Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM FOR COLLECTING AND CONDENSING LIGHT
Field of the Invention
The invention relates to systems for collecting and condensing electromagnetic
radiation, such as light, and, in particular, to a system employing a pair of
opposed
concave reflector surfaces for collecting radiation emitted from a radiation
source and
focusing the collected radiated onto a target.
Background of the Invention
The obj ective 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
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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.
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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 mufti-layer dielectric coating for use in
various color
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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
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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 SO may be a
conventional, bi-
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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, l Ob, and l Oc 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 l Ob 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
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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
SOa, SOb, SOc are positioned along the common optical axes between the
reflectors 10a
and 20a, lOb and 20b, and lOc and 20c, respectively.
Figure S 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 mufti-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.
