Radar systems with dual fiber coupled lasers

Patent metadata

Field	Value
Publication number	US-9618619-B2
Application number	US-201313841021-A
Country	US
Kind code	B2
Filing date	Mar 15, 2013
Priority date	Nov 21, 2012
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

Laser radar systems include a pentaprism configured to scan a measurement beam with respect to a target surface. A focusing optical assembly includes a corner cube that is used to adjust measurement beam focus. Target distance is estimated based on heterodyne frequencies between a return beam and a local oscillator beam. The local oscillator beam is configured to propagate to and from the focusing optical assembly before mixing with the return beam. In some examples, heterodyne frequencies are calibrated with respect to target distance using a Fabry-Perot interferometer having mirrors fixed to a lithium aluminosilicate glass-ceramic tube.

First claim

We claim:

1. An optical measurement apparatus, comprising:
a beam pointing system, comprising an elevational stage and an azimuthal stage;
an optical system secured so as to be rotatable with the azimuthal stage, wherein the optical system is configured to:
receive, focus, and shape a measurement beam for delivery to a target area as a probe beam, wherein the target area is based on an elevational angle and an azimuthal angle established by the beam pointing system,
combine a portion of the probe beam returned from the target with a portion of the measurement beam in an optical fiber, and
a rotatable reflective surface situated so as to establish an elevational angle for the probe beam; and

a signal processing system configured to provide an estimate of a target distance based on the combined beam.

2. The optical measurement apparatus of claim 1 , wherein the optical system includes at least one translatable optical element configured to focus the probe beam, wherein the portion of the measurement beam combined with the returned portion of the probe beam is coupled through the at least one translatable optical element.

3. The optical measurement system of claim 2 , further comprising a measurement detector coupled to the combined probe beam and measurement beam portions, wherein the signal processing system is electrically coupled to the measurement detector and configured to provide the estimate of the target distance based on an electrical signal from the measurement detector.

4. The optical measurement system of claim 2 , further comprising a beam delivery system configured to couple the measurement beam to the optical system with an optical fiber.

5. The optical measurement system of claim 3 , wherein the beam delivery system is fixed.

6. The optical measurement system of claim 3 , wherein the beam delivery system comprises at least a first laser and a second laser coupled to provide a combined measurement beam in an optical fiber, and a housing situated to temperature stabilize at least the first laser and the second laser.

7. The optical measurement system of claim 3 , wherein the measurement detector is secured so as to be rotatable with the azimuthal stage.

8. The optical measurement system of claim 3 , wherein the measurement detector is secured so as to be fixed with respect to elevational and azimuthal rotations provided by the beam pointing system.

9. The optical measurement system of claim 3 , wherein the rotatable reflective surface is a surface of a plane mirror.

10. The optical measurement system of claim 3 , wherein the rotatable reflective surface is a surface of a prism.

11. The optical measurement system of claim 10 , wherein the prism is a pentaprism.

12. The optical measurement system of claim 3 , wherein the rotatable reflective surface is a surface of a pentamirror.

13. The optical measurement system of claim 3 , wherein the rotatable reflective surface is defined by a multilayer dielectric coating.

14. The optical measurement apparatus of claim 3 , further comprising at least first and second measurement lasers coupled to provide a dual wavelength measurement beam to the optical fiber of the rotatable optical system.

15. The optical measurement apparatus of claim 14 , wherein the portion of the measurement beam and the returned portion of the probe beam are combined so as to have corresponding optical paths in the at least one translatable optical element.

16. The optical measurement apparatus of claim 15 , wherein the portion of the measurement beam and the returned portion of the probe beam that are combined so as to have a common number of transits of the at least one translatable optical element.

17. The optical measurement apparatus of claim 16 , wherein the at least one translatable optical element is a corner cube.

18. The measurement apparatus of claim 17 , further comprising an enclosure configured to retain the reference length, and a temperature controller thermally coupled to the enclosure and configured to establish a temperature of the enclosure.

19. The measurement apparatus of claim 18 , further comprising a pointing laser that produces a visible optical beam and configured so that the visible optical beam is coupled with the dual wavelength measurement beam to the optical fiber of the rotatable optical system.

20. The measurement apparatus of claim 19 , wherein the optical fiber of the rotatable optical system is a polarization maintaining single mode optical fiber.

21. The optical measurement apparatus of claim 1 , further comprising:
a reference length that includes a Fabry-Perot resonator coupled to receive a portion of the dual wavelength measurement beam; and
a reference detector optically coupled to the Fabry-Perot resonator and electrically coupled to the signal processing system so as to provide a reference electrical signal, wherein the signal processing system is configured to provide the estimate of target distance based the reference electrical signal.

22. The optical measurement apparatus of claim 21 , wherein the reference electrical signal includes signal portions corresponding to a plurality of transits of a cavity defined by the Fabry-Perot resonator.

23. The measurement apparatus of claim 1 , further comprising a camera secured so as to be rotatable with the azimuthal stage and situated to image along a propagation axis of the probe beam.

Assignees

• Nikon Corp
• Nikon Metrology Nv

Inventors

• Rezk Mina A
• Slotwinski Anthony R
• Smith Daniel G
• Goodwin Eric Peter
• Cooper Alexander
• Hedges Thomas M

Classifications

• G01S17/34 Primary

  using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal · CPC title

• G01S7/4917

  superposing optical signals in a photodetector, e.g. optical heterodyne detection · CPC title

• G01S7/4818

  using optical fibres · CPC title

• G01S7/497

  Means for monitoring or calibrating · CPC title

• G01S7/4817

  relating to scanning · CPC title