基于塔姆激元-表面等离极化激元混合模式的单缝加凹槽纳米结构的增强透射

金属单缝纳米结构因为结构简单、易于集成,常用在基于表面等离极化激元(surface plasmon polaritons,SPPs)的纳米结构中构建光源.但是,金属亚波长单缝结构一直存在透射率低的问题,如何提高其透射率一直是研究的重点.为了更好地提高金属亚波长单缝的透射率,本文对之前文献提出的分布式布拉格反射镜(distributed bragg reflector,DBR)和金属银薄膜纳米缝结构进行改进,在金属银薄膜两侧设计凹槽.当TM偏振光由DBR侧入射至DBR-银纳米缝结构时,DBR-银膜界面上和银膜入射侧凹槽一起激发的塔姆激元(Tamm plasmon polaritons,TPPs)和SPPs,以及纳米缝和银膜出射侧凹槽对的SPPs同时激发,利用凹槽激发的SPPs和银膜表面处的TPPs-SPPs混合模式的干涉相长耦合作用,通过塔姆激元的局域场增强效应和两侧凹槽与单纳米缝的干涉相长耦合作用进一步提高了表面等离极化激元模式的激发效率,再加上纳米缝中的类法布里-珀罗腔共振效应,使纳米缝的透射率得到增强.本文采用有限元方法研究了DBR-银纳米缝结构上单纳米缝加凹槽的透射特性.经过一系列参数优化,使DBR-银纳米缝凹槽结构的最大透射率增加到0.22,相对于TiO_2-银纳米缝结构的透射率(0.01)提高了22倍,比文献[23]得到的最大透射率0.166有所提高.研究结果在纳米光源设计、光子集成电路和光学信号传输等相关领域具有一定的应用价值.     

基于磁激元效应的石墨烯-金属纳米结构近红外吸收研究

石墨烯作为一种单层碳原子二维材料,在可见光和近红外波段吸收率只有2.3%左右,这限制了石墨烯在光电探测、光电调制等领域的应用.本文基于纳米超材料结构的磁激元共振效应,设计了一种金属-绝缘层-金属-石墨烯混合二维浅光栅结构,通过设计混合二维浅光栅结构尺寸来改变石墨烯化学势,实现了石墨烯在近红外波段的吸收增强和调制.利用有限元仿真和等效电路模型,系统地分析了非正入射、结构参数和石墨烯化学势对吸收特性的影响.研究结果表明,混合二维浅光栅结构的磁激元共振效应可以明显提升石墨烯在近红外波段的吸收率,并且对入射角度和极化方向不敏感.在特定结构参数下,混合二维浅光栅结构在1480nm处吸收率达到了85%,其中石墨烯的吸收率为55%,提升了24倍;通过调控石墨烯化学势从0.1eV增大到1.0eV,分别实现了不同结构尺寸下54.8%,50.3%,46.8%的反射率调制深度.     

表面等离子激元与F-P共振耦合平衡钙钛矿太阳能电池有源层内载流子产生速率

为提高有机-无机杂化钙钛矿太阳能电池（PSCs）光吸收效率、平衡有源层中载流子产生速率,将周期性纳米光栅结构引入到PSCs器件结构中。分析了光栅周期、光栅高度和有源层厚度对表面等离子激元（SPPs）与法布里-珀罗（F-P）共振耦合模式的影响。通过改变光栅周期,实现了SPPs与F-P共振耦合波长范围与钙钛矿材料的弱吸收光谱区域相重合,同时光栅高度的增加可以增大耦合模式的光谱宽度。SPPs与F-P共振耦合模式实现了金属电极与电子传输层（ETL）界面处的局域电场增强。结果表明:场增强效应扩展到有源区,有效提高了PSCs有源层远入射光侧在570~800 nm波长范围内的光吸收,进而提高了有源层远入射光区域的载流子产生速率。当光栅周期为250 nm、光栅高度为50 nm、源层厚度为300 nm时,PSCs在太阳光弱吸收光谱区域内的本征吸收提高了~12%,有源层远入射光侧载流子产生速率提高了~41%。     

Two surface plasmon resonances effects for light through the perforated metal film

Light transmission through perforated metal film has been reported and some investigations have been made into the physical origin of this phenomenon. We show that the transmission assisted with surface plasmon (SP) through a perforated metal film results from two different SP resonances effects: surface plasmon resonance due to the periodicity at the left air/metal and right metal/air interfaces and localized cavities resonance inside rectangular holes. The fields intensity is localized separately on the left and right metal-air surfaces for structure-factor-induced surface plasmon mode. And for localized cavities resonance mode, standing electromagnetic fields can also be entirely localized inside the nanohole region. The aspect ratio of the rectangular holes can affect the transmission.     

