Fig. 1. Schematic diagram of a SHCD system

Fig. 2. Schematic diagram of a DSCD-DQPSK system

Fig. 3. Schematic diagram of a DSCD-DQPSK receiver structure

Fig. 4. Comparison of tolerance for transmission-path mismatch between SHCD-QPSK and DSCD-DQPSK systems under different laser linewidths. (a) 17 dB OSNR; (b) 20 dB OSNR

Fig. 5. Noise sources in optical communication system

Fig. 6. Effect of different power separation ratios on the BER of SHCD-QPSK systems with dominant electrical noise

Fig. 7. Ideal BTB performance curves of IMDD-PAM4, SHCD-QPSK, and DSCD-DQPSK systems at 200 Gbit/s transmission

Fig. 8. Optimal transmitter laser power separation ratio of the SHCD system for three different optical filtering configurations on the remote LO at various power ratios of optical and electrical noise

Fig. 9. Receiver sensitivity comparison of the DSCD and SHCD systems. (a) Required received optical signal power of DSCD and SHCD systems at 1×10^-3 BER under different noise power ratios; (b) comparison of BER and OSNR curves between DSCD and SHCD systems, when power ratio of optical and electrical noise is 10 dB

Fig. 10. BER and OSNR performance curves of the IMDD-PAM4, SHCD-QPSK, and DSCD-DQPSK systems transmission distances

Fig. 11. Performance curves of the IMDD-PAM4, SHCD-QPSK, and DSCD-DQPSK systems at different transmission distances