Given the enhanced channel capacity of wave chirality,acoustic communications based on the orbital angular momentum(OAM)of acoustic-vortex(AV)beams are of significant interest for underwater data transmissions.However...Given the enhanced channel capacity of wave chirality,acoustic communications based on the orbital angular momentum(OAM)of acoustic-vortex(AV)beams are of significant interest for underwater data transmissions.However,the stringent beam alignment is required for the coaxial arrangement of transceiver arrays to ensure the accuracy and reliability of OAM decoding.To avoid the required multiple measurements of the traditional orthogonality based algorithm,the beam alignment algorithm based on the OAM spectrum decomposition is proposed for AV communications by using simplified ring-arrays.Numerical studies of the single-OAM and OAM-multiplexed AV beams show that the error of the OAM spectrum increases with the translation distance and the deflection angle of the transceiver arrays.To achieve an ideal arrangement,two methods of the single-array translation alignment and the dual-array deflection alignment are developed based on the least standard deviation of the OAM spectrum(SD-OAM).By decreasing the SD-OAM towards zero using transceiver arrays of 16 transmitters and 16 receivers,accurate beam alignments are accomplished by multiple adjustments in three dimensions.The proposed method is also demonstrated by experimental measurements of the OAM dispersion and the SD-OAM for misaligned beams.The results demonstrate the feasibility of the rapid beam alignment based on the OAM spectrum decomposition by using simplified transceiver ring-arrays,and suggest more application potentials for acoustic communications.展开更多
The extreme ultraviolet(XUV)light beam carrying orbital angular momentum(OAM)can be produced via high-order harmonic generation(HHG)due to the interaction of an intense vortex infrared laser and a gas medium.Here we s...The extreme ultraviolet(XUV)light beam carrying orbital angular momentum(OAM)can be produced via high-order harmonic generation(HHG)due to the interaction of an intense vortex infrared laser and a gas medium.Here we show that the OAM spectrum of vortex HHG can be readily tailored by varying the radial node(from 0 to 2)in the driving laser consisting of two mixed Laguerre-Gaussian(LG)beams.We find that due to the change in spatial profile of HHG,the distribution range of the OAM spectrum can be broadened and its shape can be modified by increasing the radial node.We also show that the OAM mode range becomes much wider and its distribution shape becomes more symmetric when the harmonic order is increased from the plateau to the cutoff when the driving laser has the nonzero radial nodes.Through the map of coherence length and the evolution of harmonic field in the medium,we reveal that the favorable off-axis phase-matching conditions are greatly modified due to the change of intensity and phase distributions of driving laser with the radial node.We anticipate this work to stimulate some interests in generating the XUV vortex beam with tunable OAM spectrum through the gaseous HHG process achieved by manipulating the mode properties of the driving laser beam.展开更多
随着第五代移动通信技术(5th Generation Mobile Communication Technology,5G)网络技术的持续进步和广泛应用,低地球轨道(Low Earth Orbit,LEO)卫星技术被认为是提高其性能的核心要素之一。LEO卫星在提高带宽、降低时延、扩展网络覆盖...随着第五代移动通信技术(5th Generation Mobile Communication Technology,5G)网络技术的持续进步和广泛应用,低地球轨道(Low Earth Orbit,LEO)卫星技术被认为是提高其性能的核心要素之一。LEO卫星在提高带宽、降低时延、扩展网络覆盖范围以及改善通信质量等方面可显著优化5G网络性能。但两种技术的整合也带来了新挑战,主要表现在频谱资源分配问题、卫星通信和地面基站之间的配合、自然因素在通信中的作用以及安全性与隐私保护等方面。本研究为应对上述挑战提出了优化策略,主要包括频谱资源管理、卫星-地面通信系统集成方案、预报和减缓天气影响技术及强化通信安全性与隐私保护措施等,目的是进一步提高5G网络性能与可靠性。展开更多
Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra...Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra of Laguerre-Gaussian（LG） beams under both weak/medium and strong atmospheric turbulences. We propose fixing the radius to the extreme point of the intensity distribution, review the expression for the OAM spectrum under weak/medium turbulence,derive the OAM spectrum expression for an LG beam under strong turbulence, and simplify both of them to concise forms.Then, we investigate the accuracy of the simplified expressions through simulations. We find that the simplified expressions permit accurate calculation of the OAM spectrum for large transmitted OAM numbers under any type of turbulence. Finally,we use the simplified expressions to analytically address the broadening of the OAM spectrum caused by atmospheric turbulence. This work should contribute to the concise theoretical derivation of analytical expressions for OAM channel matrices for FSO-OAM communications and the analytical study of the laws governing OAM spectra.展开更多
