Note: Descriptions are shown in the official language in which they were submitted.
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
DUAL PARABOLOID REFLECTOR AND DUAL ELLIPSOID
REFLECTOR SYSTEMS WITH OPTIMIZED MAGNIFICATION
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application
Serial
No. 60/695,934 filed June 30, 2005 and is a continuation-in-part of
Application Serial No.
11/274,241, filed November 14, 2005, which is a continuation of Application
Serial No.
10/660,492, filed September 12, 2003, which is a continuation of Application
Serial No.
09/669,841, filed Septeinber 27, 2000 (now U.S. Patent 6,634,759), which
claims the
benefit of U.S. Provisional Application No. 60/192,321 filed March 27, 2000,
each of
which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to systems for collecting and condensing
electromagnetic radiation, particularly a system incorporating asymmetric
parabolic
reflectors for collecting radiation emitted from a radiation sotirce and
focusing the
collected radiation onto a target.
BACKGROUND OF THE INVENTION
[0003] The fimctional objective for systems that collect, condense, and couple
electromagnetic radiation into a waveguide, such as a single fiber or fiber
bundle, or
outputs to a homogenizer of a projector, is to maximize the brightness (i.e.,
maximize the
flux intensity) of the electromagnetic radiation at the target. The prior art
teaches the use
of so-called on-axis reflector systems involving spherical, ellipsoidal, and
parabolic
reflectors and off-axis reflector systeins involving spherical, toroidal, and
ellipsoidal
reflectors. Where the target has dimensions that are similar to the size of
the arc gaps of
the electromagnetic radiation source, off-axis reflector systems achieve
higher efficiency
and briglitness at the target than on-axis systems, thereby maximizing the
amourit of light
that can be collected by a fiber optic target. For targets having dimensions
that are much
larger than the arc gaps of the electromagnetic source, both on-axis and off-
axis reflector
systems are effective for collecting, condensing, and coupling the radiation
from a
radiation source into a wave guide.
[0004] An optical collecting and condensing system comprises various optical
elements, such as reflectors and lenses that receives liglits energy from a
light source,
1
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
such as a light bulb, and directs the light energy toward a target. In
particular, the optical
system collects and condenses electromagnetic radiation to couple the light
energy to a
standard waveguide, such as a single fiber or fiber bundle or to otitput the
light energy to
a homogenizer of a projector. The ftuictional objective for the optical system
is to
maximize the brightness (i.e., the flux intensity) of the electromagnetic
radiation at the
target.
[0005] Optical systems for collecting and condensing light from a light source
are
generally classified as either "on-axis" or "off-axis." In the on-axis
systems, the
reflectors are positioned on the optical axis between light source, and the
target. FIG. 1
illustrates a lalown on-axis optical system that uses a paraboloid reflector
with an imaging
lens. The paraboloid reflector has the feature that light energy emanating
from a focus is
substantially collimated to travel parallel to the optical axis. The optical
system of FIG. 1
uses this feature of the paraboloid reflector by positioning the light source
at tlie focus in
order to collimate the light from the ligllt source. A condensing lens
positioned in the
optical stream receives the substantially collimated light energy and
redirects the light
energy toward the target. In this way, the light energy is collected and
condensed at the
target. The use of the paraboloid reflector fi.irther allows the use of
various types of
optical filters to improve the performance and durability of the optical
system. However,
the divergence of the light varies continuously along the reflector, with rays
traveling near
the optical axis having the greatest divergence. As a result, the
magnification of the
system varies along the different paths taken by the light emitted from the
light source,
causing degradation of the brightness of the system. Moreover, the focusing
lens
produces a distorted image even under perfect conditions and under actual
operation
typically produces badly aberrated images wllich effectively increase the
image size and
reduce flux intensity at the target.
[0006] FIG. 2 illustrates another luiown on-axis optical system. This system
uses
an ellipsoidal reflector, which ahs the feature that all light emanating from
one focal point
is directed to a second focal point. The optical system of FIG. 2 uses an
ellipsoidal
reflector with a light source placed at the first focus and a target placed at
the second
focus. As in the previous system, the on-axis ellipsoidal system suffers from
brightness
degradation caused because the divergence of the light varies continuously
along the
reflector, with rays traveling near the optical axis having the greatest
divergence.
2
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
[0007] Overall, on-axis systems generally suffer from the basic limitations of
losing brightness in the coupling, tllus degrading the overall efficiency of
the optical
illumination and projection system. In particular, the divergence of the
reflected beam in
lcnown on-axis systems is undesirably dependent on the angle of emission from
the
radiation source. Additionally, the outputs of the on-axis system are
substantially circular
and syn7nietric and, therefore, may not be suitable for non-circular targets,
such as a
rectangular homogenizer for use in projection.
