WO2002079859A1

WO2002079859A1 - Multi-wavelength dispersive radiation source

Info

Publication number: WO2002079859A1
Application number: PCT/US2002/008873
Authority: WO
Inventors: Douglas S. Goodman
Original assignee: Polaroid Corporation
Priority date: 2001-03-30
Filing date: 2002-03-21
Publication date: 2002-10-10

Abstract

An improved multi-wavelength light source is provided that may be used, for example, in a projection device. The light source includes a plurality of discrete radiation devices emitting a plurality of source radiation beams of different wavelengths. An optical relay system, such as a lens, relays the source radiation beams to a dispersive optical element, such as a prism or a grating. The dispersive optical element redirects the relayed radiation beams as a plurality of dispersed radiation beams. The optical relay system and the dispersive optical element are positioned and oriented so that the dispersed radiation beams overlap in position and angle to form a combined radiation beam that includes the wavelengths of the source radiation beams. The combined radiation beam thereby serves as a virtual multi-wavelength radiation source. The optical system provides the combined radiation beam within a predetermined area, such as an entrance pupil of an imaging lens in a projection device, to provide a high-power source of multi-wavelength radiation.

Description

Multi-Wavelength Dispersive Radiation Source

BACKGROUND

Field of the Invention

The present invention relates to an apparatus for combining a plurality of radiation beams having a plurality of wavelengths, and, more particularly, to an apparatus for overlapping such radiation beams in position and angle to form a multi-wavelength radiation beam.

Related Art

There continues to be a need for radiation sources providing ever- increasing levels of radiative power and brightness in applications such as printing, fabrication, telecommunications, photochemical processes, and medical treatment. Modern imaging devices increasingly use solid state light sources as discrete sources of radiation. These light sources are typically monochromatic or quasi-monochromatic (such as LEDs). As a result, it is necessary to combine the light produced by these light sources to produce multi-wavelength light. Such combination of light, however, can be difficult to perform efficiently. In many cases, imaging systems using such discrete light sources are made larger and more complex to accommodate the multiple light sources. In addition to the need for increasing levels of radiative power, there is also an increasing need for systems providing such radiative power to be small, easy to manufacture, and energy efficient. What is needed, therefore, is an improved system for efficiently providing a multi-wavelength radiation source.

SUMMARY

In one embodiment, the invention provides an optical system including an improved multi-wavelength light source that may be used, for example, in a projection device. The light source includes a plurality of discrete radiation devices emitting a plurality of source radiation beams of different wavelengths. An optical relay system, such as a lens, relays the source radiation beams to a dispersive optical element, such as a prism or a grating. The dispersive optical element redirects the relayed radiation beams as a plurality of dispersed radiation beams. The optical relay system and the dispersive optical element are positioned and oriented so that the dispersed radiation beams overlap in position and angle to form a combined radiation beam that includes the wavelengths of the source radiation beams. The combined radiation beam thereby serves as a virtual multi-wavelength radiation source. The optical system provides the combined radiation beam within a predetermined area, such as an entrance pupil of an imaging lens in a projection device, to provide a high-power source of multi-wavelength radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E are diagrammatic side views of prior art projection condenser systems.

FIG. 2A is a diagrammatic side view of a generalized multi-wavelength radiation source according to one embodiment of the present invention.

FIG. 2B is a diagrammatic side view of a generalized multi-wavelength radiation source according to another embodiment of the present invention. FIG. 3 is a diagram illustrating dispersion of light.

FIG. 4 is a diagrammatic side view of a multi-wavelength light source according to one embodiment of the present invention using a grating.

FIG. 5 is a diagrammatic side view of a multi-wavelength light source according to one embodiment of the present invention using a prism. FIG. 6 is a diagrammatic side view of a multi-wavelength light source according to one embodiment of the present invention using a monolithic dispersive optical element including a grating mounted to a surface of a curved mirror.

FIG. 7 is a diagrammatic side view of a multi-wavelength light source according to one embodiment of the present invention using a monolithic dispersive optical element including a grating mounted to a surface of a convex lens. FIG. 8 is a diagrammatic side view of a multi-wavelength light source according to one embodiment of the present invention in which a bi-convex lens is used to implement both an optical relay system and a dispersive optical element. FIGS. 9A-9D are diagrammatic side views of multi-wavelength light sources according to embodiments of the present invention each incorporating a beamsplitter and a reflective liquid crystal display.

FIG. 10 is a diagrammatic side view of a projection condenser system including a dispersive optical element according to one embodiment of the present invention.

FIG. 11 is a diagrammatic side view of a system in which one embodiment of the present invention provides a multi-wavelength light source to a uniformizer system.

DETAILED DESCRIPTION In one embodiment, the invention provides an improved light source that may be used, for example, in a projection device. The light source includes a plurality of discrete radiation devices emitting a plurality of source radiation beams of different wavelengths. The source radiation beams may, for example, be red (640nm wavelength), green (520 nm wavelength), and blue (460 nm wavelength) light beams emitted by distinct red, green, and blue

LEDs, respectively. An optical relay system, such as a lens, relays the source radiation beams to a dispersive optical element, such as a prism or a grating. The dispersive optical element redirects the relayed radiation beams as a plurality of dispersed radiation beams. The optical relay system and the dispersive optical element are positioned and oriented so that the dispersed radiation beams overlap in position and angle to form a combined radiation beam that includes the wavelengths of the source radiation beams. The combined radiation beam thereby serves as a virtual multi-wavelength radiation source. The optical system provides the combined radiation beam within a predetermined area, such as an entrance pupil of an imaging lens in a projection device, to provide a high-power source of multi-wavelength radiation.. This multi-wavelength radiation source can provide almost as much power as all of the discrete radiation devices combined. Use of the dispersive optical element makes it possible to couple the multiple source beams within a smaller predetermined area than is typically possible with conventional systems that use multiple discrete radiation sources. This enables low power, solid state components to be used as radiation sources while maintaining high f-number imaging systems, thereby greatly decreasing the cost and size of such systems.

