3-Dimensional vision system utilizing coherent optical detection

• US 5,114,226 A
• Filed: 09/28/1990
• Issued: 05/19/1992
• Est. Priority Date: 03/20/1987
• Status: Expired due to Fees

• Current Assignee: MetricVision, Inc. (Nikon Corporation)
• Original Assignee: Digital Optronics Corp.
• Inventors: Simonson, Dana, Goodwin, Frank E.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US07/589,625
• Time in Patent Office: 599 Days
• Field of Search: 356/4.5, 356/5, 356/28.5, 356/141, 356/152, 356/351, 250/203.2, 250/206.2
• US Class Current: 356/4.09
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02002 using two or more frequencies
• CPC Class Codes: G01B 9/02061 Reduction or prevention of effects of tilts or misalignment
• CPC Class Codes: G01S 17/06 Systems determining position data of a target
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/499 using polarisation effects
• CPC Class Codes: G02F 2/00 Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light G02F1/35 takes precedence

Abstract

A three-dimensional optical scanning vision system capable of producing high-resolution images in real-time includes an optical source for producing a source light beam. The source light beam is directed to a beam splitter which splits it into a local oscillator beam and a signal beam. The local oscillator beam is directed toward a photodetector, while the signal light beam is directed toward a target. Light reflected from the target is received by the beam splitter and directed toward a retroreflector which returns the beam to the beam splitter interface. Quarter wave plates and the retroreflector insure that the return light beam and the local oscillator beam are collimated and have the same polarization state. Mixing of the local oscillator beam and the return light beam occurs at the beam splitter interface, thus providing coherent optical detection by the photodetector. The photodetector thus provides an output signal providing a high degree of information about the target. The system also includes scanner optics to scan the signal light beam across the target. A processor is also included for outputting a three-dimensional image of the target, and for controlling the scanner optics.

Claims

1. A vision system for determining characteristics of a target comprising:

optical source means for providing a source light beam which is linearly polarized in a first orientation;

beam splitter means for splitting said source beam into a target beam and a reference beam both of which are linearly polarized in said first orientation;

quarter wave plate means for converting said target beam to circular polarization in a first rotational direction and directing said target beam toward the target, and for receiving a return light beam reflected from said target which is circularly polarized in a second rotational direction opposite to said first rotational direction, said quarter wave plate means converting said return light beam to linear polarization in a second orientation perpendicular to said first orientation;

retroreflector means for converting said return light beam which is linearly polarized in said second orientation to linear polarization in said first orientation and for reflecting said return beam;

detector means for optical heterodyne detection of said reference and return beams which are both linearly polarized in said first orientation, and for providing an output signal including information about said

scanning means for scanning said target beam across said target; and

processing means for controlling said scanning.

2. The vision system according to claim 1 wherein said beam splitter means is a beam splitter device comprising a thin film dielectric coating for splitting said source beam by passing said target beam and by reflecting said reference beam due to inherent imperfections in said thin film coating;

wherein said quarter wave plate means comprises first quarter wave means, optically coupled between said beam splitter device and said target, for converting the polarization of said target beam and said return beam; and

wherein said retroreflector means comprises second quarter wave means, optically coupled between said beam splitter device and a retroreflector, for converting the polarization of said reference beam.

3. Apparatus according to claim 2 further including:

first lens means for collimating said source beam and directing it to said beam splitter device;

second lens means for focusing said target beam on said target; and

third lens means for focusing said reference beam and said return beam on said detector means.

4. Apparatus according to claim 3 further including integral housing means for integrally supporting:

said optical source means;

said beam splitter device;

said detector means;

said first and second quarter wave means; and

said first, second, and third lens means.

5. Apparatus according to claim 1 wherein said optical source means includes:

laser diode means for providing said source beam; and

laser driver means for sweep frequency modulating said source beam.

6. Apparatus according to claim 1 wherein said scanning means include:

facet wheel means for scanning said target beam in a first direction; and

galvanometer means for scanning said target beam in a second direction.

7. Apparatus according to claim 1 wherein said scanning means includes a holographic scanner.

8. Apparatus according to claim 1 wherein said detector means includes a PIN detector.

9. Apparatus according to claim 1 wherein said processing means receives said output signal from said detector means and includes means for storing a 256×

256×

256 volume of information about said target.

10. An optical apparatus for splitting a source light beam which is linearly polarized in a first orientation into a target beam and a reference beam, and ensuring that a return light beam reflected from a target is linearly polarized in said first orientation, said apparatus comprising:

beam splitter means for splitting said source beam into said target beam and said reference beam both of which are linearly polarized in said first orientation,

quarter wave plate means for converting said target beam to circular polarization in a first rotational direction and directing it toward said target, and receiving said return light beam reflected from said target which is circularly polarized in a second rotational direction opposite to said first rotational direction, said quarter wave plate means converting said return light beam to linear polarization in a second orientation perpendicular to said first orientation,

retroreflector means for converting said return beam which is linearly polarized in said second orientation to linear polarization in said first orientation and directing said return beam along an optical axis coincidental with an axis of said reference beam.

11. An optical apparatus according to claim 10 wherein said beam splitter means comprises:

a beam splitter device for splitting said source beam by passing said target beam and by reflecting said reference beam due to inherent imperfections in said beam splitter device;

wherein said quarter wave plate means comprises first quarter wave means, optically coupled between said beam splitter device and said target, for converting the polarization of said target beam and said return beam; and

wherein said retroreflector means comprises second quarter wave means, optically coupled between said beam splitter device and a retroreflector, for converting the polarization of said reference beam.

