Abrupt Phase Shift Research Articles

Ultrafast spallation dynamics of a thin gold film characterized by imaging pump-probe interferometry

Interferometry allows to measure microscopic displacements in the nanometer scale. This work introduces an imaging pump-probe interferometer that enables to detect the spatially resolved phase shift of the probe radiation being reflected on a sample surface after ultrashort pulsed laser excitation with a temporal resolution of 40 fs and a maximum temporal delay of 3 ns. The capability of the pump-probe interferometer is demonstrated on the spallation of a thin gold film upon femtosecond laser irradiation. The pump-probe interferometer enables to measure a minimum phase change of Δφ<π/10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta \\varphi <\\pi /10$$\\end{document} which corresponds to a displacement of Δh<\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta h<$$\\end{document} 12.5 nm for the applied probe wavelength of 500 nm. Upon irradiation, two distinct phase changes are observable: First, an abrupt minor phase shift has been measured in the femtosecond range, which is attributed to the changed optical properties of the sample surface after excitation. Second, a more pronounced continuing phase shift increase is detectable after a few tens of picoseconds resulting from the onset of spallation. Based on the measured spatially resolved phase shift, the transient surface topography during the spallation is reconstructed. The determined velocity of the ablated material reaches a maximum of a few 1000 m/s at ten picosecond after irradiation and decreases to 250 m/s afterwards. Consequently, the introduced imaging pump-probe interferometer provides important insights into the physical processes during laser excitation as well as the subsequent laser-induced ablation, and will enable to validate theoretical models quantitatively in following studies.

Nanoscale visualization and spectral fingerprints of the charge order in ScV6Sn6 distinct from other kagome metals

Charge density waves (CDWs) in kagome metals have been tied to many exotic phenomena. Here, using spectroscopic-imaging scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we study the charge order in kagome metal ScV6Sn6. The similarity of electronic band structures of ScV6Sn6 and TbV6Sn6 (where charge ordering is absent) suggests that charge ordering in ScV6Sn6 is unlikely to be primarily driven by Fermi surface nesting of the Van Hove singularities. In contrast to the CDW state of cousin kagome metals, we find no evidence supporting rotation symmetry breaking. Differential conductance dI/dV spectra show a partial gap Δ1CO ≈ 20 meV at the Fermi level. Interestingly, dI/dV maps reveal that charge modulations exhibit an abrupt phase shift as a function of energy at energy much higher than Δ1CO, which we attribute to another spectral gap. Our experiments reveal a distinctive nature of the charge order in ScV6Sn6 with fundamental differences compared to other kagome metals.

Graphene-Enabled Tunable Phase Gradient Metasurface for Broadband Dispersion Manipulation of Terahertz Wave.

With the increasing demand for the miniaturization and flexibility of optical devices, graphene-based metasurfaces have emerged as a promising ideal design platform for realizing planar and tunable electromagnetic or optical devices. In this paper, we propose a tunable metasurface with low-dispersion phase gradient characteristics that is composed of an array of double-layer graphene ribbons sandwiched with a thin insulating layer and a polymer substrate layer with a gold ground plane. As two typical proof-of-concept examples, metasurfaces act as a planar prism and a planar lens, respectively, and the corresponding performances of tunable broadband dispersion are demonstrated through full-wave simulation experiments. By changing the Fermi level of each graphene ribbon individually to introduce abrupt phase shifts along the metasurface, the broadband continuous dispersion effect of abnormal reflection and beam focusing is achieved within a terahertz (THz) frequency region from 3.0 THz to 4.0 THz, and the dispersion results can be freely regulated by reconfiguring the sequence of Fermi levels via the bias voltage. The presented graphene metasurface provides an avenue for the dispersion manipulation of a broadband terahertz wave and may have great prospects in the fields of optics, imaging, and wireless communication.