For example, in one embodiment of the present invention, the multi- wavelength radiation source is used as a light source within a projection condenser system for printing. Use of the multi-wavelength radiation source enables the use of a smaller imaging lens than in conventional systems, reducing the total size and cost of the system.

Referring to FIG. 1A, a conventional projection condenser system 100 is shown. The system 100 includes light sources 102a, 102b, and 102c for emitting radiation beams of different wavelengths. The light sources 102a-c may, for example, be light-emitting diodes (LEDs) that emit red, green, and blue light beams, respectively. The system 100 also includes a condenser lens 104, an object plane 106 (which may contain an object, such as a slide, film, or LCD, to be imaged by the projection condenser system 100), an imaging lens 108, and an image plane 110 onto which an image of the object (e.g., the slide) is formed. The purpose of the projection condenser system

100 is to illuminate the object in the object plane 106 so that the image formed by the imaging lens 108 at the image plane is bright and evenly illuminated. Conventional projection condenser systems are described in more detail in, e.g., Modern Optical Engineering, 2^nd Ed., Warren J. Smith, McGraw-Hill (1990), pp.228-231 , which is hereby incorporated by reference.

As is well known to those of ordinary skill in the art, the imaging lens 108 includes an entrance pupil 109 and an exit pupil (not shown). The entrance pupil 109 is depicted in FIG. 1A (and in subsequent figures) in block form for purposes of illustration and ease of description. It should be appreciated, however, that the entrance pupil 109 is not a structure separate from the imaging lens 108.

Referring to FIG. 1 B, a portion of the system 100 is shown in which the light source 102b emits a source radiation beam 112. The source radiation beam 112 is represented by a central ray 112a (illustrated with a dashed line) and two marginal rays 112b-c (illustrated with solid lines). Other radiation beams shown in the drawings are similarly represented by central and marginal rays. Although, as described in more detail below, in normal operation all three of the light sources 102a-c typically emit radiation beams simultaneously within the system 100, the light source 102b is shown in isolation in FIG. 1 B for ease of illustration and to more clearly point out particular characteristics of the system 100.

The source radiation beam 112 is incident upon a surface of the condenser lens 104, which captures the source radiation beam 112 and relays it as a condensed radiation beam 114 (represented by central ray 114a and marginal rays 114b-c), which forms^' an image 116 of the light source 102b at the entrance pupil 109 of the imaging lens 108. Although the condenser lens 104 is depicted in the drawings as a single lens, this is not a limitation of the present invention. Rather, multiple lenses and/or other optical elements may be used to perform the functions of the condenser lens 104. Similarly, referring to FIG. 1C, a portion of the system 100 is shown in which the light source 102a emits a source radiation beam 118. Although the source radiation beam is depicted using a central ray and two marginal rays, the reference number 118 refers to the source radiation beam 118 itself. Other radiation beams are similarly labeled in FIG. 1C and subsequent figures. The source radiation beam 118 is incident upon a surface of the condenser lens 104, which captures the source radiation beam 112 and relays it as a condensed radiation beam 120, which forms an image 122 of the light source 102a at the entrance pupil 109 of the imaging lens 108.

Finally, referring to FIG. 1 D, a portion of the system 100 is shown in which the light source 102c emits a source radiation beam 124. The source radiation beam 124 is incident upon a surface of the condenser lens 104, which captures the source radiation beam 124 and relays it as a condensed radiation beam 126, which forms an image 128 of the light source 102c at the entrance pupil 109 of the imaging lens 108. Referring to FIG. 1 E, the combined effect of the FIGS. 1 B-1 D is shown.

The imaging lens 108 relays the condensed radiation beams 114, 120, and 126 as imaged radiation beams 130, 132, and 134, respectively, to form an image at the image plane 110 of the object (e.g., the slide) at the object plane 106. As can be seen in FIG. 1E, the separation of the light sources 102a-c results in separation -of the images 116, 122, and 128 at the entrance pupil 109 of the imaging lens 108. As a result, the imaging lens 112 has a lower f- number (and correspondingly larger size) than would be required if a single light source were used in place of the light sources 102a-c. The size of the light sources 102a-c and the geometry of the system 100, however, impose limits on how closely the light sources 102a-c may be placed to each other.

Referring to FIG. 2A, an optical imaging system 200 according to one embodiment of the present invention is shown. The system 200 includes discrete radiation devices 202a, 202b, and 202c emitting source radiation beams 204a-c, respectively. Radiation devices 202a-c may, for example, be solid state radiation devices such as light emitting diodes (LEDs), and the source radiation beams 204a-c may, for example, be monochromatic or quasi- monochromatic. For example, the source radiation beams 204a-c may be red, green, and blue light beams, respectively.

