Passive ranging and a three-dimensional imaging system through wavefront coding

A single-image passive ranging and three-dimensional(3 D) imaging system with chiral phase encoding was proposed in 2011 [Opt. Lett. 36, 115(2011)]. A new theoretical analysis of the system in space domain is presented in this paper. We deduce the analytic relationships between the object distance and the point spread function, and between the object distance and the encoded image, respectively. Both the point spread function and the processed spectrum of the encoded image have two spots, which will rotate with the variation of the object distance. Then the depth map is extracted from the encoded image and it can be used to set up 3 D images. The theoretical analysis is verified by a wavefront coding system with a chiral phase which is generated by a phase-only liquid-crystal spatial light modulator. The phase generated by the liquid-crystal spatial light modulator is more flexible than the fixed phase mask and can be adjusted in real time. It is especially suitable for observing the object with a large depth of field.     

三维信息测量的运动声源无源测距

针对运动声源无源测距问题,给出了目标方位、多普勒频移和距离特征量作为测量信息来估计目标初始距离的方法。通过伪线性化的处理方法,构造了一个异方差的线性模型。在声呐平台直航条件下,证明了非径向运动的声源目标,利用3个目标方位、2个多普勒频移和2个距离特征量的观测信息,可以唯一地确定目标的距离、速度和航向,而仅利用目标方位和距离特征量的观测信息,系统是不可观测的。蒙特卡洛数值模拟表明:对于初始距离5 nm(海里)的情形,三维信息测量方法比参考方法的目标距离的平均收敛时间要少200 s左右,收敛时间标准差要少40 s左右。随着初始距离的增加,两种方法收敛时间差有变大的趋势,这意味着三维信息构造的方法的稳健性优于参考方法。实验数据也进一步验证了在300 s左右,目标距离的估计逐渐趋于收敛。因此,该方法可以在稳定的干涉结构条件下,实现运动声源的无源定位。     

Passive three-dimensional imaging using polarimetric diversity

The results of experiments in developing a method for extracting three-dimensional information from a scene by means of a polarimetric passive imaging sensor are summarized. This sensor provides a full Stokes vector at each sensor pixel location from which degree and angle of linear polarization are computed. The angle of linear polarization provides the azimuth angle of the surface normal vector. The depression angle of this surface normal vector is obtained in terms of the emitting object's index of refraction from the solution of an equation derived from Fresnel equations, Snell's law, and percent of linear polarization. Results of the application of this approach to simulated infrared polarimetric data are provided.     

Passive ranging of a moving sound source using three-dimensional measured information

To solve the problem of passive ranging of a moving sound source,a method of estimating the initial distance of target is presented by using the measured inform...     

Frequency-multiplexed profilometric phase coding for three-dimensional object recognition without 2pi pi phase ambiguity

A novel phase-coding technique based on Fourier-transform profilometry (FTP) is proposed for three-dimensional object recognition. Two spatially multiplexed grating patterns of different spatial frequencies are projected simultaneously onto the objects-target, and the phase changes in the distorted patterns are detected. An algebraic addition or subtraction of these phase values is utilized to code the two-dimensional plans of the objects-target with spatial harmonic modulations. The phase-coded plans of the objects and the target are cross correlated digitally to yield a high correlation peak at the target location. The 2pi ambiguity of the phase associated with FTP has been resolved in correlation results without recourse to phase unwrapping. Experimental results show an excellent discrimination capability for target recognition.     

Frequency-multiplexed profilometric phase coding for three-dimensional object recognition without 2pi phase ambiguity: errata

In the title of our previous Letter,(1) the "pi" was incorrectly printed as "mu". The correct title should be "Frequency-multiplexed profilometric phase coding for three-dimensional object recognition without 2pi phase ambiguity" as submitted.     

Simple, flexible calibration of phase calculation-based three-dimensional imaging system

One important step of phase-based three-dimensional imaging system is calibration, which defines the relationship between phase and depth data. Existing calibration methods are complicated and hard to carry out because of using a translation stage or gauge block in a laboratory environment. This Letter introduces a new simple, flexible calibration method by using a checkerboard and a white plate having discrete markers with known separation. The checkerboard determines the internal parameters of a CCD camera. The plate gives phase and depth data of each pixel to establish their relationship. Experimental results and performance evaluation show that the proposed calibration method can reliably build up the accurate relationship between phase map and depth data in a simple, flexible way.     

Holographic real-time imaging through a phase distorted medium

In this note we report on a new experiment using Fe-doped LiNbO₃ crystal (manufactured by ourselves) as a recording medium. It can compensate in real-time for the phase distorted wavefront of an object caused by a phase distorted medium (PDM). The wavefront of the object is required to pass through the PDM once only.     

Layer-by-layer three-dimensional chiral photonic crystals

We fabricate and characterize polymeric three-dimensional layer-by-layer chiral photonic crystals. The obtained circular dichroism from polarization stop bands is comparable with that of recently demonstrated circular-spiral photonic crystals. Moreover, telecommunication wavelengths are easily accessible with the layer-by-layer approach; even visible wavelengths are in reach.     

