A reflective beam splitter is proposed and verified. The unit cell of the beam splitter is composed of a metal pattern, a dielectric substrate, and a metallic ground. Each subarray structure of the device is composed ...A reflective beam splitter is proposed and verified. The unit cell of the beam splitter is composed of a metal pattern, a dielectric substrate, and a metallic ground. Each subarray structure of the device is composed of four unit cells, which are gradually rotated at 45°. The horizontal and vertical subarrays form a 4×4 gradient metasurface supercell. In the operating frequency band, the incident linearly polarized terahertz wave is reflected and divided into four beams of approximately equal power but different propagation directions. The proposed terahertz beam splitter based on metasurface has the advantages of small size, low cost and easy processing, and can be applied to terahertz stealth and imaging.展开更多
The terahertz(THz)vortex beam generators are designed and theoretically investigated based on single-layer ultra-thin transmission metasurfaces.Noncontinuous phase changes of metasurfaces are obtained by utilizing Pan...The terahertz(THz)vortex beam generators are designed and theoretically investigated based on single-layer ultra-thin transmission metasurfaces.Noncontinuous phase changes of metasurfaces are obtained by utilizing Pancharatnam-Berry phase elements,which possess different rotation angles and are arranged on two concentric rings centered on the origin.The circularly polarized incident THz beam could be turned into a cross-polarization transmission wave,and the orbital angular momentum(OAM)varies in value by lh.The l values change from±1 to±5,and the maximal cross-polarization conversion efficiency that could be achieved is 23%,which nearly reaches the theoretical limit of a single-layer structure.The frequency range of the designed vortex generator is from 1.2 THz to 1.9 THz,and the generated THz vortex beam could keep a high fidelity in the operating bandwidth.The propagation behavior of the emerged THz vortex beam is analyzed in detail.Our work offers a novel way of designing ultra-thin and single-layer vortex beam generators,which have low process complexity,high conversion efficiency and broad bandwidth.展开更多
Last decade has witnessed a rapid development of the generation of terahertz(THz)vortex beams as well as their wide applications,mainly due to their unique combination characteristics of regular THz radiation and orbi...Last decade has witnessed a rapid development of the generation of terahertz(THz)vortex beams as well as their wide applications,mainly due to their unique combination characteristics of regular THz radiation and orbital angular momentum(OAM).Here we have reviewed the ways to generate THz vortex beams by two representative scenarios,i.e.,THz wavefront modulation via specific devices,and direct excitation of the helicity of THz vortex beams.The former is similar to those wavefront engineering devices in the optical and infrared(IR)domain,but just with suitable THz materials,while the latter is newly-developed in THz regime and some of the physical mechanisms still have not been explained explicitly enough though,which would provide both challenges and opportunities for THz vortex beam generation.As for their applications,thanks to the recent development of THz optics and singular optics,THz vortex beams have potentials to open doors towards a myriad of practice applications in many fields.Besides,some representative potential applications are evaluated such as THz wireless communication,THz super-resolution imaging,manipulating chiral matters,accelerating electron bunches,and detecting astrophysical sources.展开更多
The transmission of terahertz(THz)Bessel vortex beams through a multi-layered anisotropic magnetized plasma slab is investigated by using a hybrid method of cylindrical vector wave functions(CVWFs)and Fourier transfor...The transmission of terahertz(THz)Bessel vortex beams through a multi-layered anisotropic magnetized plasma slab is investigated by using a hybrid method of cylindrical vector wave functions(CVWFs)and Fourier transform.On the basis of the electromagnetic boundary conditions on each interface,a cascade form of expansion coefficients of the reflected and transmitted fields is obtained.Taking a double Gaussian distribution of the plasma density as an example,the influences of the applied magnetic field,the incident angle and polarization mode of the incident beams on the magnitude,OAM mode and polarization of the transmitted beams are analyzed in detail.The results indicate that the applied magnetic field has a major effect upon the polarization state of the transmitted fields but not upon the transmitted OAM spectrum.The incident angle has a powerful influence upon both the amplitude profile and the OAM spectrum of the transmitted beam.Furthermore,for multiple coaxial vortex beams,an increase of the maximum value of the plasma density causes more remarkable distortion of both the profile and OAM spectrum of the transmitted beam.This research makes a stable foundation for the THz OAM multiplexing/demultiplexing technology in a magnetized plasma environment.展开更多
This study has proposed and numerically demonstrated a compact terahertz wave polarization beam splitter. The splitter is built by using a asymmetrical directional coupler consisting of a bend waveguide and a slot ben...This study has proposed and numerically demonstrated a compact terahertz wave polarization beam splitter. The splitter is built by using a asymmetrical directional coupler consisting of a bend waveguide and a slot bend waveguides and achieves a high extinction ratio of 24.88 dB and 16.55 dB for cross and through ports. The optimal coupling region length is found to be 26 ttm. By using such a polarization beam splitter, the size of the terahertz wave system could he reduced significantly. The simulation results show that the designed polarization beam splitter can split TE- and TM-polarized terahertz wave into different propagation directions with high efficiency over the terahertz wave frequency range from 9.40 THz to 9.65 THz. The device obtained is readily used for a polarization diversity terahertz wave integrated circuit field, particularly for platforms with slot waveguide.展开更多