The optical imaging system 200 also includes an optical relay system 206 and a dispersive optical element 210, shown in FIG. 2 in generalized block form. Particular examples of the optical relay system 206 and the dispersive optical element 210 are described below. The optical relay system 206 is disposed in the optical paths of the source radiation beams 204a-c. The optical relay system 206 captures the source radiation beams 204a-c and relays them as first relayed radiation beam 208a-c, respectively. The dispersive optical element 210 is disposed in the optical paths of the first relayed radiation beams 208a-c and redirects them as dispersed radiation beams 222a-c, respectively. The optical relay system 206 and the dispersive optical element 210 are positioned and oriented so that the dispersed radiation beams 222a-c substantially overlap in both position and angle (i.e., they are all directed in substantially the same direction). The optical system 200 couples the dispersed radiation beams 212a-c within a predetermined area 214, such as an entrance pupil of an imaging lens in a projection condenser system, as described in more detail below. It should be appreciated that although the source radiation beam 204a, the first relayed radiation beam 208a, and the dispersed radiation beam 222a are labeled and described herein as separate beams, they may alternatively be considered to be different segments of a single beam. The distinct labeling of these beams (and other similar beams), therefore, does not constitute a limitation of the present invention and is provided merely for clarity of illustration and description.

Referring to FIG. 2B, in another embodiment of the present invention an optical system 220 operates similarly to the optical system shown in FIG. 2A, except that the dispersed radiation beams 222a-c shown in FIG. 2A are combined into a single combined radiation beam 212 that produces an image 224 of a virtual multi-wavelength radiation source within the predetermined area 214. The combined radiation beam 212 includes the wavelengths of the source radiation beams 204a-c. It should be appreciated that in particular implementations the first relayed radiation beams 208a-c may not be combined perfectly into the single combined radiation beam 212 but may rather be combined into the multiple dispersed radiation beams 222a-c shown in FIG. 2A. The system 220 of FIG. 2B is shown, however, to more clearly illustrate the manner in which various embodiments of the present invention may be used to provide a high-power source of multi-wavelength radiation within the predetermined area 214.

For example, in one embodiment of the present invention, principal axes of the dispersed radiation beams 222a-c intersect the predetermined area 214 within a very small region so that irradiance distributions of the dispersed radiation beams 222a-c substantially (or at least partially) overlap within the predetermined area 214. In this manner, the system 200 may be used to produce a high-power source of multi-wavelength light that approximates a point source of light within the predetermined area 214.

It should be appreciated that the elements depicted in the drawings are not drawn to scale and that the various angles shown in the drawings (such as the angles of incidence, reflection, and refraction of the various radiation beams shown in the drawings) are purely illustrative and may not represent angles that are used in particular embodiments of the present invention.

Before describing the operation of various embodiments of the present invention in more detail, refraction and dispersion will be briefly described. It is well known to those of ordinary skill in the art that refraction causes light passing from one medium to another to change direction, and that light of different wavelengths bends by different amounts. For example, referring to FIG. 3, a ray 302a of white light passes from a first medium 300a having refractive index n to a second medium 300b having refractive index n'. The ray 302a of white light is incident upon a surface 306 of the second medium 300b at an angle < to the normal 308 of the surface 306. Passage of the ray 302a from the first medium 300a to the second medium 300b gives rise to refracted rays 304a-c of different colors, each of which has a different angle ff to the normal 308, in accordance with Snell's Law.. For example, the ray 304a may be red, the ray 304b may be yellow, and the ray 304c may be blue. The refractive index n' of the second medium 300b varies with color (wavelength)!

The angular divergence of rays 304c and 304a is a measure of the dispersion produced by the passage from the first medium 300a to the second medium 300b. Dispersion is the change in direction of light as a function of the light's wavelength (color). Any device causing dispersion is referred to herein as a dispersive optical element.

Although the preceding discussion refers to use of a dispersive optical element to cause angular divergence of radiation beams of multiple wavelengths, it should be appreciated that, due to the reversible behavior of light beams, a dispersive optical element may also be used in reverse to cause the angular convergence (combination) of multiple source radiation beams of varying wavelengths into a single radiation beam including the wavelengths of all of the source radiation beams, and that this process is also referred to herein as dispersion.

As is well known to those of ordinary skill in the art, prisms disperse light. A prism, therefore, is one example of a dispersive optical element as that term is used herein. The prism includes two planar surfaces, which are inclined at an angle α. Except at normal incidence, multi-wavelength light is dispersed by the first surface and further dispersed by the second surface.

The total dispersion of light produced by the prism is a function of the dispersive index of the prism material, the angle α, the angle of incidence of the light upon the first surface of the prism, and the component wavelengths of the light. Prisms and dispersion are described in more detail in Fundamentals of Optics, 4^th Ed., Francis A. Jenkins and Harvey E. White, McGraw-Hill

(1981), pp. 18-23, 28-43, and 474-496, which is hereby incorporated by reference.

As is well known to those of ordinary skill in the art, a diffraction grating also disperses light, and is therefore an example of a dispersive optical element as that term is used herein. For example, when white light is passed through a diffraction grating, the grating separates the white light into its component colors (wavelengths). As used herein, the terms "diffraction grating" and "grating" refer to any arrangement which is equivalent in its action to a number of parallel equidistant slits of the same width. Diffraction gratings typically have many thousands of very fine slits.

Consider a beam of light having wavelength λ and a grating having a period P. If the beam of light is incident upon the grating at an angle normal to the surface of the grating, then the angle θ by which the beam is refracted by the grating is defined by the grating equation: sin θ = λ/P. The angular dispersion of a grating refers to the rate of change of the angle θ produced by the grating in response to changes in the wavelength λ. Diffraction gratings are described in more detail in Fundamentals of Optics, 4^th Ed., Francis A. Jenkins and Harvey E. White, McGraw-Hill (1981), pp. 355-377, which is hereby incorporated by reference.

