Fig. 1. Schematic diagram of the core structure of an 18-tupling frequency multiplication PDM-16QAM modulation system

Fig. 2. Internal structure diagram of Sub-1

Fig. 3. Spectral diagram of the outputs at various points. (a) Optical spectrum of ±6th-order sidebands; (b) Optical spectrum of generated ±12th-order sidebands; (c) Optical spectrum of vector signal coupled with ±12th-order sidebands

Fig. 4. Spectral diagram of the outputs at various points

Fig. 5. Relationship between PD received optical power and bit error rate

Fig. 6. Constellation diagrams of X and Y polarization states at different transmission distances. (a) X polarization state (BTB); (b) Y polarization state (BTB); (c) X polarization state (20 km); (d) Y polarization state (20 km); (e) X polarization state (30 km); (f) Y polarization state (30 km)

Fig. 7. Relationship between optical signal-to-noise ratio and bit error rate

Fig. 8. Relationship between SOA injection current and bit error rate