Coupled-core Multicore Fibers Research Articles

Coiling Size Dependence of Group Delay Spread in Coupled Multicore Fibers Without Intentional Twisting

Coiling size dependence of group delay spread (GDS) in coupled multicore fibers (MCFs) without intentional twisting is investigated by using a coupled-wave theory. It is shown that the GDS does not simply decrease with increasing bending radius and the optimum coiling size to decrease GDS depends on a core-to-core distance of MCFs. It is also found that a coupled MCF with a trench-assisted profile is suitable for realizing lower GDS with higher spatial density compared with a coupled MCF with a step-index profile.

Record-Low Spatial Mode Dispersion and Ultra-Low Loss Coupled Multi-Core Fiber for Ultra-Long-Haul Transmission

Newly developed 125-μm-cladding coupled four-core fibers realized the record-low spatial mode dispersion (SMD) of 3.14 ± 0.17 ps/√km over C-band and the ultra-low attenuation of 0.158 dB/km at 1550 nm, both of which are the lowest ever reported among the optical fibers for the space-division multiplexed transmission. The SMD was observed to be proportional to the fiber bend curvature, i.e., inversely proportional to the bend radius, and the SMD of 3.14 ± 0.17 ps/√km was measured at the bending radius of ∼31 cm. By assuming the 3.14-ps/√km SMD accumulation, the tap count of the multiple-input multiple-output digital signal processing for the crosstalk compensation is estimated to be only 63 taps for covering 99.99% power of the impulse response after 10 000-km propagation when the 25-GBaud (50-GHz sampling) is assumed. The present results demonstrate the strong applicability of the coupled multicore fiber to the ultralong-haul submarine transmission system.

The Role of Effective Area in the Design of Weakly Coupled MCF: Optimization Guidance and OSNR Improvement

We propose a propagation model for the weakly coupled multicore fiber (MCF), taking into account crosstalk random behavior with respect to both frequency and spatial distribution. Based on the analytical model, the effect of crosstalk on the MCF transmission can be treated as a Gaussian-like noise source, independent of amplified spontaneous emission noise and nonlinear interference (NLI) noise. Consequently, we link the modified GN model with the waveguide design of weakly coupled MCF, in order to evaluate the transmission performance in terms of received optical signal-to-noise ratio (OSNR). Especially, we investigate the role of MCF effective area on the transmission performance with balanced mitigation of both NLI noise and crosstalk. Based on the reported MCF parameters, we are able to improve the OSNR by 1 dB, only through increasing the trench width by 1.6 μm.

Fiber Twisting- and Bending-Induced Adiabatic/Nonadiabatic Super-Mode Transition in Coupled Multicore Fiber

The characteristics of power transfer between super-modes in coupled multicore fiber are investigated numerically and experimentally. We reveal that fiber twisting and macrobending cause mode coupling through an adiabatic/nonadiabatic process, which is different from the mode coupling caused by structural perturbation, namely microbending. We also investigate the impulse response characteristics of coupled two-core fibers, and find that there is an optimum core pitch for minimizing the complexity of the MIMO processing. Finally, we conduct a 4 × 4 MIMO transmission experiment using two-core fibers to evaluate their transmission characteristics. We show that strongly coupled multicore fiber can reduce the quality difference between the received signals even when the transmission line has large core-dependent gain/loss values.

Coupled Multicore Fiber Design With Low Intercore Differential Mode Delay for High-Density Space Division Multiplexing

A moderately coupled multicore fiber (MCF) design is proposed with the aim of realizing both low intercore multiple-input multiple-output (MIMO) processing complexity and high-space utilization efficiency. We numerically and experimentally investigated the influence of mode coupling on the intercore differential mode delay (DMD) in homogeneous core MCF, and show a moderately coupled MCF design to avoid increasing the intercore DMD, which enables us to compensate for the intercore crosstalk by MIMO processing with low computational complexity. Finally, we fabricated 125-μm-cladding two LP-mode six-core fiber and experimentally realized the highest normalized channel multiplicity of 18 without a noticeable DMD increase induced by mode coupling.

Coupled-Core Multi-Core Fibers for Spatial Multiplexing

Coupled-core multi-core fibers (MCFs) offer characteristics that are beneficial for long-haul spatially multiplexed transmission. Using full-vector solution of the wave equation, we study the number of propagating modes and several modal characteristics, including intermodal beat lengths, group delay spread, mode-dependent chromatic dispersion, and intramodal and intermodal effective areas. We identify a range of design parameters that simultaneously optimizes these characteristics. Our results demonstrate the limited accuracy of perturbation-based analyses in characterizing MCFs with closely spaced cores.