ENSO-driven abrupt phase shift in North Atlantic oscillation in early January

El Niño-Southern Oscillation (ENSO) teleconnections exhibit a strong dependency on seasonally and intraseasonally varying mean states, leading to impactful short-term variations in regional climate. The North Atlantic Oscillation (NAO)-ENSO relation is a typical example, in that its phase relationship reverses systematically between the early and late winter. Here based on observations and an ensemble of atmosphere-only climate model simulations, we reveal that this NAO phase reversal occurs synchronously in early January, showing strong abruptness. We demonstrate that this abrupt NAO phase reversal is caused by the change in ENSO-induced Rossby wave-propagating direction from northeastward to southeastward over the northeastern North American region, which is largely governed by a climatological alteration of the local jet meridional shear. We also provide evidence that the North Atlantic intrinsic eddy–low-frequency flow feedback further amplifies the NAO responses. This ENSO-related abrupt NAO change offers an avenue for intraseasonal climate forecasting in the Euro-Atlantic region.

Tunable Polarization‐Preserving Vortex Beam Generator Based on Diagonal Cross‐Shaped Graphene Structures at Terahertz Frequency

AbstractThe vortex beams carrying orbital angular momentum (OAM) are of extreme importance for applications in communication, nanoscience, and optical micro‐manipulation. The development of dynamically tunable vortex beam generators with compact size is a critical step in the realization of vortex beam modulation and application. Here, a series of ultrathin OAM‐tunable polarization‐preserving vortex beam generators based on graphene metasurfaces are proposed, which offer a new scheme to generating vortex beams with variable topological charges at terahertz frequency. By introducing the diagonal cross‐shaped graphene structures, the abrupt phase shift range reaches 2π for linearly polarized incident light while maintaining the original polarization state. Planar spiral phase generators are theoretically constructed to convert beams with plane wavefront into beams with spiral phase. More importantly, the topological charges of the generated vortex beams can be dynamically tuned by the graphene Fermi energy in a broadband frequency range from 4.5 to 5.5 THz. This work provides a simple technology for the generation of vortex beams and the flexible modulation of the topological charge, which would inspire the application potential of the vortex beam.

Optical meta-cage based on phase gradient metagrating

&lt;sec&gt;How to effectively control the refraction, reflection, propagation and wavefront of electromagnetic wave or light is always one of the advanced researches in the field of optics. In recent years, much effort has been devoted to both theoretical and experimental studies of optical phase gradient metagratings (PGMs) due to the fundamental interest and practical importance of PGMs, such as the generalized Snell’s law (GSL). Typically, the PGMs are constructed as periodic gratings consisting of a supercell spatially repeated along an interface, and each supercell consists of &lt;i&gt;m&lt;/i&gt; unit cells, with &lt;i&gt;m&lt;/i&gt; being an integer. The key idea of PGMs is to introduce an abrupt phase shift covering the range from 0 to &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$2\pi $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; discretely through &lt;i&gt;m&lt;/i&gt; unit cells to ensure the complete control of the outgoing waves. The phase gradient provides a new degree of freedom for the manipulation of light propagation, which has allowed a series of ultrathin devices to realize anomalous scattering, the photon spin Hall effect, and many other phenomena.&lt;/sec&gt;&lt;sec&gt;Intuitively, the number of unit cells &lt;i&gt;m&lt;/i&gt; in a supercell does not influence the PGM diffraction characteristics, except that a small value of &lt;i&gt;m&lt;/i&gt; will lead to a reduced diffraction efficiency. However, some recent studies have shown that the integer &lt;i&gt;m&lt;/i&gt; plays a fundamental role in determining the high-order PGM diffractions when the incident angle is beyond the critical angle predicted by the GSL. In particular, for high-order PGM diffractions, &lt;i&gt;m&lt;/i&gt; leads to a new set of diffraction equations expressed as&lt;/sec&gt;&lt;sec&gt; &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$ \left\{ {\begin{aligned} &amp;{{k_x} = k_x^t - nG,{\text{ for odd L,}}} \\ &amp;{{k_x} = k_x^r - nG,{\text{ for even L}}{\text{. }}} \end{aligned}} \right. $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;&lt;/sec&gt;&lt;sec&gt;In addition to the phase gradient, the integer number of unit cells &lt;i&gt;m&lt;/i&gt; in a supercell is another degree of freedom that can be employed to control the light propagation. By the parity of &lt;i&gt;m&lt;/i&gt;, the higher-order outgoing wave can be reversed between the anomalous transmission channel and the anomalous reflection channel.&lt;/sec&gt;&lt;sec&gt;In this work, according to the concept of abrupt phase and the parity-dependent diffraction law in phase gradient metagrating, we theoretically design and study an optical meta-cage. The meta-cage is a periodic structure with one period that contains &lt;i&gt;m&lt;/i&gt; different unit cells. Through numerical simulations and rigorous analytical calculations, we find that the ability of meta-cage to trap light is related to the parity of the number of unit cells &lt;i&gt;m&lt;/i&gt; in a supercell. Specifically, when the number of unit cells is odd, the point source placed in the meta-cage can perfectly radiate out of the meta-cage without any reflection. On the contrary, when the number of unit cells is even, the point source can hardly radiate out of the meta-cage, and all the energy is localized within the meta-cage. Moreover, such a phenomenon is robust against the disorder. These results can provide new ideas and theoretical guidance for designing new radar radome and photonic isolation devices.&lt;/sec&gt;

