基于耦合介质纳米线的深亚波长局域波导

提出了一种基于耦合介质纳米线的深亚波长局域波导,通过两根紧邻的高折射率介质纳米线的耦合,该波导可以将光场有效束缚在纳米线之间的低折射率纳米缝隙中. 计算模拟的结果表明,该波导的有效模场面积达到Λ²₀/200,比单根纳米线波导小一个数量级,这种深亚波长的模场束缚能力可以与表面等离激元混合波导相比拟. 计算模拟的结果还表明,纳米线可能带有的低折射率氧化膜、低折射率衬底的存在、以及纳米线间尺寸存在的一定差异对于该波导结构的实际应用都不会产生很大 关键词： 介质波导 亚波长局域 表面等离激元波导 纳米线     

紫外表面等离激元在基于氧化锌纳米线的半导体-绝缘介质-金属结构中的输运特性研究

研究了紫外表面等离激元在半导体纳米线-绝缘介质-金属构成的波导结构中的输运问题,借助有限元方法,对这种波导所支持导模的电磁能分布、有效折射率、传播长度和有效模场面积随电磁参数和几何结构参数的依赖关系进行了分析.计算结果表明:以氧化锌纳米线作为增益介质,绝缘材料选择折射率小的空气,金属选择铝能够实现对输出光场的亚波长约束,有效模场面积达到λ2/100,同时保持低的传输损耗和高场强限制能力;有望用作纳米光源,使得相关的生物探测器件和医疗诊断设备实现更高的灵敏度和更小的体积.     

Wave propagation in deep-subwavelength mode waveguides

This Letter proposes a dielectric waveguide with deep-subwavelength mode sizes. Results of both frequency domain and time domain analysis show that the effective mode area is below λ(0)(2)/400 and can even reach λ(0)(2)/1000 (λ(0) is the wavelength in vacuum). The effective electrical mode area can be comparable to that of a hybrid plasmonic subwavelength confinement waveguide, with reduced optical absorption. In contrast to slot waveguides, which guide light in low-index materials, the proposed structure guides light in high-index materials. Results obtained in this Letter show that the losses are sensitive to the surface roughness on the tens of nanometers scale. The structure can be used to design ring resonators with a quality factor comparable to that of a diffraction-limited dielectric ring resonator with the same standing wave numbers. The property can be applied in nonlinear effect enhancement or laser design with ultralow threshold.     

Reducing crosstalk between nanowire-based hybrid plasmonic waveguides

Hybrid plasmonic waveguides based on a surface oxidized dielectric nanowire placed on a metal surface can facilitate simultaneously deep subwavelength mode confinement and large propagation length. Directional coupling based on such waveguides are theoretically investigated. Much lower crosstalk is noticed for such hybrid plasmonic waveguides compared to conventional waveguides based on bare dielectric nanowires. Some modifications, such as vertically placing the metal surfaces or using a metallic block between the nanowires, are studied which can further reduce the crosstalk between two waveguides. The proposed low crosstalk structures based on hybrid plasmonic waveguides can provide a simple platform for plasmonic integration which can at the same time easily interface with traditional photonic circuits.     

Enhancing Bremsstrahlung production from ultraintense laser-solid interactions with front surface structures

A new type of a coaxial multi-layer plasmonic waveguide is proposed. The mode propagation properties are analyzed at the communication working wavelength. Theoretical investigations reveal that the enhanced optical confinement can be achieved in the two low-index dielectric media layers. The mode size can be sub- or deep sub-wavelength scale. The mode propagation loss can be well compensated by replacing the high-index dielectric media with gain material to achieve longer propagation length with better mode confinement. The comparisons of the mode properties between the proposed waveguide and waveguides studied in the published literatures are also considered. These investigations potentially lay the groundwork for the further applications of nanowire type multilayer hybrid structures. This structure could also enable various applications such asnanophotonic waveguides, high-quality nanolasers, and optical trapping and biosensors.     

混合表面等离子体激元的纳米激光器设计

为了实现纳米激光器的性能优化,设计了一种基于纳米线、半圆形氟化镁、三角形空气槽和金属脊结构的纳米激光器模型。模型中耦合在低折射率电介质层中的SPP模式和纳米线波导可以在低折射率间隙下像电容器那样存储光能,从而使低折射率的空气槽场强明显增大。应用有限元法在COMSOL Multiphysics软件下,分析了该纳米激光器模型的电场分布、模式特性、品质因数和增益阈值随着设计结构几何参数变化的规律,通过各部分折线图的综合分析来得出模型性能的数据。分析表明：该模型的光场约束能力较强且传播损耗较低,其中归一化面积最小可达到0.004 8,有效传输损耗最小可达到0.002。波导模场区域和限制因素表明,该激光器模型可以实现输出光场的亚波长约束。该模型基本实现了低增益阈值、低传输损耗和高品质因数的要求。     

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.     

