WO2013062930A1

WO2013062930A1 - Tilted dichroic polarized color combiner

Info

Publication number: WO2013062930A1
Application number: PCT/US2012/061411
Authority: WO
Inventors: Craig R. Schardt; Stephan J. WILLETT; Zhisheng Yun; Yarn Chee Poon; Xiaohui Cheng; Andrew J. Ouderkirk
Original assignee: 3M Innovative Properties Company
Priority date: 2011-10-24
Filing date: 2012-10-23
Publication date: 2013-05-02
Also published as: TW201327014A

Abstract

The disclosure generally relates to color combiners, and in particular color combiners useful in small size format projectors such as pocket projectors. The disclosed color combiners include a tilted dichroic plate having at least two reflectors configured with light collection optics to combine at least two colors of light into a combined polarized light.

Description

_,

TILTED DICHROIC POLARIZED COLOR COMBINER

RELATED APPLICATIONS

This application is related to the following U.S. Patent Applications, which are incorporated by reference: U.S. Patent Application Serial No. 61/385237 entitled "Tilted Dichroic Color Combiner I" (Attorney Docket No. 66530US002); U.S. Patent Application Serial No. 61/385241 entitled "Tilted Dichroic Color Combiner Π" (Attorney Docket No.

66791US002); and U.S. Patent Application Serial No. 61/385248 entitled "Tilted Dichroic Color Combiner III" (Attorney Docket No. 66792US002); all of which were filed on September 22, 2010; and also to U.S. Patent Application entitled TILTED DICHROIC POLARIZING

BEAMSPLITTER (Attorney Docket No. 67923US002), filed on an even date herewith.

Background

Projection systems used for projecting an image on a screen can use multiple color light sources, such as light emitting diodes (LEDs), with different colors to generate the illumination light. Several optical elements are disposed between the LEDs and the image display unit to combine and transfer the light from the LEDs to the image display unit. The image display unit can use various methods to impose an image on the light. For example, the image display unit may use polarization, as with transmissive or reflective liquid crystal displays.

Still other projection systems used for projecting an image on a screen can use white light configured to imagewise reflect from a digital micro-mirror (DMM) array, such as the array used

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in Texas Instruments' Digital Light Processor (DLP ) displays. In the DLP display, individual mirrors within the digital micro-mirror array represent individual pixels of the projected image. A display pixel is illuminated when the corresponding mirror is tilted so that incident light is directed into the projected optical path. A rotating color wheel placed within the optical path is timed to the reflection of light from the digital micro-mirror array, so that the reflected white light is filtered to project the color corresponding to the pixel. The digital micro-mirror array is then switched to the next desired pixel color, and the process is continued at such a rapid rate that the entire projected display appears to be continuously illuminated. The digital micro-mirror projection system requires fewer pixelated array components, which can result in a smaller size projector. Image brightness is an important parameter of a projection system. The brightness of color light sources and the efficiencies of collecting, combining, homogenizing and delivering the light to the image display unit all affect brightness. As the size of modern projector systems decreases, there is a need to maintain an adequate level of output brightness while at the same time keeping heat produced by the color light sources at a low level that can be dissipated in a small projector system. There is a need for a light combining system that combines multiple color lights with increased efficiency to provide a light output with an adequate level of brightness without excessive power consumption by light sources.

Such electronic projectors often include a device for optically homogenizing a beam of light in order to improve brightness and color uniformity for light projected on a screen. Two common devices are an integrating tunnel and a fly's eye array (FEA) homogenizer. Fly's eye homogenizers can be very compact, and for this reason is a commonly used device. Integrating tunnels can be more efficient at homogenization, but a hollow tunnel generally requires a length that is often 5 times the height or width, whichever is greater. Solid tunnels often are longer than hollow tunnels, due to the effects of refraction.

Pico and pocket projectors have limited available space for efficient color combiners, light integrators, and/or homogenizers. As a result, efficient and uniform light output from the optical devices used in these projectors (such as color combiners and polarization converters) can require compact and efficient optical designs.

Summary

The disclosure generally relates to color combiners, and in particular color combiners useful in small size format projectors such as pocket projectors. The disclosed color combiners include a tilted dichroic plate having at least two reflectors configured with light collection optics to combine at least two colors of light. In one aspect, the present disclosure provides a color combiner that includes: a light collection optic having a light input surface and an optical axis; a first and a second light source disposed to inject a first and a second color light into the light input surface, at least one of the first and second light sources displaced from the optical axis; and a first reflective polarizer disposed facing the light collection optic opposite the light input surface, capable of splitting both the first and the second color light into a transmitted light having a first polarization direction and a reflected light having a second polarization direction. The color combiner further includes a half-wave retarder disposed to convert the transmitted light having the first polarization direction into a converted light having the second polarization direction; a second reflective polarizer disposed to reflect the converted light having the second polarization direction parallel to the reflected light having the second polarization direction; and a quarter-wave retarder disposed to intercept the reflected light having the second polarization direction and the converted light having the second polarization direction. The color combiner still further provides a tilted dichroic plate disposed adjacent the quarter- wave retarder and opposite the first reflective polarizer and the second reflective polarizer, the tilted dichroic plate including: a first dichroic reflector capable of reflecting the first color light and transmitting other color light; and a second reflector capable of reflecting the second color light, wherein the first dichroic reflector and the second reflector are each tilted such that the first and the second color light are both reflected in an output direction through the first reflective polarizer and the second reflective polarizer, the first and the second color light forming a combined color light beam having the first polarization direction. In yet another aspect, the present disclosure provides an image projector that includes the color combiner, a spatial light modulator disposed to impart an image to the polarized first, second, and third color light, and projection optics.

In another aspect, the present disclosure provides a color combiner that includes: a light collimation optic having a light input surface and an optical axis; a first, a second, and a third light source, at least two of the first, the second, and the third light source displaced from the optical axis and disposed to inject a first, a second, and a third color light into the light input surface; and a first polarizing beam splitter (PBS) disposed facing the light collimation optics opposite the light input surface, capable of splitting the first, the second, and the third color light into a transmitted light having the first polarization direction and a reflected light having the second polarization direction. The color combiner further includes a half-wave retarder disposed to convert the transmitted light having the first polarization direction into a converted light having the second polarization direction; a second PBS disposed to reflect the converted light having the second polarization direction parallel to the reflected light having the second polarization direction; and a quarter-wave retarder disposed to intercept the reflected light having the second polarization direction and the converted light having the second polarization direction. The color combiner still further includes a tilted dichroic plate disposed adjacent the quarter-wave retarder and opposite the first and the second PBS, the tilted dichroic plate, including: a first dichroic reflector capable of reflecting the first color light and transmitting the second and the third color light; a second dichroic reflector capable of reflecting the second color light and transmitting the third color light; and a third reflector capable of reflecting the third color light, wherein the first dichroic reflector, the second dichroic reflector, and the third reflector are each tilted such that the first, the second, and the third color light are each reflected in an output direction through the first PBS and the second PBS, the first, the second, and the third color light forming a combined color light beam having the first polarization direction. In yet another aspect, the present disclosure provides an image projector that includes the color combiner, a spatial light modulator disposed to impart an image to the polarized first, second, and third color light, and projection optics.

In yet another aspect, the present disclosure provides a color combiner that includes: a light collection optic having a light input surface and an optical axis; a first and a second light source disposed to inject a first and a second color light into the light input surface, at least one of the first and second light sources displaced from the optical axis; and a first reflective polarizer disposed facing the light collection optic opposite the light input surface, capable of splitting both the first and the second color light into a transmitted light having a first polarization direction and a reflected light having a second polarization direction. The color combiner further includes a quarter-wave retarder disposed to intercept the reflected light having the second polarization direction; and a first tilted dichroic plate disposed adjacent the quarter- wave retarder and opposite the first reflective polarizer, the first tilted dichroic plate including: a first dichroic reflector capable of reflecting the first color light and transmitting other color light; and a second dichroic reflector capable of reflecting the second color light. The color combiner still further includes a second tilted dichroic plate disposed to intercept the transmitted light having the first polarization direction, the second tilted dichroic plate including: a third dichroic reflector capable of reflecting the first color light and transmitting other color light; and a fourth dichroic reflector capable of reflecting the second color light, wherein the first and second dichroic reflectors are tilted such that the first and the second color light are both reflected in an output direction through the first reflective polarizer, and the third and fourth dichroic reflectors are tilted such that the first and the second color light are both reflected in the output direction, the first and the second color light forming a combined color light beam having the first polarization direction. In yet another aspect, the present disclosure provides an image projector that includes the color combiner, a spatial light modulator disposed to impart an image to the polarized first, second, and third color light, and projection optics. The above summary is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The figures and the detailed description below more particularly exemplify illustrative embodiments.

