Speckle Mitigation In Laser Scanner Projector Systems

• US 20100110524A1
• Filed: 11/06/2008
• Published: 05/06/2010
• Est. Priority Date: 11/06/2008
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Gollier, Jacques
• Granted Patent: US 7,944,598 B2
• Time in Patent Office: Days
• US Class Current: 359/279
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: H04N 9/3129 scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161

Abstract

Laser scanner projection systems that reduce the appearance of speckle in a scanned laser image are provided. The laser projection system includes a visible light source having at least one laser, a scanning element and a system controller. The system controller is programmed to generate a scanned laser image. The system further includes a first lens that focuses a scanned output beam onto an intermediate image and a second lens that projects the intermediate image onto a projection surface. A periodic phase mask having a period that is approximately equal to or greater than the beam waist diameter of the scanned output beam is positioned at the intermediate laser image. The period of the periodic phase mask is such that the projection of the scanned output beam jumps progressively from pixel to pixel, thereby reducing speckle contrast in the scanned laser image.

Claims

1. A laser projection system comprising:

a visible light source comprising at least one laser;

a system controller programmed to generate a scanned laser image by operating the laser for optical emission of encoded image data and controlling a scanning element to scan an output beam of the visible light source across a plurality of image pixels;

a first lens configured to focus the scanned output beam to form an intermediate laser image;

a second lens configured to project the intermediate laser image onto a projection surface;

a periodic phase mask positioned closer to the intermediate laser image than to the first and second lenses and comprising a period that is approximately equal to or greater than a beam waist diameter of the scanned output beam at the intermediate laser image, wherein the periodic phase mask generates a plurality of orders of diffraction; and

a pupil phase mask comprising a plurality of pixels positioned in an optical path that is after the second lens and configured to modify a relative phase of the orders of diffraction generated by the periodic phase mask,

wherein projection of the scanned output beam jumps progressively from pixel to pixel, thereby reducing speckle contrast in a scanned laser image that is projected onto the projection surface.

2. The laser projection system as claimed in claim 1, wherein the periodic phase mask creates a single sub-beam when the scanned output beam is focused on a center portion of an individual period of the periodic phase mask, and creates at least two sub-beams when the scanned output beam is focused between at least two periods of the periodic phase mask.

3. The laser projection system as claimed in claim 1, wherein an average angle of incidence projected onto the projection surface is varied as the scanned output beam scans the periodic phase mask.

4. The laser projection system as claimed in claim 1, wherein the first lens is configured to focus the scanned output beam such that the beam waist diameter is less than or equal to the period of the periodic phase mask at the intermediate laser image.

5. The laser projection system as claimed in claim 1, wherein the periodic phase mask comprises a lens array, each lens having a diameter that is approximately equal to or greater than the beam waist diameter of the scanned output beam at the intermediate laser image.

6. The laser projection system as claimed in claim 5, wherein a pitch of the lens array multiplied by a magnification factor of the second lens is less than or approximately equal to an eye resolution element.

7. The laser projection system as claimed in claim 1, wherein the periodic phase mask comprises at least one holographic beam splitter.

8. The laser projection system as claimed in claim 1, wherein the periodic phase mask comprises a sinusoidal grating.

9. The laser projection system as claimed in claim 1, wherein the pupil phase mask comprises a static phase mask positioned in a Fourier plane of the second lens and is configured to alter the relative phase of the orders of diffraction generated by the periodic phase mask such that phases of multiple orders of diffraction are equal.

10. The laser projection system as claimed in claim 1, wherein the pupil phase mask comprises a dynamic phase mask positioned in a Fourier plane of the second lens and is modulated such that each pixel of the dynamic phase mask changes the phase of each diffraction order as a function of time.

11. The laser projection system as claimed in claim 1, wherein the pupil phase mask is incorporated into the second lens.

12. The laser projection system as claimed in claim 11, wherein the second lens is configured to modify the relative phase of the orders of diffraction generated by the periodic phase mask

13. The laser projection system as claimed in claim 1, wherein the system controller is programmed to:

control the scanning element such that the scanning element operates at a fast scanning direction to create a line of the scanned laser image and at a slow scanning direction to create multiple lines of the scanned laser image; and

misalign an angle of the scanning element at a frame-per-frame frequency such that the scanned laser image in a slow axis direction is shifted by an amplitude smaller that the period of the periodic phase mask.

14. A laser projection system comprising:

a visible light source comprising at least one laser;

a system controller programmed to generate an intermediate laser image at an intermediate plane by operating the laser for optical emission of encoded image data and controlling a scanning element to scan an output beam of the visible light source across a plurality of image pixels; and

a periodic phase mask positioned at the intermediate plane comprising a period that is approximately equal to or greater than a beam waist diameter of the scanned output beam at the intermediate plane and configured to generate a plurality of orders of diffraction.

15. The laser projection system as claimed in claim 14, wherein the periodic phase mask creates a single sub-beam when the scanned output beam is focused on a center portion of an individual period of the periodic phase mask, and creates at least two sub-beams when the scanned output beam is focused between at least two periods of the periodic phase mask.

16. The laser projection system as claimed in claim 14, wherein the periodic phase mask comprises a holographic beam splitter or a sinusoidal grating.

17. The laser projection system as claimed in claim 14, wherein the laser projection system further comprises:

a first lens configured to focus the scanned output beam to form the intermediate laser image; and

a second lens configured to project the intermediate laser image onto a projection surface.

18. The laser projection system as claimed in claim 17, wherein projection of the scanned output beam jumps progressively from pixel to pixel, thereby creating multiple speckle patterns.

19. The laser projection system as claimed in claim 17, wherein the second lens is configured to modify a relative phase of the orders of diffraction generated by the periodic phase mask.

20. The laser projection system as claimed in claim 19, wherein the second lens is configured to defocus the scanned laser image that is projected onto the projection surface.

21. A laser projection system comprising:

a visible light source comprising at least one laser;

a system controller programmed to generate an intermediate laser image at an intermediate plane by operating the laser for optical emission of encoded image data and controlling a scanning element to scan an output beam of the visible light source across a plurality of image pixels; and

a periodic phase mask positioned at the intermediate plane configured to create a single sub-beam when the scanned output beam is focused on a center portion of an individual period of the periodic phase mask, and create at least two sub-beams when the scanned output beam is focused between at least two periods of the periodic phase mask.

22. A method of reducing speckle in a projected image of a laser scanner projection system, said method comprising:

passing a scanning laser beam comprising encoded image data through a first lens that focuses the laser beam to form an intermediate laser image;

passing the scanning laser beam comprising the intermediate laser image through a periodic phase mask having a period that is equal to or greater than a beam waist diameter of the scanning laser beam at the intermediate laser image;

generating a plurality of orders of diffraction of the scanning laser beam;

projecting the intermediate laser image through a second lens and then through a pupil phase mask to form a projected image on a surface, wherein

the projected intermediate laser image comprises a projected scanned output beam that jumps progressively from pixel to pixel to reduce speckle contrast in a the projected image.