Fig. 1. PB-based OPU frame structure

Fig. 2. Schematic diagram of M-OTN combined with the DS-QKD system

Fig. 3. Schematic diagram of the time-domain scrambling/descrambling of the OSU optical signal. (a) TCM array; (b) single TCM

Fig. 4. Experimental system for real-time OSU optical signal time scrambling and key transmission via DS-QKD

Fig. 5. Eye diagram of OSU electrical signal

Fig. 6. Eye diagrams of OSU optical signal scrambling and descrambling. (a) Before scrambling; (b) after scrambling; (c) after matched key descrambling; (d) after unmatched key descrambling

Fig. 7. Running key performance. (a) Real-time key bit rate at 50.0 km; (b) key bit rate vs. transmission distance

Fig. 8. Bit error rate of the received OSU signal