Fig. 1. Principle of polarization phase detection by optical heterodyne beat frequency

Fig. 2. Schematic diagram for polarization beam combination system of two beams by the optical heterodyne phase locking

Fig. 3. Homodyne beat signal and spectrum before and after modulation by phase modulation signal. (a) Homodyne beat signal detected by photodetector without phase modulation; (b)(c) heterodyne beat signal and its spectrum detected by photodetector with phase modulation added; (d) error signal after mixing demodulation

Fig. 4. Model of laser phase-locked loop

Fig. 5. Bode and Nyquist diagrams of laser phase-locked system in open loop. (a) Bode diagram; (b) Nyquist diagram

Fig. 6. Error signal and power spectral density of phase noise. (a) Error signal in open and closed loops; (b) power spectral density of phase noise in closed loop

Fig. 7. Snapshots of the spot intensity profiles before and after phase locking. (a)-(c) Three snapshots of the spot intensity profiles without phase locking; (d)(e) spot snapshots after phase locking in the lowest and highest powers

Fig. 8. Polarization extinction ratio of combined beam in closed loop

Fig. 9. Influence of laser power noise on polarization extinction ratio