METHODS FOR CONFOCAL OPTICAL PROTRACTOR WITH STRUCTURED LIGHT ILLUMINATION TO DETERMINE ANGLES

• US 20200132444A1
• Filed: 05/14/2019
• Published: 04/30/2020
• Est. Priority Date: 10/26/2018
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Inventors: RUMALA, YISA S.
• Granted Patent: US 10,809,057 B2
• Time in Patent Office: Days
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01B 9/00 Measuring instruments characterised by the use of optical techniques
• CPC Class Codes: G01C 1/00 Measuring angles
• CPC Class Codes: G01D 5/266 by interferometric means G01D5/353 takes precedence
• CPC Class Codes: G01P 3/36 Devices characterised by the use of optical means, e.g. using infrared, visible, or ultraviolet light G01P3/68 takes precedence; gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams G01C19/64
• CPC Class Codes: G02B 17/004 Systems comprising a plurality of reflections between two or more surfaces, e.g. cells, resonators multipass arrangements for optical cuvettes G01N21/031; laser resonators H01S3/05
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: G02B 27/0927 Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat
• CPC Class Codes: G02B 5/04 Prisms
• CPC Class Codes: H01S 3/08045 Single-mode emission

Abstract

A method for simultaneously measuring roll angle, pitch angle and yaw angle of an element. The method includes directing a laser beam into a spiral phase plate resonator (SPPR) device to generate an optical vortex intensity pattern having a centroid and radial light peaks. The method reflects the laser beam off of the element after it has propagated through the SPPR device so that the laser beam is directed onto a camera that generates images of the optical vortex intensity pattern. The method determines a location of the centroid in the images, determines integrated counts along a radial direction from the centroid in the images, and determines a location of the radial light peaks in the images using the integrated counts. The method changes the frequency of the laser beam to rotate the radial light peaks, and estimates the roll angle of the element from the change in frequency.

Claims

1. A method for measuring pitch, yaw and roll angles of an element, said method comprising:

providing a frequency tunable laser beam;

directing the laser beam through a spiral phase plate resonator (SPPR) device, said SPPR device including opposing reflective surfaces that reflect the laser beam back and forth in the device, wherein one of the reflective surfaces includes a spiral step index that causes multiple reflected amplitudes having different phases to be combined and generate an optical vortex intensity pattern defined by the phases of the multiple amplitudes, where the intensity pattern includes a singularity centroid and radial light peaks, said SPPR device reflecting or transmitting a first beam and transmitting a second beam;

reflecting the first beam off of a closed shutter so that the first beam is directed onto a first camera that generates images of the optical vortex intensity pattern;

directing the second beam onto a second camera that generates images of the optical vortex intensity pattern;

determining an initial frequency of the laser beam by an angular position of the radial light peaks in the images generated by the first and second cameras;

synchronizing a registration between the images generated by the first and second cameras;

determining a location of the centroid in the images generated by the first camera and determining a location of the centroid in the images generated by the second camera;

determining integrated counts along a radial direction from the centroid in the images generated by the first camera as a function of beam roll angle;

determining a location of the radial light peaks in the images generated by the first camera using the integrated counts;

determining integrated counts along a radial direction from the centroid in the images generated by the second camera as a function of beam roll angle;

determining a location of the radial light peaks in the images generated by the second camera using the integrated counts;

opening the shutter so that the first beam propagates through the open shutter onto the element and a reflected first beam from the element is directed onto the first camera that again generates images including the optical vortex intensity pattern;

again determining the location of the centroid in the images generated by the first camera;

again determining the integrated counts along the radial direction from the centroid in the images generated by the first camera as a function of beam roll angle;

changing the frequency of the laser beam to rotate the radial light peaks in the optical vortex intensity pattern in the images generated by the first camera; and

estimating the roll angle of the element from the change in frequency that rotated the optical vortex intensity pattern.

2. The method according to claim 1 wherein determining the location of the radial light peaks includes using a non-linear fitting routine.

3. The method according to claim 1 further comprising determining the pitch angle of the element by a shift of the vortex intensity pattern in one plane in the images generated by the first camera when the shutter is open, and determining the yaw angle of the element by a shift of the vortex intensity pattern in a plane orthogonal to the one plane in the images generated by the first camera when the shutter is open.

4. The method according to claim 1 wherein the SPPR device is a mid to high internal reflectivity device and the first beam is transmitted through the SPPR device, and wherein the radial light peaks have a high contrast fringe.

5. The method according to claim 4 wherein determining the location of the centroid of the optical vortex intensity pattern in the images generated by the first and second cameras includes segmenting the images generated by the first or second camera into a number of quadrants representative of the number of radial light peaks, estimating the location of the centroid and the width of the radial light peak in each quadrant, applying a non-linear fitting routine to each radial light peak, estimating the location of the centroid and the width of the radial light peaks using the non-linear fitting routine, and computing the centroid of the optical vortex intensity pattern using the estimated centroid and width of the radial light peaks in the individual quadrants.

6. The method according to claim 1 wherein the SPPR device is a low internal reflectivity device and the first beam is reflected off of the SPPR device, and wherein the radial light peaks have a low contrast fringe.

