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Fano Resonances in the Linear and Nonlinear Plasmonic Response: Physics and Applications
Abstract
Fano resonances manifest novel phenomena both in linear and nonlinear response of plasmonic nanomaterials. They can extend the lifetime of plasmonic excitations, enabling the operation of nanolasers, or they can increase the fluorescence of quantum emitters. They also provide control over nonlinear optical processes such as second harmonic generation and surface enhanced Raman scattering. Fano resonances can both enhance and suppress nonlinear response. Interference of two or more absorption/conversion paths is responsible for the appearance of these effects. In this Chapter, we demonstrate explicitly—on a single equation—how path interference takes part in linear and nonlinear Fano resonances.
... The strong interaction between a QE and a MNP makes path interference effects visible: Fano resonances [24], the plasmon analog of electromagnetically induced transparency (EIT) [25]. Similar to EIT-like behaviors in atomic clouds [25], Fano resonances can be used to control the refractive index [26][27][28][29] and nonlinear conversion processes [30][31][32][33]. The origin of these interference effects, e.g., enhancement and suppression of linear and/or nonlinear response, can be demonstrated with a basic analytical model. ...
... is an overlap integral, which determines the strength of the down conversion process [32]. Here, one can consider χ (2) (r) as a 3D step function that is zero outside the crystal body. ...
... We note that the analytical model we base our results on does not take the retardation effects and increased density of modes into account. 3D finite difference time domain (FDTD) solutions to Maxwell equations show that retardation effects do not destroy the appearance of Fano resonances when nonlinearity takes place on (or close to) a nanoparticle [32,61]. The case we study here, however, considers a nonlinearity conversion that takes place all over the nonlinear crystal, i.e., not only on the hot spot. ...
Control of the nonlinear response of nanostructures via path interference effects, i.e., Fano resonances, has been studied extensively. In such studies, a frequency conversion process takes place near a hot spot. Here, we study the case where the frequency conversion process takes place along the body of a nonlinear crystal. Metal nanoparticle–quantum emitter dimers control the down-conversion process, taking place throughout the crystal body, via introducing interfering conversion paths. Dimers behave as interaction centers. We show that two orders of magnitude enhancement is possible, on top of the enhancement due to localization effects. That is, this factor multiplies the enhancement taking place due to the field localization.
... Recently, it was shown that 'the path interference effects' which has a similar origin to FRs can control the plasmonic responses in the linear and the nonlinear regimes [26][27][28][29]. In this manuscript, we revisit the EOT in the perspective of FRs. ...
... From Heisenberg equations ℏ̂̇= [̂,̂], the equation of motion can be obtained wherêis the annihilation operator of plasmonic field, | ⟩ (| ⟩) is the ground (excited) state of the QE, , is the measure of coupling between QE and Au structure where all the energies are in the unit of Hz. By doing required algebraic procedures; such as replacingâ nd̂= | ⟩⟨ | with complex quantities and respectively [33], one could obtain steady state solution for the plasmon amplitudẽas reported in [26][27][28][29] as follows; ...
... where = − is the population inversion [27]. ...
In this work, we explore extra-ordinary-transmission (EOT) behavior where localized and propagating surface plasmon fields due to the sub-wavelength periodical holes in a relatively thick metal film (opaque) are under an interaction with two-level quantum emitters. First, the transmission properties (plasmon modes, electrical field amplitudes etc.) of Au hole arrays are investigated through FDTD analysis. Then, the physics behind this interaction, also known as Fano resonance or path-interference, is explained. In addition, numerical analysis and FDTD simulations are performed to enhance/suppress near field localization to control the strength of EOT signal. Moreover, suppression of EOT signal is obtained through FDTD simulations by solving Maxwell’ equations while acquiring its bulk-sensitivity. As the spectral position of plasmon peak changes due to change in refractive index of surrounding environment, the suppression phenomena stays unchanged at the same spectral position. Results show that this concept could carry strong potential for sensing of fluorescent molecules whose excitation and plasmon field spectra of fabricated structure overlaps without altering the output signal of designed sensor.
... For creating a tunable stop band, we make use of the recently explored phenomenon: plasmon-analog of index enhancement. 26 While plasmon analogs of electromagnetically induced transparency (EIT), 28,40,41 in the linear (Fano resonances [42][43][44] ) and nonlinear response, [45][46][47][48] have been demonstrated before, demonstration of the plasmon analog of index enhancement 49 could theoretically be obtained just recently. 26 The phenomenon is also demonstrated experimentally. ...
... Owing to the shape resonance (selective coupling 50 ) of nanorods, x,y-polarized pulses can excite "only" the x,y-aligned nanorods, respectively. Beyond studying the enhancement using a basic analytical model, which has widely been demonstrated to work very well for plasmonic path interference effects, 47,51,52 Panahpour and colleagues also demonstrated the phenomenon via numerical solutions of 3D Maxwell equations for silver nanorods of dimensions 20 Â 60 Â 20 nm 3 . This scheme not only enhances the refractive index by an order of magnitude but also results in a canceled absorption at the enhancement frequency-just the same as in its EIT counterpart. ...
We propose a miniaturized photonic switch, which utilizes (recently discovered) plasmon analog of index enhancement. An index is tuned via a control (auxiliary) pulse. The operation principle of the proposed device, composed of a few layers of nanorod dimers, is different than the conventional photonic switches. In the proposed device, a stop band is created at the desired frequency determined by the control pulse frequency. Calculated modulation depths are quite large, and response time is determined by the plasmon lifetime. The method we propose here is based on linear operation that requires low power and has very small foot-print that satisfies the major needs to be the choice of a switching scheme for integrated optics.
... Such a lifetime enhancement also enables the operation of spasersmetal nanoparticles (MNPs) coated with molecules. 38 A Fano resonance, demonstrating a dip in its steady-state excitation spectrum, 36,39 ironically, enhances the plasmon energy accumulation in its temporal dynamics. 32,34 Reference 32 demonstrates that surface charge oscillations of a MNP near a longlife nanomaterial last much longer than the lifetime of the bright plasmon. ...