The various elements shown and described above with respect to FIGS. 2A-2B may be implemented in any of a variety of ways. For example, the discrete radiation sources 202a-c may be any of a variety of light sources. The discrete radiation sources 202a-c may, for example, be light emitting diodes (LEDs) which may, for example, emit red, green, and blue light, respectively. The discrete radiation sources 202a-c may, for example, be monochromatic or quasi-monochromatic light sources, such as laser radiation sources. The discrete radiation sources 202a-c may be of the same type or differ from each other in any combination, and may be driven in unison or separately in any combination. For example, the discrete radiation sources

202a-c may be activated simultaneously when the system 200 is used as a light source for a projection device; alternatively, the discrete radiation sources 202a-c may be activated in succession if the system 200 is used within a film printing system to successively produce a red image, a blue image, and a green image as superimposed images. The discrete radiation sources 202a-c may be wired in series, in parallel, independently, or in any combination thereof. Furthermore, the discrete radiation sources 202a-c may be modulated independently of each other. The discrete radiation sources 202a- c may be ends of light guides (such as optical fibers) that emit light produced by remote sources.

If the total power provided by all of the discrete radiation sources 202a- c is not necessary or desired, fewer than all of the discrete radiation sources 202a-c may be utilized at any particular time. Additional discrete radiation sources that are perpendicular to the plane of bilateral symmetry of the system 200 may be provided. For example, additional discrete radiation sources may be utilized as backup radiation sources to be switched on in the event that one of the other discrete radiation sources 202a-c fails. Although three discrete radiation sources 202a-c are shown in FIGS.

2A-2B, this number of radiation sources is not a requirement of the present invention. Rather, at least two light sources may be used in embodiments of the present invention. Furthermore, although the source radiation beams 204a-c shown in FIGS. 2A-2B have distinct wavelengths, source radiation beams 204a-c having spectra that overlap to varying degrees are also within the scope of the present invention. It should be appreciated, however, that (in accordance with conservation of brightness) only disjoint regions of such V. ,4 spectra may be combined. For example, if there is any overlap among the spectra of the source radiation beams 204a-c, the positions and orientations of the optical relay system 206 and the dispersive optical element 210 may be adjusted to combine only disjoint regions of the spectra into the combined radiation beam 212. Such a technique may be employed, for example, with discrete radiation sources such as those shown in FIGS. 2A-2B, or with one or more multi-wavelength radiation sources to select and combine only disjoint regions of the spectra of the radiation emitted by such sources.

Although red, green, and blue light beams are described above with respect to FIG. 2A-2B, this is not a requirement of the present invention. Rather, each of the discrete radiation sources 202a-c may emit radiation of any wavelength, consistent with the description above. The system 200 is not limited to providing a source of radiation within any particular environment. For example, as described in more detail below with respect to FIG. 10, the system 200 may serve as a light source within a projection device. Alternatively, the system 200 may provide a source of light in a laser printer. The system 200 may also provide a source of light to a light guide (such as an optical fiber). In other words, the predetermined area 214 may be the input end of a light guide. Various embodiments of the present invention may be particularly advantageous as light sources for light guides because of their ability to provide light beams: (1) in a small area (such as the input end of the light guide), and (2) having predetermined and substantially identical angles that fall within the required acceptance angle of the light guide.

In one embodiment, the present invention may be used to assist in the alignment by visual inspection of non-visible radiation, such as infrared light. For example, referring again to FIG. 2B, assume that the radiation source 202a emits non-visible radiation that needs to be aligned. A source of visible light may be chosen as the radiation source 202b. As described above, the optical system 200 overlaps the outputs of the radiation sources 202a and 202b within the combined radiation beam 212. Therefore, the combined radiation beam 212 includes two colinear portions: a visible portion corresponding to the source radiation beam 204b, and a non-visible portion corresponding to the source radiation beam 204a. To align the non-visible source radiation beam 202a, angular adjustments may be made to the visible '* radiation source 204b and the effects of such adjustments on the combined radiation beam 212 may be observed by the unaided eye. Corresponding adjustments may be made to the non-visible radiation source 202a. Such adjustments may be made until the desired alignment is obtained, as determined visually. This will result in the desired alignment of the non-visible source radiation beam 202a, since the optical system 200 overlaps the source radiation beams 204a and 204b in both position and angle within the combined radiation beam 212, as described above.

The optical relay system 206 and the dispersive optical element 210 may be refractive, reflective, or any combination thereof. The optical relay system 206 may, for example, be a lens, such as a biconvex lens, or a mirror. The dispersive optical element 210 may, for example, be a prism or a grating. The optical relay system 206 and the dispersive optical element 210 may be combined into a single physical element or further divided into additional elements for performing the same functions.

Although in FIGS. 2A-2B the optical relay system 206 is shown as preceding the dispersive optical element 210, it should be appreciated that the optical relay system 206 and the dispersive optical element 210 may be arranged in any order. For example, the order of the optical relay system 206 and the dispersive optical element 210 may be reversed so that the source radiation beams 204a-c are incident upon and dispersed by the dispersive optical element 210. The dispersed radiation beams thereby produced by the dispersive optical element 210 may then be relayed by the optical relay system 206 as first relayed radiation beams, which are thereby coupled within the predetermined area 214.

The dispersive optical element 210 shown in FIGS. 2A-2B may be any optical element or combination of optical elements that disperses the first relayed radiation beams 208a-c. For example, referring to FIG. 4, an optical imaging system 400 according to one embodiment of the present invention is shown in which the dispersive element 210 of FIG. 2 is implemented using a grating 410. The grating may be any grating as that term is defined herein. The system 400 includes discrete radiation devices 402a, 402b, and 402c emitting source radiation beams 404a, 404b, and 404c, respectively.

