COHERENT LIDAR SYSTEM BASED ON A SEMICONDUCTOR LASER AND AMPLIFIER

• US 20100277714A1
• Filed: 10/08/2008
• Published: 11/04/2010
• Est. Priority Date: 10/09/2007
• Status: Active Grant

• Current Assignee: Windar Photonics A/S (Windar Photonics Plc)
• Original Assignee: Danmarks Pã¦Dagogiske Universitet
• Inventors: Pedersen, Christian, Hansen, Rene Skov
• Granted Patent: US 8,891,069 B2
• Time in Patent Office: Days
• US Class Current: 356/28
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

The present invention relates to a compact, reliable and low-cost coherent LIDAR (Light Detection And Ranging) system for remote wind-speed determination, determination of particle concentration, and/or temperature based on an all semiconductor light source and related methods. The present invention provides a coherent LIDAR system comprising a semiconductor laser for emission of a measurement beam of electromagnetic radiation directed towards a measurement volume for illumination of particles in the measurement volume, a reference beam generator for generation of a reference beam, a detector for generation of a detector signal by mixing of the reference beam with light emitted from the particles in the measurement volume illuminated by the measurement beam, and a signal processor for generating a velocity signal corresponding to the velocity of the particles based on the detector signal.

Claims

1. A coherent LIDAR system comprising

an all semiconductor laser assembly for emission of a measurement beam of electromagnetic radiation directed towards a measurement volume for illumination of particles in the measurement volume,

a reference beam generator for generation of a reference beam,

a detector for generation of a detector signal by mixing of the reference beam with light emitted from the particles in the measurement volume illuminated by the measurement beam, and

a signal processor for generating a velocity signal corresponding to the velocity of the particles based on the detector signal.

2. A coherent LIDAR system according to claim 1, wherein the signal processor is further configured for determination of wind velocity.

3. A coherent LIDAR system according to claim 1, wherein the signal processor is further configured for determination of turbulence in the measurement volume.

4. A coherent LIDAR system according to claim 1, wherein the signal processor is further configured for determination of temperature in the measurement volume.

5. A coherent LIDAR system according to claim 1, wherein the signal processor is configured for generating a concentration signal corresponding to the concentration of the particles in the measurement volume based on the detector signal.

6. A coherent LIDAR system according to claim 1, wherein the signal processor is configured for determination of particle concentration in the measurement volume.

7. A coherent LIDAR system according to claim 1, further comprising an optical fiber for transmission of the measurement beam between the all semiconductor laser assembly and an optical output of the LIDAR system.

8. A coherent LIDAR system according to claim 1, wherein the all semiconductor laser assembly comprises a tapered semiconductor laser.

9. A coherent LIDAR system according to claim 1, wherein the all semiconductor laser assembly comprises a semiconductor laser and a semiconductor tapered power amplifier for amplification of the beam emitted by the semiconductor laser.

10. A coherent LIDAR system according to claim 9, wherein the semiconductor laser is of the semiconductor MOPA type.

11. A coherent LIDAR system according to claim 10, wherein the semiconductor MOPA type laser comprises a semiconductor chip with a distributed feedback master oscillator and a semiconductor tapered power amplifier.

12. A coherent LIDAR system according to claim 1, wherein the reference beam generator is a beam splitter for dividing the beam emitted by the all semiconductor laser assembly into the reference beam and the measurement beam directed towards the measurement volume.

13. A coherent LIDAR system according to claim 1, wherein the reference beam generator is the all semiconductor laser assembly that is configured to emit the reference beam and the measurement beam.

14. A coherent LIDAR system according to claim 1, further comprising a spatial filter for filtering the reference beam thereby reducing the non-Gaussian spatial components of the reference beam.

15. A coherent LIDAR system according to claim 14, further comprising a Fourier lens positioned in the propagation path of the reference beam, and wherein the spatial filter is positioned in the Fourier plane of the Fourier lens for reduction of the non-Gaussian spatial components of the reference beam.

16. A coherent LIDAR system according to claim 14, wherein the spatial filter comprises an aperture, the size of which is matched to the size of the detector.

17. A coherent LIDAR system according to claim 1, further comprising a beam combiner for combining the reference beam with light emitted from the target.

