Patent Application
20070268460
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense.
As described herein, a coupling lens is provided for a digital projection system with common path projection and illumination optics. The coupling lens operates to minimize the amount of stray light in the projection system to increase the full on and full off contrast of the system. To do so, the coupling lens is configured to maximize a distance between the stop of the system and the surface of coupling lens that is nearest to the aperture stop by cementing together a group of lenses that form the coupling lens. The surface of the coupling lens that receives the illumination beam forms a relatively steep surface with respect to the illumination beam to reduce the Fresnel reflections that enter the projection path of the projection system. Further, the indices of refraction of the lenses and cements may be optimized to minimize ghosting in the system.
Modulation device 114 modulates the illumination beam from coupling lens 110 according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beam is reflected from modulation device 114 through coupling lens 110 along an optical path 116. Coupling lens 110 telecentrically directs the imaging beam from modulation device 114 through a projection lens 120 along a projection path 118 such that an optical axis of projection path 118 is parallel or substantially parallel to normal 100 and the optical axis of illumination path 108. Projection lens 120 focuses and may zoom the imaging beam along an optical path 122 to cause still or video images to be formed on a screen or other display surface (not shown). Projection lens 120 images modulation device 114 through coupling lens 110 onto the screen or other display surface used for final display.
In projection system 10, illumination relay 106, coupling lens 110, and projection lens 120 are situated so as to minimize the overlap of the illumination and imaging beams along illumination path 108 and projection path 118. In particular, the illumination beam and the imaging beam each intersect different areas of an optical aperture stop plane 124 of the system such that the imaging beam is spatially separated from the illumination beam at aperture stop plane 124. Accordingly, illumination path 108 is effectively separated from projection path 118. In the embodiment of
Illumination source 102 may be a mercury ultra high pressure, xenon, metal halide, or other suitable projector lamp that provides a monochromatic or polychromatic illumination beam. Modulation device 114 transmits or reflects selected portions of the illumination beam through coupling lens 110 and projection lens 120 in response to an image input signal (not shown) to cause images to be projected onto a screen or other surface. Modulation device 114 comprises at least one digital modulator such as a spatial light modulator like LCos, liquid crystal display (LCD), digital micromirror display (DMD) or other type. In one embodiment, modulation device 114 includes a separate digital modulator for each color, e.g., red, blue, and green.
Fold mirror 202 reflects the illumination beam from illumination relay 106 through coupling lens 110 along an illumination path 204 such that an optical axis of illumination path 204 of the illumination beam is parallel or substantially parallel to optical axis 100 of modulation device 114 between fold mirror 202 and coupling lens 110. In the embodiment shown in
Coupling lens 110 refracts and focuses the illumination beam onto modulation device 114 through a beamsplitter 206 along optical path 112. Beamsplitter 206 separates the illumination beam into separate components (e.g., red, blue, and green components) that are provided to different modulators 114A, 114B, and 114C of modulation device 114. Modulators 114A, 114B, and 114C may be set in any suitable arrangement with respect to beamsplitter 206. Beamsplitter 206 may be a dichroic prism, a dichroic plate, a dichroic x-cube, or other element configured to separate the illumination beam into separate components. Beamsplitter 206 may be omitted in embodiments where modulation device 114 includes a single modulator. Coupling lens 110 refracts illumination beam 202 onto modulation device 114 at a non-zero angle of incidence.
Modulation device 114 modulates the illumination beam from coupling lens 110 according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beam is reflected from modulation device 114 through beamsplitter 206 and into coupling lens 110 along optical path 116. Coupling lens 110 refracts the imaging beam from modulation device 114 through projection lens 120 such that the imaging beam travels along an optical axis of optical path 118 which is parallel or substantially parallel to normal 100 to plane 101 of modulation device 114 and an optical axis of illumination path 204 of the illumination beam between coupling lens 110 and pupil plane 124. Projection lens 120 focuses and may zoom the imaging beam along optical path 122 to cause still or video images to be formed on a screen or other display surface.
In projection system 10A, illumination relay 106, coupling lens 110, and projection lens 120 are situated so as to minimize the overlap of the illumination beam and the imaging beam along illumination path 204 and optical path 118. In particular, the illumination beam and the imaging beam each intersect different areas of aperture stop plane 124 of the system such that the imaging beam is spatially separated from the illumination beam at aperture stop plane 124. Accordingly, the illumination path is effectively separated from the projection path.
Coupling lens 110, beamsplitter 206, and modulation device 114 operate as described with reference to
Fold mirror 212 reflects the imaging beam from coupling lens 110 into projection lens 120 along an optical path 214. In the embodiment shown in
In projection system 10B, illumination relay 106, coupling lens 110, and projection lens 120 are situated so as to minimize the overlap of the illumination and imaging beams along illumination path 108 and projection path 118. In particular, the illumination beam and the imaging beam each intersect different areas of aperture stop plane 124 of the system such that the imaging beam is spatially separated from the illumination beam at aperture stop plane 124. Accordingly, illumination path 108 is effectively separated from projection path 118.
