Tricolor lighting system

A tricolor lighting system uses first and second dichroic filters or mirrors to separate light into different colors, primarily red, green, and blue. The light is directed into input ends of respective first, second, and third light guides for a desired end use at a remote location. Various embodiments use either paraboloid or ellipsoidal reflective surfaces associated with the light source and in selected embodiments, the first and second mirrors are disposed in a crossed relation to provide a compact system.

BACKGROUND OF THE INVENTION 
This invention pertains to the art of projection lighting systems and 
particularly to systems that use a high brightness light source and 
transmit light to a remote location with light guides. The invention is 
particularly applicable to a lighting system such as a tricolor video 
system that splits the light into three colors, namely, red, green and 
blue. Although these systems are increasing in popularity they still 
suffer from optical design problems. Therefore, the invention will be 
described with particular reference to a lighting system that is 
particularly relevant to tricolor video system. However, it will be 
appreciated that the invention has broader applications and may be 
advantageously employed in related lighting environments and applications. 
The current development of tricolor video systems suffer from various 
drawbacks. For example, light emitted by the source is inefficiently used. 
One solution to obtaining uniformity has been to use only the central 
portion of a projected light beam and disregard the outer portions of the 
beam. Obviously, this is counterproductive to an overall goal of 
maximizing light output from the system. 
Still another problem is the overall size of the lighting system and the 
need to miniaturize the optical arrangement without any resultant loss in 
performance. It is oftentimes difficult to meet size limitations while 
simultaneously addressing efficiency in the lighting arrangement. Use of a 
high brightness light source, for example on the order of 50,000 lumens 
per square centimeter or greater, as disclosed in commonly assigned U.S. 
Pat. No. 5,341,445 is one factor for consideration in a compact unit. How 
the light is subsequently handled, i.e. after being emitted from the light 
source, is just as important in providing effective propagation of the 
light in a compact system. 
Parity or uniformity between the three colors is another problem with 
systems of this type. Ultimately, the final image relies on all three 
color portions so that it is necessary to achieve as uniform a 
distribution as possible between the three colors. 
In addition to splitting the light into component colors, the system design 
must address averaging, or providing a substantially equal intensity of 
light, across the entire cross-section of the light guides or fibers. It 
is desired that the intensity of light in each "blue" fiber be equal to 
the light intensity in every other "blue" fiber, and that the intensity of 
light in each "red" fiber be equal to the light intensity of every other 
"red" fiber, etc. 
Accordingly, the need exists to improve on tricolor systems in a manner 
that overcomes the above-referenced problems and others and provides a 
simple, economical, and compact arrangement. 
SUMMARY OF THE INVENTION 
According to the present invention, a lighting system includes a high 
brightness light source located at a focus of a reflective surface, such 
as a paraboloid, ellipsoid, or other curvilinear reflective surface. First 
and second dichroic filters or mirrors receive the light directed from the 
reflective surface and transmit a first portion of the light received on 
the dichroic mirror and reflect any remaining light that is not 
transmitted. First, second, and third light guides are located to receive 
the respective portions of the light after it has been separated by the 
dichroic mirrors. 
According to a more limited aspect of the invention, the first and second 
dichroic mirrors are disposed in a crossed relationship for purposes of 
compactness. 
According to another aspect of the invention, light is directed into 
individual light guides through the use of lenses, prisms, or bent light 
rods. 
A principal advantage of the invention is the effective use of all of the 
light emitted from the source. 
A further advantage of the invention resides in the various manners of 
achieving a compact arrangement. 
Another advantage is the uniform distribution of light into three colors. 
Yet another advantage is found in averaging the light distribution among 
the individual light guides or fibers. 
Still other advantages and benefits of the invention will become apparent 
to those skilled in the art upon a reading and understanding of the 
following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings wherein the showings are for the purposes of 
illustrating the preferred embodiments of the invention only and not for 
purposes of limiting same, the FIGURES show a tricolor lighting system 
that uses a high brightness light source in conjunction with at least a 
pair of dichroic filters or mirrors to separate the light into separate 
colors for transmission through a light guide assembly. 
