We report an indium phosphide nanowire(NW)-induced cavity in a silicon planar photonic crystal(PPC)waveguide to improve the light–NW coupling.The integration of NW shifts the transmission band of the PPC waveguide in...We report an indium phosphide nanowire(NW)-induced cavity in a silicon planar photonic crystal(PPC)waveguide to improve the light–NW coupling.The integration of NW shifts the transmission band of the PPC waveguide into the mode gap of the bare waveguide,which gives rise to a microcavity located on the NW section.Resonant modes with𝑄factors exceeding 103 are obtained.Leveraging on the high density of the electric field in the microcavity,the light–NW interaction is enhanced strongly for efficient nonlinear frequency conversion.Second-harmonic generation and sum-frequency generation in the NW are realized with a continuous-wave pump laser in a power level of tens of microwatts,showing a cavity-enhancement factor of 112.The hybrid integration structure of NW-PPC waveguide and the self-formed microcavity not only opens a simple strategy to effectively enhance light–NW interactions,but also provides a compact platform to construct NW-based on-chip active devices.展开更多
Cooperative unmanned aerial vehicles(UAVs)cluster technology is considered a prospective solution for area coverage problems,enabling network access and emergency communications in remote areas.In this paper,we invest...Cooperative unmanned aerial vehicles(UAVs)cluster technology is considered a prospective solution for area coverage problems,enabling network access and emergency communications in remote areas.In this paper,we investigate how to control UAV cluster to achieve long-term and stable regional coverage while maintaining link connectivity and minimizing energy consumption,given the limited communication range and energy consumption of the UAVs themselves.To this end,we propose a cooperative UAV cluster strategy based on multi-agent deep reinforcement learning(MADRL)to achieve fair coverage of communication regions,which we call MADRL-based cooperative UAV cluster strategy(MADRL-CUCS).Our solution is a centralized training distributed execution architecture and defines a cluster structure for leader UAVs and follower UAVs.Under the premise of comprehensively considering the maximum coverage,we use a new energy efficiency function to minimize energy consumption,so as to extend the network lifetime of the UAVs cluster networks.The new fairness index and collision avoidance factor are used to ensure that the UAV cluster achieve effective and secure regional coverage.We adopt depth first search algorithm to check the link connectivity of the UAVs during the coverage process.Experiments show that the MADRL-CUCS algorithm outperforms the benchmark algorithm.展开更多
Two-dimensional materials are attractive for constructing high-performance photonic chip-integrated photodetectors because of their remarkable electronic and optical properties and dangling-bond-free surfaces.However,...Two-dimensional materials are attractive for constructing high-performance photonic chip-integrated photodetectors because of their remarkable electronic and optical properties and dangling-bond-free surfaces.However,the reported chip-integrated two-dimensional material photodetectors were mainly implemented with the configuration of metalsemiconductor-metal,suffering from high dark currents and low responsivities at high operation speed.Here,we report a van der Waals PN heterojunction photodetector,composed of p-type black phosphorous and n-type molybdenum telluride,integrated on a silicon nitride waveguide.The built-in electric field of the PN heterojunction significantly suppresses the dark current and improves the responsivity.Under a bias of 1 V pointing from n-type molybdenum telluride to p-type black phosphorous,the dark current is lower than 7 nA,which is more than two orders of magnitude lower than those reported in other waveguide-integrated black phosphorus photodetectors.An intrinsic responsivity up to 577 mA W^(−1) is obtained.Remarkably,the van der Waals PN heterojunction is tunable by the electrostatic doping to further engineer its rectification and improve the photodetection,enabling an increased responsivity of 709 mA W^(−1).Besides,the heterojunction photodetector exhibits a response bandwidth of~1.0 GHz and a uniform photodetection over a wide spectral range,as experimentally measured from 1500 to 1630 nm.The demonstrated chip-integrated van der Waals PN heterojunction photodetector with low dark current,high responsivity and fast response has great potentials to develop high-performance on-chip photodetectors for various photonic integrated circuits based on silicon,lithium niobate,polymer,etc.展开更多
基金Key Research and Development Program(2017YFA0303800)National Natural Science Foundation of China(11634010,61775183,61905196,91950119)+5 种基金Key Research and Development Program in Shaanxi Province of China(2017KJXX-12,2018JM1058)Fundamental Research Funds for the Central Universities(310201911cx032,3102019JC008)Aalto University Doctoral School,Walter Ahlstrom Foundation,Nokia Foundation,Academy of Finland(298297)Academy of Finland Flagship Program(320167,PREIN)Horizon 2020 Framework Programme(820423)European Research Council(834742).
