Planar optical waveguides are the key elements in a modern, high-speed optical network. An important problem facing the optical fiber communication system, specifically planar optical waveguides, is coupling. The curr...Planar optical waveguides are the key elements in a modern, high-speed optical network. An important problem facing the optical fiber communication system, specifically planar optical waveguides, is coupling. The current study presents a coupling model for planar optical waveguides and optical fibers. The various effects of the optical properties of the coupling interface were analyzed by the scalar finite difference beam propagation method, including the thickness, with or without the matching refractive index of the interface adhesive. The findings can serve as a guide for planar optical waveguide packaging.展开更多
To improve the service and machining performance of the workpiece, the tool wear mechanisms, surface machining quality, and wear resistance in conventional side milling(CSM)and longitudinal-torsional ultrasonic vibrat...To improve the service and machining performance of the workpiece, the tool wear mechanisms, surface machining quality, and wear resistance in conventional side milling(CSM)and longitudinal-torsional ultrasonic vibration side milling(LTUVSM) of GH4169 superalloy at different cutting lengths are investigated systematically. Tool wear mechanisms are revealed and the correlation between machined surface quality with tool wear is analyzed correspondingly. Tool wear patterns mainly include adhesive wear, diffusion wear, abrasive wear, and chipping sticking.Better surface quality is achieved in LTUVSM due to a maximum reduction of flank wear bandwidth and wear rate by 71.9% and 71.5%, respectively, compared to CSM. The friction coefficient,initial wear stage time, and wear volume of dry sliding wear were measured to evaluate the workpiece wear resistance. The maximum reductions in friction coefficient and wear volume in LTUVSM are 18.2% and 15.8% compared to CSM. The regular ultrasonic vibration textures suppress the friction and the growth of contact nodes in the contact area, decreasing the degree of surface wear, which is demonstrated by a 38.8% increase in initial wear stage time compared to CSM.In conclusion, the workpiece in LTUVSM exhibits higher wear resistance because of the improvement of tool wear and the guarantee of surface quality.展开更多
Moirésuperlattices in van der Waals structures have emerged as a powerful platform for studying the novel quantum properties of two-dimensional materials.The periodic moirépatterns generated by these structu...Moirésuperlattices in van der Waals structures have emerged as a powerful platform for studying the novel quantum properties of two-dimensional materials.The periodic moirépatterns generated by these structures lead to the formation of flat mini-bands,which alter the electronic energy bands of the material.The resulting flat electronic bands can greatly enhance strong correlative interactions between electrons,leading to the emergence of exotic quantum phenomena,including moiréphonons and moiréexcitons.While extensive research has been conducted on the exotic quantum phenomena in twisted bilayers of transition metal dichalcogenides(TMDs),and the regulatory effect of stacked layers on moiréexcitons remains unexplored.In this study,we report the fabrication of a twisted WSe_(2)/WSe_(2)/WSe_(2) homotrilayer with two twist angles and investigate the influence of stacked layers on moiréexcitons.Our experiments reveal multiple moiréexciton splitting peaks in the twisted trilayer,with moirépotential depths of 78 and 112 meV in the bilayer and trilayer homostructures,respectively.We also observed the splitting of the moiréexcitons at 90 K,indicating the presence of a deeper moirépotential in the twisted trilayer.Moreover,we demonstrate that stacked layers can tune the moiréexcitons by manipulating temperature,laser power,and magnetic field.Our results provide a new physical model for studying moirésuperlattices and their quantum properties,which could potentially pave the way for the development of quantum optoelectronics.展开更多
Exploiting the valley degrees of freedom as information carriers provides new opportunities for the development of valleytronics.Monolayer transition metal dichalcogenides(TMDs)with broken space-inversion symmetry exh...Exploiting the valley degrees of freedom as information carriers provides new opportunities for the development of valleytronics.Monolayer transition metal dichalcogenides(TMDs)with broken space-inversion symmetry exhibit emerging valley pseudospins,making them ideal platforms for studying valley electronics.However,intervalley scattering of different energy valleys limits the achievable degree of valley polarization.Here,we constructed WSe_(2)/yttrium iron garnet(YIG)heterostructures and demonstrated that the interfacial magnetic exchange effect on the YIG magnetic substrate can enhance valley polarization by up to 63%,significantly higher than that of a monolayer WSe_(2)on SiO_(2)/Si(11%).Additionally,multiple sharp exciton peaks appear in the WSe_(2)/YIG heterostructures due to the strong magnetic proximity effect at the magnetic-substrate interface that enhances exciton emission efficiency.Moreover,under the effect of external magnetic field,the magnetic direction of the magnetic substrate enhances valley polarization,further demonstrating that the magnetic proximity effect regulates valley polarization.Our results provide a new way to regulate valley polarization and demonstrate the promising application of magnetic heterojunctions in magneto-optoelectronics.展开更多
文摘Planar optical waveguides are the key elements in a modern, high-speed optical network. An important problem facing the optical fiber communication system, specifically planar optical waveguides, is coupling. The current study presents a coupling model for planar optical waveguides and optical fibers. The various effects of the optical properties of the coupling interface were analyzed by the scalar finite difference beam propagation method, including the thickness, with or without the matching refractive index of the interface adhesive. The findings can serve as a guide for planar optical waveguide packaging.
