Chirped coherent laser radar system and method

• US 7,920,272 B2
• Filed: 02/26/2009
• Issued: 04/05/2011
• Est. Priority Date: 02/14/2005
• Status: Active Grant

• Current Assignee: Aeva, Inc.
• Original Assignee: Digital Signal Corporation (StereoVision Imaging, Inc.)
• Inventors: Belsley, Kendall, Sebastian, Richard
• Primary Examiner(s): LEE, HWA S
• Application Number:
  US12/393,522
• Publication Number:
  US 20090153872A1
• Time in Patent Office: 768 Days
• Field of Search: 356/486, 356/493, 356/498, 356/484
• US Class Current: 356/486
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/06 Systems determining position data of a target
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/34 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 Class Codes: G01S 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/4911 Transmitters

Abstract

A laser radar system using collocated laser beams to unambiguously detects a range of a target and a range rate at which the target is moving relative to the laser radar system. Another aspect of various embodiments of the invention may relate to a laser radar system that uses multiple laser radar sections to obtain multiple simultaneous measurements (or substantially so), whereby both range and range rate can be determined without various temporal effects introduced by systems employing single laser sections taking sequential measurements. In addition, other aspects of various embodiments of the invention may enable faster determination of the range and rate of the target, a more accurate determination of the range and rate of the target, and/or may provide other advantages.

Claims

1. A laser radar system comprising:

a first coherent laser radar section including;

a first laser source that generates a first laser beam,

an interferometer that splits the first laser beam into a first target beam and a first local oscillator beam, and generates a first combined target beam from a first reflected portion of the first target beam and the first local oscillator beam;

a second coherent laser radar section including;

a second laser source that generates a second laser beam,

an interferometer that splits the second laser beam into a second target beam, incident on the target at the same location as the first target beam, and a second local oscillator beam, and generates a second combined target beam from a second reflected portion of the second target beam and the second local oscillator beam; and

a processor that determines a range and a range rate of the target unambiguously from the first combined target beam and the second combined target beam,

wherein the first laser source or the second laser source further comprises;

one or more optical elements that form a optical cavity through which electromagnetic radiation is circulated, and

a frequency shifting device that applies a frequency shift to the electromagnetic radiation circulating through the optical cavity.

2. The system of claim 1, wherein the first laser beam has a first chirp rate, wherein the second laser beam has a second chirp rate, and wherein the first chirp rate is in the opposite direction from the second chirp rate.

3. The system of claim 1, further comprising:

a combiner that generates a combined target beam from the first target beam and the second target beam prior to emission; and

an input/output port that directs the combined target beam toward the target and receives reflected electromagnetic radiation reflected from the target to form a portion of a common optical path.

4. The system of claim 3, wherein the input/output port is provided by one or more of a circulator, an optical coupler, and an optical fiber.

5. The system of claim 3, wherein the common optical path includes a scanning element that enables the first target beam and the second target beam to be scanned across the target.

6. The system of claim 3, wherein the first laser source and the second laser source have substantially the same optical frequency.

7. The system of claim 1, wherein the processor electrically mixes a first beat signal related to the first combined target beam and a second beat signal related to the second combined target beam.

8. The system of claim 1, wherein the frequency shifting device applies a constant frequency shift to the electromagnetic radiation circulating through the optical cavity.

9. The system of claim 1, wherein the frequency shifting device is an acousto-optic Bragg cell.

10. The system of claim 1, wherein at least one of the first laser source and the second laser source is periodically and automatically linearized.

11. The system of claim 10, wherein the at least one of the first laser source and the second laser source is automatically linearized once per chirp.

12. The system of claim 1, wherein the first target beam and the second target beam are focused on the common measurement point.

13. The system of claim 1, wherein the first laser beam has a first chirp rate, wherein the second laser beam has a second chirp rate, and wherein the first chirp rate differs from the second chirp rate.

14. A laser radar system comprising:

a first coherent laser radar section including;

a first laser source that generates a first laser beam at a first chirp rate,

an interferometer that splits the first laser beam into a first target beam and a first local oscillator beam, and generates a first combined target beam from a first reflected portion of the first target beam and the first local oscillator beam;

a second coherent laser radar section including;

a second laser source that generates a second laser beam at a fixed frequency,

an interferometer that splits the second laser beam into a second target beam, incident on the target at the same location as the first target beam, and a second local oscillator beam, and generates a second combined target beam from a second reflected portion of the second target beam and the second local oscillator beam; and

a processor that determines a range and a range rate of the target unambiguously from the first combined target beam and the second combined target beam,

wherein the first laser source further comprises;

one or more optical elements that form a optical cavity through which electromagnetic radiation is circulated; and

a frequency shifting device that applies a frequency shift to the electromagnetic radiation circulating through the optical cavity.

15. The system of claim 14, wherein the second laser radar section further includes a frequency shifting device that provides a frequency shift to the second local oscillator beam.

16. The system of claim 14, further comprising:

a combiner that generates a combined target beam from the first target beam and the second target beam prior to emission; and

an input/output port that directs the combined target beam toward the target and receives reflected electromagnetic radiation reflected from the target to form a portion of a common optical path.

17. The system of claim 16, wherein the input/output port is provided by one or more of a circulator, an optical coupler, and an optical fiber.

18. The system of claim 16, further comprising a scanning element, included in the combined optical path, that receives the combined target beam from the input/output port and scans the first target beam and the second target beam across the target.

19. The system of claim 16, wherein the first laser source and the second laser source have substantially the same optical frequency.

20. The system of claim 14, wherein the frequency shifting device applies a constant frequency shift to the electromagnetic radiation circulating through the optical cavity.

21. The system of claim 14, wherein the frequency shifting device is an acousto-optic Bragg cell.

22. The system of claim 14, wherein the first laser source is automatically and periodically linearized.

23. The system of claim 22, wherein the first laser source is periodically linearized once per chirp.

24. The system of claim 14, wherein the first target beam and the second target beam are focused on the common measurement point.

25. The system of claim 15, wherein the first laser beam has a first chirp rate, wherein the second laser beam has a second chirp rate, and wherein the first chirp rate differs from the second chirp rate.

26. The system of claim 25, wherein the first chirp rate is in the opposite direction from the second chirp rate.