Frequency-stabilized 1550-nm single-frequency all-fiber pulsed laser for coherent Doppler lidar

In this work, an all-fiber high-power cascaded master-oscillator power amplifier (MOPA) system emitting frequency-stabilized single-frequency laser pulses at 1550 nm is presented. An external cavity laser diode with a narrow linewidth of 5 kHz is used as the seed source. Owing to the use of frequency locking components and a matched closed-loop system, the seed source has stable output frequency and power. The on-off extinction ratio of 80 dB is achieved by using digital and analog acousto-optic modulators in series. Then the seed laser is amplified by a three-stage cascaded all-fiber amplifier consisting of two pre-amplifiers and one main amplifier. The MOPA system delivers 200-ns laser pulses with a peak power of 800 W at a repetition rate of 10 kHz. The output laser has an operating linewidth close to the transform-limited. The polarization-extinction ratio is 20 dB, and the optical signal-to-noise ratio is higher than 45 dB. The monolithic all-fiber Erbium-Ytterbium co-doped pulsed fiber amplifier can be used as the high-energy radar transmitter of compact long-distance coherent Doppler lidar systems.