Method of and apparatus for reducing speckle-pattern noise in a planar laser illumination and imaging (PLIIM) based system

• US 7,131,586 B2
• Filed: 12/08/2003
• Issued: 11/07/2006
• 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): Kim, Ahshik
• Application Number:
  US10/730,481
• Publication Number:
  US 20050023353A1
• Time in Patent Office: 1,065 Days
• Field of Search: 235/454, 235/462.11, 235/462.14, 235/462.22, 235/462.24, 235/462.32
• US Class Current: 235/454
• 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

Methods of and systems for illuminating objects using planar laser illumination beams having substantially-planar spatial distribution characteristics that extend through the field of view (FOV) of image formation and detection modules employed in such systems. Each planar laser illumination beam is produced from a planar laser illumination beam array (PLIA) comprising an plurality of planar laser illumination modules (PLIMs). Each PLIM comprises a visible laser diode (VLD, a focusing lens, and a cylindrical optical element arranged therewith. The individual planar laser illumination beam components produced from each PLIM are optically combined to produce a composite substantially planar laser illumination beam having substantially uniform power density characteristics over the entire spatial extend thereof and thus the working range of the system. Preferably, each planar laser illumination beam component is focused so that the minimum beam width thereof occurs at a point or plane which is the farthest or maximum object distance at which the system is designed to acquire images, thereby compensating for decreases in the power density of the incident planar laser illumination beam due to the fact that the width of the planar laser illumination beam increases in length for increasing object distances away from the imaging optics. By virtue of the present invention, it is now possible to use both VLDs and high-speed CCD-type image detectors in conveyor, hand-held and hold-under type scanning applications alike, enjoying the advantages and benefits that each such technology has to offer, while avoiding the shortcomings and drawbacks hitherto associated therewith.

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, so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and a plurality of substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof;

(c) detecting said plurality of 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 step (b) involves applying a spatial phase shifting technique during the transmission of said PLIB toward the target.

3. The method of claim 2, 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.

4. The method of claim 2, wherein the spatial phase shifting technique practiced during step (b) is selected from the group consisting of:

moving the relative position 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 cell enabling steering of said transmitted PLIB using ultrasonic waves; and

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

5. The method of claim 2, 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.

6. The method of claim 2, 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.

7. The method of claim 2, 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.

8. The method of claim 2, 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.

9. The method of claim 2, 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.

10. 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 a 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 so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and a plurality of substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof;

whereby said plurality of 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.

11. The PLIIM based system of claim 10, wherein said speckle-pattern noise reduction subsystem applies a spatial phase shifting technique during the transmission of said PLIB towards the target.

12. The PLIIM based system of claim 11, 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.

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

means for moving the relative position 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 cell enabling steering of said transmitted PLIB using ultrasonic waves; and

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

14. The PLIIM based system of claim 11, 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.

15. The PLIIM based system of claim 11, 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.

16. The PLIIM based system of claim 11, 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.

17. The PLIIM based system of claim 11 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.

18. The PLIIM based system of claim 11, wherein said speckle-pattern 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.