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 propose a novel waveguide design of a polarization-maintaining few mode fiber (PM-FMF) supporting ≥10 non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core, a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δneff between the adjacent guided modes could be kept larger than 1.32×10 4 over the whole C+L band. The proposed fiber structure can be flexibly tailored to support an even larger number of modes in PM-FMF (14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.

We experimentally demonstrate a real-time quasi-full-duplex 400G/300G optical interconnection over 20 km multicore fibers (MCFs), using 10G-class transponders operated in the C-band. Optical delay interferometer (ODI)-based optical frequency equalization is applied to mitigate chirp and dispersion induced impairments, so that the tolerance to inter-symbol interference (ISI) can be enhanced, thus enabling 4×25 Gb/s on-off keying (OOK) transmission per core over severely limited bandwidth channels. Real-time bit error ratio (BER) performances of the bidirectional 400 Gb/s transmission are measured without using extra digital signal processing (DSP) or electrical equalization, which ensures low complexity and less power consumption.

Wepresent a novel method for engineering ultra-flattened-dispersion photonic crystal fibers with uniform air holes by rotations of inner air-hole rings around the fiber core. By choosing suitable rotation angles of each inner ring, theoretical results show that normal, anomalous, and nearly zero ultra-flattened-dispersion fibers in wide spectra ranges of interest can be obtained alternatively. Moreover, in our dispersion sensitive analysis, these types of fibers are robust to variations from optimal design parameters. The method is suitable for the accurate adjustment of fiber dispersion within a small range, which would be valuable for the fabrication of ultra-flattened-dispersion fibers and also have potential applications in wide-band high-speed optical communication systems.