In other embodiments, fold mirrors 202 (
Coupling lens 110 may be configured according to embodiments 110A, 110B, and 110C of
Lens 302 is a biconvex lens with a spherical convex surface 302A and a spherical convex surface 302B. Lens 302 receives the illumination beam along Illumination path 108 and refracts the illumination beam into lens 304. Surface 302A forms a relatively steep surface with respect to the illumination beam to minimize the amount of light from the illumination beam that reflects off of surface 302A an into projections lens 120. Lens 304 is a biconcave lens with a spherical concave surface 304A and a spherical concave surface 304B. Lens 304 receives the illumination beam from lens 302 and refracts the illumination beam into lens 306. Lens 306 is a piano-convex lens with a spherical convex surface 306A and a planar surface 306B. Lens 306 receives the illumination beam from lens 304 and refracts the illumination beam into beamsplitter 206.
Beamsplitter 206 splits the illumination beam into separate components and refracts each component onto a suitable modulator of modulation device 114. Each modulator modulates the illumination beam from beamsplitter 206 according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beams are reflected from the modulators and refracted by beamsplitter 206 to combine into a single imaging beam. Lens 306 receives the combined imaging beam and refracts the imaging beam into lens 304. Lens 304 receives the imaging beam from lens 306 and refracts the imaging beam into lens 302. Lens 302 receives the imaging beam from lens 304 and refracts the imaging beam along projection path 118.
The cements that adhere lenses 302, 304, 306, and beamsplitter 206 are chosen to minimize Fresnel reflections and increase the full on and full off contrast of projection system 10. In particular, the cements are chosen to match the indices of refraction of lenses with equal indices of refraction and approximate the average of the indices of refraction of lenses with unequal indices of refraction.
Surfaces 302B and 304A have an equal or approximately equal radius of curvature and are adhered together at an interface 312 using cement that has an index of refraction that is between an index of refraction of lens 302 and an index of refraction of lens 304. Similarly, surfaces 304B and 306A have an equal or approximately equal radius of curvature and are adhered together at an interface 314 using cement that has an index of refraction that is between an index of refraction of lens 304 and an index of refraction of lens 306. Further, surfaces 306B and 206A are planar or substantially planar and are adhered together at an interface 316 using cement that has an index of refraction that is equal or approximately equal to the indices of refraction of lens 306 and beamsplitter 206.
In one embodiment, lenses 302 and 306 and beamsplitter 206 have equal or approximately equal indices of refraction, and lens 304 has an index of refraction that is higher than the indices of refraction of lenses 302 and 306 and beamsplitter 206. In other embodiments, the indices of refraction of lenses 302, 304, and 306 and beamsplitter 206 may have other relationships.
In one embodiment, coupling lens 110A follows the lens prescription of Table 1. In another embodiment, coupling lens 110A follows the lens prescription of Table 2. In other embodiments, coupling lens 110A follows other lens prescriptions.
Lens 322 is a convex-concave lens with an even aspherical convex surface 322A and a spherical concave surface 322B. Lens 322 receives the illumination beam along Illumination path 108 and refracts the illumination beam into lens 324. Surface 322A forms a relatively steep surface with respect to the illumination beam to minimize the amount of light from the illumination beam that reflects off of surface 322A an into projections lens 120. Lens 324 is a convex-concave lens with a spherical convex surface 324A and a spherical concave surface 324B. Lens 324 receives the illumination beam from lens 322 and refracts the illumination beam into lens 326. Lens 326 is a plano-convex lens with a spherical convex surface 326A and a planar surface 326B. Lens 326 receives the illumination beam from lens 324 and refracts the illumination beam into beamsplitter 206.
Beamsplitter 206 splits the illumination beam into separate components and refracts each component onto a suitable modulator of modulation device 114. Each modulator modulates the illumination beam from beamsplitter 206 according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beams are reflected from the modulators and refracted by beamsplitter 206 to combine into a single imaging beam. Lens 326 receives the combined imaging beam and refracts the imaging beam into lens 324. Lens 324 receives the imaging beam from lens 326 and refracts the imaging beam into lens 322. Lens 322 receives the imaging beam from lens 324 and refracts the imaging beam along projection path 118.
The cements that adhere lenses 322, 324, 326, and beamsplitter 206 are chosen to minimize Fresnel reflections and increase the full on and full off contrast of projection system 10. In particular, the cements are chosen to match the indices of refraction of lenses with equal indices of refraction and approximate the average of the indices of refraction of lenses with unequal indices of refraction.
