Perfect extinction in subwavelength dual metallic transmitting gratings

We investigate the strong electromagnetic coupling that settles in dual metallic grating structures. This coupling is evidenced to lead to a perfect optical extinction in the transmission spectrum. The behavior of this perfect extinction that strongly depends on the longitudinal space and the lateral displacement between the two gratings can be explained by a simple model that describes the interference between a propagating mode and a couple of evanescent modes. The results show that the electromagnetic transmission of the structure can be tuned by controlling the position of this perfect transmission extinction and thus pave the way to new types of infrared tunable filters.     

亚波长金属光栅的光耦合增强效应及透射局域化的模拟研究

介质层上的亚波长金属光栅产生的表面等离子体（surface plasmons,SPs）可以极大地增强光栅下介质层内的透射光强.增强作用从500 nm延续到近红外区域.在波长610 nm附近有接近110%的增强,在波长700 nm及740 nm处也有180%左右的增强.而这个波长范围与薄膜太阳能电池的吸收谱很相近,因此这种结构有望大幅度提高薄膜太阳能电池及不同波长光探测器等光电转换器件的光耦合效率. 关键词： 表面等离子体 亚波长光栅 薄膜太阳能电池 透射增强     

亚波长光栅的偏振闪耀特性

 使用琼斯矩阵的方法推导了连续结构亚波长光栅的衍射方程,给出了光栅衍射效率表达式,对偏振特性与衍射特性进行了研究。发现连续结构亚波长光栅仅存在３个衍射级,总衍射效率为100%,且衍射效率可在衍射级间任意分配,0级的偏振态与入射光的偏振态相同,±1级衍射光偏振态与入射光无关,－1级为左旋圆偏振光,＋1级为右旋圆偏振光。通过设置入射光偏振态与光栅相位延迟等参数,可使光栅具有闪耀特性,据此可用于设计高效偏振光分束器和偏振光开关。     

Transmission resonances of metallic compound gratings with subwavelength slits

Transmission metallic gratings with subwavelength slits are known to produce enhanced transmitted intensity for certain resonant wavelengths. One of the mechanisms that produce these resonances is the excitation of waveguide modes inside the slits. We show that by adding slits to the period, the transmission maxima are widened and, simultaneously, this generates phase resonances that appear as sharp dips in the transmission response. These resonances are characterized by a significant enhancement of the interior field.     

Plasmonic critical angle in optical transmission through subwavelength metallic gratings

We observe and theoretically analyze the plasmonic analog of the critical angle phenomenon in optical transmission through subwavelength gratings milled in an optically thick metal film. The total transmission from a denser medium to a less dense one vanishes while the total reflection holds very strong, providing the incidence angle increases past the plasmonic critical angle (PCA). The conditions and physical origins of the total internal reflection above the PCA are clarified.     

Compact middle-wave infrared Fabry-Perot interferometer with double metallic subwavelength gratings

We demonstrate a compact middle-wave IR (MWIR) Fabry-Perot (FP) interferometer by replacing the traditional distributed Bragg reflectors consisting of thick multilayer films with two identical metallic subwavelength gratings. The transmission efficiency, resonance peak position, and finesse of the FP interferometer can be controlled by tuning the structural parameters. The performance of the MWIR FP interferometer is verified by experiment, which shows its potential application as, for example, narrowband MWIR filter for gas detection.     

Optical bistability of subwavelength metallic film coated by Kerr dielectric gratings

We studied the optical bistability of subwavelength metallic film coated by Kerr dielectric gratings numerically. It is found that the effect of optical bistability in the structure is explained by the excitations of the coupled surface plasmon polaritons at the coated metallic films. The effect of thickness of the metallic films on bistability loop is analyzed in detail, and the authors attribute the change of the bistability loop to the lifetime of the coupled surface plasmon polaritons.     

