Highly directional emission from photonic crystal waveguides of subwavelength width

Recently it has been shown that it is possible to achieve directional emission out of a subwavelength aperture in a periodically corrugated metallic thin film. We report on theoretical and experimental studies of a related phenomenon concerning light emitted from photonic crystal waveguides that are less than a wavelength wide. We find that the termination of the photonic crystal end facets and an appropriate choice of the wavelength are instrumental in achieving very low numerical apertures. Our results hold promise for the combination of photonic crystal waveguides with conventional optical systems such as fibers, waveguides, and freely propagating light beams.     

Various evaluations of a diffractive transmitted field of light through a one-dimensional metallic grating with subwavelength slits

We compare the Fresnel-Kirchhoff diffraction formula, the superposition of cylindrical waves, and the twodimensional (2D) Green’s function diffraction formula with a rigorous vector algorithm in calculating the near and intermediately transmitted field of light through a one-dimensional metallic grating with subwavelength slits. It is found that the results calculated by the 2D Green’s function diffraction formula coincide well with the precise result. The other evaluations deviate from the exact result by varying proportions. Our findings may provide a useful and precise way to analyze the transmitted field features of a metallic grating and subsequent possibility of achieving optimal designs for metallic optical elements with subwavelength scale.     

双层金属纳米光栅的TE偏振光异常透射特性

根据在亚波长金属光栅表面添加电介质会引起TE偏振光的透射异常性, 应用严格耦合波理论和时域有限差分方法, 研究了双层金属纳米光栅在TE偏振光入射时产生的异常透射现象. 利用等效折射率方法建立了双层金属光栅的等效模型, 得到了TE偏振光透射率与聚合物的折射率、厚度以及金属层厚度的变化关系. 确认了结构中聚合物是透射异常出现的必要条件, TE偏振光以波导电磁模式在其中传播, 并认为类Fabry-Perot腔谐振是透射峰值产生的主要原因.     

Controlling the phase delay of light transmitted through double-layer metallic subwavelength slit arrays

We demonstrate that the phase of light transmitted through double-layer subwavelength metallic slit arrays can be controlled through lateral shift of the two layers. Our samples consist of two aluminum layers, each of which contains an array of subwavelength slits. The two layers are placed in sufficient proximity to allow coupling of the evanescent fields at resonance. By changing the lateral shift between the layers from zero to half the period, the phase of the transmitted electromagnetic field is increased by pi, while the transmitted intensity remains high. Such a controllable phase delay could open new capabilities for nanophotonic devices that cannot be achieved with single-layer structures.     

Resonant transmission of light through finite chains of subwavelength holes in a metallic film

In this Letter we show that the extraordinary optical transmission phenomenon found before in 2D hole arrays is already present in a linear chain of subwavelength holes, which can be considered as the basic geometrical unit showing this property. In order to study this problem, we have developed a new theoretical framework, able to analyze the optical properties of finite collections of subwavelength apertures and/or dimples (of any shape and placed in arbitrary positions) drilled in a metallic film.     

Analysis of phase shift of surface plasmon polaritons at metallic subwavelength hole arrays

We present the transmission spectra of light transmitting a metallic thin film perforated with differently shaped sub- wavelength hole arrays, which are calculated by a plane-wave-based transfer matrix method. We analyze the transmission peak positions and the phase-shift angles of different surface plasmon polariton （SPP） modes by using the microscopic theoretical model proposed by Haitao Liu and Philippe Lalanne [Liu Haitao, and Lalanne Philippe 2008 Nature 452 728], in which the phase shift properties of the SPPs scattered by the subwavelength hole arrays are considered. The results show that the transmission peak position and the minus phase shift angle of the SPP increase as the hole size increases. On the other hand, the effective dielectric constant of the metallic film can be deduced by the microscopic theoretical model.     

Electron-spin-dependent terahertz light transport in spintronic-plasmonic media

In this Letter, we demonstrate that electron spin can influence near-field mediated light propagation through a dense ensemble of subwavelength bimetallic ferromagnetic/nonmagnetic microparticles. In particular, we show that ferromagnetic particles coated with nonmagnetic metal nanolayers exhibit an enhanced magnetic field controlled attenuation of the electromagnetic field propagated through the sample. The mechanism is related to dynamic, electromagnetically induced electron spin accumulation in the nonmagnet. The discovery of an electron spin phenomenon in the light interaction with metallic particles opens the door to the marriage of spintronic and plasmonic technologies and could pave the way for the development of light-based devices that exploit the electron spin state.     