Dielectric‐loaded plasmonic waveguide components: Going practical

Surface plasmon propagating modes supported by metal/dielectric interfaces in various configurations can be used for radiation guiding similarly to conventional dielectric waveguides. Plasmonic waveguides offer two attractive features: subdiffraction mode confinement and the presence of conducting elements at the mode‐field maximum. The first feature can be exploited to realize ultrahigh density of nanophotonics components, whereas the second feature enables the development of dynamic components controlling the plasmon propagation with ultralow signals, minimizing heat dissipation in switching elements. While the first feature is yet to be brought close to the domain of practical applications because of high propagation losses, the second one is already being investigated for bringing down power requirements in optical communication systems. In this review, the latest application‐oriented research on radiation modulation and routing using thermo‐optic dielectric‐loaded plasmonic waveguide components integrated with silicon‐based photonic waveguides is overviewed. Their employment under conditions of real telecommunications is addressed, highlighting challenges and perspectives.     

A hybrid long-range surface plasmon waveguide comprising a narrow metal stripe surrounded by the low-index dielectric regions

A novel hybrid long-range surface plasmon waveguide structure comprising a narrow metal stripe, two relative low-index dielectric regions and dielectric ridges is proposed and analyzed. With the dielectric ridges and the two relative low-index dielectric regions symmetrically distributed on both sides of the narrow metal stripe, a symmetric hybrid long range mode with low electromagnetic transmission loss and subwavelength scale confinement is achieved. By optimizing the parameters, the propagation length of the proposed waveguide is increased to over two times to that of the conventional symmetric dielectric loaded surface plasmon waveguide, but the mode size only increases about 20%. For this benefit, the hybrid long-range surface plasmons waveguide is a good candidate for realizing high density photonic integration circuits.     

Design of a subwavelength bent C-aperture waveguide

We present a design for a subwavelength C-shaped optical waveguide with a 90 degrees junction that efficiently transports light while maintaining tight confinement with an exit spot size of lambda/7. Finite-difference time-domain simulations of perfect electric conductors and Au C-aperture waveguides are performed for optical frequencies. A design resonant near 780 nm is presented, with a spot size of 107 nm x 107 nm and an energy density enhancement factor of 10 for a bent waveguide of total length 1.4 microm.     

Tunable coupling of a hybrid plasmonic waveguide consisting of two identical dielectric cylinders and a silver film

The propagation length of surface plasmon polaritons(SPPs) is intrinsically limited by the metallic ohmic loss that is enhanced by the strongly confined electromagnetic field. In this paper, we propose a new class of hybrid plasmonic waveguides(HPWs) that can support long-range SPP propagation while keeping subwavelength optical field confinement. It is shown that the coupling between the waveguides can be well tuned by simply varying the structural parameters. Compared with conventional HPWs, a larger propagation length as well as a better optical field confinement can be simultaneously realized. The proposed structure with better optical performance can be useful for future photonic device design and optical integration research.     

Simulation investigation on channel surface plasmon guiding by terahertz wave through subwavelength metal V-groove

The waveguide propagation properties of terahertz wave through subwavelength metallic triangular groove channels have been simulationally investigated. The effects of groove depth, groove angle and dielectric filling materials on propagation property have been shown and discussed. The results show that with increasing of groove depth and angle degree the propagation constant of channel surface plasmon polariton mode decreases. The propagation constant of poor conductive metal is larger than that of good conductive metal, which may result from the fact that the former has larger skin depth. In addition, the confinement of CSPP mode could be improved by increasing the refractive index of dielectric filling materials.     

亚波长尺度下混合等离子泄漏模式激光

由于光存在衍射极限,因此传统方法不能实现亚波长尺度下的激光激射.为了打破这一衍射极限,本文设计了金属-介电层-半导体堆叠结构来实现深亚波长尺度下的激光激射,并讨论了相关结构对模式传播的影响.结构设计上,采用低介电常数金属银作为衬底、10?nm厚的LiF作为介电层、具有六边形截面的半导体纳米线ZnO作为高介电常数层,采用...     

Polarization-independent grating couplers for silicon-on-insulator nanophotonic waveguides

We propose the use of subwavelength structures in a waveguide grating to achieve polarization-independent coupling of light between an optical fiber and a silicon-on-insulator (SOI) optical waveguide. The subwavelength structure allows the mode effective indices of the TE and TM modes in the grating section to be precisely engineered. We calculate that coupling efficiency of over 64% is possible using the proposed design for polarization-independent coupling between single-mode optical fibers and SOI nanophotonic waveguides.     