基金supported by the National Natural Science Foundation of China Regional Innovation and Development Joint Fund (Hunan Province) (No. U22A20200)。
文摘To improve the service and machining performance of the workpiece, the tool wear mechanisms, surface machining quality, and wear resistance in conventional side milling(CSM)and longitudinal-torsional ultrasonic vibration side milling(LTUVSM) of GH4169 superalloy at different cutting lengths are investigated systematically. Tool wear mechanisms are revealed and the correlation between machined surface quality with tool wear is analyzed correspondingly. Tool wear patterns mainly include adhesive wear, diffusion wear, abrasive wear, and chipping sticking.Better surface quality is achieved in LTUVSM due to a maximum reduction of flank wear bandwidth and wear rate by 71.9% and 71.5%, respectively, compared to CSM. The friction coefficient,initial wear stage time, and wear volume of dry sliding wear were measured to evaluate the workpiece wear resistance. The maximum reductions in friction coefficient and wear volume in LTUVSM are 18.2% and 15.8% compared to CSM. The regular ultrasonic vibration textures suppress the friction and the growth of contact nodes in the contact area, decreasing the degree of surface wear, which is demonstrated by a 38.8% increase in initial wear stage time compared to CSM.In conclusion, the workpiece in LTUVSM exhibits higher wear resistance because of the improvement of tool wear and the guarantee of surface quality.
基金The study presented herein was generously supported by multiple funding agencies,including the National Natural Science Foundation of China(No.61775241)the Hunan Province Key Research and Development Project(No.2019GK2233)+9 种基金the Hunan Provincial Science Fund for Distinguished Young Scholars(No.2020JJ2059)the National Natural Science Foundation of China(Nos.62090035 and U19A2090)the Youth Innovation Team(No.2019012)of CSU,the Key Program of Science and Technology Department of Hunan Province(Nos.2019XK2001 and 2020XK2001)the Science and Technology Innovation Basic Research Project of Shenzhen(No.JCYJ20190806144418859)the Postdoctoral Science Foundation of China(No.2022M713546)The authors also express their gratitude to the High-Performance Complex Manufacturing Key State Lab Project,Central South University(No.ZZYJKT2020-12)the Australian Research Council(ARC Discovery Project,DP180102976)for their support of ZWLCTW is grateful for support from the National Natural Science Foundation of China(No.11974387)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB33000000)H.H.Z.acknowledges support from the Postdoctoral Science Foundation of China(No.2022M713546).
文摘Moirésuperlattices in van der Waals structures have emerged as a powerful platform for studying the novel quantum properties of two-dimensional materials.The periodic moirépatterns generated by these structures lead to the formation of flat mini-bands,which alter the electronic energy bands of the material.The resulting flat electronic bands can greatly enhance strong correlative interactions between electrons,leading to the emergence of exotic quantum phenomena,including moiréphonons and moiréexcitons.While extensive research has been conducted on the exotic quantum phenomena in twisted bilayers of transition metal dichalcogenides(TMDs),and the regulatory effect of stacked layers on moiréexcitons remains unexplored.In this study,we report the fabrication of a twisted WSe_(2)/WSe_(2)/WSe_(2) homotrilayer with two twist angles and investigate the influence of stacked layers on moiréexcitons.Our experiments reveal multiple moiréexciton splitting peaks in the twisted trilayer,with moirépotential depths of 78 and 112 meV in the bilayer and trilayer homostructures,respectively.We also observed the splitting of the moiréexcitons at 90 K,indicating the presence of a deeper moirépotential in the twisted trilayer.Moreover,we demonstrate that stacked layers can tune the moiréexcitons by manipulating temperature,laser power,and magnetic field.Our results provide a new physical model for studying moirésuperlattices and their quantum properties,which could potentially pave the way for the development of quantum optoelectronics.
基金The authors would like to acknowledge the National Natural Science Foundation of China(Nos.61775241,62090035,and U19A2090)the Hunan Province Key Research and Development Project(No.2019GK2233)+8 种基金the Hunan Provincial Science Fund for Distinguished Young Scholars(No.2020JJ2059)the Youth Innovation Team of CSU(No.2019012)the Key Program of Science and Technology Department of Hunan Province(Nos.2019XK2001 and 2020XK2001)the Science and Technology Innovation Basic Research Project of Shenzhen(No.JCYJ20190806144418859)the Postdoctoral Science Foundation of China(No.2022M713546)The authors would also like to express their gratitude to the High-Performance Complex Manufacturing Key State Lab Project,Central South University(No.ZZYJKT2020-12)the Australian Research Council(ARC)Discovery Project(No.DP180102976)for their support of Z.W.L.C.T.W.acknowledges support from the National Natural Science Foundation of China(No.11974387)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB33000000)H.H.Z.is grateful for the support from the Postdoctoral Science Foundation of China(No.2022M713546).
文摘Exploiting the valley degrees of freedom as information carriers provides new opportunities for the development of valleytronics.Monolayer transition metal dichalcogenides(TMDs)with broken space-inversion symmetry exhibit emerging valley pseudospins,making them ideal platforms for studying valley electronics.However,intervalley scattering of different energy valleys limits the achievable degree of valley polarization.Here,we constructed WSe_(2)/yttrium iron garnet(YIG)heterostructures and demonstrated that the interfacial magnetic exchange effect on the YIG magnetic substrate can enhance valley polarization by up to 63%,significantly higher than that of a monolayer WSe_(2)on SiO_(2)/Si(11%).Additionally,multiple sharp exciton peaks appear in the WSe_(2)/YIG heterostructures due to the strong magnetic proximity effect at the magnetic-substrate interface that enhances exciton emission efficiency.Moreover,under the effect of external magnetic field,the magnetic direction of the magnetic substrate enhances valley polarization,further demonstrating that the magnetic proximity effect regulates valley polarization.Our results provide a new way to regulate valley polarization and demonstrate the promising application of magnetic heterojunctions in magneto-optoelectronics.