[0008] The off-axis optical collecting systems, the reflectors are positioned
off the
optical axis between the light source and the target. For example, FIG. 3
illustrates an
optical system in which the light source is positioned at a focal point of a
retro-reflector
aiid the target is positioned on a focal point of a primary reflector, but the
reflectors are
positioned off the optical axis between the ligllt source and the target. In
the illustrated
optical system, light energy from the light source reflects from the retro-
reflector and
travels to the primary reflector. The optical energy then reflects from the
primary
reflector and converges at the target.
[0009] With the off axis system of FIG. 3, the magnification is very close to
1- to
-1 for all angles of ligllt when the numerical aperture of the system is
small. When the
system uses mirrors having higller numerical apertures (e.g., attempts to
collect more
light energy from the same ligllt source) the larger angle light rays are
reflected with high
divergence angles, causing the magnification to deviate from 1-to-1. Again,
the
magnification reduces the brightness at the target and overall decreases the
performance
of the optical systein. The amount of deviation in the magnification depends
on the size
of the mirror, the radius of curvatures, and the separation of the arc lamp
and the target.
Accordingly, the off-axis configuration of FIG. 3 is more suitable for
applications that use
smaller numerical apertures.
[0010] Different off-axis optical systems are also luiown. For example, U.S.
Patent No. 4,757,431 ("th.e '431 patent") provides a condensing and collecting
system
einploying an off-axis spherical concave reflector which ei-d-iances the
maximum flux
intensity illuminating a small target and the amount of collectable flux
density by the
small target. EiAiancements to the optical system of the '431 patent are
provided by U.S.
Patent No. 5,414,600 ("the '600 patent"), in which the off-axis concave
reflector is an
ellipsoid, and by U.S. Patent No. 5,430,634 ("the '634 patent"), in which the
off-axis
concave reflector is a toroid. Although the toroidal system described in the
'634 patent
3
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
corrects for astigmatism, and the ellipsoidal system of the '600 patent
provides a more
exact coupling tllan the spherical reflector of the '431 patent, each of these
systems
requires the application of an optical coating onto a highly curved reflective
surface,
which is relatively expensive and difficult to apply in a uniform thiclaless.
[0011] Overall, the known off-axis optical systems provide a generally near 1-
to-1
(i.e., m.agnification free) image of the light source at the target and
conserve briglltness.
However, in the luiown off-axis systeins, the magnification deviates from 1-to-
1 as the
amount of light collected is increased by increasing the collection angle of
the reflector.
Thus, as a greater portion of light energy from a light source is collected to
increase
optical intensity, the overall perfoililance of the optical system degrades.
[0012] To address problems in the lclown optical collection and condensing
systems, U.S. Patent No. 6,672,740 provides an on-axis, dual paraboloid
reflector system
that is advantageous in many respects to other known systems, including the
achievement
of near 1-to-1 magnification for small-sized light source. This optical
collection and
condensing system, as illustrated in FIG. 4, uses two generally syinmetric
paraboloid
reflectors that are positioned so that light reflected from the first
reflector is received in a
corresponding' section of the second reflector. In particular, light emitted
from the light
source is collected by the first paraboloid reflector and collimated along the
optical axis
toward the second reflector. The second receives the collimated beam of light
and
focuses this light at the target positioned at the focal point.
[0013] To facilitate the description of this optical systein, FIG. 4 includes
the light
paths for three different rays (a, b, and c) emitted from the light source.
Ray a travels a
relatively small distance before intersecting the first parabolic reflector,
but the
divergence of ray a at the first parabolic reflectors is relatively large. In
contrast, ray c
travels further between the light source and the first parabolic reflector but
has a smaller
relative divergence at the first parabolic reflector but has a smaller
relative divergence at
the first reflector. Ray b, positioned between rays a and c, travels an
intermediate
distance before intersecting the first parabolic reflector and has an
intermediate
divergence. In this optical system, due to the syinmetry of the two parabolic
reflectors,
the rays a, b, and c are reflected at coiTesponding positions in the second
parabolic
reflector such that the distance fro each ray between the second parabolic
reflector and the
target is the same as the distance between the second parabolic reflector and
the target is
the same as the distance between the light source and the first parabolic
reflector. In this
4
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
way, the second reflector compensates for the divergence. Consequently, the
optical
system collects and condenses light energy from the light source with a near 1-
to-1
magnification and preserves the brightness of the light source.
[0014] The optical system of FIG. 4 may further employ a retro-reflector in
conjunction with the first paraboloid reflector to capture radiation emitted
by the source
in a direction away from the first paraboloid reflector and reflect the
captured radiation
back through the source. In particular, the retro-reflector has a generally
spherical shape
with a focus located substantially near the light source (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.
[0015] Since on-axis, dual-paraboloid optical system arises because the light
sotuce is very close to the apex side of the reflector in the above described
on-axis, dual-
paraboloid optical system, the system produces a large angle of divergence
near the light
source (i.e., along the patlls similar to ray a). In particular, a large angle
of divergence
causes light energy traveling along a path similar to ray a to compass a
relatively large
area on the second paraboloid reflector, tlius producing unwanted aberrations
and a loss
of brightness. None of these references, however, describe a system for
dealing wit11
large angle of divergence and optimizing magnification between the source and
the
focused image so as to obtain the maxiinum flux intensity with the miniinuin
distortion at
the target.
