通过磨砂玻璃滤光片产生浴帘效应抑制水下噪声

该文提出并实验验证了一种可通过磨砂玻璃滤光片诱导的浴帘效应来抑制水下噪声的方法.在实验中,在水槽中的水被蓝色墨水污染,以添加随机分布的散射颗粒,并使用蠕动泵产生湍流噪声.携带图像信息的扩展光束穿过水槽,进入电荷耦合器(CCD)用于图像记录.对比结果表明:由于磨砂玻璃滤光片起到空间低通滤光的作用,所以可以大大提高记录图像的可见度;通过高斯拉普拉斯(LoG)算法和人工智能算法,插入磨砂玻璃滤光片的图像处理效果也优于没有磨砂玻璃滤光片的.该方法方便且经济,在资源勘探和海底考古中具有潜在的应用价值.

Orbital angular momentum conversion of acoustic vortex beams via planar lattice coupling

Orbital angular momentum(OAM)conversion is critical in understanding interactions between a structural sound field and a planar lattice.Herein,we explore the evolution of a monochromatic acoustic vortex beam(AVB)that is scattered by a phononic crystal(PnC)or a correlated random lattice.The phenomenon is ascribed to the enhanced orbit–orbit angular momentum coupling induced by the band structure.By modifying the coupling condition,accurate and continuous micromanipulation of AVBs can be achieved,including the transverse/lateral gravity shift,the dynamics of the phase singularities,and the spatial distribution of acoustic pressure,etc.This research provides insight to the inhomogeneous coupling of AVBs with both propagating Bloch waves and localized Anderson modes,and may facilitate development of novel OAM-based acoustic devices for active sound field manipulation.

Morphological analysis for thermodynamics of cavitation collapse near fractal solid wall

A fractal geometric boundary with natural wall features is introduced into a hybrid lattice-Boltzmann-method(LBM)multiphase model. The physical model of cavitation bubble collapse near the irregular geometric wall is established to study the thermodynamic characteristics of the bubble collapse. Due to the lack of periodicity, symmetry, spatial uniformity and obvious correlation in the LBM simulation of the bubble collapse near the fractal wall, the morphological analysis based on Minkowski functional is introduced into the thermodynamic investigation of cavitation bubble so as to analyze and obtain the effective information. The results show that the Minkowski functional method can employed to study the temperature information in complex physical fields hierarchically and quantitatively. The high/low temperature region of the cavitation flow is explored, and thermal effect between irregular and fractal geometric wall and cavitation bubble can be revealed. It illustrates that LBM and morphological analysis complement each other, and morphological analysis can also be used as an optional and potential tool in research field of complex multiphase flows.

黄炎培产教融合思想下城轨PLC课程“岗课赛证创”教学改革探索

PLC课程是城市轨道交通专业的核心课程,在传统教学模式下出现了“课岗脱节”“课赛脱节”“课证脱节”“课创脱节”等痛点问题。为深化教学改革,培养高素质全面技能型人才来适应当下城市轨道交通快速发展的需要,应以黄炎培产教融合思想为基本导向,探索“岗课赛证创”课程教学,将城市轨道交通岗位任务、技能竞赛、职业证书、创新创业项目融入PLC与变频器技术课程教学,以更好地培养“技术硬、上手快、证书全、敢创新、善协作”的高素质技术技能型人才。

Surface lattice resonance of circular nano-array integrated on optical fiber tips

As metallic nanoparticles are arranged to form a 2D periodic nano-array,the coupling of the localized surface plasmonic resonance(LSPR)results in the well-known phenomenon of surface lattice resonances(SLRs).We theoretically investigate the SLR effect of the circular nano-array fabricated on the fiber tips.The difference between the 2D periodic and circular periodic arrays results in different resonant characteristics.For both structures,the resonant peaks due to the SLRs shift continuously as the array structures are adjusted.For some specific arrangements,the circular nano-array may generate a single sharp resonant peak with extremely high enhancement,which originates from the collective coupling of the whole array.More interestingly,the spatial pattern of the vector near-field corresponding to the sharp peak is independent of the polarization state of the incidence,facilitating its excitation and regulation.This finding may be helpful for designing multifunctional all-fiber devices.