Optical and microwave analysis of mushroom-type waveguides for traveling wave electroabsorption modulators based on asymmetric intra-step-barrier coupled double strained quantum wells by full-vectorial method

The finite difference method is exploited for a full-vectorial analysis of mushroom-type waveguides for traveling wave electroabsorption modulators (TWEAM) based on asymmetric intra-step-barrier coupled double strained quantum wells (AICD-SQW). In this analysis, the discontinuities of the normal components of the electric field across abrupt dielectric interfaces which are known as the limitations of scalar and semivectorial approximation methods are considered. The optical field distributions in mushroom-type TWEAM based on AICD-SQW and conventional ridge-type TWEAM of the same active region for 1.55 μm operation are presented. The important parameters in the high-frequency TWEAM design such as optical effective index which defines optical velocity and transverse mode confinement factor are calculated. Then, the transmission line microwave properties (microwave index, microwave loss, and characteristic impedance) of TWEAMs are obtained. The modulation response of mushroom-type TWEAM is calculated using circuit model by considering interaction between microwave and optical fields in waveguide and compared with conventional ridge-type TWEAM. It is found that increasing the width of p-cladding layer with the same i-layer to reduce the resistance in p-i-n mushroom-type waveguide of TWEAM based on AICD-SQW can improve the microwave propagation loss and thus the high-speed electro-optical response.     

Analysis and design of efficient coupling in photonic crystal circuits

A rigorous analysis and design of efficient coupling from photonic crystal (PhC) waveguides into conventional dielectric waveguides is reported. Closed-form expressions for the reflection and transmission matrices that completely characterize the scattering that occurs at the interface are derived based on an eigenmode expansion technique and a Bloch basis. Analytic expressions are used to analyze the reflection into PhC waveguides. We obtain that negligible reflection can be achieved by choosing a certain interface within a PhC unit cell. Furthermore, analytic expressions are used to design a novel and compact coupler structure in order to achieve high coupling efficiency when broad dielectric waveguides are considered. Thereby, transmission efficiencies near 100 from the fundamental guided Bloch mode into the fundamental waveguide mode are achieved.     

Efficient second-harmonic generation in nonlinear plasmonic waveguide

We theoretically studied a nonlinear optical process in a hybrid plasmonic waveguide composed of a nonlinear dielectric waveguide and a metal film with a separation of a thin air gap. Owing to the hybridization effect of guided mode and surface plasmon polariton mode, this particular waveguide is able to confine the optical-field in a deep subwavelength scale together with low propagation loss. Based on this, efficient second-harmonic generations (SHG) were revealed at the fundamental wavelength of λ=1.55?μm with good field confinement. The SHG efficiency, as well as the coupling coefficient and mode area, were analyzed and discussed in detail with respect to the structural parameters.     

Nanotube based hybrid plasmon polariton waveguide for propagation loss reduction and enhanced field confinement inside the gap region at the subwavelength scale

We present a comprehensive numerical investigation on the guiding properties of a nanotube based hybrid plasmonic waveguide, which comprises a high-index dielectric nanotube placed above a metallic substrate. It is shown that the incorporation of the nanotube offers additional freedom for tuning the optical performance of the hybrid plasmonic structure when compared to the traditional nanowire based hybrid counterparts, which enables further reduction of the propagation loss and enhanced field confinement inside the gap region, while simultaneously maintaining a subwavelength mode size at appropriate geometries. Systematic geometric parameters mapping considering the size of the nanotube and the dimension of the gap reveals that the tradeoff between the confinement and loss could be further balanced through optimizing key physical parameters. These investigations potentially lay the groundwork for the further applications of nanotube based hybrid structures.     

Hybrid vertical directional coupling between a long range surface plasmon polariton waveguide and a dielectric waveguide

To investigate light coupling between a long range surface plasmon polariton (LRSPP) waveguide and a conventional integrated optical component, a hybrid vertical directional coupler consisting of a LRSPP waveguides and a dielectric waveguide is investigated and fabricated. In the proposed coupler the dielectric waveguide and LRSPP waveguide are vertically configured for dense integration and strong coupling. The characteristics of the even and odd super-modes of the coupler are also analyzed to design the device. The fabricated device exhibits damped sinusoidal behavior along the coupling length due to propagation loss of the LRSPP waveguide. The maximum power transfer of 86% from the LRSPP waveguide to the dielectric waveguide is achieved at the coupling length of 600 μm. The measured characteristics of the device are in relatively good agreement with a theoretical analysis.     

Optical field enhancement in nanoscale slot waveguides of hyperbolic metamaterials

Nanoscale slot waveguides of hyperbolic metamaterials are proposed and demonstrated for achieving large optical field enhancement. The dependence of the enhanced electric field within the air slot on waveguide mode coupling and permittivity tensors of hyperbolic metamaterials is analyzed both numerically and analytically. Optical intensity in the metamaterial slot waveguide can be more than 25 times stronger than that in a conventional silicon slot waveguide, due to tight optical mode confinement enabled by the ultrahigh refractive indices supported in hyperbolic metamaterials. The electric field enhancement effects are also verified with the realistic metal-dielectric multilayer waveguide structure.