[0016] Therefore, there remains a need to provide a method of collecting and
concentrating electromagnetic radiation usmg asyinmetric parabolic reflectors
that
maxiirdzes the flux intensity of the focused radiation beam at the target.
SUMMARY OF THE INVENTION
[0017] In accordance with an embodiment of the present invention, an improved
systeni for collecting and condensing electromagnetic radiation employs
opposing
asynunetric reflectors and optimizes magnification between a source image and
a focused
image at a target, thereby producing maximum focused intensity at the target.
In
particular, the present invention is directed to an optical device for
collecting
electromagnetic radiation from a source of electromagnetic radiation and
focusing the
collected radiation onto a target to be illuminated with at least a portion of
the
electromagnetic radiation emitted by the source. The device comprises a first
and second
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
reflectors, each reflector generally comprising at least a portion of a
paraboloid or
ellipsoid of revolution and has an optical axis A and a focal point on the
optical axis A. A
source located proximate the focal point of the first reflector produces
collimated rays of
radiation reflected from the first reflector in a direction parallel to the
optical axis A. The
second reflector comprises at least a portion of a paraboloid or ellipsoid of
revolution and
has an optical axis B and a focal point on the optical axis B. The second
reflector is
positioned and oriented with respect to the first reflector so that the rays
of radiation
reflected from the first reflector are reflected by the second reflector and
focused toward a
target located proximate the focal point of the second reflector. The first
and second
reflectors have slightly different shapes and sizes. Alteniatively, the second
reflector is
positioned and oriented with respect to the first reflector so that the rays
of radiation
reflected from the first reflector converse at a focal point of the second
reflector. The
rays of radiation then continue until reflected by the second reflector and
focused toward
a target located proximate a second focal point of the second reflector. The
first and
second reflectors can be oriented optically about asyinmetrically with respect
to each
other to optimize inagi.iification.
[0018] A retro-reflector may be used in conjunction with the first reflector
to
capture radiation emitted by the source in a direction away from the first
reflector and
reflect the captured radiation back through the source (i.e., tluough the
focal point of the
first reflector) toward the first reflector to thereby increase the intensity
of the rays
reflected therefrom.
[0019] The first and second reflectors can be arranged in an opposed, facing
relationship witll their respective optical axes arranged in parallel with
respect to each
other, or they can be arranged with their optical axes arrarlged at an angle
with respect to
each other, in which case a redirecting reflector is employed to redirect the
rays reflected
by the first reflector toward the second reflector.
[0020] In accordance with an exemplary embodiment of the present invention,
the
first and second reflectors comprise an asyinmetric ellipsoid/hyperboloid pair
with one of
the first and second reflectors having a substantially ellipsoid shape, and
the other of the
first and second reflectors having a corresponding substantially hyperboloid
shape with
each reflector of the ellipsoid/hyperboloid pair having a corresponding size
and optical
orientation with respect to each other so that each ray of radiation reflected
by a surface
portion of the first reflector is reflected by a corresponding surface portion
of the second
6
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
reflector toward the target so as to preferably optimize magnification between
the source
and an image focused onto the target.
[0021] In accordance with an exemplary embodiment of the present invention, an
optical device for illuminating a target with rays of electromagnetic
radiation coinprises a
first reflector and a second reflector. The first reflector comprises a first
focal length, a
first focal point and a first optical axis, the rays of electromagnetic
radiation being
directed substantially proximate to the first focal point of the first
reflector. The second
reflector comprising a second focal length, a second focal point and a second
optical axis,
which is not coincident witli the first optical axis. The second reflector
being positioned
and oriented with respect to the first reflector to receive at least a portion
of the rays of
radiation reflected from the first reflector and reflect the portion of the
rays of radiation to
a target located substantially proximate to the second focal point of the
second reflector.
The second reflector being asyinmetric with respect to the first reflector.
[0022] In accordance with an exemplary embodiment of the present invention,
the
focal length of the second reflector is longer than the focal length of the
first reflector,
which lowers the incidence angle of the rays of radiation inputted to the
target, thereby
reducing the Fresnel reflection loss.
[0023] In accordance with an exemplary embodiment of the present invention,
the
asyinmetric characteristics of the first and second reflectors are selected to
maximize net
output coupling efficiency.
[0024] In accordance with an exemplary enibodiment of the present invention,
the
focal length difference between the focal lengths of the two reflectors is
selected to
optimize the tradeoff between Fresnel reflection loss and image aberration,
thereby
providing a maximum net output coupling efficiency.
