Antichiral gyromagnetic photonic crystal(GPC)in a honeycomb lattice with the two interpenetrating triangular sublattices A and B magnetically biased in opposite directions can realize antichiral one-way edge states pr...Antichiral gyromagnetic photonic crystal(GPC)in a honeycomb lattice with the two interpenetrating triangular sublattices A and B magnetically biased in opposite directions can realize antichiral one-way edge states propagating along the same direction at its two parallel edges.Here,we report the construction and observation of topological beam splitting with the easily adjustable right-to-left ratio in an antichiral GPC.The splitter is compact and configurable,has high trans-mission efficiency,and allows for multi-channel utilization,crosstalk-proof,and robust against defects and obstacles.This magnificent performance is attributed to the peculiar property that antichiral one-way edge states exist only at zigzag edge but not at armchair edge of antichiral GPC.When we combine two rectangular antichiral GPCs holding left-and right-propagating antichiral one-way edge states respectively,bidirectionally radiating one-way edge states at two paral-lel zigzag edges can be achieved.Our observations can enrich the understanding of fundamental physics and expand to-pological photonic applications.展开更多
Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size, which facilitates circumvention of ...Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size, which facilitates circumvention of a directional band gap. Experiments reveal that two distinct beams emerge at crystal output, in agreement with the numerical results obtained through the finite-element method. Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space. Split beams propagate in equal amplitude, whereas beam splitting is destructed for oblique incidence above a critical incidence angle.展开更多
Beam splitting is one of the main approaches to achieving x-ray ghost imaging, and the intensity correlation between diffraction beam and transmission beam will directly affect the imaging quality. In this paper, we i...Beam splitting is one of the main approaches to achieving x-ray ghost imaging, and the intensity correlation between diffraction beam and transmission beam will directly affect the imaging quality. In this paper, we investigate the intensity correlation between the split x-ray beams by Laue diffraction of stress-free crystal. The analysis based on the dynamical theory of x-ray diffraction indicates that the spatial resolution of diffraction image and transmission image are reduced due to the position shift of the exit beam. In the experimental setup, a stress-free crystal with a thickness of hundredmicrometers-level is used for beam splitting. The crystal is in a non-dispersive configuration equipped with a double-crystal monochromator to ensure that the dimension of the diffraction beam and transmission beam are consistent. A correlation coefficient of 0.92 is achieved experimentally and the high signal-to-noise ratio of the x-ray ghost imaging is anticipated.Results of this paper demonstrate that the developed beam splitter of Laue crystal has the potential in the efficient data acquisition of x-ray ghost imaging.展开更多
Multiphoton entanglement with high information capacity plays an essential role in quantum information processing.The appearance of parallel beam splitting(BS)in a gradient metasurface provides the chance to prepare t...Multiphoton entanglement with high information capacity plays an essential role in quantum information processing.The appearance of parallel beam splitting(BS)in a gradient metasurface provides the chance to prepare the multiphoton entanglement in one step.Here,we use a single metasurface to construct multiphoton path-polarization entanglement.Based on the parallel BS property,entanglement among N unentangled photons is created after they pass through a gradient metasurface.Also,with this ability,entanglement fusion among several pairs of entangled photons is set up,which can greatly enlarge the entanglement dimension.These theoretical results pave the way for manipulating metasurface-based multiphoton entanglement,which holds great promise for ultracompact on-chip quantum information processing.展开更多
Terahertz(THz)communication is considered to be a promising technology for future 6G network.To overcome the severe attenuation and relieve the high power consumption,massive multipleinput multiple-output(MIMO)with hy...Terahertz(THz)communication is considered to be a promising technology for future 6G network.To overcome the severe attenuation and relieve the high power consumption,massive multipleinput multiple-output(MIMO)with hybrid precoding has been widely considered for THz communication.However,accurate wideband channel estimation,which is essential for hybrid precoding,is challenging in THz massive MIMO systems.The existing wideband channel estimation schemes based on the ideal assumption of common sparse channel support will suffer from a severe performance loss due to the beam split effect.In this paper,we propose a beam split pattern detection based channel estimation scheme to realize reliable wideband channel estimation in THz massive MIMO systems.Specifically,a comprehensive analysis on the angle-domain sparse structure of the wideband channel