Non-rigidly coupled, overlapping, non-feedback, optical systems for spatial filtering of fourier transform optical patterns and image shape content characterization

• US 7,988,297 B2
• Filed: 10/19/2007
• Issued: 08/02/2011
• Est. Priority Date: 10/19/2007
• Status: Active Grant

• Current Assignee: Look Dynamics, Inc.
• Original Assignee: Look Dynamics, Inc.
• Inventors: Crill, Rikk
• Primary Examiner(s): Epps; Georgia Y
• Assistant Examiner(s): CHOWDHURY, SULTAN U.
• Application Number:
  US11/875,770
• Publication Number:
  US 20090103052A1
• Time in Patent Office: 1,383 Days
• Field of Search: 353/20, 353/25, 353/30, 353/34, 353/38, 353/69, 353/98, 353/122, 382/106, 382/127, 382/140, 382/146, 382/151, 382/152, 382/168, 382/177, 382/189, 382/199, 382/203, 382/210, 382/211, 382/248, 382/250, 382/260, 382/266, 382/274, 382/278, 382/280, 359/1, 359/11, 359/13, 359/19, 359/27, 359/29, 359/35, 359/371, 359/372, 359/383, 359/385, 359/386, 359/397, 359/237, 348/46, 348/744, 348/E13.074, 348/E9.025, 372/99, 372/103, 372/22, 372/50.11, 372/50.124, 250/327.2, 250/337, 250/484.1, 250/397, 250/311
• US Class Current: 353/20
• CPC Class Codes: G06V 10/88 Image or video recognition using optical means, e.g. reference filters, holographic masks, frequency domain filters or spatial domain filters
• CPC Class Codes: G06V 10/895 the filter being related to phase processing, e.g. phase-only filters

Abstract

Non-rigidly coupled, overlapping, non-feedback optical systems for spatial filtering of Fourier transform optical patterns and image shape characterization comprises a first optical subsystem that includes a lens for focusing a polarized, coherent beam to a focal point, an image input device that spatially modulates phase positioned between the lens and the focal point, and a spatial filter at the Fourier transform pattern, and a second optical subsystem overlapping the first optical subsystem includes a projection lens and a detector. The second optical subsystem is optically coupled to the first optical subsystem.

Claims

1. Apparatus for processing an optical image isolating shape content and characterization of the optical image, comprising:

a source of coherent, monochromatic light for propagating a beam of planar polarized, coherent, monochromatic light along a beam path;

a first optical subsystem comprising a focusing lens positioned in the beam path and shaped to focus the beam to a focal point at a focal plane, an image input device positioned between the focusing lens and the focal point, wherein the image input device has the capability of modulating the beam of light with spatially dispersed phase changes that result in diffracted light of an image in the beam, and a spatial filter positioned in the beam where a Fourier transform pattern of the image is presented; and

a second optical subsystem overlapping the first optical subsystem in the beam path comprising a projection lens having respective focal points at respective focal distances on opposite sides of the projection lens, and a detector, wherein the second optical subsystem is optically coupled to the first optical subsystem with the projection lens and both of the focal points of the projection lens positioned on the beam path between the image input device and the detector and with the spatial filter positioned optically between the image input device and the projection lens.

2. The apparatus of claim 1, wherein the image input device is positioned anywhere between the focusing lens and the focal point where the beam illuminates the full image.

3. The apparatus of claim 2, wherein the projection lens is positioned anywhere between the spatial filter and the detector where it scales the image from the image input device to a desired size on the detector.

4. The apparatus of claim 2, wherein the image input device includes a pixilated imaging spatial light modulator that modulates phase of light in the beam on a pixel-by-pixel basis to rotate plane of polarization and diffract the light in a manner that writes the image into the beam.

5. The apparatus of claim 4, including a polarizer/analyzer positioned between the imaging spatial light modulator and the spatial filter for separating pixels of light polarized indifferent planes to pass light comprising the image toward the detector and remove from the beam light that is not part of the image.