Metal nanostructures support plasmon oscillations on their surfaces, which normally decay very quickly. Nevertheless, the lifetime of these oscillations can be extended near a longer lifetime particle, e.g., a molecule. We utilize this phenomenon for ultrahigh (single-molecule) resolution ultrafast apertureless (scattering) applications. We demonstrate the phenomenon with the numerical solutions of 3D Maxwell equations. We use a nm-sized quantum emitter (QE) for the long lifetime particle. We place the QE at the apex of a metal-coated atomic force microscope tip. We illuminate the tip with a femtosecond laser. The near-field on the metal apex decays quickly. After some time, one receives the scattering signal only from the vicinity of the QE. Thus, the resolution becomes single-QE size. We propose the use of a stress-induced defect center in a 2D material as the QE. The tip indentation of the 2D material, transferred to the tip, originates a defect center located right at the sharpest point of the tip, which is exactly at its apex. Our method can equally be facilitated for single-molecule-size chemical manipulation.
... Rapid and dramatic progresses in (quantum) plasmonics not only enabled plasmonic nanolasers (i.e., spasers [11,12]), nanometer-size optical (scanning near-field optical microscopy (SNOM) [13,14]) and Raman (surface enhanced Raman scattering (SERS) [15,16]) imaging, but also allowed quantum optics effects to appear in nanostructures. Analogs of electromagnetically induced transparency (EIT)-like [17] path interference effects appear also in linear [18][19][20][21] and nonlinear [22][23][24] plasmonic response. Surprisingly, squeezed or entangled photons, converted into and back from nanowire plasmon oscillations, are experimentally shown to keep quantum features for times (i.e., 10 −10 s [25][26][27][28]) much longer than plasmons' decay intervals. ...
Mode-entanglement-based criteria and measures become insufficient for broadband emission, e.g., from spasers (plasmonic nanolasers). We introduce criteria and measures for the (i) total entanglement of two wave packets, (ii) entanglement of a wave packet with an ensemble, and (iii) total nonclassicality of a wave packet. We discuss these criteria in the context of (i) entanglement of two wave packets emitted from two initially entangled cavities (or two initially entangled atoms) and (ii) entanglement of an emitted wave packet with an ensemble or atom for spontaneous emission and single-photon superradiance. We also show that, (iii) when two constituent modes of a wave packet are entangled, this creates nonclassicality in the wave packet as a noise reduction below the standard quantum limit. The criteria we introduce are all compatible with near-field detectors.
... Besides facilitating the movements in CR imaging, MNSs also provided a medium for observing plasmon analogs [10] of electromagnetically-induced transparency (EIT)-like effects [26][27][28], originally observed for three or more level atoms [29][30][31]. Fano resonances [26,27,32], plasmon-analog of EIT, and nonlinear response enhancement [33][34][35][36] have been demonstrated in MNSs. Very recently, the plasmon-analog of refractive index enhancement was finally also demonstrated via simple analytical calculations which are supported by the exact solutions of the three-dimensional (3D) Maxwell equations [37]. ...
A recent study [PRB 100, 075427 (2019)], finally, demonstrated the plasmon-analog of refractive index enhancement in metal nanostructures (MNSs), which has already been studied in atomic clouds for several decades. Here, we simply utilize this phenomenon for achieving continuously-tunable enhanced Cherenkov radiation (CR) in MNSs. Beyond enabling CR from slow-moving particles, or increasing its intensity, the phenomenon can be used in continuous-tuning of the velocity cutoff of particles contributing to CR. More influentially, this allows a continuously-tunable analysis of the contributing particles as if the data is collected from many different detectors, which enables data correction. The phenomenon can also be integrated into lattice MNSs, for continuous medium tuning, where a high density of photonic states is present and the threshold for the CR can even be lifted. Additionally, vanishing absorption can heal radiation angle distortion effects caused by the metallic absorption.
... Physically, f quantifies the strength of the coupling between the near-fields of the two plasmon modes. It is proportional to an overlap integral which runs over the spatial overlap of the bright and dark modes [39]. A nonzero f corresponds to a case when the two MNSs are brought together; close enough for the polarization fields induced on the structures to overlap and hence interact. ...
Metallic nanoparticles can localize the incident light to hot spots as plasmon oscillations, where the intensity can be enhanced by up to four orders of magnitude. Even though the lifetime of plasmons is typically short, it can be increased via interactions with quantum emitters, e.g., spaser nanolasers. However, molecules can bleach in days. Here, we study the lifetime enhancement of plasmon excitations due to the coupling with longer-lifetime dark plasmon modes. We apply an analytical model based on harmonic oscillators to demonstrate that a coupled system of bright and dark plasmon modes decays more slowly than the bright mode alone. Furthermore, exact solutions of the three-dimensional Maxwell equations, i.e., finite-difference time domain, demonstrate that the lifetime of the coupled system significantly increases at the hot spot, which is not predictable by far-field response. The decay of the overall energy of such a coupled system, which can be extracted from experimental absorption measurements, is substantially different from the decay of the hot spot field. This observation enlightens the plasmonic applications in which the hot spot intensity enables the detection of the optical responses.
... When ω eg of the QE or the interaction strengths are tuned properly, the new term can cancel the non-resonant term in the conversion, which creates the enhancement. Depending on these parameters better cancellation can be made and larger enhancement at the output signal can be obtained [33]. ...
Metallic nanoparticles provide extreme localization and enhancement of optical fields. The existence of quantum emitter in the vicinity~(hot spots) of these plasmonic particles introduces the weak hybridization in the excited state of plasmon and leads to create Fano resonances. Here we demonstrate that using such hybrid structures as the interaction centers in a nonlinear crystal, one can enhance generated down-converted fields. The results indicate that the intenstiy of down-converted field can be strengthened 6-orders of magnitude with reliable interaction strengths and by choosing the appropriate level spacing for the quantum emitter.
Integration of devices generating non-classical states (such as entanglement) into photonic circuits is one of the major goals in achieving integrated quantum circuits (IQCs). This is demonstrated successfully in recent decades. Controlling the non-classicality generation in these micron-scale devices is also crucial for the robust operation of the IQCs. Here, we propose a micron-scale quantum entanglement device whose nonlinearity (so the generated non-classicality) can be tuned by several orders of magnitude via an applied voltage without altering the linear response. Quantum emitters (QEs), whose level-spacing can be tuned by voltage, are embedded into the hotspot of a metal nanostructure (MNS). QE-MNS coupling introduces a Fano resonance in the “nonlinear response”. Nonlinearity, already enhanced extremely due to localization, can be controlled by the QEs’ level-spacing. Nonlinearity can either be suppressed or be further enhanced by several orders. Fano resonance takes place in a relatively narrow frequency window so that ∼meV voltage-tunability for QEs becomes sufficient for a continuous turning on/off of the non-classicality. This provides as much as 5 orders of magnitude modulation depths.