is provided by considering the beam split effect.Based on the analysis,we define a series of index sets called as beam split patterns,which are proved to have a one-to-one match to different physical channel directions.Inspired by this one-to-one match,we propose to estimate the physical channel direction by exploiting beam split patterns at first.Then,the sparse channel supports at different subcarriers can be obtained by utilizing a support detection window.This support detection window is generated by expanding the beam split pattern which is determined by the obtained physical channel direction.The above estimation procedure will be repeated path by path until all path components are estimated.Finally,the wideband channel can be recovered by calculating the elements on the total sparse channel support at all subcarriers.The proposed scheme exploits the wideband channel property implied by the beam split effect,i.e.,beam split pattern,which can significantly improve the channel estimation accuracy.Simulation results show that the proposed scheme is able to achieve higher accuracy than existing schemes.展开更多
A novel hybrid solar concentrating Photovoltaic/Thermal (CPV/T) system with beam splitting technique is presented. In this system, a beam splitter is used to separate the concentrated solar radiation into two parts: o...A novel hybrid solar concentrating Photovoltaic/Thermal (CPV/T) system with beam splitting technique is presented. In this system, a beam splitter is used to separate the concentrated solar radiation into two parts: one for the PV power generation and the other for thermal utility. The solar concentrator is a flat Fresnel-type concentrator with glass mirror reflectors. It can concentrate solar radiation onto solar cells with high uniformity, which is beneficial to improving the efficiency of solar cells. The thermal receiver is separated to the solar cells, and therefore, the thermal fluid can be heated to a relatively high temperature and does not affect the performance of solar cells. A dimensionless model was developed for the performance analysis of the concentrating system. The effects of the main parameters on the performance of the concentrator were analyzed. The beam splitter with coating materials Nb2O3 /SiO2 was designed by using the needle optimization technique, which can reflect about 71% of the undesired radiation for silicon cell(1.1m < 3m) to the thermal receiver for thermal utility. The performance of this CPV/T system was also theoretically analyzed.展开更多
Monochromatization of high-harmonic sources has opened fascinating perspectives regarding time-resolved photoemission from all phases of matter.Such studies have invariably involved the use of spectral filters or spec...Monochromatization of high-harmonic sources has opened fascinating perspectives regarding time-resolved photoemission from all phases of matter.Such studies have invariably involved the use of spectral filters or spectrally dispersive optical components that are inherently lossy and technically complex.Here we present a new technique for the spectral selection of near-threshold harmonics and their spatial separation from the driving beams without any optical elements.We discover the existence of a narrow phase-matching gate resulting from the combination of the non-collinear generation geometry in an extended medium,atomic resonances and absorption.Our technique offers a filter contrast of up to 104 for the selected harmonics against the adjacent ones and offers multiple temporally synchronized beamlets in a single unified scheme.We demonstrate the selective generation of 133,80 or 56 nm femtosecond pulses from a 400-nm driver,which is specific to the target gas.These results open new pathways towards phase-sensitive multi-pulse spectroscopy in the vacuum-and extreme-ultraviolet,and frequencyselective output coupling from enhancement cavities.展开更多
We propose a novel on-line beam diagnostic method based on single-shot beam splitting phase retrieval. The incident beam to be measured is diffracted into many replicas by a Dammann grating and then propagates through...We propose a novel on-line beam diagnostic method based on single-shot beam splitting phase retrieval. The incident beam to be measured is diffracted into many replicas by a Dammann grating and then propagates through a weakly scattering phase plate with a known structure; the exiting beams propagate along their original direction and form an array of diffraction patterns on the detector plane. By applying the intensity of diffraction patterns into an iterative algorithm and calculating between the grating plane, weakly scattering plane, and detector plane, the complex field of the incident beam can be reconstructed rapidly; the feasibility of this method is verified experimentally with wavelengths of 1053 and 632.8 nm.展开更多
