METHOD OF SPECKLE-NOISE PATTERN REDUCTION AND APPARATUS THEREFOR BASED ON REDUCING THE TEMPORAL COHERENCE OF THE PLANAR LASER ILLUMINATION BEAM BEFORE IT ILLUMINATES THE TARGET OBJECT BY APPLYING TEMPORAL INTENSITY MODULATION TECHNIQUES DURING THE TRANSMISSION OF THE PLIB TOWARDS THE TARGET

• US 6,991,165 B2
• Filed: 04/30/2002
• Issued: 01/31/2006
• 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): AVERY, JEREMIAH L
• Application Number:
  US10/136,182
• Publication Number:
  US 20030071123A1
• Time in Patent Office: 1,372 Days
• Field of Search: 23546201-46247, 235/472.01, 235/472.02, 235/472.03, 235/454, 235/455, 235/470, 235/494
• 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 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 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 temporal-coherence of the PLIB before the PLIB illuminates a target object.

Claims

1. A method of reducing speckle-pattern noise at the image detection array of a planar laser illumination and imaging (PLIIM) based camera 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 temporal-coherence of said PLIB before said PLIB illuminates a target object, by applying a temporal intensity modulation technique during the transmission of said PLIB towards the target, so that the object is illuminated with a temporally 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 temporal intensity modulation technique practiced during step (b) comprises:

modulating the temporal intensity of the transmitted PLIB along the planar extent thereof according to a temporal intensity modulation function (TIMF) so as to modulate the temporal intensity 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 temporal intensity modulation technique practiced during step (b) is selected from the group consisting of:

using visible mode-locked laser diodes (MLLDs) in a planar laser illumination array to produce said transmitted PLIB;

using electro-optical temporal intensity modulation panels (i.e. shutters) along the optical path of the transmitted PLIB;

using electrically-passive optically-reflective cavities affixed external to laser diodes employed in said PLIIM-based system;

using electro-optical temporal intensity modulators disposed along the optical path of a composite planar laser illumination beam;

using laser beam frequency-hopping devices;

using internal and external type laser beam frequency modulation (FM) devices; and

using internal and external laser beam amplitude modulation (AM) devices.

4. The method of claim 2, wherein step (b) comprises temporal intensity modulating said PLIB employing high-speed beam gating/shutter principles, prior to target object illumination.

5. The method of claim 2, wherein said PLIB is temporal intensity modulated prior to target object illumination employing visible mode-locked laser diodes (MLLDs).

6. The method of claim 2, wherein said PLIB is temporal intensity modulated prior to target object illumination employing current-modulated visible laser diodes (VLDs) operated in accordance with temporal intensity modulation functions (TIMFS) which exhibit a spectral harmonic constitution that results in a substantial reduction in the RMS power of speckle-pattern noise observed at the image detection array of PLIIM-based systems.

7. The method of claim 3, wherein said PLIB is temporal intensity modulated prior to target object illumination, employing electro-optical temporal intensity modulation panels (i.e. shutters) disposed along the optical path of the transmitted PLIB.

8. The method of claim 3, wherein said PLIB is temporal intensity modulated prior to target object illumination employing electrically-passive optically-reflective cavities affixed external to the VLD of a planar laser illumination module (PLIM) employ in the PLIIM-based system.

9. The method of claim 3, wherein said PLIB is temporal intensity modulated prior to target object illumination employing electro-optical temporal intensity modulators disposed along the optical path of a composite planar laser illumination beam.

10. The method of claim 3, wherein said PLIB is temporal intensity modulated prior to target object illumination employing laser beam frequency-hopping devices.

11. The method of claim 3, wherein said PLIB is temporal intensity modulated prior to target object illumination, employing internal and/or external type laser beam frequency modulation (FM) devices.

12. The method of claim 3, wherein said PLIB is temporal intensity modulated prior to target object illumination, employing internal and external laser beam amplitude modulation (AM) devices.

13. A planar laser illumination and imaging (PLIIM) based system capable of producing digital images with reduced levels of speckle-pattern noise, said PLIIM-based camera system having a working range and 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 it is moving past said PLIIM-based PLIIM-based camera 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 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 temporal-coherence of said PLIB before said PLIB illuminates a target object;

said speckle-pattern noise reduction subsystem applying a temporal intensity modulation technique during the transmission of said PLIB towards the target, so that the object is illuminated with a temporally 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;

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.

14. The PLIIM-based camera system of claim 13, wherein the temporal intensity modulation technique comprises modulating the temporal intensity of the transmitted PLIB along the planar extent thereof according to a temporal intensity modulation function (TPMF) so as to modulate the temporal intensity 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.

15. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem is selected from the group consisting of:

visible mode-locked laser diodes (MLLDs) employed in said planar laser illumination array;

electro-optical temporal intensity modulation panels (i.e. shutters) disposed along the optical path of the transmitted PLIB;

electrically-passive optically-reflective cavities affixed external to said laser diodes;

electro-optical temporal intensity modulators disposed along the optical path of a composite PLIB;

laser beam frequency-hopping devices;

internal and external type laser beam frequency modulation (FM) devices; and

internal and external laser beam amplitude modulation (AM) devices.

16. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises high-speed beam gating/shutter principles for temporal intensity modulating said planar laser illumination beam PLIB prior to target object illumination.

17. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises visible mode-locked laser diodes (MLLDs) for producing a PLIB that is temporal intensity modulated prior to target object illumination.

18. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises current-modulated visible laser diodes (VLDs) operated in accordance with temporal intensity modulation functions (TIMFS) which exhibit a spectral harmonic constitution that results in a substantial reduction in the RMS power of speckle-pattern noise observed at said image detection array of PLIIM-based system.

19. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises electro-optical temporal intensity modulation panels (i.e. shutters) disposed along the optical path of the transmitted PLIB so that said PLIB is temporal intensity modulated prior to target object illumination.

20. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises electrically-passive optically-reflective cavities affixed external to said laser diodes in said PLIIM-based system, so that said PLIB is temporal intensity modulated prior to target object illumination.

21. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises one or more electro-optical temporal intensity modulators disposed along the optical path of said planar laser illumination beam so that said PLIB is temporal intensity modulated prior to target object illumination.

22. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises a laser beam frequency-hopping device so that said PLIB is temporal intensity modulated prior to target object illumination employing.

23. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises internal and/or external type laser beam frequency modulation (FM) devices for temporal intensity modulating said PLIB is prior to target object illumination.

24. The PLIIM-based camera system of claim 13, wherein said speckle-pattern noise reduction subsystem comprises internal and/or external laser beam amplitude modulation (AM) devices, for temporal intensity modulating said PLIB prior to target object illumination.