Illumination – Light fiber – rod – or pipe
Reexamination Certificate
2000-03-09
2001-11-20
O'Shea, Sandra (Department: 2875)
Illumination
Light fiber, rod, or pipe
C362S560000, C362S303000, C362S305000, C362S304000
Reexamination Certificate
active
06318885
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and systems for collecting and condensing electromagnetic radiation.
BACKGROUND OF THE INVENTION
Generally, systems for collecting and condensing electromagnetic radiation emphasize redirecting a maximum amount of light from a source of radiation (typically approximated by a point source). Specifically in the area of optical condensing and collecting systems which use reflectors, the fundamental system consists of a reflector
2
in the shape of an ellipsoid portion which has two focal points
4
and
5
as depicted by FIG.
1
. The source
1
of radiation will be placed at one focus
4
, and the target
3
is located at the other focus
5
. One of the natural reflecting properties of a ellipsoidal shaped reflector is that light emitted at a first focus
4
will be all collected and focused onto the second focus
5
. Due to physical limitations, for example, physical limitations (size of lamps, reflectors, retro-reflectors and targets), angular distributions, etc., only a portion of the ellipsoidal surface can be used advantageously in a given reflector system.
The most common system known in the art is the on-axis system wherein reflector
2
is symmetric about the major axis
7
of the ellipsoid
10
as shown in FIG.
1
. The light emitted by the light source
1
at the first focus
4
is collected by the reflector
2
and focused onto the target
3
at the second focus
5
. Considering a light ray emitted from the light source at the first focus
4
following the path L
1
and S
1
to reach the target
3
at the second focus
5
, the magnification M
1
of the light ray traveling this line is represented by the formula:
M
1
=
S
1
/
L
1
Identity (1)
Similarly, for a light ray traveling along paths L
2
and S
2
, the magnification M
2
of the light in this instance is given by the formula:
M
2
=
S
2
/
L
2
Identity (2)
As shown in
FIG. 1
, the magnification M
1
of the ray traveling along L
1
and S
1
is greater than the magnification M
2
of the ray traveling along the path L
2
and S
2
. Thus, the light emitted by the light source
1
, depending on the angle of emission, will produce images having different magnifications at the target
3
. This produces a larger spot size for some angles of emission and a smaller spot for other angles. The magnification of output spots produced by such a system can generally range from about 2 to 8. As magnification varies, a loss in flux density is experienced at the target which causes an attendant loss in brightness of the image produced from the original light source.
FIG. 2
depicts another configuration known in the art which utilizes a different portion of an ellipsoidal reflecting surface. In the system depicted by
FIG. 1
, the reflector is shaped substantially like the surface of an ellipsoid around one end of its major axis, while in the system of
FIG. 2
, the reflector is shaped substantially like the surface of an ellipsoid around one end of its minor axis. The configuration depicted in
FIG. 2
is disclosed in U.S. Pat. No. 5,414,600, and is known in the art as an off-axis system because the source
1
and target
3
, located at focal points
4
and
5
, respectively, are disposed upon opposite sides of the minor axis
8
of the ellipsoid
10
. Referring to
FIG. 2
, light rays traveling along the paths indicated by L
1
′ to S
1
′ and L
2
′ to S
2
′, would have magnifications M
1
′ and M
2
′, respectively, given by the identities:
M
1
′=
S
1
′/
L
1
′ Identity (3)
and,
M
2
′=
S
2
′/
L
2
′ Identity (4)
As shown in the figure, both M
1
′ and M
2
′ are very close to unity. This is especially the case when the source
1
to target
3
distance is made small. In such cases where the resultant image of the light source at the target substantially has a unity magnification along all travel paths, the brightness of the image spot is maximized. Furthermore, for such off-axis configurations, a retro-reflector
11
can be added as shown in
FIG. 2
such that the light collected by the retro-reflector
11
will be imaged back through the source
1
increasing the brightness transmitted to the target
3
. Commonly, improvements of up to 60% in flux density at the target can be readily produced by the use of retro-reflectors.
Both of the above detailed systems have their relative strengths and drawbacks. In the on-axis system, the output at the target has a large diameter and a small numerical aperture, but the brightness is reduced due to the large range of magnifications produced by the various paths from source to target. In the off-axis system, the output spot at the target is approximately the same size of the light arc produced by the source. Thus, the off-axis system has improved brightness due to the lack of magnification. However, the numerical aperture of the light produced at the target by such off-axis systems is usually very large so as to maximize the amount of light collected by the reflector. Such high numerical aperture condensed light is often difficult to efficiently couple into suitable targets, such as optical fibers having relatively low numerical apertures. Thus, the large numerical apertures produced makes the prior art off axis system unsuitable for efficient coupling into small numerical aperture targets directly.
For certain applications, particularly when the spot size created at the target is required to be larger than the size of the source, or when it is necessary for the numerical aperture of the target spot to be smaller than that inherently produced by the reflector system, transforming devices such as lenses, waveguides, and other well known devices are commonly used. Although such systems theoretically can preserve brightness at the target spot while transforming spot sizes and numerical apertures to the input characteristics of various applications, in practice, these light transforming devices can be expensive, complex, and space consuming. Additionally, such devices often introduce insertion losses such that the output flux is smaller than the source flux even though the collection system preserves brightness.
Thus, there remains a need in the art for an optimized system and method for optical condensing and collecting which efficiently and compactly produces low numerical aperture light without adding expensive components.
SUMMARY OF THE INVENTION
The invention relates to efficiently collecting radiation onto a large spot size with minimum cost and complexity. The present invention advantageously produces an image of a radiation source which has variable magnification ratios and small numerical apertures by using a reflector shaped like a particular portion of an ellipsoid. Although the magnification produced in embodiments of the present invention may not be constant over all angles of emission from the source (thus introducing loss in brightness), for applications whereby size and cost constraints require simplicity and prohibit the introduction of extra optical elements, the invention is particularly suitable.
The present invention comprises a method and system for condensing and collecting electromagnetic radiation. The system is comprised generally of a radiation source, a reflector and a target. The reflector has a reflecting surface for reflecting the radiation from the source which is substantially in the shape of a cut out portion of an ellipsoid. This ellipsoidal reflector surface portion has an elliptical curvature which is concave relative to both the target and the source, and which has a major axis, a minor axis, and a first and second focal points. The system of the present invention redirects radiation emitted from the source, located near the first focal point of the ellipsoid, to produce a magnified image of the source at the target, located near the second focal point of the ellipsoid. To achieve a spot size magnification, the ellipsoidal reflector surface comprises
Chen Chingfa
Li Kenneth K.
Okino Marvin
Cogent Light Technologies Inc.
DelGizzi Ronald E.
O'Shea Sandra
Rothwell Figg Ernst & Manbeck
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