Surface waves at the interface between tunable LC–MTMs and nonlinear media

The surface wave propagation at the interface between tunable metamaterials (MTMs) and nonlinear media is investigated. Tunable MTMs have a refractive index which can be tuned to negative?Czero?Cpositive values. The nonlinear media are assumed to have a Kerr-like refractive index. The dispersion equation is analytically derived and solved numerically. Results display the different behaviors of the propagating waves as the refractive index is tuned.     

Optically implemented broadband blueshift switch in the terahertz regime

We experimentally demonstrate, for the first time, an optically implemented blueshift tunable metamaterial in the terahertz (THz) regime. The design implies two potential resonance states, and the photoconductive semiconductor (silicon) settled in the critical region plays the role of intermediary for switching the resonator from mode 1 to mode 2. The observed tuning range of the fabricated device is as high as 26% (from 0.76 THz to 0.96 THz) through optical control to silicon. The realization of broadband blueshift tunable metamaterial offers opportunities for achieving switchable metamaterials with simultaneous redshift and blueshift tunability and cascade tunable devices. Our experimental approach is compatible with semiconductor technologies and can be used for other applications in the THz regime.     

太赫兹液晶材料与器件研究进展

液晶是一种性能优异的可调控光电功能材料,基于液晶的太赫兹器件有着广泛的应用前景,但高性能太赫兹功能器件的研发仍处于初级阶段.本文综述了太赫兹领域液晶材料与器件的研究现状,探讨了液晶技术与太赫兹技术相结合的发展趋势.     

银纳米颗粒复合超材料的数值和模拟研究

理论分析了单层银纳米颗粒及其复合超材料的电磁特性,并采用MATLAB数值计算和CST模拟对理论进行了验证.结果显示:4.75 nm银颗粒所形成的单层阵列的数值和模拟结果都有Lorentz共振效应出现,模拟结果相对于数值计算有红移现象,且有微弱的磁共振效应.进一步对采用4.75 nm颗粒复合而成的100 nm大颗粒模拟,结果表明:在800~1 000 nm区间共振得到负的实有效介电常量、负的实有效磁导率和负的折射率,说明100 nm复合球形颗粒具有很强的磁共振效应,与理论分析相符.     

Optimized guided mode resonant structure as thermooptic sensor and liquid crystal tunable filter

Applicability of guided mode resonant structures to tunable optical filtering and sensing is demonstrated using nematic liquid crystals. As a sensor, a minimum refractive index detectivity of 10^-5 is demonstrated while as a tunable filter, tunability range of few tens of nanometers with 2-nm bandwidth is presented. The optimum design is achieved by maximizing the evanescent field region in the analyte which maximizes the overlap integral. The device can be operated in reflection or transmission modes at normal incidence. It can also be operated at a single wavelength by measuring the angular profile of the light beam.     

Microwave generator based on tunnel-coupled semiconductor-metamaterial structure

We propose a model of a tunable laser based on a tunnel-coupled waveguide semiconductormetamaterial structure. The waveguide semiconductor channel has a positive refractive index and a high Kerr nonlinearity coefficient. In the frequency range under investigation, the channel formed by the magnetoactive metamaterial is characterized by a negative refractive index. Computer simulation is used for investigating the peculiarities of generation of microwave radiation under pumping due to modulated instability in the semiconductor channel and a distributed feedback. The generation frequency is controlled using the dependence of the refractive index of the metamaterial on the external magnetic field.     

Novel optical devices based on the tunable refractive index of magnetic fluid and their characteristics

As a new type of functional material, magnetic fluid (MF) is a stable colloid of magnetic nanoparticles, dressed with surfactant and dispersed in the carrier liquid uniformly. The MF has many unique optical properties, and the most important one is its tunable refractive index property. This paper summarizes the properties of the MF refractive index and the related optical devices. The refractive index can be easily controlled by external magnetic field, temperature, and so on. But the tunable refractive index of MF has a relaxation effect. As a result, the response time is more than milliseconds and the MF is only suitable for low speed environment. Compared with the traditional optical devices, the magnetic fluid based optical devices have the tuning ability. Compared with the tunable optical devices (the electro-optic devices (LiNbO₃) of more than 10 GHz modulation speed, acoustic-optic devices (Ge) of more than 20 MHz modulation speed), the speed of the magnetic fluid based optical devices is low. Now there are many applications of magnetic fluid based on the refractive index in the field of optical information communication and sensing technology, such as tunable beam splitter, optical-fiber modulator, tunable optical gratings, tunable optical filter, optical logic device, tunable interferometer, and electromagnetic sensor. With the development of the research and application of magnetic fluid,a new method, structure and material to improve the response time can be found, which will play an important role in the fields of optical information communication and sensing technology.     

