Entropy-loaded digital subcarrier multiplexing transmission adaptive to the loss-spectrum ripples of hollow-core fiber

Hollow-core fibers (HCFs) are promising candidates for photonic data-center interconnects (DCIs) owing to their low loss, low latency, ultra-low nonlinearity, low dispersion, and broad transmission window. However, loss-spectrum ripples significantly constrain both the usable bandwidth and the achievable capacity. To address such issue, we propose and experimentally demonstrate an entropy-loaded digital subcarrier multiplexing (DSM) transmission scheme over the nested anti-resonant nodeless fiber (NANF). Here, dynamic entropy is allocated to each subcarrier (SC) based on the signal-to-noise ratio (SNR) variation induced by the loss-spectrum ripples. For single-channel transmission centered at 1550.12 nm, entropy-loaded probabilistic constellation shaping dual-polarization 256 quadrature amplitude modulation (PCS-DP-256QAM) DSM signals can realize a net bit-rate of 613.3 Gbit/s adaptive transmission over 2 km NANF having a peak-to-peak loss-spectrum ripple of 0.4 dB within a channel spacing of 0.51 nm. Meanwhile, this transmission remains nonlinear impairment-free even at a record-high launch power of 39 dBm. Furthermore, we demonstrate 40-channel dense wavelength division multiplexing (DWDM) DSM transmission over 10 km NANF, achieving a net bit-rate of more than 602.7 Gbit/s per wavelength and a total capacity of 24.14 Tbit/s, when the entropy-loaded PCS-DP-256QAM DSM signals are individually generated under a peak-to-peak loss-spectrum ripple of 0.7 dB over the extended C-band. Compared with conventional uniform-entropy DSM, our proposed scheme enhances the aggregate capacity by 18.28%. Such an innovative transmission scheme adaptive to broadband loss-spectrum ripples effectively unlocks the HCF full potential for photonic DCIs.