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In this work, we grew Bi4Ge3O12 (BGO) crystals of two types by Bridgmen–Stockbarger technology in different temperature gradients and compared their optical transmissions and energy resolutions before and after ultraviolet irradiation. It was found that the optical transmissions and energy resolutions of the two types of BGO crystals are similar before UV-irradiation. After UV-irradiation, the optical transmissions at 480 nm of the first type of BGO crystals which were grown in higher temperature gradient cut down about 20% and their energy resolutions obviously deteriorated from about 12–18%. But the optical transmissions and energy resolutions of the second type of BGO crystals which were grown in lower temperature gradient keep unchanged on the whole. After 250 °C/4 h annealing, the optical transmissions and energy resolutions of the second type of BGO crystals can be completely recovered, whereas the optical transmissions and energy resolutions of the first type of BGO crystals cannot be completely recovered until through 600 °C/8 h annealing. The reason for the difference between the first and second type of BGO crystals is discussed. [Copyright &y& Elsevier]

In this paper, we propose a reference-modulated permutation index differential chaos shift keying (RM-PI-DCSK) over multipath fading channels. Due to quasi-orthogonal property between different permutated chaotic signals, the proposed scheme can remarkably suppress the inter-sequence interference to recover the desired information. Moreover, the proposed RM-PI-DCSK has one more modulation bit in the reference segment than the conventional permutation index differential chaos shift keying (PI-DCSK). Both the reference signal in the first time-slot and a permuted replica of the reference in the second time-slot are modulated for efficient transmission. The theoretical bit-error-rate (BER) performance and the highly consistent simulation results demonstrate that the proposed RM-PI-DCSK can achieve a performance gain 3 dB over the conventional PI-DCSK at a BER of $10^{-4}$ , and this gain becomes larger in a high-delay-spread channel. In particular, the performance superiority of the RM-PI-DCSK is further demonstrated in a typical ultra-wideband (UWB) channel with narrow-band interference. Therefore, this proposed scheme can be deemed as an efficient transmission alternative for chaotic-based wireless communications, such as in wireless local area network (WLAN) applications and indoor applications of the transmitted-reference UWB. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A compact and broadband polarization beam splitter (PBS) based on silicon (Si) nitride (SiN)-on-Si-on-insulator multilayer platform with vertical asymmetrical directional coupler (ADC) is designed and analyzed. The vertical ADC is consisted of two waveguides, which are placed in the bottom Si layer and upper SiN layer separately. It is found that by properly choosing the values of the structure parameters, especially taking advantages of the extra freedom of the relative location between these two waveguides, the performance of the PBS can be significantly improved. By incorporating tapered structures into the coupling region in the further step, bandwidth of 294 nm, which is determined by the insertion loss of <1 dB and the extinction ratio of >20 dB in both polarizations, is realized within a coupling length as compact as 6.9 μm. The proposed device has a good potential to be applied in three-dimensional photonic integration, where higher integration density or more on-chip functions can be realized. [ABSTRACT FROM AUTHOR]

Owing to their many intriguing properties, transparent metal oxide semiconductors have become the most attractive alternatives for silicon-based semiconductors widely used today and been widely investigated by researchers. However, most of high performance metal oxide thin film transistor (TFT) relied on vacuum processing equipment and expensive rare element indium in the manufacturing process, the need for developing low cost indium-free metal oxide TFT has become urgent. In this work, a bilayer TFT composed of ZnO nanoparticles (NPs)/SnO 2 was prepared by solution method. In this device structure, SnO 2 film can provide high conductivity and carrier mobility, while the ZnO NPs in the upper layer can modulate and control channel conductance and further protect SnO 2 film from air environment. The obtained device exhibits the excellent performances including μ FE of 22.9 cm2V−1s−1 and I on /I off about 1 × 107, subthreshold swing (SS) value about 0.36 V dec−1, and excellent environmental stability have been effectively achieved. Furthermore, the performance enhancement mechanism for the bilayer transistor with the help of simulation and related experiments was further explored. The bilayer ZnO NPs/SnO 2 TFT has great cost advantage compared with indium based metal oxide TFTs and exhibits excellent potential in low cost thin-film electronic devices. [Display omitted] • The indium free thin film transistor was prepared by solution method with a high on/off current ratio, a small sub-threshold swing. • The trap density and conductivity of bilayer channel were greatly reduced, and the bilayer transistor exhibited low cut-off current and good stability. • Based on the device structure of the bilayer transistor, TCAD simulation was used to investigate the position of the conductive channel. [ABSTRACT FROM AUTHOR]