In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric gr...In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.展开更多
It is theoretically investigated the generation of higher harmonics of two-dimensional and three-dimensional terahertz electromagnetic beams in nonlinear crystals. The attention is paid to crystalline paraelectrics li...It is theoretically investigated the generation of higher harmonics of two-dimensional and three-dimensional terahertz electromagnetic beams in nonlinear crystals. The attention is paid to crystalline paraelectrics like SrTiO<sub>3</sub> under the temperatures 60 - 200 K, these crystals possess the cubic nonlinearity. The bias electric field is applied to provide the dominating quadratic nonlinearity. The initial focusing of the beams not only increases the efficiency of generation of higher harmonics, but alto makes possible to select maxima of different higher harmonics at some distances from the input. At lower temperatures the nonlinearity behaves at smaller input amplitudes, whereas at higher temperatures the harmonic generation can be observed at higher frequencies up to 1.5 THz. In three-dimensional beams the peak amplitudes of higher harmonics can be bigger than in two-dimensional beams, but the ratios of these peak values to the maximum values of the focused first harmonic are smaller than in two-dimensional beams.展开更多
To accommodate the ever-increasing wireless capacity,the terahertz(THz)orbital angular momentum(OAM)beam that combines THz radiation and OAM technologies has attracted much attention recently,with contributing efforts...To accommodate the ever-increasing wireless capacity,the terahertz(THz)orbital angular momentum(OAM)beam that combines THz radiation and OAM technologies has attracted much attention recently,with contributing efforts to explore new dimensions in the THz region.In this paper,we provide an overview of the generation and detection techniques of THz-OAM beams,as well as their applications in communications.The principle and research status of typical generation and detection methods are surveyed,and the advantages and disadvantages of each method are summarized from a viewpoint of wireless communication.It is shown that developing novel THz components in generating,detecting and(de)multiplexing THz-OAM beams has become the key engine to drive this direction forward.Anyway,beneficial from the combination of infinite orthogonal modes and large bandwidth,THz-OAM beams will have great potential in delivering very large capacity in next generation wireless communications.展开更多
基金supported by the New Direction Cultivation Project of Chongqing University of Posts and Telecommunications (No.A2014-116)the Key Research Program of Chongqing University of Posts and Telecommunications on Interdisciplinary and Emerging Field (No.A2018-01)。
文摘A reflective beam splitter is proposed and verified. The unit cell of the beam splitter is composed of a metal pattern, a dielectric substrate, and a metallic ground. Each subarray structure of the device is composed of four unit cells, which are gradually rotated at 45°. The horizontal and vertical subarrays form a 4×4 gradient metasurface supercell. In the operating frequency band, the incident linearly polarized terahertz wave is reflected and divided into four beams of approximately equal power but different propagation directions. The proposed terahertz beam splitter based on metasurface has the advantages of small size, low cost and easy processing, and can be applied to terahertz stealth and imaging.
基金the National Natural Science Foundation of China(Grant No.62071312)the Important R&D Projects of Shanxi Province,China(Grant No.201803D121083)the Shanxi Scholarship Council(Grant No.2020-135).
文摘The terahertz(THz)vortex beam generators are designed and theoretically investigated based on single-layer ultra-thin transmission metasurfaces.Noncontinuous phase changes of metasurfaces are obtained by utilizing Pancharatnam-Berry phase elements,which possess different rotation angles and are arranged on two concentric rings centered on the origin.The circularly polarized incident THz beam could be turned into a cross-polarization transmission wave,and the orbital angular momentum(OAM)varies in value by lh.The l values change from±1 to±5,and the maximal cross-polarization conversion efficiency that could be achieved is 23%,which nearly reaches the theoretical limit of a single-layer structure.The frequency range of the designed vortex generator is from 1.2 THz to 1.9 THz,and the generated THz vortex beam could keep a high fidelity in the operating bandwidth.The propagation behavior of the emerged THz vortex beam is analyzed in detail.Our work offers a novel way of designing ultra-thin and single-layer vortex beam generators,which have low process complexity,high conversion efficiency and broad bandwidth.
基金Project supported partly by the National Natural Science Foundation of China(Grant Nos.61775142 and 61705132)Shenzhen Fundamental Research and Discipline Layout Project,China(Grant Nos.JCYJ20170412105812811,JCYJ20190808164007485,JCYJ20190808121817100,and JCYJ20190808115601653).
文摘Last decade has witnessed a rapid development of the generation of terahertz(THz)vortex beams as well as their wide applications,mainly due to their unique combination characteristics of regular THz radiation and orbital angular momentum(OAM).Here we have reviewed the ways to generate THz vortex beams by two representative scenarios,i.e.,THz wavefront modulation via specific devices,and direct excitation of the helicity of THz vortex beams.The former is similar to those wavefront engineering devices in the optical and infrared(IR)domain,but just with suitable THz materials,while the latter is newly-developed in THz regime and some of the physical mechanisms still have not been explained explicitly enough though,which would provide both challenges and opportunities for THz vortex beam generation.As for their applications,thanks to the recent development of THz optics and singular optics,THz vortex beams have potentials to open doors towards a myriad of practice applications in many fields.Besides,some representative potential applications are evaluated such as THz wireless communication,THz super-resolution imaging,manipulating chiral matters,accelerating electron bunches,and detecting astrophysical sources.