Raman scattering signal can be enhanced through localization of incident field into sub-wavelength hot-spots through plasmonic nanostructures (surface-enhanced raman scattering—SERS). Recently, further enhancement of SERS signal via quantum objects are proposed by Postaci (Nanophotonics 7:1687, 2018) without increasing the hot-spot intensity (silent-enhancement) where this suggestion prevents the modification of vibrational modes or the breakdown of molecules. The method utilizes path interference in the nonlinear response of Stokes-shifted Raman modes. In this work, we extend this phenomenon to tune the spectral position of silent-enhancement factor where the multiple vibrational modes can be detected with a better signal-to-noise ratio, simultaneously. This can be achieved in two different schemes by employing either (i) graphene structures with quantum emitters or (ii) replacing quantum emitters with graphene spherical nano-shell in Postaci (Nanophotonics 7:1687, 2018). In addition, the latter system is exactly solvable in the steady-state. These suggestions not only preserve conventional nonlinear Raman processes but also provide flexibility to enhance (silently) multiple vibrational Raman modes due to the tunable optical properties of graphene.
Surface plasmon-induced nonlinear optical resonances have shown immense potential in advanced optical imaging and nonlinear photonic devices. However, the ultrashort lifetime of these intense nonlinear fields inhibits their effective use in the vast applications of quantum plasmonics. Here, we propose enhancement in the lifetime of fast decaying second harmonic (SH) plasmon mode through a weak and pure resonant interaction with a two-level quantum emitter (QE). We compute the time evolution of SH response under a two-coupled oscillator model, in which we examine the interaction of short-lived SH mode supported by Au nanoparticle (AuNP) with long-lived Dark mode (DM) or QE systems. To analyze the effect of spectral and temporal properties of DM and QE on the SH field, we evaluate the lifetime enhancement factor as a function of coupling strength and tuned resonant frequencies. The results show that a tiny object like QE with sharp spectral bandwidth, small decay rate, and large oscillating strength is more efficient to control and probe the temporal dynamics of the SH field, as compared to DM which has a wide spectral bandwidth. Also, we control the lifetime of the SH mode after the natural decay time of the fundamental mode (FM), which distinguishes SH mode irrespective of its spatial convolution with elementary modes. Our proposed AuNP-QE coupled plasmonic system supporting nonlinear signal with enhanced temporal character paves its way for designing efficient on-chip nonlinear optical devices and can be a powerful tool in ultrahigh-resolution nonlinear optical imaging.
We construct mode-selective effective models describing the interaction of N quantum emitters (QEs) with the localised surface plasmon polaritons (L-SPPs) supported by a spherical metal nanoparticle (MNP) in an arbitrary geometric arrangement of the QEs. We develop a general formulation in which the field response in the presence of the nanosystem can be decomposed into orthogonal modes with the spherical symmetry as an example. We apply the model in the context of quantum information, investigating on the possibility of using the L-SPPs as mediators of an efficient control of population transfer between two QEs. We show that a Stimulated Raman Adiabatic Passage configuration allows such a transfer via a decoherence-free dark state when the QEs are located on the same side of the MNP and very closed to it, whereas the transfer is blocked when the emitters are positioned at the opposite sides of the MNP. We explain this blockade by the destructive superposition of all the interacting plasmonic modes.
We study the exciton-plasmon dynamics that lead to optical loss mitigation via ultrafast transient absorption spectroscopy (UTAS) on hybrid aggregates of core-shell quantum dots (QDs) and Au nanoparticle (NP). We highlight that generating hot electrons in plasmonic NPs contribute to the transient differential absorption spectrum under optical excitation. The results suggest modifying the method of analyzing the transient absorption spectra of loss mitigated systems. Additionally, we investigate the effect of Electron Oscillation frequency-Phonon Resonance Detuning (EOPRD) on loss mitigation efficiency. Moreover, power dependent UTAS reveal a frequency pulling like effect in the transient bleach maximum towards the gain emission. We show that appropriate choice of the pump wavelength and by changing the pump power we can conclusively prove the existence of loss mitigation using UTAS. Finally, we study the transient kinetics of hybrid gain-plasmon systems and report interesting hybrid transient kinetics.
Spaser is an acronym for surface plasmon amplification by stimulated emission of radiation. A spaser is effectively a nanoscale laser with subwavelength dimensions and a low-Q plasmonic resonator, which sustains its oscillations using stimulated emission of surface plasmons. The concept of stimulated emission to sustain plasmonic oscillations in a resonator was first described by David Bergman and Mark Stockman in 2003. Using a unified notation, we provide an up-to-date literature review of the major developments and latest advances in spaser theory and carry out a systematic exposition of some of the key results useful to understand the operation of spasers. Our presentation covers both semiclassical and quantum-mechanical formulations of spaser models as well as various designs and technologies demonstrated/suggested to illustrate key aspects of this technology. Even though many advances have already been made in spaser technology, there are many hurdles that need to be overcome to bring this technology up to the level of modern laser technology. We take especially great care to highlight the main challenges facing various spaser designs and the limitations of widely used methods and materials. This review is written for both specialists in the field and a general engineering–physics–chemistry readership.
Strategies for in-liquid molecular detection via Surface Enhanced Raman Scattering (SERS) are currently based on chemically-driven aggregation or optical trapping of metal nanoparticles in presence of the target molecules. Such strategies allow the formation of SERS-active clusters that efficiently embed the molecule at the “hot spots” of the nanoparticles and enhance its Raman scattering by orders of magnitude. Here we report on a novel scheme that exploits the radiation pressure to locally push gold nanorods and induce their aggregation in buffered solutions of biomolecules, achieving biomolecular SERS detection at almost neutral pH. The sensor is applied to detect non-resonant amino acids and proteins, namely Phenylalanine (Phe), Bovine Serum Albumin (BSA) and Lysozyme (Lys), reaching detection limits in the μg/mL range. Being a chemical free and contactless technique, our methodology is easy to implement, fast to operate, needs small sample volumes and has potential for integration in microfluidic circuits for biomarkers detection.