Tree-Ring Isotopic Records Suggest Seasonal Importance of Moisture Dynamics Over Glacial Valleys of the Central Himalaya

Accelerated glacier mass loss is primarily attributed to greenhouse-induced global warming. Land–climate interactions have increasingly been recognized as an important forcing at the regional-local scale, but the related effects on the Himalayan glaciers are less explored and thought to be an important factor regulating spatial heterogeneity. The aim of the present study is a multi-decadal approximation of glacier—hydroclimate interaction over the western region of the central Himalaya (WCH). Multi-species, highly coherent, tree-ring cellulose δ18O chronologies from three sites across the WCH were used to derive atmospheric humidity (Atmospheric Moisture Content: AMC) record of the last four centuries. Annual-scale AMC reconstruction implies a decreasing regional atmospheric moisture since the mid-19th century and a sharp decline in recent decades (1960s). Coherency analyses between regional AMC and glacier mass balance (GMB) indicate an abrupt phase-shift in the relationship after the 1960s within a common record of the last 273 years. To ascertain the cause of this phase-shift, annual AMC was disintegrated into seasonal-scale, utilizing ∼200 years of δ18O record of a deciduous tree species. Seasonal (winter: October–March; summer: April–September) AMC reconstructions and disaggregation results indicate higher sensitivity of regional ice-mass variability to winter moisture dynamics than summer.Winter season AMC reconstruction confirms a revival of winter westerlies-driven moisture influx in the region since the 1970 s. Meanwhile, the record for the summer season AMC indicates a gradual decline in moisture influx from the beginning of the 20th century. Interestingly, despite a prominent decline in Indian summer monsoon (ISM) precipitation after the mid-20th century, the summer season AMC—GMB relation remained stable. We hypothesize that decadal-scale greening, and consequently increased evapotranspiration and pre-monsoon precipitation might have been recycled through the summer season, to compensate for the ISM part of precipitation. However, isotope-enabled ecophysiological models and measurements would strengthen this hypothesis. In addition, high-resolution radiative forcing and long-term vegetation greening trends point towards a probable influence of valley greening on GMB. Our results indicate that attribution of ice mass to large-scale dynamics is likely to be modulated by local vegetation changes. This study contributes to the understanding of long-term hydroclimate—ice mass variability in the central Himalaya, where predictions are crucial for managing water resources and ecosystems.

Understanding of Wood Anomalies in Metallic Gratings From Phase Gradient Metasurfaces

Phase-gradient metasurfaces (PGMs) have provided unprecedented opportunities for manipulating light. Here, we reexamine ordinary and well-studied subwavelength metallic gratings (OMGs) from the concept of PGMs to provide more insight into their diffraction properties. We will show that due to the existence of gauge invariance in PGMs, i.e., the diffraction law of PGMs is independent of the choice of initial value of abrupt phase shift that induces the phase gradient, the well-studied OMGs can be regarded as a PGM strictly, with its diffraction properties can be fully predicted by generalized diffraction law with phase gradient. In particular, the generalized diffraction law reveals that the phase gradient plays a significant role in the famous effect of Wood’s anomalies and Rayleigh’s conjecture.

