Optimal design of sub-wavelength metal rectangular gratings for polarizing beam splitter based on effective medium theory

A novel optimal design of sub-wavelength metal rectangular gratings for the polarizing beam splitter （PBS） is proposed. The method is based on effective medium theory and the method of designing single layer antireflection coating. The polarization performance of PBS is discussed by rigorous couple-wave analysis （RCWA） method at a wavelength of 1550 nm. The result shows that sub-wavelength metal rectangular grating is characterized by a high reflectivity, like metal films for TE polarization, and high transmissivity, like dielectric films for TM polarization. The optimal design accords well with the results simulated by RCWA method.

Polarization control and tuning efficiency of tunable vertical-cavity surface-emitting laser with internal-cavity sub-wavelength grating

We design an 850 nm tunable vertical-cavity surface-emitting laser(VCSEL)structure using an internal-cavity sub-wavelength grating.The use of such a tuning structure allows for wider wavelength tuning range and more stable single-polarization as compared to conventional tunable VCSELs.The features of the internal-cavity grating effect on the wavelength tuning and polarization characteristics of the tunable VCSEL are analyzed.The simulation results show that the largest wavelength tuning range achieves 44.2 nm,and the maximum orthogonal polarization suppression ratio(OPSR)is 33.4 dB(TE-type)and 38.7 dB(TM-type).

Direct and real-time sub-wavelength resolution photoacoustic imaging method based on acoustic lens with negative refractive index

The signal processing technology based on material with negative refractive index provides researchers with the latest ideas. As a new nondestructive bio-photonic technology, photoacoustic tomography is a kind of imaging method based on the differences of optical absorption within the biological organization However, photoacoustic tomography by the scanning sensor or by the sensors array at present has its inherent disadvantages that may lead to poor real-time performance and high cost in the imaging process. The characteristics of acoustic lens with negative refractive index such as focusing, filtering and directional control on acoustic wave, are very suitable for solving the problem in photoacoustic tomography. With an analysis on the nega-tive quality response of acoustic lens and the advantages of negative refractive imaging, we proposed an approach using the lens to change the current photoacoustic imaging methods. The experiment showed that the imaging effectiveness of photoacoustic tomography by the designed lens is very impressive that the pressure distribution of the absorber is basically consistent with the image of the absorber. In addition, the result of 0. 6 times wavelength in the experimental image is demonstrated on sub-wave-length photoacoustic imaging through the lens designed in this work.

Theoretical investigation of hierarchical sub-wavelength photonic structures fabricated using high-order waveguide-mode interference lithograph

This paper presents the theoretical investigation of hierarchical sub-wavelength photonic structures with various periods and numbers of layers, which were fabricated using a high-order waveguide-mode interference field. A 442-nm laser was used to excite high-order waveguide modes in an asymmetric metal-cladding dielectric waveguide structure. The dispersion curve of the waveguide modes was theoretically analyzed, and the distribution of the interference field of high-order waveguide modes was numerically simulated using the finite-element method. The various dependences of the characteristics of hierarchical sub-wavelength photonic structures on the thickness and refractive index of the photoresist and the waveguide mode were investigated in detail. These hierarchical sub-wavelength photonic structures have various periods and numbers of layers and can be fabricated by a simple and low-cost method.

Lowering plasma frequency by enhancing the effective mass of electrons: A route to deep sub-wavelength metamaterials

Deep sub-wavelength metamaterials are the key to the further development of practical metamaterials with small volumes and broadband properties. We propose to reduce the electrical sizes of metamaterials down to more sub-wavelength scales by lowering the plasma frequencies of metallic wires. The theoretical model is firstly established by analyzing the plasma frequency of continuous thin wires. By introducing more inductance elements, the effective electron mass can be enhanced drastically, leading to significantly lowered plasma frequencies. Based on this theory, we demonstrate that both the electric and the magnetic plasma frequencies of metamaterials can be lowered significantly and thus the electrical sizes of metamaterials can be reduced to more sub-wavelength scales. This provides an efficient route to deep sub-wavelength metamaterials and will give rigorous impetus for the further development of practical metamaterials.

