Real time optical correlation system

• US 5,327,286 A
• Filed: 08/31/1992
• Issued: 07/05/1994
• Est. Priority Date: 08/31/1992
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Bienstock, Rachelle J., Sampsell, Jeffrey B.
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): Collins, Darryl J.
• Application Number:
  US07/937,987
• Time in Patent Office: 673 Days
• Field of Search: 359/559, 359/561, 359/560, 382/31, 382/42, 382/43
• US Class Current: 359/561
• CPC Class Codes: G01N 21/95623 using a spatial filtering method per se G02B
• CPC Class Codes: G01N 2201/0675 SLM
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G06E 3/005 using electro-optical or opto-electronic means
• CPC Class Codes: G06V 10/895 the filter being related to phase processing, e.g. phase-only filters

Abstract

An optical correlation unit for correlating the images of an inspection object and a reference object. The unit uses two phase modulating reflective spatial light modulators. A first spatial light modulator receives electronic input in the form of image data representing the inspection object. It modulates incoming light with this input and reflects the modulated output to a first Fourier transform lens. This lens provides the optical input to a second spatial light modulator, whose electronic input is transform data representing the complex conjugate of the Fourier transform of the reference image. The electronic input modulates the optical input, resulting in the Fourier product of the two images, which is then transformed to provide correlation data.

Claims

1. An optical correlation unit for providing a correlation image from image data representing a first object and Fourier transform image data representing a second object, comprising:

a first phase modulating spatial light modulator, having an array of reflective elements and means for receiving electronic input to each reflective element, wherein said electronic input represents a point of an input image and controls the phase modulation by said reflective;

element of light incident on its surface;

a coherent light source for illuminating the surface of said reflective elements of said first spatial light modulator;

a first Fourier transform lens for receiving light reflected from the surface of said first phase modulating spatial light modulator;

a second phase modulating spatial light modulator, having an array of reflective elements and having means for receiving electronic input to each reflective element, wherein said electronic input represents a point of an input image and that controls the phase modulation by said reflective element, and wherein said second phase modulating spatial light modulator is located at the Fourier image plane of said first Fourier transform lens;

means for directing light reflected from said second spatial light modulator to a second Fourier transform lens;

a second Fourier transform lens for receiving said light reflected from said second spatial light modulator; and

an image capture device located at the Fourier image plane of said second Fourier transform lens.

2. The optical correlation unit of claim 1, wherein said second spatial light modulator is tilted at an angle with respect to the image plane of said first Fourier transform lens.

3. The optical correlation unit of claim 1, wherein at least one of said spatial light modulators is a deformable micro-mirror device.

4. The optical correlation unit of claim 1, wherein said means for directing light is a beam splitter.

5. The optical correlation unit of claim 1, wherein each said spatial light modulator modulates light incident at its surface by adjusting the position of said reflective elements so as to change the path length of incoming light to an image plane.

6. The optical correlation unit of claim 1, wherein image data is obtained by viewing a real object, and further comprising an image capture unit for obtaining image data representing said one of said objects.

7. The optical correlation unit of claim 1, wherein said transform data is obtained by viewing a real object, and further comprising a transform image capture unit for obtaining transform image data representing one of said objects.

8. The optical correlation unit of claim 1, and further comprising a moveable stage for aligning said first object and said second object while said image data and said transform image data are captured, wherein said motion stage has a platform for moving one of said objects with respect to the other.

9. A method for correlating the image of a first object with the image of a second object, comprising the steps of:

obtaining a set of image data representing the image of a first object;

obtaining a set of transform data representing the complex conjugate of the transform image of a second object;

delivering said image data to the electronic input means of a first reflective phase modulating spatial light modulator;

delivering said transform data to the electronic input means of a second reflective phase modulating spatial light modulator;

illuminating the surface of said first spatial light modulator with incident light;

using said first spatial light modulator to modulate said incident light such that a phase encoded version of said image data is reflected from its surface;

directing light reflected from the surface of said first spatial light modulator through a first Fourier transform lens to said second spatial light modulator in the Fourier image plane of said first Fourier transform lens, resulting in a transform of said image data on the reflective surface of said second spatial light modulator;

using said second spatial light modulator to modulate said transform of said image data;

directing light reflected from said second spatial light modulator to a second Fourier transform lens; and

capturing the correlation image from said second Fourier transform lens with an image capture device.

10. The method of claim 9, and further comprising the step of tilting said second spatial light modulator to separate said correlation image from other output data.

11. The method of claim 9, and further comprising the step of delivering data representing the correlation image and the image of one of said object to a processor and using said processor to generate a composite image.

12. The method of claim 9, wherein said image data is obtained from a real object, and further comprising the steps of capturing a video image of one of said objects and converting said image to said image data.

13. The method of claim 9, wherein said capturing step is performed in real time with respect to the rest of the correlation steps.

14. The method of claim 9, wherein said transform data is obtained from a real object and further comprising the steps of capturing a Fourier image of one of said objects and converting said image to said transform data.

15. An optical correlation system for providing a correlation image from image data representing a first object and Fourier transform image data representing a second object, comprising:

an image capture unit for obtaining image data representing a first one of said objects;

a transform image capture unit for obtaining transform image data representing a second one of said objects;

a first phase modulating spatial light modulator, having an array of reflective elements and means for receiving said image data as electronic input to each element, which controls the phase modulation of said element;

a coherent light source for illuminating the surface of said first spatial light modulator;

a first Fourier transform lens for receiving light reflected from the surface of said first phase modulating spatial light modulator;

a second phase modulating spatial light modulator, having an array of reflective elements and having means for receiving said transform data as electronic input to each reflective;

element for controlling the phase modulation by said element, wherein said second phase modulating spatial light modulator is located at the Fourier image plane of said first Fourier transform lens;

means for directing light reflected from said second spatial light modulator to a Fourier transform lens;

a second Fourier transform lens for receiving said light reflected from said second spatial light modulator; and

an image capture device located at the Fourier image plane of said second Fourier transform lens.

16. The optical correlation unit of claim 15, and further comprising a moveable motion stage for aligning said first object and said second object while said image data and said transform image data are captured, wherein said motion stage has a platform for moving one of said objects with respect to the other.

17. The optical correlation unit of claim 15, wherein at least one of said spatial light modulators is a deformable micro-mirror device.

18. The optical correlation unit of claim 15, wherein said spatial light modulator modulates light incident at its surface by adjusting the position of said reflective elements so as to change the path length of incoming light to an image plane.