Recurrent large‐scale sea urchin mass mortality and the establishment of a long‐lasting alternative macroalgae‐dominated community state

AbstractRelationships between sea urchins and noncrustose macroalgae are typically nonlinear, and an abrupt phase shift from a barren to a macroalgae‐dominated state and vice versa happens when the sea urchin abundance exceeds a critical threshold. Here, we have used two mass mortality events as a natural experiment to study progressive changes and dynamics between these stable states. In 2009–2010 and 2018, two mass mortalities decimated the populations of the sea urchin Diadema africanum in the Canary Islands (Eastern Subtropical Atlantic). In these islands, this sea urchin is a key‐herbivore controlling the growth of macroalgae, and sea urchin barrens have persisted for more 60 yr. Mass mortality events differed in intensity both in space and time, and two phase shifts from sea urchin barrens to macroalgal beds were detected in both when sea urchin density declined below a critical threshold of 4 indv. · m−2. The first mass mortality was greater in La Palma Island, consequently in this island a long‐lasting alternative state dominated by noncrustose macroalgae has been established. Subsequently, a recurrent mass mortality also favored the transition from the sea urchin barrens to noncrustose macroalgal beds in Tenerife Island. After mass mortalities, D. africanum populations were reduced by 94–98% in both islands. No signs of recovery of these populations have been identified after phase shifts; ecosystem feedbacks may be the cause of the low population density of D. africanum.

Interference between atomic Rb (5d 5/2–5p 3/2) and (5p 3/2–5s 1/2) coherences: observation of an exceptional point by quantum beating at ∼2.1 THz

Coupled oscillators are prevalent in nature and fundamental to fields as disparate as astrophysics, photonics, the mechanical sciences, and geophysics. Theory has identified singularities in the response of coupled oscillators, known as exceptional points (EPs), that are associated with non-Hermitian operators and lie at the transition between weak and strong coupling of the oscillator. Although several EPs have been reported or predicted to exist in nanophotonic resonators and Feshbach resonances, for example, tuning the phase of two interfering atomic or molecular coherences near an EP has not been demonstrated previously. We report the observation of an EP associated with a pair of interfering atomic coherences in Rb, oscillating at 386.3 and 384.2 THz, and confirm the theoretical prediction of an abrupt phase shift of ∼π/4 as the EP is traversed by independently varying two experimental parameters. Pairs (and trios) of coupled coherences in thermal Rb atoms are established among the 7s 1/2, 5d 5/2, 5p 3/2, and 5s 1/2 states in pump–probe experiments with <200 fs laser pulses, and observed directly in the temporal and spectral domains through the ensuing quantum beating in the ∼2–36 THz interval. Interference between the (5d 5/2–5p 3/2) and (5p 3/2–5s 1/2) coherences is mediated by the 5p 3/2 state and detected through quantum beating in the vicinity of the (5d 5/2–5p 3/2)–(5p 3/2–5s 1/2) difference frequency of 2.11 THz which is monitored by a parametric four-wave mixing process. Phase of this composite atomic oscillator is first controlled by varying the mean Rb–Rb nearest neighbor distance (⟨R⟩) in a thermalized vapor. A discontinuous transition of (0.8 ± 0.2) ∼ π/4 radians in the phase of the coupled oscillator occurs when ⟨R⟩ is varied over the ∼80–90 nm interval, a phase shift associated with the transformation of a broadband, dissipative oscillator (characterized by a Fano interference window) into a strongly-coupled system resonant at 2.1 THz.

Elastic Metasurfaces for Full Wavefront Control and Low-Frequency Energy Harvesting

Abstract Controlling and manipulating elastic/acoustic waves via artificially structured metamaterials, phononic crystals, and metasurfaces have gained an increasing research interest in the last decades. Unlike others, a metasurface is a single layer in the host medium with an array of subwavelength-scaled patterns introducing an abrupt phase shift in the wave propagation path. In this study, an elastic metasurface composed of an array of slender beam resonators is proposed to control the elastic wavefront of low-frequency flexural waves. The phase gradient based on Snell’s law is achieved by tailoring the thickness of thin beam resonators connecting two elastic host media. Through analytical and numerical models, the phase-modulated metasurfaces are designed and verified to accomplish three dynamic wave functions, namely, deflection, non-paraxial propagation, and focusing. An oblique incident wave is also demonstrated to show the versatility of the proposed design for focusing of wave energy incident from multiple directions. Experimentally measured focusing metasurface has nearly three times wave amplification at the designed focal point which validates the design and theoretical models. Furthermore, the focusing metasurface is exploited for low-frequency energy harvesting and the piezoelectric harvester is improved by almost nine times in terms of the harvested power output as compared to the baseline harvester on the pure plate without metasurface.