Experimental and numerical studies on the receiving gain enhancement modulated by a sub-wavelength plasma layer

A novel technique based on sub-wavelength plasma structure effects on enhancement of RF communication signals on a receiving antenna is carried out in this paper in laboratory experiments and analyzed by corresponding numerical simulations.Considerable intensification on receiving signal gain up to -10 d B in comparison with that without the plasma modulation is observed experimentally in -1 GHz RF band,with an effective enhancement bandwidth of -340 MHz and the fractional bandwidth of -34%.Then,the optimal modulation parameters of plasma are further studied by a numerical simulation.It is shown that the number density,the layer thickness,and the collision frequency of the plasma,as well as the relative distance between the plasma layer and antenna synergistically affect the modulation.Compared to the metallic antenna with the same overall dimension,the modulated antenna covered by the subwavelength plasma structure features higher receiving efficiency and lower radar cross section in the studied RF band.The mechanism of the reception enhancement is further revealed by analyzing characteristics of electromagnetic scattering and electric field distribution in the subwavelength plasma layer.The results then exhibit scientific significance and application potential of sub-wavelength plasma modulation on compact receiving antennas with higher performance and better feature of radar stealth.

Studies on omnidirectional enhancement of giga-hertz radiation by sub-wavelength plasma modulation

The technology of radio frequency （RF） radiation intensification for radio compact antennas based on modulation and enhancement effects of sub-wavelength plasma structures represents an innovative developing strategy. It exhibits important scientific significance and promising potential of broad applications in various areas of national strategic demands, such as electrical information network and microwave communication, detection and control technology. In this paper, laboratory experiments and corresponding analyses have been carried out to investigate the modulation and enhancement technology of sub-wavelength plasma structure on the RF electromagnetic radiation. An application focused sub-wavelength plasma-added intensification up to ~7 dB higher than the free-space radiation is observed experimentally in giga-hertz （GHz） RF band. The effective radiation enhancement bandwidth covers from 0.85 to 1.17 GHz, while the enhanced electromagnetic signals transmitted by sub-wavelength plasma structures maintain good communication quality. Particularly, differing from the traditional RF electromagnetic radiation enhancement method characterized by focusing the radiation field of antenna in a specific direction, the sub-wavelength plasma-added intensification of the antenna radiation presents an omnidirectional enhancement, which is reported experimentally for the first time. Corresponding performance characteristics and enhancement mechanism analyses are also conducted in this paper. The results have demonstrated the feasibility and promising potential of sub-wavelength plasma modulation in application focused RF communication, and provided the scientific basis for further research and development of sub-wavelength plasma enhanced compact antennas with wide-range requests and good quality for communication.

变周期亚波长介质光栅多层膜的双重Fano共振特性

现在众多传感结构模型只能对单变量待测样本折射率进行传感检测,为实现不同待测样本的高通量检测并降低环境因素的干扰,提出了一种基于波长调制的变周期亚波长介质光栅多层膜复合结构。以双周期为例进行分析,变周期光栅层由两个具有不同光栅周期的介质光栅A和B组成,通过有限元法对传输特性进行分析,TE偏振入射光以垂直于光栅层表面的方式入射至介质光栅表面,当在介质光栅区域A和B内分别满足相位匹配条件时,变周期亚波长介质光栅会形成GMR,提供两个具有单一窄带的双离散态共振缺陷峰;由于类F-P腔中含有周期性光子晶体,光波传播到光子晶体会产生光子禁带,提供一个较宽频带的连续态。在满足相位匹配条件时,变周期亚波长波导结构中形成的双离散态共振缺陷峰与周期性光子晶体多层介质薄膜构成的类F-P腔中形成的连续态发生耦合,实现双重Fano共振。然后通过探究波导层厚度dw和光子晶体周期数N对传感特性的影响,选择dw=97 nm和N=3,使其达到FOM值最大。最终因变周期介质光栅层是由两种具有不同介质折射率的材料构成,在介质光栅区域A和B的光栅凹槽部分可设置两个传感检测单元,建立基于波长调制的双重Fano共振全电介质传感模型,设置不同的传感检测区域,发现双重Fano光谱曲线在不同传感检测区域内都能随着ns1和ns2变化,间接实现了对待测样本折射率的动态检测,因而可在同一传感结构模型中实现对不同待测样本折射率区间的多变量检测。结果表明,在传感检测单元A内,FR1和FR2的FOM值分别为631.53和463.7 RIU^(-1);在传感检测单元B内,FOM值分别为480.67和834.04 RIU^(-1)。所设计的传感结构模型通过结构参数优化,实现了传感结构的高反射率、高FOM值和较宽的检测范围,对双重Fano共振提供了理论参考,对待测样本折射率的多变量检测具有一定的研究价值。