Electrically connected optical metasurfaces with high efficiencies are crucial for developing spatiotemporal metadevices with ultrahigh spatial and ultrafast temporal resolutions.While efficient metal–insulator–meta...Electrically connected optical metasurfaces with high efficiencies are crucial for developing spatiotemporal metadevices with ultrahigh spatial and ultrafast temporal resolutions.While efficient metal–insulator–metal(MIM)metasurfaces containing discretized meta-atoms require additional electrodes,Babinet-inspired slot-antenna-based plasmonic metasurfaces suffer from low efficiencies and limited phase coverage for copolarized optical fields.Capitalizing on the concepts of conventional MIM and slot-antenna metasurfaces,we design and experimentally demonstrate a new type of optical reflective metasurfaces consisting of mirrorcoupled slot antennas(MCSAs).By tuning the dimensions of rectangular-shaped nanoapertures atop a dielectric-coated gold mirror,we achieve efficient phase modulation within a sufficiently large range of 320 deg and realize functional phase-gradient metadevices for beam steering and beam splitting in the near-infrared range.The fabricated samples show(22%2%)diffraction efficiency for beam steering and(17%1%)for beam splitting at the wavelength of 790 nm.The considered MCSA configuration,dispensing with auxiliary electrodes,offers an alternative and promising platform for electrically controlled reflective spatiotemporal metasurfaces.展开更多
With the development of millimeter-wave(mmWave)communication systems,large-scale reconfigurable intelligent surfaces(RISs)have gained considerable attention as a promising technology for signal strength enhancement an...With the development of millimeter-wave(mmWave)communication systems,large-scale reconfigurable intelligent surfaces(RISs)have gained considerable attention as a promising technology for signal strength enhancement and coverage extension.However,as the antenna scale and bandwidth increase,RIS-assisted wideband orthogonal frequency division multiplexing(OFDM)communication systems face challenges due to the near-field range expansion and the beam split effect over the high-frequency band,complicating the acquisition of channel state information(CSI).To tackle these challenges,we present a codebook-based three-stage beam training scheme by using the beam split effect to bypass CSI estimation.Specifically,by analyzing the beam split effect in RIS-assisted OFDM communication systems,we propose a beam-split-aware codebook capable of covering both the near and far fields with fewer codewords compared to conventional narrow-band codebooks.Using such a codebook,a three-stage beam training mechanism is adopted to obtain the optimal codeword with low time overhead,thereby facilitating subsequent beamforming.Simulation results demonstrate that the proposed scheme outperforms existing near-and far-field codebook-based schemes in terms of the beam training resolution and sum rate in the hybrid near–far field.展开更多
A simultaneously transmitting and reflecting reconfigurable intelligent surface(STAR-RIS)assisted multiuser near-field wideband communication system is investigated,in which a robust deep reinforcement learning(DRL)ba...A simultaneously transmitting and reflecting reconfigurable intelligent surface(STAR-RIS)assisted multiuser near-field wideband communication system is investigated,in which a robust deep reinforcement learning(DRL)based algorithm is proposed to enhance the users’achievable rate by jointly optimizing the active beamforming at the base station(BS)and passive beamforming at the STAR-RIS.To mitigate the beam split issue,the delay-phase hybrid precoding structure is introduced to facilitate wideband beamforming.Considering the coupled nature of the STARRIS phase-shift model,the passive beamforming design is formulated as a problem of hybrid continuous and discrete phase-shift control,and the proposed algorithm controls the high-dimensional continuous action through hybrid action mapping.Additionally,to address the issue of biased estimation encountered by existing DRL algorithms,a softmax operator is introduced into the algorithm to mitigate this bias.Simulation results illustrate that the proposed algorithm outperforms existing algorithms and overcomes the issues of overestimation and underestimation.展开更多
In modern science and technology,on-demand control of the polarization and wavefront of electromagnetic(EM)waves is crucial for compact opto-electronic systems.Metasurfaces composed of subwavelength array structures i...In modern science and technology,on-demand control of the polarization and wavefront of electromagnetic(EM)waves is crucial for compact opto-electronic systems.Metasurfaces composed of subwavelength array structures inject infinite vitality to shape this fantastic concept,which has fundamentally changed the way humans engineer matter–wave interactions.However,achieving full-space arbitrarily polarized beams with independent wavefronts in broadband on a single metasurface aperture still remains challenging.Herein,the authors propose a generic method for broadband transmission-reflection-integrated wavefronts shaping with multichannel arbitrary polarization regulation from 8 to 16 GHz,which is based on the chirality effect of full-space non-interleaved tetrameric meta-molecules.Through superimposing eigen-polarization responses of the two kinds of enantiomers,the possibility for high-efficiency evolution of several typical polarization states with specific wavefronts is demonstrated.As proofs-of-concept,the feasibility of our methodology is validated via implementing miscellaneous functionalities,including circularly polarized(CP)beam splitting,linearly polarized(LP)vortex beams generation,and CP and LP multifoci.Meanwhile,numerous simulated and experimental results are in excellent agreement with the theoretical predictions.Encouragingly,this proposed approach imaginatively merges broadband polarization and phase control into one single full-space and shared-aperture EM device,which can extremely enhance the functional richness and information capacity in advanced integrated systems.展开更多