The optical relay system 206 of FIG. 2 is implemented using a condenser lens 406 disposed in the optical paths of the source radiation beams 404a-c. The condenser lens 406 captures the source radiation beams 404a-c and relays them as first relayed radiation beams 408a-c. The grating 410 is disposed in the optical paths of the first relayed radiation beams 408a- c. The first relayed radiation beams 408a-c are incident upon a surface of the grating 410 and are redirected by the grating 410. The condenser lens 406 and the grating 410 are positioned and oriented so that the first relayed radiation beams 408a-c are combined into a combined radiation beam 412 that includes the wavelengths of the source radiation beams 404a-c. The combined radiation beam 412 is provided within a predetermined area 414 to form an image 416 of a virtual multi-wavelength radiation source within the predetermined area 414. The predetermined area 414 may, for example, be at least part of an entrance pupil of an imaging lens in a projection system, as described in more detail below.

In one embodiment of the present invention, the grating 410 has a grating period of 1.0μm, and the source radiation beams 402a-c have wavelengths of .46μm (blue), .52μm (green), and .64μm (red), respectively. Because a dispersive optical element (i.e., the grating 410) is used to redirect the first relayed radiation beams 408a-c, the first relayed radiation beams 408a-c are redirected differently based on their wavelengths. In particular, in one embodiment the grating 410 is positioned and oriented so that the angles between the combined radiation beam 412 and the first relayed radiation beams 408a-c are approximately 27.4°, 31.3°, and 39.8°, respectively. Referring to FIG. 5, an optical imaging system 500 according to another embodiment of the present invention is shown in which the dispersive element 210 of FIG. 2 is implemented using a prism 510. The system 500 includes discrete radiation devices 502a, 502b, and 502c emitting source radiation beams 504a, 504b, and 504c, respectively. The ' optical relay system 206 of FIG. 2 is implemented using a condenser lens 506 disposed in the optical paths of the source radiation beams 504a-c. The condenser lens 506 captures the source radiation beams 504a-c and relays them as first relayed radiation beams 508a-c. The prism 510 is disposed in the optical paths of the first relayed radiation beams 508a- c. The first relayed radiation beams 508a-c are incident upon a surface of the prism 510 and are redirected by the prism 510. The condenser lens 506 and the prism 510 are positioned and oriented so that the first relayed radiation beams 508a-c are combined into a combined radiation beam 512 that includes the wavelengths of the source radiation beams 504a-c. The combined radiation beam 512 is provided within a predetermined area 514 to form an image 516 of a virtual multi-wavelength radiation source within the predetermined area 514.

Referring to FIG. 6, an optical imaging system 600 according to another embodiment of the present invention is shown, in which a unitary optical relay system 610 is used to implement both the optical relay system

206 and the dispersive optical element 210 of FIGS. 2A-2B The optical imaging system 600 includes discrete radiation devices 602a, 602b, and 602c emitting source radiation beams 604a, 604b, and 604c, respectively.

The unitary optical relay system 610 includes a curved mirror 618 and a grating 616 coupled to the surface of the mirror 618. The grating 616 may be coupled the surface of the mirror 618 in any manner, such as by etching the grating 616 into the surface or by forming the grating 616 onto the surface by a plastic injection molding process. The unitary optical relay system 610 is disposed in the optical paths of the source radiation beams 604a-c. The unitary optical relay system 610 captures the source radiation beams 604a-c and both reflects and redirects them. In particular, the mirror 618 reflects the source radiation beams 604a-c and the grating 616 redirects them. The mirror 618 and the grating 616 coupled thereto are positioned and oriented so that the source radiation beams 602a-c combined (as a result of the reflection and redirection just described) into a combined radiation beam 612 that includes the wavelengths of the source radiation beams 602a-c. The combined radiation beam 612 is provided within a predetermined area 616 to form an image 616 of a virtual multi-wavelength radiation source within the predetermined area 614. Referring to FIG. 7, an optical imaging system 700 according to another embodiment of the present invention is shown, in which a unitary optical relay system 710 implements both the optical relay system 206 and the dispersive optical element 210 shown in FIGS. 2A-2B. The system 700 includes discrete radiation devices 702a, 702b, and 702c emitting source radiation beams 704a, 704b, and 704c, respectively.

The unitary optical relay system 710 includes a convex lens 718 and a grating 716 coupled to a convex surface of the lens 718. The grating 716 may be coupled the surface of the lens 718 in any manner, such as by etching the grating 716 into the surface of the lens 718 or by forming the grating 716 onto the surface of the lens 718 by a plastic injection molding process.

Furthermore, the grating 716 may be coupled to a planar surface of the lens 710 rather than to a convex surface. The unitary optical relay system 710 is disposed in the optical paths of the source radiation beams 704a-c. The lens 718 of the unitary optical relay system 710 relays the source radiation beams 704a-c and the grating 716 redirects the relayed radiation beams to produce a combined radiation beam 712 that includes the wavelengths of the source radiation beams 704a-c. The combined radiation beam 712 is provided within a predetermined area 714 to form an image 716 of a virtual multi-wavelength radiation source within the predetermined area 714. Various other unitary elements may be used to implement both the optical relay system 206 and the dispersive optical element 210. For example, in one embodiment of the present invention, a diffractive optic element implements both the optical relay system 206 and the dispersive optical element 210. As is well known, a diffractive optic element includes a surface having a pattern such as a plurality of concentric circles. The diffractive optic element may be positioned and oriented within the system 700 in a manner similar to the unitary optical relay system 710, as will be understood by those of ordinary skill in the art.

