Radiative intensity solution and thermal emission analysis of a semitransparent medium layer with a sinusoidal refractive index

The radiative intensity in a sinusoidal refractive index semitransparent medium layer is solved by the curved ray-tracing method in combination with the pseudo-source adding method. One boundary of the medium layer is an opaque diffuse substrate wall. The other boundary is a semitransparent specular or diffuse surface, from which the medium thermal emission emerges. With considering a linear temperature distribution, the radiative intensity formulae are, respectively, deduced under the two boundary conditions. On the basis of the radiative intensity solutions, the directional and hemispherical emission of the medium layer with a specular surface as well as the hemispherical emission of that with a diffuse surface are calculated. The influences of the optical thickness, sinusoidal refractive index distribution and linear temperature distribution on the thermal emission are investigated. The results show that the effects of refractive index and temperature distribution are significant and are different under the two reflecting modes of the surface.     

Design and optimization of a SiC thermal emitter/absorber composed of periodic microstructures based on a non-linear method

Spectral and directional control of thermal emission based on excitation of confined electromagnetic resonant modes paves a viable way for the design and construction of microscale thermal emitters/absorbers. In this paper, we present numerical simulation results of the thermal radiative properties of a silicon carbide(Si C) thermal emitter/absorber composed of periodic microstructures. We illustrate different electromagnetic resonant modes which can be excited with the structure,such as surface phonon polaritons, magnetic polaritons and photonic crystal modes, and the process of radiation spectrum optimization based on a non-linear optimization algorithm. We show that the spectral and directional control of thermal emission/absorption can be efficiently achieved by adjusting the geometrical parameters of the structure. Moreover, the optimized spectrum is insensitive to 3% dimension modification.     

Ultrafast dynamics of surface plasmon polaritons in plasmonic metamaterials

Using near-field scanning optical microscopy and ultrafast laser spectroscopy, we study the linear optical properties of subwavelength nanoslit and nanohole arrays in metal films, which are prototype structures for novel plasmonic metamaterials. Near-field microscopy provides direct evidence for surface plasmon polariton (SPP) excitation and allows for spatial imaging of the corresponding SPP modes. By employing spectral interferometry with ultrashort 11-fs light pulses, we directly reconstruct the temporal structure of the electric field of these pulses as they are transmitted through the metallic nanostructures. The analysis of these data allows for a quantitative extraction of the plasmonic band structure and the radiative damping of the corresponding SPP modes. Clear evidence for plasmonic band gap formation is given. Our results reveal that the coherent coupling between different SPP modes can result in a pronounced suppression of radiative SPP damping, increasing the SPP lifetime from 30 fs to more than 200 fs. These findings are relevant for optimizing and manipulating the optical properties of novel nano-plasmonic devices. PACS 42.70.Qs; 07.79.Fc; 42.25.-p     

Effect of phonons on optical properties of RbCl quantum pseudodot qubits

In this work, an electron which is strongly coupled to the strong electron-longitudinal optical (LO) phonon in RbCl quantum pseudodot qubits is considered. First, we employ the Pekar variational method and obtain the eigenenergies and eigenfunctions of the ground and the first-excited states of the system. Then, we have studied optical properties of the system under strong electron-LO phonon coupling. In this regard, the refractive index changes and absorption coefficient of the system are obtained using compact-density-matrix approach and iterative method. It is found that the absorption coefficients show saturation in the presence of phonon effect. This behavior occurs at small quantum size and for different potential height. Our results show that both the structure parameters and phonon effect have a great effect on the total absorption and refractive index changes.     

Efficient directional excitation of surface plasmon polaritons by partial dielectric filling slit structure

In this paper, we investigate the excitation of surface plasmon polariton (SPP) in the metallic slit partly filled with dielectric by using the finite-difference time-domain method. It is found that the slit structure displays high asymmetry in the field distribution and SPP excitation due to the difference in matching degree of SPP wavevector on the two sides of slit exit. At certain incident wavelengths, the power flow carried by SPP modes on one side of slit exit is over three orders of magnitude greater than that on the other side, an efficient directional excitation is achieved. The SPP generation efficiencies on both sides of slit exit can be periodically adjusted by the dielectric width, but their changes are not synchronous, implying that such slit structure could be acted as a directional splitter/coupler. Moreover, the asymmetry degree of SPP excitation can also be modulated by the refractive index of dielectric layer.     