Brief Description of the Drawings

Throughout the specification reference is made to the appended drawings, where like reference numerals designate like elements, and wherein:

FIGS. 1A-1B show a cross-section schematic of a tilted dichroic polarized color combiner;

FIGS. 1C-1D show a cross-section schematic of a tilted dichroic polarized color combiner;

FIGS. IE- IF show a cross-section schematic of a tilted dichroic polarized color combiner;

FIGS. 2A-2B show a cross-section schematic of a tilted dichroic polarized color combiner;

FIGS. 2C-2D show a cross-section schematic of a tilted dichroic polarized color combiner;

FIG 3 is a perspective view of a polarizing beam splitter (PBS);

FIG 4 is a perspective view of the alignment of a quarter- wave retarder to a PBS; and

FIG. 5 shows a schematic diagram of an image projector.

The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

Detailed Description

This disclosure generally relates to image projectors, in particular image projectors having an improved uniformity of light by combining the light using a tilted dichroic reflector plate. In one particular embodiment, the tilted dichroic reflector plate includes a plurality of dichroic filters laminated together, wherein each of the dichroic filters can be tilted at an angle to a normal to the dichroic reflector plate, and the combined light is a polarized light. The optical elements described herein can be configured as color combiners that receive different wavelength spectrum lights and produce a combined light output that includes the different wavelength spectrum lights. In one aspect, the received light inputs are unpolarized, and the combined light output is polarized. In some embodiments, the combined light has the same etendue as each of the received lights. The combined light can be a polychromatic combined light that comprises more than one wavelength spectrum of light. The combined light can be a time sequenced output of each of the received lights. In one aspect, each of the different wavelength spectra of light corresponds to a different color light (for example red, green and blue), and the combined light output is white light, or a time sequenced red, green and blue light. For purposes of the description provided herein, "color light" and "wavelength spectrum light" are both intended to mean light having a wavelength spectrum range which may be correlated to a specific color if visible to the human eye. The more general term "wavelength spectrum light" refers to both visible and other wavelength spectrums of light including, for example, infrared light.

Also for the purposes of the description provided herein, the term "aligned to a desired polarization state" is intended to associate the alignment of the pass axis of an optical element to a desired polarization state of light that passes through the optical element, that is, a desired polarization state such as s-polarization, p-polarization, right-circular polarization, left-circular polarization , or the like. In one embodiment described herein with reference to the Figures, an optical element such as a polarizer aligned to the first polarization state means the orientation of the polarizer that passes the p-polarization state of light, and reflects or absorbs the second polarization state (in this case the s-polarization state) of light. It is to be understood that the polarizer can instead be aligned to pass the s-polarization state of light, and reflect or absorb the p-polarization state of light, if desired.

Also for the purposes of the description provided herein, the term "facing" refers to one element disposed so that a perpendicular line from the surface of the element follows an optical path that is also perpendicular to the other element. One element facing another element can include the elements disposed adjacent each other. One element facing another element further includes the elements separated by optics so that a light ray perpendicular to one element is also perpendicular to the other element.

In one particular embodiment, a color combiner is described that includes at least two light emitting diodes (LEDs), each with a different color. The light emitted from the two LEDs is collimated into beams that substantially overlap, and the light from the two LEDs is combined and converted to a single polarization state. The combined single polarization state light has a lower etendue and higher brightness than the light emitted by the two LEDs.

The LEDs may be used to illuminate projectors. Since LEDs emit light over an area with a near Lambertian angular distribution, the brightness of a projector is limited by the etendue of the source and the projection system. One method for reducing the etendue of the LED light source is to use dichroic reflectors to make two or more colors of LEDs spatially overlap, such that they appear to be emitting from the same region. Ordinarily, color combiners use the dichroic reflectors at an angle of about 45 degrees. This causes a strong reflective band shift, and limits the useful spectra and angular range of the dichroic reflector. In one particular embodiment, the present disclosure describes an article that combines different color LEDs using dichroic reflectors that are at near normal angles to the incident light beam.

In one aspect, the disclosure provides a compact method of efficiently combining the output from different color light sources. This can be particularly useful for producing illuminators for compact projection systems that are etendue limited. For example, a linear array of red, green, and blue LEDs, where the output of each LED is partially collimated by a set of primary optics, is incident on a polarization converter that includes a tilted reflector plate assembly. The tilted reflector plate assembly contains dichroic reflector plates that reflect the red, green, and blue light at different angles. The reflected light is then output as a polarized collimated combined color light beam.

The configuration of the 3 LEDs can be expanded to other colors, including yellow and infrared light, as understood by one of skill in the art. The LEDs can be arranged in various patterns, including linear arrays and triangular arrays. The light sources may include lasers combined with LEDs, and may be also be based on an all laser system. The LEDs may consist of a set emitting at least primary colors on short wavelength range of red, green, and blue, and a second set emitting the primary colors on the long wavelength range of red, green, and blue. Further, the aperture at which point the light is mixed may incorporate a Fly Eye Array (FEA) to provide further color integration. This may consist of a one or two dimensional array of lenses, with at least one dimension having 2 to about 20 lenses, as described elsewhere.

LCoS-based portable projection systems are becoming common due to the availability of low cost and high resolution LCoS panels. A list of elements in an LED-illuminated LCoS projector may include LED light source or sources, optional color combiner, optional pre- polarizing system, relay optics, PBS, LCoS panel, and projection lens unit. For LCoS-based projection systems, the efficiency and contrast of the projector is directly linked to the degree of polarization of light entering the PBS. For at least this reason, a pre-polarizing system that either utilizes a reflection/recycling optic or a polarization-conversion optical element, is often required.

Polarization conversion schemes utilizing polarizing beam splitters and half-wave retarders are one of the most efficient ways to provide polarized light into the PBS. One challenge with polarization-converted light is that it may suffer from spatial nonuniformity, leading to artifacts in the displayed image. Therefore, in systems with polarization converters, a homogenization system can be desirable, as described elsewhere.

In one particular embodiment, an illuminator for an image projector includes a light source in which emitted unpolarized light is directed into a polarization converter. The polarization converter separates the light into two paths, one for each polarization state. The path length for each of the two polarization states are approximately equal, and the polarized beams of light can then pass through to a monolithic FEA integrator. The monolithic FEA integrator can cause the light beams to diverge, and the light beams are then directed for further processing, for example, by using a spatial light modulator to impart an image to the light beams, and projection optics to display the image on a screen.

In some cases, optical projectors use a non-polarized light source, such as a light emitting diode (LED) or a discharge light, a polarization selecting element, a first polarization spatial modulator, and a second polarization selecting element. Since the first polarization selecting element rejects 50% of the light emitted from the non-polarized light source, polarization- selective projectors can often have a lower efficiency than non-polarized devices.

One technique of increasing the efficiency of polarization-selective projectors is to add a polarization converter between the light source and the first polarization selecting element.

Generally, there are two ways of designing a polarization converter used in the art. The first is to partially collimate the light emitting from the light source, pass the partially collimated beam of light through an array of lenses, and position an array of polarization converters at each focal point. The polarization converter typically has a polarizing beam splitter having polarization selective tilted film (for example MacNeille polarizer, a wire grid polarizer, or birefringent optical film polarizer), where the reflected polarization is reflected by a tilted reflector such that the reflected beam propagates parallel to the beam that is transmitted by the tilted polarization selective film. Either one or the other beams of polarized light is passed through half-wave retarders, such that both beams have the same polarization state.

Another technique of converting the unpolarized light beam to a light beam having a single polarization state is to pass the entire beam of light through a tilted polarization selector, and the split beams are conditioned by reflectors and half-wave retarders such that a single polarization state is emitted. Illuminating a polarization selective spatial light modulator directly with a polarization converter can result in illuminance and color non-uniformity.

