Outcoupling surface plasmons into propagation modes using a subwavelength dielectric grating for device applications

Coupling of surface plasmon polaritons to radiation modes by use of a one-dimensional subwavelength dielectric grating on a thin metal slab is discussed. The surface plasmon waves obtained in Kretschmann configuration are resonant outcoupled to radiation modes by using a subwavelength dielectric grating. A peak outcoupling efficiency is predicted to be 74.57% with rigorous coupled-wave analysis. In addition, potential applications of these results in the design and improvement of various optoelectronic devices, such as polarizers, wavelength filters and biochemical sensors are discussed.     

Surface plasmon-assisted optical switching/bistability at telecommunication wavelengths in nonlinear dielectric gratings

In this paper, we numerically investigate nonlinear optical responses in dielectric gratings coated by flat metallic surface, where the structural parameters are chosen for wavelengths of operation at the telecom regime. The presented designs show the output light reflection with respect to the incident intensity of increasing, decreasing, and non-monotonic belt-shape functions. Nonlinear optical responses including switching and bistability appeared in the telecom region owing to assistance of surface plasmon resonance excited at the metal/dielectric interface, which enhances the diffraction efficiency and induces the momentum matching for the leaky modes of the dielectric grating. This results in electric intensity-effective refractive index dependence enhancement in the Kerr nonlinear media. Our design and investigation of the linear and nonlinear optical responses will provide a general guideline for a hybrid metallic-dielectric structure-based optical switching/bistability device design.     

Generation of 1D interference patterns of Bloch surface waves

Interference patterns of Bloch surface waves with a period that is significantly less than the wavelength of incident radiation are formed using dielectric diffraction gratings located on the surface of photonic crystal. The simulation based on electromagnetic diffraction theory is used to demonstrate the possibility of high-quality interference patterns due to resonant enhancement of higher evanescent diffraction orders related to the excitation of the Bloch surface waves. The contrast of the interference patterns is close to unity, and the period is less than the period of the diffraction structure by an order of magnitude.     

On the effect of nonequidistance of dielectric coatings and the groove profile on the energy characteristics of holographic diffraction gratings

The diffraction efficiency and the resistance to radiation damage of gratings with a multilayer dielectric coating, which are used for compression of high-power laser pulses, are studied. The effect of smoothing of the profile of the metallized surface of the grating upon deposition of dielectric coatings on the energy characteristics of the grating at the wavelength λ=1.05 μm is analyzed. Gratings with various profiles of the metallic surface relief and with different contrast of the refractive indices of the dielectrics forming the coating are considered.     

Tunable terahertz radiation from arbitrary profile dielectric grating coated with graphene excited by an electron beam

In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.     

Extraction of guided modes from organic emission layers by compound binary gratings

The extraction of guided modes from a 100 nm organic emission layer by compound binary gratings with multiple superimposed periods at different ratios is investigated. We measure angle-dependent photoluminescence from samples with double-period (350 and 450 nm), triple-period (350, 400, and 450 nm), and multiperiod (350, 400, 450, and 500 nm) gratings and show that each period component produces two outcoupling features due to first-order Bragg scattering of the TE(0) guided mode. The averaged angular color change is reduced by up to a factor of 11 compared to a single-period grating structuring.     

Polarizing beam splitter of two-layer dielectric rectangular transmission gratings in Littrow mounting

We theoretically investigated the design of polarizing beam splitters (PBS) of two-layer dielectric rectangular transmission gratings in Littrow mounting. The PBS grating is aimed to separate TE and TM polarized waves into two different transmitted orders, i.e. the 0th and −1st orders. The polarization-dependent diffraction process is analyzed by using a simplified modal method. The mode reflection and transmission at the interface of the two layers are illustrated. Design equations are given based on the average mode indices of the even and odd modes inside the grating region, which are verified by using rigorous coupled wave analysis. Moreover, with simulated annealing algorithm, two kinds of two-layer PBS gratings are optimized for operation over the C-band (1520-1570 nm). Compared with the single-layer transmission PBS gratings, such two-layer scheme exhibits a great flexibility of design. The PBSs of two-layer dielectric transmission gratings should be useful for practical applications.     

