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Meter-scale spatial-resolution-coherent Doppler wind lidar based on Golay coding
Abstract:
Generally, the pulse duration of a coherent Doppler wind lidar (CDWL) is shortened to minimize the spatial resolution at the sacrifice of carrier-to-noise ratio, since the peak power of a laser source is limited by the stimulated Brillouin scattering or other nonlinear optical phenomena. To solve this problem, an all-fiber CDWL incorporating Golay coding is proposed and demonstrated. Given the peak power of the laser pulse, the Golay coding method can improve the measuring precision by improving the pulse repetition frequency of the outgoing laser. In the experiment, the Golay coding implementation is optimized by normalizing the intensity of every single pulse of the outgoing laser with a closed-loop feedback, achieving a spatial resolution of 6 m and a temporal resolution of 2 s with a maximum detection range of 552 m. The wind profile in line of sight and the result derived from another noncoding CDWL show good agreement.
Fig. 1. Optical layout of the Golay coding CDWL. CW, continuous-wave laser; AOM, acoustic–optic modulator; EOM, electro-optic modulator; AWG, arbitrary pulse generator; EDFA, erbium-doped fiber amplifier; BS, beam splitter; BD, balanced detector; ADC, analogto-digital converter.
Fig. 2. Laser pulse sequence. (a) Golay coding seed laser and (b) amplified laser sequence without feedback control; (c) Golay coding seed laser; (d) amplified laser sequence with feedback control; (e) enlarged waveform of (d).
Fig. 3. Power spectra of Golay coding CDWL and noncoding CDWL. (a) Power spectra distribution of noncoding CDWL; (b) power spectra distribution Golay coding CDWL; (c) raw power spectra at around 100 m; the circle is the power spectra of noncoding CDWL, and the line is that of coding CDWL. (d) Raw power spectra at around 300 m; (e) raw power spectra at around 500 m.