[0025] In accordance with an exemplary embodiment of the present invention, an
optical device for illuminating a target witll rays of electromagnetic
radiation comprises a
first reflector and a second reflector. The first reflector comprises a first
focal length, a
first focal point, a second focal point, and a first optical axis. The rays of
electromagnetic
radiation being directed substantially proximate to the first focal point of
the first reflector
to reflect from the first reflector and substantially converge at the second
focal point. The
second reflector comprising a second focal length, a first focal point and a
second focal
point and a second optical axis, which is not coincident with the first
optical axis. A
target being located substantially proximate to the first focal point of the
second reflector
7
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
to receive at least a portion of the rays of radiation that pass through the
second focal
point of the second reflector and are reflected by the second reflector to
substantially
converge at the first focal point of the second reflector. The second
reflector being
positioned and oriented with respect to the first reflector such that the
second focal point
of the first reflector and the second focal point of the second reflector are
positioned
substantially proximate. The second reflector being asyinmetric witll respect
to the first
reflector, which optimizes net output coupling efficiency.
[0026] In accordance with an exemplary enibodiment of present invention, a
method for collecting rays of electromagnetic radiation and focusing the
collected rays of
electromagnetic radiation onto a target. The method comprises the steps of
directing the
rays of electromagnetic radiation substantially proximate to a focal point on
a first optical
axis of a first reflector; positioning and orienting a second reflector with
respect to the
first reflector to receive at least a portion of the rays of radiation
reflected from the first
reflector; and positioning the target proximate to a focal point of the second
reflector to
receive at least portion of the rays of radiation reflected from the second
reflector,
wherein the second reflector being asyinmetric with respect to the first
reflector to
effectively reduce Fresnel reflection loss.
[0027] In accordance with an exemplary embodiment of the present invention, a
method for collecting rays of electromagnetic radiation and focusing the
collected rays of
electromagnetic radiation onto a target. The method comprising the steps of:
directing the
rays of electromagnetic radiation substantially proximate to a first focal
point on a first
optical axis of a first reflector so that the first reflector substantially
converges the rays of
radiation reflected from the first reflector at a second focal point on the
first optical axis;
positioning a second reflector so that a first focal point on a second optical
axis of the
second reflector is substantially proximate with the second focal point of the
first
reflector, whereby the converging rays of radiation reflected from the first
reflector pass
through the first focal point of the first reflector and are redirected by the
second reflector
toward a second focal point on the second optical axis; and positionv.lg the
target
proximate to the second focal point of the second reflector, wherein the
second reflector
being asyminetric with respect to the first reflector to effectively reduce
Fresnel reflection
loss.
[0028] Filters or other optical elements can be ai7anged between the
collimating
and focusing reflectors.
8
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
[0029] The shape of the first and second reflectors may deviate from an
ellipsoid
or a paraboloid as needed by the system. Similarly, the first and second
reflectors may
have a toroidal or spherical shape that approximate an ellipsoid.
DESCRIPTION OF THE DRAWINGS
[0030] Embodiments of the present invention will be described with reference
to
the attached drawings in which like components or features in the various
figures are
represented by like reference numbers:
[0031] FIG. 1 is a schematic diagram, shown in cross-section, of a 1clZown on-
axis
condensing and collecting optical system that uses a paraboloid reflector and
a focusing
lens;
[0032] FIG. 2 is a schematic diagram, shown in cross-section, of a known on-
axis
condensing and collecting optical system that uses an ellipsoidal reflector;
[0033] FIG. 3 is a schematic diagraln, shown in cross-section, of a Iclown off-
axis
condensing and collecting optical systein;
[0034] FIG. 4 is a schematic diagram, shown in cross-section, of a Ialown on-
axis
condensing and collecting optical system that uses two paraboloid reflectors;
[0035] FIG. 5 is a schematic diagranl, shown in cross-section, of an off-axis
condensing and collecting optical system using two ellipsoidal reflectors in
aceordance
witli an exemplary embodiment of the present invention;
[0036] FIG. 6 is a schematic diagram, shown in cross-section, of a condensing
and collecting optical system using two reflectors of greater eccentricity in
accordance
with an exemplary embodiment of the present invention;
[0037] FIGS. 7a-7j are schematic views of a plurality of waveguide targets in
cross-sections which may be employed in embodiments of the present invention;
[0038] FIG 8a is a sclleinatic view of a dual paraboloid reflector system in
accordance with an exemplary embodiment of the present invention;
[0039] FIG 8b is a schematic view of angles of incidences with a standard dual
paraboloid reflector system;
[0040] FIG 9a-9b are schematic views of a dual paraboloid or ellipsoidal
reflector
system in accordance with an exemplary embodiment of the present invention;
and
[0041] FIG 10 is a schematic view of a dual paraboloid or ellipsoidal
reflector
system in accordance with an exemplary embodiment of the present invention.
9
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0042] With reference to the figures, exemplary embodiments of the invention
are
now described. These embodiments illustrate principles of the invention and
should not
be construed as limiting the scope of the invention.