Referring to FIG. 8, an optical imaging system 800 according to another embodiment of the present invention is shown, in which a bi-convex lens 810 implements both the optical relay system 206 and the dispersive optical element 210 shown in FIGS. 2A-2B The system 800 includes discrete radiation devices 802a, 802b, and 802c emitting source radiation beams 804a, 804b, and 804c, respectively. The bi-convex lens 810 is disposed in the optical paths of the source radiation beams 804a-c. An axis 820 of the bi-convex lens is shown that runs through a plane of the lens 810 at approximately half of the lens' height. The lens 810 is positioned and oriented so that the source radiation beams 804a-c are incident upon a first surface 818a of the lens within a region of the surface that does not include the axis 820. It should be appreciated that the first surface 818a and a second surface 818b of the lens 810 act as two surfaces of a prism. Therefore, the first and second surfaces 818a-b both relay and redirect the source radiation beams 804a to produce a combined radiation beam 812 that includes the wavelengths of the source radiation beams 804a- c. The combined radiation beam 812 is provided within a predetermined area

814 to form an image 816 of a virtual multi-wavelength radiation source within the predetermined area 814.

Those of ordinary skill in the art will appreciate how to select curvatures of the surfaces 818a-b and how to position and orient the lens 810 so that the dispersed radiation beams 812a-c are coupled within the predetermined area. It should be appreciated that only a portion of the lens 810 (such as a portion 822 of the lens that is above the axis 820) may be included in the system 800 to reduce the size of the system 800. Although in FIG. 8 the axis 820 is positioned at approximately half the height of the lens 810, this is not a limitation of the present invention. Furthermore, lenses other than bi-convex lenses, such as Fresnel lenses, may be used in place of the lens 810.

Referring to FIG. 9A, an optical imaging system 900 according to another embodiment of the present invention is shown in which the dispersive element 210 of FIG. 2 is implemented using a prism 910. The system 900 includes discrete radiation devices 902a, 902b, and 902c emitting source radiation beams 904a, 904b, and 904c, respectively. As described in more detail below, the systems shown in FIGS. 9A-9D may be used to provide a light source for an object viewed in reflection. A reflective liquid crystal display (LCD) 918 is an example of such an object.

The optical relay system 206 of FIG. 2 is implemented in FIG. 9A using a condenser lens 906 disposed in the optical paths of the source radiation beams 904a-c. The condenser lens 906 captures the source radiation beams 904a-c and relays them as first relayed radiation beams 908a-c. The prism 910 is disposed in the optical paths of the first relayed radiation beams 908a- c. The first relayed radiation beams 908a-c are redirected by the prism 910 and are thereby combined into a first combined radiation beam 922 (depicted by central ray 922a and marginal rays 922b-c) that illuminates the surface of the reflective LCD 920. The prism 910 includes a first surface 918a and a second surface

918b. The second surface 918b is coated with a thin film coating that only transmits light of a predetermined polarization. As a result, the prism 910 acts V. A as a polarizing beam splitter so that the first combined radiation beam 922 has a single polarization. In one embodiment, the prism 910 is positioned and oriented so that the angle between the normal to the surface 918b and the first combined radiation beam 922 is Brewster's angle, to facilitate the polarizing effect of the prism 910.

As is well known to those of ordinary skill in the art, a reflective LCD includes a two-dimensional array of pixels. Each pixel may be in one of two different states, referred to herein for ease of description as a first state and a second state. The LCD can be in one of two modes. In one mode, pixels in the first state reflect light without altering the polarization of the light, while pixels in the second state reverse the polarization of the light that they reflect. In the other mode, pixels in the first state reverse the polarization of the light that they reflect, while pixels in the second state reflect light without altering the polarization of the light. In either case, the light reflected by pixels in the first state has a polarization that is orthogonal to the light reflected by pixels in the second state, thereby producing an image corresponding to the states of the array of pixels. Returning to FIG. 9A, the first combined radiation beam 922 illuminates the pixels of the reflective LCD 920. The pixels reflect the first combined radiation beam 922 as a second combined radiation beam 924 (depicted by central ray 924a and marginal rays 924b-c). The second combined radiation beam 924 includes light of varying polarizations based on the pattern of pixels in the reflective LCD 920, as described above. The second combined radiation beam 924 is reflected by the second surface 918b of the prism 910 as third combined radiation beam 912, which is provided within a predetermined area 914 to form an image 916 of a virtual multi-wavelength radiation source within the predetermined area 916. The image specified by the pixels of the reflective LCD 920 is thereby produced within the predetermined area 914.

FIGS. 9B-9D illustrate embodiments that are similar to the system 900 shown in FIG. 9A. For example, referring to FIG. 9, a plane parallel plate beamsplitter 930 having a grating coupled to one of its surfaces 932 is used in place of the prism 910 shown in FIG. 9A. Referring to FIG. 9C, a cube beamsplitter 940 (consisting of elements 940a and 940b) coupled to a prism 942 is used in place of the prism 910 shown in FIG. 9A. Dotted line 944 indicates a border between the prism 942 and element 940a of the beamsplitter. The prism 942 and the element 940a of the beamsplitter 940 may be separately manufactured parts, in which case prism 942 and element 940a may be joined using, e.g., cement. Alternatively, prism 942 and element 940a may be integral, e.g., they may be formed from the same piece of glass, in which case line 944 represents a logical rather than a physical boundary. Referring to FIG. 9D, yet another embodiment is shown in which a cube beamsplitter 950 having a grating coupled to one of its surfaces 952 is used in place of the prism 910 shown in FIG. 9A. It should be appreciated that proper positioning and orientation of the elements shown in FIG. 9A-9D to achieve the results herein will be understood to those of ordinary skill in the art based on the description provided elsewhere above.

Various embodiments of the present invention may be used as multi- wavelength radiation sources for a variety of applications. For example, referring to FIG. 10, a projection condenser system 1000 is shown according to one embodiment of the present invention in which the system 400 of FIG. 4 provides a multi-wavelength light source to the projection condenser system 1000.