In one particular embodiment, a polarization converter can incorporate a fly's eye array (FEA) to homogenize the light in a projection system. The output side of the polarization converter includes a monolithic FEA to homogenize the light. The input and output side of the monolithic FEA include the same number of lenses, with each lens on the output side centered approximately at the focal point of a matching lens at the input side. The lenses can be cylindrical, bi-convex, spherical, or aspherical; however, in many cases spherical lenses can be preferred. The fly's eye integrator and polarization converter can significantly improve the illuminance and color uniformity of the projector, as described elsewhere.

FIGS. 1A-1F show a cross-section schematic of a tilted dichroic polarized color combiner 100 according to one aspect of the disclosure. In FIGS. 1A-1F, the tilted dichroic polarized color combiner 100 includes a light collection optics 105 and a tilted dichroic polarization converter 106. Light collection optics 105 includes a first lens element 110 and a second lens element 120, a light input surface 114, and an optical axis 102 perpendicular to the light input surface 114. A first light source 140, a second light source 150, and an optional third light source 160 are each disposed on a light injection surface 104 that faces the light input surface 114. At least two of the first, the second, and the optional third light sources 140, 150, 160, are displaced from the optical axis 102, and one of the first, the second, and the optional third light sources 140, 150, 160 can be positioned on the optical axis. Each of the first, the second, and the optional third light sources 140, 150, 160, are disposed to inject a first color light 141, a second color light 151, and an optional third color light 161, respectively, into the light input surface 114, as described elsewhere.

In one particular embodiment, light collection optics 105 can be a light collimator that serves to collimate the light emitted from the first, second, and optional third light sources 140, 150, 160. Light collection optics 105 can include a one lens light collimator (not shown), a two lens light collimator (shown), a diffractive optical element (not shown), or a combination thereof. The two lens light collimator has first lens element 1 10 that includes a first convex surface 112 disposed opposite the light input surface 114. Second lens element 120 includes a second surface 122 facing the first convex surface 112, and a third convex surface 124 opposite the second surface 122. Second surface 122 can be selected from a convex surface, a planar surface, and a concave surface.

Each of the first color light 141, second color light 151, and optional third color light 161 become a collimated first color light 141c, a collimated second color light 151c, and a collimated optional third color light 161c upon exiting the light collection optics 105. Since each of the first light source 140, second light source 150, and optional third light source 160 are disposed on light injection surface 104 at differing separations from the optical axis 102 of light collection optics 105, each of the collimated first, second, and optional third color light 141c, 151c, 161c are collimated at slightly different angles relative to the optical axis, as they enter the tilted dichroic polarization converter 106.

In one particular embodiment, tilted dichroic polarization converter 106 includes a first reflective polarizer 172, a second reflective polarizer 182, and a half- wave retarder 192 disposed between the first reflective polarizer 172 and the second reflective polarizer 182. In one particular embodiment, first reflective polarizer 172 can be disposed on the diagonal surface of an optional prismatic first polarizing beam splitter (PBS) 170, and second reflective polarizer 182 can be disposed on the diagonal surface of an optional prismatic second PBS 180. Each of the first and second reflective polarizers 172, 182 are aligned to pass a first polarization direction 190, herein described as being p-polarization.

The tilted dichroic polarization converter 106 further includes a quarter- wave retarder 194, and a tilted dichroic plate 130. The described components of the tilted dichroic polarization converter 106 collectively convert each of the collimated (and unpolarized) first, second, and optional third color light 141c, 151c, 161c into a collimated combined polarized light, where each of the different collimated light colors are collimated in the same direction, as described with reference to the Figures.

In some cases, first and second reflective polarizers 172, 182 can be Cartesian reflective polarizers aligned to a first polarization direction 190, such that a first polarization direction light (for example, p-polarized light) incident on the reflective polarizer 172, 182, is transmitted through the reflective polarizer, and a second orthogonal polarization direction (for example, s- polarized light) light is reflected from the reflective polarizer, as described elsewhere. In some cases, first and second reflective polarizers 172, 182 can be disposed on the diagonal faces of a polarizing beam splitter (as shown in the Figures), or alternatively, they can be retained as pellicles (not shown) in the optical path. Quarter- wave retarder 194 can aligned at a 45 degree angle to the first polarization direction 190, such that reflected s-polarized light can be rotated to p-polarized light, as described with reference to FIG. 3 and FIG. 4.

In one particular embodiment, tilted dichroic polarized color combiner 100 further includes a tilted dichroic plate 130 disposed facing the quarter-wave retarder 194 and opposite the first and second reflective polarizers 172, 182. The tilted dichroic plate 130 includes a first dichroic reflector 132 capable of reflecting the first color light 141 and transmitting other colors of light. The tilted dichroic plate 130 further includes a second dichroic reflector 134 capable of reflecting the second color light 151 and transmitting other colors of light. The tilted dichroic plate 130 still further includes an optional third dichroic reflector 136 that is capable of reflecting the optional third color light 161. In some cases, for example when only a first and a second light source 140, 150 are included (that is, optional third light source 160 is omitted), second dichroic reflector can be instead a generic reflector such as a broadband mirror, since there is no need to transmit other wavelengths (that is, colors) of light. The tilted dichroic plate 130 is fabricated such that each of the first, second, and optional third dichroic reflectors 132, 134, 136, are tilted such that incident collimated light that is reflected from each of the dichroic reflectors as reflected collimated light, is travelling in a parallel direction, as described elsewhere.

Turning to FIG. 1A, the path of the first color light 141 from first light source 140 can be traced through tilted dichroic polarized color combiner 100. First color light 141 includes a first central light ray 142 travelling in the first light propagation direction, and a cone of rays within first input light collimation angle ΘΠ, the boundaries of which are represented by first boundary light rays 144, 146. The first central light ray 142 is injected from first light source 140 into light input surface 1 14 in a direction generally parallel to the optical axis 102, passes through first lens element 1 10, second lens element 120, and emerges from light collection optics 105 as first central light ray 142 that is central to first collimated color light 141c. Each of the first boundary light rays 144, 146 are injected into the light input surface 114 in a direction generally at the first input light collimation angle ΘΠ to the optical axis 102, passes through first lens element 110, second lens element 120, and emerges from light collection optics 105 as first boundary light rays 144, 146 that form boundaries to first collimated color light 141c. As can be seen from FIG. 1A, the light collection optics 105 serve to collimate the first color light 141 passing from the first light source 140 to emerge as first collimated color light 141c, the paths of which continue in FIG. IB as indicated by the indicia A, B, C.

Each of the first central light ray 142 and the first boundary light rays 144, 146, enter first PBS 170 of tilted dichroic polarization converter 106 and intercept first reflective polarizer 172. The paths of each of the first central light ray 142 and the first boundary light rays 144, 146, are schematically represented in FIGS. 1A-1B, but for brevity only the path of the first central light ray 142 will be described herein. It is to be understood that the description of each of the first boundary light rays 144, 146, can be readily determined from each of their respective paths and the description of the path of first central light ray 142 within FIGS. 1A-1B.

First central light ray 142 is split into transmitted first p-polarized central light ray 142p and reflected first s-polarized central light ray 142s. Reflected first s-polarized central light ray 142s exits first PBS 170, passes through quarter- wave retarder 194 where it changes to circularly polarized light 141cr. Circularly polarized light 141cr reflects from first dichroic reflector 132 changing the direction of circular polarization, and passes through quarter- wave retarder 194 where it changes to first output p-polarized central light ray 143p, is transmitted through first reflective polarizer 172, and exits first PBS 170 in a direction perpendicular to the optical axis 102.

Transmitted first p-polarized central light ray 142p exits first PBS 170, passes through half-wave retarder 192 changing to converted first s-polarized central light ray 142s2, enters second PBS 180, reflects from second reflective polarizer 182, exits first PBS 180 and passes through quarter- wave retarder 194 where it changes to circularly polarized light 141cr.

Circularly polarized light 141cr reflects from first dichroic reflector 132 changing the direction of circular polarization, and passes through quarter- wave retarder 194 where it changes to first converted output p-polarized central light ray 143p2. First converted output p-polarized central light ray 143p2 enters second PBS 180, is transmitted through second reflective polarizer 182, and exits second PBS 180 in a direction perpendicular to the optical axis 102, and parallel to first output p-polarized central light ray 143p.

