Surface Plasmon Polariton Modes Research Articles

Birefringence modes of surface plasmon polariton at the interface of chiral and gold media

Birefringence modes of surface plasmon polariton at the interface of chiral and gold media

Momentum-resolved EELS and CL study on 1D-plasmonic crystal prepared by FIB method.

We investigate a one-dimensional plasmonic crystal (1D PlC) using momentum-resolved electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) techniques, which are complementary in terms of available optical information. The PlC sample is fabricated from large aluminum grains through the focused ion beam (FIB) method. This approach allows curving nanostructures with high crystallinity, providing platforms for detailed analysis of plasmonic nanostructures using both EELS and CL. The momentum-resolved EELS visualizes dispersion curves outside the light cone, confirming the existence of the surface plasmon polaritons (SPP) and local modes, while the momentum-resolved CL mapping analysis identified these SPP and local modes. Such synergetic approach of two electron-beam techniques offers full insights into both radiative and non-radiative optical properties in plasmonic or photonic structures.

The Nanoplasmonic Purcell Effect in Ultrafast and High-Light-Yield Perovskite Scintillators.

The development of X-ray scintillators with ultrahigh light yields and ultrafast response times is a long sought-after goal. In this work, a fundamental mechanism that pushes the frontiers of ultrafast X-ray scintillator performance is theoretically predicted and experimentally demonstrated: the use of nanoscale-confined surface plasmon polariton modes to tailor the scintillator response time via the Purcell effect. By incorporating nanoplasmonic materials in scintillator devices, this work predicts over tenfold enhancement in decay rate and 38% reduction in time resolution even with only a simple planar design. The nanoplasmonic Purcell effect is experimentally demonstrated using perovskite scintillators, enhancing the light yield by over 120% to 88 ± 11 ph/keV, and the decay rate by over 60% to 2.0 ± 0.2 ns for the average decay time, and 0.7 ± 0.1 ns for the ultrafast decay component, in good agreement with the predictions of ourtheoretical framework. Proof-of-concept X-ray imaging experiments are performed using nanoplasmonic scintillators, demonstrating 182% enhancement in the modulation transfer function at four line pairs per millimeter spatial frequency. This work highlights the enormous potential of nanoplasmonics in optimizing ultrafast scintillator devices for applications including time-of-flight X-ray imaging and photon-counting computed tomography.

Multi-Mode Long-Wavelength GaAs/AlGaAs Quantum Well Infrared Photodetectors for Circular Polarization Detection

We present an integrated device combining a double L-shaped chiral metasurface with long-wavelength GaAs/AlGaAs quantum well infrared photodetectors (QWIPs), achieving a circular polarized extinction ratio (CPER) as high as 45 in the long-wavelength infrared range of 7–9 μm. The unit of the chiral metasurface array consists of two structurally identical L-shaped gold structures with central symmetry. The CPER of the double L-shaped QWIPs is 14 times higher than that of a single L-shaped QWIP. The device operates in three modes within the detection band: the microcavity mode, the surface plasmon polariton (SPP) mode, and the hybrid mode. The double L-shaped chiral structure selects and reflects a small portion of left-handed circularly polarized light (LCP), while the majority enters the device and excites SPP modes with the bottom gold grating layer, leading to an absorption enhancement. In contrast, right-handed circularly polarized light (RCP) is mostly reflected with limited excitation of SPP waves. QWIPs exhibit a peak absorption of 0.8 and a coupling efficiency of 2700% in the active region of the quantum well due to the combined effects of the microcavity and SPP modes, in which the SPP mode plays a dominant role. The proposed device maintains high circular polarization discrimination capability under large incident angles and can be applied in spectral imaging.