By dint of unique physical/chemical properties and bio-compatibility, graphene can work as a building block for a SERS substrate and open up a unique platform for tumor cells detection with high sensitivity. Herein we demonstrate a facile system with highly enhanced surface enhanced Raman spectroscopy of graphene (G-SERS). The system consists of a reduced graphene oxide (rGO) sandwiched by silver and gold nanostructures. Due to the ultrasmall thickness of rGO, the inter-coupling between Ag and Au nanoparticles is precisely controlled and the local field enhancement has been improved to more than 70 times. Associated with the unique chemical mechanism of rGO, the hybrid system has been utilized to identify tumor cells without using any biomarkers. We believe this research will be important for the applications of rGO in cancer screening.
Since 2000, there has been an explosion of activity in the field of plasmon-enhanced
Raman spectroscopy (PERS), including surface-enhanced Raman spectroscopy (SERS),
tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman
spectroscopy (SHINERS). In this Review, we explore the mechanism of PERS and discuss PERS
hotspots — nanoscale regions with a strongly enhanced local electromagnetic field — that
allow trace-molecule detection, biomolecule analysis and surface characterization of various
materials. In particular, we discuss a new generation of hotspots that are generated from hybrid
structures combining PERS-active nanostructures and probe materials, which feature a strong
local electromagnetic field on the surface of the probe material. Enhancement of surface
Raman signals up to five orders of magnitude can be obtained from materials that are weakly
SERS active or SERS inactive. We provide a detailed overview of future research directions in
the field of PERS, focusing on new PERS-active nanomaterials and nanostructures and the
broad application prospect for materials science and technology.
Surface plasmon polaritons are electromagnetic waves coupled to collective electron oscillations propagating along metal-dielectric interfaces, exhibiting a bosonic character. Recent experiments involving surface plasmons guided by wires or stripes allowed the reproduction of quantum optics effects, such as antibunching with a single surface plasmon state, coalescence with a two-plasmon state, conservation of squeezing, or entanglement through plasmonic channels. We report the first direct demonstration of the wave-particle duality for a single surface plasmon freely propagating along a planar metal-air interface. We develop a platform that enables two complementary experiments, one revealing the particle behavior of the single-plasmon state through antibunching, and the other one where the interferences prove its wave nature. This result opens up new ways to exploit quantum conversion effects between different bosonic species as shown here with photons and polaritons.
Surface enhanced coherent anti-Stokes Raman scattering (SECARS) is a sensitive tool and promising for single molecular detection and chemical selective imaging. However, the enhancement factors (EF) were only 10~100 for colloidal silver and gold nanoparticles usually used as SECARS substrates. In this paper, we present a design of SECARS substrate consisting of three asymmetric gold disks and strategies for maximizing the EF by engineering near-field properties of the plasmonic Fano nanoassembly. It is found that the E-field “hot spots” corresponding to three different frequencies involved in SECARS process can be brought to the same spatial locations by tuning incident orientations, giving rise to highly confined SECARS “hot spots” with the EF reaching single-molecule sensitivity. Besides, an even higher EF of SECARS is achieved by introducing double Fano resonances in this plasmonic nanoassembly via further enlarging the sizes of the constituent disks. These findings put an important step forward to the plasmonic substrate design for SECARS as well as for other nonlinear optical processes.
We examine the superradiance of a Bose-Einstein condensate pumped with a Laguerre-Gaussian laser of high winding number, e.g., $\ell = 7$. The laser beam transfers its orbital angular momentum (OAM) to the condensate at once due to the collectivity of the superradiance. An $\ell$-fold rotational symmetric structure emerges with the take place of rotatory superradiance. $\ell$ number of single-charge vortices appear at the arms of this structure. Even though the pump and the condensate profiles initially have cylindrical symmetry, we observe that it is broken to $\ell$-fold rotational symmetry during the superradiance. Breaking of the cylindrical symmetry into the $\ell$-fold symmetry and OAM transfer to the BEC become possible after the same critical pump strength. Reorganization of the condensate resembles the ordering in the experiment by Esslinger and colleagues [Nature, {\bf 264}, 1301 (2010)]. We show that the critical point for the onset of the reorganization follows the form of the Dicke quantum phase transition.
Surface plasmon polaritons (SPPs) are electron density waves excited at the interfaces between metals and dielectric materials (1). Owing to their highly localized electromagnetic fields, they may be used for the transport and manipulation of photons on subwavelength scales (2-9). In particular, plasmonic resonant cavities represent an application that could exploit this field compression to create ultrasmall-mode-volume devices. A key figure of merit in this regard is the ratio of cavity quality factor, Q (related to the dissipation rate of photons confined to the cavity), to cavity mode volume, V (refs 10, 11). However, plasmonic cavity Q factors have so far been limited to values less than 100 both for visible and near-infrared wavelengths (12-16). Significantly, such values are far below the theoretically achievable Q factors for plasmonic resonant structures. Here we demonstrate a high-Q SPP whispering-gallery microcavity that is made by coating the surface of a high-Q silica microresonator with a thin layer of a noble metal. Using this structure, Q factors of 1,376 ± 65 can be achieved in the near infrared for surface-plasmonic whispering-gallery modes at room temperature. This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method. The SPP eigenmodes, as well as the dielectric eigenmodes, are confined within the whispering-gallery microcavity and accessed evanescently using a single strand of low-loss, tapered optical waveguide (17, 18). This coupling scheme provides a convenient way of selectively exciting and probing confined SPP eigenmodes. Up to 49.7 per cent of input power is coupled by phase-matching control between the microcavity SPP and the tapered fibre eigenmodes.
Recent experiments demonstrate that plasmonic resonators can enhance the four-wave mixing (FWM) process by several orders of magnitude, due to the localization of the incident fields. We show that, when the plasmonic resonator is coupled to two quantum emitters, a three orders of magnitude enhancement can be obtained on top of the enhancement due to the localization. We explicitly demonstrate—on an expression for the steady-state FWM amplitude—how the presence of a Fano resonance leads to the cancellation of nonresonant terms in a FWM process. A cancellation in the denominator gives rise to an enhancement in the nonlinearity. The explicit demonstration we present here guides one to a method for achieving even larger enhancement factors by introducing additional coupling terms. The method is also applicable to Fano resonances induced by all-plasmonic couplings, which are easier to control in experiments.
