Illumination – Light source and modifier – Including reflector
Reexamination Certificate
2001-09-20
2003-09-16
O'Shea, Sandra (Department: 2875)
Illumination
Light source and modifier
Including reflector
C362S299000, C362S305000, C362S551000
Reexamination Certificate
active
06619820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to illumination and projection systems that collect and condense light spread over a wide collection angle to a small target.
2. Description of the Related Art
The objective of systems that collect, condense, and couple electromagnetic radiation into a target such as a standard waveguide, e.g. a single fiber or fiber bundle, or output electromagnetic radiation to the homogenizer of a projector, is to maximize the brightness of the electromagnetic radiation at the target. There are several common systems for collecting and condensing light from a lamp for such illumination and projection applications.
U.S. Pat. No. 4,757,431 (“the '431 patent”), the disclosure of which is incorporated by reference, describes a light condensing and collecting system employing an off-axis spherical concave reflector to enhance the flux illuminating a small target/and the amount of collectable flux density reaching the small target. Another light condensing and collecting system is provided by U.S. Pat. No. 5,414,600 (“the '600 patent”), the disclosure of which is incorporated by reference, describes the use of an ellipsoid concave reflector. Similarly, U.S. Pat. No. 5,430,634 (“the '634 patent”), the disclosure of which is incorporated by reference, describes the use of a toroid concave reflector.
The systems of the '431, the '600 and the '634 patents provide a near 1:1 (unit magnification) image and conserve brightness from the light source. However, these systems lose their 1:1 (unit) magnification, thus degrading overall projection system performance, as the collection angle of the reflector is raised to increase the amount of collected light. Therefore, in these systems, increasing the collection efficiency decreases the quality of the produced image.
To address problems in the known optical collection and condensing systems, U.S. patent application Ser. No. 09/604,921, the disclosure of which is incorporated by reference, provides a dual-paraboloid reflector system that is advantageous in many respects to other known systems, including the achievement of 1:1 magnification for small-sized light sources.
This optical collection and condensing system, as illustrated in FIG.
1
(
a
), uses two generally symmetric paraboloid reflectors
10
,
11
that are positioned so that light reflected from the first reflector
10
is received in a corresponding section of the second reflector
11
. In particular, light emitted from a light source
12
, such as an arc lamp, is collected by the first parabolic reflector
10
and collimated along the optical axis toward the second reflector
11
. The second reflector
11
receives the collimated beam of light and focuses this light at the target
13
positioned at the focal point.
To facilitate the description of this optical system,
FIG. 1
includes the light paths for four different rays (a, b, c and d) emitted from the light source
12
. The light output from an arc lamp subtends a cone angle of about 90° when viewed in a direction normal to the lamp axis, as shown in FIG.
1
(
a
). The light output from an arc lamp subtends a cone angle of nearly 180° when viewed in a direction parallel to the lamp axis, as shown in FIG.
1
(
b
). Rays a and d indicate the extents of the cone angle.
The optical system of
FIG. 1
may employ a retro-reflector
14
in conjunction with the first paraboloid reflector
10
to capture radiation emitted by the light source
12
in a direction away from the first paraboloid reflector
10
and reflect the captured radiation back through the light source
12
. In particular, the retro-reflector
14
has a generally spherical shape with a focus located substantially near the light source
12
(i.e., at the focal point of the first paraboloid reflector) toward the first paraboloid reflector to thereby increase the intensity of the collimated rays reflected therefrom.
One shortcoming of the above described dual-paraboloid optical system is that a large input angle is produced, resulting in numerical apertures as high as 1.0. As a result, some of the rays strike the target
13
at high angles of incidence relative to the target surface. Such high angles of incidence produce Fresnel reflections that introduce losses.
In U.S. application Ser. No. 09/669,841, the disclosure of which is incorporated by reference, a dual ellipsoidal reflector system is described as providing 1:1 magnification for small light source target. This optical collection and condensing system, as illustrated in
FIG. 2
, uses two generally symmetric ellipsoid reflectors
20
,
21
that are positioned so that light reflected from the first reflector
20
is received in a corresponding section of the second reflector
21
. In particular, light emitted from the light source
22
is collected by the first elliptical reflector
20
and focused onto the optical axis
25
and diverged toward the second reflector
21
. The second reflector
21
receives the divergent beam of light and focuses this light at the target
23
positioned at the focal point.
As may be seen in
FIG. 2
, the dual-ellipsoid system suffers from the same disadvantage as the dual-paraboloid system in that some rays strike the target at large angles of incidence, producing Fresnel reflections. But as with the systems described above, Fresnel reflections caused by the large collection angle introduce losses.
Another embodiment of the dual-ellipsoid system may be seen in FIG.
3
. This dual-ellipsoid system suffers from the same disadvantage as the above-mentioned dual-paraboloid and dual-ellipsoid systems in that some rays strike the target at large angles of incidence, also producing Fresnel reflections.
A tapered light pipe
40
with a flat input surface
42
for use with the above systems is shown in FIG.
4
. Rays of light a′, b′, c′, and d′ reflected by second reflector
41
converge at flat surface
42
of tapered light pipe
40
at large angles of incidence as shown in FIG.
4
. The tapering of light pipe
40
will transform the large input angles into smaller output angles. The degree to which the angles are transformed will depend on the degree of taper. The output angles are designed for a specific system by matching the output device to the light pipe. As shown in
FIG. 4
, the input angle at input surface
42
of the light pipe
40
between rays a′ and d′ can approach 180 degrees, i.e. an angle of incidence of 90 degrees. Such a high angle of incidence will introduce high losses due to Fresnel reflections. For uncoated light pipes made with glass or quartz, the Fresnel reflection loss becomes very significant at angles of incidence larger than about 75 degrees.
Therefore, there remains a need to provide a method of coupling light from a small source to illumination and projection systems with reduced losses due to Fresnel reflections.
SUMMARY
An optical coupling element for use in large numerical aperture collecting and condensing systems. The optical coupling element includes a lens with a center and a curved surface. The optical coupling element is placed substantially at the input end of a fiber, fiber bundle, or homogenizer. The curved surface reduces the angle of incidence of the light striking the input end of the optical coupling element such that the Fresnel reflection is greatly reduced.
In particular, a collecting and condensing system comprises a source of electromagnetic radiation, and an optical coupling element to be illuminated with at least a portion of the electromagnetic radiation emitted by the source. The optical coupling element comprises a lens and a tapered light pipe, the lens having a center and a curved surface distributed about the center. A first reflector having a first optical axis and a first focal point is arranged facing substantially symmetrically a second reflector having a second optical axis and a second focal point on the optical axis, such that the first and second optical axes are substantially collinear. The so
Cogent Light Technologies Inc.
O'Shea Sandra
Rothwell, Figg Ernst & Manbeck, PC
Truong Bao
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