双孔散斑照相用于物体通过漫射介质成象

物体通过大雾等漫射介质的成象问题一直吸引众多研究者的注意。光学全息技术、光栅干涉仪技术已经显示出在实验室条件下的有效性。但由于所使用的设备比较复杂，很容易受外界震动的干扰，使其应用场所受到很大制约。本文提出了使用双孔散斑照相技术使物体通过漫射介质成象。用这种技术得到的实验结果显示这项技术在象的对比度方面比直接得到的象有很大提高。同时所使用的设备简单，受外界震动的影响小，因而具有很大的实用价值。     

Matched swept-frequency digital modulation for binary signaling in inhomogeneous dispersive media

A digital modulation technique which is most suitable for binary signaling through inhomogeneous dispersive media is introduced. Space-time rays are used to synthesize frequency-modulated input pulses that are either compressed in the medium with enhanced output or dispersed in the medium with widely spread output. The synthesized binary signals are shown to be in the form of swept-frequency signals which are matched to the dispersive properties of the medium. For media with quadratic phase functions, or under narrow-band conditions, the matched binary signals are linearly frequency modulated (chirp) with sweep rates that are related to the medium dispersion. The medium response to the matched chirp-modulated signals is investigated in detail. Conditions for the enhancement of the performance of the proposed modulation technique due to the available bandwidth are also discussed.     

Time-of-Flight透散射介质成像技术综述

Time-of-Flight (ToF)成像是利用光在目标和相机之间的飞行时间来获取场景的深度信息,具有体积小、成本低、实时成像等优势。在散射环境中,由于散射介质对光的散射作用,ToF成像受到多径干扰的影响,深度测量误差较大,限制了ToF相机在散射场景中的应用。ToF透散射介质成像技术是校正因散射光引起的多径干扰效应,从传感器接收到的混叠信号中分离出目标分量,实现散射场景中的深度信息恢复,其在雾天自动驾驶、水下勘测、生物医学等领域具有广阔的应用前景。依据ToF成像系统的不同,详细介绍了PL-ToF和CW-ToF成像的基本原理,阐述和分析了散射场景中ToF稳态成像和瞬态成像的机理和特点,分别回顾和总结了ToF稳态成像和瞬态成像的透散射介质成像研究现状,并介绍了ToF透散射介质成像的应用前景,最后依据现有ToF透散射介质成像技术的优缺点,对未来发展趋势进行了展望。     

高效学习的透过未知散射介质的相位恢复方法

透过散射介质对目标进行准确的重建仍然是阻碍人们对深层生物组织成像分析和深空天文观测的主要挑战之一。基于深度学习的散射计算成像方法虽然在成像质量和效率等方面取得了很大的进展,但是针对实际系统中散射介质状态不固定,目标结构具有较高复杂度以及可获取的训练散射数据有限的情况下,单纯利用数据驱动的方法已无法进行准确高效的重建。将散斑相关原理和卷积神经网络强大的数据挖掘和映射能力进行有效的结合,进一步挖掘和利用散斑所包含的冗余信息,实现了仅利用一块薄散射介质对应的散斑数据即可实现透过具有不同统计特性散射介质的复杂目标重构。该方法针对实际散射场景复杂多变和训练样本数据有限的情况,实现了对复杂目标的高质量恢复,有力地推动了基于物理感知的学习方法在实际散射场景中的应用。     

Light extraction from OLEDs for lighting applications through light scattering

OLEDs are gaining increasing interest for lighting applications as large-area light sources. Their lifetime and overall efficiency can be increased by the optimization of light outcoupling.In this article, scattering films on the viewer’s side of the substrate to increase the outcoupling efficiency of OLEDs for lighting applications are examined. Experimental results show that the increase of outcoupling efficiency is dependent from the absolute number of scattering particles in the matrix.Theoretical considerations expect an increase of outcoupling efficiency of up to 70%. Experimental results yield an increase of outcoupling efficiency of about 22%. A software model based on raytracing to simulate light outcoupling from OLEDs through a scattering layer is introduced to gain a deeper understanding of the light extraction mechanism. We found that the scattering anisotropy factor g determined using the Henyey–Greenstein phase function and the effective absorbance of the OLED device have strong impact on outcoupling efficiency.     