Investigating the impact of polarization on surface plasmon polariton characteristics in plasmonic waveguides under periodic driving fields

This study examines the impact of polarization in the driving field on the surface plasmon polariton (SPP) modes within plasmonic waveguides under the influence of a periodic driving field. Addressing a significant knowledge gap in the existing literature, we present a comprehensive investigation employing Floquet engineering techniques, with a specific emphasis on elliptically polarized fields as the dressing field. Our analysis reveals that the use of generalized Floquet states allows us to derive Floquet states for specific polarized dressing fields, such as linear, left-handed circular, and right-handed circular polarization. Remarkably, we demonstrate that Floquet states depend on the chirality of the dressing field’s polarization. Employing the Floquet-Fermi golden rule, we assess electron transport under various polarization types and find that the specific polarization type influence electron transport properties. However, we establish that the chirality of the polarization of the dressing field does not impact the transport properties. During our numerical analysis, we assess the alterations in SPP characteristics arising from two distinct types of polarization in dressing fields: linear polarization and circular polarization. Our results underscore the potential of employing a dressing field to effectively mitigate the propagation losses of SPPs in plasmonic metals, with the extent of improvement contingent on the specific polarization type. To quantify the performance enhancements of commonly used plasmonic metals under linearly and circularly polarized dressing fields, we employ a figure of merit (FoM). This study offers insights into the practical utilization of periodic driving fields as a powerful tool in advancing plasmonic communication within chip-scale environments.

Refractive index sensing of spoof surface plasmon polaritons excited on graphene strips based on cylindrical dielectric metasurface coupling

In this paper, we present a novel terahertz plasmonic sensing concept that utilizes a metasurface coupler to excite spoof surface plasmon polaritons (SSPs) modes on graphene strips. The dielectric metasurface unit cell consists of two silicon cylindrical rods with different radii on a quartz substrate. Vertically incident terahertz waves are deflected by the metasurface, resulting in a transverse wave-vector within the substrate that matches the SSPs wave-vector supported by the graphene strips. This enables efficient excitation of SSPs modes on the graphene strips surface, leading to absorption resonances in the range of 0.420–0.430 THz with a high quality (Q) factor of 152. We then applied this device for refractive index sensing, and the investigation results indicate that the high Q resonances in the absorption spectrum experience shifts with changes in the refractive index of the target substance, with a sensitivity of 110 GHz/RIU. The designed structure in this study exhibits significant potential for applications in trace substance absorption spectrum detection.

A Tunable artificial plasmonic nanolaser with wide spectrum emission operating at room temperature

Abstract With information and communication technology developing fast, a key objective in the field of optoelectronic integrated devices is the reduction of nano-laser size and energy consumption. Photonics nanolasers are unable to exceed the diffraction limit and typically exhibit low modulation rates of several GHz. In contrast, plasmonic nanolaser utilize highly confined surface plasmon polariton (SPP) modes that can surpass diffraction limit and their strong Purcell effect can accelerate the modulation rates to several THz. Here, we propose a parametrically tunable artificial plasmonic nanolasers based on Metal-Insulator-Semiconductor-Insulator-Metal (MISIM) structure, which demonstrates the capability to compress the mode field volume to λ/14. As the pump power increases, the proposed artificial plasmonic nanolasers exhibits wide output spectrum of 20nm. Additionally, we investigate the impact of various cavity parameters on the nanolaser’s output threshold, offering potentials for realizing low-threshold artificial plasmonic nanolasers. Moreover, we observe a blue shift in the center wavelength of the nanolaser output with thinner gain layer thickness, predominantly attributed to the increased exciton–photon coupling strength. Our work brings inspiration to several areas, including Spaser-based interconnects, Nano-LEDs, spontaneous emission control, miniaturization of photon condensates, eigenmode engineering of plasmonic nanolasers, and optimal design driven by Artificial Intelligence (AI).