Programmable metasurface enables controlling electromagnetic (EM) waves in real time. By programming the states of active device embedded in metasurface element, the EM properties of the digital metasurface can be cha...Programmable metasurface enables controlling electromagnetic (EM) waves in real time. By programming the states of active device embedded in metasurface element, the EM properties of the digital metasurface can be changed quickly without redesigning their structures. However, large numbers of long-distance wires are required to connect the programmable metasurface to provide the coded signals from field programmable gate array (FPGA) when controlling the metasurface at a long distance, which is complicated and inconvenient. Here, we propose an infrared-controlled programmable metasurface that can be programmed remotely. The infrared transceiver is able to switch the coding sequences stored in the FPGA controller, thus controlling the voltage on the varactors integrated in the metasurface. Experiment is performed at microwave frequencies, and the measured results verify that the scattering beams of the metasurface sample can be changed remotely by using infrared ray. The proposed infrared-controlled programmable metasurface opens up avenues for constructing a new class of remotely-tuning dynamic metasurfaces.展开更多
Phase carried by two orthogonal polarizations can be manipulated independently by controlling both the geometric size and orientation of the dielectric nanopost.With this characteristic,we demonstrate a novel multifun...Phase carried by two orthogonal polarizations can be manipulated independently by controlling both the geometric size and orientation of the dielectric nanopost.With this characteristic,we demonstrate a novel multifunctional metasurface,which converts part of the incident linearly polarized light into its cross-polarization and encodes the phase of the two orthogonal polarizations independently.A beam splitter and a bifocal metalens were realized in a single-layer dielectric metasurface by this approach.We fabricated the bifocal metalens and demonstrated that two focal spots in orthogonal polarizations can be separated transversely or longitudinally at will.The proposed approach shows a new route to design multifunctional metasurfaces with various applications in holography and three-dimensional display.展开更多
Thermodynamics analysis was carried out for solar thermal receivers with different selective coatings.The relation between the energy conversion efficiency of a medium-high temperature solar thermal system,the spectra...Thermodynamics analysis was carried out for solar thermal receivers with different selective coatings.The relation between the energy conversion efficiency of a medium-high temperature solar thermal system,the spectral properties of selective coating and the operating temperature of the receiver were discussed.Furthermore,the relation between the optimum operating temperatures,the exergy efficiencies and the incident solar flux were analyzed for the traditional concentrating system and concentrating beam splitting system,respectively.According to the analysis results for the thermal receiver with blackbody surface and selective coatings,the optimum cutoff wavelength was obtained for the ideal selective coating.An analysis method for the optimum operating temperature calculation was developed for thermal receivers with selective coating.The optimum operating temperature for an actual selective coating was analyzed on the basis of the proposed theory.展开更多
This paper proposes a power system concept that integrates photovoltaic （PV） and thermoelectric （TE） technologies to harvest solar energy from a wide spectral range. By introduction of the ＇spectrum beam splittin...This paper proposes a power system concept that integrates photovoltaic （PV） and thermoelectric （TE） technologies to harvest solar energy from a wide spectral range. By introduction of the ＇spectrum beam splitting＇ technique, short wavelength solar radiation is converted directly into electricity in the PV cells, while the long wavelength segment of the spectrum is used to produce moderate to high temperature thermal energy, which then generates electricity in the TE device. To overcome the intermittent nature of solar radiation, the system is also coupled to a thermal energy storage unit. A systematic analysis of the integrated system is carried out, encompassing the system configuration, material properties, thermal management, and energy storage aspects. We have also attempted to optimize the integrated system. The results indicate that the system configuration and optimization are the most important factors for high overall efficiency.展开更多
基金the National Natural Science Foundation of China(11974119)Science and Technology Project of Guangdong(2020B010190001)+1 种基金Guangdong Innovative and Entrepreneurial Research Team Program(2016ZT06C594)National Key R&D Program of China(2018YFA 0306200).