7. The method according to claim 6 wherein determining the location of the centroid of the optical vortex intensity pattern in the images generated by the first and second cameras includes estimating the location of the centroid and the width of the second beam, applying a non-linear fitting routine to the second beam, estimating the location of the centroid and the width of the second beam using the non-linear fitting routine, rotating the optical vortex intensity pattern in the second beam by changing the frequency of the laser beam and repeating estimating the location of the centroid and the width of the second beam, applying a non-linear fitting routine to the second beam, and estimating the location of the centroid and the width of the second beam using the non-linear fitting routine.

8. The method according to claim 1 further comprising stabilizing an intensity of the laser beam using a beam intensity detector and a pattern orientation detector before determining the location of the centroid in the images generated by the first and second cameras.

9. The method according to claim 1 further comprising removing background from the images after the centroid in the images generated by the first and second cameras is located.

10. The method according to claim 1 wherein the optical vortex intensity pattern includes four radial light peaks.

11. A method for measuring pitch, yaw and roll angles of an element, said method comprising:

providing a frequency tunable laser beam;

directing the laser beam into a spiral phase plate resonator (SPPR) device, said SPPR device including opposing reflective surfaces that reflect the laser beam back and forth in the device, wherein one of the reflective surfaces includes a spiral step index that causes multiple reflected amplitudes having different phases to be combined and generate an optical vortex intensity pattern defined by the phases of the multiple amplitudes, where the intensity pattern includes a singularity centroid and radial light peaks;

reflecting the laser beam off of the element after it has propagated through the SPPR device so that the laser beam is directed onto a camera that generates images of the optical vortex intensity pattern;

determining a location of the centroid in the images generated by the camera;

determining integrated counts along a radial direction from the centroid in the images generated by the camera as a function of beam roll angle;

determining a location of the radial light peaks in the images generated by the camera using the integrated counts;

changing the frequency of the laser beam to rotate the radial light peaks in the optical vortex intensity pattern in the images generated by the camera; and

estimating the roll angle of the element from the change in frequency that rotated the optical vortex intensity pattern.

12. The method according to claim 11 wherein determining the location of the radial light peaks includes using a non-linear fitting routine.

13. The method according to claim 11 further comprising determining the pitch angle of the element by a shift of the vortex intensity pattern in one plane in the images generated by the camera, and determining the yaw angle of the element by a shift of the vortex intensity pattern in a plane orthogonal to the one plane in the images generated by the camera.

14. The method according to claim 11 wherein the SPPR device is a mid to high internal reflectivity device and the laser beam is transmitted through the SPPR device, and wherein the radial light peaks have a high contrast fringe.

15. The method according to claim 14 wherein determining the location of the centroid of the optical vortex intensity pattern in the images generated by the camera includes segmenting the images generated by the camera into a number of quadrants representative of the number of radial light peaks, estimating the location of the centroid and the width of the radial light peak in each quadrant, applying a non-linear fitting routine to each radial light peak, estimating the location of the centroid and the width of the radial light peaks using the non-linear fitting routine, and computing the centroid of the optical vortex intensity pattern using the estimated centroid and width of the radial light peaks from the individual quadrants.

16. The method according to claim 11 wherein the SPPR device is a low internal reflectivity device and the laser beam is reflected off of the SPPR device, and wherein the radial light peaks have a low contrast fringe.

17. The method according to claim 16 wherein determining the location of the centroid of the optical vortex intensity pattern in the images generated by the camera includes estimating the location of the centroid and the width of the laser beam, applying a non-linear fitting routine to the laser beam, estimating the location of the centroid and the width of the laser beam using the non-linear fitting routine, rotating the optical vortex intensity pattern in the laser beam by changing the frequency of the laser beam and repeating estimating the location of the centroid and the width of the laser beam, applying a non-linear fitting routine to the laser beam, and estimating the location of the centroid and the width of the laser beam using the non-linear fitting routine.

18. The method according to claim 11 further comprising stabilizing an intensity of the laser beam using a beam intensity detector and a pattern orientation detector before determining the location of the centroid in the images generated by the camera.

19. The method according to claim 11 wherein the optical vortex intensity pattern includes four radial light peaks.

20. A method for measuring pitch, yaw and roll angles of an element, said method comprising:

providing a frequency tunable laser beam;

stabilizing an intensity of the laser beam using a beam intensity detector and a pattern orientation detector;

directing the laser beam into a spiral phase plate resonator (SPPR) device, said SPPR device including opposing reflective surfaces that reflect the laser beam back and forth in the device, wherein one of the reflective surfaces includes a spiral step index that causes multiple reflected amplitudes having different phases to be combined and generate an optical vortex intensity pattern defined by the phases of the multiple amplitudes, where the intensity pattern includes a singularity centroid and four radial light peaks;

reflecting the laser beam off of the element after it has propagated through the SPPR device so that the laser beam is directed onto a camera that generates images of the optical vortex intensity pattern;

determining a location of the centroid in the images generated by the camera;

determining integrated counts along a radial direction from the centroid in the images generated by the camera as a function of beam roll angle;

determining a location of the radial light peaks in the images generated by the camera using the integrated counts;

changing the frequency of the laser beam to rotate the radial light peaks in the optical vortex intensity pattern in the images generated by the camera;

estimating the roll angle of the element from the change in frequency that rotated the optical vortex intensity pattern;

determining the pitch angle of the element by a shift of the vortex intensity pattern in one plane in the images generated by the camera; and

determining the yaw angle of the element by a shift of the vortex intensity pattern in a plane orthogonal to the one plane in the images generated by the camera.