液晶调控下的亚波长金光栅反射相位

空间光调制器(Spatial Light Modulator,SLM)是实现光场调控的关键器件。本文研究了一种将亚波长金光栅嵌入硅基液晶(Liquid Crystal on Silicon,LCoS)构成的SLM(G-LCoS)器件模型的反射相位特性,该器件模型以ITO透明导电层和液晶构成G-LCoS中亚波长金光栅的非对称边界。首先运用散射矩阵原理给出了亚波长金光栅反射相位的计算表达式,其次给出了下表面液晶的有效折射率计算公式。在此基础上,利用TechWiz 3D软件模拟加电情况下金光栅下表面液晶指向矢的变化,给出金光栅下表面液晶有效折射率的变化值。将得到的有效折射率数据导入到FDTD Solutions软件,对该器件结构开展了相关的仿真实验和结果分析。综合考虑了上表面的ITO色散情况、金光栅高度变化以及不同电压下液晶有效折射率值,实现了可见光范围内多波长的近2π相位调制。本文研究的器件也为AR/VR显示系统以及全息视频显示的优化提供了一种新思路。

倾斜入射下超透镜亚波长聚焦特性研究

亚波长聚焦透镜被广泛应用于光学显微、成像和光刻等光学领域,具有亚波长结构的聚焦光场在倾斜入射下存在着严重影响光学成像质量的轴外像差。文章展示了一种高数值孔径(0.970)的光学超透镜设计方法,利用具有宽角度响应超原子的光场调控功能,结合孔径对倾斜入射光场的矫正,可同时满足倾斜入射时亚波长紧聚焦和宽带操作。数值仿真结果表明,在带有5μm孔径的超透镜中,可在倾斜入射角±30°范围内实现亚波长紧聚焦,峰值半高全宽范围为0.600~0.885λ;在550~750nm的入射波长范围内实现亚波长聚焦,并且其操作带宽达到200nm。

组合型亥姆霍兹通风吸声体低频宽带吸声特性研究

为解决低频段通风吸声效果差的问题,提出一种亚波长厚度的颈部嵌入式亥姆霍兹通风超材料吸声体,该结构由中央通风开放区域和周围布置的多谐振器两部分组成。通过精确设计每个共振单元,使吸声体在445~678 Hz频率范围内具有优异的吸声特性,吸声系数均在0.85以上。该结构厚度为40 mm,仅是445 Hz波长的1/20。分析嵌入颈部的吸声机制,指出结构在颈部位置处,会具有很强的黏性来耗散声波能量,且共振频率随着颈部嵌入的长度增加而向低频偏移。随后,通过实验验证通风吸声体的传递损失与计算结果符合良好,目标频段内传递损失平均提高6dB。因此,该功能结构的通风吸声体材料为在低频域实现高吸声能力的可行性得到验证。

基于TiO_(2)的近红外大数值孔径、高聚焦效率、高透射率会聚透镜

利用相位调控原理设计了一种基于TiO_(2)材料的具有非周期同心圆环形高折射率差亚波长光栅结构的会聚透镜,可实现大数值孔径、高聚焦效率、高透射率、低损耗特性,同时具有体积小、易集成的优点。采用时域有限差分法对提出的透镜结构进行仿真和分析,工作波长为850 nm时,该透镜透射率为90.5%,焦距约为10.4μm,焦斑的半高全宽为0.61μm。通过对仿真得到的数据进行分析,可得数值孔径为0.92,聚焦效率高达91.07%,损耗为0.41 dB,平衡了高数值孔径与高聚焦效率之间的矛盾,可在小器件直径下接近衍射极限实现点会聚效果。

基于微纳光纤双模式干涉的亚波长聚焦光场及光捕获应用

本文报道了一种基于微纳光纤中双模式干涉的亚波长聚焦方法.利用微纳光纤中两种特定导模在微纳光纤端面处的干涉效应,在微纳光纤端面出口处获得了具有单焦点或多焦点的聚焦光场,并可通过调节两个模式之间的相位差、功率比分别实现聚焦光场的焦深、焦斑相对强度调谐,从而实现对纳米颗粒可调谐的选择性捕获.根据聚焦光场中不同焦点处所对应的捕获刚度和势阱深度的不同,可以对不同大小的纳米颗粒实现分类.这种微型化全光纤的亚波长聚焦方法,将可应用于操纵纳米颗粒、超分辨率光学成像和纳米光刻等领域.

