Fully degeneracy-lifted bow-tie elliptical ring-core multi-mode fiber

Design of a side-hole-assisted weakly coupled rectangular ring-core multimode fiber for mode-division-multiplexing networks

We present a side-hole-assisted weakly coupled polarization-maintaining rectangular ring-core multimode fiber supporting 68 eigenmodes. The rectangular ring-core and side-hole structures are introduced to effectively split eigenmodes. The impact of parameters on mode utilization rate η and mode number is evaluated at the wavelength of 1550 nm. We also analyze bending loss and broadband performance of the entire C band, including n_eff, Δn_eff, A_eff, nonlinearity, and differential mode delay. By optimizing the design parameters, the 68 eigenmodes are completely separated with Δn_eff between adjacent modes larger than 10^-4 over the whole C band. The designed fiber can be used for eigenmode-division multiplexing networks to improve transmission capacity and spectral utilization.

Design of steering wheel-type ring depressed-core 10-mode fiber with fully improved mode spacing

We present a steering wheel-type ring depressed-core few-mode fiber (SWTR-DC-FMF) that features a central depressed step-index core and a novel SWTR structure consisted of two symmetrical high-index parts and low-index parts, respectively. The DC and SWTR make great contribution to separate the non-degenerated LP modes and spatial modes in the circular symmetry core, resulting in fully improved mode spacing. The designed fiber is able to support 10 spatial modes with the minimum effective index difference (Min Δneff) between adjacent spatial modes larger than 1.93 × 10^-4 and the Min Δneff between adjacent LP modes above 1.51 × 10^-3 at the same time, facilitating potential fiber spatial mode multiplexing transmission with less multiple-input multiple-output (MIMO-less) digital signal processing technique. The broadband performance including n_eff, Δneff, effective mode area (A_eff) and differential mode delay (DMD) is comprehensively investigated over the whole C and L band. Moreover, the birefringence and fabrication tolerance are discussed. The designed fiber targets emerging applications in short-reach weakly coupled space-division multiplexing (SDM) optical networking to increase transmission capacity and spectral efficiency and further reduce the system complexity effectively.

Photonic crystal fibers supporting fully separated eigenmodes

We present two kinds of fully degeneracy-lifted solid-core photonic crystal multi-mode fibers aiming at multiple-input multiple-output-free direct fiber vector eigenmode multiplexing transmission. One of the target fiber structures is able to support 52 fully separated eigenmodes with effective index difference above 1.37×10^-4 and confinement loss below 3.28×10^-5  dB/km over the whole C+Lband (1530-1625 nm). Specifically, it is suggested that >10^-4 effective index separation is sufficient to possess polarization-maintaining properties, while for short-reach stable mode-division multiplexing transmission, the effective index difference >10^-3 is highly desired. In particular, the other target fiber structure can further increase effective index separation above 1.10×10^-3 among 24 eigenmodes with confinement loss below 6.68×10^-4  dB/km over the whole C+L band.

Design of PANDA-type elliptical-core multimode fiber supporting 24 fully lifted eigenmodes

We present a novel PANDA-type elliptical-core multimode fiber featured by the combination of an elliptical core and two symmetrical circular stress-applying parts (SAPs). The characterization results indicate that such a special fiber design is able to support 24 fully separated eigenmodes with minimum effective index difference (min(Δn_eff)) between adjacent modes larger than 1.35×10^-4 over the whole C band. Specifically, the fiber geometric dimensions and doping concentrations are deviation tolerant and reasonable within the existing fiber manufacture facility restriction, thus would be promising for practical fabrication. The fiber bending effects are also investigated based on conformal mapping. Moreover, ultra-broadband performance is analyzed over the whole C+L band ranging from 1530 nm to 1625 nm. The designed fiber is targeted at applications in direct fiber vector eigenmode-division multiplexing combined with the mature wavelength-division multiplexing technique while eliminating the complex multiple-input multiple-output digital signal processing.