12. Apparatus according to claim 11 further including:

first lens means for collimating said source beam and directing it to said beam splitter device;

second lens means for focusing said target beam on said target; and

third lens means for focusing said reference beam and said return beam along said optical axis.

13. Apparatus according to claim 12 further including:

optical source means for providing said source beam; and

detector means for optical heterodyne detection of said reference and return beams; and

for providing an output signal containing information about said target.

14. Apparatus according to claim 13 further including integral housing means for integrally supporting:

said optical source means;

said beam splitter device;

said detector means;

said first and second quarter wave means; and

said first, second, and third lens means.

15. Apparatus according to claim 13 further including:

scanner means for scanning said target beam across said target; and

processor means for controlling said scanner means, for receiving said output signal from said detector means, and for storing three-dimensional information about said target.

16. An optical apparatus for splitting a source light beam which is linearly polarized in a first orientation into a reference beam and a target beam, and for ensuring that a return light beam reflected from a target is linearly polarized in said first orientation, comprising:

beam splitter means for splitting said source beam into said reference beam and said target beam, both of which are linearly polarized in said first orientation, and for directing said reference beam along an optical detection axis;

first quarter wave means for converting said target beam to circular polarization in a first rotational direction, and for converting said return light beam, which is circularly polarized in a second rotational direction opposite to said first rotational direction, to linear polarization in a second orientation perpendicular to said first orientation;

said beam splitter means reflecting said return beam after it has passed through said first quarter wave means;

second quarter wave means for converting the reflected return beam to circular polarization in said second rotational direction;

retroreflector means for receiving said reflected return beam after it has passed through said second quarter wave means and retroreflecting it along said optical detection axis;

the retroreflected return beam being circularly polarized in said first rotational direction; and

said second quarter wave means converting the retroreflected return beam to linear polarization in said first orientation to cause optical heterodyne mixing of said retroreflected return and reference beams along said optical detection axis.

19. Apparatus according to one of claims 16, 17 or 18 further including:

detector means disposed on said optical detection axis, for coherent optical detection of said mixed reference and return beams, and for providing an output signal containing information about said target; and

laser diode means for providing said source light beam.

20. Apparatus according to claim 19 further including:

scanning means for scanning said target beam across said target; and

processing means for controlling said scanning means, and for receiving said output signal from said detector means, and for providing image signals containing three-dimensional information about said target.

21. Apparatus according to claim 19 further including:

first lens means, optically coupled between said laser diode means and said beam splitter means, for collimating said source light beam;

second lens means, optically coupled between said beam splitter means and said target, for focusing said target beam on said target; and

third lens means, optically coupled between said beam splitter means and said detector means, for focusing said mixed return and reference beams on said detector means.

22. Apparatus according to claim 21 further including integral support means for integrally housing:

said laser diode means;

said detector means;

said retroflector means;

said first and second quarter wave means; and

said first, second, and third lens means.

17. An optical apparatus for splitting a source light beam which is linearly polarized in a first orientation into a reference beam and a target beam, and for ensuring that a return light beam reflected from a target is linearly polarized in said first orientation, comprising:

beam splitter means for splitting said source beam into said reference beam and said target beam, both of which are linearly polarized in said first orientation, and for directing said reference beam in a first direction along an optical detection axis;

first quarter wave means for converting said target beam to circular polarization in a first rotational direction, and for converting said return light beam, which is circularly polarized in a second rotational direction opposite to said first rotational direction, to linear polarization in a second orientation perpendicular to said first orientation;

said beam splitter means reflecting said return beam after it has passed through said first quarter wave means in a second direction along said optical detection axis;

second quarter wave means for converting the reflected return beam to circular polarization in said second rotational direction;

retroreflector means for receiving said reflected return beam after it has passed through said second quarter wave means and retroreflecting it along said optical detection axis in said first direction, the retroreflected return beam being circularly polarized in said first rotational direction;

said second quarter wave means converting the retroreflected return beam to linear polarization in said first orientation to cause optical heterodyne mixing of said retroreflected return and reference beams along said optical detection axis in said first direction.

18. An optical apparatus for splitting a source light beam which is linearly polarized in a first orientation into a reference beam and a target beam, and for ensuring that a return light beam reflected from a target is linearly polarized in said first orientation, said apparatus comprising:

beam splitter means for splitting said source beam into said reference beam and said target beam, both of which are linearly polarized in said first orientation, and for directing said target beam toward said target along an optical target axis and for transmitting said reference beam along an optical detection axis;

first quarter wave means for converting said target beam to circular polarization in a first rotational direction, and for converting said return light, which is circularly polarized in a second rotational direction opposite to said first rotational direction, to linear polarization in a second orientation perpendicular to said first orientation;

said beam splitter means transmitting therethrough said return beam after it has passed through said first quarter wave means;

second quarter wave means for converting the transmitted return beam to circular polarization in said second rotational direction;

retroreflector means for receiving said transmitted return beam after it has passed through said second quarter wave means and retroreflecting it along said optical target axis, the retroreflected return beam being circularly polarized in said first rotational direction; and

said second quarter wave means converting the retroreflected return beam to linear polarization in said first orientation, optical heterodyne mixing of said return and reference beams taking place along said optical detection axis.