| 1 | Nature-inspired chiral metasurfaces for circular polarization detection and full-Stokes polarimetric measurements显示文摘The manipulation and characterization of light polarization states are essential for many applications in quantum communication and computing,spectroscopy,bioinspired navigation,and imaging.Chiral metamaterials and metasurfaces facilitate ultracompact devices for circularly polarized light generation,manipulation,and detection.Herein,we report bioinspired chiral metasurfaces with both strong chiral optical effects and low insertion loss.We experimentally demonstrated submicron-thick circularly polarized light filters with peak extinction ratios up to 35 and maximum transmission efficiencies close to 80% at near-infrared wavelengths(the best operational wavelengths can be engineered in the range of 1.3-1.6μm).We also monolithically integrated the microscale circular polarization filters with linear polarization filters to perform full-Stokes polarimetric measurements of light with arbitrary polarization states.With the advantages of easy on-chip integration,ultracompact footprints,scalability,and broad wavelength coverage,our designs hold great promise for facilitating chip-integrated polarimeters and polarimetric imaging systems for quantum-based optical computing and information processing,circular dichroism spectroscopy,biomedical diagnosis,and remote sensing applications. | Ali Basiri Xiahui Chen Jing Bai Pouya Amrollahi Joe Carpenter Zachary Holman Chao Wang Yu Yao | 2019 | Light(Science & Applications)2019，8，1： | 12 |
| 2 | On the mechanism and control for the ultra-low frequency oscillation in NY Power Grid with large-scale hydropower显示文摘The power grid with large proportion of hydropower may engage the ultra-low frequency oscillation (ULFO),which threatening the operation of system.To the NY Power Grid system,whose dimension is over thousands,this paper reveals the cause of ULFO with the phase portrait method,i.e.,lies in the saturation of the different limits of the governor system of the generators,in other words,the occurrence of limit cycle is due to the non-smooth bifurcation.And furthermore,it proposes two methods to suppress ULFO with the philosophy of destroying the condition of non-smooth bifurcation.In detail,first,the phenomenon of ULFO in NY Power Grid,the damping characteristics and the limits in the governor system of the hydropower units are presented.Second,based on the non-smooth bifurcation theory,the mathematical basis of the oscillation in the non-smooth system caused by the saturation of limits is introduced.And then,the non-oscillation and oscillation dynamic of the system corresponding to without/with limits in the governor system are analyzed.Furthermore,it discusses the influence of the saturation of single limit on the characteristics of ULFO with the phase portraits.Moreover,the phase portraits of the ULFO under different faults is analyzed,and it shows that the limiting saturation occurs with a large enough disturbance.Thus,the ULFO is resulting from the negative damping of generation and the saturation of multiple limits under a large enough disturbance.In addition,according to the above mechanism,two strategies to suppress the ULFO,i.e.,the governor parameters tuning and the fault strength relief are designed.The simulation shows the effectiveness of proposed strategies. | Ancheng XUE Jiawei WANG Chao ZHENG Joe H.CHOW Tianshu BI | 2019 | Control Theory and Technology2019，17，3： | 11 |
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