Resonances on metallic compound transmission gratings with subwavelength wires and slits

We investigate the response of gratings formed by subwavelength wires in a dielectric medium. For gratings with a single wire per period, most of the incident power is transmitted through the structure. If the distance between adjacent wires is small enough, the excitation of waveguide modes can lead to reflection resonances. However, only when the period is formed by several wires (compound grating), new degrees of freedom are introduced for the phase distribution of the field inside the slits, allowing a new class of resonances analyzed in this letter. We give numerical examples illustrating the combined effect produced by both types of resonances in the grating response.     

线双折射传感光栅中的传输光偏振态分析

 深入研究了线双折射光栅中透射光偏振特性的演变过程。采用耦合模理论和琼斯矩阵分析了传输距离、双折射大小、入射起偏态等因素对透射光偏振特性的影响,并利用邦加球中描绘了偏振态的演变趋势。结果表明：光栅中的线双折射和传输距离会改变传输光的偏振态,偏振态的波长相关曲线会随传输距离和线双折射的增大而不断扩展,入射起偏态的不同并不改变偏振态的拓展趋势。同时,第一斯托克斯参量与偏振相关损耗在峰值波长点上存在对应关系,两者幅值均与线双折射呈单调递增关系,可应用于传感测量。     

亚波长金属光栅的表面等离子体激元共振特性

亚波长金属光栅在共振波长处有光场局域增强、异常透射等现象,为深入认识其共振机制,本文研究了亚波长金属光栅的表面等离子体激元（SPP）共振特性。通过研究不同金属光栅的几何结构以及金属介电常数对SPP共振波长的影响,获得了3种共振波长的基本物理机制。采用周期边界元法进行数值模拟,在边界积分方程的基础上结合平面波展开方法来处理任意形状的周期性结构。模拟结果表明,3种共振波长可以分别由金属的材料、金属光栅周期和金属光栅厚度所调谐。该研究为微纳米光学器件的设计提供了依据。     

亚波长金属光栅的表面等离子体激元共振特性

亚波长金属光栅在共振波长处有光场局域增强、异常透射等现象,为深入认识其共振机制,本文研究了亚波长金属光栅的表面等离子体激元(SPP)共振特性。通过研究不同金属光栅的几何结构以及金属介电常数对SPP共振波长的影响,获得了3种共振波长的基本物理机制。采用周期边界元法进行数值模拟,在边界积分方程的基础上结合平面波展开方法来处理任意形状的周期性结构。模拟结果表明,3种共振波长可以分别由金属的材料、金属光栅周期和金属光栅厚度所调谐。该研究为微纳米光学器件的设计提供了依据。     

Antireflective properties of AZO subwavelength gratings patterned by holographic lithography

We fabricate the aluminum-doped zinc oxide (AZO) subwavelength gratings (SWG) on Si and glass substrates by holographic lithography and sequent CH₄/H₂/Ar reactive ion etching process. The etch selectivity of AZO over photoresist mask as well as the nano-scale shape is optimized for better antireflection performance. To analyze the antireflective properties of AZO SWG surface, the optical reflectivity is measured and then calculated together with a rigorous coupled-wave analysis. The reflectance spectrum can be considerably changed by incorporating the SWG into AZO film. As the SWG height of AZO on Si substrate increases, the magnitude of interference oscillations in the reflectance spectrum tends to be reduced with the larger difference between its maxima. The use of optimized SWG can significantly reduce the surface reflection of AZO film at the desired wavelengths. The measured reflectance data of AZO SWG are reasonably consistent with the simulation results. No considerable change in transmission characteristics is observed for AZO SWG structures.     

