## 6 Conclusions  
In conclusion, we have demonstrated a real-time single-span 106 km CDM field trial using commercial 130 Gbaud PCS-16 QAM 800 Gb/s OTN transceivers over deployed  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Bit Rate** & **Baud Rate** & **Modulation** & **OSNR** & **Input Power of** & **OSNR After** & **OSNR** \\
**(Gb/s)** & **(Gbaud)** & **Format** & **(dB)** & **(dBm)** & **(dB)** & **(dB)** \\ \hline
400 & 130 & QPSK & 16 & +11 & 25.6 & 9.6 \\
800 & 260 & QPSK & 19.1 & +14 & 28.6 & 9.5 \\
800 & 130 & PCS-16 QAM & 23.2 & +11 & 25.6 & 2.4 \\
800 & 118 & 16 QAM & 24.6 & +10.6 & 25.2 & 0.6 \\
800 & 98 & PCS-64 QAM & 27.4 & +9.8 & 24.4 & \(-\)3 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Performance of single-span 106 km CDM transmission systems using different modulation formats.  
4-core MCF cable. Enabled by the high modulation rate and the noise-tolerant modulation format, the 800 Gb/s OTN transceivers could tolerate a span loss of over 33.6 dB and achieve long-span unrepeated optical transmission. The high baud rate was enabled by the optoelectronic multiple-chip module (OE-MCM) packaging technique, which aims to minimize the path of high-speed signals and thus ensure enough modulation bandwidth. The 4-core 800 Gb/s CDM transmission system achieved a real-time capacity of 256 Tb/s with fully loaded 80 wavelength channels over the C+L band. The transmission distance of this single-span unrepeated field trial could be further extended by reducing the splicing losses of the MCF cable and increasing the modulation rate of the modulator. To the best of our knowledge, this work is the first real-time unrepeated single-span field trial over more than 100 km MCF cable with commercial 800 Gb/s OTN transceivers, and we believe it will be beneficial to next-generation high-speed optical interconnection systems.  
Conceptualization, J.C., C.W., Z.L., and Y.D.; methodology, J.C., C.Z., B.Y. ([PERSON]), and Y.C.; software, J.C.; validation, J.C., Y.W., J.W., and L.Z. ([PERSON]); formal analysis, B.H., B.W., and T.Z.; investigation, J.C., L.S., and L.Z. ([PERSON]); resources, C.W., B.H., H.S., J.L., Y.S., Q.W., and N.G.; data curation, J.C., C.W., L.Z. ([PERSON]), Y.D., and X.C.; writing--original draft preparation, J.C., C.W., Z.L., and Y.D.; writing--review and editing, Y.S., C.C., and B.Y. ([PERSON]); visualization, C.W.; supervision, J.C. and X.C.; project administration, J.C., Y.D., Y.W., T.Z., L.Z. ([PERSON]), and C.C.; funding acquisition, J.C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
Authors [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] were employed by the company Department of Networks, China Mobile Communications Group Co., Ltd.; authors [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] were employed by the company Network Management Center, China Mobile Communications Group Shandong Co., Ltd.; authors [PERSON], [PERSON], [PERSON], and [PERSON] were employed by the company WDM System Department of Wireline Product R&D Institute, ZTE Corporation; authors [PERSON], [PERSON], [PERSON], and [PERSON] were employed by the company State Key Laboratory of Optical Fibre and Cable Manufacture Technology, YOFC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.