利用线谱起伏实现目标测距

常见水中目标辐射噪声的线谱会随目标运动而出现强弱起伏。不同号简正波之间的干涉是目标声强随距离起伏的主要原因,利用简正波水平波数差和波导不变量之间的关系,推导了不同线谱随距离变化起伏的理论关系式。基于此关系式,提出利用两条或多条线谱声强起伏进行声源测距的方法。针对两条线谱起伏测距方法存在的旁瓣问题,解释其形成原因,并提出用多条线谱声强起伏抑制旁瓣。数值仿真验证了方法的可行性,利用多条线谱声强起伏测距的方法可有效抑制旁瓣。海试数据分析表明,当连续谱部分非常微弱无法有效测距时,利用多条线谱声强起伏测距的方法仍能稳定的估计渔船目标距离,估计距离的平均相对误差为12%。     

Subwavelength imaging enhancement through a three-dimensional plasmon superlens with rough surface

In this Letter we investigate the subwavelength imaging of a three-dimensional plasmon superlens based on the full vector wave simulations of optical wave propagation and transmission. The optical transfer functions are computed. Comparisons are made between the results of lenses with flat and periodic/random rough surfaces. We also study the problem of practical imaging system geometry using laser as an illumination source. Results show that the lens with periodic or random roughness can reduce the field interference effects, and provide improved focus on the transmission field and the Poynting flux. We illustrate that the subwavelength roughness in a plasmon lens can enhance the image resolution over a flat lens for both matched and unmatched permittivity conditions. The enhancement of resolution occurs because the introduced subwavelength roughness can amplify the evanescent wave components and suppress the surface plasmon resonance peaks.     

时间和相位混合编码的量子密钥分发方案

提出了一种在双马赫-曾德尔干涉仪量子保密通信系统上同时实现时间编码和相位编码的混合量子密钥分发方案.提出的方案将原来相位编码方案中丢弃的脉冲进行时间编码,因此成码率是原方案的二倍.系统同时获得时间编码密钥和相位编码密钥,既可以一组用于通信,另一组用于监视窃听,又可以将两组密钥组合成新密钥.系统具有良好的应用前景. 关键词： 量子保密通信 量子密钥分发 相位编码 时间编码     

Instantons and the chiral phase transition

We examine the role of instantons in the zero-temperature chiral phase transition in an SU(N) gauge theory. For a range of N_f (the number of fermion flavors) depending on N, the theory exhibits an infrared fixed point at coupling _*. As N_f decreases, _* increases, and it eventually exceeds a critical value sufficient to trigger chiral symmetry breaking. For the case N = 2, we estimate the critical values of N_f and _* due to instantons by numerically solving a gap equation with an instanton-generated kernel. We find instanton effects of strength comparable to that of gluon exchange.     

The chiral and deconfinement phase transitions

By introducing the dressed Polayakov loop or dual chiral condensate as a candidate order parameter to describe the deconfinement phase transition for light flavors, we discuss the interplay between the chiral and deconfinement phase transitions, and propose the possible QCD phase diagram at finite temperature and density. We also introduce a dynamical gluodynamic model with dimension-2 gluon condensate, which can describe the color electric deconfinement as well as the color magnetic confinement.     

Direct-to-video holographic readout in quantum wells for three-dimensional imaging through turbid media

Customized photorefractive quantum-well devices have been developed for real-time video acquisition of coherence-gated, three-dimensional images in turbid media. Large-field-of-view holographic imaging with direct video capture is now possible. We have evaluated the role of intensity-limited device performance in Fourier-plane and image-plane holography in such devices and, using near-infrared light, have imaged through turbid phantoms of 13 mean free paths' scattering depth with 50-microm transverse and 60-microm depth resolution.     

Optical properties of a three-dimensional chiral metamaterial

A three-dimensional chiral metamaterial with four-fold rotational symmetry is designed, and its optical properties are investigated by numerical simulations. The results show that this chiral metamaterial has the following features: high polarization conversion, perfect circular dichroism, and asymmetric transmission of circularly polarized light. A comparison of the results of chiral metamaterials without and with weak coupling between the constituent nanostructures enables us to confirm that the optical properties of our proposed nanostructure are closely related to the coupling between the single nanoparticles. This means that the coupling between nanoparticles can enhance the polarization conversion, circular dichroism, and asymmetric transmission. Due to the excellent optical properties, our metamaterial might have potential applications in the development of future multi-functional optical devices.     

Passive scalars,three-dimensional volume-preserving maps,and chaos

The dynamics of a medium-sized particle (passive scalar) suspended in a general time-periodic incompressible fluid flow can be described by three-dimensional volume-preserving maps. In this paper, these maps are studied in limiting cases in which some of the variables change very little in each iteration and others change quite a lot. The former are called slow variables or actions, the latter fast variables or angles. The maps are classified by their number of actions. For maps with only one action we find strong evidence for the existence of invariant surfaces that survive the nonlinear perturbation in a KAM-like way. On the other hand, for the two-action case the motion is confined to invariant lines that break for arbitrary small size of the nonlinearity. Instead, we find that adiabatic invariant surfaces emerge and typically intersect the resonance sheet of the fast motion. At these intersections surfaces are locally broken and transitions from one to another can occur. We call this process, which is analogous to Arnold diffusion, singularity-induced diffusion. It is characteristic of two-action maps. In one-action maps, this diffusion is blocked by KAM-like surfaces.On leave of absence from the Departamento de Fisica, Universidad Nacional de La Plata, (1990), La Plata, Argentina.