Radar systems with dual fiber coupled lasers

Patent metadata

Field	Value
Publication number	US-10139492-B2
Application number	US-201715443967-A
Country	US
Kind code	B2
Filing date	Feb 27, 2017
Priority date	Nov 21, 2012
Publication date	Nov 27, 2018
Grant date	Nov 27, 2018

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. A apparatus, comprising:
a dual wavelength fiber-optic transmitter and receiver system that includes:
first and second lasers coupled to provide a combined beam to an input/output optical fiber,
a reference length coupled to receive a portion of the combined beam and to couple a reference beam to a reference fiber, and
a thermally controlled enclosure configured to retain at least the reference length; and

a beam shaping optical system coupled to receive the combined beam from the input/output optical fiber of the dual wavelength fiber-optic transmitter and receiver system, the beam shaping optical system including a beam focusing lens and at least one translatable focus adjustment optical element configured to focus a dual wavelength probe beam at a target surface.

2. The apparatus of claim 1 , further comprising an azimuthal stage configured to direct the dual wavelength probe beam to the target surface on a selected azimuthal angle, wherein the beam shaping optical system is configured to direct the dual wavelength probe beam along an axis of rotation of the azimuthal stage.

3. The apparatus of claim 2 , further comprising a rotatable reflective surface configured to receive the dual wavelength probe beam and direct the dual wavelength probe beam along a selected elevational angle.

4. The apparatus of claim 1 , further comprising a rotatable reflective surface configured to receive the dual wavelength probe beam and direct the dual wavelength probe beam along a selected elevational angle.

5. The apparatus of claim 2 , further comprising a camera configured to image a target surface along the axis of rotation of the azimuthal stage.

6. The apparatus of claim 5 , further comprising:
a rotatable reflective surface configured to receive the dual wavelength probe beam and direct the dual wavelength probe beam along a selected elevational angle; and
a cold mirror configured to transmit the dual wavelength probe beam to the rotatable reflective surface and reflect imaging optical radiation to the camera.

7. The apparatus of claim 1 , further comprising an elevational stage and an azimuthal stage configured to select a target location, wherein the beam shaping optical system is secured to so as to be rotatable based on a selected elevational angle.

8. The apparatus of claim 1 , further comprising a signal processor configured to provide a target distance estimate based on portions of the probe beam returned from the target.

9. The apparatus of claim 8 , wherein the beam shaping optical system is configured to form a combined local oscillator (LO) beam, wherein the signal processor is configured to provide the target distance estimate based on the portions of the probe beam returned from the target and the combined LO beam.

10. The apparatus of claim 9 , wherein the LO beam is formed so as to have an optical path in the translatable focus adjustment optical element corresponding to an optical path in the translatable focus adjustment optical element of the returned probe beam portions to and from the target.

11. The apparatus of claim 10 , wherein the target distance is estimated based on a difference frequency between the probe beam and the LO beam.

12. The apparatus of claim 10 , further comprising a first detector and a second detector configured to receive returned probe beam portions and LO beam portions corresponding to the first laser and the second laser, respectively, and the target distance is estimated based on difference frequencies between the probe beam and the LO beam at the first detector and the second detector.

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

• G01S7/4917

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

• G01S7/4812

  transmitted and received beams following a coaxial path · CPC title

• 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

• G01S7/4817

  relating to scanning · CPC title

• G01S7/497

  Means for monitoring or calibrating · CPC title