Asymmetric plasmonic-dielectric coupler with short coupling length, high extinction ratio, and low insertion loss

Asymmetric directional coupling between a hybrid plasmonic waveguide with subwavelength field confinement and a conventional dielectric waveguide is investigated. The proposed hybrid coupler features short coupling length, high coupling efficiency, high extinction ratio, and low insertion loss; it can also be integrated into a silicon-based platform. This coupler can be potentially adopted for signal routing between plasmonic waveguides and dielectric waveguides in photonic integrated circuits. Furthermore, it can be exploited to efficiently excite hybrid plasmonic modes with conventional dielectric modes.     

Nanoplasmonics: Engineering and observation of localized plasmon modes

This review article focuses on the basic physics of LSPR modes, and how they can be observed. For dipolar modes, observation is rather straightforward. However, higher order modes often require the use of more advanced experimental conditions or dedicated spectroscopic techniques such as electron energy‐loss spectroscopy (EELS). Eventually, bespoke LSPR modes can be engineered when different cavities are brought together to interact, giving rise to super‐ or sub‐radiant modes, as well as Fano resonances, which in the right conditions can evolve into plasmonic induced transparency.     

基于双矩形腔边耦合波导的等离子体诱导透明效应

为了降低功耗、实现超快速响应,设计了一种基于双矩形腔边耦合等离子体波导系统,并研究了其等离子体诱导透明效应.采用光学Kerr效应超快调控石墨烯-Ag复合材料波导结构,实现1 ps量级的超快响应时间.动态调控等离子体波导的传输相移,当泵浦光强为5.83 MW/cm^2时,等离子体诱导透明系统能够实现透射光谱π相移,这是因为基于石墨烯-Ag复合材料结构等离子体波导具有大的等效光学Kerr非线性系数,表面等离子体激元局域光场和等离子体诱导透明效应慢光对光学Kerr效应产生了协同增强作用,大大降低了系统获得透射光谱π相移的泵浦光强.等离子体诱导透明效应透明窗口的可调谐带宽为40 nm,系统的群延时控制在0.15 ps到0.85 ps之间,并且光波通过间接耦合或者相位耦合机制实现了等离子体诱导透明效应相移倍增效应.耦合模式理论计算结果很好地吻合了时域有限差分法仿真模拟结果,研究结果对于低功耗、超快速非线性响应和紧凑型光子器件的设计和制作具有一定的参考意义.     

Transparency induced by the quantum interference of a six-level atom in photonic crystals with defect modes

The absorption-dispersion spectra of a six-level atom embedded in double-band photonic crystals are investigated. It is shown that if there is no defect mode in the photonic band gap, there are three types of transparency windows appear in the absorption-dispersion spectra. If a defect mode is introduced into the photonic band gap, we found some additional transparency windows in the absorption-dispersion spectra. One type of them appears as long as the defect mode exists, but the others appear only when the quantum interference occurs. The transparency windows can be changed by varying the parameters of the defect mode.     

数值模拟二维间隙表面等离子波导传输特性

利用表面等离子激元的新颖特性,设计了二维间隙表面等离子波导.以这种结构为基础通过变形和组合形成90°直角弯曲波导、T型光功率分配器和光开光,采用时域有限差分法研究了它们的传输特性.结果表明:不同于介质光波导的弯曲损耗来自于辐射泄漏,90°直角弯曲间隙表面等离子波导的能量损耗主要来自于金属中的欧姆热损耗.在间隙达到40 nm以上后,当直行段的长度适当时,弯曲段的透射率较相同长度的直波导的透射率要大.T型光功率分配器在两输出波导的间隙宽度比达到0.6及以上时,不同于传统介质波导的分光原则,能量主要沿等效折射率较小的输出臂流出.当两输入光的相位反相时,T型光开关处于输出截止的状态,当两输入光的相位同相时,T型光开关处于输出导通的状态.所有波导间隙均小于衍射极限,实现了超衍射极限传播,可用于未来了超大规模集成光路中.     

等离子体金属波导在外磁场调制下的传输模式

在通信系统中波导的设计向着多功能和可调制方向发展。波导基于等离子体金属材料在外磁场作用下设计平面波导。等离子体金属材料在外磁场作用下会产生表面等离子体激元和非互易传播双重功能。从基本的麦克斯韦方程和边界条件出发,详细推导了模式的色散方程,并根据模式特征进行了分类。波导具有明显的非互易传播和可调制的特性。     

基于表面等离子体的太赫兹光束方向调控的模拟研究

本文根据锑化铟(InSb)材料在THz波段下复介电常数对温度的响应特性,采用了带有光栅的锑化铟-介质-锑化铟的表面等离子体波导结构,实现了1THz频率光束的准直出射,并能够通过调整结构两侧光栅的温度差来控制出射光束的角度.由时域有限差分方法得到光束偏转角度与温度差之间的关系.理论上利用表面等离子体波导模式的光栅耦合机理解释光束方向改变的原因. 关键词： 表面等离子体 太赫兹 时域有限差分方法 光束方向控制     