Evanescently coupled resonance in surface plasmon enhanced transmission

The optical transmission through subwavelength holes in metal films can be enhanced by several orders of magnitude by enabling interaction of the incident light with independent surface plasmon (SP) modes on either side of the film. Here, we show that this transmission is boosted by an additional factor of 10 when the energies of the SP modes on both sides are matched. These results, confirmed by a three-dimensional theoretical analysis, give a totally new understanding of the phenomenon of SP enhanced transmission. It is found that the holes behave like subwavelength cavities for the evanescent waves coupling the SPs on either side of the film. In this unusual device, the reflection at either end of the cavity is provided by the SP modes which act as frequency dependent mirrors.     

Enhanced optical reflection and multiple-peak transmission from a subwavelength slit with surface corrugations

We have observed a new phenomenon of the enhanced optical reflection and transmission from a subwavelength metallic slit with surface corrugations. The reflected energy is focused by the periodic structure and our experiment shows that it is more effective than a planar metal surface in real situations. The transmission spectrum performs the feature of a multipeak narrow-band transmission with a wavelength spacing of 1.4 nm resulting from the FP cavity resonance in the substrate film. Such optical response properties of our sample will be very useful for applications in many fields including wavelength-division-multiplexing (WDM) optical communications systems.     

Nonresonant broadband funneling of light via ultrasubwavelength channels

Enhancing and funneling light efficiently through deep subwavelength apertures is essential in harnessing light-matter interaction. Thus far, this has been accomplished resonantly, by exciting the structural surface plasmons of perforated nanostructured metal films, a phenomenon known as extraordinary optical transmission. Here, we present a new paradigm structure which possesses all the capabilities of extraordinary optical transmission platforms, yet operates nonresonantly on a distinctly different mechanism. Our proposed platform demonstrates efficient ultrabroadband funneling of optical power confined in an area as small as ～(λ/500)(2), where optical fields are enhanced, thus exhibiting functional possibilities beyond resonant platforms. We analyze the nonresonant mechanism underpinning such a phenomenon with a simple quasistatic picture, which shows excellent agreement with our numerical simulations.     

Tuning the extraordinary optical transmission through subwavelength hole array by applying a magnetic field

The transmission of light through a thin Ag film with a periodic subwavelength hole array can be influenced by the presence of the externally applied magnetic field H. Using a three-dimensional finite element method, we show that the spectral locations of the transmission peak resonances can be shifted by varying the magnitude and direction of the H. The transmission peaks have blueshift, and the higher the magnitude of H the larger the blueshift. The shift is due to the change of cavity resonance condition as a result of the magneto-induced anisotropy in the optical properties of the Ag film. Hence, high transmittance for any desired wavelength can be achieved by applying an appropriate H to the metallic film of optimized material and hole parameters.     

Subwavelength propagation and localization of light using surface plasmons: A brief perspective

Surface plasmons at the metal–dielectric interface have emerged as an important candidate to propagate and localize light at subwavelength scales. By tailoring the geometry and arrangement of metallic nanoarchitectures, propagating and localized surface plasmons can be obtained. In this brief perspective, we discuss: (1) how surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) can be optically excited in metallic nanoarchitectures by employing a variety of optical microscopy methods; (2) how SPPs and LSPs in plasmonic nanowires can be utilized for subwavelength polarization optics and single-molecule surface-enhanced Raman scattering (SERS) on a photonic chip; and (3) how individual plasmonic nanowire can be optically manipulated using optical trapping methods.     

Enhanced light transmission through a single subwavelength aperture

The optical transmission through a subwavelength aperture in a metal film is strongly enhanced when the incident light is resonant with surface plasmons at the corrugated metal surface surrounding the aperture. Conversely, the aperture acts as a novel probe of the surface plasmons, yielding useful insights for optimizing the transmission enhancement. For the optimal corrugation geometry, a set of concentric circular grooves, three times more light is transmitted through the central subwavelength aperture than directly impinges upon it. This effect is useful in the fabrication of near-field optical devices with extremely high optical throughput.     

Fabrication methods of 3D periodic metallic nano/microstructures for photonics applications

Periodic metallic nano/microstructures have received a great a deal of attention in the photonics research community over the last few decades due to their intriguing optical properties. Three‐dimensional metallic nano/microstructures such as metallic photonic crystals, metamaterials, and plasmonic devices possess unique characteristics of tailored thermal radiation, negative refraction and deep subwavelength confinement of light. In this article, the recent progress on the experimental methods for the realisation of three‐dimensional periodic metallic and thin metal film coated dielectric nano/microstructures operating from optical to mid‐infrared frequencies has been reviewed. Advancement of the state‐of‐the‐art nanofabrication methods over the last few decades have led to the development of metallic nano/microstructures of diverse geometries, high resolution features and large scale production. The recent progress in the novel fabrication methods have inspired the development of functional and exciting photonic devices based on periodic metallic nano/microstructures with various applications in photonics including communications, photovoltaics, and biophotonics.     

