Narrow Results

The transport efficiency of a network is strongly related to the underlying structure. In this paper, we propose an efficient strategy named high-betweenness-first (HBF) for the purpose of improving the traffic handling capacity of scale-free networks by limiting a fraction of undirected links to be unidirectional ones based on the links’ betweenness. Compared with the high-degree-first (HDF) strategy, the traffic capacity can be more significantly enhanced under the proposed link-directed strategy with the shortest path (SP) routing protocol. Simulation results in the Barabási–Albert (BA) model for scale-free networks show that the critical generating rate $R_c$ which can evaluate the overall traffic capacity of a network system is larger after applying the HBF strategy, especially with nonrandom direction-determining rules. Because of the strongly improved traffic capacity, this work is helpful to design and optimize modern communication networks such as the software defined network.

In this paper, we have proposed a novel periodic surface plasmon polariton (SPP) waveguide to realize a one-way mode converter which is based on a parity–time (PT) symmetry broken system, and it converts the fundamental TM mode to the first-order TM mode in only forward direction. Periodic gain potentials are put in place to construct the system mentioned in periodic SPP waveguide. Further, as the mode converter contains gain and loss material, light signals will be amplified when it propagates forward, and they will be attenuated toward when they propagate backward. The unidirectional mode converter has wide applications in nonlinearity induced isolation, mode insensitive element and on-chip mode locked laser.