文摘Antichiral gyromagnetic photonic crystal(GPC)in a honeycomb lattice with the two interpenetrating triangular sublattices A and B magnetically biased in opposite directions can realize antichiral one-way edge states propagating along the same direction at its two parallel edges.Here,we report the construction and observation of topological beam splitting with the easily adjustable right-to-left ratio in an antichiral GPC.The splitter is compact and configurable,has high trans-mission efficiency,and allows for multi-channel utilization,crosstalk-proof,and robust against defects and obstacles.This magnificent performance is attributed to the peculiar property that antichiral one-way edge states exist only at zigzag edge but not at armchair edge of antichiral GPC.When we combine two rectangular antichiral GPCs holding left-and right-propagating antichiral one-way edge states respectively,bidirectionally radiating one-way edge states at two paral-lel zigzag edges can be achieved.Our observations can enrich the understanding of fundamental physics and expand to-pological photonic applications.
基金Project supported by Akdeniz University Scientific Research Projects Coordination Unit
文摘Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size, which facilitates circumvention of a directional band gap. Experiments reveal that two distinct beams emerge at crystal output, in agreement with the numerical results obtained through the finite-element method. Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space. Split beams propagate in equal amplitude, whereas beam splitting is destructed for oblique incidence above a critical incidence angle.
基金Project supported by the National Key Research and Development Program of China (Grant Nos.2022YFF0709103,2022YFA1603601,2021YFF0601203,and 2021YFA1600703)the National Natural Science Foundation of China (Grant No.81430087)the Shanghai Pilot Program for Basic Research-Chinese Academy of Sciences,Shanghai Branch (Grant No.JCYJ-SHFY-2021-010)。
文摘Beam splitting is one of the main approaches to achieving x-ray ghost imaging, and the intensity correlation between diffraction beam and transmission beam will directly affect the imaging quality. In this paper, we investigate the intensity correlation between the split x-ray beams by Laue diffraction of stress-free crystal. The analysis based on the dynamical theory of x-ray diffraction indicates that the spatial resolution of diffraction image and transmission image are reduced due to the position shift of the exit beam. In the experimental setup, a stress-free crystal with a thickness of hundredmicrometers-level is used for beam splitting. The crystal is in a non-dispersive configuration equipped with a double-crystal monochromator to ensure that the dimension of the diffraction beam and transmission beam are consistent. A correlation coefficient of 0.92 is achieved experimentally and the high signal-to-noise ratio of the x-ray ghost imaging is anticipated.Results of this paper demonstrate that the developed beam splitter of Laue crystal has the potential in the efficient data acquisition of x-ray ghost imaging.
基金supported by the National Natural Science Foundation of China(Grant Nos.12474370,11974032,12161141010,and T2325022)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0301500).
文摘Multiphoton entanglement with high information capacity plays an essential role in quantum information processing.The appearance of parallel beam splitting(BS)in a gradient metasurface provides the chance to prepare the multiphoton entanglement in one step.Here,we use a single metasurface to construct multiphoton path-polarization entanglement.Based on the parallel BS property,entanglement among N unentangled photons is created after they pass through a gradient metasurface.Also,with this ability,entanglement fusion among several pairs of entangled photons is set up,which can greatly enlarge the entanglement dimension.These theoretical results pave the way for manipulating metasurface-based multiphoton entanglement,which holds great promise for ultracompact on-chip quantum information processing.
基金supported in part by the National Key Research and Development Program of China(Grant No.2020YFB1805005)the National Natural Science Foundation of China(Grant No.62031019)the European Commission through the H2020-MSCA-ITN META WIRELESS Research Project under Grant 956256.
文摘Terahertz(THz)communication is considered to be a promising technology for future 6G network.To overcome the severe attenuation and relieve the high power consumption,massive multipleinput multiple-output(MIMO)with hybrid precoding has been widely considered for THz communication.However,accurate wideband channel estimation,which is essential for hybrid precoding,is challenging in THz massive MIMO systems.The existing wideband channel estimation schemes based on the ideal assumption of common sparse channel support will suffer from a severe performance loss due to the beam split effect.In this paper,we propose a beam split pattern detection based channel estimation scheme to realize reliable wideband channel estimation in THz massive MIMO systems.Specifically,a comprehensive analysis on the angle-domain sparse structure of the wideband channel is provided by considering the beam split effect.Based on the analysis,we define a series of index sets called as beam split patterns,which are proved to have a one-to-one match to different physical channel directions.Inspired by this one-to-one match,we propose to estimate the physical channel direction by exploiting beam split patterns at first.Then,the sparse channel supports at different subcarriers can be obtained by utilizing a support detection window.This support detection window is generated by expanding the beam split pattern which is determined by the obtained physical channel direction.The above estimation procedure will be repeated path by path until all path components are estimated.Finally,the wideband channel can be recovered by calculating the elements on the total sparse channel support at all subcarriers.The proposed scheme exploits the wideband channel property implied by the beam split effect,i.e.,beam split pattern,which can significantly improve the channel estimation accuracy.Simulation results show that the proposed scheme is able to achieve higher accuracy than existing schemes.