文摘We report an indium phosphide nanowire(NW)-induced cavity in a silicon planar photonic crystal(PPC)waveguide to improve the light–NW coupling.The integration of NW shifts the transmission band of the PPC waveguide into the mode gap of the bare waveguide,which gives rise to a microcavity located on the NW section.Resonant modes with𝑄factors exceeding 103 are obtained.Leveraging on the high density of the electric field in the microcavity,the light–NW interaction is enhanced strongly for efficient nonlinear frequency conversion.Second-harmonic generation and sum-frequency generation in the NW are realized with a continuous-wave pump laser in a power level of tens of microwatts,showing a cavity-enhancement factor of 112.The hybrid integration structure of NW-PPC waveguide and the self-formed microcavity not only opens a simple strategy to effectively enhance light–NW interactions,but also provides a compact platform to construct NW-based on-chip active devices.
基金supported by the National Natural Science Foundation of China(No.62376165).
文摘Cooperative unmanned aerial vehicles(UAVs)cluster technology is considered a prospective solution for area coverage problems,enabling network access and emergency communications in remote areas.In this paper,we investigate how to control UAV cluster to achieve long-term and stable regional coverage while maintaining link connectivity and minimizing energy consumption,given the limited communication range and energy consumption of the UAVs themselves.To this end,we propose a cooperative UAV cluster strategy based on multi-agent deep reinforcement learning(MADRL)to achieve fair coverage of communication regions,which we call MADRL-based cooperative UAV cluster strategy(MADRL-CUCS).Our solution is a centralized training distributed execution architecture and defines a cluster structure for leader UAVs and follower UAVs.Under the premise of comprehensively considering the maximum coverage,we use a new energy efficiency function to minimize energy consumption,so as to extend the network lifetime of the UAVs cluster networks.The new fairness index and collision avoidance factor are used to ensure that the UAV cluster achieve effective and secure regional coverage.We adopt depth first search algorithm to check the link connectivity of the UAVs during the coverage process.Experiments show that the MADRL-CUCS algorithm outperforms the benchmark algorithm.
基金supported by the National Key R&D Program of China(Grant Nos.2018YFA0307200 and 2017YFA0303800)the National Natural Science Foundation of China(Grant Nos.61905198,61775183,11634010,and 61675171)+1 种基金Key Research and Development Program in Shaanxi Province of China(Grant Nos.2017KJXX-12,2018JM1058,and 2018KW-009)the Fundamental Research Funds for the Central Universities(Grant Nos.3102017jc01001,3102018jcc034,and 3102017HQZZ022)。
文摘Two-dimensional materials are attractive for constructing high-performance photonic chip-integrated photodetectors because of their remarkable electronic and optical properties and dangling-bond-free surfaces.However,the reported chip-integrated two-dimensional material photodetectors were mainly implemented with the configuration of metalsemiconductor-metal,suffering from high dark currents and low responsivities at high operation speed.Here,we report a van der Waals PN heterojunction photodetector,composed of p-type black phosphorous and n-type molybdenum telluride,integrated on a silicon nitride waveguide.The built-in electric field of the PN heterojunction significantly suppresses the dark current and improves the responsivity.Under a bias of 1 V pointing from n-type molybdenum telluride to p-type black phosphorous,the dark current is lower than 7 nA,which is more than two orders of magnitude lower than those reported in other waveguide-integrated black phosphorus photodetectors.An intrinsic responsivity up to 577 mA W^(−1) is obtained.Remarkably,the van der Waals PN heterojunction is tunable by the electrostatic doping to further engineer its rectification and improve the photodetection,enabling an increased responsivity of 709 mA W^(−1).Besides,the heterojunction photodetector exhibits a response bandwidth of~1.0 GHz and a uniform photodetection over a wide spectral range,as experimentally measured from 1500 to 1630 nm.The demonstrated chip-integrated van der Waals PN heterojunction photodetector with low dark current,high responsivity and fast response has great potentials to develop high-performance on-chip photodetectors for various photonic integrated circuits based on silicon,lithium niobate,polymer,etc.
