Coherent LIDAR system based on a semiconductor laser and amplifier
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.
1. A monostatic coherent LIDAR system comprising:
an integrated semiconductor laser assembly configured for emission of a measurement beam of electromagnetic radiation directed towards a measurement volume of air for illumination of suspended particles in the measurement volume of air,
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 suspended particles in the measurement volume illuminated by the measurement beam of air, and
a signal processor for generating a velocity signal corresponding to the velocity of the air suspended particles based on the detector signal,
wherein the integrated semiconductor laser assembly is a master oscillator power amplifier (MOPA) having a semiconductor laser and a tapered semiconductor amplifier integrated on the same substrate, or the integrated semiconductor laser assembly is a tapered semiconductor laser.
2. A monostatic coherent LIDAR system according to claim 1 , wherein the signal processor is further configured for determination of wind velocity.
3. A monostatic coherent LIDAR system according to claim 1 , wherein the signal processor is further configured for determination of turbulence in the measurement volume.
4. A monostatic coherent LIDAR system according to claim 1 , wherein the signal processor is further configured for determination of temperature in the measurement volume.
5. A monostatic 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 monostatic coherent LIDAR system according to claim 1 , wherein the signal processor is configured for determination of particle concentration in the measurement volume.
7. A monostatic coherent LIDAR system according to claim 1 , further comprising an optical fiber for transmission of the measurement beam between the integrated semiconductor laser assembly and an optical output of the LIDAR system.
8. A monostatic coherent LIDAR system according to claim 1 , wherein the integrated semiconductor laser assembly comprises a semiconductor laser and a semiconductor tapered power amplifier for amplification of the beam emitted by the semiconductor laser.
9. A monostatic coherent LIDAR system according to claim 8 , wherein the semiconductor laser is of the semiconductor MOPA type.
10. A monostatic coherent LIDAR system according to claim 9 , wherein the semiconductor MOPA type laser comprises a semiconductor chip with a distributed feedback master oscillator and a semiconductor tapered power amplifier.
11. A monostatic coherent LIDAR system according to claim 1 , wherein the reference beam generator is a beam splitter for dividing the beam emitted by the integrated semiconductor laser assembly into the reference beam and the measurement beam directed towards the measurement volume.
12. A monostatic coherent LIDAR system according to claim 1 , wherein the reference beam generator is the integrated semiconductor laser assembly that is configured to emit the reference beam and the measurement beam.
13. A monostatic 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.
14. A monostatic coherent LIDAR system according to claim 13 , 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.
15. A monostatic coherent LIDAR system according to claim 13 , wherein the spatial filter comprises an aperture, the size of which is matched to the size of the detector.
16. A monostatic coherent LIDAR system according to claim 1 , further comprising a beam combiner for combining the reference beam with light emitted from the target.
17. A monostatic coherent LIDAR system according to claim 16 , 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 integrated 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.
18. A monostatic coherent LIDAR system according to claim 1 , wherein the integrated semiconductor laser assembly is operated in response to a signal from the detector for optimization of the laser output of the integrated semiconductor laser assembly.
19. A monostatic coherent LIDAR system according to claim 1 , comprising a beam cleanup device with a single mode fiber forming the measurement beam.
20. A monostatic coherent LIDAR system according to claim 19 , wherein the beam cleanup device comprises a focusing lens, a pinhole, and a collimating lens.
21. A monostatic coherent LIDAR system according to claim 1 , comprising a frequency shifting element for frequency shifting the measurement beam or the reference beam.
22. A wind turbine comprising a monostatic coherent LIDAR system according to claim 1 .
23. A sailing-boat comprising a monostatic coherent LIDAR system according to claim 1 .
24. A method for particle velocity determination based on light scattered by particles, comprising the steps of:
emitting a measurement beam of electromagnetic radiation and transmitting the measurement beam through imaging optics towards a measurement volume of air for illumination of suspended particles in the measurement volume of air,
generating a reference beam,
mixing the reference beam with backscattered light emitted from the suspended particles in the measurement volume of air illuminated by the measurement beam for generation of a velocity signal corresponding to the velocity of the suspended particles, the backscattered light received through the same imaging optics transmitting the measurement beam,
wherein the step of emitting a measurement beam comprises provision of an integrated semiconductor laser assembly comprising a tapered semiconductor laser or a semiconductor laser and a tapered semiconductor amplifier integrated on the same substrate for the emission of the measurement beam.
25. A method according to claim 24 , wherein the step of generating a reference beam, comprises the step of dividing the beam emitted by the integrated semiconductor laser assembly into the reference beam and the measurement beam directed towards the measurement volume.
26. A method according to claim 24 , wherein the step of generating a reference beam comprises the step of providing the integrated semiconductor laser assembly configured to emit the reference beam and the measurement beam.
27. A method according to claim 24 , 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.
28. A method according to claim 24 , 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.
29. A method according to claim 24 , further comprising the step of spatially filtering the reference beam thereby reducing the non-Gaussian spatial components of the reference beam.
30. A method according to claim 24 , further comprising the step of performing beam cleanup by provision of a single mode fiber forming the measurement beam.
31. A method according to claim 24 , further comprising the step of adjusting pitch of the blades of a wind turbine in response to the determined velocity signal.
32. A method according to claim 24 , further comprising the step of trimming a sailing-boat in response to the determined velocity signal.
33. A monostatic coherent LIDAR system according to claim 1 , wherein the measurement beam operates at eye-safe wavelengths such as 1.5 mu·m.
34. A monostatic coherent LIDAR system according to claim 1 , wherein the measurement beam is of continuous wave type.
35. A monostatic coherent LIDAR system according to claim 1 , wherein the power of the measurement beam is in the order of hundreds of milliwatts or orders of Watts.
36. A method according to claim 24 , wherein the step of emitting a measurement beam comprises emitting a continuous wave type measurement beam.