Plasmonic Mach-Zehnder interferometric sensor based on a metal-insulator-metal nanostructure

A plasmonic Mach-Zehnder interferometric sensor based on a semicircular aperture-slit nanostructure patterned on a metal-insulator-metal film is proposed and demonstrated by finite difference time domain(FDTD) simulation. Due to the interference between two different surface plasmon polariton modes in this design, the transmission spectra exhibit oscillation behaviors in a broad bandwidth, and can be readily tailored by changing the SPP path length and core layer thickness. Based on this principle, the characteristics of refractive index sensing are also demonstrated by simulation. This structure is illuminated with a collimated light source from the back side to avoid impacts on the interference. Meanwhile,these results show that the proposed structure is promising for portable, efficient, and sensitive biosensing applications.     

涂覆石墨烯的非对称并行电介质纳米线波导的模式特性分析

采用多级展开方法,对涂覆石墨烯的非对称并行电介质纳米线波导的模式特性进行了分析.首先对这种波导中的表面等离子模式进行分类,然后对七种低阶模式的有效折射率和传播长度随工作频率、几何结构参数和石墨烯费米能的依赖关系进行详细的分析.结果表明,通过改变工作频率、几何结构参数和石墨烯的费米能,可以在较大范围内调节模式的特性.与有限元法进行的对比表明,基于多级方法的半解析结果与有限元法的数值结果非常符合.研究结果可为涂覆石墨烯的非对称并行电介质纳米线的设计和制作提供一定的理论基础.     

不同包层直径的倾斜光纤光栅折射率传感特性

倾斜光纤光栅的透射谱中有纤芯模和大量的包层模,它们具有与布拉格光栅相同的温度特性.利用HF酸腐蚀的方法得到具有不同包层直径的倾斜光纤光栅,研究了其对外界折射率的传感特性.结果表明,外界环境折射率在1.333～1.4532之间变化时,同一直径倾斜光纤光栅的高阶包层模的敏感性要比低阶包层模强;随着包层直径的减小,包层模的敏感性增强,且在折射率比较高的环境中有更高的敏感性.因此,利用倾斜光纤光栅的温度特性不仅可以解决温度交叉敏感问题,而且通过小同的腐蚀程度能定制所需要的灵敏度,以实现对环境折射率的高灵敏度测量.该办法可应用于对生物和化学等高灵敏度传感领域的各种溶液进行实时监控.     

Thermal emission and volumetric absorption of a graded index semitransparent medium layer

Both thermal emission and volumetric absorption characteristics of a graded index semitransparent medium layer are investigated numerically. The semitransparent and specular emerging surface of the medium layer is parallel to an opaque and diffuse substrate wall. Monochromatic spectrum or gray medium is considered in the analysis. A pseudo-source adding method is combined with a ray-splitting and -tracing technique to solve the radiative transfer in the medium. As examples, constant and linear refractive index distributions are examined for an isothermal layer and the medium layer with a linear temperature distribution. Directional and hemispherical thermal emissions from the emerging surface as well as the volumetric absorption to the diffuse and parallel incidence of radiation are investigated, respectively. The results show that the refractive index distribution has significant influences on thermal emission and volumetric absorption of a semitransparent medium layer. The optical thickness, temperature distribution and the reflectivity of substrate wall react in combination with the refractive index distribution.     

Effect of reflecting modes on combined heat transfer within an anisotropic scattering slab

Under various interface reflecting modes, different transient thermal responses will occur in the media. Combined radiative-conductive heat transfer is investigated within a participating, anisotropic scattering gray planar slab. The two interfaces of the slab are considered to be diffuse and semitransparent. Using the ray tracing method, an anisotropic scattering radiative transfer model for diffuse reflection at boundaries is set up, and with the help of direct radiative transfer coefficients, corresponding radiative transfer coefficients (RTCs) are deduced. RTCs are used to calculate the radiative source term in energy equation. Transient energy equation is solved by the full implicit control-volume method under the external radiative-convective boundary conditions. The influences of two reflecting modes including both specular reflection and diffuse reflection on transient temperature fields and steady heat flux are examined. According to numerical results obtained in this paper, it is found that there exits great difference in thermal behavior between slabs with diffuse interfaces and that with specular interfaces for slabs with big refractive index.     

