Metasurfaces,especially tunable ones,have played a major role in controlling the amplitude,phase,and polari-zation of electromagnetic waves and attracted growing interest,with a view toward a new generation of minia-turized devices.However,to date,most existing reconfigurable devices are bounded in volatile nature with sustained external energy to maintain and single functionality,which restrict their further applications.Here,we demonstrate for the first time,to our knowledge,nonvolatile,reconfigurable,and dynamic Janus metasurfaces by incorporating phase-change material Ge2Se2Te5(GST)in the terahertz(THz)regime.First,we experimentally show the reversible switching characteristic of GST on large areas by applying a single nanosecond laser pulse,which exhibits excellent contrast of THz properties in both states.Then,we present a multiplex metasurface scheme.In each metasurface,three sets of structures are adopted,in which two sets integrate GST.The effective structures can be reversely modulated by the amorphization and crystallization of GST.As a proof of concept,the dynamic beam splitter,bifocal metalens,dual-mode focusing optical vortex generators,and switchable metalens/focusing optical vortex generators are designed,fabricated,and experimentally characterized,and can be switched reversibly and repeatedly with the help of optical and thermal stimuli.Our scheme will pave the way toward the development of multifunctional and compact THz devices and may find use for applications in THz imaging,sensing,and communications.

SHOUJUN ZHANG;XIEYU CHEN;KUAN LIU;HAIYANG LI;YUEHONG XU;XIAOHAN JIANG;YIHAN XU;QINGWEI WANG;TUN CAO;ZHEN TIAN

Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering,Key Laboratory of Optoelectronic Information Technology(Ministry of Education of China),Tianjin University,Tianjin 300072,China;School of Optoelectronic Engineering and Instrumentation Science,Dalian University of Technology,Dalian 116024,China;Georgia Tech Shenzhen Institute(GTSI),Tianjin University,Shenzhen 518067,China

光子学研究（英文）

[1]SHOUJUN ZHANG;XIEYU CHEN;KUAN LIU;HAIYANG LI;YUEHONG XU;XIAOHAN JIANG;YIHAN XU;QINGWEI WANG;TUN CAO;ZHEN TIAN-.Nonvolatile reconfigurable dynamic Janus metasurfaces in the terahertz regime)[J].光子学研究（英文）,2022(07):1731-1743

turized,Ge2Se2Te5,bifocal

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