6. The apparatus of claim 5, wherein the imaging spatial light modulator is a reflecting spatial light modulator in which the image is written into the beam by liquid crystal material adjacent a reflection plane that reflects the light beam, and wherein the reflecting spatial light modulator is oriented such that the beam has angle of incidence at the imaging spatial light modulator reflection plane of more than zero degrees.

7. The apparatus of claim 6, wherein the angle of incidence of the beam at the imaging spatial light modulator reflection plane is great enough so that any light in the beam reflected by the polarizer/analyzer back to the spatial light modulator gets reflected by the imaging spatial light modulator reflection plane.

8. The apparatus of claim 7, wherein the spatial filter comprises a filtering spatial light modulator comprising a filter plane that is oriented optically parallel to the imaging spatial light modulator where a Fourier transform of the image occurs.

9. The apparatus of claim 8, wherein the detector has a detection plane that is optically parallel to the imaging plane.

10. The apparatus of claim 8, wherein the spatial filter is configured to spatially select light in radially extending sectors where the Fourier transform of the image occurs for projection onto the detector.

11. The apparatus of claim 10, wherein the detector comprises a matrix of sensors and the projection lens is shaped and positioned at a location between the filtering spatial light modulator and the detector where the image filtered by the filtering spatial light modulator is scaled to match sizes of sensors and/or groups of sensors of the detector.

12. The apparatus of claim 10, wherein:

spatially filtering spatial light modulator spatially filters the Fourier transform of the image by activating liquid crystal material in selected portions of the filtering plane to rotate plane of polarization of light in selected portions of the beam; and

a polarizer/analyzer is positioned in the beam between the spatially filtering spatial light modulator and the detector to block portions of the light beam which are not selected from reaching the detector.

13. The apparatus of claim 2, wherein the beam is flared before the focusing lens to illuminate the full image.

14. A method of processing an optical image for isolating shape content and characterization of the optical image, comprising:

propagating a beam of coherent, monochromatic light along a beam path through a focusing lens positioned in the beam path to focus the beam to a focal point at a focal plane;

illuminating an object image in the beam between the focusing lens and the focal point in a manner that spatially modulates the beam of light by imposing spatially dispersed phase changes which result in diffracted light of the object image in the beam so that a Fourier transform of the object image occurs at the focal plane of the focusing lens;

spatially filtering the beam where a Fourier transform pattern of the object image is presented; and

projecting the object image in the spatially filtered beam onto a detector with a projection lens that is positioned with its focal points between the object image and a detector.

15. The method of claim 14, including writing the object image into the beam at an imaging plane with a pixilated spatial light modulator that modulates phase of light in the beam on a pixel-by-pixel basis to rotate plane of polarization and diffract the light as desired for the object image.

16. The method of claim 15, including passing the beam comprising the object image through a polarizer/analyzer to separate pixels of light polarized in different planes in order to block unwanted light and pass light comprising the object image.

17. The method of claim 16, including positioning a planar reflective surface at or adjacent the imaging plane and orienting the imaging plane and planar reflective surface so that the angle of incidence of the beam on the imaging plane and planar reflective surface is enough to reflect any feedback light reflected from the polarizer/analyzer to the imaging plane away from the detector.

18. The method of claim 17, including spatially filtering the beam where the Fourier transform of the object image occurs with a spatial light modulator that has a filtering plane positioned in the beam optically parallel to the imaging plane and that rotates plane of polarization of the light in selected portions of the Fourier transform plane as selected for separation from the rest of the light in the beam.

19. The method of claim 18, including blocking light that is not selected to reach the detector with a polarizer/analyzer so that only selected portions of the light reaches the detector to form a filtered image at the detector.

20. The method of claim 19, including detecting the object image as filtered by the filtering spatial light modulator on a detector plane of the detector that is oriented optically parallel to the imaging plane, which can be physically parallel, or, if the beam is folded with a spectral mirror, can be perpendicular to the imaging plane.

21. The method of claim 15, including positioning the image plane anywhere between the focusing lens and its focal point that the beam illuminates all of the pixels of the object image.

22. The method of claim 21, including flaring the beam in before it reaches the focusing lens to fully illuminate all of the pixels of the object image.