Sensing pulse-synchronous temporal entropy loading technique for co-wavelength optical fiber ISAC system

Co-wavelength optical fiber integrated sensing and communication (ISAC) improves spectral utilization but suffers from pulse-synchronous nonlinear impairments when high-peak-power sensing pulses overlap with communication symbols. Here, we propose a sensing pulse-synchronous temporal entropy loading (SP-TEL), which adapts probabilistically constellation-shaped (PCS) symbols to the sensing pulse-induced time-varying channel by assigning different entropies to corresponding pulse-overlapped and non-overlapped communication symbols, respectively. We experimentally validate the effectiveness of SP-TEL in a 40 GBaud four-subcarrier PCS-DP-64QAM co-wavelength ISAC system over 10.91 km standard single-mode fiber (SSMF). Compared with the traditional uniform-entropy technique, SP-TEL can improve the generalized mutual information (GMI) by 0.2 bit/symbol and reduce the required optical signal-to-noise ratio (OSNR) by up to 3 dB at the target GMI of 4.6 bit/symbol. Meanwhile, reliable 1 kHz vibration localization is secured with 10 m spatial resolution and a vibration SNR of 30.04 dB.