随着隐身技术的发展,雷达目标的边缘绕射等逐渐取代镜面散射成为主要的散射源,因此基于几何绕射理论(geometric theory of diffraction,GTD)的散射中心模型对隐身目标电磁散射特性的描述要比衰减指数和模型更为精确。显然,准确估计出GT...随着隐身技术的发展,雷达目标的边缘绕射等逐渐取代镜面散射成为主要的散射源,因此基于几何绕射理论(geometric theory of diffraction,GTD)的散射中心模型对隐身目标电磁散射特性的描述要比衰减指数和模型更为精确。显然,准确估计出GTD散射中心参数对刻画目标散射特性犹为重要。针对经典多重信号分类(multiple signal classification,MUSIC)法仅利用目标原始回波数据、参数估计精度不高这一问题,提出一种改进的MUSIC算法对散射参数估计提取。改进的MUSIC算法通过对原始回波数据取共轭,构建新的总协方差矩阵,有效利用了目标原始回波数据的共轭信息。仿真结果表明,与经典MUSIC算法相比,改进的MUSIC算法参数估计精度更高,雷达散射截面重构拟合程度更好,且运算量增加不大,可有效提取出隐身目标的散射中心。展开更多
The measurement of the optical transmission matrix(TM)of an opaque material is an advanced form of space-variant aberration correction.Beyond imaging,TM-based methods are emerging in a range of fields,including optica...The measurement of the optical transmission matrix(TM)of an opaque material is an advanced form of space-variant aberration correction.Beyond imaging,TM-based methods are emerging in a range of fields,including optical communications,micro-manipulation,and computing.In many cases,the TM is very sensitive to perturbations in the configuration of the scattering medium it represents.Therefore,applications often require an up-to-the-minute characterisation of the fragile TM,typically entailing hundreds to thousands of probe measurements.Here,we explore how these measurement requirements can be relaxed using the framework of compressive sensing,in which the incorporation of prior information enables accurate estimation from fewer measurements than the dimensionality of the TM we aim to reconstruct.Examples of such priors include knowledge of a memory effect linking the input and output fields,an approximate model of the optical system,or a recent but degraded TM measurement.We demonstrate this concept by reconstructing the full-size TM of a multimode fibre supporting 754 modes at compression ratios down to∼5%with good fidelity.We show that in this case,imaging is still possible using TMs reconstructed at compression ratios down to∼1%(eight probe measurements).This compressive TM sampling strategy is quite general and may be applied to a variety of other scattering samples,including diffusers,thin layers of tissue,fibre optics of any refractive profile,and reflections from opaque walls.These approaches offer a route towards the measurement of high-dimensional TMs either quickly or with access to limited numbers of measurements.展开更多
Scattering of waves, e.g., light, due to medium inhomogeneity is ubiquitous in physics and isconsidered detrimental for many applications. Wavefront shaping technology is a powerful tool to defeatscattering and focus ...Scattering of waves, e.g., light, due to medium inhomogeneity is ubiquitous in physics and isconsidered detrimental for many applications. Wavefront shaping technology is a powerful tool to defeatscattering and focus light through inhomogeneous media, which is vital for optical imaging, communication,therapy, etc. Wavefront shaping based on the scattering matrix (SM) is extremely useful in handling dynamicprocesses in the linear regime. However, the implementation of such a method for controlling light in nonlinearmedia is still a challenge and has been unexplored until now. We report a method to determine the SM ofnonlinear scattering media with second-order nonlinearity. We experimentally demonstrate its feasibility inwavefront control and realize focusing of nonlinear signals through strongly scattering quadratic media.Moreover, we show that statistical properties of this SM still follow the random matrix theory. The scattering-matrix approach of nonlinear scattering medium opens a path toward nonlinear signal recovery, nonlinearimaging, microscopic object tracking, and complex environment quantum information processing.展开更多
