Fig. 1. (a) The working principle of phase stability transmission system. BPF: bandpass filter; PS: power splitter; DRO: dielectric resonant oscillator; OCXO: oven-controlled crystal oscillator; PID: proportional-integral-differential; OC: optical coupler; PD: photodetector; EDFA: erbium-doped fiber amplifier; OF: optical filter; LPF: low-pass filter; FM: Faraday mirror. (b)–(d) The signal and spectrum analyzer observes the demodulated RF signals from PD₁, PD₂, and PD₃ (black: remote site internally employs OC2 and an FM; red: remote site internally uses OC2 and an optical circulator). (e) Observed demodulated RF signal from PD₃ under a narrower frequency range.

Fig. 2. (a) Schematic of two-section analog DML; the inset is a picture of the analog DML chip after packaging and in use. (b) Comparison between the P-I curve of the adjusted two-section analog DML and the previous analog DML. (c) Modulation amplitude response of the two-section analog DML when I_RS = 0 mA. (d) Modulation amplitude response of the two-section analog DML when I_LS = 100 mA. (e) Lorentzian fitting for 3 dB linewidth when I_RS = 0, 20, 30 mA and I_RS^′ = 0 mA; the inset is an enlargement of the linewidth fitting results when I_RS^′ = 0 mA. (f) Laser spectra when I_RS is set to 0, 30, and 40 mA.

Fig. 3. (a) 50 km fiber link delay variation before and after compensation. (b) Phase noise of the frequency signal through 50 km fiber link (red: original rubidium atomic clock; black: free running; blue: phase-locked). (c) Temperature variation inside the temperature control box (red: constant temperature; black: variable temperature). (d) Preliminary fractional frequency stability of the 50 km free running link (black line), compensated link at 100 MHz when I_RS^′ = 0 mA (red line), 30 mA (green line), and I_RS = 0 mA (purple line), and compensated link during temperature fluctuations (golden line).