parabolic reflectors, and off-axis reflectors of various shapes have been used. Since the brightness of the image created at the target theoretically only can be conserved in an ideal optical system (and is reduced in a non-ideal system) it is impossible to increase the total flux at the target above the amount which is emitted by the source.
Specifically in the area of optical condensing and collecting systems which use reflectors, the fundamental system, exemplified by
FIG. 1
a
, is comprised of a primary reflector
2
having a generally concave shape. Concave reflectors having a variety of shapes are known in the art, including spherical, paraboloidal, ellipsoidal, and torroidal reflectors.
FIG. 1
a
specifically depicts a common ellipsoidal shaped concave reflector
2
which has two focal points
4
and
5
. In such an ellipsoidal system, typically the source
1
of radiation will be placed near one focus
4
, and the target surface
3
, typically the input end of an optical fiber, homogenizer, or lens, is located near the other focus
5
. One of the natural reflecting properties of an ellipsoidal shaped reflector is that light emitted at one of its foci will be collected and focused onto its other focus.
A technique commonly used by the prior art to combat the fundamental limitation that the total flux at the target surface must be at most equal to the flux emitted by the source is the use of an arc lamp as the source in combination with a retro-reflector. This combination takes the light emitted from one side of the arc lamp and redirects it with the retro-reflector back through the arc of the lamp. Since the absorption of the reflected light by the arc is very small, light emitted from the opposite side of the arc lamp when a retro-reflector is used is comprised of both the light radiating from the arc itself as well as the retro-reflected light. Thus, the total light flux emitted from the side of the lamp opposite the retro-reflector is effectively doubled. Other prior art methods have extended this concept by reflecting light from the arc back into itself multiple times, thus increasing the flux further as in U.S. Pat. No. 4,957,759 to Goldenberg et al.
As depicted by
FIG. 1
b
, retro-reflectors have been commonly used in projection systems having an optical axis
17
. A spherical retro-reflector
16
is placed behind the source
11
, typically an arc lamp, with the arc
11
a
placed at the center of curvature
19
of the spherical retro-reflector
16
. This orientation causes the light collected at the back of the source
11
to be imaged back through the arc
11
a
itself and be collected by condensing optics
18
, such as lenses, at the front of the system. Such a retro-reflector
16
would effectively double the brightness being delivered to the condensing optics under the ideal circumstances, and in practice typically leads to around a 60% to 80% increase in flux density at the target surface
13
.
To improve the flux density of the light delivered by the a reflector-based condensing system such as in
FIG. 1
a
, a compound reflector system as shown by
FIG. 2
has been developed by the prior art. Referring to
FIG. 2
, such a compound reflector system has on the opposite side of the source
21
from the target surface
23
an ellipsoidal primary reflector
22
which collects light from the source
21
located at a first focus
24
an reflects it toward a second focus
25
. A concave spherical retro-reflector
26
, situated with its center of curvature
29
being coincident with the first focus
24
, collects a portion of the radiation emitted by the source
21
and reflects it back through the source
21
such that its effective flux density is nearly doubled. This retro-reflected light is then collected by the ellipsoidal primary reflector
22
same as the original light and delivered to the second focus
25
, thus increasing the overall flux density at the target surface
23
.
FIG. 3
shows another configuration of such a compound reflector system where the concave spherical retro-reflector
36
is placed behind the source
31
and the ellipsoidal primary reflector is placed between the source and the target surface
33
. As with the compound reflector system depicted by
FIG. 2
, the source
31
is located near the first focus
34
of the primary reflector
32
and the center of curvature of the retro-reflector
36
, and the target surface is placed near the second focus
35
. Flux density at the target surface
33
in this case is also nearly doubled when compared to the case with no retro-reflection.
Although both the systems depicted by
FIGS. 2 and 3
employ concave spherical retro-reflectors to increase the flux density at the target surface, the compound reflector system used in both is intricate and costly to manufacture. Furthermore, proper alignment between the lamp and the reflector is difficult. Thus, there remains a need in the art for an optimized system and method for optical condensing and collecting which increases the flux density of radiation emitted by a source toward a target surface which is simple and inexpensive to manufacture.
SUMMARY OF THE INVENTION
The present invention provides a method and system for condensing and collecting electromagnetic radiation to increase flux density at a target surface. Systems according to the present invention comprise a source of radiation emitting substantially uniform radiation flux, such as an arc lamp, a primary reflector having a substantially concave shaped reflective surface, a focal point, and an optical axis, and a retro-reflector having a non-concave shaped reflective surface. According to the present invention, the substantially concave shape of the primary reflector and the non-concave shape of the retro-reflector are chosen such that the two shapes are complementary. That is, the shapes of the primary reflector and retro-reflector are such that light directed from the primary reflector will intersect the non-concave reflective surface of the retro-reflector at a right angle such that the light hitting the retro-reflector will be returned to the source substantially along its original path.
The method of the present invention comprises the steps of emitting radiation from a source, collecting the radiation with a substantially concave shaped primary reflector and redirecting the emitted radiation in at least two portions toward a target surface, such as the input end of a fiber optic, a field homogenizer, or a lens. The method further comprises reflecting at least one of the portions of radiation redirected by the primary reflector substantially back along its original path and through the source using a non-concave retro-reflector which is shaped complementary to the primary reflector.
The present invention overcomes the disadvantages and drawbacks present in the prior art in that it efficiently condenses a light onto a target surface with high flux density without the need for costly and complicated compound reflectors or condensing lenses. The above and other advantages, features and aspects of the invention will be more readily perceived from the following description of the preferred embodiments thereof taken together with the accompanying drawings and claims. The present invention is illustrated by way of example and not limitation in the drawings, in which like reference numerals indicate like parts.
REFERENCES:
patent: 4956759 (1990-09-01), Goldenberg et al.
patent: 4957759 (1990-09-01), Swartzel et al.
patent: 5414600 (1995-05-01), Strobl et al.
patent: 5430634 (1995-07-01), Baker et al.
patent: 575
Cogent Light Technologies Inc.
DelGizzi Ronald E.
O'Shea Sandra
Rothwell Figg Ernst & Manbeck
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