Phase slips and metastability in granular boron-doped nanocrystalline diamond microbridges

A phase slip is a localized disturbance in the coherence of a superconductor allowing an abrupt 2π phase shift. Phase slips are a ubiquitous feature of one-dimensional superconductors and also have an analogue in two-dimensions. Here we present electrical transport measurements on boron-doped nanocrystalline diamond (BNCD) microbridges where, despite their three-dimensional macroscopic geometry, we find clear evidence of phase slippage in both the resistance-temperature and voltage-current characteristics. We attribute this behavior to the unusual microstructure of BNCD. We argue that the columnar crystal structure of BNCD forms an intrinsic Josephson junction array that supports a line of phase slippage across the microbridge. The voltage-state in these bridges is metastable and we demonstrate the ability to switch deterministically between different superconducting states by applying electromagnetic noise pulses. This metastability is remarkably similar to that observed in δ-MoN nanowires, but with a vastly greater response voltage.

Graphene-embedded coding metasurface for dynamic terahertz manipulation

With the rapid development of terahertz wave technology and application systems, the dynamic manipulation of terahertz radiation is highly needed. We have investigated the performances of a graphene-embedded coding metasurface that can dynamically control the terahertz wave transmission. The coding element consists of gold substrate, silicon-polyimide interlayer and the top graphene-embedded metallic pattern that can realize abrupt reflection phase shift by adjusting the graphene Fermi level. Especially, by changing the Fermi energy of the graphene through bias voltage and pre-designed coding sequence, the new coding metasurface structure can control the reflected terahertz wave beams to various directions. The method brings us much freedom in design of terahertz wave manipulation device.

Spectrally and Spatially Tunable Terahertz Metasurface Lens Based on Graphene Surface Plasmons

In this paper, we propose a spectrally and spatially tunable terahertz metasurface lens based on the surface plasmons of graphene ribbons. By tuning the graphene Fermi energy, the optical property of graphene surface plasmons can be dynamically modulated, leading to tailored abrupt phase shifts of the reflected light. We demonstrate a resulting large spectral tuning range from 4 to 6 THz for the proposed metasurface lens with a spatially adjustable focal point in tens of micrometers. The influence of electron relaxation time of graphene and thickness of ion-gel on the performance of the metasurface lens is also discussed. Such a terahertz metasurface lens with a large spectral and spatial tunability is expected to show the great potentials in realizing active terahertz elements.

Mass-stiffness substructuring of an elastic metasurface for full transmission beam steering

The metasurface concept has a significant potential due to its novel wavefront-shaping functionalities that can be critically useful for ultrasonic and solid wave-based applications. To achieve the desired functionalities, elastic metasurfaces should cover full 2π phase shift and also acquire full transmission within subwavelength scale. However, they have not been explored much with respect to the elastic regime, because the intrinsic proportionality of mass-stiffness within the continuum elastic media causes an inevitable trade-off between abrupt phase shift and sufficient transmission. Our goal is to engineer an elastic metasurface that can realize an inverse relation between (amplified) effective mass and (weakened) stiffness in order to satisfy full 2π phase shift as well as full transmission. To achieve this goal, we propose a continuum elastic metasurface unit cell that is decomposed into two substructures, namely a mass-tuning substructure with a local dipolar resonator and a stiffness-tuning substructure composed of non-resonant multiply-perforated slits. We demonstrate analytically, numerically, and experimentally that this unique substructured unit cell can satisfy the required phase shift with high transmission. The substructuring enables independent tuning of the elastic properties over a wide range of values. We use a mass-spring model of the proposed continuum unit cell to investigate the working mechanism of the proposed metasurface. With the designed metasurface consisting of substructured unit cells embedded in an aluminum plate, we demonstrate that our metasurface can successfully realize anomalous steering and focusing of in-plane longitudinal ultrasonic beams. The proposed substructuring concept is expected to provide a new principle for the design of general elastic metasurfaces that can be used to efficiently engineer arbitrary wave profiles.