[0043] Referring to FIGS. 5-6 and 8-10 as showing representative exeinplary
embodiments of the present invention, the invention has associated therewith
the
following four main components: an electromagnetic source 10, a first
reflector 20, a
second reflector 30 and a target or tapered light pipe (TLP) 50.
[0044] The electromagnetic source 10 is preferably a ligllt source having an
envelope 12. Most preferably, the source 10 comprises an arc lamp such as a
xenon
lamp, a metal-halide lamp, a HID lamp, or a mercury lamp. For certain
applications,
filament lamps, e.g., halogen lamps, can be used, provided the systein is
modified to
accommodate the non-opaque filaments of the lainp, as will be described in
more detail
below. However, any source of electromagnetic radiation which is of similar
size to or
smaller than the target may be used (e.g., fiber, filament lamp, gas discharge
lamp, laser,
LED, semiconductor, etc.)
[0045] The size of the electromagnetic source here is better defined by the
1/e
intensity of the intensity contour map which characterizes the brightness
(flux density
over angular extent) of the source. Brightness is related to the size of the
arc gap and
detennines the theoretical limit of coupling efficiency. For the specific case
of an arc
lamp, the contour approxiinates axial syinmetry and is a complex fiinction of
electrical
rating, electrode design and composition, gas pressure, arc gap size, and gas
composition.
For the specific case of an arc lainp having an aspherical curved envelope,
the effective
relative position and intensity distribution of the source imaged by the
reflector undergoes
aberration. This is caused by the shape of the envelope which essentially
functions as a
lens and requires a compensating optical element. Optical compensation can be
achieved
either by modifying the design of the reflector to compensate for the
astigmatism caused
by the envelope or by inserting a coiTecting optic between the source and the
target.
Additionally, optical coatings can be applied to the envelope to minimize
Fresnel
reflections and thereby maximize collectable radiation at the target or to
control and/or
filter the radiation flux.
[0046] The first reflector 20 coinprises a portion of an ellipsoid or a
paraboloid of
revolution having an optical axis 22 and focal points 24 and 26. The first
reflector 20
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
preferably has a reflective coating 28 (e.g., aluminum or silver) and the
surface is highly
polished. For certain applications, the first reflector 20 can be made from
glass coated
with a wavelength-selective multi-layer dielectric coating. For example, the
coating 28
may be a cold coating witll higll reflectivity only in the visible wavelengths
for use in
visual light applications. With the source 10 placed at the first focal point
24 of the first
reflector 20, electromagnetic radiation that contacts the first reflector 20
is reflected as a
beam of energy that converges the second focal point 26 of the first reflector
20. Where
the source 20 is an arc lainp, the arc gap is preferably small compared to the
focal length
of the first reflector 20.
[0047] The second reflector 30 comprises a portion of an ellipsoid or a
paraboloid
of revolution having an optical axis 32 and focal points 34 and 36. The second
reflector
30 may also have a coating 38, as described above to selectively reflect light
energy. The
second reflector 30 can differ in shape or size from first reflector 20. That
is, the first and
second reflectors are asymmetric with respect to each other.
[0048] The second reflector 30 is positioned and oriented so that the
electromagnetic radiation reflected by the first ellipsoidal reflector 20
converges at the
second focal point 36 of the second reflector 30. The radiation continues
until impinging
the surface of the second reflector 30 and is thereafter focused toward the
first focal point
34 of the second reflector 30. In order to optimizes magnification between the
first
reflector 20 and the second reflector 30 (i.e., a focused image that is
substantially the
saine size as the source), it is iinportant that each ray of electromagnetic
radiation
reflected and focused by a surface portion of the first reflector 20 be
reflected and focused
by a substantially corresponding surface portion of the second reflector 30 in
order to
achieve a focus at the first focal point 34 that is of the maxinnim possible
brightiiess. In
the context of the present disclosure, orienting and positioning the first
reflector 20 and
the second reflector 30 with respect to each other so that each ray of
electromagnetic
radiation collimated by a surface portion of the first reflector 20 is focused
by a
substantially corresponding surface portion of the second ellipsoidal
reflector 30.
[0049] The target 50 is a small object requiring illumination with the highest
intensity possible. In an exemplary embodiment of the present invention, the
target 50 is
a waveguide, such as a light pipe, a tapered light pipe, single core optic
fiber, a fused
bundle of optic fibers, and a fiber bundle, as illustrated in FIG. 6. An input
end of the
target (e.g., a proximal end of the optic fiber) is positioned at the first
focal point 34 of the
11
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
second reflector 30 to receive the focused rays of electromagnetic radiation
reflected by
the second reflector 30.
