Fig. 1. Schematic diagram of the experimental setup of the actively mode-locked fiber laser. MZIM, Mach–Zehnder intensity modulator; RF, radio-frequency signal generator; ISO, isolator; EDF, erbium-doped fiber; WDM, wavelength division multiplexer; OC, optical coupler; ODL, optical delay line; SOA, semiconductor optical amplifier; PC, polarization controller.

Fig. 2. Phase noise when the repetition rate is 2.5 GHz and the pulse width is 4 ps.

Fig. 3. Output pulse trains of the laser with repetition rate and SOA current of (a1) 1 GHz, 500 mA, (b1) 1 GHz, 174 mA, (c1) 2.5 GHz, 500 mA, (d1) 2.5 GHz, 174 mA, (e1) 6 GHz, 500 mA, (f1) 6 GHz, 260 mA, (a2)–(f2) the corresponding pulse width fitting curve, and (a3)–(f3) the corresponding RF spectra.

Fig. 4. Autocorrelation curves of different SOA currents at the repetition rate of 2.5 GHz.

Fig. 5. Spectra of the laser at different SOA currents at the repetition rate of 2.5 GHz.

Fig. 6. Pulse width and TBP at different SOA currents.

Fig. 7. Pulse width under different PC states at 2.5 GHz repetition rate. The blue line represents the SOA current of 500 mA, and the black line represents the SOA current of 190 mA.

Fig. 8. Schematic diagram of the experiment setup investigating the influence of SOA on the laser polarization state. DFB laser, distributed feedback laser; SOA, semiconductor optical amplifier; PBS, polarization beam splitter; P, P-polarized light; S, S-polarized light.

Fig. 9. Trends of the power of P-polarized light, S-polarized light, and extinction ratio (P/S) with current change.