Projection system having low astigmatism

• US 7,329,006 B2
• Filed: 12/18/2003
• Issued: 02/12/2008
• Est. Priority Date: 06/11/2001
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Eckhardt, Stephen K., Bruzzone, Charles L., Ma, Jiaying, Aastuen, David J. W.
• Primary Examiner(s): Sever; Andrew T
• Application Number:
  US10/740,287
• Publication Number:
  US 20040130681A1
• Time in Patent Office: 1,517 Days
• Field of Search: 353/8, 353/20, 353/33, 353/34, 353/81, 349/8, 349/9, 349/15, 349/62, 359/464, 359/465, 359/490, 359494-502, 359831-837
• US Class Current: 353/20
• CPC Class Codes: G02B 27/1026 for use with reflective spatial light modulators
• CPC Class Codes: G02B 27/1033 having a single light modulator for all colour channels
• CPC Class Codes: G02B 27/126 The splitting element being a prism or prismatic array, including systems based on total internal reflection
• CPC Class Codes: G02B 27/145 having sequential partially reflecting surfaces
• CPC Class Codes: G02B 27/149 using crossed beamsplitting surfaces, e.g. cross-dichroic cubes or X-cubes
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10
• CPC Class Codes: H04N 9/3167 for polarizing the light beam polarizing optical systems per se G02B27/28

Abstract

Generally, the present invention relates to an apparatus for reducing astigmatism in a projection system that is particularly well suited to reducing astigmatism in LCD projection systems. A projection system includes a light source to generate light, conditioning optics to condition the light from the light source and an imaging core to impose on image on conditioned light from the conditioning optics to form image light. The imaging core includes a polarizing beamsplitter and at least one imager, and at least one element in the imaging core is adapted to reduce astigmatism in the image light. The astigmatism may arise in the polarizing beamsplitter. A projection lens system projects the astigmatism-reduced image light from the imaging core.

Claims

1. An image generating unit for a projection system, comprising:

an imaging core comprising at least a first imager, at least a first polarizing beamsplitter and a color combining unit, the color combining unit being substantially free of astigmatism, the first imager being capable of modulating illumination light incident thereon to produce first image light, the first image light being directed from the first imager to the color combining unit via the polarizing beamsplitter, wherein the first polarizing beamsplitter comprises a polarization sensitive film disposed between covers, at least one of the covers having a first refractive index higher than a second refractive index of the polarization sensitive film; and

an astigmatism-reducing element disposed on a path of the first image light comprising a sheet of material lying between the covers of the polarizing beam splitter, the sheet of material having a third refractive index higher than the first refractive index.

2. A unit as recited in claim 1, wherein the polarization sensitive film comprises a multilayer film.

3. A unit as recited in claim 1, wherein the color combining unit comprises an x-cube color combiner.

4. A unit as recited in claim 1, further comprising a projection lens unit to project an image of light received from the color combining unit, and a light source to generate the illumination light.

5. A unit as recited in claim 4, wherein the at least a first imager comprises three imagers, and further comprising color separating optics disposed to split the illumination light into different color bands directed to respective imagers, image light from the three imagers being combined into a single, combined image beam by the color combining unit.

6. An image generating unit for a projection system, comprising:

an imaging core comprising at least a first imager, at least a first polarizing beamsplitter and a color combining unit, the color combining unit being substantially free of astigmatism, the first imager being capable of modulating illumination light incident thereon to produce first image light the first image light being directed from the first imager to the color combining unit via the polarizing beamsplitter; and

an astigmatism-reducing element disposed on a path of the first image light to reduce astigmatism introduced in the image light within the imaging core wherein the astigmatism-reducing element comprises at least one refractive element having a first refractive index and being disposed obliquely relative to an axis of light passing through the at least one refractive element and wherein the at least one refractive element is disposed beside at least one other element having a second refractive index less than the first refractive index.

7. An imaging generating unit for a projection system, comprising:

an imaging core comprising at least a first imager, at least a first polarizing beamsplitter and a color combining unit comprising at least one prism, the first imager capable of modulating illumination light incident thereon to produce first image light, the first image light being directed from the first irnager to the color combining unit via the polarizing beamsplitter, the first polarizing beamsplitter comprising a polarization sensitive film disposed between covers, at least one of the covers having a first refractive index higher than a second refractive index of the multilayer, polarization sensitive film, the polarization sensitive film introducing astigmatism to image light propagating in the polarization sensitive film; and

an astigmatism-reducing element disposed on a path of the first image light to reduce astigmatism in the image light passing out of the imaging core, wherein the astigmatism-reducing element comprises a sheet of material lying between the covers of the polarizing beamsplitter, the sheet of material having a third refractive index higher than the first refractive index.

8. A unit as recited in claim 7, wherein the color combining unit comprises an x-cube color combiner.

9. A unit as recited in claim 7, wherein the polarization sensitive film comprises a multilayer film.

10. A unit as recited in claim 7, further comprising a projection lens unit to project an image of light received from the color combining unit, and a light source to generate the illumination light.

11. A unit as recited in claim 10, wherein the at least a first imager comprises three imagers, and further comprising color separating optics disposed to split the illumination light into different color bands directed to respective imagers, image light from the three imagers being combined into a single, combined image beam by the color combining unit.

12. An imaging generating unit for a projection system, comprising:

an imaging core comprising at least a first imager, at least a first polarizing beamsplitter and a color combining unit comprising at least one prism, the first imager capable of modulating illumination light incident thereon to produce first image light, the first image light being directed from the first imager to the color combining unit via the polarizing beamsplitter; and

an astigmatism-reducing element disposed on a path of the first image light to reduce astigmatism in the image light passing out of the imaging core, wherein the astigmatism-reducing element comprises at least one refractive element having a first refractive index and being disposed obliquely relative to an axis of light passing through the at least one refractive element wherein the at least one refractive element is disposed beside at least one other element having a refractive index less than the first refractive index.

13. A unit as recited in claim 12, wherein the at least one refractive element comprises a sheet of material of the first refractive index.