In this paper, we present a fast mode decomposition method for few-mode fibers, utilizing a lightweight neural network called MobileNetV3-Light. This method can quickly and accurately predict the amplitude and phase information of different modes, enabling us to fully characterize the optical field without the need for expensive experimental equipment. We train the MobileNetV3-Light using simulated near-field optical field maps, and evaluate its performance using both simulated and reconstructed near-field optical field maps. To validate the effectiveness of this method, we conduct mode decomposition experiments on a few-mode fiber supporting six linear polarization (LP) modes (LP01, LP11e, LP11o, LP21e, LP21o, LP02). The results demonstrate a remarkable average correlation of 0.9995 between our simulated and reconstructed near-field light-field maps. And the mode decomposition speed is about 6 ms per frame, indicating its powerful real-time processing capability. In addition, the proposed network model is compact, with a size of only 6.5 MB, making it well suited for deployment on portable mobile devices.

We experimentally transmit eight wavelength-division-multiplexing (WDM) channels, 16 quadratic-amplitude-modulation (QAM) signals at 32-GBaud, over 1000 km few mode fiber (FMF). In this experiment, we use WDM, mode division multiplexing, and polarization multiplexing for signal transmission. Through the multiple-input–multiple-output (MIMO) equalization algorithms, we achieve the total line transmission rate of 4.096 Tbit/s. The results prove that the bit error rates (BERs) for the 16QAM signals after 1000 km FMF transmission are below the soft-decision forward-error-correction (SD-FEC) threshold of 2.4×10-2, and the net rate reaches 3.413 Tbit/s. Our proposed system provides a reference for the future development of high-capacity communication.

Four-channel off-axis holography is proposed to simultaneously understand the polarization states and the mode coefficients of linearly polarized (LP) modes in few-mode fiber. Far-field off-axis holograms in the four polarization directions of the fiber laser were acquired at the same moment through a four-channel holographic device. The weights, the relative phase differences, and the polarization parameters of the vector fiber laser mode can be solved simultaneously. The simulated and experimental mode analysis of the laser output by 1060-XP fiber with 6 LP modes at 632.8 nm is conducted, which shows that the similarity of the total intensity distribution of the laser before and after mode analysis is above 0.97. The mode polarization states, the mode weights, and the relative phase differences of the few-mode laser can be determined simultaneously in a single shot by four-channel off-axis holography.