Turning to FIG. 1C, the path of the second color light 151 from second light source 150 can be traced through tilted dichroic polarized color combiner 100. Second color light 151 includes a second central light ray 152 travelling in the second light propagation direction, and a cone of rays within second input light collimation angle 92i, the boundaries of which are represented by second boundary light rays 154, 156. The second central light ray 152 is injected from second light source 150 into light input surface 114 in a direction generally parallel to the optical axis 102, passes through first lens element 1 10, second lens element 120, and emerges from light collection optics 105 as second central light ray 152 that is central to second collimated color light 151c. Each of the second boundary light rays 154, 156 are injected into the light input surface 1 14 in a direction generally at the second input light collimation angle 92i to the optical axis 102, passes through first lens element 110, second lens element 120, and emerges from light collection optics 105 as second boundary light rays 154, 156 that form boundaries to second collimated color light 151c. As can be seen from FIG. 1C, the light collection optics 105 serve to collimate the second color light 151 passing from the second light source 150 to emerge as second collimated color light 151c, the paths of which continue in FIG. ID as indicated by the indicia A', B', C

Each of the second central light ray 152 and the second boundary light rays 154, 156, enter first PBS 170 of tilted dichroic polarization converter 106 and intercept first reflective polarizer 172. The paths of each of the second central light ray 152 and the second boundary light rays 154, 156, are schematically represented in FIGS. 1C-1D, but for brevity only the path of the second central light ray 152 will be described herein. It is to be understood that the description of each of the second boundary light rays 154, 156, can be readily determined from each of their respective paths and the description of the path of second central light ray 152 within FIGS. 1C-1D.

Second central light ray 152 is split into transmitted second p-polarized central light ray

152p and reflected second s-polarized central light ray 152s. Reflected second s-polarized central light ray 152s exits first PBS 170, passes through quarter- wave retarder 194 where it changes to circularly polarized light 151cr. Circularly polarized light 151cr reflects from second dichroic reflector 134 changing the direction of circular polarization, and passes through quarter-wave retarder 194 where it changes to second output p-polarized central light ray 153p, is transmitted through first reflective polarizer 172, and exits first PBS 170 in a direction perpendicular to the optical axis 102.

Transmitted second p-polarized central light ray 152p exits first PBS 170, passes through half-wave retarder 192 changing to converted second s-polarized central light ray 152s2, enters second PBS 180, reflects from second reflective polarizer 182, exits second PBS 180 and passes through quarter- wave retarder 194 where it changes to circularly polarized light 151cr.

Circularly polarized light 151cr reflects from second dichroic reflector 134 changing the direction of circular polarization, and passes through quarter- wave retarder 194 where it changes to second converted output p-polarized central light ray 153p2. Second converted output p- polarized central light ray 153p2 enters second PBS 180, is transmitted through second reflective polarizer 182, and exits second PBS 180 in a direction perpendicular to the optical axis 102, and parallel to second output p-polarized central light ray 153p.

Turning to FIG. IE, the path of the optional third color light 161 from optional third light source 160 can be traced through tilted dichroic polarized color combiner 100. In one particular embodiment shown in FIG. IE, optional third light source 160 can be disposed on the optical axis; however, it can also be disposed near the optical axis, as described elsewhere. Third color light 161 includes a third central light ray 162 travelling in the third light propagation direction, and a cone of rays within third input light collimation angle 93i, the boundaries of which are represented by third boundary light rays 164, 166. The third central light ray 162 is injected from third light source 160 into light input surface 1 14 in a direction generally parallel to the optical axis 102, passes through first lens element 1 10, second lens element 120, and emerges from light collection optics 105 as third central light ray 162 that is central to third collimated color light 161c. Each of the third boundary light rays 164, 166 are injected into the light input surface 1 14 in a direction generally at the third input light collimation angle 93i to the optical axis 102, passes through first lens element 110, second lens element 120, and emerges from light collection optics 105 as third boundary light rays 164, 166 that form boundaries to third collimated color light 161c. As can be seen from FIG. IE, the light collection optics 105 serve to collimate the third color light 161 passing from the third light source 160 to emerge as third collimated color light 161c, the paths of which continue in FIG. IF as indicated by the indicia A", B", C".

Each of the third central light ray 162 and the third boundary light rays 164, 166, enter first PBS 170 of tilted dichroic polarization converter 106 and intercept first reflective polarizer 172. The paths of each of the third central light ray 162 and the third boundary light rays 164, 166, are schematically represented in FIGS. 1E-1F, but for brevity only the path of the third central light ray 162 will be described herein. It is to be understood that the description of each of the third boundary light rays 164, 166, can be readily determined from each of their respective paths and the description of the path of third central light ray 162 within FIGS. 1E-1F.

Third central light ray 162 is split into transmitted third p-polarized central light ray 162p and reflected third s-polarized central light ray 162s. Reflected third s-polarized central light ray 162s exits first PBS 170, passes through quarter- wave retarder 194 where it changes to circularly polarized light 161cr. Circularly polarized light 161cr reflects from third dichroic reflector 136 changing the direction of circular polarization, and passes through quarter- wave retarder 194 where it changes to third output p-polarized central light ray 163p, is transmitted through first reflective polarizer 172, and exits first PBS 170 in a direction perpendicular to the optical axis 102.

Transmitted third p-polarized central light ray 162p exits first PBS 170, passes through half-wave retarder 192 changing to converted third s-polarized central light ray 162s2, enters second PBS 180, reflects from second reflective polarizer 182, exits second PBS 180 and passes through quarter- wave retarder 194 where it changes to circularly polarized light 161cr.

Circularly polarized light 161cr reflects from third dichroic reflector 136 changing the direction of circular polarization, and passes through quarter-wave retarder 194 where it changes to third converted output p-polarized central light ray 163p2. Third converted output p-polarized central light ray 163p2 enters second PBS 180, is transmitted through second reflective polarizer 182, and exits second PBS 180 in a direction perpendicular to the optical axis 102, and parallel to third output p-polarized central light ray 163p.

In one particular embodiment, each of the first, the second, and the third input collimation angles ΘΠ, 92i, 93i can be the same, and injection optics (not shown) associated with each of the first, the second, and the optional third input light sources 140, 150, 160, can restrict these input collimation angles to angles between about 10 degrees and about 80 degrees, or between about 10 degrees to about 70 degrees, or between about 10 degrees to about 60 degrees, or between about 10 degrees to about 50 degrees, or between about 10 degrees to about 40 degrees, or between about 10 degrees to about 30 degrees or less. In one particular embodiment, each of the input collimation angles ranges from about 60 to about 70 degrees.

FIGS. 2A-2B shows a cross-section schematic of a tilted dichroic polarized color combiner 101, according to one aspect of the disclosure. Each of the elements 102-194' shown in FIGS. 2A-2B correspond to like-numbered elements 102-194 shown in FIGS. 1A-1F, which have been described previously. For example, optical axis 102 of FIGS. 2A-2B corresponds to optical axis 102 of FIGS. 1A-1F, and so on. In this particular embodiment, the tilted dichroic plate 130 shown in FIGS. 1A-1F has been subdivided into three tilted dichroic plate sections 130', 130", 130"', and the quarter-wave retarder 194 has also been subdivided into two sections. It is to be understood that the function of the tilted dichroic plate 130 and quarter-wave retarder 194 of FIGS. 1A-1F can be retained by subdividing (for example, as shown in FIGS. 2A-2B) as desired, since each section functions in the same manner. In some cases, subdivided tilted dichroic plates can be preferred, since the total thickness of the plate can be reduced by decreasing the size of the plate.

In FIGS. 2A-2B, the tilted dichroic polarized color combiner 101 includes a light collection optics 105 and a tilted dichroic polarization converter 106'. Light collection optics 105 includes a first lens element 1 10 and a second lens element 120, a light input surface 1 14, and an optical axis 102 perpendicular to the light input surface 1 14. A first light source 140, a second light source 150, and an optional third light source 160 are each disposed on a light injection surface 104 that faces the light input surface 1 14. At least two of the first, the second, and the optional third light sources 140, 150, 160, are displaced from the optical axis 102, and one of the first, the second, and the optional third light sources 140, 150, 160 can be positioned on the optical axis. Each of the first, the second, and the optional third light sources 140, 150, 160, are disposed to inject light into the light input surface 114 in a manner similar to that described with reference to FIGS. 1A-1F. For brevity, only the path of a second color light 151 will be described with reference to FIGS. 2A-2B; however, it is to be understood that a first color light 141, and an optional third color light 161 will follow similar paths through tilted dichroic polarized color combiner 101, as described elsewhere.

