Optically addressed spatial light modulator and method

• US 5,691,836 A
• Filed: 07/11/1995
• Issued: 11/25/1997
• Est. Priority Date: 07/11/1995
• Status: Expired due to Fees

• Current Assignee: Mems Optical, Inc. (Jenoptik AG)
• Original Assignee: SY Technology, Inc. (L3Harris Technologies, Inc.)
• Inventors: Clark, Rodney L.
• Primary Examiner(s): Epps, Georgia Y.
• Assistant Examiner(s): BEY, DAWN MARIE
• Application Number:
  US08/501,171
• Time in Patent Office: 868 Days
• Field of Search: 359/290, 359/291, 359/846, 359/850, 359/247, 359/263
• US Class Current: 359/247
• CPC Class Codes: G02B 26/02 for controlling the intensity of light G02B26/004 takes precedence
• CPC Class Codes: G09G 2360/142 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/3433 using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices using liquid crystal devices G09G3/36; using electrochromic devices G09G3/38
• CPC Class Codes: H04N 5/7458 the modulator being an array of deformable mirrors, e.g. digital micromirror device [DMD]

Abstract

An optically addressed spatial light modulator includes a reflective modulation element, a detector for detecting radiation, a micro-lens focusing a write beam on the detector and a read beam on the modulator element, and a circuit receiving a signal output from the detector generated in response to the write beam. The circuit alters the modulation element in accordance with the signal from the photodetector. The read beam is thus modulated in accordance with the amount of alteration of the modulation element. The read and write beams intercept the micro-lens at different angles and may have the same or differing wavelengths. Including multiple photodetectors on a single pixel allows use of a plurality of write beams. An array of the elements may be used to modulate a plurality of read beams.

Claims

1. An optically addressed spatial light modulator comprising:

a reflective modulator element including a metallic strip mounted above a conductor;

a detector for detecting incident radiation;

a focusing unit which focuses a write beam on said detector and a read beam on said reflective modulation element; and

a circuit receiving a signal output from said detector generated in response to said write beam and altering a modulation characteristic of said reflective modulator element in accordance with said signal, said read beam being modulated in accordance with an amount of alteration of said reflective modulator element,

wherein said modulation characteristic is a position of said metallic strip above said conductor, and said circuit alters said position by injecting a charge output in response to said signal into said conductor.

2. The optically addressed spatial light modulator as recited in claim 1, wherein said focusing unit comprises a micro-lens.

3. The optically addressed spatial light modulator as recited in claim 1, wherein said read beam and said write beam are incident on said focusing means at different angles.

4. The optically addressed spatial light modulator as recited in claim 3, wherein said read beam is normally incident on said focusing means.

5. The optically addressed spatial light modulator as recited in claim 1, wherein said read beam and said write beam have the same wavelength.

6. The optically addressed spatial light modulator as recited in claim 1, wherein said read beam and said write beam have different wavelengths.

7. The optically addressed spatial light modulator as recited in claim 1, wherein said detector comprises a plurality of photodetectors for detecting a corresponding plurality of write beams.

8. The optically addressed spatial light modulator as recited in claim 1, wherein said reflective modulator, said detector, and said circuit are integrated into a single pixel.

9. The optically addressed spatial light modulator as recited in claim 8, further comprising a plurality of said single pixels and a corresponding array of said focussing means.

10. The optically addressed spatial light modulator as recited in claim 9, wherein said focussing means comprises a micro-lens array having a pixel pitch equal to a pixel pitch of an array formed by said single pixels.

11. The optically addressed spatial light modulator as recited in claim 9, wherein each of said focussing means receives a corresponding read beam.

12. A method of spatially modulating light, comprising the steps of:

focusing an input write beam only onto a photodetector via a focusing unit;

focusing a read beam only onto a reflective modulator element via said focusing unit;

converting a signal output from said photodetector into a charge injection signal;

deforming said reflective modulator element in accordance with said charge injection signal, said deforming step including

injecting said charge injection signal into a conductor of said reflective modulator element, and

deflecting a metallic mirror of said reflective modular element in accordance with a charge on said conductor; and

outputting a modulated read beam reflected from a deformed reflective modulator element.

13. The method as recited in claim 12, further comprising, prior to said focusing steps, intercepting said read beam and said write beam at different angles on a micro-lens of said focusing unit.

14. The method as recited in claim 12, wherein said input write beam focussing step further comprises focussing a plurality of write beams onto a corresponding plurality of photodetectors.

15. The method as recited in claim 12, wherein said read beam focussing step comprises focussing a plurality of read beams onto a corresponding plurality of reflective modulator elements.