Relationship between chronobiology and aging: adjustments facing the technological world

Although there is no consensus in literature regarding which are the rhythmicity changes that occur during the aging process, it is believed that advanced age may affect the circadian rhythms, leading to a decreased ability to tolerate abrupt phase shift, decreased amplitude of rhythms, phase advance and reduced endogenous period. Therefore, understanding the mechanisms involved in the aging process has become essential for the development of new treatment approaches in order to improve quality of life of the elderly population. The use of technologies has increased over the past years, becoming an important factor to be considered an influence in the circadian rhythms. There is a limited number of studies linking the relationship between sleep-wake cycle and the effect of light and media use in the modern world. Thus, the aim of this review was to analyze the relationship between light, technology, and circadian rhythms in the elderly population.

Terahertz beam switching by electrical control of graphene-enabled tunable metasurface

Controlling the terahertz wave, especially the dynamical and full control of terahertz wavefront, is highly demanded due to the increasing development of practical devices and application systems. Recently considerable efforts have been made to fill the ‘terahertz gap’ with the help of artificial metamaterial or metasurface incorporated with graphene material. Here, we propose a scheme to design tunable metasurface consisting of metallic patch array on a grounded polymer substrate embedded with graphene layers to electrically control the electromagnetic beam reflection at terahertz frequency. By adjusting geometric dimension of the patch elements, 360 degree reflection phase range may be achieved, thus abrupt phase shifts can be introduced along the metasurface for tailoring the reflected wavefront. Moreover, the reflective phase gradient over the metasurface can be switched between 90 and 360 degree by controlling the Fermi energy of the embedded graphene through voltage biasing, hence dynamically switching the reflective beam directions. Numerical simulations demonstrate that either single beam or dual beam dynamically switching between normal and oblique reflection angles can be well attained at working frequency. The proposed approach will bring much freedom in the design of beam manipulation devices and may be applied to terahertz radiation control.

Optical gears in a nanophotonic directional coupler.

Gears are rotating machines, meshing with each other by teeth to transmit torque. Interestingly, the rotating directions of two meshing gears are opposite, clockwise and counterclockwise. Although this opposite handedness motion has been widely investigated in machinery science, the analogue behavior of light remains undiscovered. Here, we present a simple nanophotonic directional coupler structure which can generate two light beams with opposite handedness of polarization states-optical gears. Due to the abrupt phase shift effect and birefringence effect, the angular momentum (AM) states of photons vary with the propagation distance in two adjacent waveguides of the coupler. Thus, by the choice of coupling length, it is able to obtain two light beams with opposite handedness of polarization, confirming the appearance of optical gears. The full control in the handedness of output beams is achieved via tuning the relative phase between two orthogonal modes at the input port. Optical gears thus offer the possibility of exploring light-matter interactions in nanoscale, opening up new avenues in fields of integrated quantum computing and nanoscale bio-sensing of chiral molecules.

Plasmonic quarter-wave plate with U-shaped nanopatches

A plasmonic quarter-wave plate which is based on U-shaped silver nanopatches array in the near-infrared range is designed and presented by us. It utilizes localized surface plasmon resonances with an abrupt phase shift to achieve the desired phase modulation in the transmitted field. The optimized quarter-wave plate can perfectly convert a linearly polarized light to circularly polarized light, whose ellipticity reaches to 1 at the wavelength of 1.55μm. The bandwidth, in which the ellipticity is larger than 0.83, is 120nm. This structure offers an enormous potential applications in optical sensor systems, advanced nanophotonic devices and integrated optical circuits.

Dynamic Control of Double Plasmon-Induced Transparencies in Aperture-Coupled Waveguide-Cavity System

A theoretical model, for dynamic control of double plasmon-induced transparencies in aperture-coupled metal-dielectric-metal (MDM) waveguide-cavity system, is proposed. Based on the theoretical and numerical results, the formation and evolution mechanisms of double plasmon-induced transparencies are investigated more accurately compared to previous works. The symmetries, positions and measured full width at half maximum (FWHM) of the double transparent windows, and the transmission phase shift can be tuned freely by structural parameters. Moreover, the slot cavity location relative to aperture affects the phase difference between the left and right slot cavities to aperture center and determines the wavelength of resonance mode in aperture-side-coupled slot cavity, which plays an important role in the appearance or disappearance of transparent windows. In particular, supported by the consistency between the theoretical analysis and simulations, we obtain the threshold of coupling distance between two apertures, at which the abrupt phase shift happens. The detailed analysis may open up the possibility for precise control of light in highly integrated optical circuits.