Fig. 1. Configuration of Figure-9 fiber laser

Fig. 2. Repetition-rate-locking of the laser. (a) Diagrammatic sketch of PZT frequency tuning mechanism; (b) photo of the PZT; (c) schematic diagram of repetition-rate-locking principle

Fig. 3. Prototype of picosecond fiber laser. (a) Structural diagram of aluminum box for optical module; (b) structure layout of the electronic module; (c) photo of the developed prototype

Fig. 4. Output pulse characteristics of the laser. (a) Measured pulse train; (b) pulse intensity autocorrelation trace (points for the measured data, line for the Gaussian fitting); (c) measured laser pulse spectrum

Fig. 5. Measured results when the repetition rate is locked. (a) Measured repetition rate varies with time; (b) Allan variance of repetition-rate instability calculated with measured data in Fig. 5(a)

Fig. 6. Measured results when the repetition rate is locked at temperature of -40, 0 and 50 ℃, respectively. (a) Repetition rate as a function of time; (b) Allan variance of repetition-rate instability calculated with measured data in Fig. 6(a)

Fig. 7. Measured results when the laser operates in vibration environment. (a) Photo of the vibration environment scene; (b) measured repetition rate as functions of time when the vibration is superimposed on each of the three coordinate axes; (c) Allan variance of repetition-rate instability calculated with measured data in Fig. 7(b)

Fig. 8. Test results of the laser operating in the outdoor environment. (a) Photo of the test scene; (b) recorded temperature of the test site measured with the thermometer; (c) locked repetition rate as a function of time from 9:00 to 12:00; (d) locked repetition rate as a function of time from 12:10 to 15:10