In one particular embodiment, tilted dichroic polarization converter 106' includes a first reflective polarizer 172, a second reflective polarizer 182, and a half- wave retarder 192 disposed between the first reflective polarizer 172 and the second reflective polarizer 182. In one particular embodiment, first reflective polarizer 172 can be disposed on the diagonal surface of an optional prismatic first polarizing beam splitter (PBS) 170, and second reflective polarizer 182 can be disposed on the diagonal surface of an optional prismatic second PBS 180. Each of the first and second reflective polarizers 172, 182 are aligned to pass a first polarization direction 190, herein described as being p-polarization.

The tilted dichroic polarization converter 106' further includes a quarter- wave retarder 194', a first tilted dichroic plate 130', a second tilted dichroic plate 130", and a third tilted dichroic plate 130" '. Each of the first, second, and third tilted dichroic plates 130', 130", 130' ", include the same material composition and relative tilt of the dielectric mirror surfaces as described elsewhere, for example with reference to tilted dichroic plate 130 of FIGS. 1A-1F. The described components of the tilted dichroic polarization converter 106' collectively convert each of the collimated (and unpolarized) first, second, and optional third color light 141c, 151c, 161c into a collimated combined polarized light, where each of the different collimated light colors are collimated in the same direction, as described with reference to the Figures.

In one particular embodiment, tilted dichroic polarized color combiner 101 further includes the first tilted dichroic plate 130' disposed facing the quarter-wave retarder 194' and opposite the first polarizer 172, and the second tilted dichroic plate 130" and the third tilted dichroic plate 130" ' disposed facing the quarter-wave retarder 194' and opposite the second polarizer 182. The first, the second, and the third tilted dichroic plates 130', 130", 130" ', each include a first dichroic reflector 132', 132", 132"', respectively, capable of reflecting the first color light 141 and transmitting other colors of light. The first, the second, and the third tilted dichroic plates 130', 130", 130" ', each further includes a second dichroic reflector 134', 134", 134' ", respectively, capable of reflecting the second color light 151 and transmitting other colors of light. The first, the second, and the third tilted dichroic plates 130', 130", 130" ', each still further includes an optional third dichroic reflector 136', 136", 136" ', respectively, capable of reflecting the third color light 161 and transmitting other colors of light. In some cases, for example when only a first and a second light source 140, 150 are included (that is, optional third light source 160 is omitted), second dichroic reflector can be instead a generic reflector such as a broadband mirror, since there is no need to transmit other wavelengths (that is, colors) of light. The first, the second, and the third tilted dichroic plates 130', 130", 130" ' are fabricated such that each of the first, second, and optional third dichroic reflectors 132, 134, 136, are tilted such that incident collimated light that is reflected from each of the dichroic reflectors as reflected collimated light, is travelling in a parallel direction, as described elsewhere. Turning to FIG. 2A, the path of the second color light 151 from second light source 150 can be traced through tilted dichroic polarized color combiner 101. Second color light 151 includes a second central light ray 152 travelling in the second light propagation direction, and a cone of rays within second input light collimation angle 92i, the boundaries of which are represented by second boundary light rays 154, 156. The second central light ray 152 is injected from second light source 150 into light input surface 114 in a direction generally parallel to the optical axis 102, passes through first lens element 1 10, second lens element 120, and emerges from light collection optics 105 as second central light ray 152 that is central to second collimated color light 151c. Each of the second boundary light rays 154, 156 are injected into the light input surface 1 14 in a direction generally at the second input light collimation angle 92i to the optical axis 102, passes through first lens element 110, second lens element 120, and emerges from light collection optics 105 as second boundary light rays 154, 156 that form boundaries to second collimated color light 151c. As can be seen from FIG. 2A, the light collection optics 105 serve to collimate the second color light 151 passing from the second light source 150 to emerge as second collimated color light 151c, the paths of which continue in FIG. 2B as indicated by the indicia D, E, F.

Each of the second central light ray 152 and the second boundary light rays 154, 156, enter first PBS 170 of tilted dichroic polarization converter 106' and intercept first reflective polarizer 172. The paths of each of the second central light ray 152 and the second boundary light rays 154, 156, are schematically represented in FIGS. 2A-2B, but for brevity only the path of the second central light ray 152 will be described herein. It is to be understood that the description of each of the second boundary light rays 154, 156, can be readily determined from each of their respective paths and the description of the path of second central light ray 152 within FIGS. 2A-2B.

152p and reflected second s-polarized central light ray 152s. Reflected second s-polarized central light ray 152s exits first PBS 170, passes through quarter- wave retarder 194' where it changes to circularly polarized light 151cr. Circularly polarized light 151cr enters first tilted dichroic plate 130', reflects from second dichroic reflector 134' changing the direction of circular polarization, and passes through quarter-wave retarder 194' where it changes to second output p-polarized central light ray 153p, is transmitted through first reflective polarizer 172, and exits first PBS 170 in a direction perpendicular to the optical axis 102. Transmitted second p-polarized central light ray 152p exits first PBS 170, passes through half-wave retarder 192 changing to converted second s-polarized central light ray 152s2, enters second PBS 180, reflects from second reflective polarizer 182, exits first PBS 180 and passes through quarter-wave retarder 194' where it changes to circularly polarized light 151cr.

Circularly polarized light 151cr enters third tilted dichroic plate 130" ', reflects from second dichroic reflector 134" ' changing the direction of circular polarization, and passes through quarter-wave retarder 194' where it changes to second converted output p-polarized central light ray 153p2. Second converted output p-polarized central light ray 153p2 enters second PBS 180, is transmitted through second reflective polarizer 182, and exits second PBS 180 in a direction perpendicular to the optical axis 102, and parallel to second output p-polarized central light ray 153p.

FIGS. 2C-2D shows a cross-section schematic of a tilted dichroic polarized color combiner 103, according to one aspect of the disclosure. Each of the elements 102-194' shown in FIGS. 2C-2D correspond to like-numbered elements 102-194 shown in FIGS. 1A-1F, which have been described previously. For example, optical axis 102 of FIGS. 2C-2D corresponds to optical axis 102 of FIGS. 1A-1F, and so on. In this particular embodiment, the tilted dichroic plate 130 shown in FIGS. 1A-1F has been subdivided into two tilted dichroic plate sections 130a', 130b', the quarter- wave retarder 194 is positioned only adjacent one of the tilted dichroic plate sections, the half-wave retarder has been removed, and the tilted dichroic plate sections are positioned at an angle relative to each other, as described elsewhere.

In FIGS. 2C-2D, the tilted dichroic polarized color combiner 103 includes a light collection optics 105 and a tilted dichroic polarization converter 106". Light collection optics 105 includes a first lens element 1 10 and a second lens element 120, a light input surface 1 14, and an optical axis 102 perpendicular to the light input surface 1 14. A first light source 140, a second light source 150, and an optional third light source 160 are each disposed on a light injection surface 104 that faces the light input surface 1 14. At least two of the first, the second, and the optional third light sources 140, 150, 160, are displaced from the optical axis 102, and one of the first, the second, and the optional third light sources 140, 150, 160 can be positioned on the optical axis. Each of the first, the second, and the optional third light sources 140, 150, 160, are disposed to inject light into the light input surface 1 14 in a manner similar to that described with reference to FIGS. 1A-1F. For brevity, only the path of a second color light 151 will be described with reference to FIGS. 2A-2B; however, it is to be understood that a first color light 141, and an optional third color light 161 will follow similar paths through tilted dichroic polarized color combiner 101, as described elsewhere.

In one particular embodiment, tilted dichroic polarization converter 106" includes a reflective polarizer 172 disposed to intercept light entering the converter. In one particular embodiment, reflective polarizer 172 can be disposed on the diagonal surface of an optional prismatic first polarizing beam splitter (PBS) 170, and a second prism 183 can be disposed adjacent first PBS 170, to support second tilted dichroic plate 130b', as described elsewhere. The reflective polarizer 172 is aligned to pass a first polarization direction 190, herein described as being p-polarization.

The tilted dichroic polarization converter 106" further includes a quarter-wave retarder

194, a first tilted dichroic plate 130', and a second tilted dichroic plate 130"". Each of the first and second tilted dichroic plates 130a', 130"", include the same material composition and relative tilt of the dielectric mirror surfaces as described elsewhere, for example with reference to tilted dichroic plate 130 of FIGS. 1A-1F. The described components of the tilted dichroic polarization converter 106" collectively convert each of the collimated (and unpolarized) first, second, and optional third color light 141c, 151c, 161c into a collimated combined polarized light, where each of the different collimated light colors are collimated in the same direction, as described with reference to the Figures.