金属亚波长狭缝中凹槽对其透过特性的影响

利用时域有限差分方法,研究了单个二维金属亚波长狭缝中空气凹槽的结构、位置等参数变化对其透过特性的影响. 整个缝槽结构可以类比为LC振荡环路,凹槽结构变化时,不同程度地改变振荡电路的电感和电容,从而使共振透射峰出现移动. 凹槽位置变化时,电路的驱动源改变,从而改变缝槽结构中的电磁场分布,使得共振透射峰出现分裂. 利用LC共振原理分析了凹槽各个参数变化时共振透射峰的变化情况. 关键词： 表面等离子体 透射率 LC振荡')" href="#">LC振荡     

一维金属光栅的透射光学特性

利用时域有限差分法模拟了一维金属光栅的透射光场的分布及光栅厚度等因素对透射光谱的影响.结果表明:特定波长的光通过金属光栅中的亚波长狭缝时有异常大的透过率增强.分析其物理起源,认为是类FabryPerot(FP)腔作用的结果.基底介电常量对类FP腔长度的调制导致了对透射光谱的影响.金属光栅表面激发的表面等离子体激元波与多缝干涉一样,对透射光谱有一定的影响,但不是形成增强的原因 关键词： 金属光栅 透射光学特性     

Super-transmission of light through subwavelength annular aperture arrays in metallic films: Spectral analysis and near-field optical images in the visible range

This paper presents experimental studies of the enhanced light transmission through metallic films pierced by subwavelength annular apertures. Two different methods (e-beam lithography and focused ion beam) have been used to build the nano-structures. We have experimentally recorded their far-field spectral response in the visible range and the optical near-field above the nano-structures when they are excited at 633 nm. The spectral response exhibits a transmission peak at 700 nm with maximum efficiency around 16%. The near-field exhibits a characteristic two-lobe structure just above the aperture. Finite difference time domain (FDTD) simulations reproduce quite well the experimental results.     

Polarization properties of subwavelength hole arrays consisting of rectangular holes

The influence of hole shape on extraordinary optical transmission was investigated using hole arrays consisting of rectangular holes with different aspect ratios. It was found that the transmission could be tuned continuously by rotating the hole array. Furthermore, a phase was generated in this process, and linear polarization states could be changed to elliptical polarization states. This phase was correlated with the aspect ratio of the holes. An intuitional model was presented to explain these results.     

Polarization independent broadband terahertz antireflection by deep‐subwavelength thin metallic mesh

Broadband antireflection coatings for passive terahertz (THz) components are extremely important in the application of THz technology. Metallic nano‐films are commonly used for this purpose. Here a new approach to realize polarization independent broadband antireflection in THz range, based on a meta‐surface design is experimentally demonstrated. The internal reflection of a broadband THz pulse (spectral bandwidth of 0.06 – 4 THz) at a Si/air interface can be fully suppressed with a Cr square mesh with deep‐subwavelength dimensions. Small nonuniformity of the meta‐surface structure can enhance the tolerance on structural parameters for achieving the AR condition. The design concept is applicable to other metals and frequency ranges as well, which opens a new window for future AR coatings.     

Dynamic analysis of holographic gratings in amulti-wavelength visible light sensitive photopolymer

A dynamic theoretical model of photochemistry and hologram formation in holographic photopolymer is established, and the dynamic development process of holographic gratings in the photopolymer is discussed with the model. A novel multi-wavelength visible light sensitive photopolymer for holographic storage is prepared. The influence of exposure wavelength on holographic storage characteristics is analysed. By fitting the experimental data of transmittance and diffraction efficiency to a function of time with different exposure intensities and wavelengths, the variations of dynamic parameters of photochemistry and photopolymerization diffusion are presented.     

Terahertz transmission properties of thin, subwavelength metallic hole arrays

We present experimental results of the transmission magnitude and phase change of terahertz pulses through thin metallic films patterned with subwavelength hole arrays on silicon wafers. Terahertz time-domain spectroscopy measurements reveal a sharp phase peak centered on the surface plasmon resonance. Correspondingly, and consistent with the Kramers-Kronig relations, the measured transmission magnitude has the shape of the derivative of this peak. In addition, we determine that the aperture shape has a notable effect on the transmission properties of two-dimensional hole arrays.