The system 1000 includes discrete radiation devices 402a, 402b, and 402c emitting source radiation beams 404a, 404b, and 404c, respectively. The system 1000 also includes condenser lens 406 and grating 410, which operate as described above with respect to FIG. 4 to produce a first combined radiation beam 412 that includes the wavelengths of the source radiation beams 404a-c. The first combined radiation beam 412 passes through a object plane 1010, which may contain an object (such as a slide, film, or LCD) to be imaged by the projection condenser system 1000. The first combined radiation beam 412 forms an image at an entrance pupil 1009 of an imaging lens 1004, which captures the first combined radiation beam 412 and relays it as a second combined radiation beam 1006. The second combined radiation beam 1006 produces an image of the object (e.g., the slide) at an image plane 1008.

It should be appreciated that various embodiments of the present invention may also be used as light sources in other systems, such as non- condensing imaging systems. It should also be appreciated that although the system 400 of FIG. 4 is used as a light source in the projection condenser system 1000, this is not a limitation of the present invention. Rather, any multi-wavelength light source within the scope of the claims, such as those shown in FIGS. 4-9, may be used as a multi-wavelength light source within the system 1000.

Referring to FIG. 11 , a system 1100 is shown in which an embodiment of the present invention is used to provide a light source for a uniformizer system 1102. For purposes of example, the system 400 of FIG. 4 is shown in FIG. 11 , although any system embodying the present invention may be used to provide a light source to the uniformized system 1102.

The condenser lens 406 and grating 410 operate as described above with respect to FIG. 4 to produce combined radiation beam 412, which is provided at an input end 1106 of a uniformizer 1104. The uniformizer is part of the uniformizer system 1102, which also includes relay lenses 1112a-b. The uniformizer 1104 uniformizes the combined radiation beam 412 in a manner well-known to those of ordinary skill in the art to produce a uniform radiation beam 1110 at an output end 1108 of the uniformizer 1104. The uniform radiation beam 1110 is relayed by the relay lens 1112a as a first relayed radiation beam 1114, which is in turn relayed by the relay lens 1112b as a second relayed radiation beam 1116, which passes through object plane 1118 and forms an image 1122 within predetermined area 1120 at entrance pupil 1109 of imaging lens 1124.

Among the advantages of the invention are one or more of the following.

Various embodiments of the present invention provide means for obtaining high-efficiency coupling of multiple radiation beams. In particular, as shown in FIGS. 2A-2B source radiation beams 204a-c of different wavelengths produced by discrete radiation sources 202a-c may be coupled to produce a virtual multi-wavelength radiation source that advantageously provides higher- power radiation than is typically provided by conventional systems using multiple discrete radiation sources. The virtual multi-wavelength radiation source effectively acts as a single radiation source that provides almost as much power as all of the discrete radiation sources 202a-c combined. Furthermore, use of the virtual multi-wavelength radiation source facilitates provision of this large amount of power in the small predetermined area 214, such as an entrance pupil of an imaging lens or an input end of a uniformizer or fiber.

As shown and described above with respect to FIG. 10, various embodiments of the present invention may be used to provide a high-power multi-wavelength light source within a projection device. Use of the multi- wavelength light source makes it possible to use simpler and smaller imaging lenses that may be manufactured less expensively than conventional imaging lenses. For example, the imaging lens 1004 shown in FIG. 10 may be smaller and therefore manufactured less expensively than the imaging lens 108 in the conventional system 100 of FIG. 1 due to the inclusion of the grating 410 in the system 1000 of FIG. 10. Similarly, the ability of various embodiments of the present invention to provide light within a small area allows the input end

1106 of the uniformizer 1104 shown in FIG. 11 to be small, reducing the required size of the uniformizer 1104 and potentially of the entire uniformizer system 1102.

It is to be understood that although the invention has been described above in terms of particular embodiments, the foregoing embodiments are provided as illustrative only, and do not limit or define the scope of the invention. Other embodiments are also within the scope of the present invention, which is defined by the scope of the claims below.

What is claimed is:

Claims

1. An optical system comprising: a plurality of source radiation beams including a plurality of wavelengths; a first optical relay system disposed in optical paths of the plurality of source radiation beams to relay the plurality of source radiation beams; and a dispersive optical element disposed in optical paths of the plurality of source radiation beams to redirect the plurality of source radiation beams, wherein the first optical relay system and the dispersive optical element are positioned and oriented to direct the plurality of source radiation beams in substantially the same direction and to couple the plurality of source radiation beams within a first predetermined area.

2. The optical system of claim 1 , wherein the first optical relay system and the dispersive optical element are positioned and oriented to combine the plurality of source radiation beams into a combined radiation beam that forms an image of a virtual multi-wavelength radiation source within the first predetermined area.

3. The optical system of claim 1, wherein the dispersive optical element is disposed in optical paths of the plurality of source radiation beams to redirect the plurality of source radiation beams as a plurality of dispersed radiation beams; wherein the first optical relay system is disposed in optical paths of the plurality of dispersed radiation beams to relay the plurality of dispersed radiation beams as a plurality of first relayed radiation beams; and wherein the first optical relay system and the dispersive optical element are positioned and oriented to direct the plurality of first relayed radiation beams in substantially the same direction and to couple the plurality of first relayed radiation beams within the first predetermined area.

