Fig. 1. Sequence diagram of time-delay measurement

Fig. 2. Principle of subcarrier modulation of 1PPS signal. (a) Frequency domain relation when ROF signal is baseband signal; (b) frequency domain relation when 1PPS signal is modulated to the center frequency of ROF signal; (c) the frequency-domain relation for the new time-frequency signal mixed transmission; (d) the frequency domain relation after the signal is transmitted to the receiving end and then photoelectric detection

Fig. 3. Scheme of time-delay measurement

Fig. 4. Waveforms of combined signal. (a) Original combined signal of 1PPS*+100 MHz+1.5 GHz; (b) combined signal in PIN detection

Fig. 5. Waveforms of time-frequency signals. (a) Restored 1PPS* signal; (b) restored 100 MHz signal

Fig. 6. Spectra of 1.5 GHz signal. (a) Directly mixed modulation; (b) subcarrier modulation

Fig. 7. Background time-delay of 25 km link. (a) Only with measurement links; (b) with ROF and measurement links

Fig. 8. EVMRMS of system

Fig. 9. Time delay of 25 km fiber link when temperature rises and falls. (a) Coarse value; (b) fine value; (b) FTD value

Fig. 10. Allen variance and EVMRMS of 1.5 GHz signal. (a) Allen variance; (b) EVMRMS of 1.5 GHz signal