基金supported by the National Basic Research Program of China ("973" Program), (Grantt No. 2010CB227305)the CAS Solar Energy Action Program (Grant No. CX2090130012)
文摘A novel hybrid solar concentrating Photovoltaic/Thermal (CPV/T) system with beam splitting technique is presented. In this system, a beam splitter is used to separate the concentrated solar radiation into two parts: one for the PV power generation and the other for thermal utility. The solar concentrator is a flat Fresnel-type concentrator with glass mirror reflectors. It can concentrate solar radiation onto solar cells with high uniformity, which is beneficial to improving the efficiency of solar cells. The thermal receiver is separated to the solar cells, and therefore, the thermal fluid can be heated to a relatively high temperature and does not affect the performance of solar cells. A dimensionless model was developed for the performance analysis of the concentrating system. The effects of the main parameters on the performance of the concentrator were analyzed. The beam splitter with coating materials Nb2O3 /SiO2 was designed by using the needle optimization technique, which can reflect about 71% of the undesired radiation for silicon cell(1.1m < 3m) to the thermal receiver for thermal utility. The performance of this CPV/T system was also theoretically analyzed.
基金support from a starting grant(project No.307270-ATTOSCOPE)of the European Research Councilthe Swiss National Science Foundation via the National Centre of Competence in Research Molecular Ultrafast Science and Technology.
文摘Monochromatization of high-harmonic sources has opened fascinating perspectives regarding time-resolved photoemission from all phases of matter.Such studies have invariably involved the use of spectral filters or spectrally dispersive optical components that are inherently lossy and technically complex.Here we present a new technique for the spectral selection of near-threshold harmonics and their spatial separation from the driving beams without any optical elements.We discover the existence of a narrow phase-matching gate resulting from the combination of the non-collinear generation geometry in an extended medium,atomic resonances and absorption.Our technique offers a filter contrast of up to 104 for the selected harmonics against the adjacent ones and offers multiple temporally synchronized beamlets in a single unified scheme.We demonstrate the selective generation of 133,80 or 56 nm femtosecond pulses from a 400-nm driver,which is specific to the target gas.These results open new pathways towards phase-sensitive multi-pulse spectroscopy in the vacuum-and extreme-ultraviolet,and frequencyselective output coupling from enhancement cavities.
基金supported by the National Natural Science Foundation of China(No.61675215)the Shanghai Sailing Program(No.18YF1426600)
文摘We propose a novel on-line beam diagnostic method based on single-shot beam splitting phase retrieval. The incident beam to be measured is diffracted into many replicas by a Dammann grating and then propagates through a weakly scattering phase plate with a known structure; the exiting beams propagate along their original direction and form an array of diffraction patterns on the detector plane. By applying the intensity of diffraction patterns into an iterative algorithm and calculating between the grating plane, weakly scattering plane, and detector plane, the complex field of the incident beam can be reconstructed rapidly; the feasibility of this method is verified experimentally with wavelengths of 1053 and 632.8 nm.
基金funded by the Villum Fonden(Award in Technical and Natural Sciences 2019 and Grant No.37372)Danmarks Frie Forskningsfond(Grant No.1134-00010B)+1 种基金support from the European Union’s Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie Action(Grant Agreement No.713694)support from the China Scholarship Council(Grant No.202108330079).