[0050] When the optical collection and condensing systems of the present
invention are applied to applications for illuminations or projection of an
image, there is a
need to homogenize the output intensity profile at the target such that the
output is more
uniform. For exainple, for illumination dtuing a medical procedure such as
endoscopy, it
is desirable to have unifonn illumination so that the doctor can observe areas
in the center
and the periphery of the illuinination witll equal clarity. In the case of
illuminations using
optical fibers, the uniform intensity allows higher power to be coupled to a
particular
fiber optic configuration without being damaged by hot spots. In the case of
projections,
the uniform intensity will be needed to produce a uniform intensity profile at
the screen.
In particular, it is desirable for visual aesthetics that the center and the
periphery of the
displayed image have equal level of illumination.
[0051 ] Accordingly, the target may be a homogenizer, as illustrated in FIG. 5
that
adjusts the output intensity profile. The waveguide may be polygonal (square,
rectangle,
triangle, etc.) in cross-section as shown in as shown in FIGS. 7a-7f or
rounded (circular,
elliptical, etc.) in cross-section as shown in as shown in FIGS. 7g-7h.
[0052] Depending on the output requirement in tenns of numerical aperture and
size, the homogenizer can be tapered from smaller to larger sizes or vice
versa. Thus, the
target 50 can be an increasing taper waveguide as shown in FIG. 7i, or a
decreasing taper
waveguide as shown in FIG. 7j. In this way, the homogenizer allows changes in
the
shape of the output of the illumination. For example in projection displays in
which an
image source 60 is placed in the output stream of the target 50 through a
condenser lens
80 and a projection lens 90 to create a projected image 70, the ideal output
of the
homogenizer will be rectangular with a ratio of width-to-height of 4-to-3 or
16-to-9, or
other ratios, depending on the fonnat of the displays. Neverth.eless, the
angle of the
illuminating radiation in both directions should be similar and such that a
circular
projection lens 90 can be used with the optical system efficiently.
[0053] While the target and the source are intimately associated with the
collecting and condensing system of the present invention, in accordance with
an
exemplary embodiment of the present invention, the system relates to the use
of two
reflectors of slightly different size and/or shape arranged so as to share a
single focal
12
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
point (i.e., the second focal point 26 of the first reflector 20 and the
second focal point 36
of the second reflector 30 are located substantially identical positions).
[0054] Continuing witll the description of the collecting an condensing
systenl, in
the arrangements shown in FIGS. 5-6, the first reflector 20 and the second
reflector 30 are
positioned in an opposed, facing relation with respect to each other so as to
be concave
toward each other. Optical symmetry is achieved in the arrangements of FIGS. 5-
6 by
arranging the first reflector 20 and the second reflector 30 so that their
respective optical
axes 22 and 32 are collinear and so that the reflective surface of the first
reflector 30 is an
opposed, facing relation with the substantially coiTesponding reflecting
surface of the
second reflector 30 optimizing magnification.
[0055] In FIGS. 5-6, tluee rays a, b, and c are drawn to illustrate the
function of
the reflectors in view of different possible paths for the electromagnetic
radiation
produced by the source 10. In FIGS. 5-6, the rays a, b, and c are in
substantially the same
positions as in FIG. 4 in order to illustrate the effectiveness of the present
optical system
in reducing abeiTation. Each of the rays a, b, and c emitted from the light
source 10
impinges the first reflector 20 at a different point, each point having a
different distance
from source 10. But each of the rays a, b, and c is also focused onto the
target 50 from a
con=esponding position of the second reflector 30, thus produces a
substantially 1:1
magnification or slight magnification for the three rays.
[0056] As before, ray a has the shortest distance from the source 10 and the
first
reflector 20 and consequentially produces a larger divergence in coinparison
to rays b and
c. Witli the optical system of the present invention, radiation fiom the light
source is
focused from the first focal point 24 of the first reflector 20 to the second
point 26. As a
result, the distances traveled by the radiation from the source 10, even those
emitted at
high angles such as ray a, is relatively larger than the corresponding
distance in the
system of FIG. 4 that uses paraboloid reflectors. The larger distance reduces
the amount
of aberration because the distances of rays a, b, and c are now relatively
more uniform.
[0057] To reduce aberration even fiirther, FIG. 6 shows an exemplary
embodiment of the present invention in which the first and second reflectors
20' and 30'
have greater eccentricity (i.e., the first and second reflectors are more
circular). As a
result of the greater curvature of the first and second reflectors 20' and 30'
in this
exemplary embodiment, the distance between the first focus 24' of the first
reflector 20'
and the first focus 34' of the second reflector 30' is reduced. At the same
time, the
13
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
greater cuivature of the reflectors 20' and 30' increased the distance between
the first
reflector 20' and its first focus 24' along ray a. Likewise, the corresponding
distance
between the second reflector 30' and its first focus 34' along ray a is
increased. As a
result, the distances traveled between the radiation source 10' and the first
reflector 20'
(as well as the total distance between the source 10' and the target 50') for
the rays a, b,
and c in FIG. 6 are relatively more uniforin in coniparison to the embodiment
of FIG. 5.
