Fig. 1. Curves of discrete sine wave frequency modulation signals under different modulation indices. (a) Absorption lines curves; (b) Frequency discrimination signals curves

Fig. 2. Comparison of absorption lines curve and frequency discrimination signals curves under discrete sine wave frequency modulation (DSWFM) and binary frequency shift keying (2FSK). (a) Unshifted atomic absorption lines under two modulations;(b) Shifted atomic absorption lines under two modulations; (c) Unshifted frequency discrimination curves under two modulations; (d) Shifted frequency discrimination curves under two modulations

Fig. 3. Experimental schematic of CPT atomic clock

Fig. 4. Functional block diagram of phase-locked loop chip

Fig. 5. Frequency offset versus sampling time diagram

Fig. 6. CPT atomic clock hardware connection

Fig. 7. 3.417 GHz signal spectrum

Fig. 8. Spectrum of different modulation sources. (a) 2FSK; (b) DSWFM

Fig. 9. Demodulation signals. (a) 2FSK; (b) DSWFM

Fig. 10. Frequency stability test results. (a) Diagram of Allan deviation for 2FSK modulation;(b) Diagram of Allan deviation for DSWFM; (c) Comparison of Allan deviation between two modulation types