Fig. 1. QPSK signal phase regeneration process and stepped phase transfer function. (a) QPSK signal phase regeneration process; (b) stepped phase transfer function

Fig. 2. Cascaded FWM for QPSK phase regeneration and multicasting process

Fig. 3. All-optical regeneration and multicast scheme of QPSK signal in space laser communication network

Fig. 4. Relationships between phase-sensitive gain, output phase and input relative phase under different pump optical power levels.

Fig. 5. All-optical regeneration and multicast experimental system of QPSK signal

Fig. 6. Spectrogram of FWM input and output. (a) FWM input; (b) FWM output

Fig. 7. Curves of EVM value of three-way multicast channel and spectra of maximum phase-sensitive gain and attenuation. (a) Curves of EVM of three-way multicast channel with the input relative phase; (b) curves of EVM value of three-way multicast channel with the pump power; (c) spectra of maximum phase-sensitive gain and attenuation

Fig. 8. Constellation diagrams of each signal and BER and EVM curves. (a) Original degraded signal; (b) the regenerated signal; (c) multicast channel 1; (d) multicast channel 2; (e) BER curves; (f) EVM curves

Fig. 9. All-optical regeneration and multicast experiment platform of QPSK signal

Fig. 10. Spectrogram of optical frequency comb, FWM input and output. (a) Optical frequency comb spectrogram; (b) FWM input; (c) FWM output

Fig. 11. Characteristics of signal optical power, phase-sensitive gain, attenuation, and EVM performance as functions of pump phase. (a) Variation of signal power with pump phase; (b) spectrogram of maximum phase-sensitive gain and attenuation; (c) EVM curves of three signals under different pump phases

Fig. 12. Constellation diagram of each signal. (a) Un-degraded signal; (b) phase-degraded signal; (c) after phase regeneration signal; (d) multicast channel 1; (e) multicast channel 2 constellation diagram.

Fig. 13. Relationship between output power and BER of each signal