This feature allows the system to produce less aberration between the light
source and the
target, even with electromagnetic energy traveling near the optical axis 22',
such as
energy traveling paths similar to ray a.
[0058] By coinparing the patll of the same ray c in FIGS. 5 and 6, it can be
seen
that the embodinzent of FIG. 6 uses reflectors 20' and 30' covering a greater
portion of an
ellipsoid in order to collect the saine angle of output radiation from the
source 10.
However, it can be seen that reflectors 20' and 30' in FIG. 6 have
approximately the same
diameter as reflectors 20' and 30' in FIG. 5.
[0059] As shown in FIGS. 5 and 6, the collecting and condensing system of the
present invention may incorporate the use of a retro-reflector 40, which, in
the illustrated
embodiment, is a spherical retro-reflector. The retro-reflector 40 is
positioned to capture
electromagnetic radiation emitted by the source 10 that would not otherwise
impinge on
the first ellipsoidal reflector 20. More particularly, the spherical retro-
reflector 40 is
constructed and arranged so that radiation einitted by the source 10 in a
direction away
from the first reflector 20 is reflected by the retro-reflector 40 back
through the first focal
point 24 of the first reflector 20 and thereafter toward the first reflector
20. This
additional radiation reflected by the first reflector 20 is added to the
radiation that
impinges the first reflector 20 directly from the source 10 to thereby
increase the intensity
of the radiation reflected toward the second reflector 30. Gonsequently, the
intensity of
the radiation at the first focal point 34 of the second reflector 30 is also
increased.
[0060] If a filament lamp is employed as the source 10, the retro-reflector
cannot
be oriented so that it focuses radiation back tlirough the first focal point
24 of the first
reflector 20, because the retro-reflected radiation would be blocked by the
opaque
filaments located at the first focal point 24. In this case, the position of
the retro-reflector
40 should be adjusted so that the retro-reflected radiation passes near but
not precisely
through the first focal point 24.
14
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
[0061] It should be appreciated that several different retro-reflectors 40 are
lalown
and may be employed in the present invention. For example, as an alternative
to a
spherical retro-reflector 40, the retro-reflecting ftulction can be perforined
by a two-
dimensional corner cube array (not shown) with unit elements sized on the
order of the
are size of the source 10 or smaller. Employing a two-dimensional corner cube
array
eliminates the need for precisely positioning a retro-reflector and will
produce a tighter
focus at the arc of the source 10.
[0062] It should be ftirther appreciated that, although the above einbodiments
descrilie conflgUratlons with first and second reflectors having an
ellipsoidal or a
parabolic shape, it is lalown and anticipated by the present invention that
first and second
reflector 20 and 30 may be approximated using shapes that are slightly
different from an
ideal geometric ellipsoid or paraboloid shape. For exainple, the first and
second reflector
20 and 30 may have altered ellipsoidal or parabolic shapes to coinpensate of
various
paraineters, such as bulb envelops, filters, etc. In this case, the deviation
in the shape of
the generally ellipsoidal or parabolic reflectors 20 and 30 can be small and
the final
oUtput may be slightly different from the optimum. Deviations in the shape of
the
reflectors can also be introduced to reduce cost of the reflectors 20 and 30,
or increase
perfoi7nance for particular lamp types and arc shapes. For example, it is
1u1own and
anticipated by the present invention that reflectors 20 and 30 can be
approximated by
toroidal reflectors (having two perpendicular and tu-iequal radii of
curvature) or spherical
reflectors, which can be manufactured at a lower relative cost. If non-
ellipsoidal
reflectors are used, the output coupling may not be optimum, but the reduced
expense for
the first and second reflectors 20 and 30 may be sufficient to justify the
loss througli the
inefficient coupling.
[0063] In standard DPR system, the two reflectors are symmetric with respect
to
each other. The image of the arc is not generally distorted or become fuzzy as
in elliptical
or parabolic reflector systems. The coupling efficiency is higlier especially
for small
entendue application. A characteristic of a standard DPR system is that the
light entering
the tapered light pipe or target 50 can be as high as ::L90 as shown in FIG.
8b, which is a
glazing angle in which the Fresnel reflection loss is high. Tunling now to
FIG. 8a, in
accordance with an exemplary embodiment of the present invention, a dual
paraboloid
reflector (DPR) system 100 comprises a first reflector 20 and a second
reflector 30, wllich
are asymmetric wit11 respect to each other. Alternatively, the first and
second reflectors
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
20, 30 can be replaced witli a single reflector having two sections of
different shape
arid/or size. The asyinmetric relationship of these two reflectors 20, 30
results in slight
magnification, wllich introduces image distortion. But, the light or radiation
inputted to
the TLP 50 has smaller angles of incidences than standard DPR system, thereby
maximizing net output coupling efficiency.
