Fig. 1. Schematic diagram of electro-optical converter^[16]

Fig. 2. Micro cavity converters. (a) LN 3D cavity converter ^[21]; (b)‒(d) integrate LN converters^[22-24]

Fig. 3. Integrate AlN converters. (a) Proposed by Fan et al.^[25]; (b) proposed by Han et al.^[26]

Fig. 4. Integrate silicon-organic converter^[27]

Fig. 5. Energy level transition diagrams of atomic conversion system^[16]. (a) Hyperfine transition energy level diagram; (b) Rydberg transition energy level diagram

Fig. 6. Experimental principle of reference [33]. (a) Energy-level diagram for Er∶YSO; (b) representation of the up-conversion apparatus

Fig. 7. Experiment in reference [43]. (a) Relevant energy levels of a 87Rb atom; (b) experiment setup

Fig. 8. Experiment in reference [45]. (a) Relevant energy levels of a 87Rb atom; (b) experiment setup

Fig. 9. Schematics of electro-opto-mechanical systems ^[55-57]

Fig. 10. Piezoelectric optomechanical crystal cavity converters^[62-65]

Fig. 11. Superconducting piezoelectric converters ^[67-68,70]

Fig. 12. Magneton system. (a)YIG sphere and 3D microwave cavity^[83]; (b)-(d) YIG sphere based converters^[85-87]

Fig. 13. Schematic diagram of experimental setup in reference [92]

Fig. 14. Comparison in conversion efficiency and conversion bandwidth between different transduction approaches