We show that under certain conditions the plasmonic field of a hybrid system consisting of a metallic nanoparticle and a semiconductor quantum dot can be converted into ultrashort stationary pulses with temporal widths as short as 300 ps. This happens as this system interacts with an infrared and visible laser fields, both with time-independent amplitudes. These fields generate quantum coherence via simultaneous interband and intersubband transitions of the quantum dot, forcing the polarization dephasing rate of the quantum dot to become negative during the plasmon pulses. This makes the amplitudes of such pulses time-independent (undamped), indicating total suppression of quantum decoherence of the quantum dot. These results suggest that hybrid quantum dot-metallic nanoparticle systems can act as undamped coherent-plasmonic oscillators.
The discovery of the photoelectric effect by Heinrich Hertz in 1887 set the foundation for over 125 years of hot carrier science and technology. In the early 1900s it played a critical role in the development of quantum mechanics, but even today the unique properties of these energetic, hot carriers offer new and exciting opportunities for fundamental research and applications. Measurement of the kinetic energy and momentum of photoejected hot electrons can provide valuable information on the electronic structure of materials. The heat generated by hot carriers can be harvested to drive a wide range of physical and chemical processes. Their kinetic energy can be used to harvest solar energy or create sensitive photodetectors and spectrometers. Photoejected charges can also be used to electrically dope two-dimensional materials. Plasmon excitations in metallic nanostructures can be engineered to enhance and provide valuable control over the emission of hot carriers. This Review discusses recent advances in the understanding and application of plasmon-induced hot carrier generation and highlights some of the exciting new directions for the field.
We show that second harmonic generation can be enhanced by Fano resonant
coupling of asymmetric plasmonic metal nanostructures. We develop a theoretical
model examining the effects of electromagnetic interaction between two metal
nanostructures on the second harmonic generation. We compare the second
harmonic generation efficiency of a single plasmonic metal nanostructure with
that of two coupled ones. We show that second harmonic generation from a single
metal nanostructure can be enhanced about 30 times by attaching a second metal
nanostructure with a 10 times higher quality factor than that of the first one.
The origin of this enhancement is Fano resonant coupling of the two metal
nanostructures. We support our findings on Fano enhancement of second harmonic
generation by an experimental study of a coupled plasmonic system composed of a
silver nanoparticle and a silver nanowire on glass surface in which the ratio
of the quality factors are also estimated to be around 10 times.
We show that nonlinear optical processes of nanoparticles can be controlled by the presence of interactions with a molecule or a quantum dot. By choosing the appropriate level spacing for the quantum emitter, one can either suppress or enhance the nonlinear frequency conversion. We reveal the underlying mechanism for this effect, which is already observed in recent experiments: (i) suppression occurs simply because transparency induced by Fano resonance does not allow an excitation at the converted frequency, and (ii) enhancement emerges since the nonlinear process can be brought to resonance. The path interference effect cancels the nonresonant frequency terms. We demonstrate the underlying physics using a simplified model, and we show that the predictions of the model are in good agreement with the three-dimensional boundary element method (MNPBEM toolbox) simulations. Here, we consider the second harmonic generation in a plasmonic converter as an example to demonstrate the control mechanism. The phenomenon is the semi-classical analog of nonlinearity enhancement via electromagnetically induced transparency.
Plasmonic nanostructures are of particular interest as substrates for the spectroscopic detection and identification of individual molecules. Single-molecule sensitivity Raman detection has been achieved by combining resonant molecular excitation with large electromagnetic field enhancements experienced by a molecule associated with an interparticle junction. Detection of molecules with extremely small Raman cross-sections (~10(-30) cm(2) sr(-1)), however, has remained elusive. Here we show that coherent anti-Stokes Raman spectroscopy (CARS), a nonlinear spectroscopy of great utility and potential for molecular sensing, can be used to obtain single-molecule detection sensitivity, by exploiting the unique light harvesting properties of plasmonic Fano resonances. The CARS signal is enhanced by ~11 orders of magnitude relative to spontaneous Raman scattering, enabling the detection of single molecules, which is verified using a statistically rigorous bi-analyte method. This approach combines unprecedented single-molecule spectral sensitivity with plasmonic substrates that can be fabricated using top-down lithographic strategies.
The exceptional enhancement of Raman scattering cross-section by localized
plasmonic resonances in the near-field of metallic surfaces, nanoparticles or
tips has enabled spectrocopic fingerprinting of single-molecules and is widely
used in material, chemical and biomedical analysis. Contrasting with this
overwhelming practical success, conventional theories based on electromagnetic
"hot spots" and electronic or chemical effects cannot account for all
experimental observations. Here we present a novel theory of plasmon-enhanced
Raman scattering by mapping the problem to cavity optomechanics. Using FEM and
DFT simulations we calculate the optomechanical vacuum coupling rate between
individual molecules and hot spots of metallic dimers. We find that dynamical
backaction of the plasmon on the vibrational mode can lead to amplification of
molecular vibrations under blue-detuned laser excitation, thereby revealing an
enhancement mechanism not contemplated be- fore. The optomechanical theory
provides a quantitative framework for the calculation of enhanced
cross-sections, recovers known results, and enables the design of novel systems
that leverage dynamical backaction to achieve additional, mode-selective
enhancement. It yields a new understanding of plasmon-enhanced Raman scattering
and opens a route to molecular quantum optomechanics.
We have investigated second harmonic generation (SHG) from Ag-coated LiNbO3 (LN) core-shell nanocuboids and found that giant SHG can occur via deliberately designed double plasmonic resonances. By controlling the aspect ratio, we can tune fundamental wave (FW) and SHG signal to match the longitudinal and transverse plasmonic modes simultaneously, and achieve giant enhancement of SHG by 3 × 10⁵ in comparison to a bare LN nanocuboid and by about one order of magnitude to the case adopting only single plasmonic resonance. The underlying key physics is that the double-resonance nanoparticle enables greatly enhanced trapping and harvesting of incident FW energy, efficient internal transfer of optical energy from FW to the SHG signal, and much improved power to transport the SHG energy from the nanoparticle to the far-field region. The proposed double-resonance nanostructure can serve as an efficient subwavelength coherent light source through SHG and enable flexible engineering of light-matter interaction at nanoscale.
