Femtosecond laser direct inscription is a technique especially useful for prototyping purposes due to its distinctive advantages such as high fabrication accuracy, true 3D processing flexibility, and no need for mold or photomask. In this paper, we demonstrate the design and fabrication of a planar lightwave circuit (PLC) power splitter encoded with waveguide Bragg gratings (WBG) using a femtosecond laser inscription technique for passive optical network (PON) fault localization application. Both the reflected wavelengths and intervals of WBGs can be conveniently tuned. In the experiment, we succeeded in directly inscribing WBGs in 1×4 PLC splitter chips with a wavelength interval of about 4 nm and an adjustable reflectivity of up to 70% in the C-band. The proposed method is suitable for the prototyping of a PLC splitter encoded with WBG for PON fault localization applications.

Edge blockchains, the blockchains running on edge computing infrastructures, have attracted a lot of attention in recent years. Thanks to data privacy, scalable computing resources, and distributed topology nature of edge computing, edge blockchains are considered promising solutions to facilitating future blockchain applications. However, edge blockchains face unique security issues caused by the deployment of vulnerable edge devices and networks, including supply chain attacks and insecure consensus offloading, which are mostly not well studied in previous literature. This paper is the first survey that discusses the attacks and countermeasures of edge blockchains. We first summarize the three-layer architecture of edge blockchains: blockchain management, blockchain consensus, and blockchain lightweight client. We then describe seven specific attacks on edge blockchain components and discuss the countermeasures. At last, we provide future research directions on securing edge blockchains. This survey will act as a guideline for researchers and developers to design and implement secure edge blockchains.

A polarized reconfigurable patch antenna is proposed in this paper. The proposed antenna is a dual cross-polarized patch antenna with a programmable power divider. The programmable power divider consists of two branch line couplers (BLC) and a digital phase shifter. By adjusting the phase of the phase shifter, the power ratio of the power divider can be changed, and thus the feed power to the antenna input port can be changed to reconfigure the antenna polarization. The phase-controlled power divider and the cross dual-polarized antenna are designed, fabricated and tested, and then they are combined to realize the polarized reconfigurable antenna. By moving the phase of the phase shifter, the antenna polarization is reconfigured into vertical polarization (VP), horizontal polarization (HP), and circular polarization (CP). The test is conducted at the frequency of 915 MHz, which is widely used for simultaneous wireless information and power transfer (SWIPT) in radio-frequency identification (RFID) applications. The results demonstrate that when the antenna is configured as CP, the axial ratio of the antenna is less than 3 dB, and when the antenna is configured as HP or VP, the axial ratio of the antenna exceeds 20 dB. Finally, experiments are conducted to verify the influence of antenna polarization changes on wireless power transmitting. As expected, the reconfigured antenna polarization can help improve the power transmitting efficiency.

Many science and engineering applications involve solving a linear least-squares system formed from some field measurements. In the distributed cyber-physical systems (CPS), each sensor node used for measurement often only knows partial independent rows of the least-squares system. To solve the least-squares all the measurements must be gathered at a centralized location and then perform the computation. Such data collection and computation are inefficient because of bandwidth and time constraints and sometimes are infeasible because of data privacy concerns. Iterative methods are natural candidates for solving the aforementioned problem and there are many studies regarding this. However, most of the proposed solutions are related to centralized/parallel computations while only a few have the potential to be applied in distributed networks. Thus distributed computations are strongly preferred or demanded in many of the real world applications, e.g. smart-grid, target tracking, etc. This paper surveys the representative iterative methods for distributed least-squares in networks.