Trapped ion quantum computation with transverse phonon modes

We propose a scheme to implement quantum gates on any pair of trapped ions immersed in a large linear crystal, using interaction mediated by the transverse phonon modes. Compared with the conventional approaches based on the longitudinal phonon modes, this scheme is much less sensitive to ion heating and thermal motion outside of the Lamb-Dicke limit thanks to the stronger confinement in the transverse direction. The cost for such a gain is only a moderate increase of the laser power to achieve the same gate speed. We also show how to realize arbitrary-speed quantum gates with transverse phonon modes based on simple shaping of the laser pulses.     

Transmission properties of periodically patterned triangular prisms

Transmission properties of plasmonic structure arrays are simulated by finite element method. The array unit is composed of two combined triangular prisms. Results reveal that several resonant modes are found in the transmission spectra, which are due to the resonance of the surface plasmon polariton in the metal slit or to the localized surface plasmon resonance of the combined prisms. The resonant wavelengths can be tuned by changing the structural parameters of the combined prisms. In addition, the resonant modes are sensitive to small refractive index changes of the surrounding media, revealing potential detection applications in nanophotonic systems.     

Influence of surface scattering on the thermal properties of spatially confined GaN nanofilm

Gallium nitride(GaN), the notable representative of third generation semiconductors, has been widely applied to optoelectronic and microelectronic devices due to its excellent physical and chemical properties. In this paper, we investigate the surface scattering effect on the thermal properties of GaN nanofilms. The contribution of surface scattering to phonon transport is involved in solving a Boltzmann transport equation(BTE). The confined phonon properties of GaN nanofilms are calculated based on the elastic model. The theoretical results show that the surface scattering effect can modify the cross-plane phonon thermal conductivity of GaN nanostructures completely, resulting in the significant change of size effect on the conductivity in GaN nanofilm. Compared with the quantum confinement effect, the surface scattering leads to the order-of-magnitude reduction of the cross-plane thermal conductivity in GaN nanofilm. This work could be helpful for controlling the thermal properties of Ga N nanostructures in nanoelectronic devices through surface engineering.     

超光谱成像仪中棱镜的热光谱特性

为了确定超光谱成像仪热控指标和开展热设计,研究了超光谱成像仪中棱镜的热光谱特性。介绍了超光谱成像仪的工作原理以及热光谱特性的含义,分析了棱镜的环境热效应,论述了棱镜热光谱特性研究内容及技术路线,推导了温度变化时棱镜偏转角以及角色散的函数关系,进一步得到光谱中心平移及光谱带宽随温度变化规律。借助有限元分析,比较了K9、熔石英两种材料的棱镜的入射角、顶角、材料色散、光谱中心平移及光谱带宽随温度变化规律,确定了棱镜的热控指标,并设计了热光谱试验。理论分析和试验结果表明由于热变形引起的光谱带宽和光谱分辨率改变可以忽略不计,光谱平移主要由材料折射率温度系数决定;棱镜材料色散(dn/dλ)对温度变化不敏感,因此温度变化对其光谱带宽影响不明显; 本文研究方法合理,结果可信,对确定棱镜的热控指标和优化热设计具有指导意义。     

Refractive index sensor based on high-order surface plasmon resonance in gold nanofilm coated photonic crystal fiber

We propose a novel kind of wide-range refractive index optical sensor based on photonic crystal fiber(PCF) covered with nano-ring gold film.The refractive index sensing performance of the PCF sensor is analyzed and simulated by the finite element method(FEM).The refractive index liquid is infiltrated into the cladding air hole of the PCF.By comparing the sensing performance of two kinds of photonic crystal fiber structures, a wide range and high sensitivity structure is optimized.The surface plasmon resonance(SPR) excitation material is chose as gold, and large gold nanorings are embedded around the first cladding air hole of the PCF.The higher order surface plasmon modes are generated in this designed optical fiber structure.The resonance coupling between the fundamental mode and the 5 th order surface plasmon polariton(SPP)modes is excited when the phase matching condition is matched.Therefore, the 3 rd loss peaks appear obvious red-shift with the increase of the analyte refractive index, which shows a remarkable polynomial fitting law.The fitnesses of two structures are 0.99 and 0.98, respectively.When the range of refractive indices is from 1.40 to 1.43, the two kinds of sensors have high linear sensitivities of 1604 nm/RIU and 3978 nm/RIU, respectively.     