文摘Electrically connected optical metasurfaces with high efficiencies are crucial for developing spatiotemporal metadevices with ultrahigh spatial and ultrafast temporal resolutions.While efficient metal–insulator–metal(MIM)metasurfaces containing discretized meta-atoms require additional electrodes,Babinet-inspired slot-antenna-based plasmonic metasurfaces suffer from low efficiencies and limited phase coverage for copolarized optical fields.Capitalizing on the concepts of conventional MIM and slot-antenna metasurfaces,we design and experimentally demonstrate a new type of optical reflective metasurfaces consisting of mirrorcoupled slot antennas(MCSAs).By tuning the dimensions of rectangular-shaped nanoapertures atop a dielectric-coated gold mirror,we achieve efficient phase modulation within a sufficiently large range of 320 deg and realize functional phase-gradient metadevices for beam steering and beam splitting in the near-infrared range.The fabricated samples show(22%2%)diffraction efficiency for beam steering and(17%1%)for beam splitting at the wavelength of 790 nm.The considered MCSA configuration,dispensing with auxiliary electrodes,offers an alternative and promising platform for electrically controlled reflective spatiotemporal metasurfaces.
基金Project supported by the Natural Science Foundation of Beijing Municipality,China(Nos.QY23039,4222005,and L212027)the National Natural Science Foundation of China(Nos.62322101,62227809,and 62271012)。
文摘With the development of millimeter-wave(mmWave)communication systems,large-scale reconfigurable intelligent surfaces(RISs)have gained considerable attention as a promising technology for signal strength enhancement and coverage extension.However,as the antenna scale and bandwidth increase,RIS-assisted wideband orthogonal frequency division multiplexing(OFDM)communication systems face challenges due to the near-field range expansion and the beam split effect over the high-frequency band,complicating the acquisition of channel state information(CSI).To tackle these challenges,we present a codebook-based three-stage beam training scheme by using the beam split effect to bypass CSI estimation.Specifically,by analyzing the beam split effect in RIS-assisted OFDM communication systems,we propose a beam-split-aware codebook capable of covering both the near and far fields with fewer codewords compared to conventional narrow-band codebooks.Using such a codebook,a three-stage beam training mechanism is adopted to obtain the optimal codeword with low time overhead,thereby facilitating subsequent beamforming.Simulation results demonstrate that the proposed scheme outperforms existing near-and far-field codebook-based schemes in terms of the beam training resolution and sum rate in the hybrid near–far field.
基金Project supported by the National Natural Science Foundation of China(Nos.62101205 and 62101308)the Key Research and Development Program of Hubei Province,China(No.2023BAB061)。
文摘A simultaneously transmitting and reflecting reconfigurable intelligent surface(STAR-RIS)assisted multiuser near-field wideband communication system is investigated,in which a robust deep reinforcement learning(DRL)based algorithm is proposed to enhance the users’achievable rate by jointly optimizing the active beamforming at the base station(BS)and passive beamforming at the STAR-RIS.To mitigate the beam split issue,the delay-phase hybrid precoding structure is introduced to facilitate wideband beamforming.Considering the coupled nature of the STARRIS phase-shift model,the passive beamforming design is formulated as a problem of hybrid continuous and discrete phase-shift control,and the proposed algorithm controls the high-dimensional continuous action through hybrid action mapping.Additionally,to address the issue of biased estimation encountered by existing DRL algorithms,a softmax operator is introduced into the algorithm to mitigate this bias.Simulation results illustrate that the proposed algorithm outperforms existing algorithms and overcomes the issues of overestimation and underestimation.
基金National Key Research and Development Program of China(SQ2022YFB3806200)National Natural Science Foundation of China(62301596,62101588)+1 种基金Young Talent Fund of Association for Science and Technology in Shaanxi(20240129)Postdoctoral Fellowship Program of CPSF(GZC20242285)。
文摘In modern science and technology,on-demand control of the polarization and wavefront of electromagnetic(EM)waves is crucial for compact opto-electronic systems.Metasurfaces composed of subwavelength array structures inject infinite vitality to shape this fantastic concept,which has fundamentally changed the way humans engineer matter–wave interactions.However,achieving full-space arbitrarily polarized beams with independent wavefronts in broadband on a single metasurface aperture still remains challenging.Herein,the authors propose a generic method for broadband transmission-reflection-integrated wavefronts shaping with multichannel arbitrary polarization regulation from 8 to 16 GHz,which is based on the chirality effect of full-space non-interleaved tetrameric meta-molecules.Through superimposing eigen-polarization responses of the two kinds of enantiomers,the possibility for high-efficiency evolution of several typical polarization states with specific wavefronts is demonstrated.As proofs-of-concept,the feasibility of our methodology is validated via implementing miscellaneous functionalities,including circularly polarized(CP)beam splitting,linearly polarized(LP)vortex beams generation,and CP and LP multifoci.Meanwhile,numerous simulated and experimental results are in excellent agreement with the theoretical predictions.Encouragingly,this proposed approach imaginatively merges broadband polarization and phase control into one single full-space and shared-aperture EM device,which can extremely enhance the functional richness and information capacity in advanced integrated systems.
