Continuous-wave Heterodyne Laser Doppler Anemometer

Laser Doppler anemometer is used to measure the speed of wind in the atmosphere based on the theory of Doppler technology. Compared with traditional technology & equipment, the laser Doppler anemometer has many advantages, such as un-perturbing of target's moving; the signal stability; high precision; non-touch etc. So it's used widely in meteorologic,military,aeronautic,scientific erea etc. Because of these advantages and attractive application domains, many countries and companies are developing this anemometer technology very quickly recent years, and some products have been reported in the USA, U.K., Russia,France. Laser radar is composed of laser, transmitting unit, emitter-receiver unit, detecting & signal processing unit. Actually, the system measure aerosol's speed instead of wind's speed, because the aerosol's speed is equal to the wind's speed. And after measuring the Doppler shift of scattered light, the wind's speed can be calculated.In this work, the experiment of measuring hard target's speed with CO₂ laser beams and the experiment of measuring speed of wind in the atmosphere with all-fiber laser system at 1.55μm are described separately. For the first one, the CO2 laser is divided into Local Oscillator (LO) and a high power beam by thin film polarization (TFP), the last beam is transmitted to the moving target through emitter-receiver optic-antenna. And the scattered lights come back to the system through the optic-antenna mixing with LO. The light signal ,after transformed into the electric signal by the detector and amplified by the electronic unit, can be transformed to Doppler signal through FTT. The speed of hard target is measured in the experiment and the precision is up to 2%, the distance is up to 100 m. The success of this experiment supports next experiment theoretically and experientially. The CW coherent all-fiber laser Doppler anemometer is composed of fiber laser, fiber-optic circulator, optic-antenna, detector and signal processing unit. Compared with the first one, the all-fiber system has much more advantages on laser configuration, laser transmitting, cooling system, detecting mode, etc. It's propitious to build small and robust systems. As short range radar, The all-fiber laser radar can measure in-sight wind's speed from 5 m to 200 m. In order to measure actual wind's speed and direction, the scan device will add to the system at the next step.