Fig. 1. Principle of the proposed dual-mode stabilization.

Fig. 2. Schematic diagram of the experimental setup. EDFL, erbium-doped fiber laser; f-AOM, fiber-coupled acoustic optic modulator; f-EOM, fiber-coupled electro-optic modulator; f-S, fiber splitter; f-SSM, fiber-coupled single-sideband modulator; f-C, fiber collimator; MML, mode-matching lens; λ/2, half-wave plate; λ/4, quarter-wave plate; PBS, polarization beam splitter; VCO, voltage-controlled oscillator; PD1,2, photodetector; FG, frequency generator; PID, proportional-integral-derivative servo; SG, signal generator; PS, phase shift; LP, low-pass filter.

Fig. 3. Error signals for the two PDH locking processes. (a) Without and (c) with locking for the first laser; (b) without and (d) with locking for the second laser.

Fig. 4. PSD of the frequency deviation for (a) the first laser and (b) the second laser.

Fig. 5. Locking performance for the phase locking: the phase noise (a) without and (b) with locking; (c) the PSD result of the frequency deviation retrieved from the phase noise.

Fig. 6. Laser frequency stability evaluated by the frequency comb: the long-term laser frequency (a) with and (b) without phase locking and (c) their Allan deviation.