In some cases, reflective polarizer 172 can be a Cartesian reflective polarizer aligned to a first polarization direction 190, such that a first polarization direction light (for example, p- polarized light) incident on the reflective polarizer 172 is transmitted through the reflective polarizer, and a second orthogonal polarization direction (for example, s-polarized light) light is reflected from the reflective polarizer, as described elsewhere. In some cases, reflective polarizer 172 can be disposed on the diagonal face of a polarizing beam splitter (as shown in the Figures), or alternatively, they can be retained as pellicles (not shown) in the optical path.

Quarter- wave retarder 194 can aligned at a 45 degree angle to the first polarization direction 190, such that reflected s-polarized light can be rotated to p-polarized light, as described with reference to FIG. 3 and FIG. 4.

In one particular embodiment, tilted dichroic polarized color combiner 103 further includes the first tilted dichroic plate 130' disposed facing the quarter-wave retarder 194' and opposite the reflective polarizer 172. The second tilted dichroic plate 130"" is disposed at an angle relative to the reflective polarizer 172, such that light transmitted through the reflective polarizer 172 reflects such that it exits tilted dichroic polarized color combiner 103 at an angle perpendicular to the optical axis 102 and parallel to all other light exiting the combiner. In some cases, the second tilted dichroic plate 130" " can be disposed adjacent a diagonal face 184 of prism 183 as shown in the Figure.

The first and second tilted dichroic plates 130', 130" " each include a first dichroic reflector 132', 132" ", respectively, capable of reflecting the first color light 141 and transmitting other colors of light. The first and second tilted dichroic plates 130', 130" ", each further includes a second dichroic reflector 134', 134" ", respectively, capable of reflecting the second color light 151 and transmitting other colors of light. The first and second tilted dichroic plates 130', 130" ", each still further includes an optional third dichroic reflector 136', 136" ", respectively, capable of reflecting the third color light 161 and transmitting other colors of light. In some cases, for example when only a first and a second light source 140, 150 are included (that is, optional third light source 160 is omitted), second dichroic reflector can be instead a generic reflector such as a broadband mirror, since there is no need to transmit other wavelengths (that is, colors) of light. The first and second tilted dichroic plates 130', 130" " are fabricated such that each of the first, second, and optional third dichroic reflectors 132', 132" ", 134', 134"", 136', 136"", are tilted such that incident collimated light that is reflected from each of the dichroic reflectors as reflected collimated light, is travelling in a parallel direction, as described elsewhere.

Turning to FIG. 2C, the path of the second color light 151 from second light source 150 can be traced through tilted dichroic polarized color combiner 103. Second color light 151 includes a second central light ray 152 travelling in the second light propagation direction, and a cone of rays within second input light collimation angle 92i, the boundaries of which are represented by second boundary light rays 154, 156. The second central light ray 152 is injected from second light source 150 into light input surface 114 in a direction generally parallel to the optical axis 102, passes through first lens element 1 10, second lens element 120, and emerges from light collection optics 105 as second central light ray 152 that is central to second collimated color light 151c. Each of the second boundary light rays 154, 156 are injected into the light input surface 1 14 in a direction generally at the second input light collimation angle 92i to the optical axis 102, passes through first lens element 110, second lens element 120, and emerges from light collection optics 105 as second boundary light rays 154, 156 that form boundaries to second collimated color light 151c. As can be seen from FIG. 2C, the light collection optics 105 serve to collimate the second color light 151 passing from the second light source 150 to emerge as second collimated color light 151c, the paths of which continue in FIG. 2D as indicated by the indicia G, H, I.

Each of the second central light ray 152 and the second boundary light rays 154, 156, enter first PBS 170 of tilted dichroic polarization converter 106" and intercept reflective polarizer 172. The paths of each of the second central light ray 152 and the second boundary light rays 154, 156, are schematically represented in FIGS. 2C-2D, but for brevity only the path of the second central light ray 152 will be described herein. It is to be understood that the description of each of the second boundary light rays 154, 156, can be readily determined from each of their respective paths and the description of the path of second central light ray 152 within FIGS. 2C-2D.

Second central light ray 152 is split into transmitted second p-polarized central light ray 152p and reflected second s-polarized central light ray 152s. Reflected second s-polarized central light ray 152s exits first PBS 170, passes through quarter- wave retarder 194' where it changes to circularly polarized light 151cr. Circularly polarized light 151cr enters first tilted dichroic plate 130', reflects from second dichroic reflector 134' changing the direction of circular polarization, and passes through quarter-wave retarder 194' where it changes to second output p-polarized central light ray 153p, is transmitted through reflective polarizer 172, and exits first PBS 170 in a direction perpendicular to the optical axis 102.

Transmitted second p-polarized central light ray 152p exits first PBS 170, passes through diagonal surface 184 of prism 183, enters second tilted dichroic plate 130" ", reflects from second dichroic reflector 134" ", and passes through prism 183 in a direction perpendicular to the optical axis 102, and parallel to second output p-polarized central light ray 153p.

FIG 3 is a perspective view of a PBS. PBS 200 includes a reflective polarizer 290 disposed between the diagonal faces of prisms 210 and 220. Prism 210 includes two end faces 275, 285, and a first and second prism face 230, 240 having a 90° angle between them. Prism 220 includes two end faces 270, 280, and a third and fourth prism face 250, 260 having a 90° angle between them. The first prism face 230 is parallel to the third prism face 250, and the second prism face 240 is parallel to the fourth prism face 260. The identification of the four prism faces shown in FIG 3 with a "first", "second", "third" and "fourth" serves only to clarify the description of PBS 200 in the discussion that follows. First reflective polarizer 290 can be a Cartesian reflective polarizer or a non-Cartesian reflective polarizer. A non-Cartesian reflective polarizer can include multilayer inorganic films such as those produced by sequential deposition of inorganic dielectrics, such as a MacNeille polarizer. A Cartesian reflective polarizer has a polarization axis state, and includes both wire- grid polarizers and polymeric multilayer optical films such as can be produced by extrusion and subsequent stretching of a multilayer polymeric laminate. In one embodiment, reflective polarizer 290 is aligned so that one polarization axis is parallel to a first polarization state 295, and perpendicular to a second polarization state 296. In one embodiment, the first polarization state 295 can be the s-polarization state, and the second polarization state 296 can be the p- polarization state. In another embodiment, the first polarization state 295 can be the p- polarization state, and the second polarization state 296 can be the s-polarization state. As shown in FIG 3, the first polarization state 295 is perpendicular to each of the end faces 270, 275, 280, 285.

A Cartesian reflective polarizer film provides the polarizing beam splitter with an ability to pass input light rays that are not fully collimated, and that are divergent or skewed from a central light beam axis, with high efficiency. The Cartesian reflective polarizer film can comprise a polymeric multilayer optical film that comprises multiple layers of dielectric or polymeric material. Use of dielectric films can have the advantage of low attenuation of light and high efficiency in passing light. The multilayer optical film can comprise polymeric multilayer optical films such as those described in U.S. Patent 5,962,1 14 (Jonza et al.) or U.S. Patent 6,721,096 (Bruzzone et al).

FIG 4 is a perspective view of the alignment of a quarter- wave retarder to a PBS, as used in some embodiments. Quarter-wave retarders can be used to change the polarization state of incident light. PBS retarder system 300 includes PBS 200 having first and second prisms 210 and 220. A quarter-wave retarder 220 is disposed adjacent the first prism face 230. Reflective polarizer 290 is, for example, a Cartesian reflective polarizer film aligned to first polarization state 295. Quarter-wave retarder 320 includes a quarter-wave polarization state 395 that can be aligned at 45° to first polarization state 295. Although FIG 4 shows polarization state 395 aligned at 45° to first polarization state 295 in a clockwise direction, polarization state 395 can instead be aligned at 45° to first polarization state 295 in a counterclockwise direction. In some embodiments, quarter-wave polarization state 395 can be aligned at any degree orientation to first polarization state 295, for example from 90° in a counter-clockwise direction to 90° in a clockwise direction. It can be advantageous to orient the retarder at approximately +/- 45° as described, since circularly polarized light results when linearly polarized light passes through a quarter- wave retarder so aligned to the polarization state. Other orientations of quarter- wave retarders can result in s-polarized light not being fully transformed to p-polarized light, and p- polarized light not being fully transformed to s-polarized light upon reflection from the mirrors, resulting in reduced efficiency of the optical elements described elsewhere in this description.

