GENERALIZED METHOD OF SPECKLE-NOISE PATTERN REDUCTION AND PARTICULAR FORMS OF APPARATUS THEREFOR BASED ON REDUCING THE SPATIAL-COHERENCE OF THE PLANAR LASER ILLUMINATION BEAM AFTER IT ILLUMINATES THE TARGET BY APPLYING SPATIAL INTENSITY MODULATION TECHNIQUES DURING THE DETECTION OF THE REFLECTED/SCATTERED PLIB

• US 6,971,576 B2
• Filed: 04/30/2002
• Issued: 12/06/2005
• Est. Priority Date: 06/07/1999
• Status: Expired due to Fees

• Current Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Original Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Inventors: Good, Timothy A., Knowles, C. Harry, Jankevics, Andrew, Tsikos, Constantine J., Wirth, Allan
• Primary Examiner(s): LE, THIEN MINH
• Application Number:
  US10/136,028
• Publication Number:
  US 20030042309A1
• Time in Patent Office: 1,316 Days
• Field of Search: 23546201-46248, 235/472.01, 235/472.02, 235/472.03, 235/470, 235/454, 235/455
• US Class Current: 235/462.01
• CPC Class Codes: G02B 19/0014 at least one surface having optical power
• CPC Class Codes: G02B 19/0052 the light source comprising a laser diode coupling into light guides using intermediate optical elements G02B6/4204; semiconductor lasers having optical devices external to the laser cavity H01S5/005
• CPC Class Codes: G02B 19/0085 for use with both a detector and a source , e.g. in a transceiver, G02B19/009, G02B19/0095 take precedence
• CPC Class Codes: G02B 19/009 for use with infrared radiation
• CPC Class Codes: G02B 19/0095 for use with ultraviolet radiation
• CPC Class Codes: G02B 26/10 Scanning systems
• CPC Class Codes: G02B 27/095 Refractive optical elements
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G06K 7/10 by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
• CPC Class Codes: G06K 7/10594 Beam path
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/146 the method including quality enhancement steps
• CPC Class Codes: G06Q 10/00 Administration; Management
• CPC Class Codes: G06Q 30/00 Commerce
• CPC Class Codes: G06V 20/62 Text, e.g. of license plates, overlay texts or captions on TV images
• CPC Class Codes: G06V 30/144 using a slot moved over the image; using discrete sensing elements at predetermined points; using automatic curve following means
• CPC Class Codes: H01S 5/005 Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping H01S5/026, H01S5/18388 take precedence
• 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) 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 the 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 IFD, for reducing the spatial-coherence of said planar laser illumination beam (PLIB) after the PLIB has illuminated and reflected/scattered off the target object. The speckle-pattern noise reduction subsystem carries out a spatial intensity modulation technique after the reflection/scattering of the PLIB off the target, so that the laser illumination reflected/scattered off the object consists of spatially coherent-reduced planar laser illumination, causing numerous substantially different time-varying speckle-noise patterns to be 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 RMS 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 (PLLIM) based camera system, said method comprising the steps of:

(a) producing a planar laser illumination 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 the planar laser illumination beam after it illuminates and reflects/scatters off a target object, by applying a spatial intensity modulation technique during the detection of the reflected/scattered PLIB, so that image detection array detects a spatialty 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 RMS power of observable speckle-noise patterns at said image detection array.

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

modulating the spatial intensity of the return PLIB produced by the transmitted PLIB illuminating and reflecting and scattering off the target object so that a spatially coherent-reduced laser beam is detected at said image detector, and numerous time-varying speckle-noise patterns are detected over the photo-integration time period of said image detection array.

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

using high-speed electro-optical (e.g. ferro-electric, LCD, etc.) dynamic spatial filters, located before the image detector along the optical axis of the camera subsystem; and

physically rotating spatial filters, and/or any other spatial intensity modulation element arranged before the image detector along the optical axis of the camera subsystem, through which the received PLIB beam may pass during illumination and image detection operations for spatial intensity modulation without causing optical image distortion at said image detection array.

4. The method of claim 1, wherein the spatial intensity modulation technique practiced during step (b) comprises using a mechanism for physically rotating a spatial intensity modulator (e.g. apertures, irises, etc.) about the optical axis of the imaging lens of said PLIIM based camera system.

5. The method of claim 1, wherein the spatial intensity modulation technique practiced during step (b) comprises using a mechanism for photo-electronically rotating an axially-symmetric spatial intensity modulation element arranged before the entrance pupil of said PLIIM based camera system, through which the received PLIB beam may enter at any angle or orientation during illumination and image detection operations.

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

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

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

wherein said PLIB and FOV are arranged in a coplanar relationship along the working range of said PLIIM based camera 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 planar laser illumination beam (PLIB) after said PLIB illuminates and reflects/scatters off the target object;

said speckle-pattern noise reduction subsystem applying a spatial intensity modulation technique after the PLIB illuminates mid reflects/scatters off the target object, so as to produce a spatially coherent-reduced planar laser illumination beam (PLIB) that is detected at said image detection array, causing numerous substantially different time-varying speckle-noise patterns to be produced at said image detection array over the photo-integration 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 RMS power of observable speckle-noise patterns at said image detection array.

7. The PLIIM based camera system of claim 6, wherein the spatial intensity modulation technique comprises modulating the spatial intensity of the reflected/scattered PLIB along the planar extent thereof according to a spatial intensity modulation function (SIMF) so as to modulate the spatial intensity of said reflected/scattered PLIB along its wavefront.

8. The PLIIM based camera system of claim 6, wherein said speckle-pattern noise reduction subsystem is selected from the group consisting of:

using high-speed electro-optical (e.g. ferro-electric, LCD, etc.) dynamic spatial filters, located before the image detector along the optical axis of the camera subsystem; and

physically rotating spatial filters, and/or any other spatial intensity modulation element arranged before the image detector along the optical axis of the camera subsystem, through which the received PLIB beam may pass during illumination and image detection operations for spatial intensity modulation without causing optical image distortion at said image detection array.

9. The PLIIM based camera system of claim 6, wherein said speckle-pattern noise reduction subsystem comprises a mechanism for physically rotating a spatial intensity modulator (e.g. apertures, irises, etc.) about the optical axis of the imaging lens of said PLIIM based camera system.

10. The PLIIM based camera system of claim 6, wherein said speckle-pattern noise reduction subsystem comprises a mechanism for photo-electronically rotating an axially-symmetric spatial intensity modulation element arranged before the entrance pupil of the PLIIM based camera system, through which the received PLIB beam may enter at any angle or orientation during illumination and image detection operations.