Fig. 1. System diagram of optical phase-locked loop

Fig. 2. The transfer function of Raman laser’s phase noise

Fig. 3. Rubidium 87 D₂ transition hyperfine structure and the corresponding frequencies of the Raman laser system

Fig. 4. Block diagram of Raman laser system

Fig. 5. The optical path of MTS for frequency locking of reference laser and the MTS signals acquired by an oscillator

Fig. 6. The optical phase-locked loop with a frequency difference of 1 GHz and the phase-locked frequency signals observed in spectrum analyzer

Fig. 7. The frequency signals observed in spectrum analyzer after phase locked by the optical phase-locked loop with a frequency difference of 6.8 GHz

Fig. 8. The phase noise of the optical phase-locked loop with frequency differences of 1 GHz & 6.8 GHz and the corresponding signals generated from signal generators

Fig. 9. The amplification， combination， polarization unification and frequency modulation of Raman lasers and their long-term stabilities of powers