Information encoding by spectral anomalies of spatially coherent light diffracted by an annular aperture

Extensive experimental study is carried out to investigate spectral behavior of spatially polychromatic coherent light diffracted by an annular aperture. It is found that the spectrum at the observation plane exhibits anomalous behavior after passing through the annular aperture. Experimental observations show that at a particular diffraction angle, the diffracted spectrum splits into two halves, while at other diffraction angles the spectrum either shifts towards lower wavelengths (blue-shift) or shifts towards higher wavelengths (red-shift). These spectral changes take place in the vicinity of the dark ring of the Airy pattern. Moreover, the behavior of the spectrum in the Fraunhofer region around a small circular loop centered at a critical direction is also studied and it is found that these spectral changes are qualitatively different from the spectral changes of the spectrum of the focused waves on a circle centered at the singular point. It is discussed in detail that such spectral anomalies of spatially coherent light may be exploited for information encoding and information hiding for free-space communications. The possibility to entangle bits in the spectral anomalies is also proposed. Such technique might be very useful to improve the throughput of information transmission in free space.     

Spectral anomalies and spectral switches of partially coherent and polychromatic light diffracted at an aperture

Inrecentyearsanewbranchofmodernphysicalopticscalledsingularoptics[1]hasbeendeveloped.In2002theworkinsingularopticswasextendedfrommonochromaticlighttospatiallyfullycoherentandpolychromaticlightbyGburetal.[2—4].Itwasfoundthat,whenaconverging,spatiallyfullycoherentandpolychromaticsphericalwaveisdiffractedatanaperture,anomalousspectralchangestakeplaceclosetozerosoftheintensityinthefarfield;i.e.thespectrumisredshiftedatsomepoints,blueshiftedatothers,andsplitintotwolineselsewhere.Thepredictionsofsp…     

任意发光类型的多色光照明下光栅塔尔博特效应的研究

利用部分相干光理论对多色光源照明下光栅的菲涅耳衍射进行了理论分析,得到了适用于任意发光类型(脉冲或连续发光)的多色光源的衍射光强的一般公式,理论结果表明菲涅耳衍射区的平均衍射光强的形式只与光源的频谱分布有关,这对借助于连续发光光源来研究脉冲光源照明下光栅的塔尔博特效应以及用来确定脉冲光源的性能参量提供了有力的参考依据。此外,详细讨论了光源的频谱分布对光栅塔尔博特效应的影响并进行了相应的数值计算。实验中通过选用不同频率的激光分别照明光栅,拍摄到对应于不同频率的衍射光强分布图像,从而间接获得多色光同时照明光栅时总的衍射光强分布。实验结果表明,理论和实验符合较好。     

Shaping and switching of polychromatic light in arrays of periodically curved nonlinear waveguides

We overview our recent theoretical results on spatio-spectral control, diffraction management, and broadband all-optical switching of polychromatic light in periodically curved one and two dimensional arrays of coupled optical waveguides. In particular, we show that polychromatic light beams and patterns produced by white-light and supercontinuum sources can experience wavelength-independent normal, anomalous, or zero diffraction in specially designed structures. We also demonstrate that in the nonlinear regime, it is possible to achieve broadband all-optical switching of polychromatic light in a directional waveguide coupler with special bending of the waveguide axes. Our results suggest novel opportunities for creation of all-optical logical gates and switches which can operate in a very broad frequency region, e.g., covering the entire visible spectrum. Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujście, Poland     

Polychromatic interface solitons in nonlinear photonic lattices

We demonstrate that interfaces between two nonlinear periodic photonic lattices offer unique possibilities for controlling the nonlinear interaction between different spectral components of polychromatic light, and a change in the light spectrum can have a dramatic effect on the propagation along the interface. We predict the existence of polychromatic surface solitons that differ fundamentally from their counterparts in infinite lattices.     

