Fig. 1. Experimental setup of passively synchronized Yb-doped fiber laser. WDM: wavelength-division multiplexer; YDF: Yb-doped fiber; PBS: polarization beam splitter; WP: waveplate; BF: birefringent filter; Col: collimator; PC: polarization controller; PD: photodetector; PI-ISO: polarization-independent isolator; PD-ISO: polarization-dependent isolator; SMF: single-mode fiber.

Fig. 2. The output characteristics of the two lasers in independent mode locking are measured. (a)–(c) Spectrum, autocorrelation trace, and radio-frequency spectrum of master laser (laser1); (d)–(f) spectrum, autocorrelation trace, and radio-frequency spectrum of the slave laser (laser2).

Fig. 3. Simultaneous pulse trains of two lasers in synchronous regime.

Fig. 4. Characteristics of both lasers in synchronous regime. (a) Repetition frequency drift of the slave laser versus cavity length mismatch. (b) Tolerance of cavity length mismatch vs. the slave laser’s pump power. (c) Spectral evolution of the slave laser within a mismatch range of 180 μm, as the slave laser’s cavity length deviates from the zero-difference position.

Fig. 5. Real-time characterization of the buildup and breakdown dynamics in synchronization for the slave laser. (a) Long-range DFT image during the buildup of synchronization. (b) Long-range DFT image during the breakdown of synchronization. (c) Field autocorrelation during the buildup of synchronization. (d) Field autocorrelation during the breakdown of synchronization.

Fig. 6. (a) Short-range DFT image corresponding to the buildup of synchronization. (b) Short-range DFT image corresponding to the breakdown of synchronization. (c) Spectral evolution during the buildup of synchronization. (d) Spectral evolution during the breakdown of synchronization.

Fig. 7. DFT images during the buildup of induced synchronization state. (a) Entire buildup of mode locking for the master laser. (b) Entire buildup of mode locking for the slave laser (also the synchronization buildup process). (c) Field autocorrelation corresponding to the DFT of the master laser. (d) Field autocorrelation corresponding to the DFT of the slave laser.

Fig. 8. Spectral evolution of two lasers during mode-locking buildup. (a), (b) Short-range DFT images of master laser and slave laser, respectively. (c), (d) Characteristic spectra of master laser and slave laser, respectively.

Fig. 9. DFT images in ISS. (a), (b) Entire mode-locking extinction process of the master laser and slave laser, respectively. (c), (d) Field autocorrelation corresponding to the DFT of the master laser and slave laser, respectively.

Fig. 10. Comparison of the spectra of DFT and OSA for the slave laser. (a) Spectrum in NSS; (b) spectrum in ISS.