Controlling polariton coupling in intersubband microcavities

We report the external control of the intersubband polariton coupling by manipulating the carrier density in quantum wells resonantly coupled to a GaAs/AlGaAs microcavity. The electrons in the wells were tuned by means of a depletion gate bias or by utilizing charge transfer between the energetically aligned ground subbands of asymmetric tunnel-coupled quantum wells. We propose the use of tunnel-assisted control of the polariton ground state in an asymmetrically coupled quantum well for implementing ultrafast modulation of intersubband polaritons.     

A double‐lined metasurface for plasmonic complex‐field generation

Since the surface plasmon polariton (SPP) has received a great deal of attention because of its capability of guiding light within the subwavelength scale, finding methods for arbitrary SPP field generation has been a significant issue in the area of integrated optics. To achieve such a goal, it will be necessary to generate a plasmonic complex field. In this paper, we propose a novel method for generating a plasmonic complex field propagating with arbitrary curvatures by using double‐lined distributed nanoslits. As a unit cell, two facing nanoslits are used for tuning both the amplitude and the phase of excited SPPs as a function of their tilted angles. For verification of the proposed design rule, the authors experimentally demonstrate some plasmonic caustic curves and Airy plasmons.

     

Identification and control of multiple leaky plasmon modes in silver nanowires

Leaky plasmon modes (LPMs) in metal nanowires (NWs), which combine the physical characteristic of both “plasmonics” and “leaky radiation”, present distinguished performances in terms of guiding and radiating light. In contrast to traditional light‐guiding in metal NWs with one single LPM, multiple LPMs are crucial for advanced uses such as augmenting data transmission channels, enhancing sensing performance, manipulating polarization and converting mode. Here, we demonstrate experimentally the control over multiple LPMs in pentagonal silver NWs. By combining far‐field real‐space imaging and leakage radiation microscopy, the three typical LPMs with fields mainly concentrating in corners surrounded by air are specifically identified. By manipulating excitation wavelengths and NW diameters, the number of the excited LPMs can be controlled. These findings reveal the physics of LPMs in silver NWs, thereby paving the way towards applying the high‐order leaky modes in silver NWs for photonic integrated circuits, nanoscale confinement, plasmonic sensing, QD‐nanowire coupling, etc.

     

Omnidirectional and compact Tamm phonon-polaritons enhanced mid-infrared absorber

Narrow band mid-infrared (MIR) absorption is highly desired in thermal emitter and sensing applications. We theoretically demonstrate that the perfect absorption at infrared frequencies can be achieved and controlled around the surface phonon resonance frequency of silicon carbide (SiC). The photonic heterostructure is composed of a distributed Bragg reflector (DBR)/germanium (Ge) cavity/SiC on top of a Ge substrate. Full-wave simulation results illustrate that the Tamm phonon-polaritons electric field can locally concentrate between the Ge cavity and the SiC film, contributed to the improved light-phonon interactions with an enhancement of light absorption. The structure has planar geometry and does not require nano-patterning to achieve perfect absorption of both polarizations of the incident light in a wide range of incident angles. Their absorption lines are tunable via engineering of the photon band-structure of the dielectric photonic nanostructures to achieve reversal of the geometrical phase across the interface with the plasmonic absorber.     

Highly integrated plasmonic sensor design for the simultaneous detection of multiple analytes

Herein, a highly integrated plasmonic sensor based on a multichannel metal-insulator-metal waveguide scheme for the simultaneous detection of multiple analytes is proposed. The numerical study is conducted via the finite element method based on commercially available software COMSOL. The sensor design is highly sensitive which can detect a minute change in the refractive index of the analyte. In this study, we have used the refractive index values of three different concentrations of ethanol and d-glucose solution to determine the sensor performance. It is observed that the device is highly sensitive as the operational wavelength lies in the deep shortwave infrared region. The numerically calculated sensitivity as high as 1948.67 nm/RIU is obtained for the cavity length of 325 nm which can be further improved by designing the device with large cavities. We believe that the proposed study is beneficial for the realization of the highly integrated plasmonic sensors for the lab-on-chip operations.     

The theoretic analysis of maskless surface plasmon resonant interference lithography by prism coupling

The use of an attenuated total reflection-coupling mode of prism coated with metal film to excite the interference of the surface plasmon polaritons （SPPs） was proposed for periodic patterning with a resolution of subwavelength scale. High intensity of electric field can be obtained because of the coupling between SPPs and evanescence under a resonance condition, which can reduce exposure time and improve contrast. In this paper, several critical parameters for maskless surface plasmon resonant lithography are described, and the preliminary simulation based on a finite difference timedomain technique agrees well with the theoretical analysis, which demonstrates this scheme and provides the theoretical basis for further experiments.