Numerical simulation of the optical reflection and transmission coefficients of a periodic surface of metallic nanowire grating

The optical reflection and transmission coefficients of a metallic nanograting have been studied with the use of numerical simulation in a wide range of the size of structural units of the grating. The grating is composed of silver nanowires arranged periodically on a quartz substrate. The cases of s- and p-polarized incident waves have been considered. In particular, it has been found that the spectral dependence of the reflection and transmission coefficients of the nanograting becomes oscillatory and exhibits several deep minima when all structural parameters of the grating (the nanowire’s width and height, and the grating period) approach tens of nanometers. The physical reason of the appearance of these oscillations has been analyzed. It has been shown how the depth and position of the discovered minima depend on the light angle of the incident wave and the rotation angle of the grating around its normal surface.     

Phase modulation of Bloch surface waves with the use of a diffraction microrelief at the boundary of a one-dimensional photonic crystal

Phase modulation methods for surface electromagnetic waves propagating at the interface between a homogeneous medium and a one-dimensional photonic crystal have been analyzed numerically and theoretically. Modulation is performed by changing the geometrical parameters of the microrelief on the surface of the photonic crystal. The phase modulation methods under consideration can be used to create optical elements for surface waves, in particular, lenses, prisms, and diffraction gratings. A Bragg grating has been calculated as an example. According to the simulation results, the average coefficient of reflection of a surface wave in the band gap is 0.95.     

Four-step pulses of fractional-order surface plasmons

The 0-order transmission of a 1D metallic grating, on a high-resistivity silicon wafer in optical contact with a silicon plate, has been characterized by terahertz time-domain spectroscopy with subpicosecond resolution over a 400 ps scan range. Two new long-time-delay, powerful pulses are observed after the second reflected pulse. In the frequency domain, these two strong and fast-ringing structures correspond to the bandwidth ranges between the [0, 1] and [0, 2] surface plasmon modes and the range above [0, 2], respectively. A physical optics ray analysis provides an intuitive understanding of these new four-step (reflection, diffraction, total reflection, and diffraction) pulses, caused by fractional-order surface plasmon type beam coupling.     

The surface ace plasmon resonance effect in holography

A hologram has been made using a surface plasmon resonance wave as the reference beam. The surface wave was stimulated on a 1200-line/mm aluminum reflection grating that was coated with a thin layer of high resolution photographic emulsion. Experimental results are presented.     

基于导模共振效应提高石墨烯表面等离子体的局域特性

本文构建了一种包含石墨烯和亚波长光栅的复合结构, 借助衍射光栅的导模共振效应, 在石墨烯表面激发高局域性表面等离子体激元, 研究了石墨烯与光栅结构对表面等离子体激元局域特性的影响规律, 并借助基于有限元法的COMSOL软件, 分析了缓冲层厚度、光栅周期、载流子迁移率和费米能级对石墨烯的表面电场、品质因子Q和有效模式面积S_eff的影响. 结果表明, 石墨烯表面等离子体激元的局域性在特定的参数点获得显著提高: 当μ = 0.7 m²/(V·s)时, 品质因子达到最大值Q_max = 1793; 当p = 235 nm或E_F = 0.72 eV时, 表面电场达到了入射光的3000倍以上. 强烈的局域性导致强烈 的光-物质相互作用, 因而本文提出的复合结构可实现高灵敏度传感器和高效率的非线性光学设备, 极大地扩展了石墨烯在纳米光学领域中的应用.     

Dispersion of surface plasmons in InSb-gratings

The reflection of a monochromatic plane electromagnetic wave by a grating consisting of grooves in the surface of a semiconductor plasma (InSb) is investigated theoretically, in particular in that region of frequencies where the complex permittivity of the semiconductor plasma has a negative real part. From the numerically obtained reflection factor pertaining to anH-polarized incident wave, the excitation and the dispersion of surface plasmons at the boundary of the medium is discussed. The grating problem is rigorously formulated as a boundary value problem employing a Green's function technique. Numerical results pertaining to the reflection factor are presented for different grating parameters.     

Direct Fabrication Methods of Surface Relief Electro-Optic Gratings in Azo-Polymer Films

Two fabrication methods of surface relief electro-optic (EO) gratings in azo-polymer films are described: surface deformation by a continuous wave laser and laser ablation by a pulse laser. In the fabrication process, the periodic intensity modulation of laser beams is formed by an interference fringe or a phase mask. The surface relief EO grating is fabricated by poling the surface relief grating (SRG) after the SRG fabrication process. The linear dependence of an applied voltage in the modulation efficiency of the first-order diffraction beam is observed. The proposed methods are effective for highly-efficient surface relief EO grating fabrication.     

