101.47-b/s/Hz spectral efficiency transmission using probabilistic shaping 16-QAM in 7-core 3-mode fiber

The exponential growth of global data traffic has caused conventional single-mode fiber systems to approach the Shannon limit, which will require breakthroughs to meet future communication demands. This paper experimentally demonstrates the first 7-core 3-mode optical fiber system based on probabilistic shaping 16-quadrature amplitude modulation (PS-16QAM). The transmitted symbols employed a Maxwell-Boltzmann probability distribution to optimize the constellation point energy allocation, reducing signal peak-to-average power ratio (PAPR) compared with conventional 16QAM. The transmission fiber employed a graded-index profile and trench-assisted structure to suppress inter-core crosstalk. The system integrated wavelength division multiplexing (WDM), polarization division multiplexing (PDM), and space division multiplexing (SDM). This achieved parallel transmission for 126 channels (7 cores × 3 modes × 3 wavelengths × 2 polarizations) over an 80.6-km positive-negative differential group delay (DGD) compensated link. A data-assisted joint frequency offset estimation and synchronization algorithm and a multiple-input multiple-output least mean squares (MIMO-LMS) equalization algorithm integrated with maximum likelihood phase recovery ensured reliable signal recovery. Under a 25.5% soft-decision forward error correction (FEC) threshold, the system achieved a maximum spectral efficiency of 101.47 b/s/Hz. Experiments validated the feasibility of probabilistic shaping techniques in multi-core few-mode fiber systems, providing crucial technical support for next-generation ultra-high-capacity optical communication systems.