FIG. 5 shows a schematic diagram of an image projector 1, according to one aspect of the disclosure. Image projector 1 includes a color combiner module 10 that is capable of injecting a partially collimated combined color light output 24 into a homogenizing polarization converter module 30 where the partially collimated combined color light output 24 becomes converted to a homogenized polarized light 45 that exits the homogenizing polarization converter module 30 and enters an image generator module 50. The image generator module 50 outputs an imaged light 65 that enters a projection module 70 where the imaged light 65 becomes a projected imaged light 80.

In one aspect, color combiner module 10 includes different wavelength spectrum input light sources that are input through light collection optics 505, as described elsewhere. The light collection optics 505 produces a partially collimated combined color light output 24 that includes the different wavelength spectrum lights, as described elsewhere.

In one aspect, the input light sources are unpolarized, and the partially collimated combined color light output 24 is also unpolarized. The partially collimated combined color light output 24 can be a polychromatic combined light that comprises more than one wavelength spectrum of light. The partially collimated combined color light output 24 can be a time sequenced output of each of the received lights. In one aspect, each of the different wavelength spectra of light corresponds to a different color light (for example red, green and blue), and the combined light output is white light, or a time sequenced red, green and blue light. For purposes of the description provided herein, "color light" and "wavelength spectrum light" are both intended to mean light having a wavelength spectrum range which may be correlated to a specific color if visible to the human eye. The more general term "wavelength spectrum light" refers to both visible and other wavelength spectrums of light including, for example, infrared light.

According to one aspect, each input light source comprises one or more light emitting diodes (LEDs). Various light sources can be used such as lasers, laser diodes, organic LEDs (OLEDs), and non solid state light sources such as ultra high pressure (UHP), halogen or xenon lamps with appropriate collectors or reflectors. Light sources, light collimators, lenses, and light integrators useful in the present invention are further described, for example, in Published U.S. Patent Application No. US 2008/0285129, the disclosure of which is herein included in its entirety.

In one aspect, homogenizing polarization converter module 30 includes a tilted dichroic polarization converter 506 that is capable of converting unpolarized partially collimated combined color light output 24 into homogenized collimated polarized light 45. Homogenizing polarization converter module 30 further can include a monolithic array of lenses 42, such as a optional monolithic FEA of lenses described elsewhere that can homogenize and improve the uniformity of the partially collimated combined color light output 24 that exits the homogenizing polarization converter module 30 as homogenized polarized light 45. Representative arrangements of optional FEA associated with the homogenizing polarization converter module 30 are described, for example, in co-pending U.S. Patent Serial Nos. 61/346183 entitled FLY EYE INTEGRATOR POLARIZATION CONVERTER (Attorney Docket No. 66247US002, filed May 19, 2010); 61/346190 entitled POLARIZED PROJECTION ILLUMINATOR

(Attorney Docket No. 66249US002, filed May 19, 2010); and 61/346193 entitled COMPACT ILLUMINATOR (Attorney Docket No. 66360US002, filed May 19, 2010).

In one aspect, image generator module 50 includes a polarizing beam splitter (PBS) 56, representative imaging optics 52, 54, and a spatial light modulator 58 that cooperate to convert the homogenized polarized light 45 into an imaged light 65. Suitable spatial light modulators (that is, image generators) have been described previously, for example, in U.S. Patent Nos. 7,362,507 (Duncan et al), 7,529,029 (Duncan et al); in U.S. Publication No. 2008-0285129-A1 (Magarill et al); and also in PCT Publication No. WO2007/016015 (Duncan et al). In one particular embodiment, homogenized polarized light 45 is a divergent light originating from each lens of the optional FEA. After passing through imaging optics 52, 54 and PBS 56, homogenized polarized light 45 becomes imaging light 60 that uniformly illuminates the spatial light modulator. In one particular embodiment, each of the divergent light ray bundles from each of the lenses in the optional FEA illuminates a major portion of the spatial light modulator 58 so that the individual divergent ray bundles overlap each other. In one aspect, projection module 70 includes representative projection optics 72, 74, 76, that can be used to project imaged light 65 as projected light 80. Suitable projection optics 72, 74, 76 have been described previously, and are well known to those of skill in the art.

Following are a list of embodiments of the present disclosure.

Item 1 is a color combiner, comprising: a light collection optic having a light input surface and an optical axis; a first and a second light source disposed to inject a first and a second color light into the light input surface, at least one of the first and second light sources displaced from the optical axis; a first reflective polarizer disposed facing the light collection optic opposite the light input surface, capable of splitting both the first and the second color light into a transmitted light having a first polarization direction and a reflected light having a second polarization direction; a half-wave retarder disposed to convert the transmitted light having the first polarization direction into a converted light having the second polarization direction; a second reflective polarizer disposed to reflect the converted light having the second polarization direction parallel to the reflected light having the second polarization direction; a quarter-wave retarder disposed to intercept the reflected light having the second polarization direction and the converted light having the second polarization direction; and a tilted dichroic plate disposed adjacent the quarter-wave retarder and opposite the first reflective polarizer and the second reflective polarizer, the tilted dichroic plate including: a first dichroic reflector capable of reflecting the first color light and transmitting other color light; and a second reflector capable of reflecting the second color light, wherein the first dichroic reflector and the second reflector are each tilted such that the first and the second color light are both reflected in an output direction through the first reflective polarizer and the second reflective polarizer, the first and the second color light forming a combined color light beam having the first polarization direction.

Item 2 is the color combiner of item 1, wherein the reflective polarizer comprises a diagonal face of a polarizing beam splitter (PBS) or a pellicle.

Item 3 is the color combiner of item 1 or item 2, wherein the light collection optic comprises light collimation optics.

Item 4 is the color combiner of item 3, wherein the light collimation optics comprises a one lens design, a two lens design, a diffractive optical element, or a combination thereof.

Item 5 is the color combiner of item 1 to item 4, wherein the light collection optics comprises: a first lens having a first convex surface opposite the light input surface; and a second lens having a second surface facing the first convex surface, and a third convex surface opposite the second surface.

Item 6 is the color combiner of item 1 to item 5, wherein the second reflector comprises a broadband mirror.

Item 7 is the color combiner of item 1 to item 6, wherein the second reflector comprises a second dichroic reflector capable of reflecting the second color light and transmitting other color light.

Item 8 is the color combiner of item 1 to item 7, further comprising a third light source disposed to inject a third color light into the light input surface and wherein the tilted dichroic plate further comprises a third reflector capable of reflecting the third color light to exit in the output direction as the combined color light beam having the first polarization direction.

Item 9 is the color combiner of item 8, wherein the third reflector comprises a broadband mirror.

Item 10 is the color combiner of item 8, wherein the third reflector comprises a third dichroic reflector capable of reflecting the third color light and transmitting other color light.

Item 1 1 is the color combiner of item 8, wherein the first, the second, and the third color light comprises a red, a green, and a blue color light.

Item 12 is the color combiner of item 1 to item 11, wherein the reflective polarizer comprises a polymeric multilayer optical film polarizer, a wire-grid polarizer, or a MacNeille polarizer.

Item 13 is a color combiner, comprising: a light collimation optic having a light input surface and an optical axis; a first, a second, and a third light source, at least two of the first, the second, and the third light source displaced from the optical axis and disposed to inject a first, a second, and a third color light into the light input surface; a first PBS disposed facing the light collimation optics opposite the light input surface, capable of splitting the first, the second, and the third color light into a transmitted light having a first polarization direction and a reflected light having a second polarization direction; a half-wave retarder disposed to convert the transmitted light having the first polarization direction into a converted light having the second polarization direction; a second PBS disposed to reflect the converted light having the second polarization direction parallel to the reflected light having the second polarization direction; a quarter-wave retarder disposed to intercept the reflected light having the second polarization direction and the converted light having the second polarization direction; and a tilted dichroic plate disposed adjacent the quarter-wave retarder and opposite the first and the second PBS, the tilted dichroic plate, including: a first dichroic reflector capable of reflecting the first color light and transmitting the second and the third color light; a second dichroic reflector capable of reflecting the second color light and transmitting the third color light; and a third reflector capable of reflecting the third color light, wherein the first dichroic reflector, the second dichroic reflector, and the third reflector are each tilted such that the first, the second, and the third color light are each reflected in an output direction through the first PBS and the second PBS, the first, the second, and the third color light forming a combined color light beam having the first polarization direction.