光子晶体中四能级系统的量子相干效应

研究了处于光子带隙材料中的四能级原子系统的电磁感应透明、自发辐射和光子开关效应，分析了其稳态与瞬态特性, 发现特殊的模密度能够导致反常的吸收、色散、自发辐射及瞬态无反转增益, 并可以通过外加调制场进行控制.详细讨论了特殊频率处模密度的变化对透明窗口和光子开关效应的影响. 关键词： 光子带隙材料 电磁感应透明 模密度 光子开关     

Photonic bandgap plasmonic waveguides

A type of a plasmonic waveguide has been proposed featuring an "open" design that is easy to manufacture, simple to excite and offers convenient access to a plasmonic mode. Optical properties of photonic bandgap (PBG) plasmonic waveguides are investigated experimentally by leakage radiation microscopy and numerically using the finite element method confirming photonic bandgap guidance in a broad spectral range. Propagation and localization characteristics of a PBG plasmonic waveguide have been discussed as a function of the wavelength of operation, waveguide core size, and the number of ridges in the periodic reflector for fundamental and higher order plasmonic modes of the waveguide.     

Slow propagation of plasmonic modes in a symmetrical waveguide containing anisotropic metamaterial

We study the slow propagation of plasmonic modes in a three-layer symmetric waveguide with anisotropic metamaterial claddings and a dielectric core. The dispersion equations for symmetric and anti-symmetric plasmonic modes are derived, and a graphic method is used to verify the zero-group-velocity point on the dispersion curves. Simulation results show the influences of signs of tensors and anisotropy of metamaterial on trapped plasmonic modes.     

Efficient coupling of light into and out of a photonic crystal waveguide via surface modes

In this paper, we show how the coupling of light into a photonic crystal waveguide can be greatly enhanced by creating a periodic modulation in the dielectric structure surrounding the entrance of the waveguide. In this way, surface modes supported by the system can funnel the light that impinges onto the surface into the interior of the waveguide. Moreover, we also demonstrate that the shape and direction of the beam that emerges from the structure can be tailored by constructing a periodic corrugation near the exit side of the waveguide.     

Optical modes in a plasmonic waveguide with electrically anisotropic metamaterial

We study the optical modes in a plasmonic waveguide with electrically anisotropic metamaterial and dielectric, including symmetric (anti-symmetric) photonic mode and symmetric (anti-symmetric) plasmonic mode. The dispersion curves for these modes are derived, and a graphical method is used to calculate the solution of symmetric photonic mode and anti-symmetric plasmonic mode. By simulation results the conditions of the existence for these modes are deduced in each case.     

Characteristics analysis of hybrid plasmonic waveguide for low-loss lightwave guiding

It has been experimentally demonstrated that a low-loss guided hybrid mode is supported if a metal strip is embedded in a low index polymer layer surrounded by two high index slabs. In this paper, further numerical analyses on the guided hybrid modes are reported to fully elucidate the characteristics of the hybrid plasmonic waveguide. For a one-dimensional slab structure with a metal film of infinite width, simulation results exhibit that low-loss guided hybrid modes are associated with surface plasmon modes and dual dielectric slab modes. The optical properties of the guided modes are improved by increasing the field intensity which is confined into lossless dielectric layers by decreasing the metal film thickness and increasing the refractive index and thickness of the high-index slabs. The finite element method is used to investigate the lateral mode confinement of the optical guided modes by the corresponding metal strip. By reducing the metal film width, the guided modes are confined in the plane transverse to the direction of propagation and the characteristics are significantly improved. The hybrid plasmonic waveguide can be exploited for long-range propagation-based application such as optical interconnection.     

Induced transparency in nanoscale plasmonic resonator systems

An optical effect analogous to electromagnetically induced transparency (EIT) is observed in nanoscale plasmonic resonator systems. The system consists of a slot cavity as well as plasmonic bus and resonant waveguides, where the phase-matching condition of the resonant waveguide is tunable for the generation of an obvious EIT-like coupled resonator-induced transparency effect. A dynamic theory is utilized to exactly analyze the influence of physical parameters on transmission characteristics. The transparency effect induced by coupled resonance may have potential applications for nanoscale optical switching, nanolaser, and slow-light devices in highly integrated optical circuits.     