基金This work was supported by the National Key Research and Development Program of China(2017YFA0700201,2017YFA0700203 and 2016YFC0800401)National Natural Science Foundation of China(61890544,61522106,61631007,61571117,61731010,61735010,61722106,61701107,and 61701108)+3 种基金Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX19_0081)Scientific Research Foundation of Graduate School of Southeast University(YBPY1938)Foundation of National Excellent Doctoral Dissertation of China(201444)the 111 Project(111-2-05).
文摘Programmable metasurface enables controlling electromagnetic (EM) waves in real time. By programming the states of active device embedded in metasurface element, the EM properties of the digital metasurface can be changed quickly without redesigning their structures. However, large numbers of long-distance wires are required to connect the programmable metasurface to provide the coded signals from field programmable gate array (FPGA) when controlling the metasurface at a long distance, which is complicated and inconvenient. Here, we propose an infrared-controlled programmable metasurface that can be programmed remotely. The infrared transceiver is able to switch the coding sequences stored in the FPGA controller, thus controlling the voltage on the varactors integrated in the metasurface. Experiment is performed at microwave frequencies, and the measured results verify that the scattering beams of the metasurface sample can be changed remotely by using infrared ray. The proposed infrared-controlled programmable metasurface opens up avenues for constructing a new class of remotely-tuning dynamic metasurfaces.
基金the National Natural Science Foundation of China(NSFC)(Nos.11674303 and 11574293)the Anhui Provincial Science andTechnology Major Projects(No.18030901005)。
文摘Phase carried by two orthogonal polarizations can be manipulated independently by controlling both the geometric size and orientation of the dielectric nanopost.With this characteristic,we demonstrate a novel multifunctional metasurface,which converts part of the incident linearly polarized light into its cross-polarization and encodes the phase of the two orthogonal polarizations independently.A beam splitter and a bifocal metalens were realized in a single-layer dielectric metasurface by this approach.We fabricated the bifocal metalens and demonstrated that two focal spots in orthogonal polarizations can be separated transversely or longitudinally at will.The proposed approach shows a new route to design multifunctional metasurfaces with various applications in holography and three-dimensional display.
基金supported by the National Basic Research Program of China("973" Project)(Grant No.2010CB227305)
文摘Thermodynamics analysis was carried out for solar thermal receivers with different selective coatings.The relation between the energy conversion efficiency of a medium-high temperature solar thermal system,the spectral properties of selective coating and the operating temperature of the receiver were discussed.Furthermore,the relation between the optimum operating temperatures,the exergy efficiencies and the incident solar flux were analyzed for the traditional concentrating system and concentrating beam splitting system,respectively.According to the analysis results for the thermal receiver with blackbody surface and selective coatings,the optimum cutoff wavelength was obtained for the ideal selective coating.An analysis method for the optimum operating temperature calculation was developed for thermal receivers with selective coating.The optimum operating temperature for an actual selective coating was analyzed on the basis of the proposed theory.
基金supported by the Focused Deployment Project of the Chinese Academy of Sciences(KGZD-EW-302-1)the Key Technologies R&D Program of China(grant no.2012BAA03B03)a UK EPSRC grant under EP/K002252/1
文摘This paper proposes a power system concept that integrates photovoltaic （PV） and thermoelectric （TE） technologies to harvest solar energy from a wide spectral range. By introduction of the ＇spectrum beam splitting＇ technique, short wavelength solar radiation is converted directly into electricity in the PV cells, while the long wavelength segment of the spectrum is used to produce moderate to high temperature thermal energy, which then generates electricity in the TE device. To overcome the intermittent nature of solar radiation, the system is also coupled to a thermal energy storage unit. A systematic analysis of the integrated system is carried out, encompassing the system configuration, material properties, thermal management, and energy storage aspects. We have also attempted to optimize the integrated system. The results indicate that the system configuration and optimization are the most important factors for high overall efficiency.