Item 14 is the color combiner of item 13, wherein the third reflector is a broadband mirror.

Item 15 is the color combiner of item 13, wherein the third reflector is a third dichroic reflector capable of reflecting the third color light and transmitting other color light.

Item 16 is the color combiner of item 13 to item 15, wherein each of the first and the second PBS comprise a polymeric multilayer optical film polarizer, a wire-grid polarizer, or a MacNeille polarizer.

Item 17 is a color combiner, comprising: a light collection optic having a light input surface and an optical axis; a first and a second light source disposed to inject a first and a second color light into the light input surface, at least one of the first and second light sources displaced from the optical axis; a first reflective polarizer disposed facing the light collection optic opposite the light input surface, capable of splitting both the first and the second color light into a transmitted light having a first polarization direction and a reflected light having a second polarization direction; a quarter-wave retarder disposed to intercept the reflected light having the second polarization direction; a first tilted dichroic plate disposed adjacent the quarter-wave retarder and opposite the first reflective polarizer, the first tilted dichroic plate including: a first dichroic reflector capable of reflecting the first color light and transmitting other color light; a second dichroic reflector capable of reflecting the second color light; and a second tilted dichroic plate disposed to intercept the transmitted first polarization direction, the second tilted dichroic plate including: a third dichroic reflector capable of reflecting the first color light and transmitting other color light; a fourth dichroic reflector capable of reflecting the second color light, wherein the first and second dichroic reflectors are tilted such that the first and the second color light are both reflected in an output direction through the first reflective polarizer, and the third and fourth dichroic reflectors are tilted such that the first and the second color light are both reflected in the output direction, the first and the second color light forming a combined color light beam having the first polarization direction.

Item 18 is the color combiner of item 17, further comprising a third light source disposed to inject a third color light into the light input surface and wherein the first and the second tilted dichroic plate each further comprises a third reflector capable of reflecting the third color light to exit in the output direction as the combined color light beam having the first polarization direction.

Item 19 is an image projector, comprising: the color combiner of item 1 to item 18; a spatial light modulator disposed to impart an image to the polarized first, second, and third color light; and projection optics.

Item 20 is the image projector of item 19, wherein the spatial light modulator comprises a liquid crystal on silicon (LCoS) imager or a transmissive liquid crystal display (LCD).

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure, except to the extent they may directly contradict this disclosure. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed is:

1. A color combiner, comprising:

a light collection optic having a light input surface and an optical axis;

a first and a second light source disposed to inject a first and a second color light into the light input surface, at least one of the first and second light sources displaced from the optical axis;

a first reflective polarizer disposed facing the light collection optic opposite the light input surface, capable of splitting both the first and the second color light into a transmitted light having a first polarization direction and a reflected light having a second polarization direction;

a half-wave retarder disposed to convert the transmitted light having the first polarization direction into a converted light having the second polarization direction;

a second reflective polarizer disposed to reflect the converted light having the second polarization direction parallel to the reflected light having the second polarization direction;

a quarter-wave retarder disposed to intercept the reflected light having the second polarization direction and the converted light having the second polarization direction; and

a tilted dichroic plate disposed adjacent the quarter- wave retarder and opposite the first reflective polarizer and the second reflective polarizer, the tilted dichroic plate including:

a first dichroic reflector capable of reflecting the first color light and transmitting other color light; and

a second reflector capable of reflecting the second color light, wherein the first dichroic reflector and the second reflector are each tilted such that the first and the second color light are both reflected in an output direction through the first reflective polarizer and the second reflective polarizer, the first and the second color light forming a combined color light beam having the first polarization direction.

2. The color combiner of claim 1, wherein the reflective polarizer comprises a diagonal face of a polarizing beam splitter (PBS) or a pellicle.

3. The color combiner of claim 1, wherein the light collection optic comprises light collimation optics.

4. The color combiner of claim 3, wherein the light collimation optics comprises a one lens design, a two lens design, a diffractive optical element, or a combination thereof. 5. The color combiner of claim 1, wherein the light collection optics comprises:

a first lens having a first convex surface opposite the light input surface; and

a second lens having a second surface facing the first convex surface, and a third convex surface opposite the second surface. 6. The color combiner of claim 1, wherein the second reflector comprises a broadband mirror.

7. The color combiner of claim 1, wherein the second reflector comprises a second dichroic reflector capable of reflecting the second color light and transmitting other color light.

8. The color combiner of claim 1, further comprising a third light source disposed to inject a third color light into the light input surface and wherein the tilted dichroic plate further comprises a third reflector capable of reflecting the third color light to exit in the output direction as the combined color light beam having the first polarization direction.

9. The color combiner of claim 8, wherein the third reflector comprises a broadband mirror.

10. The color combiner of claim 8, wherein the third reflector comprises a third dichroic reflector capable of reflecting the third color light and transmitting other color light.

1 1. The color combiner of claim 8, wherein the first, the second, and the third color light comprises a red, a green, and a blue color light.

12. The color combiner of claim 1, wherein the reflective polarizer comprises a polymeric multilayer optical film polarizer, a wire-grid polarizer, or a MacNeille polarizer.

13. A color combiner, comprising:

a light collimation optic having a light input surface and an optical axis;

a first, a second, and a third light source, at least two of the first, the second, and the third light source displaced from the optical axis and disposed to inject a first, a second, and a third color light into the light input surface;

a first PBS disposed facing the light collimation optics opposite the light input surface, capable of splitting the first, the second, and the third color light into a transmitted light having a first polarization direction and a reflected light having a second polarization direction;

a second PBS disposed to reflect the converted light having the second

polarization direction parallel to the reflected light having the second polarization direction;

a tilted dichroic plate disposed adjacent the quarter- wave retarder and opposite the first and the second PBS, the tilted dichroic plate, including:

a first dichroic reflector capable of reflecting the first color light and transmitting the second and the third color light;

a second dichroic reflector capable of reflecting the second color light and transmitting the third color light; and

a third reflector capable of reflecting the third color light, wherein the first dichroic reflector, the second dichroic reflector, and the third reflector are each tilted such that the first, the second, and the third color light are each reflected in an output direction through the first PBS and the second PBS, the first, the second, and the third color light forming a combined color light beam having the first polarization direction.

14. The color combiner of claim 13, wherein the third reflector is a broadband mirror.

15. The color combiner of claim 13, wherein the third reflector is a third dichroic reflector capable of reflecting the third color light and transmitting other color light.

16. The color combiner of claim 13, wherein each of the first and the second PBS comprise a polymeric multilayer optical film polarizer, a wire-grid polarizer, or a MacNeille polarizer.

17. A color combiner, comprising:

a light collection optic having a light input surface and an optical axis;

a quarter-wave retarder disposed to intercept the reflected light having the second polarization direction;

a first tilted dichroic plate disposed adjacent the quarter- wave retarder and

opposite the first reflective polarizer, the first tilted dichroic plate including:

a first dichroic reflector capable of reflecting the first color light and transmitting other color light;

a second dichroic reflector capable of reflecting the second color light; and

a second tilted dichroic plate disposed to intercept the transmitted light having the first polarization direction, the second tilted dichroic plate including: a third dichroic reflector capable of reflecting the first color light and transmitting other color light;

a fourth dichroic reflector capable of reflecting the second color light,

wherein the first and second dichroic reflectors are tilted such that the first and the second color light are both reflected in an output direction through the first reflective polarizer, and the third and fourth dichroic reflectors are tilted such that the first and the second color light are both reflected in the output direction, the first and the second color light forming a combined color light beam having the first polarization direction.

18. The color combiner of claim 17, further comprising a third light source disposed to inject a third color light into the light input surface and wherein the first and the second tilted dichroic plate each further comprises a third reflector capable of reflecting the third color light to exit in the output direction as the combined color light beam having the first polarization direction. image projector, comprising:

the color combiner of claim 1, claim 13, or claim 17;

a spatial light modulator disposed to impart an image to the polarized first,

second, and third color light; and

projection optics.

20. The image projector of claim 19, wherein the spatial light modulator comprises a liquid crystal on silicon (LCoS) imager or a transmissive liquid crystal display (LCD).