Simulation investigation of CO ₂ absorption-induced performance degradation in hollow-core fiber transmission systems and spectrum-optimized digital sub-carrier multiplexing design for circumvention

Hollow-core fiber (HCF) is developing rapidly, with its minimum attenuation already surpassing that of traditional solid-core fiber and continually setting new records. However, recent reports have pointed out that the CO₂ absorption peaks present in the attenuation spectrum of HCF can severely affect the performance of high-speed signal transmission. Using a high-precision insertion loss test platform and a swept-frequency light source, we measured the attenuation spectrum of an HCF sample and found that under high-precision wavelength interval scanning, certain wavelength positions in this sample exhibited up to 0.5 dB/km extra loss due to CO₂ absorption. We imported the experimental test attenuation results into VPITransmissionMaker for simulation analysis and found that in the wavelength regions where the CO₂ absorption peaks are severe, the bit-error rate (BER) performance of both conventional single-carrier (SC) signals and digital sub-carrier multiplexing (DSCM) signals after 100 km transmission deteriorates significantly. To address this issue, we proposed a spectrum-optimized DSCM modulation scheme with sub-carrier center frequency optimization to circumvent the overlap between the CO₂ absorption peaks and the effective components of the DSCM signal spectrum. Simulation results show that within a 150 GHz grid at a center frequency of 186.05 THz, for the 100 km HCF fiber measured in this study with pronounced CO₂ absorption peaks, the proposed novel, to the best of our knowledge, DSCM scheme achieves a >10 × BER improvement compared to conventional SC and DSCM schemes, when the optical signal-to-noise ratio of the transmission system is above 26 dB.