Boresight error monitor for laser radar integrated optical assembly

Patent metadata

Field	Value
Publication number	US-9587977-B2
Application number	US-201314010375-A
Country	US
Kind code	B2
Filing date	Aug 26, 2013
Priority date	Aug 31, 2012
Publication date	Mar 7, 2017
Grant date	Mar 7, 2017

Abstract

Boresight and other pointing errors are detected based on a monitor beam formed by diverting a portion of a probe beam. The monitor beam is directed to a position sensitive photodetector, and the optical power received at the position sensitive photodetector is used to estimate or correct such pointing errors.

First claim

We claim:

1. An optical measurement system for determining a target dimension, comprising:
a measurement beam source configured to produce a measurement beam;
a measurement beam optical system configured to direct the measurement beam at a target, the measurement beam optical system including a moveable focus element for focusing the measurement beam at the target;
a beam splitter configured to select a portion of the measurement beam after propagating through the movable focus element so as to form a monitor beam;
a monitor beam photodetection system configured to receive the monitor beam and provide an indication of a measurement beam pointing error that is associated with the movement of the moveable focus element; and
a measurement beam photodetection system configured to estimate the target dimension and a coordinate associated with a target location of the target based on a portion of the measurement beam returned from the target, wherein at least one of the estimated coordinate or the target location is adjusted based on the indicated pointing error.

2. The optical measurement system of claim 1 , further comprising a bifurcated mirror configured to direct at least portions of the monitor beam to the monitor beam detection system.

3. The optical measurement system of claim 1 , wherein the moveable focus element is a corner cube.

4. The optical measurement system of claim 1 , wherein the measurement beam optical system includes at least one lens configured to shape the measurement for delivery to the target, and the beam splitter is situated to form the monitor beam based on the shaped measurement beam.

5. The optical measurement system of claim 4 , wherein the monitor beam photodetection system includes a multi-element photodetector, and the beam splitter is configured to direct the monitor beam to the multi-element detector.

6. The optical measurement system of claim 5 , further comprising a monitor beam lens situated to receive the monitor beam from the beam splitter and direct the monitor beam to the multi-element detector.

7. The optical measurement system of claim 6 , wherein the monitor beam lens includes a plurality of lens segments associated with at least two different curvatures and configured to direct monitor beam portions to respective elements of the multi-element detector.

8. The optical measurement system of claim 5 , wherein the monitor beam photodetection system is configured to determine a pointing error based at least one monitor beam portion associated with a selected measurement beam focus.

9. The optical measurement system of claim 5 , wherein the measurement beam source includes an optical fiber having an output surface configured to emit the measurement beam, and the monitor beam lens is situated to image the output surface of the optical fiber at the multi-element detector.

10. The optical measurement system of claim 9 , wherein the multi-element photodetector is situated proximate the output surface of the optical fiber.

11. The optical measurement system of claim 5 , wherein the multi-element photodetector is a quadrant photodetector.

12. The optical measurement apparatus of claim 6 , further comprising a prism, wherein the monitor beam is situated to be directed at the prism so as to couple portions of the monitor beam to respective elements of the multi-element photodetector.

13. The optical measurement system of claim 5 , further comprising a reflective surface situated to reflect the monitor beam received from the beam splitter to the multi-element photodetector.

14. The optical measurement system of claim 13 , wherein the reflective surface includes a plurality of segments associated with corresponding curvatures, wherein monitor beam portions associated with the segments are directed to corresponding elements of the multi-element photodetector.

15. The optical measurement system of claim 14 , wherein the monitor beam photodetection system is configured to determine a pointing error based at least one monitor beam portion associated with a selected measurement beam focus.

16. The optical measurement system of claim 5 , further comprising a beam divider system configured to receive the monitor beam from the beam splitter and direct first and second monitor beam portions to the multi-element photodetector.

17. The optical measurement system of claim 16 , wherein the beam divider system includes a cube beam splitter situated to direct the first monitor beam portion to the multi-element photodetector, and a reflector situated to receive the second monitor beam portion and direct the second monitor beam portion to the multi-element photodetector.

18. The optical measurement system of claim 17 , wherein the reflector is situated to direct the second monitor beam portion to the multi-element photodetector by transmission through the cube beam splitter.

19. The optical measurement system of claim 16 , wherein the beam divider system includes a cube beam splitter situated to direct the first monitor beam portion to a first reflector and the second monitor beam portion to a second reflector, and the first and second reflectors are situated to direct the first and second monitor beam portions to the multi-element photodetector.

20. The optical measurement system of claim 19 , wherein the monitor beam photodetection system is configured to determine a pointing error based on interference between the first and second monitor beam portions.

21. The optical measurement system of claim 19 , further comprising an auxiliary lens configured to direct the first and second monitor beam portions to the multi-element photodetector.

22. The optical measurement system of claim 21 , wherein the monitor beam photodetection system is configured to determine a pointing error based on a distribution of optical power from the first and second monitor beam portions at the multi-element photodetector.

23. The optical measurement system of claim 22 , wherein the auxiliary lens is bonded to the cube beam splitter and the reflective surface is a surface of the cube beam splitter.

24. The optical measurement apparatus of claim 1 , further comprising a dual axis rotational stage configured to select a target location for the measurement beam, wherein the beam measurement beam optical system and the beam splitter are secured to the dual axis rotational stage.

25. A measurement method for determining a target dimension, comprising:
obtaining a portion of a measurement beam directed toward a target from a moveable focus element situated to focus the measurement beam at the target, wherein the portion obtained provides a monitor beam;
based on a propagation direction of the monitor beam, detecting a pointing direction of the measurement beam associated with a movement of the moveable focus element and determining a pointing error of the measurement beam that is associated with the movement of the moveable focus element; and
estimating a coordinate associated with a selected location of the target and a dimension of the target based on a portion of the measurement beam returned from the target;
wherein at least one of the estimated coordinate or the selected target location is adjusted based on the determined pointing error.

26. The method of claim 25 , wherein the pointing direction is associated with a boresight error resulting from focusing, shaping, or pointing of the measurement beam.

Assignees

• Nikon Corp

Inventors

• Smith Daniel G
• Novak W Thomas

Classifications

• G01S7/481

  Constructional features, e.g. arrangements of optical elements · CPC title

• G01J1/00 Primary

  Photometry, e.g. photographic exposure meter (spectrophotometry G01J3/00; specially adapted for radiation pyrometry G01J5/00 {; exposure meters built in cameras G03B17/06}) · CPC title

• G01S7/497 Primary

  Means for monitoring or calibrating · CPC title