Slow-light optical bullets in arrays of nonlinear Bragg-grating waveguides

We demonstrate that propagation direction and velocity of optical pulses can be controlled independently in the structures with multiscale modulation of the refractive index in transverse and longitudinal directions. We reveal that, in arrays of waveguides with phase-shifted Bragg gratings, the refraction angle does not depend on the speed of light, allowing for efficient spatial steering of slow light. In this system, both spatial diffraction and temporal dispersion can be designed independently, and we identify the possibility for self-collimation of slow light when spatial diffraction is suppressed for certain propagation directions. We also show that broadening of pulses in space and time can be eliminated in nonlinear media, supporting the formation of slow-light optical bullets that remain localized irrespective of propagation direction.     

光谱开关与多色光场的奇点光学效应

推导出多色高斯光束和高斯-谢尔模型光束通过杨氏实验双缝传输的谱强度公式.对完全空间相干光和部分空间相干光照明杨氏实验装置出现的光谱开关作了详细研究,并判断其是否属于奇点光学效应. 结果表明：多色场奇点光学效应的判据应当是光谱开关出现时的谱强度极小值S_min=0,而不是总光强极小值I_min=0. 当用多色高斯-谢尔模型光束照明杨氏实验装置时,在近场和远场产生的光谱开关都不属于奇点光学效应. 当用多色高斯光束照明杨氏实验装置时,只有远场产 关键词： 光谱开关 奇点光学效应 完全相干和部分相干 多色光场     

Nonlinear directional coupler for polychromatic light

We demonstrate that a nonlinear directional coupler with special bending of waveguide axes can be used for all-optical switching of polychromatic light with a very broad spectrum covering all of the visible region. The bandwidth of the suggested device is enhanced five times compared with conventional couplers. Our results suggest novel opportunities for the creation of all-optical logical gates and switches for polychromatic light with white-light and supercontinuum spectra.     

基于开口环阵列结构的表面晶格共振产生及二次谐波增强

理论研究了二维周期排列的金开口环谐振器的磁共振模式与周期阵列的衍射模式发生强耦合所需满足的条件及其对二次谐波产生效率的影响.通过控制阵列结构在x和y方向的周期大小,使得衍射模式只在其中一个方向产生,当衍射模式的电场方向与入射光电场偏振方向一致时,衍射模式才会与开口环谐振器的磁共振模式发生强耦合作用,产生表面晶格共振进而实现近场场增强.在此基础上,进一步计算了金开口环谐振器阵列的二次谐波产生效率,随着阵列周期逐渐增大,即开口环谐振器的数密度减小,二次谐波强度呈现先增加后降低的趋势,当开口环谐振器数密度降为原来的1/4左右时,二次谐波强度可以增强2倍以上.本文的研究为金属超表面二次谐波产生效率的提高提供了一种新的可能途径.     

The correlation of the energy resolution of incident light with the measured reflectance of multilayers

This paper presents an expression for describing the correlation of the energy resolution of incident light with the measured reflectance of multilayers, and gives a new method for calculating the polychromatic-light reflectance of multilayers. Using this method we give the reflectance spectrum of some multilayers in the case in which the incident light is polychromatic. The theoretical analysis shows that for the multilayers of a given design the peak reflectance of the polychromatic light is smaller than that of the monochromatic light, but no-peak reflectance of the polychromatic light is bigger than that of the monochromatic light. Further, the measured reflectance spectrum will be a line if the energy resolution is less than a decided value. The shorter the design-wavelength of the multilayer, the stronger the effect of the energy resolution on the reflectance.     

Spectral changes of light produced by scattering from disordered anisotropic media

We investigate theoretically changes in the spectrum of polychromatic light scattered by a disordered, birefringent medium. We derive an expression for the spectrum of scattered light for ordinary and extraordinary incident waves within the accuracy of the first Born approximation. Using this result, we analyze the changes in the spectrum of light due to the combined action of disorder and anisotropy in the scattering process.     

Frequency shifts of spectral lines induced by scattering from a rotational anisotropic particle

We investigate the scattering of a polychromatic plane light wave incident upon an anisotropic particle. It is different from light wave scattered by an isotropic particle that the frequency shifts of spectral lines will be induced by the rotation of the anisotropic particle. The analytical expression for the spectrum of the scattered field is derived and numerical examples are also illustrated. We suggest an application that the angular speed of rotation of the anisotropic scatterer can be scaled by measurement of the spectrum of the scattered field.     