Polarization detection analysis of dual-channel surface plasmon resonance sensing for silicone oils based on the D-shaped fiber with a central hole

We present and numerically characterize a dual channel surface plasmon resonance (SPR) sensor based on a D-shaped fiber with a central hole for silicone oil detections. The proposed design incorporates two metalized channels to facilitate the simultaneous detection of one group of silicone oils, which can consist of two different species. It has been demonstrated that the p-polarized input light can induce two peaks among surface plasmon resonance places, which come from the coupling between the core-guided mode and the fundamental surface plasmon polariton (SPP) modes at the D-shaped surface and around the central hole surface. However, the s-polarized input light can only induce one peak among surface plasmon resonance places, which comes from the coupling between the core-guided mode and the fundamental SPP mode around the central hole surface. The simulation results show that the characteristic responses of two channels independently correspond to the refractive index variations in the silicone oils with which they are in contact. A maximum sensitivity of 3500 nm/RIU (refractive index unit) and 4400 nm/RIU are achieved for channel A and B, respectively. This kind of sensor structure and polarization related demodulation method is promising in the simultaneous multi-analytes sensing applications in the future.     

金孔阵列电介质与金电介质孔阵列的强透射特性

采用时域有限差分（FDTD）法研究了金膜厚度、电介质折射率及其厚度对金孔阵列电介质与金电介质孔阵列两种结构强透射特性的影响。研究发现这两种结构都具有较好的强透射特性,这表明光与金膜表面自由电子的电荷密度波耦合成表面等离子激元（SPP）,对增强透射起到了关键作用。金膜厚度是影响强透射特性的主要因素,其衰减长度为35 nm;而与金膜相邻的电介质膜厚度对强透射特性影响极小。电介质折射率大小对强透射特性影响明显,折射率为1.8时能够获得较好的强透射特性。     

Effects of surface charges on phonon properties and thermal conductivity in GaN nanofilms

Surface charges can modify the elastic modulus of nanostructure, leading to the change of the phonon and thermal properties in semiconductor nanostructure. In this work, the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated. In the framework of continuum mechanics,the modified elastic modulus can be derived for the nanofilm with surface charges. The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation, phonon group velocity, density of states of phonons in nanofilm with the surface charges. The phonon thermal conductivity of nanofilm can be obtained by considering surface charges. The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm. Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons. The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm. Based on these theoretical results, one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.     

Cr doping induced structural, phonon and excitonic properties of ZnO nanoparticles

We report systematic study of structural, phonon and optical properties of Cr-doped ZnO nanoparticles. These particles are synthesized through simple sol–gel technique. Structural studies carried out by X-ray diffraction method, confirm that the prepared particles are in hexagonal wurtzite structure and lattice parameters change considerably while increasing the doping. Raman and Fourier transform infrared spectral studies show that the intensity of the phonon modes decreased and also blue shift due to ion doping, respectively. Apart from this, transmission electron microscopic studies show reduction in particle size where the particle diameters reduced from 36 to 11 nm. Optical absorption spectral measurements show a blue shift in the band-gap and increment in excitonic oscillator strength. Photoluminescence studies show doping altered the near-band edge emission but there is no change in the other emission bands which is due to oxygen vacancy, surface defects and surface dangling bonds.     

Unidirectional excitation of surface plasmon polaritons in T-shaped waveguide with nanodisk resonator

The unidirectional excitation of surface plasmon polaritons (SPPs) in a novel configuration is numerically investigated by the finite-difference time-domain method. It is found that the transmission varies periodically with the increase of distance between the nanodisk resonator and horizontal nanoslit, which can be interpreted by the interference theory. The operating wavelength of this structure can be tuned by altering the refractive index of the nanodisk resonator. This subwavelength-scale structure exhibits high transmission (～58%) due to the constructive interference of the SPP modes, and thus can find important applications on the manipulation of SPP excitation in highly integrated optical circuits.