C + L band seamless PM-256QAM DWDM transmission over 20.6 km low-loss hollow-core fiber enabled by low-complexity misaligned pilot-aided carrier recovery

Overcoming the capacity bottleneck of single-mode fiber (SMF), we exploit the exceptionally low-loss and low-nonlinearity characteristics of hollow-core fiber (HCF) to demonstrate a 198-channel × 40 Gbaud polarization multiplexed 256QAM (PM-256QAM) WDM system over a 20.6 km nested anti-resonant nodeless fiber (NANF) transmission link. A hardware-efficient, low-complexity carrier recovery algorithm is employed, relying entirely on polarized misaligned pilot symbols for robust frame synchronization and high-precision carrier recovery, eliminating the need for training sequences. Compared to conventional methods constrained by fourth-power operations and pilot symbol intervals, our approach offers a wider frequency offset estimation (FOE) range and enhanced carrier phase recovery (CPR). Experimental results demonstrate that the bit error rate (BER) of all 198 WDM channels remains below the 20% soft-decision forward error correction (SD-FEC) threshold, achieving spectral efficiencies of 12.8 bit/s/Hz in the C-band and 13.1 bit/s/Hz in the L-band. Benefiting from the unique properties of HCF, the system demonstrates superior performance compared to conventional single-mode fiber, particularly at high launch powers. This work paves the way for future ultra-high-capacity, low-latency optical networks, providing a viable technological path for next-generation communication systems.