太赫兹波段超材料的制作、设计及应用

本文从制作方法、结构设计和材料选择几方面综述了超材料在太赫兹波段的电磁响应特性和潜在应用。首先,介绍了获得不同维度、具有特异电磁响应以及结构可调超材料的各种微加工制作方法,进而分析和讨论了超材料的电磁响应特性。文中指出,结构设计可以控制超材料的电磁响应特性,如各向异性、双各向异性、偏振调制、多频响应、宽带响应、不对称透射、旋光性和超吸收等。超材料的电磁响应依赖于周围微环境的介电性质,因而可用于制作对环境敏感的传感器件。此外,电光、磁光、相变、温度敏感等功能材料的引入可以获得光场、电场、磁场、温度等主动控制的太赫兹功能器件。最后,简单介绍了超材料在太赫兹波段进一步发展所面临的机遇和挑战。     

Tunable negative index metamaterial using yttrium iron garnet

A magnetic field tunable, broadband, low-loss, negative refractive index metamaterial is fabricated using yttrium iron garnet (YIG) and a periodic array of copper wires. The tunability is demonstrated from 18 to 23 GHz under an applied magnetic field with a figure of merit of 4.2 GHz/kOe. The tuning bandwidth is measured to be 5 GHz compared to 0.9 GHz for fixed field. We measure a minimum insertion loss of 4 dB (or 5.7 dB/cm) at 22.3 GHz. The measured negative refractive index bandwidth is 0.9 GHz compared to 0.5 GHz calculated by the transfer function matrix theory and 1 GHz calculated by finite element simulation.     

基于锑化铟亚波长阵列结构的太赫兹聚焦器件

基于锑化铟材料在太赫兹波段的横向磁光效应,提出了一种金属-空气-锑化铟-金属非对称周期性亚波长线栅阵列结构的表面等离子体器件,研究了外加磁场和温度对不同频率透射波聚焦特性的影响.结果表明,在外加磁场强度B=0.6 T、温度T=172 K时,可实现0.8 THz透射光束的聚焦,焦点处能流密度透过率比没有外加磁场时增强28倍.对于不同频率入射波,通过主动调节磁场强度和温度,能实现从0.4—0.8 THz宽频带的聚焦,而且焦点处的透过率相比于无外加磁场时的普通狭缝聚焦透过率增强20倍以上,该器件是太赫兹波段理想的可调谐、宽频段、高透过率的聚焦器件.     

吡虫啉的太赫兹(THz)光谱研究

由超短激光脉冲产生的脉冲波是具有较宽频带的电磁辐射,属于远红外波段,该波段电磁波与物质的相互作用是个崭新的研究领域。文章利用太赫兹时域光谱技术测量了室温下吡虫啉在0.2～2.0 THz范围内的吸收谱和折射率谱。结果表明吡虫啉在此波段有明显的特征吸收峰且吸收系数随频率的增加而增大,折射率也随频率的增加而有所增大,其平均折射率为1.65。实验研究的同时,运用半经验理论计算了吡虫啉分子的结构及其在太赫兹波段的振动频率,并根据计算结果对实验数据进行了解析。计算结果与实验光谱吻合得很好,实验光谱的特征吸收峰是由分子的集体振动及扭转形成, 不同的吸收峰位对应分子不同的振转模式。实验和理论研究的对比表明：分子的远红外吸收特征对于分子的结构和空间排列非常敏感,THz-TDS是研究生物分子集体振动模式和构象结构的好方法。     

Interaction dynamics of bright solitons in linearly coupled asymmetric systems

In this research work, composite media based on metamaterials including random distribution of spherical nanoparticles in a polymeric foam host are suggested to achieve negative effective refractive index in the visible spectrum. For this purpose structures including single, two and three layer spherical particles are investigated. Based on simulation results, media including single layer spheres (metallic and dielectric particles) and two layer nanospheres (core–shell particles consist of metallic core and dielectric shell) based on superposition of nanoparticles with different sizes and fill fractions are proposed for desired result. In this work, to obtain optimized band with negative RI media, superposition of three layer nanoparticles and doped semiconductor are designed.

     

紧凑型自由电子激光THz源上四极磁铁的设计及测量

基于自由电子激光（FEL）的太赫兹源具有高功率、高效率、波谱范围宽且连续可调、波束质量好等显著优点,目前是获得最高输出功率的方法。紧凑型太赫兹源使整体装置小型化,减少了装置成本和占用空间,但依然可以提供高功率、高品质的太赫兹波束,是一种便利可靠的用户装置。由于空间限制,FEL上的磁铁要尽可能地减小其尺寸,并仍能满足束流参数设计要求。本文设计的四极磁铁磁轭孔径与有效长度,其中2块是64 mm100 mm,另外3块是45 mm100 mm。这些四极磁铁的磁场梯度可以达到0.6~1.9 Tm-1。采用Poisson和Oprra-3D软件进行四极磁铁的二维和三维仿真计算,设计优化四极磁铁的结构,并测量了加工完成后的四极磁铁的磁场。     

