METHOD OF SPECKLE-NOISE PATTERN REDUCTION AND APPARATUS THEREFOR BASED ON REDUCING THE SPATIAL-COHERENCE OF THE PLANAR LASER ILLUMINATION BEAM BEFORE THE BEAM ILLUMINATES THE TARGET OBJECT BY APPLYING SPATIAL PHASE SHIFTING TECHNIQUES DURING THE TRANSMISSION OF THE PLIB THERETOWARDS

• US 6,742,707 B1
• Filed: 02/12/2001
• Issued: 06/01/2004
• Est. Priority Date: 06/07/2000
• Status: Expired due to Fees

• Current Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Original Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Inventors: Zhu, Xiaoxun, Amundsen, Thomas, Naylor, Charles A., Knowles, Carl Harry, Jankevics, Andrew, Schnee, Michael D., Tsikos, Constantine J., Wirth, Allan, Dobbs, Russell Joseph
• Primary Examiner(s): Frech, Karl D.
• Assistant Examiner(s): Kim, Ahshik
• Application Number:
  US09/781,665
• Time in Patent Office: 1,205 Days
• Field of Search: 235/462.01, 235/462.11, 235/462.14, 235/462.24, 235/472.01, 356/237.1, 356/237.5
• US Class Current: 235/462.01
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: G02B 26/10 Scanning systems
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/10811 Focalisation
• CPC Class Codes: H01S 5/02325 Mechanically integrated components on mount members or optical micro-benches
• CPC Class Codes: H01S 5/4025 Array arrangements, e.g. constituted by discrete laser diodes or laser bar H01S5/42 takes precedence

Abstract

A planar laser illumination and imaging (PLIIM) based camera system capable of producing digital images with reduced levels of speckle-pattern noise. The PLIIM based camera system comprises a planar laser illumination array (PLIA) including a plurality of laser diodes for producing and projecting a planar laser illumination beam (PLIB) through a light transmission aperture, so as to illuminate an object as it is moving past said PLIIM based camera system. An image formation and detection (IFD) module is provided having a image detection array and imaging forming optics for providing said image detection array with a field of view (FOV). The PLIB and FOV are arranged in a coplanar relationship along the working range of the PLIIM based camera system so that the PLIB illuminates primarily within the FOV of the IFD module. A speckle-pattern noise reduction subsystem is integrated with the PLIA, for reducing the spatial-coherence of said planar laser illumination beam (PLIB) before the PLIB illuminates a target object. The speckle-pattern noise reduction subsystem carries out a spatial phase shifting technique during the transmission of the PLIB towards the target, so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and numerous substantially different time-varying speckle-noise patterns are produced at the image detection array over the photo-integration time period thereof. The numerous substantially different time-varying speckle-noise patterns are detected at the image detection array over the photo-integration time period, and the detected speckle-noise patterns are temporally averaged at said image detection array during the photo-integration time period thereof. As a result of such temporal averaging, the power of observable speckle-noise patterns is reduced at the image detection array. By virtue of the present invention, it is now possible to enjoy the benefits of laser-based illumination during high-speed imaging operations, without the adverse effects of speckle-pattern noise.

Claims

1. A method of reducing speckle-pattern noise at the image detection array of a planar laser illumination and imaging (PLIIM) based system, said method comprising the steps of:

(a) producing a planar laser illumination laser beam (PLIB) within a planar laser illumination and imaging (PLIIM) based system including an image detection array having image forming optics with a field of view (FOV) arranged in a coplanar relationship with said PLIB;

(b) reducing the spatial-coherence of said PLIB before said PLIB illuminates a target object, by applying a spatial phase shifting technique during the transmission of said PLIB towards the target, so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and numerous substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof;

(c) detecting said numerous substantially different time-varying speckle-noise patterns over said photo-integration time period; and

(d) temporally averaging said detected speckle-noise patterns at said image detection array during said photo-integration time period thereof, thereby reducing the power of observable speckle-noise patterns at said image detection array.

2. The method of claim 1, wherein the spatial phase shifting technique practiced during step (b) comprises:

shifting the spatial phase of the transmitted PLIB along the planar extent thereof so as to modulate the phase along the wavefront of the PLIB and produce said numerous substantially different time-varying speckle-noise patterns at the image detection array during the photo-integration time period thereof.