Surface plasmon polaritons, propagating bound oscillations of electrons and light at a metal surface, have great potential as information carriers for next-generation, highly integrated nanophotonic devices1, 2. Since the term ‘active plasmonics’ was coined in 20043, a number of techniques for controlling the propagation of guided surface plasmon polariton signals have been demonstrated4, 5, 6, 7. However, with sub-microsecond or nanosecond response times at best, these techniques are likely to be too slow for future applications in such fields as data transport and processing. Here we report that femtosecond optical frequency plasmon pulses can propagate along a metal–dielectric waveguide and that they can be modulated on the femtosecond timescale by direct ultrafast optical excitation of the metal, thereby offering unprecedented terahertz modulation bandwidth—a speed at least five orders of magnitude faster than existing technologies.
Scattering forces in focused light beams push away metallic particles. Thus, trapping metallic particles with conventional optical tweezers, especially those of Mie particle size, is difficult. Here we investigate a mechanism by which metallic particles are attracted and trapped by plasmonic tweezers when surface plasmons are excited and focused by a radially polarized beam in a high-numerical-aperture microscopic configuration. This contrasts the repulsion exerted in optical tweezers with the same configuration. We believe that different types of forces exerted on particles are responsible for this contrary trapping behaviour. Further, trapping with plasmonic tweezers is found not to be due to a gradient force balancing an opposing scattering force but results from the sum of both gradient and scattering forces acting in the same direction established by the strong coupling between the metallic particle and the highly focused plasmonic field. Theoretical analysis and simulations yield good agreement with experimental results.
When light interacts with metal nanostructures, it can couple to
free-electron excitations near the metal surface. The electromagnetic
resonances associated with these surface plasmons depend on the details
of the nanostructure, opening up opportunities for controlling light
confinement on the nanoscale. The resulting strong electromagnetic
fields allow weak nonlinear processes, which depend superlinearly on the
local field, to be significantly enhanced. In addition to providing
enhanced nonlinear effects with ultrafast response times, plasmonic
nanostructures allow nonlinear optical components to be scaled down in
size. In this Review, we discuss the principles of nonlinear plasmonic
effects and present an overview of their main applications, including
frequency conversion, switching and modulation of optical signals, and
soliton effects.
We theoretically and numerically investigate metal enhanced fluorescence of plasmonic core-shell nanoparticles doped with rare earth (RE) ions. Particle shape and size are engineered to maximize the average enhancement factor (AEF) of the overall doped shell. We show that the highest enhancement (11 in the visible and 7 in the near-infrared) is achieved by tuning either the dipolar or the quadrupolar particle resonance to the rare earth ion's excitation wavelength. Additionally, the calculated AEFs are compared to experimental data reported in the literature, obtained in similar conditions (plasmon mediated enhancement) or when a metal-RE energy transfer mechanism is involved.
The ability to achieve energy saving in architectures and optimal solar energy utilisation affects the sustainable development of the human race. Traditional smart windows and solar cells cannot be combined into one device for energy saving and electricity generation. A VO2 film can respond to the environmental temperature to intelligently regulate infrared transmittance while maintaining visible transparency, and can be applied as a thermochromic smart window. Herein, we report for the first time a novel VO2-based smart window that partially utilises light scattering to solar cells around the glass panel for electricity generation. This smart window combines energy-saving and generation in one device, and offers potential to intelligently regulate and utilise solar radiation in an efficient manner.
Quantum plasmonics is a rapidly growing field of research that involves the study of the quantum properties of light and its interaction with matter at the nanoscale. Here, surface plasmons - electromagnetic excitations coupled to electron charge density waves on metal-dielectric interfaces or localized on metallic nanostructures - enable the confinement of light to scales far below that of conventional optics. We review recent progress in the experimental and theoretical investigation of the quantum properties of surface plasmons, their role in controlling light-matter interactions at the quantum level and potential applications. Quantum plasmonics opens up a new frontier in the study of the fundamental physics of surface plasmons and the realization of quantum-controlled devices, including single-photon sources, transistors and ultra-compact circuitry at the nanoscale.
We present a two-dimensional (2D) snapshot multispectral imager that utilizes the optical transmission characteristics of nanohole arrays (NHAs) in a gold film to resolve a mixture of input colors into multiple spectral bands. The multispectral device consists of blocks of NHAs, wherein each NHA has a unique periodicity that results in transmission resonances and minima in the visible and near-infrared regions. The multispectral device was illuminated over a wide spectral range, and the transmission was spectrally unmixed using a least-squares estimation algorithm. A NHA-based multispectral imaging system was built and tested in both reflection and transmission modes. The NHA-based multispectral imager was capable of extracting 2D multispectral images representative of four independent bands within the spectral range of 662 nm to 832 nm for a variety of targets. The multispectral device can potentially be integrated into a variety of imaging sensor systems.
We investigate the dynamics of a plasmonic oscillation over a metal nanoparticle when it is strongly coupled to a quantum emitter (e.g. quantum dot, molecule). We simulate the density matrix evolution for a simple model, a coupled classical-quantum oscillators system. We show that the lifetime of the plasmonic oscillations can be increased several orders of magnitude, up to the decay time of the quantum emitter. This effect shows itself as the narrowing of the plasmon emission band in the spaser (surface plasmon amplification by the stimulated emission of radiation) experiment [Nature, 2009, 460, 1110], where a gold nanoparticle interacts with the surrounding molecules. Enhancement of the plasmonic excitation lifetime enables stimulated emission to overcome the spontaneous one. The enhancement occurs due to the emergence of a phenomenon analogous to electromagnetically induced transparency (EIT). The effect can find applications in many areas of nanoscale physics, such as in quantum information with plasmons and in increasing solar cell efficiency.
Plasmonic nanoclusters, an ordered assembly of coupled metallic nanoparticles, support unique spectral features known as Fano resonances due to the coupling between their subradiant and superradiant plasmon modes. Within the Fano resonance, absorption is significantly enhanced, giving rise to highly localized, intense near fields with the potential to enhance nonlinear optical processes. Here, we report a structure supporting the coherent oscillation of two distinct Fano resonances within an individual plasmonic nanocluster. We show how this coherence enhances the optical four-wave mixing process in comparison with other double-resonant plasmonic clusters that lack this property. A model that explains the observed four-wave mixing features is proposed, which is generally applicable to any third-order process in plasmonic nanostructures. With a larger effective susceptibility χ((3)) relative to existing nonlinear optical materials, this coherent double-resonant nanocluster offers a strategy for designing high-performance third-order nonlinear optical media.