We studied the system of pure Rashba spin–orbit coupled Bose gas with an in-plane magnetic field. Based on the mean field theory, we obtained the zero temperature phase diagram of the system which exhibits three phas...We studied the system of pure Rashba spin–orbit coupled Bose gas with an in-plane magnetic field. Based on the mean field theory, we obtained the zero temperature phase diagram of the system which exhibits three phases, plane wave（PW） phase, striped wave（SW） phase, and zero momentum（ZM） phase. It was shown that with a growing in-plane field,both SW and ZM phases will eventually turn into the PW phase. Furthermore, we adopted the Bogoliubov theory to study the excitation spectrum as well as the sound speed.展开更多
Spin-wave excitation plays important roles in the investigation of the magnetic phases. In this paper, we study the spin-wave excitation spectra of two-component Bose gases with spin-orbit coupling in a deep square op...Spin-wave excitation plays important roles in the investigation of the magnetic phases. In this paper, we study the spin-wave excitation spectra of two-component Bose gases with spin-orbit coupling in a deep square optical lattice using the spin-wave theory. We find that, while the excitation spectrum of the vortex crystal phase is gapless with a linear dispersion in the vicinity of the minimum point, the spectra of the commensurate spiral spin phase and the skyrmion crystal phase are gapped. Significantly, the spin fluctuations strongly destabilize the classical ground state of the skyrmion phase with the appearance of an imaginary part in the eigenfrequencies of spin excitations. Such features of the spin excitation spectra provide further insights into the exotic spin phases.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11934009,11974187,and 12174198)
文摘Given the enhanced channel capacity of wave chirality,acoustic communications based on the orbital angular momentum(OAM)of acoustic-vortex(AV)beams are of significant interest for underwater data transmissions.However,the stringent beam alignment is required for the coaxial arrangement of transceiver arrays to ensure the accuracy and reliability of OAM decoding.To avoid the required multiple measurements of the traditional orthogonality based algorithm,the beam alignment algorithm based on the OAM spectrum decomposition is proposed for AV communications by using simplified ring-arrays.Numerical studies of the single-OAM and OAM-multiplexed AV beams show that the error of the OAM spectrum increases with the translation distance and the deflection angle of the transceiver arrays.To achieve an ideal arrangement,two methods of the single-array translation alignment and the dual-array deflection alignment are developed based on the least standard deviation of the OAM spectrum(SD-OAM).By decreasing the SD-OAM towards zero using transceiver arrays of 16 transmitters and 16 receivers,accurate beam alignments are accomplished by multiple adjustments in three dimensions.The proposed method is also demonstrated by experimental measurements of the OAM dispersion and the SD-OAM for misaligned beams.The results demonstrate the feasibility of the rapid beam alignment based on the OAM spectrum decomposition by using simplified transceiver ring-arrays,and suggest more application potentials for acoustic communications.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12274230,91950102,and 11834004)the Funding of Nanjing University of Science and Technology (Grant No.TSXK2022D005)。
文摘The extreme ultraviolet(XUV)light beam carrying orbital angular momentum(OAM)can be produced via high-order harmonic generation(HHG)due to the interaction of an intense vortex infrared laser and a gas medium.Here we show that the OAM spectrum of vortex HHG can be readily tailored by varying the radial node(from 0 to 2)in the driving laser consisting of two mixed Laguerre-Gaussian(LG)beams.We find that due to the change in spatial profile of HHG,the distribution range of the OAM spectrum can be broadened and its shape can be modified by increasing the radial node.We also show that the OAM mode range becomes much wider and its distribution shape becomes more symmetric when the harmonic order is increased from the plateau to the cutoff when the driving laser has the nonzero radial nodes.Through the map of coherence length and the evolution of harmonic field in the medium,we reveal that the favorable off-axis phase-matching conditions are greatly modified due to the change of intensity and phase distributions of driving laser with the radial node.We anticipate this work to stimulate some interests in generating the XUV vortex beam with tunable OAM spectrum through the gaseous HHG process achieved by manipulating the mode properties of the driving laser beam.