Focusing and scanning of ultrasound by spatial amplitude modulation

Spatial amplitude modulation (SAM) is proposed as an alternative to spatial phase modulation (SPM) techniques currently emplayed in most ultrasonic imaging systems. A simple implementation of a SAM-based imaging system using an optoacoustic transducer (OAT) is presented.     

Multiple radar targets detection by exploiting induced amplitude modulation

This work deals with the problem of detecting and estimating multiple radar targets present in the same range-azimuth resolution cell of a surveillance radar system with a mechanically rotating antenna. In the first part of the work, we tackled the problem of estimating target complex amplitudes, Doppler frequencies, and directions of arrival, and a consistent estimator based on the asymptotic maximum likelihood (AML) method was derived. In this second part, we tackle the "detection problem," which consists of determining the number of targets. First, the target parameters are estimated, assuming a maximum number of possible targets. Subsequently, these estimates are used in a successive hypotheses test procedure. The statistic of the test at each step of the procedure is derived by using an asymptotic expression of the generalized likelihood ratio test (GLRT) statistic. Performance of the proposed algorithm is investigated through both asymptotical analysis (as concerning the probability of false alarm) and Monte Carlo simulation.     

Electromagnetic scattering by stratified inhomogeneous anisotropic media

An analytical formulation is presented for the computation of scattering and transmission by general anisotropic stratified material. This method employs a first-order state-vector differential equation representation of Maxwell's equations whose solution is given in terms of a4 times 4transition matrix relating the tangential field components at the input and output planes of the anisotropic region. The complete diffraction problem is solved by combining impedance boundary conditions at these interfaces with the transition matrix relationship. A numerical algorithm is described which solves the state-vector equation using finite differences. The validation of the resultant computer program is discussed along with example calculations.     

Phase and amplitude modulation of light by light in silicon-on-insulator waveguides

Waveguided light modulation induced by visible light irradiation in oxidised silicon-on-insulator waveguides is reported. Both induced absorption and phase modulation were characterised. Phase modulation was measured in a waveguided Mach-Zehnder configuration. Less than 200 mW of power was required for 180/spl deg/phase change.     

High-frequency scattering by objects buried in lossy media

The uniform geometrical theory of diffraction (UTD) is extended so that it can be used to calculate the scattering from an object buried in a lossy medium. First, the accuracy of this high frequency method is examined by comparing numerical results for the scattering by a polygonal cylinder in a lossy medium of infinite extent with calculations based on a method of moments (MoM) solution. Next, the more difficult scattering problem of a polygonal cylinder in a lossy half space is treated. The UTD solution for the unbounded region is employed together with the fields of rays introduced by the interface between air and the lossy medium to obtain expressions for the scattered field in air and in the lossy medium     

双各向异性色散介质电磁波传播Z-时域有限差分分析

基于一种改进的Z变换-时域有限差分(Z-Finite-Difference Time-Domain,Z-FDTD)方法,即将双各向异性色散介质的频域本构方程先转化到Z域中,再利用Z变换的性质将其转换到时域,得到离散时域的FDTD迭代式,分析了双各向异性色散介质电磁波传播特性.由于Omega媒质是一种典型的双各向异性色散介质,以此为例编程计算了垂直入射在Omega介质板情形下产生的同极化和交叉极化电磁波的反射和透射情况,并通过算例和解析解对比验证了算法的正确性,最后对其电磁散射特性进行了分析.     

Imaging by microwave holography through aberrating media

Imaging through random aberrating media can be of interest not only in optics but also in microwaves or in acoustics. However, the holographic techniques applied in optics cannot be readily extended to microwaves without essential modifications. A different holographic method is here proposed which seems convenient at microwaves. The image is obtained by the product of the aberrated hologram with another compensating for the aberration. In the experiments two different procedures have been followed to perform the product of the two holograms, the optical and the electronic multiplication. The results obtained with the two procedures are shown, one of which allows the correction of time variant aberrations. With this technique there is no limitation in the off-set angles of the reference waves that could be also obtained by locally produced signals and no coherence is requested between the object and the compensating wave. The technique could be of interest, for instance, in plasma diagnostic and geophysical problems.     

