Fig. 1. Channel multiplexing using digital orthogonal filtering

Fig. 2. Field distributions of LP11 mode. (a) Only use LP11a mode; (b) only use LP11b mode; (c) use both LP11a mode and LP11b mode

Fig. 3. Experimental structure of PAM signal transmission in IM-DD mode division multiplexing system

Fig. 4. Diagrams of test signal generation and offline detection. (a) Modulating and framing; (b) demodulating and decoding

Fig. 5. Orthogonal filter used by the transmitter. (a) Transmitter I path filter frequency response; (b) transmitter I path filter time domain waveform; (c) transmitter Q path filter frequency response; (d) transmitter Q path filter time domain waveform

Fig. 6. Signal waveforms of I path and Q path of receiver

Fig. 7. BER curves of PAM8 signal through LP11a-LP11a channel back-to-back/500 m FMF transmission without crosstalk

Fig. 8. BER curves of PAM8 signal through LP11a-LP11a channel back-to-back/500 m FMF transmission with crosstalk

Fig. 9. BER curves of PAM8 signal through back-to-back transmission with digital orthogonal filtering and LS algorithm

Fig. 10. BER curves of PAM8 signal after 500 m FMF transmission with digital orthogonal filtering and LS algorithm

Fig. 11. BER curves of PAM8 signal through back-to-back transmission after iteration by digital orthogonal filtering and LS algorithm