Fig. 1. General framework of GNSS

Fig. 2. Space and time reference transmission process of GPS. (a) Space reference transmission process; (b) time reference transmission process

Fig. 3. Framework of O-GNSS

Fig. 4. Schematic of optical reference based on fiber MI and its cavity structure proposed by SIOM. (a) Schematic of optical reference; (b) cavity structure^[24]

Fig. 5. Frequency stabilization laser in Fengyun satellite. (a) Seed laser airtight reinforced package structure; (b) part of in-orbit power curve

Fig. 6. CO₂ active lidar optical frequency reference laser. (a) Frequency stabilization principle; (b) gas absorption pool structure^[31]

Fig. 7. Figure-9 optical frequency comb based on nested fiber resonators^[36]

Fig. 8. Amplification principle of single frequency comb line based on fiber Brillouin amplifier^[37]

Fig. 9. Several in-orbit operation LCTs developed by SIOM

Fig. 10. Ethernet-combined optical fiber time-frequency synchronization network with high precision. (a) Schematic diagram of network topology; (b) simplified structure diagram of local node; (c) simplified structure diagram of relay node; (d) simplified structure diagram of terminal node^[56]

Fig. 11. Optical fiber time-frequency synchronization engineering prototype working at -40‒50 ℃