双束延时飞秒激光调控制备二维亚波长周期阵列结构

利用偏振垂直的双束延时蓝色飞秒激光(400 nm)经柱透镜聚焦扫描钼表面,获得了二维矩形周期排列的方形和(椭)圆形阵列结构,以及六边形周期排列的三角形阵列结构。最小结构尺寸和周期达到100 nm和280 nm。研究发现双束飞秒激光的能量密度和能量比是不同类型结构形成及形貌转化的关键参数。通过优化激光参数,实现了圆形和三角形阵列结构的大面积均匀制备。两种周期排布的阵列结构的形成与双束延时飞秒激光与材料作用的超快动力学过程之间的瞬态关联作用以及作用过程中表面等离激元波的共线和非共线激发密切相关。该二维周期阵列结构加工方法及理论可拓展至其它硬质金属和半导体硅表面。

Broadband filter using multi-layer sub-wavelength high-contrast grating structure

This paper proposed a novel broadband filter using multi-layer sub-wavelength high-contrast grating （HCG） structure. This filter has wide bandwidth and good sideband suppression. We simulated and analyzed the effects of different numbers of layers and different grating indexes on filtering performance of the broadband filter. According to the simulated results, we designed a multi- layer HCG broadband filter, which has bandwidth of 843 nm and center wavelength of 1550 nm.

用于AR显示技术的亚波长Al光栅的ICP刻蚀工艺研究

铝材料因其良好的光反射率和低热线性膨胀系数,被广泛应用在增强现实设备的光栅光波导中。采用ULVAC公司生产的电感耦合等离子体(ICP)刻蚀设备NE-550对Al材料进行了干法刻蚀工艺的研究。实验中采用SiO_(2)作为刻蚀掩膜,Cl_(2)/BCl_(3)气体作为工艺气体,通过对实验工艺参数的调整,探究了ICP源功率、射频偏压功率、腔体压强以及气体流量对Al的刻蚀速率、与上层掩膜的选择比的影响。最后通过优化工艺参数,得到了底部平整、侧壁垂直的栅槽结构。此研究为亚波长尺度的光栅刻蚀工艺的优化和技术突破提供了参考。

表面修饰的亚波长金属Cu狭缝结构透射特性研究

为了深入研究表面修饰余弦凹槽的亚波长结构对太赫兹波透射特性的调控规律,提出一种表面修饰余弦凹槽的太赫兹亚波长金属Cu狭缝结构,基于时域有限差分法,对亚波长金属Cu狭缝结构的太赫兹波透射光谱特性进行模拟。仿真结果表明,通过改变金属Cu狭缝结构上下表面余弦凹槽的结构排布、数量、周期、深度及狭缝深度、宽度等参量,实现了对太赫兹波透射强度的调控。

基于亚波长金属条阵列结构的太赫兹多频吸收器

基于亚波长金属条阵列结构,设计了一种结构简单的超材料太赫兹多频吸收器。运用CST仿真软件研究了亚波长金属条阵列单元结构内金属条数量和尺寸对太赫兹吸收光谱特性的影响。在0.5~2.6 THz频谱范围内,单金属条阵列结构的吸收峰随金属条尺寸的增大,谐振频率有一定的红移。啁啾金属条阵列结构能够实现多频带吸收和一定程度的宽带吸收特性,这对研究太赫兹成像、检测和电磁隐身具有重要意义。

新型背光系统导光板技术

传统背光系统结构复杂,成本高等问题越来越引起广泛关注。国内外对新型导光板的研究有一定的进展,设计方法包括利用导光板表面结构控制光的出射方向,通过偏光效应增加导光板的光能利用效率或者采用性能更优越的新型材料等,以达到导光板一体化、轻薄化和低成本目的。文章就目前新型导光板技术进行了讨论,并对未来导光板的发展方向做出展望。

面形误差对亚波长金属光栅偏振器性能的影响

基于严格耦合波理论分析了光栅面形误差对亚波长金属光栅偏振器偏振性能的影响.通过对数值结果的分析发现,光栅圆角误差、光栅侧壁倾斜误差和光栅表面粗糙误差对光栅的TM透射效率影响不大,但它们使得光栅的消光比明显降低.因此,面形误差使得光栅的偏振性能明显降低.理论分析表明,顶角为直角、侧壁垂直和表面光滑的理想矩形光栅结构的偏振性能最好.