Fig. 1. Schematic of frequency conversion system (OFC: optical frequency comb; MZM: Mach‒Zehnder modulator; RF: radio frequency source;DeMux: demultiplexer; DP-MZM: double parallel Mach‒Zehnder modulator; EDFA: erbium-doped fiber amplifier; PD: photodiode)

Fig. 2. Diagram of frequency selection scheme

Fig. 3. Simulation diagram of frequency conversion system: OFC generation part, channelization filtering and channel selection part, and frequency shifting and signal loading part

Fig. 4. Spectra of the optical frequency comb. (a) Optical frequency comb of the local oscillation; (b) optical frequency comb of signal carrier

Fig. 5. Spectra of signal after modulation and combination. (a) After modulation; (b) after combination

Fig. 6. Spectra of the signals before after frequency conversion. (a)(d) Single frequency signal after frequency conversion; (b)(e) QPSK signal before frequency conversion; (c)(f) QPSK signal after frequency conversion

Fig. 7. Constellation diagrams of the signals after frequency conversion. (a) 70 GHz 512 MSym/s QPSK signal; (b) 70 GHz 300 MSym/s 8PSK signal; (c) 70 GHz 200 MSym/s 16QAM signal

Fig. 8. Measured plots of the signals after frequency shifting and frequency conversion. (a) Spectrum of the signals after frequency shifting; (b) EVM curve of the signal after frequency shifting; (c) EVM curve of the signal after frequency conversion

Fig. 9. Spectra of the signals after fine frequency shifting