Spectral shifts produced by scattering from rotational quasi-homogeneous anisotropic media

The scattering of the polychromatic plane light wave incident upon rotational quasi-homogeneous anisotropic media is investigated. It is different from the light wave scattered by quasi-homogeneous isotropic medium in that the spectral shift can be produced by the rotation of the anisotropic medium. We derive the analytical formula for the spectrum of the scattered field and show some numerical examples.     

Spectral changes produced by static scattering on a system of particles

A formula of considerable generality is derived for the spectrum of light produced by static scattering of polychromatic light on a system of particles. It applies to deterministic as well as to random distributions of monodispersed or polydispersed particles. We illustrate it by examples. It is suggested that spectral changes produced by scattering could be used for determining the structure of some scattering systems.     

Enhancement of the broadband modulation diffraction efficiency of liquid-crystal displays

We report a method to maximize the broadband modulation diffraction efficiency of liquid-crystal spatial light modulators for polychromatic applications requiring a wide range of wavelengths. An optimized encoding pattern based on the minimum Euclidean projection principle is applied in order to increase the diffraction efficiency at large wavelengths that exhibit phase modulation depth lower than 2π. We demonstrate modulation efficiencies over 80% on a wavelength range from 454 to 633 nm, which can reach up to 98% when the range is reduced to 60 nm. Experimental results are shown to confirm the calculations.     

New approach to spectroscopy of surface plasmons

We report a novel approach to spectroscopy of surface plasmons based on the simultaneous excitation of surface plasmons by a polychromatic light and the dispersion of light on a diffraction grating coupler of a special design. This approach shows promise for the development of new, miniaturized, spectroscopic surface plasmon resonance (SPR) sensors. Potential of this approach for SPR sensing is demonstrated in a model refractometric experiment.     

EFFECTS OF MICROSTRUCTURES WITH DIMENSIONS SMALLER THAN OPTICAL WAVELENGTH ON SINGLE GROOVE DIFFRACTION

The experimental results showed that the microstructures of defects on the edges and walls of the single groove with their dimensions smaller than the wavelength of the incident light can produce effects not only on the diffraction of different polarization light but also on the symmetry of both positive and negative diffraction orders. It is possible to cause the narrow peaks with opposite directions appearing at corresponding positions on the two diffraction intensity curves when the polarization directions of the incident light are perpendicular to each other, and to cause the diffraction peaks to be asymmetric when the incident light for the two curves is of the same polarization direction.     

Appearance of extrema in the frequency shift produced by scattering from a rotational anisotropic particle

We investigate the analytical expression of the spectrum that is produced by scattering of a polychromatic plane light wave incident upon a rotational anisotropic particle. It is found that the appearance of extrema in the frequency shift of the scattered field can be exactly predicted by our derived equations of the rotation angle. Numerical examples are presented to illustrate the theoretical results and also to show the impact of the effective radius of the scattering potential on the frequency shift.     

Polychromatic reconstruction for volume holographic memory

We propose a method of reconstructing an image from a volume hologram at a wavelength different from the recording one. Spectrally broad but spatially coherent light was used as a probe beam. Each angular spectral component of the recorded hologram could be Bragg matched at one particular wavelength within the broadband spectrum. We experimentally demonstrated that a whole image could be reconstructed by using polychromatic light, whereas only a partial image was obtained by using single-mode laser light. We discuss the required bandwidth of the probe beam and the deformation of the reconstructed image.     

一种用多色光作为激发源产生拉曼光谱的新算法

探讨用多色光代替激光作为拉曼光源的新型拉曼光谱仪的可能性。根据拉曼光谱原理, 并通过数学分析, 发现当用多色光照射在样品上时, 所得到的散射光经散射频率校正后在不同频率上的强度分布可以写成样品的Raman-Rayleigh联合散射谱和激发光光源的功率谱的卷积。利用傅里叶变换算法,有可能从多色光照射样品所得到的散射光谱中导出样品的拉曼光谱。基于上述原理,可能发展出不用激光的新一代拉曼光谱仪。