Modes splitting in graphene-based double-barrier waveguides

The graphene-based double-barrier waveguides induced by electric field have been investigated. The guided modes can only exist in the case of Klein tunneling, and the fundamental mode is absent. The guided modes in the single-barrier waveguide split into symmetric and antisymmetric modes with different incident angles in the double-barrier waveguide.The phase difference between electron states and hole states is also discussed. The phase difference for the two splitting modes is close to each other and increases with the order of guided modes. These phenomena can be helpful for the potential applications in graphene-based optoelectronic devices.     

Plasmonic waveguiding in a hexagonally ordered metal wire array

We propose the inclusion of a structured pattern of nanoscale metal wires in a silica fiber to form a symmetric plasmonic waveguide. The surface plasmon polariton modes within the waveguide are studied by varying the wire diameter and spacing. Simulation results show that hybridization of the single-wire mode and the gap plasmon mode can yield a hybrid mode with optimum propagation lengths comparable to those reported for other structures but with better light confinement. The fiber can be easily doped with a gain material to offset the loss so that the resultant waveguide will be useful for integration with electronic circuits at nanometer dimensions.     

Dynamically tunable multiband plasmon-induced transparency effect based on graphene nanoribbon waveguide coupled with rectangle cavities system

A dynamically tunable multiband plasmon-induced transparency (PIT) effect in a series of rectangle cavities coupled with a graphene nanoribbon waveguide system is investigated theoretically and numerically by tuning the Fermi level of the graphene rectangle cavity. A single-PIT effect is realized using two different methods: one is the direct destructive interference between bright and dark modes, and the other is the indirect coupling through a graphene nanoribbon waveguide. Moreover, dual-PIT effect is obtained by three rectangle cavities side-coupled with a graphene nanoribbon waveguide. Results show that the magnitude of the dual-PIT window can be controlled between 0.21 and 0.74, and the corresponding group index is controlled between 143.2 and 108.6. Furthermore, the triple-PIT effect is achieved by the combination of bright-dark mode coupling and the cavities side-coupled with waveguide mechanism. Thus, sharp PIT windows can be formed, a high transmission is maintained between 0.51 and 0.74, and the corresponding group index is controlled between 161.4 and 115.8. Compared with previously proposed graphene-based PIT effects, the size of the introduced structure is less than 0.5 μm². Particularly, the slow light effect is crucial in the current research. Therefore, a novel approach is introduced toward the realization of optical sensors, optical filters, and slow light and light storage devices with ultra-compact, multiband, and dynamic tunable.     

Plasmonic leaky‐mode lasing in active semiconductor nanowires

Leaky modes are below‐cutoff waveguide modes that lose part of their energy to the continuum of radiation modes during propagation. In photonic nanowire lasers, leaky modes have to compete with almost lossless above‐cutoff modes and are therefore usually prevented from crossing the lasing threshold. The situation is drastically different in plasmonic nanowire systems where the above‐cutoff plasmonic modes are very lossy because of their strong confinement to the metal surface. Due to gain guiding, the threshold gain of the hybrid electric leaky mode does not increase strongly with reduced wire diameter and stays below that of all other modes, making it possible to observe leaky‐mode lasing. Plasmonic ZnO nanowire lasers operating in the gain‐guided regime could be used as coherent sources of surface plasmon polaritons at the nanoscale or as surface plasmon emitting diodes with an emission angle that depends on the nanowire diameter and the color of the surface plasmon polariton.

     

光折变表面波诱导的薄层波导中的导波模式

利用数值模拟对扩散非线性机制下由光折变表面波诱导的薄层波导中导模的形成和特点进行了研究。采用分布傅里叶法对导模的传输特性进行了模拟。通过求解本征方程,对光折变表面波诱导的薄层波导中存在的导波模式进行了数值求解。通过调节传播常数和波导参数的方法,可以控制导模的阶数和传播波形。随着阶数的增加,导模轮廓的对称性越来越差;随着波导参数的增加,导模的峰值振幅单调递增。导模的能量主要聚集在晶体薄层波导中靠近-c轴的一侧,随着传播常数的增大,导模能量先减小后增大,且导模可以稳定传播。     

Theoretical investigation of hierarchical sub-wavelength photonic structures fabricated using high-order waveguide-mode interference lithograph

This paper presents the theoretical investigation of hierarchical sub-wavelength photonic structures with various periods and numbers of layers, which were fabricated using a high-order waveguide-mode interference field. A 442-nm laser was used to excite high-order waveguide modes in an asymmetric metal-cladding dielectric waveguide structure. The dispersion curve of the waveguide modes was theoretically analyzed, and the distribution of the interference field of high-order waveguide modes was numerically simulated using the finite-element method. The various dependences of the characteristics of hierarchical sub-wavelength photonic structures on the thickness and refractive index of the photoresist and the waveguide mode were investigated in detail. These hierarchical sub-wavelength photonic structures have various periods and numbers of layers and can be fabricated by a simple and low-cost method.