4. The optical system of claim 1 , wherein the first optical relay system is disposed in optical paths of the plurality of source radiation beams to relay the plurality of source radiation beams as a plurality of first relayed radiation beams; and wherein the dispersive optical element is disposed in optical paths of the plurality of first relayed radiation beams to redirect the plurality of first relayed radiation beams as a plurality of dispersed radiation beams; wherein the first optical relay system and the dispersive optical element are positioned and oriented to direct the plurality of dispersed radiation beams in substantially the same direction and to couple the plurality of dispersed radiation beams within the first predetermined area.

5. The optical system of claim 1 , wherein the dispersive optical element comprises a grating.

6. The optical system of claim 1 , wherein the dispersive optical element comprises a prism.

7. The optical system of claim 1 , wherein the first optical relay system comprises a mirror having a curved surface, and wherein the dispersive optical element comprises a grating coupled to the curved surface.

8. The optical system of claim 1 , wherein the first optical relay system comprises a lens having a convex surface and a substantially planar surface, and wherein the dispersive optical element comprises a grating coupled to the substantially planar surface.

9. The optical system of claim 1 , wherein the first optical relay system comprises a lens having a convex surface and a substantially planar surface, and wherein the dispersive optical element comprises a grating coupled to the convex surface.

10. The optical system of claim 1, wherein a single optical element comprises both the first optical relay system and the dispersive optical element.

11. The optical system of claim 1 , wherein a diffractive optic element comprises both the first optical relay system and the dispersive optical element.

12. The optical system of claim 1 , wherein a first refractive surface and a second refractive surface comprise the first optical relay system and the dispersive optical element.

13. The optical system of claim 12, wherein the first refractive surface and the second refractive surface are surfaces of a lens.

14. The optical system of claim 13, wherein the lens comprises a biconvex lens.

15. The optical system of claim 14, wherein the first optical relay system is a refractive optical relay system.

16. The optical system of claim 1 , wherein the first optical relay system is a reflective optical relay system.

17. The optical system of claim 1 , wherein the first optical relay system comprises a condenser lens.

18. The optical system of claim 1 , wherein irradiance distributions of the plurality of source radiation beams at least partially overlap within the first predetermined area.

19. The optical system of claim 1, wherein the dispersive optical element comprises a prismatic beam splitter.

20. The optical system of claim 1, wherein the dispersive optical element comprises a plate beam splitter and a grating.

21. The optical system of claim 1, wherein the dispersive optical element comprises a cube beam splitter and a prism.

22. The optical system of claim 1 , wherein the dispersive optical element comprises a cube beam splitter and a grating.

23. The optical system of claim 1 , further comprising: a reflective liquid crystal display disposed in optical paths of the plurality of source radiation beams to reflect the plurality of source radiation beams as a plurality of first reflected radiation beams; and a reflective surface to reflect the plurality of first reflected radiation beams as a plurality of second reflected radiation beams, thereby directing the plurality of second reflected radiation beams in substantially the same direction and coupling the plurality of second reflected radiation^' beams within a second predetermined area.

24. The optical system of claim 23, wherein the dispersive optical element comprises a prism, and wherein the reflective surface comprises a surface of the prism.

25. The optical system of claim 24, wherein the reflective surface is coated with a thin film coating that only transmits light having a predetermined polarization.

26. The optical system of claim 1 , further comprising: an imaging lens to image the plurality of source radiation beams.

27. The optical system of claim 26, wherein the predetermined area comprises at least a portion of an entrance pupil of the imaging lens.

28. The optical system of claim 1, wherein the plurality of source radiation beams comprises a substantially red beam of light, a substantially green beam of light, and a substantially blue beam of light.

29. The optical system of claim 1, further comprising: a plurality of discrete radiation sources to emit the plurality of source radiation beams.

30. The optical system of claim 29, wherein the plurality of discrete radiation sources comprises a plurality of light emitting diodes.

31. The optical system of claim 29, wherein the plurality of discrete radiation sources comprises a plurality of optical fibers.

32. An optical system comprising: a plurality of light-emitting diodes to emit a plurality of source radiation beams including a plurality of wavelengths; a first optical relay system disposed in optical paths of the plurality of source radiation beams to relay the plurality of source radiation beams; a dispersive optical element disposed in optical paths of the plurality of source radiation beams to redirect the plurality of source radiation beams, wherein the first optical relay system and the dispersive optical element are positioned and oriented to direct the plurality of source radiation beams in substantially the same direction and to couple the plurality of source radiation beams within an entrance pupil of an imaging lens.

33. A method for providing a multi-wavelength source of light, the method comprising steps of: relaying a plurality of source radiation beams including a plurality of wavelengths; redirecting the plurality of source radiation beams in substantially the same direction; and coupling the plurality of source radiation beams within a predetermined area.

34. The method of claim 33, further comprising a step of combining the plurality of source radiation beams into a combined radiation beam that forms an image of a virtual multi-wavelength radiation source within the predetermined area.

35. The method of claim 33, wherein the relaying step comprises a step of relaying the plurality of source radiation beams by refraction.

36. The method of claim 33, wherein the relaying step comprises a step of relaying the plurality of source radiation beams by reflection.

37. The method of claim 33, further comprising a step of imaging the plurality of source radiation beams onto an image plane.

38. In a system including a plurality of source radiation beams that include overlapping spectral regions and disjoint spectral regions, a first optical relay system disposed in optical paths of the plurality of source radiation beams to relay at least portions of the plurality of source radiation beams, and a dispersive optical element disposed in optical paths of the plurality of source radiation beams to redirect at least portions of the plurality of source radiation beams by dispersion, a method comprising a step of: adjusting the positions and orientations of the first optical relay system and the dispersive optical element to direct the portions of the plurality of source radiation beams having disjoint spectral regions in substantially the same direction and to couple the portions of the plurality of source radiation beams having disjoint spectral regions within a predetermined area.