多层介质膜脉冲宽度压缩光栅与超短脉冲作用时的性能分析

基于啁啾脉冲放大技术的超短脉冲激光系统是提供超快、超强激光的重要途径，具有良好输出波形和高损伤阈值的多层介质膜脉冲宽度压缩光栅是获得高峰值功率脉冲激光的关键. 基于傅里叶谱变换方法和严格模式理论，分析了多层介质膜光栅(MDG)在超短脉冲作用下的光学特性. 结果表明，当MDG的反射带宽小于具有高斯分布的入射脉冲的频谱宽度时，-1级反射脉冲呈非对称高斯分布，其前沿出现振荡，并且-1级反射脉冲能量开始剧烈下降. 讨论了MDG结构参数对其反射带宽的影响. 分析了MDG与超短脉冲作用时的近场光分布，对提高其抗激光损 关键词： 脉冲压缩光栅 傅里叶谱变换 模式理论 损伤阈值     

甚长波量子阱红外探测器光栅耦合的研究

采用平面波展开的散射矩阵方法研究n型甚长波量子阱红外探测器的二维衍射光栅，并同时从实验方面研究了其红外透射光谱.研究表明，n型量子阱器件的光栅耦合是传输场和倏逝场共同作用的结果.对于n型量子阱红外探测器的光栅耦合，光栅周期、光栅深度和占空比三者之间相互影响；要达到好的光学耦合效果，需要根据量子阱器件的峰值探测波长选择合适的光栅参数. 关键词： n型量子阱红外探测器 二维光栅 光耦合     

Rapid and accurate analysis of surface and pseudo-surface waves using adaptive laser ultrasound techniques

A method has been developed to measure the phase velocity of laser generated and detected surface acoustic waves. An optical grating produced by an electronically addressable spatial light modulator (SLM) was imaged onto the sample surface to generate surface acoustic waves whose frequency and wavefront was controlled by the SLM. When the grating period matched the surface acoustic wavelength, the surface wave was strongly excited, thus the wavelength and, thereby the phase velocity was determined. We present results with this method that allows the phase velocity and the angular dispersion of the generalized surface wave as well as the pseudo-surface wave on the (100) nickel to be measured. Measurements on (111) silicon single crystals are also presented. The measurement precision is approximately 0.2%. Methods to further improve the measurement precision are also discussed.     

Generalization of the Brewster phenomenon for the wave diffraction process

Polarization anomalies of the Brewster type are considered for processes such as wave reflection, wave scattering, wave diffraction by surface grating and surface plasmon waves. Generalized conditions for Brewster anomalies in wave diffraction are written in analytical form. The application of the Brewster phenomenon for integrated optical polarizers is investigated numerically.     

基于侧边抛磨光纤的表面布拉格光栅温度传感器

为了实现在侧边抛磨光纤（SPF）上制作布拉格光栅结构并提高器件设计灵活性,利用重铬酸盐明胶（DCG）作为光刻材料,提出一种新型的光纤表面布拉格光栅制作方法并对该器件温度传感特性进行研究。使用轮式抛磨系统制作SPF,并在SPF侧抛面上旋涂DCG,通过干涉光束曝光显影制作表面布拉格光栅。光谱测量表明:带有布拉格光栅的侧边抛磨光纤在1 480.2 nm处有透射谷,在相应位置反射谱有明显反射峰,其调制幅度达到15.9 dB,这是由于表面光栅的布拉格反射所致。温度传感实验表明,该布拉格反射峰的温度灵敏度为17.84 pm/℃。这种器件已在光纤传感和光纤滤波器等方面获得应用。     

Surface relief resonant Brewster filters with multiple channels

In this paper, a new type of resonant Brewster filters （RBF） with surface relief structure for the multiple channels is first presented by using the rigorous coupled-wave analysis and the S-matrix method. By tuning the depth of homogeneous layer which is under the surface relief structure, the multiple channels phenomenon is obtained. Long range, extremely low sidebands and multiple channels are found when the RBF with surface relief structure is illuminated with Transverse Magnetic incident polarization light near the Brewster angle calculated with the effective media theory of sub wavelength grating. Moreover, the wavelengths of RBF with surface relief structure can be easily shifted by changing the depth of homogeneous layer while its optical properties such as low sideband reflection and narrow band are not spoiled when the depth is changed. Furthermore, the variation of the grating thickness does not effectively change the resonant wavelength of RBF, but have a remarkable effect on its line width, which is very useful for designing such filters with different line widths at desired wavelength.     