Surfaces 322B and 324A have an equal or approximately equal radius of curvature and are adhered together at an interface 332 using cement that has an index of refraction that is between an index of refraction of lens 322 and an index of refraction of lens 324. Similarly, surfaces 324B and 326A have an equal or approximately equal radius of curvature and are adhered together at an interface 334 using cement that has an index of refraction that is between an index of refraction of lens 324 and an index of refraction of lens 326. Further, surfaces 326B and 206A are planar or substantially planar and are adhered together at an interface 336 using cement that has an index of refraction that is equal or approximately equal to the indices of refraction of lens 326 and beamsplitter 206.
In one embodiment, lenses 322 and 326 and beamsplitter 206 have equal or approximately equal indices of refraction, and lens 324 has an index of refraction that is higher than the indices of refraction of lenses 322 and 326 and beamsplitter 206. In other embodiments, the indices of refraction of lenses 322, 324, and 326 and beamsplitter 206 may have other relationships.
In one embodiment, coupling lens 110B follows the lens prescription of Table 3. In other embodiments, coupling lens 110B follows other lens prescriptions.
In Table 3, the thickness shown for lens 326 includes the thickness of beamsplitter 206.
Surface 322A of lens 322 further follows the lens prescription of Table 4.
Lens 342 is a convex-concave lens with an aspherical convex surface 342A and a spherical concave surface 342B. Lens 342 receives the illumination beam along Illumination path 108 and refracts the illumination beam into lens 344. Surface 342A forms a relatively steep surface with respect to the illumination beam to minimize the amount of light from the illumination beam that reflects off of surface 342A an into projections lens 120. Lens 344 is a convex-concave lens with a spherical convex surface 324A and a spherical concave surface 324B. Lens 344 receives the illumination beam from lens 342 and refracts the illumination beam into lens 346. Lens 346 is a plano-convex lens with a spherical convex surface 346A and a planar surface 346B. Lens 346 receives the illumination beam from lens 344 and refracts the illumination beam into beamsplitter 206.
Beamsplitter 206 splits the illumination beam into separate components and refracts each component onto a suitable modulator of modulation device 114. Each modulator modulates the illumination beam from beamsplitter 206 according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beams are reflected from the modulators and refracted by beamsplitter 206 to combine into a single imaging beam. Lens 346 receives the combined imaging beam and refracts the imaging beam into lens 344. Lens 344 receives the imaging beam from lens 346 and refracts the imaging beam into lens 342. Lens 342 receives the imaging beam from lens 344 and refracts the imaging beam along projection path 118.
The cements that adhere lenses 342, 344, 346, and beamsplitter 206 are chosen to minimize Fresnel reflections and increase the full on and full off contrast of projection system 10. In particular, the cements are chosen to match the indices of refraction of lenses with equal indices of refraction and approximate the average of the indices of refraction of lenses with unequal indices of refraction.
Surfaces 342B and 344A have an equal or approximately equal radius of curvature and are adhered together at an interface 352 using cement that has an index of refraction that is between an index of refraction of lens 342 and an index of refraction of lens 344. Similarly, surfaces 344B and 346A have an equal or approximately equal radius of curvature and are adhered together at an interface 354 using cement that has an index of refraction that is between an index of refraction of lens 344 and an index of refraction of lens 346. Further, surfaces 346B and 206A are planar or substantially planar and are adhered together at an interface 356 using cement that has an index of refraction that is equal or approximately equal to the indices of refraction of lens 346 and beamsplitter 206.
In one embodiment, lenses 342 and 346 and beamsplitter 206 have equal or approximately equal indices of refraction, and lens 344 has an index of refraction that is higher than the indices of refraction of lenses 342 and 346 and beamsplitter 206. In other embodiments, the indices of refraction of lenses 342, 344, and 346 and beamsplitter 206 may have other relationships.
In one embodiment, coupling lens 110C follows the lens prescription of Table 5. In other embodiments, coupling lens 110C follows other lens prescriptions.
With the lens prescription of Table 5, beamsplitter 206 may have any suitable thickness.
Surface 342A of lens 342 further follows the lens prescription of Table 6.
Embodiments 110A, 110B, and 110C may advantageously minimize the amount of stray light that is reflected into the projection path of projection system 10 by maximizing the distance between pupil plane 124 and the surface of coupling lens 110 that is nearest to aperture stop plane 124 (i.e., surface 302A, surface 322A, and surface 342A). The distance is maximized by cementing the lenses in each embodiment together. In addition, the curvatures of the lenses in each embodiment 110A, 110B, and 110C forms a relatively steep surface with respect to the illumination beam to reduce the Fresnel reflections that enter the projection path. As a result, the full on and full off contrast of projection system 10 may be increased. Further, the indices of refraction of the lenses and cements may be optimized as described above to minimize ghosting in the system.
An offset optical architecture as described herein may effectively separate the illumination and projection paths while maintaining the optical performance and highest possible efficiency and minimizing stray light. This architecture may also avoid complex and expensive optical components and may allow for a compact package that has a maximum number of small sized lenses to achieve a low cost compact system.
Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Those with skill in the optical, mechanical, electro-mechanical, electrical, and computer arts will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the preferred embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