18. A coherent LIDAR system according to claim 17, wherein

the measurement beam is p-polarized, and

the beam splitter and the beam combiner is one unit comprising

a Brewster window that is coated to transmit p-polarized light from the all semiconductor laser assembly and to reflect s-polarized light,

a quarter-wave birefringent optical plate for conversion of the p-polarized light into circular polarized light to form the measurement beam and conversion of circular polarized from the particles into s-polarized light for reflection by the Brewster window, and wherein

the beam splitter comprises a reflector for reflection of a part of the measurement beam to form the reference beam and for direction of the reference beam back through the quarter-wave plate for reflection towards the detector.

19. A coherent LIDAR system according to claim 1, wherein the all semiconductor laser assembly is operated in response to a signal from the detector for optimization of the laser output of the all semiconductor laser assembly.

20. A coherent LIDAR system according to claim 1, comprising a beam cleanup device with a single mode fiber forming the measurement beam.

21. A coherent LIDAR system according to claim 20, wherein the beam cleanup device comprises a focusing lens, a pinhole, and a collimating lens.

22. A coherent LIDAR system according to claim 1, comprising a frequency shifting element for frequency shifting the measurement beam or the reference beam.

23. A wind turbine comprising a coherent LIDAR system according to claim 1.

24. A sailing-boat comprising a coherent LIDAR system according to claim 1.

25. A method for velocity determination based on light scattered by particles, comprising the steps of

emitting a measurement beam of electromagnetic radiation and directing the beam towards a measurement volume for illumination of particles in the measurement volume,

generating a reference beam,

mixing the reference beam with light emitted from the particles in the measurement volume illuminated by the measurement beam for generation of a velocity signal corresponding to the velocity of the particles,

wherein the step of emitting a measurement beam comprises provision of an all semiconductor laser assembly for the emission of the measurement beam.

26. A method according to claim 25, wherein the step of generating a reference beam, comprises the step of dividing the beam emitted by the all semiconductor laser assembly, into the reference beam and the measurement beam directed towards the measurement volume.

27. A method according to claim 25, wherein the step of generating a reference beam comprises the step of providing the all semiconductor laser assembly configured to emit the reference beam and the measurement beam.

28. A method according to claim 25, further comprising the step of mixing the reference beam with light emitted from the particles in the measurement volume illuminated by the measurement beam for generation of a temperature signal corresponding to the temperature in the measurement volume.

29. A method according to claim 25, further comprising the step of mixing the reference beam with light emitted from the particles in the measurement volume illuminated by the measurement beam for generation of a concentration signal corresponding to the concentration of the particles in the measurement volume.

30. A method according to claim 25, further comprising the step of spatially filtering the reference beam thereby reducing the non-Gaussian spatial components of the reference beam.

31. A method according to claim 25, further comprising the step of performing beam cleanup by provision of a single mode fiber forming the measurement beam.

32. A method according to claim 25, further comprising the step of adjusting pitch of the blades of a wind turbine in response to the determined velocity signal.

33. A method according to claim 25, further comprising the step of trimming a sailing-boat in response to the determined velocity signal.

34. A method for determination of particle concentration based on light scattered by particles, comprising the steps of

emitting a measurement beam of electromagnetic radiation and directing the beam towards a measurement volume for illumination of particles in the measurement volume,

generating a reference beam,

mixing the reference beam with light emitted from the particles in the measurement volume illuminated by the measurement beam for generation of a concentration signal corresponding to the concentration of the particles,

wherein the step of emitting a measurement beam comprises provision of a semiconductor laser for the emission of the measurement beam.

35. A method according to claim 34, wherein the step of generating a reference beam, comprises the step of dividing the beam emitted by the semiconductor laser into the reference beam and the measurement beam directed towards the measurement volume.

36. A method according to claim 34, wherein the step of generating a reference beam comprises the step of providing a semiconductor laser that is configured to emit the reference beam and the measurement beam.

37. A method according to claim 34, further comprising the step of spatially filtering the reference beam thereby reducing the non-Gaussian spatial components of the reference beam.

38. A method according to claim 34, further comprising the step of performing beam cleanup by provision of a single mode fiber forming the measurement beam.

39. A method according to claim 34, further comprising the step of emitting a status signal in response to the determined concentration signal.