Single-mode and all-fiber coherent Doppler wind speed measurement laser radar emission source

Abstract

A single-mode and all-fiber coherent Doppler wind speed measurement laser radar emission source is characterized by being formed by sequentially connecting an all-fiber seed source, a seed isolator, a seed beam splitter, an acousto-optic modulation device, a pre-amplifier stage, a chopper and a main amplifier stage in a cascading mode. The single-mode and all-fiber coherent Doppler wind speed measurement laser radar emission source has the advantages that the all-fiber property is achieved, the human eyes are protected, the line width reaches megahertz, linear polarization is achieved, the pulse contrast is high, and single-mode polarization-maintaining lasers are output; repeated frequency, laser pulse width and laser waveform can be adjusted within the wide range, and the laser radar wind speed measurement requirements for different detection distances, different distance resolution ratios and different wind speed update rates from laser radars can be met.

Description

technical field [0001] The invention relates to an optical fiber laser, in particular to a single-mode all-fiber coherent Doppler wind speed measuring laser radar emission source, which adopts a main oscillation power amplification structure, has full optical fiber, is safe for human eyes, has a line width of megahertz, and linear polarization , High pulse contrast, single-mode polarization-maintaining laser output characteristics, repetition frequency, laser pulse width and laser waveform can be adjusted in a wide range to meet the needs of different detection distances, different distance resolutions and different wind speed update rates of laser radar. Background technique [0002] Coherent Doppler wind speed measurement lidar beats the echo containing wind speed information with the local oscillator to calculate the wind speed at different distances. It has the characteristics of high sensitivity and high speed accuracy, and can measure clear air turbulence, wind shear, a...

AI Technical Summary

Problems solved by technology

[0003] Due to its small size, compact structure, high stability, and good beam quality, fiber lasers have become the preferred emission sources for coherent Doppler wind speed measurement lidars. Most all-fiber single-frequency pulse lasers are based on main oscillation-power amplification (Master Oscillator Power Amplification, MOPA) structure, the seed source uses a semiconductor laser with a wavelength of 1.5 microns, its output power is on the order of ten to tens of milliwatts, and the pulse repetition frequency of thousands to tens of kilohertz through the acousto-optic modulator, After a pulse width of hundreds of nanoseconds, the power becomes microwatts, which belongs to small signal amplification in optical fiber amplification. The gain coefficient of single-stage amplification is generally about 30dB, but the light-to-light conversion efficiency is very low (generally less than 1%) , so it is generally necessary to add another stage of pre-amplification before entering the main amplifier stage, which makes the structure of the laser complex and requires more components; the power increase of the single-frequency narrow-linewidth fiber laser in the main amplifier stage is mainly limited by the stimulated Brillouin effect

At present, the existing methods are to use specially designed fibers to increase the mode field area or increase the gain coefficient of the fiber per unit length to reduce the effective fiber length to reduce the influence of nonlinear effects in the fiber, such as photonic crystal fibers or highly doped The single-mode and single-frequency laser output is achieved by fiber with mixed phosphate matrix, which is limited by the performance of the fiber itself, which leads to low efficiency and is not easy to be fused with commercial fiber, thus affecting the stability of the laser; in the laser radar system, in order to improve the detection sensitivity, it is required The laser pulse itself has a high extinction ratio, and the pulse extinction ratio obtained by using a single modulator can no longer meet the system requirements

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