Method for retrieving the refractive index of ordered particles from data on the photonic band gap

A method for retrieving the refractive index of spherical particles arranged into ordered structures is proposed. It is based on the solution of the inverse problem using data on the photonic band gap. The solution has been obtained within the quasi-crystalline approximation of the multiple wave scattering theory and the transfer-matrix method. Quantitative results are presented for systems of silicon oxide particles. The effective refractive indices of synthetic opal particles have been found from the available experimental data on the spectral position of the photonic band gap. The described technique is applicable for retrieving not only the refractive index of particles but also other characteristics of ordered particulate structures from the coherent transmittance spectra.     

非球形椭球粒子参数变化对光偏振特性的影响

针对自然界中多数沙尘、烟煤粒子的非球形问题, 在球形粒子偏振特性的基础上, 进一步研究非球形椭球粒子的折射率、有效半径、粒子形状等参数变化对光偏振特性的影响, 采用基于T矩阵的非球形粒子仿真方法, 模拟非偏振光经椭球粒子传输后光的偏振特性及其与球形粒子间的差异, 并以实际沙尘、海洋、烟煤三种气溶胶粒子为例说明结果的正确性. 结果表明: 当折射率实部越小, 虚部越大时, 球形粒子与非球形粒子的偏振差异越不明显; 当粒子有效半径增加时, 球形粒子偏振度的变化比非球形粒子更为明显, 且最大值分别出现在散射角为150°和120°的位置; 当粒子形状不同时, 不同形状椭球及球形粒子的差异在散射角小于60° 时并不明显, 且当椭球粒子纵横比互为倒数时, 两种粒子的偏振特性近似相同. 通过以上分析可知, 在光传输过程中, 椭球粒子多数情况下无法被近似为球形粒子进行计算.     

快速可调谐电光聚合物波导光栅

提出并设计了快速可调谐电光聚合物波导光栅.该波导光栅通过极化聚合物的线性电光效应 可实现谐振波长的纳秒级快速调谐，调谐灵敏度为61pm/V.研究了该波导光栅的反射谱和透 射谱特性与光栅周期,周期数,折射率调制函数及其调制大小的关系.讨论了波导光栅的材料 选择,制备工艺,快速可调谐性和偏振相关性.该波导光栅不仅克服了光纤光栅调谐速度慢和不利于大规模集成的不足，而且具有调谐灵敏度高,制备工艺与半导体工艺兼容和偏振无关 等优点. 关键词： 光通信器件 光波导 电光效应 聚合物 波导光栅 光纤光栅     

反式油酸的太赫兹光谱研究

应用太赫兹时域光谱技术研究了反式油酸在THz波段的光学特性,在室温氮气环境下获得了0.5～2.5 THz范围内波段的吸收光谱和折射率谱,结果表明反式油酸在此波段内存在多个特征吸收峰,样品的平均折射率为1.43.采用密度泛函理论的B3LPY方法对反式油酸分子的结构和振动频率进行了模拟,并采用Gaussian View软件...     

Thermally tunable THz filter made of semiconductors

By using the finite-difference time domain method, the transmission properties of terahertz wave passing through two different periodic subwavelength structures on InSb semiconductor slabs under different temperatures have been investigated. The results show that the peak transmittance increases and the transmittance peak has a blue shift when the temperature is increasing. It is extremely versatile to control the tunable THz filter by varying the temperature.     

Refraction of surface spin waves in spatially inhomogeneous ferrodielectrics with biaxial magnetic anisotropy

The refractive index of surface spin waves propagating in a ferromagnetic medium with a nonuniform distribution of the parameters of uniaxial and orthorhombic magnetic anisotropies and exchange coupling is determined within the spin-density formalism. The coefficients of reflection and transmission of spin waves at the interface between two homogeneous magnets with different constants of uniaxial and orthorhombic magnetic anisotropies, exchange coupling, and saturation magnetization are calculated. The dependences of the intensity of a reflected wave and the refractive index on the wave frequency and the strength of an external dc homogeneous magnetic field are determined.     

On the influence of strong electric and magnetic fields on spatial dispersion and anisotropy of the optical properties of a semiconductor

Nonperturbative methods were used to construct a single-integral equation for the photon polarization operator in a semiconductor in strong electric and magnetic fields of arbitrary orientations. Spatial dispersion was taken into account. The external field configurations at which its influence could be ignored were found. Asymptotic equations for the field dependences of the absorption coefficient and refractive index were obtained. The neglect of the spin of particles was shown to lead to a fundamentally false idea of magnetic field effects on the optical properties of nonconducting crystals.