文摘随着第五代移动通信技术(5th Generation Mobile Communication Technology,5G)网络技术的持续进步和广泛应用,低地球轨道(Low Earth Orbit,LEO)卫星技术被认为是提高其性能的核心要素之一。LEO卫星在提高带宽、降低时延、扩展网络覆盖范围以及改善通信质量等方面可显著优化5G网络性能。但两种技术的整合也带来了新挑战,主要表现在频谱资源分配问题、卫星通信和地面基站之间的配合、自然因素在通信中的作用以及安全性与隐私保护等方面。本研究为应对上述挑战提出了优化策略,主要包括频谱资源管理、卫星-地面通信系统集成方案、预报和减缓天气影响技术及强化通信安全性与隐私保护措施等,目的是进一步提高5G网络性能与可靠性。
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61575027 and 61471051)
文摘Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra of Laguerre-Gaussian（LG） beams under both weak/medium and strong atmospheric turbulences. We propose fixing the radius to the extreme point of the intensity distribution, review the expression for the OAM spectrum under weak/medium turbulence,derive the OAM spectrum expression for an LG beam under strong turbulence, and simplify both of them to concise forms.Then, we investigate the accuracy of the simplified expressions through simulations. We find that the simplified expressions permit accurate calculation of the OAM spectrum for large transmitted OAM numbers under any type of turbulence. Finally,we use the simplified expressions to analytically address the broadening of the OAM spectrum caused by atmospheric turbulence. This work should contribute to the concise theoretical derivation of analytical expressions for OAM channel matrices for FSO-OAM communications and the analytical study of the laws governing OAM spectra.
基金Project supported by the National Natural Science Foundation of China(Grant No.10774088)
文摘We studied the system of pure Rashba spin–orbit coupled Bose gas with an in-plane magnetic field. Based on the mean field theory, we obtained the zero temperature phase diagram of the system which exhibits three phases, plane wave（PW） phase, striped wave（SW） phase, and zero momentum（ZM） phase. It was shown that with a growing in-plane field,both SW and ZM phases will eventually turn into the PW phase. Furthermore, we adopted the Bogoliubov theory to study the excitation spectrum as well as the sound speed.
基金supported by the National Natural Science Foundation of China(Grant Nos.11347197,11404225,and 11474205)
文摘Spin-wave excitation plays important roles in the investigation of the magnetic phases. In this paper, we study the spin-wave excitation spectra of two-component Bose gases with spin-orbit coupling in a deep square optical lattice using the spin-wave theory. We find that, while the excitation spectrum of the vortex crystal phase is gapless with a linear dispersion in the vicinity of the minimum point, the spectra of the commensurate spiral spin phase and the skyrmion crystal phase are gapped. Significantly, the spin fluctuations strongly destabilize the classical ground state of the skyrmion phase with the appearance of an imaginary part in the eigenfrequencies of spin excitations. Such features of the spin excitation spectra provide further insights into the exotic spin phases.