[0064] In accordance with an exeniplary embodiment of the present invention,
the
DPR system 200 of FIG. 9a comprises the electromagnetic source 10, a first 20,
a second
reflector 30 and the TLP 50, wherein the two reflectors 20, 30 are asyimnetric
such that
that slight magnification is applied. Alternatively, the first and second
reflectors 20, 30
can be replaced with a single reflector having two sections of different shape
and/or size.
In accordance with an aspect of the present invention, the second reflector 30
is larger
than the first reflector 20 and has longer focal length tlian the second
reflector 30. The
sligllt magnification introduces a small amount of image distoi-tion but the
input light to
the TLP 50 has smaller angles of incidence, thereby reducing the Fresnel loss.
[0065] The first reflector 20 is preferably a parabolic reflector having
optical axis
22 (or axis of focus 22) and the second reflector 30 is preferably a parabolic
reflector
having optical axis 32 (or axis of focus 32). The two axes 22, 32 are not
coincident. The
resultant light incidence onto the TLP 50 from the second reflector 30 is
shown in FIG.
9b. When the output section or second reflector 30 is trimined to the same
focal plane 22
as the input section or first reflector 20, the axis of focus 32 of the output
section or
second reflector 30 will lie outside the DPR system 200, as shown in FIG. 9b.
This
advantageously result in incidence angle being smaller tllan 90 , which
reduces the
effect of Fresnel reflection.
[0066] It is appreciated that the DPR 200 or dual elliptical reflector (DER)
system
300 can be designed using ray tracing. The gain by reducing the Fresnel
reflection in the
presen' , invention is partly lost by sligllt distortion of the image due to
asymmetry of the
DPR or DER system 200. As a result, the present system optimizes the tradeoff
between
the Fresnel reflection loss and the iunage aberration or distortion that
maximizes the net
output coupling efficiency.
[0067] In accordance with an exemplary embodiment of the present invention,
the
DER system 200 of FIG. 10 comprises the electromagnetic source 10, a first 20,
a second
reflector 30 and the TLP 50, wherein the two ellipsoidal reflectors 20, 30 are
asymmetric
such that that slight magnification is applied. In accordance with an aspect
of the present
16
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
invention, the second reflector 30 is larger than the first reflector 20 and
has longer focal
length than the second reflector 30. The slight magnification introduces a
small amount
of image distortion but the input light to the TLP 50 has smaller angles of
incidence,
thereby reducing the Fresnel loss.
[0068] The first reflector 20 is preferably an elliptical reflector having
optical axis
22 (or axis of focus 22) and the second reflector 30 is preferably an
elliptical reflector
having optical axis 32 (or axis of focus 32). The two axes 22, 32 are not
coincident. The
resultant light incidence onto the TLP 50 from the second reflector 30 similar
to those in
FIG. 9b for the DPR system 200. When the output section or second reflector 30
is
trunined to the sanie focal plane 22 as the input section or first reflector
20, the axis of
focus 32 of the output section or second reflector 30 will lie outside the DER
system 300
(similar to those shown in FIG. 9b for the DPR system 200). This
advantageously result
in incidence angle being smaller than ---L90 , which reduces the effect of
Fresnel reflection.
[0069] Several examples of the present invention are now provided. These
exainples are meant to illustrate some possible implementations of the present
invention
but are not intended to limit the scope of the present invention.
EXAMPLES
[0070] A first pair of exemplary optical systems in accordance with the
present
invention uses a low wattage lamp, in the order of 100 Watts, as the ligllts
source. In a
reflection system in accordance with the embodiment of FIG. 5, each of the
first and
second reflectors has a diameter of 2.5 inches, and the separation between the
source and
target (i.e., the distance between the foci) is about 5 inches. In contrast, a
low wattage
reflection system of greater eccentricity in accordance with the einbodiment
illustrated in
FIG. 6 uses first and second reflectors of similar size, each having diameter
of
approximately 2.5 inches, but has a distance between the source and target of
approximately 2 inches.
[0071] In higher wattage applications, the optical system is relatively larger
to
provide desirable collection of the higher electromagnetic energy levels and
to
accommodate the potentially larger lamps. For example, when using a hig11
wattage
lamp, on the order of 5,000 Watts with the configuration of FIG. 5, each of
the primary
reflectors has a diameter of 20 inches, and the separation between the source
and the
target is about 40 inches. As before, the embodiment of FIG. 6 uses primary
reflectors of
17
CA 02608368 2007-11-13
WO 2007/005624 PCT/US2006/025608
similar size but results in a reduced distance between the source and target.
For instance,
an exemplary high wattage optical system in accordance with einbodiment of the
FIG. 6,
also uses first and second reflectors witll a diameter of approximately 20
inches but has a
distance between of the source and target of 16 inches.
[0072] The invention, having been described, it will be apparent to those
slcilled in
the art that the saine may be varied in many ways without departing from the
spirit and
scope of the invention. Any and all such modifications are intended to be
included within
the scope of the following clainls.
18
