Femtosecond laser processing is an important machining method for micro-optical components such as Fresnel zone plate(FZP).However,the low processing efficiency of the femtosecond laser restricts its application.Here,...Femtosecond laser processing is an important machining method for micro-optical components such as Fresnel zone plate(FZP).However,the low processing efficiency of the femtosecond laser restricts its application.Here,a femtosecond laser Bessel beam is proposed to process micro-FZP,which is modulated from a Gaussian beam to a Bessel annular beam.The processing time for FZP with an outer diameter of 60μm is reduced from 30 min to 1.5 min on an important semiconductor material gallium arsenide(GaAs),which significantly improves the processing efficiency.In the modulation process,a central ablation hole that has an adverse effect on the diffraction performance is produced,and the adverse effect is eliminated by superimposing the blazed grating hologram.Meanwhile,the FZP machined by spatial light modulator(SLM)has good morphology and higher diffraction efficiency,which provides a strong guarantee for the application of micro-FZP in computed tomography and solar photovoltaic cells.展开更多
Self-diffraction appears when the strong laser goes through two-dimensional material suspension,and this spatial self-phase modulation(SPPM)phenomenon can be used to measure nonlinear optical parameters and achieve op...Self-diffraction appears when the strong laser goes through two-dimensional material suspension,and this spatial self-phase modulation(SPPM)phenomenon can be used to measure nonlinear optical parameters and achieve optical switch.At present,the mechanism of SPPM is still ambiguous.The debate mainly focuses on whether the phenomenon is caused by the nonlinear refractive index of the two-dimensional material or the thermal effect of the laser.The lack of theory limits the dimension of the phase modulation to the radius of the diffraction ring and the vertical imbalance.Therefore,it is urgent to establish a unified and universal SSPM theoretical system of two-dimensional material.展开更多
In order to improve the detection accuracy of Doppler asymmetric spatial heterodyne(DASH)interferometer in harsh temperatures,an opto-mechanical-thermal integration analysis is carried out.Firstly,the correlation betw...In order to improve the detection accuracy of Doppler asymmetric spatial heterodyne(DASH)interferometer in harsh temperatures,an opto-mechanical-thermal integration analysis is carried out.Firstly,the correlation between the interference phase and temperature is established according to the working principle and the phase algorithm of the interferometer.Secondly,the optical mechanical thermal analysis model and thermal deformation data acquisition model are designed.The deformation data of the interference module and the imaging optical system at different temperatures are given by temperature load simulation analysis,and the phase error caused by thermal deformation is obtained by fitting.Finally,based on the wind speed error caused by thermal deformation of each component,a reasonable temperature control scheme is proposed.The results show that the interference module occupies the main cause,the temperature must be controlled within(20±0.05)℃,and the temperature control should be carried out for the temperature sensitive parts,and the wind speed error caused by the part is 3.8 m/s.The thermal drift between the magnification of the imaging optical system and the thermal drift of the relative position between the imaging optical system and the detector should occupy the secondary cause,which should be controlled within(20±2)℃,and the wind speed error caused by the part is 3.05 m/s.In summary,the wind measurement error caused by interference module,imaging optical system,and the relative position between the imaging optical system and the detector can be controlled within 6.85 m/s.The analysis and temperature control schemes presented in this paper can provide theoretical basis for DASH interferometer engineering applications.展开更多
针对无人机基站空对地通信链路易受窃听攻击的问题,提出一种基于隐蔽信息映射的广义空间方向调制系统(covert information mapped-generalized spatial and direction modulation,CIM-GSDM),将信息隐藏于激活接收机子集的索引及其选择...针对无人机基站空对地通信链路易受窃听攻击的问题,提出一种基于隐蔽信息映射的广义空间方向调制系统(covert information mapped-generalized spatial and direction modulation,CIM-GSDM),将信息隐藏于激活接收机子集的索引及其选择组合中,引入与合法方信道正交的人工噪声干扰窃听方。为进一步提升系统的传输安全性,研究提出了预编码矩阵和功率分配因子联合优化框架,通过有效管理多波束传输和人工噪声的功率分配,增强系统安全性。首先,推导基于系统安全速率的物理层安全性指标,以此为优化目标,联合优化预编码矩阵和人工噪声功率分配因子。为解决该非凸的联合优化问题,考虑交替优化2个变量,提出基于Nesterov下降的自然梯度下降法,通过快速迭代更新预编码矩阵,解决CIM-GSDM符号候选集规模较大带来的计算复杂度问题。基于合法方信噪比与窃听方干信噪比的乘积最大化准则,推导出功率分配因子的次优闭式解。仿真结果表明,所提优化算法在保证合法方可达到的速率前提下,显著降低窃听方的窃听速率,有效保证CIM-GSDM系统的传输安全性。相比传统波束成形算法及固定功率分配因子的方法,提出算法在安全性能上具有显著优势。展开更多
基金Projects(51875584,51875585,51975590)supported by the National Natural Science Foundation of China。
文摘Femtosecond laser processing is an important machining method for micro-optical components such as Fresnel zone plate(FZP).However,the low processing efficiency of the femtosecond laser restricts its application.Here,a femtosecond laser Bessel beam is proposed to process micro-FZP,which is modulated from a Gaussian beam to a Bessel annular beam.The processing time for FZP with an outer diameter of 60μm is reduced from 30 min to 1.5 min on an important semiconductor material gallium arsenide(GaAs),which significantly improves the processing efficiency.In the modulation process,a central ablation hole that has an adverse effect on the diffraction performance is produced,and the adverse effect is eliminated by superimposing the blazed grating hologram.Meanwhile,the FZP machined by spatial light modulator(SLM)has good morphology and higher diffraction efficiency,which provides a strong guarantee for the application of micro-FZP in computed tomography and solar photovoltaic cells.