Optical switching in metal-slit arrays on nonlinear dielectric substrates

We propose a scheme for an optical limiter and switch of the transmitted light intensity in an array of subwavelength metallic slits placed on a nonlinear Kerr-type dielectric substrate of finite thickness, where the geometrical parameters are designed for operation at telecom wavelengths. Our approach is based on the abrupt changes of the output light intensity observed in these systems near transmission minima.     

Time-domain differentiation of terahertz pulses

We report on the time-domain differentiation of light waves by metallic transmission gratings. Time-resolved terahertz experiments show that the first time derivative of an arbitrary waveform can be achieved by use of gratings of subwavelength period. The results are in accord with classical diffraction theory and may permit novel applications for tailoring few-cycle light pulses and ultrahigh-frequency optoelectronics.     

基于一维金属光子晶体平凹镜的柱矢量光束亚波长聚焦

柱矢量光束具有柱对称性的偏振分布,其独特的光场分布和聚焦特性被广泛应用于光学微操纵及光学成像等领域,并迅速向亚波长尺度拓展.通常,亚波长尺度聚焦采用等离激元透镜实现,但存在光场调控的偏振态局限性.而借助光子晶体的负折射效应,不仅能够实现亚波长聚焦或成像,而且应对正交偏振态同时有效.采用对电磁波具有更强调控能力的一维金属光子晶体结构,计算得到的能带结构和等频曲线表明其负折射效应在特定波段对正交偏振态同时有效.在此基础上设计出一维金属光子晶体柱对称平凹镜结构,通过有限元算法模拟显示了可见光波段的径向和旋向偏振光的同时亚波长聚焦行为.进一步的结果表明,改变柱矢量光束的偏振组分能够直接有效地调节焦场空间分布及偏振分布特性.所提出的平凹镜结构能够实现对任意偏振组分的柱矢量光束的亚波长尺度聚焦,且该结构的设计对于各波段情况均有参考意义.该研究结果对小尺度粒子的光学微操纵、超分辨率成像等相关领域具有潜在的应用价值.     

Extraordinary acoustic transmission through a 1D grating with very narrow apertures

Recently, there has been an increased interest in studying extraordinary optical transmission (EOT) through subwavelength aperture arrays perforated in a metallic film. In this Letter, we report that the transmission of an incident acoustic wave through a one-dimensional acoustic grating can also be drastically enhanced. This extraordinary acoustic transmission (EAT) has been investigated both theoretically and experimentally, showing that the coupling between the diffractive wave and the wave-guide mode plays an important role in EAT. This phenomenon can have potential applications in acoustics and also might provide a better understanding of EOT in optical subwavelength systems.     

Optical beam splitting and asymmetric transmission in bi-layer metagratings

In this work, inspired by advances in twisted two-dimensional materials, we design and study a new type of optical bi-layer metasurface system, which is based on subwavelength metal slit arrays with phase-gradient modulation, referred to as metagratings(MGs). It is shown that due to the found reversed diffraction law, the interlayer interaction that can be simply adjusted by the gap size can produce a transition from optical beam splitting to high-efficiency asymmetric transmission of incident light from two opposite directions. Our results provide new physics and some advantages for designing subwavelength optical devices to realize efficient wavefront manipulation and one-way propagation.     

Interference-induced enhancement of intensity and energy of a quantum optical field by a subwavelength array of coherent light sources

Recently, we have shown a mechanism that could provide great resonant and nonresonant transmission enhancements of the classical (nonquantum) light waves passed through subwavelength aperture arrays in thin metal films not by the plasmon–polariton waves, but by the constructive interference of diffracted waves (beams generated by the apertures) at the detector placed in the far-field zone. We now present a quantum reformulation of the model. The Hamiltonian describing the phenomenon of interference-induced enhancement and suppression of both the intensity and energy of a quantum optical field is derived. The basic properties of the field energy determining by the Hamiltonian are analyzed. Normally, the interference (addition) of two or more waves causes enhancement or suppression of the light intensity, but not the light energy. The model shows that the phenomenon could be observed experimentally, for instance, by using a subwavelength array of the coherent quantum light-sources (one- and two-dimensional subwavelength apertures, fibers, dipoles, and atoms).