Speckle reduction in laser illuminated projection displays having a one-dimensional spatial light modulator

• US 20070070302A1
• Filed: 09/29/2005
• Published: 03/29/2007
• Est. Priority Date: 09/29/2005
• Status: Active Grant

• Current Assignee: Coherent Inc (Coherent Corp.)
• Original Assignee: Coherent Inc (Coherent Corp.)
• Inventors: Govorkov, Sergei, Spinelli, Luis
• Granted Patent: US 7,413,311 B2
• Time in Patent Office: Days
• US Class Current: 353/94
• CPC Class Codes: G02B 26/0808 by means of one or more diffracting elements
• CPC Class Codes: G02B 26/105 with one or more pivoting mirrors or galvano-mirrors G02B26/101 takes precedence
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G03B 21/2033 LED or laser light sources
• CPC Class Codes: H04N 9/3132 using one-dimensional electronic spatial light modulators

Abstract

A projection display including a one-dimensional light modulator includes an optical arrangement for projecting light from a laser onto the modulator in the form of a line of light. Light from the laser is divided to create in effect a two-dimensional array of mutually incoherent light sources. Light from one axis of the array is projected onto the modulator to form the length of the line of light and light from the other axis of the array is projected onto the modulator to form the width of the line of light. Division of the light is accomplished without the use of any moving component.

Claims

1. A method of projecting light from a coherent light source onto a one-dimensional spatial light modulator as a line of light having a length and a width, the method comprising the steps of:

dividing the light from the light source in a manner such that the divided light is effectively formed into a rectangular, two-dimensional array of N₁×

N₂ mutually incoherent light-sources;

projecting light from the mutually incoherent light-sources along a first axis onto the spatial light modulator to form the length of the line of light;

projecting light from the mutually incoherent light-sources along a second, orthogonal axis, onto the spatial light modulator to form the width of the line of light; and

wherein the light-dividing step is accomplished without using any moving components.

2. The method of claim 1, wherein the coherent light source delivers a single beam of coherent light, with light therein having a coherence length, and wherein the beam is divided into N₁ mutually incoherent portions by a first optical arrangement and each of the N₁ beam portions is divided into N₂ mutually incoherent portions by a second optical arrangement.

3. The method of claim 2, wherein said first optical arrangement is an optical fiber arrangement having a single input end arranged to receive light from the coherent light source and N₁ output ends with optical path lengths from the input end to each of the output ends differing from each other by an amount greater than about the coherence length of light in the light beam.

4. The method of claim 3, wherein said second optical arrangement includes a stepped optical element having N₂ steps, with each of the N₂ beam portions having traveled a different optical path length in the stepped optical element, said optical path difference being greater than about the coherence length of light in the light beam.

5. The method of claim 2, wherein said first and second optical arrangements include respectively first and second stepped optical elements having respectively N₁ and N₂ steps, with steps of said first element oriented perpendicular to steps of said second optical element, wherein the N₁ beam portions travel a different optical path length in the first stepped optical element, wherein the N₂ portions travel a different optical path in the second stepped optical element, and wherein the optical path differences in said first and second stepped optical elements are greater than about the coherence length of light in the light beam.

6. The method of claim 2, wherein said first and second optical arrangements include respectively first and second optical delay lines each of said optical delay lines including a pair of spaced apart parallel plates with said parallel plate pairs being oriented perpendicular to each other, said first delay line dividing said beam into said N₁ portions by multiple partial reflections of the beam between the plates thereof and said second delay line dividing each of said beam portions in to said N₂ beam portions by multiple partial reflections of the beam between the plates thereof, and wherein the distance traveled by light between successive partial reflections in said delay lines is greater than about the coherence length of light in the light beam.

7. The method of claim 2, wherein N₁ and N₂ are equal.

8. The method of claim 7, wherein N₁ and N₂ are each equal to 8.

9. The method of claim 1, wherein the coherent light source delivers a N₁ spaced-apart beams coherent light beams incoherent with each other, and wherein an optical arrangement divides each of said N₁ beams into N₂ mutually incoherent portions.

10. The method of claim 9, wherein said second optical arrangement includes a stepped optical element having N₂ steps, with each of the N₂ beam portions having traveled a different optical path length in said stepped optical element, said optical path difference being greater than about the coherence length of light in the light beams.

11. The method of claim 9, wherein said coherent light source is a diode-laser bar including N₁ spaced-apart emitters, each of said emitters emitting one of said N₁ beams.

12. An apparatus for projecting light onto a one-dimensional spatial light modulator comprising:

a light source generating a coherent light beam;

first means for creating a plurality of mutually incoherent light portions along a first axis perpendicular to the propagation axis of the light beam;

second means for creating a plurality of mutually incoherent light portions along a second axis perpendicular to said first axis; and

optics for projecting the incoherent light portions onto the one-dimensional spatial light modulator to create a line of light, with the light propagating along said first axis defining the length of the line and with the light propagating along said second axis defining the width of the line.

13. An apparatus as recited in claim 12, wherein one of said means comprises an optical arrangement including a stepped optical element having a plurality of steps, with each of the light portions traveling a different optical path length in the stepped optical element.

14. An apparatus as recited in claim 12, wherein both of said means comprises an optical arrangement including a stepped optical element having a plurality of steps, with each of the light portions traveling a different optical path length in the stepped optical element and wherein the stepped optical element of the first means is oriented perpendicularly to the stepped optical element of the second means.

15. An apparatus as recited in claim 12, wherein one of said means comprises an optical delay line including a pair of spaced apart parallel plates, said delay line dividing said beam by multiple partial reflections of the beam between the plates thereof to create said plurality of mutually incoherent light portions.

16. An apparatus as recited in claim 12, wherein both of said means comprises an optical delay line including a pair of spaced apart parallel plates, said delay line dividing said beam by multiple partial reflections of the beam between the plates thereof to create said plurality of mutually incoherent light portions, with the parallel plates of the first means being oriented perpendicularly to the parallel plates of the second means.

17. An apparatus as recited in claim 12, wherein said first means comprises an optical fiber arrangement having a single input end arranged to receive light from the coherent light source and a plurality of output ends with optical path lengths from the input end to each of the output ends differing from each other to create said plurality of mutually incoherent light portions.