More particularly, and with initial reference to FIG. 1, a light source 10 
is preferably located at a first focus of reflective surface 12. In this 
embodiment the reflective surface is preferably a paraboloid reflective 
surface so that location of the light source at its focus results in 
substantially parallel, or collimated, light rays being directed from the 
paraboloid reflective surface. The reflective surface is mounted in an 
external housing 14 that has an opening 16 that receives the light from 
the reflective surface. Directional arrows 18 are representative of the 
collimated light rays exiting the housing through the opening 16. 
The light rays are directed to a first dichroic reflector or mirror 20. As 
shown, the dichroic mirror 20 is disposed at forty-five degrees relative 
to the travel path of the light rays 18. The first dichroic mirror 
transmits red light through the mirror and reflects the remaining light 
therefrom. Thus, directional arrows 22 represent the red light that is 
transmitted through the first dichroic mirror. Similarly, directional 
arrows 24 represent the remaining light reflected off the first dichroic 
mirror. 
Since the mirror is oriented at forty-five degrees, light rays 24 travel in 
a direction generally perpendicular to the path of light rays 18. 
Moreover, the light rays 24 are directed toward a second dichroic mirror 
30. This second dichroic mirror is disposed in parallel relation to the 
first dichroic mirror and is preferably a blue reflecting mirror. That is, 
light rays 32 represent blue light reflected by the second dichroic 
mirror. The remaining light represented by light rays 34 is transmitted 
through the second dichroic mirror and directed to a third mirror 40. 
The third mirror is preferably a reflective mirror that reflects green 
light as represented by light rays 42. Alternatively, the third mirror 
could also be a dichroic mirror, however, a simple reflective mirror is 
all that is necessary since only green light 34 remains from passage 
through the second dichroic mirror. The third mirror is also angularly 
disposed at forty-five degrees so that light impinging thereon is 
reflected or turned through ninety degrees. By disposing the first, 
second, and third mirrors in spaced parallel fashion, the separate color 
portions of light are eventually propagated in the same direction. 
Accordingly, once the light has passed through the first and second 
dichroic mirrors 20, 30, it has been divided into three separate colors 
represented by light rays 22 (red), light rays 32 (blue), and light rays 
34 or 42 (green). 
By disposing the three mirrors 20, 30, 40 in spaced, parallel relation, the 
resultant rays 22, 32, 42 of the three distinct colors are all propagated 
in parallel arrangement toward polygonal shaped optical coupling members 
44, 46, 48. Moreover, substantially all of the light that exits the 
housing 14 is efficiently transferred to the three mirrors so that little, 
if any, light is wasted. The similar treatment of the three colors also 
results in greater uniformity. 
Input ends 54, 56, 58 of the three coupling members 44, 46, 48, 
respectively, abut against a triple lens block 60. The lens block includes 
individual positive surfaced lens 64, 66, 68 adapted to receive the 
collimated light transmitted through the first dichroic mirror 20, 
reflected from the second dichroic mirror 30, and reflected from the third 
dichroic mirror 40, respectively. The positive curvature or convex lenses 
focus the collimated light rays 22, 32, 42 into the input ends 54, 56, 58 
of the individual optical coupling members. The cross-sectional shape of 
the optical coupling members is preferably selected from the group of 
rectangle, square, triangle and hexagon since these shapes provide for 
multiple internal reflections within the coupling members achieve some 
mixing of the light and reducing the differences in intensity and color 
from the outer edge to the center of the light output entering the optical 
fibers. More particular details of the coupling members are described in 
commonly assigned U.S. Pat. No. 5,341,445, the disclosure of which is 
incorporated herein by reference. 
The total internal reflection is represented by crossed light rays 74 
within the individual coupling members. Output ends 84, 86, 88 of the 
individual optical coupling members are preferably connected to a module 
fiber funnel 90 which is comprised of three groups of fibers (one for each 
color) so that light is transmitted from the coupling members, to the 
multiple fibers of the bundle 90, and to a remote location. 