基金Project(6187031976)supported by the National Natural Science Foundation of China
文摘Self-diffraction appears when the strong laser goes through two-dimensional material suspension,and this spatial self-phase modulation(SPPM)phenomenon can be used to measure nonlinear optical parameters and achieve optical switch.At present,the mechanism of SPPM is still ambiguous.The debate mainly focuses on whether the phenomenon is caused by the nonlinear refractive index of the two-dimensional material or the thermal effect of the laser.The lack of theory limits the dimension of the phase modulation to the radius of the diffraction ring and the vertical imbalance.Therefore,it is urgent to establish a unified and universal SSPM theoretical system of two-dimensional material.
文摘In order to improve the detection accuracy of Doppler asymmetric spatial heterodyne(DASH)interferometer in harsh temperatures,an opto-mechanical-thermal integration analysis is carried out.Firstly,the correlation between the interference phase and temperature is established according to the working principle and the phase algorithm of the interferometer.Secondly,the optical mechanical thermal analysis model and thermal deformation data acquisition model are designed.The deformation data of the interference module and the imaging optical system at different temperatures are given by temperature load simulation analysis,and the phase error caused by thermal deformation is obtained by fitting.Finally,based on the wind speed error caused by thermal deformation of each component,a reasonable temperature control scheme is proposed.The results show that the interference module occupies the main cause,the temperature must be controlled within(20±0.05)℃,and the temperature control should be carried out for the temperature sensitive parts,and the wind speed error caused by the part is 3.8 m/s.The thermal drift between the magnification of the imaging optical system and the thermal drift of the relative position between the imaging optical system and the detector should occupy the secondary cause,which should be controlled within(20±2)℃,and the wind speed error caused by the part is 3.05 m/s.In summary,the wind measurement error caused by interference module,imaging optical system,and the relative position between the imaging optical system and the detector can be controlled within 6.85 m/s.The analysis and temperature control schemes presented in this paper can provide theoretical basis for DASH interferometer engineering applications.
文摘针对无人机基站空对地通信链路易受窃听攻击的问题,提出一种基于隐蔽信息映射的广义空间方向调制系统(covert information mapped-generalized spatial and direction modulation,CIM-GSDM),将信息隐藏于激活接收机子集的索引及其选择组合中,引入与合法方信道正交的人工噪声干扰窃听方。为进一步提升系统的传输安全性,研究提出了预编码矩阵和功率分配因子联合优化框架,通过有效管理多波束传输和人工噪声的功率分配,增强系统安全性。首先,推导基于系统安全速率的物理层安全性指标,以此为优化目标,联合优化预编码矩阵和人工噪声功率分配因子。为解决该非凸的联合优化问题,考虑交替优化2个变量,提出基于Nesterov下降的自然梯度下降法,通过快速迭代更新预编码矩阵,解决CIM-GSDM符号候选集规模较大带来的计算复杂度问题。基于合法方信噪比与窃听方干信噪比的乘积最大化准则,推导出功率分配因子的次优闭式解。仿真结果表明,所提优化算法在保证合法方可达到的速率前提下,显著降低窃听方的窃听速率,有效保证CIM-GSDM系统的传输安全性。相比传统波束成形算法及固定功率分配因子的方法,提出算法在安全性能上具有显著优势。