共振域矩形介质光栅的逆向设计

采用模态法研究了共振域光栅分束器及闪耀光栅等光学器件的设计原理及逆向设计方法,给出了-1级非偏振闪耀光栅的典型设计示例。研究表明,自准直角入射时,光束在光栅内传输将激发产生离散模,通过调节离散模透过光栅传输时的累积相位差,可对衍射光进行调控,实现偏振(非偏振)分束、偏振(非偏振)闪耀等功能。采用严格耦合波法对基于模态法逆向设计的-1级非偏振石英闪耀光栅的几何参数进行验证,计算结果显示两者非常吻合,证明了该方法的正确性。     

Characteristics of light emission from surface plasmons based on rectangular silver gratings

We investigated the characteristics of transmitted light from propagating surface plasmons based on rectangular silver gratings. The results calculated by rigorous coupled-wave analysis presented that silver diffraction gratings can produce significant transmittance and conversion efficiency, comparable to the case of dielectric gratings. Especially, silver gratings optimized at a wide range of grating thickness and period may lead to an improved diffraction efficiency larger than 64%. Moreover, the effect of silver oxide layer on the transmittance was examined and a bimetallic structure with a thin gold coating was introduced to prevent an oxidation of silver substrates. As a practical sensor application, silver grating-based surface plasmon resonance (SPR) configuration showed an enhanced sensitivity associated with an increase of surface reaction area and strong excitations of local plasmon fields, outperforming a conventional thin-film-based SPR structure.     

Calculation and optimization of parameters of deep groove gratings with multilayer dielectric coating for compression of high-power laser pulses

The method of calculating the electromagnetic wave field diffracted by a holographic grating with a multilayer dielectric coating is developed. The method consists of the representation of the field inside dielectric layers in the form of a plane-wave expansion for weakly damped harmonics and an expansion over functions of the concomitant coordinate system for strongly damped orders. This modification of the method allows calculation of the diffraction efficiency and the electric field strength for the deep groove gratings. It is shown that a diffraction element that possess high efficiency and radiation strength can be obtained even when the profile of the dielectric layers flattens with an increase in the distance from the grating’s metallic layer.     

The Effect of Radiation on Transmission of Quasi-Periodic Multi-Layer Planar Dielectric Gratings

The transmission characteristics of quasi-periodic multi-layer planar dielectric gratings are systematically investigated by a method that combines the multimode network theory with rigorous mode matching method. The effect of radiation on the transmission characteristics of the multi-layer dielectric gratings is discussed in details, and some guidelines are given for accurate design of the gratings.     

1维介质光栅近场及其衍射的FDTD分析

 应用FDTD方法计算了单色平面波斜入射时1维介质光栅的近场，进而求出介质光栅的衍射效率。借助于周期边界条件，整个计算区域为周期结构的一个单元。考虑入射波在两种介质界面上会产生反射和透射，故在总场边界上引入入射波、反射波和透射波。给出了光栅单元截面为矩形和梯形的算例。该方法可用于斜入射情形下具有复杂结构和任意单元截面的介质栅近场及其衍射特性分析。     

Polarization effects of electron current settling when the cerenkov radiation is excited by a nonrelativistic electron beam in an open dielectric resonator

We study the effect of electron current settling of a strip nonrelativistic electron beam (EB) on the Cerenkov radiation (CR) in a metal-dielectric channel formed by the metal surface and the surface of a rectangular open dielectric resonator having isotropic properties and operated at millimeter wavelengths (3.6–5.8 mm). The choice of this channel was substantiated by theoretical studies of the CR energy density. We experimentally examined several effects, including the neutralization of the dielectric surface dipole charge by electrons, the accumulation of electron charge at the dielectric surface, and the influence of the electron charge on the EB and CR. Conclusions are drawn on the prospects of using short pulses of EB and special metal-dielectric diffraction gratings for the excitation of CR. Institute of Radioengineering and Electronics, Ukrainian National Academy of Sciences, Kharkov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 491–505, April, 1997.     

About the theory of optical grating coupler-waveguide systems

It is well known that photoresist gratings can be used for coupling light into and out of optical waveguides. To understand the coupling phenomena, and as a first step of a theoretical study, we deal here with the diffraction of a plane electromagnetic wave by a photoresist grating lying on a dielectric optical guide. Using a rigorous electromagnetic formalism, we find the sharp resonances already described by Hope and relate them with the existence of modes in the optical guide.     