As shown, the housing 14 containing the light source 10 and reflector 12 
(not shown to scale) is easily affixed to a second housing 92 that 
contains the three dichroic mirrors, the lens block 60, the individual 
coupling members 44, 46, 48, and the input ends of the individual fibers 
of bundle 90. This modular arrangement assures that the collimated light 
18 from the reflective surface 12 is accurately aligned with the first 
dichroic mirror 20. The subassembly of the three mirrors, lens block, 
coupling members, and individual light guides can be preassembled to 
minimize final assembly steps and provide for modular replacement, if 
necessary. 
A more compact tricolor lighting system is shown in FIG. 2. When possible, 
the reference numerals are increased by a factor of one hundred, i.e. the 
light source in the FIG. 1 embodiment is referenced as 10 and the light 
source in the FIG. 2 embodiment is referenced as 110 for purposes of 
consistency. The light source 110 is disposed at the focus of a paraboloid 
reflective surface 112. If desired, the light source and reflective 
surface are mounted in a common housing 114. An open end 116 of the 
reflective surface allows the collimated light rays 118 to impinge on a 
first dichroic mirror 120 disposed at forty-five degrees to the direction 
of the light rays 118. 
By way of example, the first dichroic mirror is a red reflecting mirror so 
that light rays 122 reflected thereby extend generally perpendicular to 
the path of light rays 118. Any light rays transmitted through the first 
dichroic mirror are absent of red color. 
A second dichroic mirror 130 preferably reflects blue light. It is disposed 
at an angle of one hundred thirty-five degrees relative to the path of the 
light rays 118 reflected from the surface 112. Stated another way, the 
first and second dichroic mirrors 120, 130 are disposed in a crossed, 
generally perpendicular arrangement. This crossed arrangement results in a 
much more compact lighting system, an overall goal of the subject 
invention. Light rays 132 reflected from the second dichroic mirror 130 
are blue in color and directed generally perpendicular to light rays 118 
whereas the remaining spectrum of the light that impinges on the second 
mirror is transmitted therethrough. 
Light rays 134 represent the light that has not been reflected by either 
the first or second dichroic mirror 120, 130. That is, this light is 
transmitted through both mirrors and since the red and blue spectrums have 
been reflected, light rays 134 are green. 
A cold mirror 140 is provided to direct light rays 122 toward a first 
coupling member 144. Likewise, cold mirror 140' is intended to direct the 
light rays 132 toward a second coupling member 146. The cold mirrors 140, 
140' are oriented at forty-five degree angles to the paths of the light 
reflected by the first and second dichroic mirrors, respectively, so that 
the light is redirected in a direction parallel to light rays 134 and 
toward the coupling members 144, 146. 
The third coupling member 148 receives the light rays 134. Before reaching 
the respective input ends 154, 156, 158 of the first, second, and third 
coupling members 144, 146, 148, the light rays pass through one of the 
focusing lenses 164, 166, 168, respectively. The lenses thus receive 
substantially collimated light and focus the red, blue, and green portions 
of the light into the input ends of the individual coupling members. 
Thereafter, the light is internally reflected through the coupling members 
and after it exits the couplers, it enters input ends of fiber bundles 
where the light is then conveyed to a remote location (not shown). 
The compact arrangement of FIG. 2 is achieved, in part, because of the 
crossed relation of the first and second dichroic mirrors. The mirrors 
also preferably extend from the edges of the reflective surface, as do the 
cold mirrors 140, 140', so that all of the light emitted from the source 
is effectively used in the lighting system and eventually is transmitted 
through the light guides. 
Turning now to FIG. 3, the structural arrangement and operation of the 
individual components is closely related to that in FIG. 2. Therefore, 
like numerals will be used to reference like elements and new numerals are 
used to reference new elements. Essentially, the FIG. 3 embodiment is 
substantially similar to that described above with respect to FIG. 2 
except that the cold mirrors 140, 140' have been removed, the paraboloid 
reflective surface replaced by an ellipsoidal reflective surface, and a 
pair of bent light rods or pipes used for more compact, efficient 
collection of the red and blue light reflected from the first and second 
dichroic mirrors 120, 130, respectively. 
More specifically, reflective surface 102 has an elliptical configuration 
and the light source 110 is located at a first focus thereof. The first 
and second dichroic mirrors are disposed in crossed relation, and the 
vertex defined by the crossed mirrors is interposed between the first and 
second foci of the ellipsoidal reflective surface. That is, the second 
focus 104 is preferably located rightwardly of the vertex as shown. The 
vertex is positioned along the major axis defined between the focus 104 
and the light source 110. 