金属纳米颗粒二聚体阵列的消光截面

相比单粒子阵列,金属纳米颗粒的二聚体阵列的共振效应受更多因素的影响,包括阵列的组成方式、二聚体的结构和朝向、粒子的形状、大小等,因此具有更好的可调性.本文基于修正长波近似法,通过引入两种粒子之间的阵列因子矩阵,修正了两种粒子的极化率,从而得到了二聚体阵列的消光截面的解析公式.在此基础上,讨论了整个阵列在不同偏振光激发下的共振的调制和偏振特性.

Angular-modulated spatial distribution of ultrahigh-order modes assisted by random scattering

In designing an optical waveguide with metallic films on a nanometer scale, the random scattering by the natural roughness of the thin film is always ignored. In this paper, we demonstrate that for the ultrahigh-order modes（UOMs） in the symmetric metal cladding waveguide, such a scattering leads to drastic variations in their spatial distribution at different incident angles. Owing to the high mode density of the UOMs, the random scattering induced coupling can be easily related to different modes with different propagation directions or wavenumbers. At small incident angles, the intra-mode coupling dominates, which results in a spatial distribution in the form of concentric rings. At large incident angles, the inter-mode coupling plays the most important role and leads to an array-like pattern. Experimental evidence via optically trapped nanoparticles support the theoretical hypothesis.

基于双折射MIM结构的增强光自旋霍尔效应研究

光自旋霍尔效应所产生的横向IF(Imbert-Fedorov)位移一般仅为亚波长量级,因此极大地限制了该效应在精密度量领域的应用.该文提出一种金属/双折射材料/金属(MIM)的多层结构,通过直接耦合方式激发该结构中的振荡模式,并利用双折射特性形成偏振相关的小角度共振,以此来增强光自旋霍尔效应.理论分析表明:上述设想可将可见光波段的横向IF位移增强到可以直接观察的亚毫米甚至毫米量级.

基于金属包覆光波导气体传感器的地铁空气环境光纤监测网设计

为了设计具有高灵敏度探测能力、稳定可靠和低成本等优点的地铁有毒有害气体监测系统,采用金属包覆光波导传感器作为地下空间中有毒有害气体的检测终端,并结合光纤传输技术建立完整的气体监测网络系统。通过数值仿真方法,阐明了金属包覆光波导结构作为气体传感器的工作原理,仿真结果表明传感器具有极高的灵敏度,同时给出了光纤监测网络的设计方案,相关结果为地铁环控系统中空气质量监测的方案设计提供了参考和启发。

Loss induced negative refraction and super-prism effect at highly absorptive interface

It is well-established that waves are inhomogeneous in a lossy isotropic medium, and the validation of the classical Snell's law is still questionable for light refraction at the dissipative and dispersive interface. With high absorption, direct experimental investigation is rather difficult due to the extremely short penetration depth; i.e., the skin depth. In this paper, a simple and unified description of this issue is proposed, which can be applied to both materials with anomalous dispersion and in the Drude region. The gradient ▽_k~ω is found to be incident angle θ_i-dependent, and the direction of the group velocity may deviate significantly from the phase velocity due to the loss induced permittivity structure. The physics behind the negative refraction effect is explained, and a novel loss induced super-prism effect is also predicted.