空间光孤子在具有双势垒调制的克尔介质中的传播

主要考虑了在具有对称双势垒调制的克尔介质中的空间光孤子。采用数值模拟的方法,讨论了在两种不同类型的对称双势垒的作用下,单孤子和双孤子的空间传播行为。数值模拟结果表明,通过合理设计诸如调制深度,垒间间隔,单垒的宽度等这些双势垒的参数以及初始中心偏移和入射角度等入射光束的参数,可以实现孤子的捕获和控制。     

自聚焦材料周期长度的分布散射法测量

提出一种直接测量自聚焦材料周期长度的方法,可直接观察其轴向不匀性,并随之得出相应的分布常数;还可判断自聚焦棒和轴向分布板的离子交换深度及光轴;可用来同时测量n_(λ)、A(λ)。     

Optical theorems for electromagnetic scattering by inhomogeneitiesin layered dielectric media

The optical theorem, which relates the forward scattering amplitude to the total cross section of a scatterer in free-space, is extended to problems of scattering of an incident transverse electric plane wave or guided mode by inhomogeneities in lossless, waveguiding, dielectric interfaces or layers. The cases of a compact irregularity on either the interface between two unbounded dielectric media or in the waveguiding layer of a dielectric-slab waveguide are considered. Simple formulas that connect the scattered amplitudes of the different types of waves excited by the incident energy are derived. They can be used as an independent check of numerical codes when benchmark solutions are not available or are hard to obtain. In addition, a relationship between the scattered amplitudes and the spectral power of each excited wave is derived using the method of stationary phase     

Electromagnetic scattering by inhomogeneous dielectric bodies ofrevolution embedded within stratified media

A method of moments (MoM) solution for scattering by heterogeneous bodies of revolution (BOR) embedded within a multilayered environment is given. A modal volume integral equation (VIE) is formulated in the mixed potential form and solved with the use of the specialized basis functions     

Multiple scattering by discrete random media: a summation of planardiagrams

The multiple scattering of a scalar wave by a discrete random medium is considered. The scatterers are assumed to be isotropic, incorrelated, and distributed uniformly. The Feynman-diagram technique is used to formulate the problem, and the Dyson equation is derived with the occupation-number formalism. Among the terms of the mass operator, a topological class of `planar diagrams' is defined, excluding all the interactions involving the same particle three times or more. It is possible to achieve analytically the summation of such diagrams. The corresponding mean field is computed and compared with other approximations such as those of Born and Twersky. The result does not reduce to Twersky's even in the case of small concentrations of scatterers     

Multidomain pseudospectral time-domain simulations of scattering by objects buried in lossy media

A multidomain pseudospectral time-domain (PSTD) method with a newly developed well-posed PML is introduced as an accurate and flexible tool for the modeling of electromagnetic scattering by 2-D objects buried in an inhomogeneous lossy medium. Compared with the previous single-domain Fourier PSTD method, this approach allows for an accurate treatment of curved geometries with subdomains, curvilinear mapping, and high-order Chebyshev polynomials. The effectiveness of the algorithm is confirmed by an excellent agreement between the numerical results and analytical solutions for perfectly conducting as well as permeable dielectric cylinders. The algorithm has been applied to model various ground-penetrating radar (GPR) applications involving curved objects in a lossy half space with an undulating surface. This multidomain PSTD algorithm is potentially a very useful tool for simulating antennas near complex objects and inhomogeneous media.     

关于散射成像研究现状的一些思考（特邀）

透过散射介质的光学成像是人们长期追求但一直未能真正解决的问题。研究人员提出并发展了各种各样的方法和技术,从最早只利用弹道光的时间门和空间门技术,到后来利用了散射光的波前整形、散射矩阵测量和散斑自相关成像,再到近年热门的深度学习方法。尽管这些方法和技术都经过了毛玻璃、氧化锌薄膜、生物组织切片等薄散射介质的原理性验证,但随着介质厚度增加,所有方法和技术都迅速失效。厚度一直是难以克服的瓶颈。这篇评论归纳对比了散射成像的主要方法和技术,重新审视了经过散射介质波前被完全随机化等主流观点,分析了现有方法和技术无法透过厚散射介质成像的原因,并提出了未来有望真正解决问题的研究方向。