Virtual foci 104' and 104" are located at inlet ends of coupling members 
144, 146, respectively. Thus, the red light reflected by the first 
dichroic mirror 120 is generally directed toward the virtual focus 104' of 
the bent coupling member 144. The coupling member 144 has a ninety degree 
bend so that once the light enters fiber bundle 194, it is propagated in 
generally the same direction as any light that enters second and third 
fiber bundles 196, 198. The same principles apply with regard to the 
virtual focus 104". That is, the blue light reflected by the second 
dichroic mirror 130 enters the coupling member 146. It is then bent or 
directed through a ninety degree turn so that it enters and continues to 
propagate rightwardly, as shown, through the second fiber bundle 196. 
Focus 104 receives light that has been transmitted through both of the 
dichroic mirrors and enters the third coupling member 148 positioned 
adjacent the input end of the third fiber bundle 198. The ellipsoidal 
configuration of reflective surface 102 converges light rays 118' on the 
second focus 104. Continued travel of the light is then achieved through 
internal reflection through the fiber bundle 198. 
A comparison of FIGS. 2 and 3 also illustrates the elimination of the 
lenses from the FIG. 3 embodiment. Eliminating the lenses improves overall 
system brightness since a greater amount of lumens are provided in a 
smaller area. Moreover, the overall arrangement of FIG. 3 is even more 
compact than the tricolor lighting system of FIG. 2. 
A fourth preferred embodiment in FIG. 4, not shown to scale, also employs 
many of the same structural elements as in the FIG. 3 embodiment. 
Accordingly, like numerals will again refer to like elements while new 
numerals will refer to new elements. The light source 110 is preferably 
located at a first focus of the ellipsoidal reflective surface 102. Light 
rays 118' are thereby directed toward a second focus at the input end of 
the third light fiber bundle 198. The optical coupling members 144, 146, 
148 of the FIG. 3 embodiment are eliminated and forty-five degree prisms 
employed in their place. The prisms 206, 208 are disposed so that the 
faces 210, 212, which are oriented ninety degrees relative to one another, 
are located adjacent the input end of the fiber bundle and along the 
crossed dichroic mirrors, respectively. The reflective or angular face 214 
of the prisms redirect the light through ninety degrees for total internal 
reflection of the light as it enters the respective first and second light 
guides. Light that would otherwise be directed out of the optical system 
is totally internally reflected in the prisms and remains in the desired 
optical path. 
An important aspect in using the prisms is that the surfaces 210, 212 must 
include a low index of refraction material. For example, air or magnesium 
fluoride are preferred low index of refraction materials that contribute 
to the operation of the optical system when the prisms are used. The three 
light fiber bundles or light guides 194, 196, and 198 can then be disposed 
adjacent one another and oriented in the same direction so that the light 
is generally propagated in three separate colors and in the same 
direction. 
Moreover, a commercially available cubical prism is available from Nitto 
Optical Co., Ltd. of Tokyo Japan. It includes a pair of dichroic mirrors 
contained therein and oriented in the desired crossed relation. It has 
been determined that by polishing the surfaces of the cubical prism that 
are perpendicular to both of the dichroic mirrors (since the commercially 
available prism is not so polished), a greater percentage of the light 
reflected therein is eventually transmitted from the cubical prism. 
Moreover, the polishing of the vertical and horizontal surfaces of the 
prism achieves improved light averaging and even distribution of light 
intensity. 
As shown in FIG. 5, still another preferred arrangement is disclosed using 
an ellipsoidal reflective surface. A light source 310 is disposed at one 
focus of ellipsoidal reflective surface 312. The light rays 318 generally 
converge toward the second focus. A vertex of crossed first and second 
dichroic mirrors 320, 330 is located between the first and second foci of 
the reflective surface. Before reaching the focus or vertex, however, the 
light rays pass through a negative surface lens, i.e., one having a pair 
of concave surfaces, to collimate the light prior to it reaching the 
dichroic mirrors. The mirrors are again disposed at forty-five degree 
angles relative to the propagated direction of the light exiting the lens 
360. Thus, the first dichroic mirror 320 reflects the red light into the 
first light fiber bundle or light guide 344. Likewise, the second dichroic 
mirror 330 reflects the blue light into the second light fiber bundle or 
light guide 346. The remaining light transmitted through the dichroic 
mirrors reaches the third light fiber bundle or light guide 348. 
