The rapid advancement of data-intensive technologies, including the Internet of Things (IoT) and cloud computing, presents unprecedented capacity challenges for current optical networks. Traditional optical communication networks, primarily utilizing silica single-mode fiber (SMF), have historically achieved exponential growth in information transmission capacity. However, the Kerr nonlinearity inherent in single-mode fibers imposes limitations, with maximum throughput approaching the theoretical limit of approximately 100 Tbit/s, insufficient for future data traffic demands. In response, space-division multiplexing (SDM) technology has emerged as a crucial solution to overcome the capacity constraints of single-mode fibers by enabling multiple independent data channels within a single wavelength through parallel spatial channels, offering a revolutionary approach to expanding optical network capacity.

This research presents a high-capacity, long-haul multidimensional multiplexing transmission system utilizing weakly coupled multi-core few-mode fiber (MC-FMF), achieving efficient transmission of 48 Gbaud broadband signals through a weakly coupled 19-core 6-mode fiber. The system combines SDM technology with wavelength-division multiplexing (WDM) and polarization-division multiplexing (PDM) technologies. This implementation facilitates independent transmission of four spatial modes (LP_11a, LP_11b, LP_21a, and LP_21b) and their corresponding polarization across 80 wavelength channels.

The fabrication process optimization for the multi-core few-mode fiber employed in this petabit-scale multidimensional multiplexing system is illustrated in this paper, requiring comprehensive optimizations across three key stages: core deposition, multi-core preform fabrication, and fiber drawing (Fig. 1). In the core rod deposition stage, we employ our proprietary plasma chemical vapor deposition (PCVD) technology, combined with high-purity raw materials specifically developed for MC-FMF. Through systematic optimization of deposition parameters and material ratios, we implement advanced PCVD techniques including multi-time deposition, precision doping, and interface stress control to ensure accurate realization of the computer-simulated core-cladding structures. The process optimization particularly focuses on enhancing the structural fidelity of multiple cores while maintaining low attenuation characteristics through precise stress management. The 19 cores are arranged in concentric rings to minimize inter-core crosstalk, with a uniform core spacing of 44 μm specifically designed to suppress internal crosstalk. At 1550 nm, this 19-core fiber exhibits a typical inter-core crosstalk below -40 dB/30 km, demonstrating negligible coupling effects between cores that can be effectively disregarded in system operation. Considering the geometric dimensions and refractive index profile of each core, every individual core can support six spatial modes: LP₀₁, LP_11a, LP_11b, LP_21a, LP_21b, and LP₀₂ (Fig. 3). Building upon these outstanding characteristics, the proposed high-performance weakly coupled multi-core few-mode fiber establishes a solid foundation for future deployment of high-capacity, long-haul multidimensional multiplexing optical communication systems.

Multiple-input multiple-output (MIMO) equalization, a fundamental algorithm in multidimensional multiplexing transmission systems, is widely employed to compensate for inter-channel crosstalk. Traditional multiplexing transmission systems, multiple-input multiple-output time-domain equalizers (MIMO-TDEs) exhibit high computational complexity that increases linearly with tap length. This paper addresses these limitations by proposing an MIMO frequency-domain equalizer (FDE) incorporating a decision-based carrier phase recovery (DBCPR) module (Figs. 5 and 6). The integrated decision-based carrier phase recovery module enhances phase noise resistance while improving channel estimation accuracy. This approach substantially reduces computational complexity while improving phase noise tolerance.

The bit error rate (BER) performance analysis of eight sub-channels after long-haul transmission through multi-core few-mode fiber reveals comparable BER characteristics, attributed to mode-dependent loss (MDL) suppression through optimized loop configuration. Signal degradation occurs with increasing transmission distance due to progressive pulse broadening and accumulated mode coupling. Advanced digital signal processing (DSP) algorithms at the receiver enable few-mode signals after 1000-km transmission to maintain BER threshold with 20% overhead. Uniform performance across wavelength channels is achieved through independent channel attenuation optimization via wavelength selective switch (WSS). Constellation diagrams demonstrate effective impairment compensation through the proposed MIMO-FDE-DBCPR. The SDM-MDL-PDM multidimensional multiplexing system achieves a total line rate of 1.945 Pbit/s.

This study provides essential technical references for advancing next-generation high-capacity optical transmission systems, demonstrating the significant potential of MC-FMF in multidimensional multiplexed optical communications. The research successfully implemented a petabit-scale multidimensional multiplexing transmission system utilizing weakly coupled MC-FMF. The system incorporates an innovative MIMO-FDE-DBCPR for multidimensional signal processing, which substantially reduces computational complexity while enhancing phase noise tolerance. Experimental results demonstrate that following 1000-km transmission, all wavelength channels meet the BER threshold, validating the system’s efficiency and reliability. This investigation presents valuable technical guidelines for the design and optimization of next-generation high-capacity optical transmission systems, while reinforcing the substantial application potential of MC-FMF in multidimensional multiplexed optical communications.