基金supported by National Natural Science Foundation of China(Nos.62171355,61801349,and 61875156)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2020JM-192)+1 种基金the Stable Support Project of Basic Scientific Research Institutes(Nos.A131901W14,A132001W12)the Science and Technology Foundation of State Key Laboratory of Electromagnetic Environment,and the 111 Project(No.B17035)。
文摘The transmission of terahertz(THz)Bessel vortex beams through a multi-layered anisotropic magnetized plasma slab is investigated by using a hybrid method of cylindrical vector wave functions(CVWFs)and Fourier transform.On the basis of the electromagnetic boundary conditions on each interface,a cascade form of expansion coefficients of the reflected and transmitted fields is obtained.Taking a double Gaussian distribution of the plasma density as an example,the influences of the applied magnetic field,the incident angle and polarization mode of the incident beams on the magnitude,OAM mode and polarization of the transmitted beams are analyzed in detail.The results indicate that the applied magnetic field has a major effect upon the polarization state of the transmitted fields but not upon the transmitted OAM spectrum.The incident angle has a powerful influence upon both the amplitude profile and the OAM spectrum of the transmitted beam.Furthermore,for multiple coaxial vortex beams,an increase of the maximum value of the plasma density causes more remarkable distortion of both the profile and OAM spectrum of the transmitted beam.This research makes a stable foundation for the THz OAM multiplexing/demultiplexing technology in a magnetized plasma environment.
基金supported by the Zhejiang Province Natural Science Foundation for Distinguished Young Scientists under Grant No.LR12F05001the National Natural Science Foundation of China under Grant No.61379024 and 61131005
文摘This study has proposed and numerically demonstrated a compact terahertz wave polarization beam splitter. The splitter is built by using a asymmetrical directional coupler consisting of a bend waveguide and a slot bend waveguides and achieves a high extinction ratio of 24.88 dB and 16.55 dB for cross and through ports. The optimal coupling region length is found to be 26 ttm. By using such a polarization beam splitter, the size of the terahertz wave system could he reduced significantly. The simulation results show that the designed polarization beam splitter can split TE- and TM-polarized terahertz wave into different propagation directions with high efficiency over the terahertz wave frequency range from 9.40 THz to 9.65 THz. The device obtained is readily used for a polarization diversity terahertz wave integrated circuit field, particularly for platforms with slot waveguide.
基金Project supported by the National Basic Research Program of China(Grant No.2014CB339801)the National Natural Science Foundation of China(Grant Nos.61231005,11305030,and 612111076)+1 种基金the Fundamental Research Funds for the Central Universities of China(Grant No.ZYGX2013J058)the National High-tech Research and Development Project of China(Grant No.2011AA010204)
文摘In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.
文摘It is theoretically investigated the generation of higher harmonics of two-dimensional and three-dimensional terahertz electromagnetic beams in nonlinear crystals. The attention is paid to crystalline paraelectrics like SrTiO<sub>3</sub> under the temperatures 60 - 200 K, these crystals possess the cubic nonlinearity. The bias electric field is applied to provide the dominating quadratic nonlinearity. The initial focusing of the beams not only increases the efficiency of generation of higher harmonics, but alto makes possible to select maxima of different higher harmonics at some distances from the input. At lower temperatures the nonlinearity behaves at smaller input amplitudes, whereas at higher temperatures the harmonic generation can be observed at higher frequencies up to 1.5 THz. In three-dimensional beams the peak amplitudes of higher harmonics can be bigger than in two-dimensional beams, but the ratios of these peak values to the maximum values of the focused first harmonic are smaller than in two-dimensional beams.
基金the National Key Research and Development Program of China(2020YFB18057002018YFB1801500&2018YFB2201700)the Natural National Science Foundation of China under Grant 61771424the Natural Science Foundation of Zhejiang Province under Grant LZ18F010001 and Zhejiang Lab(no.2020LC0AD01).
文摘To accommodate the ever-increasing wireless capacity,the terahertz(THz)orbital angular momentum(OAM)beam that combines THz radiation and OAM technologies has attracted much attention recently,with contributing efforts to explore new dimensions in the THz region.In this paper,we provide an overview of the generation and detection techniques of THz-OAM beams,as well as their applications in communications.The principle and research status of typical generation and detection methods are surveyed,and the advantages and disadvantages of each method are summarized from a viewpoint of wireless communication.It is shown that developing novel THz components in generating,detecting and(de)multiplexing THz-OAM beams has become the key engine to drive this direction forward.Anyway,beneficial from the combination of infinite orthogonal modes and large bandwidth,THz-OAM beams will have great potential in delivering very large capacity in next generation wireless communications.