In order to assure total internal reflection of the light reflected by or 
transmitted through the dichroic mirrors, positive surface lens 364, 366, 
368 are associated with the input ends of each of the light guides to 
obtain the highest number of lumens per square centimeter possible, i.e., 
reduce the size of the light spot. In this manner, the light is propagated 
through the light guides via total internal reflection and may be directed 
to a remote location. 
As shown in FIG. 6, yet another preferred arrangement of a tricolor 
lighting system is illustrated wherein the light source 410 is disposed at 
the first optical focal point of an ellipsoidally shaped reflector member 
412. The light rays 418 again generally converge toward the second focus. 
A beam splitting mirror 420 is disposed in the path of the light rays 418 
before the second focus and at approximately a 45 degree angle relative to 
the longitudinal axis A of the reflector member 412. Beam splitting mirror 
420 has a coating which allows such mirror 420 to filter either the long 
or the short wavelength ends of the visible spectrum with the balance of 
the light rays 418a being transmitted therethrough. Beam splitting mirrors 
of this type are commercially available from Melles Griot, Inc. and are 
identified in their product manual "Optics Guide 5" as product numbers 03 
BTF 007 and 03 BTF 023 shown at page 13-4 of this product manual. The 
light rays 418' that are reflected by the beam splitting mirror 420 are 
directed to the input end of a first optical coupler member 422 which can 
be provided by a polygonally shaped coupler member as described in U.S. 
Pat. No. 5,341,445 issued on Aug. 23, 1994 to Davenport et al and assigned 
to the same assignee as the present invention. For instance, the reflected 
light rays 418 could be those light rays that are from the blue region of 
the visible spectrum thereby resulting in the separation of blue light 
along the path formed by the first coupler member 422. 
A compound condensing lens 424 is disposed in the path of the balance of 
the light rays 418a. Compound collecting lens 424 is composed of two 
aspheric lenses 426 and 428 which are disposed in a back-to-back relation 
to one another. The compound collecting lens 424 is effective for 
collecting the balance of the light rays 418a and focussing them into a 
spot which is located at a distance equal to the distance between the 
first focus and the lens. In this manner, the light pattern or spot at the 
second focus is the same size and therefore the same brightness as the 
light spot at the first focus. Disposed in the path of the balance of the 
light rays 418a is a second beam splitting mirror 430. The second beam 
splitting mirror 430 is also disposed at a 45 degree angle relative to 
axis A and also acts as a filter having a coating thereon. The second beam 
splitting mirror 430 is effective for reflecting the light rays 418a' at 
the center part of the spectrum and transmitting the remaining end of the 
visible spectrum therethrough; such remaining light rays being identified 
as 418c. Light rays 418b' which are reflected by the second beam splitting 
mirror 430 can be for instance, the green region of the visible spectrum 
and such light rays can be focussed to a light spot which is input to a 
second optical coupler member 432. Light rays 418c which are transmitted 
through mirror 430 can be the red region of the visible spectrum and can 
be focussed into a light spot which is input to a third optical coupler 
member 434. 
In order to bring the light of all three colors out at the same side of the 
centralized light source 410, a 90 degree optical turning device 436 can 
be utilized in conjunction with the red light rays 418c. Of course, it 
should be understood that the order of blue, green and red can be reversed 
by reversing the first and second beam splitting mirrors and such a 
modification would be within the scope of the present invention. It would 
also be possible to include a bundle of optical fibers to transmit the 
various colored light outputs to different locations and such bundles of 
optical fibers can be connected at input or output ends of the optical 
coupler members 422, 432, and 434. 
The invention has been described with reference to the preferred 
embodiments. Obviously, modifications and alterations will occur to others 
upon a reading and understanding of this specification. It is intended to 
include all such modifications and alterations insofar as they come within 
the scope of the appended claims or the equivalents thereof.