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Coherent supercontinuum (SC) generation in optical fibers has spurred extensive research interest and found many applications. Here, we report a hybrid optical crystal fiber with an yttrium aluminum garnet (YAG) core. The optimized fiber features broad and flat near-zero normal dispersion and three wavelengths where the dispersion slope is zero. Through numerical modeling, we in detail investigate the influence of the pump wavelengths near the three wavelengths on the spectral broadening. The spectral broadening shows asymmetric towards the high-frequency region. The longer the pump wavelength, the more is the short wavelength components of the generated SC. Thus, the high-frequency components of the SC spectra can be engineered in the fiber. Interestingly, the occurrence of optical wave breaking (OWB) in the low-frequency region is prior to that in the high-frequency region when the pump wavelength is at 1660 nm. The broadest spectrum could be obtained when the pump wavelength is near the middle wavelength where the dispersion slope is zero. The result provides a new strategy for fiber design and broadband SC generation, which is different from the viewpoint that the broadest spectrum can be obtained when the pump wavelength near the local maximum dispersion. Combined with high nonlinearity and flat dispersion, the hybrid fiber allows octave-spanning SC generation with the pump power low to 1 kW at 1100 nm. This provides the potentials for high-power, broadband, and coherent SC generation at 1064 nm where the dispersion slope is near zero.

This paper proposes a medium access control (MAC) protocol based on deep reinforcement learning (DRL), i.e., multi-channel transmit deep-reinforcement learning multi-channel access (MCT-DLMA) in heterogeneous wireless networks (HetNets). The work concerns practical unsaturated channel traffic that arrives following a Poisson distribution instead of saturated traffic that arrives before.By learning the access mode from historical information, MCT-DLMA can well fill the spectrum holes in the communication of existing users. In particular, it enables the cognitive user to multi-channel transmit at a time, e.g., via the multi-carrier technology. Thus, the spectrum resource can be fully utilized, and the sum throughput of the HetNet is maximized. Simulation results show that the proposed algorithm provides a much higher throughput than the conventional schemes, i.e., the whittle index policy and the DLMA algorithms for both the saturated and unsaturated traffic, respectively. In addition, it also achieves a near-optimal result in dynamic environments with changing primary users, which proves the enhanced robustness to time-varying communications.

In this paper, we aim at the point which the sensing coverage for target monitor tracking and the connectivity coverage for information transmitting of WSN claim to robust, anti-fragility. We firstly present and prove a profound sensing radius of nodes; this radius can make each objective point of monitor area fall under the sensing range of at least one sensor node by the probability of tending to 1 at any time. Secondly, we analyze the problem of connectivity coverage of WSN, also present and prove a probability inequality of active nodes, which can be of the judgment scale and the critical threshold that the connectivity of WSN not to be destroyed. Thirdly, under the premise which the necessity of connectivity of WSN is satisfied, we present an algorithm that provided with robust connectivity of big probability, and doing the simulation analysis. [ABSTRACT FROM AUTHOR]

In this paper, we investigate throughput capacity theories of Hierarchical Wireless Sensor Networks (H-WSN). Firstly, we introduce the structural protocol model, node mobility tracking model and conflict graph model of H-WSN. Secondly, we give some fundamental definitions about conflict graph and conflict event. Thirdly, a fundamental theorem about graph theory is given, and then the throughput capacity is turned to the problem that can be translated into linear constraints system, and can be gotten by finding the feasible solution of linear system. Finally, we propose and prove a critical inequality of throughput capacity of H-WSN. We also propose and prove a gradual probabilistic quality and the specific expression of expectant availability of throughput capacity of H-WSN. The results enrich the theory of some famous conclusions about throughput capacity and the information theory of wireless networks. [ABSTRACT FROM AUTHOR]