多层介质膜脉宽压缩光栅的严格矢量分析

用于展宽和压缩激光脉冲的多层膜脉宽压缩光栅是由多层介质高反膜和位于其顶层的浮雕光栅构成。以设计的高反射多层膜为基础,利用傅里叶模式理论分析了其衍射场分布,给出了TE波自准直角入射的使用条件下,多层介质膜脉宽压缩光栅衍射效率的表达式。以-1级衍射效率为评价函数,分别讨论了HfO2和SiO2为顶层材料时,多层膜脉宽压缩光栅-1级衍射效率高于0.95的光栅结构参量范围。结果表明,在该条件下,选择HfO2为顶层材料时,光栅结构参量有较大的取值范围。给出了优化的光栅结构参量,并分析了光栅制作误差及其使用条件的宽容度,对光栅制作工艺和使用具有一定的指导意义。     

Beam focusing from double subwavelength metallic slits filled with nonlinear material surrounded by dielectric surface gratings

Based on the radiation properties of surface plasmon polaritons (SPPs) can be controlled by adjusting the refractive indexes of dielectric materials in the metallic slits, a novel plasmonic focusing structure formed by two subwavelength metal apertures filled with Kerr nonlinear material surrounded by surface dielectric gratings is proposed and demonstrated numerically. Directions of radiation fields are determined by the phase difference of the surface waves at the exit interface and resonance property of each surface grating. Numerical simulations using two-dimensional (2D) Finite-Difference Time-Domain (FDTD) method verify that the deflection angle and focal length can be controlled easily by changing the intensity of incident light, dynamically tunable on-axis and off-axis focusing effects can be achieved.     

Influence of two-dimensional bragg diffraction on the competition of the waveguide TE<Subscript>0</Subscript> and TM<Subscript>0</Subscript> modes during formation of spontaneous gratings in AgCl-Ag thin films

An intricate space-time instability of patterns of small-angle scattering and diffraction of a laser beam on the structures appearing in AgCl-Ag films under exposure to the same beam is investigated. The instability is related to the formation of spontaneous gratings in the film resulting from the interference of the incident beam with the waveguide modes scattered in the film. The existence of a two-dimensional Bragg diffraction on the TE₀ and TM₀ modes with subsequent formation of secondary spontaneous gratings is revealed and is theoretically substantiated. It is established that the difference in the indicatrices of the radiation scattered into the TE₀ and TM₀ modes for the s-and p-polarizations manifests itself in different kinds of diffraction and small-angle scattering patterns at the output of illuminated samples.     

Bound States in the continuum in photonics

With examples of two parallel dielectric gratings and two arrays of thin parallel dielectric cylinders, it is shown that the interaction between trapped electromagnetic modes can lead to scattering resonances with practically zero width. Such resonances are the bound states in the radiation continuum first discovered in quantum systems by von Neumann and Wigner. Potential applications of such photonic systems include: large amplification of electromagnetic fields within photonic structures and, hence, enhancement of nonlinear phenomena, biosensing, as well as perfect filters and waveguides for a particular frequency, and impurity detection.     

管靶X射线辐射输运初步研究Ⅱ.实验测量与分析

从实验上研究了X射线在管靶中辐射输运情况.给出两种分解靶：源靶、输运靶.源靶可得到X射线输运的输入条件,输运靶是近似一维X射线输运管道,对其测量可得到输运的结果;给出两种分解靶由软X射线谱仪、平响应XRD和透射光栅谱仪(配X射线CCD)测量的结果,并对实验结果进行分析;最后对输运管道内的等离子体膨胀问题进行了讨论. 关键词：     

Extension of Reflectance and Transmission Coefficient Matrix to C-method for study of periodic multilayer system

The C-method is one of the most efficient and versatile method designed for diffraction gratings. The boundary conditions of the grating can be greatly simplified when the coordinate systems coincide with the surfaces of the grating. Reflectance and Transmission Coefficient Matrix (RTCM) with clearly physical concept is a powerful propagation algorithm proposed for steady and fast calculation of multilayer gratings. In this paper, the C-method is extended to treat the multilayer diffraction grating with the identical or nonidentical surface shapes. Numerical examples including diffraction efficiencies of both dielectric and metallic grating are presented. In addition, the excellent convergence for various adjacent-heights and diffracted orders of our propagation algorithm for TE and TM polarizations is also included.