Propagation dynamics of off-axis noncanonical vortices in a collimated Gaussian beam

It is widely accepted that an off-axis noncanonical vortex moves across the free-space diffracting Gaussian beam without rotation. But our analysis shows that the vortex swirls a while before it approaches infinite. By neglecting the divergence of the host beam, we focus on this rotation characteristics of the vortices in linear homogeneous media. For the symmetrical host beam, it is found that the vortex moves along an elliptical trajectory, while the topological charge and the angular momentum of the vortex core relative to the beam axis are conserved. For the asymmetrical host beam, the vortex trajectory is rather complicated, since the noncanonical parameter varies as the light propagates, resulting in topological charge inversion. But we find that the vortices are always confined in a rectangular area, and the rotation direction is determined by the topological charge.

Fractal microstructure of Ag film via plasma discharge as SERS substrates

According to the atmospheric pressure plasma(APP)technology,we propose a rapid synthetic approach of the substrates for enhanced Raman spectroscopy.The plasma is used to modify and etch the surface of silver film,which generates large scale hotspots'aggregation.By switching the discharge polarity and adjusting the film thickness,different surface morphologies are formed due to the oxidation,reactive etch and accumulation of the plasma product in a certain space.Especially under positive corona discharge condition,dense snake-like microstructures are formed by the gradual connection of individual nanoparticles,which are driven by the influence of the electric field on surface diffusion.In addition,the experiments verify that the corresponding enhancement factor(EF)raises at least five orders of magnitude and the treatment time is about 10 min.

Highly twisted M-line of a vortex beam due to the coupling of ultrahigh-order modes

In modern optics, particular interest is devoted to the phase singularities that yield complicated and twisted phase structures by photons carrying optical angular momentum.In this paper, the traditional M-line method is applied to a vortex beam(VB) by a symmetric metal cladding waveguide chip, which can host numerous oscillating guided modes via free space coupling.These ultrahigh-order modes(UOMs) result in high angular resolution due to the high finesse of the resonant chip.Experiments show that the reflected pattern of a VB can be divided into a series of inner and outer rings, whilst both of them are highly distorted by the M-lines due to the UOMs’ leakage.Taking the distribution of the energy flux into account, a simple ray-optics-based model is proposed to simulate the reflected pattern by calculating the local incident angle over the cross section of the beam.The theoretical simulations fit well with the experimental results, and the proposed scheme may enable new applications in imaging and sensing of complicated phase structures.

Simple Raman scattering sensor integrated with a metallic planar optical waveguide: effective modulation via minor structural adjustment

We report experimental realization of Raman spectra enhancement of copper phthalocyanine, using an on-chip metallic planar waveguide of the sub-millimeter scale. The oscillating ultrahigh order modes excited by the direct coupling method yield high optical intensity at resonance, which is different from the conventional strategy to create localized ＂hot spots.＂ The observed excitation efficiency of the Raman signal is significantly enhanced,owing to the high Q factor of the resonant cavity. Furthermore, effective modulation of the Raman intensity is available by adjusting the polymethyl methacrylate（PMMA） thickness in the guiding layer, i.e., by tuning the light–matter interaction length. A large modulation depth is verified through the fact that 10 times variation in the enhancement factor is observed in the experiment as the PMMA thickness varies from 7 to 23 μm.

Negative Refraction at a Lossy Interface and a Bold Hypothesis via Complex Frequency

We investigate the negative refraction effect at a planar interface of a highly absorptive material,where the direct experimental verification is difficult because of the loss-induced skin depth effect. An apparent contradiction occurs when we try to determine the group velocity direction by the method of equifrequency contours(EFCs) in detail. This contradiction forbids any physical solution to be found for negative refraction.We conclude that this paradox is mainly caused by the definition of complex wavevector ■which is conventionally adopted in the case of complex permittivity. The complex wavevector may result in ambiguously defined optical path, which limits the application of the classical Snell’s law. We propose a bold suggestion that the complex wavevector■ should be replaced by a complex frequency■ . Therefore, the optical path can always be defined as real. The proposed hypothesis is capable of resolving the contradiction about the loss-induced negative refraction,and the obtained theoretical prediction fits well with the reported experimental results.