3. The method of claim 1, wherein the spatial phase shifting technique practiced during step (b) is selected from the group consisting of:

moving the relative position/motion of a cylindrical lens array and a laser diode array in said PLIIM based system;

reciprocating a pair of rectilinear cylindrical lens arrays relative to each other;

transmitting said PLIB through an acousto-optical Bragg-type cell enabling steering of said transmitted PLIB using ultrasonic waves; and

reflecting said PLIB off an ultrasonically-driven deformable mirror structure.

4. The method of claim 1, wherein step (b) comprises micro-oscillating a pair of refractive cylindrical lens arrays relative to each other in order to spatial phase shift said PLIB prior to target object illumination.

5. The method of claim 1, wherein step (b) comprises micro-oscillating a pair of light diffractive cylindrical lens arrays relative to each other in order to spatial phase shift said PLIB prior to target object illumination.

6. The method of claim 1, wherein step (b) comprises micro-oscillating a pair of reflective elements relative to a stationary refractive cylindrical lens array in order to spatial phase shift said PLIB prior to target object illumination.

7. The method of claim 1, wherein step (b) comprises micro-oscillating said PLIB using an acoustic-optic modulator in order to spatial phase modulate said PLIB prior to target object illumination.

8. The method of claim 1, wherein step (b) comprises micro-oscillating said PLIB using a piezo-electric driven deformable mirror structure in order to spatial phase modulate said PLIB prior to target object illumination.

9. A planar laser illumination and imaging (PLIIM) based system for producing digital images with reduced levels of speckle-pattern noise, said PLIIM based system comprising:

a planar laser illumination array (PLIA) including a plurality of laser diodes for producing and projecting a planar laser illumination beam (PLIB) through a light transmission aperture, so as to illuminate an object as it is moving past said PLIIM based system;

an image formation and detection (IFD) module having an image detection array and imaging forming optics for providing said image detection array with a field of view (FOV),

wherein said PLIB and said FOV are arranged in a coplanar relationship along the working range of said PLIIM based system so that the PLIB illuminates primarily within said FOV of the IFD module; and

a speckle-pattern noise reduction subsystem, integrated with said PLIA, for reducing the spatial-coherence of said PLIB before said PLIB illuminates a target object;

said speckle-pattern noise reduction subsystem applying a spatial phase shifting technique during the transmission of said PLIB towards the target, so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and numerous substantially different time-varying speckle-noise patterns are produced at said image detection array over the photointegration time period thereof;

whereby said numerous substantially different time-varying speckle-noise patterns are detected at said image detection array over said photo-integration time period, and said detected speckle-noise patterns are temporally averaged at said image detection array during said photo-integration time period thereof,

thereby reducing the power of observable speckle-noise patterns at said image detection array.

10. The PLIIM based system of claim 9, wherein the spatial phase shifting technique comprises modulating the spatial phase of the transmitted PLIB along the planar extent thereof so as to modulate the phase along the wavefront of said PLIB and produce said numerous substantially different time-varying speckle-noise patterns at the image detection array during the photo-integration time period thereof.

11. The method of claim 9, herein said speckle-pattern noise reduction subsystem is selected from the group consisting of:

means for moving the relative position/motion of a cylindrical lens array and a laser diode array in said PLIIM based system;

means for transmitting said PLIB through an acousto-optical Bragg-type cell enabling steering of said transmitted PLIB using ultrasonic waves; and

means for reflecting said PLIB off an ultrasonically driven deformable mirror structure.

12. The PLIIM based system of claim 9, wherein said speckle-pattern noise reduction subsystem comprises means for micro-oscillating a pair of refractive cylindrical lens arrays relative to each other in order to spatial phase modulate said PLIB prior to target object illumination.

13. The PLIIM based system of claim 9, wherein said speckle-pattern noise reduction subsystem comprises means for micro-oscillating a pair of light diffractive cylindrical lens arrays relative to each other in order to spatial phase shift said PLIB prior to target object illumination.

14. The PLIIM based system of claim 9, wherein said speckle-pattern noise reduction subsystem comprises means for micro-oscillating a pair of reflective elements relative to a stationary refractive cylindrical lens array in order to spatial phase shift said PLIB prior to target object illumination.

15. The PLIIM based system of claim 9, wherein said speckle-pattern noise reduction subsystem comprises means for micro-oscillating the planar laser illumination beam (PLIB) using an acoustic-optic modulator in order to spatial phase shift the PLIB prior to target object illumination.

16. The PLIIM based system of claim 9, wherein said speckle-patter noise reduction subsystem comprises means for micro-oscillating the planar laser illumination beam (PLIB) using a piezo-electric driven deformable mirror structure in order to spatial phase shift said PLIB prior to target object illumination.