Nanostructures enhance nonlinear response, such as surface enhanced Raman scattering (SERS), by localizing the incident field into hot spots. Fano resonances (FRs) in both plasmon bands, the excited one and the one Stokes shifted frequency overlaps, increase the field at the hot spots even more. This is shown to lead further enhancement of the Raman signal. However, hot spot enhancement is limited with the break-down of the molecule and the tunnelling regime. Here we show that Raman signal can be enhanced silently, without modifying the fields (by linear FRs) at the hot spots. Using a very basic model, we show that enhancement emerges due to the path interference effects in the nonlinear response. Our simulations with the exact solutions of 3D Maxwell equations show that hot spot fields are not enhanced and confirm the predictions of our simple model. A factor of 3 orders of magnitude multiplies the enhancement due to the localization. Thus, presented method can enhance SERS ~4000 times more in materials already operating in the break-down or tunneling regime. In difference to intensity enhancement with linear FRs, here, SERS can be enhanced by coupling to a same quality material via utilizing the path interferences in the nonlinear response.
We show how to obtain the symmetry-imposed selection rules for plasmonic enhancement in surface- (SERS) and tip-enhanced Raman scattering (TERS). Plasmon-enhanced light scattering is described as a higher-order Raman process, which introduces a series of Hamiltonians representing the interaction between light, plasmons, electrons, and phonons. Using group theory, we derive the active representations for point group symmetries of exemplary plasmonic nanostructures. The phonon representations that are enhanced by SERS and TERS are then found as induced representations for the symmetry group of the molecule or another Raman probe. The selection rules are discussed for graphene that is coupled to a nanodisk dimer as an example for SERS and coupled to a tip as a TERS example. The phonon eigenmodes that are enhanced depend on the symmetry breaking when combining the plasmonic structures with graphene. We show that the most prominent optical phonon modes (E2g and A1g) are allowed in all scattering configurations when using a nanodimer as a plasmonic hotspot. We predict the activation of the silent B2g as well as infrared-active A2u and E1u modes in SERS for crossed configurations of the incoming and scattered light. There is a systematic difference between spatially coherent and incoherent plasmon-enhanced Raman scattering, which is responsible for a dependence of TERS on the phonon coherence length.
Quantum optics is a well-established field that spans from fundamental physics to quantum information science. In the coming decade, areas including computation, communication and metrology are all likely to experience scientific and technological advances supported by this far-reaching research field.
We derive a many-particle inseparability criterion for mixed states using the relation between single-mode and many-particle nonclassicalities. It works very well not only in the vicinity of the Dicke states, but also for the superposition of them: superradiant ground state of finite/infinite number of particles and time evolution of single-photon superradiance. We also obtain a criterion for ensemble-field entanglement which works fine for such kind of states. Even though the collective excitations of the many-particle system is sub-Poissonian --which results in entanglement-- the wave function displays bunching.
We demonstrate effective background-free continuous wave nonlinear optical excitation of molecules that are sandwiched between asymmetrically constructed plasmonic gold nanoparticle clusters. We observe that near infrared photons are converted to visible photons through efficient plasmonic second harmonic generation. Our theoretical model and simulations demonstrate that Fano resonances may be responsible for being able to observe nonlinear conversion using a continuous wave light source. We show that nonlinearity enhancement of plasmonic nanostructures via coupled quantum mechanical oscillators such as molecules can be several orders larger as compared to their classical counterparts.
We report on the efficient generation, propagation, and re-emission of squeezed long-range surface-plasmon polaritons (SPPs) in a gold waveguide. Squeezed light is used to excite the non-classical SPPs and the re-emitted quantum state is fully quantum characterized by complete tomographic reconstruction of the density matrix. We find that the plasmon-assisted transmission of non-classical light in metallic waveguides can be described by a Hamiltonian analogue to a beam splitter. This result is explained theoretically.
The exact entanglement dynamics in a hybrid structure consisting of two quantum dots (QDs) in the proximity of a metal nanoshell is investigated. Nanoshells can enhance the local density of states, leading to a strong-coupling regime where the excitation energy can coherently be transferred between the QDs and the nanoshell in the form of Rabi oscillations. The long-lived entangled states can be created deterministically by optimizing the shell thickness as well as the ratio of the distances between the QDs and the surface of the shell. The loss of the system is greatly reduced even when the QDs are ultraclose to the shell, which signifies a slow decay rate of the coherence information and longtime entanglement preservation. Our protocol allows for an on-demand, fast, and almost perfect entanglement even at strong carrier-phonon interaction where other systems fail.
With the aim of developing a DNA sequencing methodology, we theoretically examine the feasibility of using nanoplasmonics to control the translocation of a DNA molecule through a solid-state nanopore and to read off sequence information using surface enhanced Raman spectroscopy. Using molecular dynamics simulations, we show that high-intensity optical hot spots produced by a metallic nanostructure can arrest DNA translocation through a solid-state nanopore, thus providing a physical knob for controlling the DNA speed. Switching the plasmonic field on and off can displace the DNA molecule in discrete steps, sequentially exposing neighboring fragments of a DNA molecule to the pore as well as to the plasmonic hot spot. Surface enhanced Raman scattering from the exposed DNA fragments reports on their nucleotide composition, might allow for identification of the nucleotide sequence of a DNA molecule transported through the hot spot. The principles of plasmonic-nanopore sequencing can be extended to detection of DNA modifications and RNA characterization.
Plasmon-enhanced Raman scattering can push single-molecule vibrational spectroscopy beyond a regime addressable by classical electrodynamics. We employ a quantum electrodynamics (QED) description of the coherent interaction of plasmons and molecular vibrations that reveal the emergence of nonlinearities in the inelastic response of the system. For realistic situations, we predict the onset of phonon-stimulated Raman scattering and a counterintuitive dependence of the anti-Stokes emission on the frequency of excitation. We further show that this QED framework opens a venue to analyze the correlations of photons emitted from a plasmonic cavity.