文摘随着隐身技术的发展,雷达目标的边缘绕射等逐渐取代镜面散射成为主要的散射源,因此基于几何绕射理论(geometric theory of diffraction,GTD)的散射中心模型对隐身目标电磁散射特性的描述要比衰减指数和模型更为精确。显然,准确估计出GTD散射中心参数对刻画目标散射特性犹为重要。针对经典多重信号分类(multiple signal classification,MUSIC)法仅利用目标原始回波数据、参数估计精度不高这一问题,提出一种改进的MUSIC算法对散射参数估计提取。改进的MUSIC算法通过对原始回波数据取共轭,构建新的总协方差矩阵,有效利用了目标原始回波数据的共轭信息。仿真结果表明,与经典MUSIC算法相比,改进的MUSIC算法参数估计精度更高,雷达散射截面重构拟合程度更好,且运算量增加不大,可有效提取出隐身目标的散射中心。
基金S.L.acknowledges support from the National Natural Science Foundation of China under Grant no.61705073C.S.,J.M.B.and V.K.G.acknowledge support from the United States National Science Foundation under Grant no.1815896+2 种基金T.C.thanks the European Regional Development Fund(CZ.02.1.01/0.0/0.0/15_003/0000476)the European Research Council(724530)for financial supportD.B.P.thanks the Royal Academy of Engineering and the European Research Council(804626)for financial support.
文摘The measurement of the optical transmission matrix(TM)of an opaque material is an advanced form of space-variant aberration correction.Beyond imaging,TM-based methods are emerging in a range of fields,including optical communications,micro-manipulation,and computing.In many cases,the TM is very sensitive to perturbations in the configuration of the scattering medium it represents.Therefore,applications often require an up-to-the-minute characterisation of the fragile TM,typically entailing hundreds to thousands of probe measurements.Here,we explore how these measurement requirements can be relaxed using the framework of compressive sensing,in which the incorporation of prior information enables accurate estimation from fewer measurements than the dimensionality of the TM we aim to reconstruct.Examples of such priors include knowledge of a memory effect linking the input and output fields,an approximate model of the optical system,or a recent but degraded TM measurement.We demonstrate this concept by reconstructing the full-size TM of a multimode fibre supporting 754 modes at compression ratios down to∼5%with good fidelity.We show that in this case,imaging is still possible using TMs reconstructed at compression ratios down to∼1%(eight probe measurements).This compressive TM sampling strategy is quite general and may be applied to a variety of other scattering samples,including diffusers,thin layers of tissue,fibre optics of any refractive profile,and reflections from opaque walls.These approaches offer a route towards the measurement of high-dimensional TMs either quickly or with access to limited numbers of measurements.
基金supported in part by the National Key R&D Program of China (No. 2018YFA0306301)the National Natural Science Foundation of China (Nos. 12192252, 62022058, 12074252, and 12004245)+2 种基金the Shanghai Municipal Science and Technology Major Project (No. 2019SHZDZX01ZX06)the Shanghai Rising-Star Program (No. 20QA1405400)the Yangyang Development Fund.
文摘Scattering of waves, e.g., light, due to medium inhomogeneity is ubiquitous in physics and isconsidered detrimental for many applications. Wavefront shaping technology is a powerful tool to defeatscattering and focus light through inhomogeneous media, which is vital for optical imaging, communication,therapy, etc. Wavefront shaping based on the scattering matrix (SM) is extremely useful in handling dynamicprocesses in the linear regime. However, the implementation of such a method for controlling light in nonlinearmedia is still a challenge and has been unexplored until now. We report a method to determine the SM ofnonlinear scattering media with second-order nonlinearity. We experimentally demonstrate its feasibility inwavefront control and realize focusing of nonlinear signals through strongly scattering quadratic media.Moreover, we show that statistical properties of this SM still follow the random matrix theory. The scattering-matrix approach of nonlinear scattering medium opens a path toward nonlinear signal recovery, nonlinearimaging, microscopic object tracking, and complex environment quantum information processing.