Temperature and orientation dependence of surface relief gratings based on dye-doped polymer film with the interface of nematic liquid crystals

The formation of surface relief grating on dye-doped polymer film with the interface of nematic liquid crystals has been investigated by means of the holographic technique. The first-order diffraction efficiency of surface relief grating depends on the temperature and the orientation of molecular director in the interface of nematic liquid crystals. The diffraction efficiency is roughly independent of thermal fluctuations of molecular director in the most part of nematic temperature range and apparently drops near the transition temperature. The morphology of surface relief grating demonstrates that the surface modulation is larger for molecular director parallel to the groove direction. The experimental result also shows that the first-order diffraction efficiency is dependent on the surface modulation of surface relief grating.     

Verification of evanescent coupling from subwavelength grating pairs

Near-field evanescent wave coupling of various subwavelength grating pairs, using a 1.55 μm infrared semiconductor laser has been demonstrated for use as an optical MEMS sensor. Subwavelength grating pairs were fabricated on both glass and silicon substrates. When coupled together the effective grating period is not subwavelength and can exhibit several diffraction orders. The 1.55 μm infrared source was incident on the coupled pairs and the first-order output intensity was recorded and compared with the output intensity from simulated results. This demonstrated evanescent wave coupling concept can be applied to MEMS systems with nanometer gap separations (e.g., pressure sensors, biosensors, and accelerometers) to allow for subnanometer displacement detection.     

Spectral enhancement of thermal radiation by laser fabricating grating structure on nickel surface

Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on polished nickel targets and measure their thermal radiation spectra at a temperature of 623 K by Fourier transform infrared(FTIR) spectrometry. The results show an obvious major enhanced peak in which the wavelength is slightly larger than the grating period. Surface plasmon resonance(SPR) and Kirchhoff's law of thermal radiation are applied to give this phenomenon a preliminary explanation. In addition, we utilized rigorous coupled wave analysis(RCWA) to simulate the absorption spectrum of the grating surface. The experiment results show good agreement with the simulation results.     

Direct fabrication of surface-relief grating by interferometric technique using femtosecond laser

A surface-relief grating is a key element in optical communication and opto-electronic integrated devices. To date, many techniques for fabricating surface-relief gratings have been reported, but the present techniques still have many limitations and disadvantages. In this paper we present a new optical configuration to imprint a surface-relief grating by two-beam interferometry using a femtosecond laser. A relatively simple set-up is proposed in order to generate two parallel laser beams and then focus them by a common focusing lens to obtain an interference pattern. With the use of the common focusing lens, the two parallel beams will interfere exactly at the focal plane. This new optical set-up not only facilitates the alignment but also enhances the tunability to obtain different grating periods. Experimental results on solid copper targets are presented. The grating surface morphologies are studied by a scanning electron microscope and the grating relief profiles are characterized by an atomic force microscope. The prominent experimental results obtained have verified the feasibility of the new technique. In addition, the influence of laser fluence and pulse number on the surface morphology is presented. PACS 42.15.Eq; 42.25.Hz; 42.62.Cf     

基于二维矩形SiO2光子晶体光栅的研究

 为解决光学系统中普遍存在的菲涅耳反射问题,提高光的透射率,设计了一种二维矩形SiO2光子晶体结构光栅。采用勒让德多项式展开法对该结构在可见 近红外波长范围入射光波的透射率进行了模拟计算,寻找到了合适的占空比e、光栅深度h和基底厚度d,使得光栅的透射率在入射角为0～60°范围内、入射波长在400 nm～1 200 nm范围内变化时,其透射率的变化相对稳定,透射率的平均值可达到96%以上。     

Use of steel substrates in diffractive optics: Near field of high surface quality steel tape gratings

Steel tape is used in optical applications due to its mechanical properties. However, roughness of steel surfaces affects to wave propagation. The effect can be observed using diffraction gratings with low periods. In such a case, self-images of the grating appear at certain periodic distances from the grating (Talbot planes). When standard steel is used, the contrast of Talbot self-images strongly decreases with the distance from the grating. In this work, we prove that controlling the surface quality of steel, it is possible to improve its optical behavior and, as a consequence, high quality surface steel represents a good choice for diffractive optics when the use of chrome-on-glass masks is not indicated. As an example, we have manufactured a diffraction grating over a high quality steel surface by means of an ablation process with a nanosecond pulsed laser. The contrast of the self-images for these gratings decreases very slowly with the distance, in comparison with the self-images obtained with standard steel tape gratings.     

基于表面等离激元的长波QWIP光栅优化

为了提高长波量子阱红外探测器的灵敏度及探测率,采用表面等离激元效应来提高量子阱红外探测器中二维光栅的耦合效率。利用三维时域有限差分算法,分析表面等离激元作用下,长波量子阱红外探测器中二维金属薄膜光栅参数对入射光的调制作用。计算结果表明,对于8 m的入射光,当光栅周期P=2.8 m,孔直径D=1.4 m,光栅层厚度L=0.04 m时,X Y平面内Z方向电场值最大,光栅的耦合效率最高。