The control of light fields on subwavelength scales in nanophotonic structures has become ubiquitous, driven by both curiosity and a multitude of applications in fields ranging from biosensing to quantum optics. Mapping these fields in detail is crucial, as theoretical modelling is far from trivial and highly dependent on nanoscale geometry. Recent developments of nanoscale field mapping, particularly with near-field microscopy, have not only led to a vastly increased resolution, but have also resulted in increased functionality. The phase and amplitude of different vector components of both the electric and magnetic fields are now accessible, as is the ultrafast temporal or spectral evolution of propagating pulses in nanostructures. In this Review we assess the current state-of-the-art of subwavelength light mapping, highlighting the new science and nanostructures that have subsequently become accessible.
The absorption spectra of Ag5-8 have been determined in the framework of the linear response equation-of-motion coupled cluster method and related techniques employing 11-electron relativistic effective core potential. In these treatments electron correlation effects for 11 electrons per atom are included, providing an accurate description of excited states of silver clusters. The calculations of transition energies and oscillator strengths have been carried out in a large energy interval for the stable structures and for the isomeric forms higher in energy. This allowed us to investigate the influence of structural properties on the spectroscopic patterns and to determine the role of d-electrons. Inclusion of d-electrons in the correlation treatment is mandatory to obtain accurate values for transition energies, but the excitations of s-electrons are primarily responsible for the spectroscopic patterns. They are characterized by the interference phenomena known in molecular spectroscopy which lead to a small number of intense and a large number of weak resonances. The calculated absorption spectra for the stable structures provide accurate predictions of the optical response properties in the gas phase and at the zero temperature. Since for neutral silver clusters the experimental data in the gas phase are not yet available, we also calculated spectra for deformed structures which model the influence of the environment such as rare-gas atoms, solid Ar-matrix or He-droplet. Comparison of our results with available experimental data permits us to identify structural properties responsible for the recorded spectral features. (C) 2001 American Institute of Physics.
Recent work has shown that collective single photon emission from an ensemble
of resonate two-level atoms is a rich field of study. For example single photon
superradiance from an extended ensemble yields enhanced directional spontaneous
emission; and when the effects of the collective Lamb shift are included it
becomes even more interesting. The present paper addresses the flip side of
superradiance, i.e., subradiance. Single photon subradiant states are
potentially stable against collective spontaneous emission and can have
ultrafast readout. In particular, it is shown how many atom collective effects
can be used to control emission by preparing and switching between subradiant
and superradiant states.
Light facilitates exploration of quantum phenomena that illuminate the basic properties of nature and also enables radical new technologies based on these phenomena. The critical features of quantum light that underpin the opportunities for discovery and application are exceptionally low noise and strong correlations. Rapid progress in both science and technology has been stimulated by adopting components developed for optical telecommunications and networking, such as highly efficient detectors, integrated photonic circuits, and waveguide- or nanostructure-based nonlinear optical devices. These provide the means to generate new quantum states of light and matter of unprecedented scale, containing many photons with quantum correlations across space and time. Notably, networks with only several tens of photons are already beyond what can be efficiently analyzed by current computers.
Copyright © 2015, American Association for the Advancement of Science.
Plasmons' progeny are invading the territory currently commanded by semiconductors.
Surface-enhanced Raman scattering (SERS) has become a mature vibrational spectroscopic technique during the last decades and the number of applications in the chemical, material, and in particular life sciences is rapidly increasing. This Review explains the basic theory of SERS in a brief tutorial and-based on original results from recent research-summarizes fundamental aspects necessary for understanding SERS and provides examples for the preparation of plasmonic nanostructures for SERS. Chemical applications of SERS are the centerpiece of this Review. They cover a broad range of topics such as catalysis and spectroelectrochemistry, single-molecule detection, and (bio)analytical chemistry.
We present a description of photon-plasmon interactions in metal nanoparticles based on the second quantization of electromagnetic fields and collective electron excitations. The quantum optical properties of nanostructured systems sustaining resonant charge oscillations will be derived by applying perturbation theory. The linear optical properties can be completely derived from the plasmon-photon coupling coefficients that apply to the particular particle material, environment, and geometry. Nonlinear electromagnetic phenomena such as second harmonic generation need instead to be described by explicitly accounting for the nonlinear corrections of the plasmon-photon interaction Hamiltonian.
Inspired by the study of atomic resonances, researchers have developed a new type of metamaterial. Their work paves the way toward compact delay lines and slow-light devices.
A particle can indeed absorb more than the light incident on it.
Metallic particles at ultraviolet frequencies are one class of such
particles and insulating particles at infrared frequencies are another.
In the former strong absorption is associated with excitation of surface
plasmons; in the latter it is associated with excitation of surface
phonons. In both instances the target area a particle presents to
incident light can be much greater than its geometrical cross-sectional
area. This is strikingly evident from the field lines of the Poynting
vector in the vicinity of a small sphere illuminated by a plane wave.
Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable 'fingerprint' for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex. However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3-15 nanometres, which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.
The exact solution of Maxwell’s equations in the presence of arbitrarily shaped dielectrics is expressed in terms of surface-integral equations evaluated at the interfaces. The electromagnetic field induced by the passage of an external electron is then calculated in terms of self-consistently obtained boundary charges and currents. This procedure is shown to be suitable for the simulation of electron energy loss spectra when the materials under consideration are described by local frequency-dependent response functions. The particular cases of translationally invariant interfaces and axially symmetric interfaces are discussed in detail. The versatility of this method is emphasized by examples of energy loss spectra for electrons passing near metallic and dielectric wedges, coupled cylinders, spheres, and tori, and other complex geometries, where retardation aspects and Cherenkov losses can sometimes be significant.
We report design, fabrication, and characterization of thermo-optic Mach–Zender interferometric modulators and directional-coupler switches whose operation utilizes the long-range surface-plasmon-polariton waveguiding along 15-nm-thin and 8-μm-wide gold stripes embedded in polymer and heated by electrical signal currents. The devices are characterized at the light wavelength of 1.55 μm, featuring low driving powers (<10 mW for modulators and <100 mW for switches), high extinction ratios (>30 dB), moderate response times (∼1 ms), and the total (fiber-to-fiber) insertion loss of ∼13 dB (for modulators) and ∼11 dB (for switches) when using single-mode fibers.