Ultra-high sensitivity surface plasmon U-channel photonic crystal fiber for hemoglobin sensing

In order to increase the wavelength response range of the U-channel sensor, a numerical study has been conducted and then the sensing structure has been optimized. A sensor in photonic crystal fiber (PCF) is proposed in which a layer of titanium dioxide is coated on the surface of the U-channel and then coated with a gold film. These two different metal films are mainly used to control the Surface plasmon resonance (SPR) peak and the corresponding resonance wavelength, thus changing the sensor performance. Just below the metal layer are two special air holes on either side. They form a leakage window in the center. In the following sections, the effects of these variables on the sensor will be studied in detail by COMSOL. The modal transmission characteristics of this fiber optic sensor are analyzed in this paper. By analyzing the obtained loss spectrum, the energy variation in the surface plasmon polariton (SPP) mode and the influence of the core mode on the sensing performance of the fiber optic sensor presented, the general rule of the optimized PCF-SPR sensor is deduced. In addition, we can make subtle adjustments to the sensor to improve its sensitivity. We found with the refractive index (RI) ranging from 1.26 to 1.42, the maximum wavelength sensitivity is 7500 nm/RIU, which corresponds to a full width at half maximum (FWHM) of 11.83 nm，a figure of merit (FOM) of 634.1 RIU−1. In addition, we also have discussed the sensor and different concentrations of hemoglobin aqueous solution to detect its RI. It is evident from the results that the sensor demonstrates excellent sensitivity and a wide detection range, which is highly desirable for practical diagnostic purposes. The potential of this sensor for clinical trials and its application to medical diagnostics is promising. Compared with complex traditional methods, the PCF has obvious advantages such as clear structure, simple manufacture, high sensitivity and strong environmental adaptability. Moreover, it has the advantage of wide wavelength response range and has a clear development prospect in the field of biochemical sensing. It has foreseeable potential practical value.

Enhanced Fiber Long‐Range Surface Plasmon Sensing Enabled by Resonance Coupling to Surface Plasmon Polaritons

A tunable fiber optic (FO) long‐range surface plasmon (LRSP) sensor with strong coupling is developed and demonstrated theoretically in this article. The sensor consists of a square lattice array of Ag nanodisks resting on the FO end face. Utilizing nanodisks with small diameters leads to the pronounced excitation of two distinct and independent resonant modes: surface plasmon polaritons (SPP) and LRSP. A systematic investigation is performed to evaluate the sensing performance and capabilities of the sensor, focusing on its bulk and surface sensitivity. Significantly, the LRSP mode demonstrates high sensitivity and favorable linearity in response to refractive index (RI) changes, with an exceptionally high figure of merit (FOM). On the contrary, the SPP mode is regarded as an ideal self‐referencing mode due to its immunity to RI fluctuations. The enlargement of nanodisks diameters results in a swift redshift in the LRSP wavelength, leading to a strong coupling with the SPP mode. This coupling facilitates the transfer of electric fields within the SPP mode, promotes sensing capabilities, and enables the realization of dual‐channel sensing functionality. The occurrence of strong coupling phenomena along with the use of FO substrates provides an innovative option for achieving multifunctionality and miniaturization in sensor platforms.

Transmission enhancement effect of distributed Bragg reflector structure covered with metal grating

In order to observe the extraordinary optical transmission (EOT) through a metal gratings, induced by Tamm plasmon polaritons (TPPs), a layered structure consisting of a distributed Bragg reflector covered with a one-dimensional metal grating is proposed in this work. When an incident light wave impinges on the DBR-metal interface normally and passes through DBR regime, the generation of TPPs and the resulting highly localized energy on the metal-DBR interface are simulated in detail by the finite element method. As a result, the surface plasmon polariton (SPPs) modes accommodated inside the slits of metal gratings can be excited more effectively by the enhanced electromagnetic field associated with TPPs located on the interface. Furthermore, the enhanced transmission of incident light waves in the structure can be achieved when the SPP mode inside the grating slits satisfies the Fabry-Perot (FP)-like resonance condition, which reveals that the EOT in this structure comes from a TPPs-FP hybrid resonance. This inference can be confirmed by the relationships between the central wavelength and the grating height for the two transmission peaks, and the magnetic field modal profiles associated with the two peaks. Quantitative effects of the slit width and duty cycle on the transmission peak of the metal grating are analyzed numerically, and the results demonstrate that when the period is determined, as the slits width increases, the two peak transmittances first increase and then decrease. On the other hand, when the three slit widths are chosen to be 40 nm, 50 nm, and 60 nm respectively, the peak transmittance first increases and then decreases with the duty cycle increasing. Meanwhile, it is found that the center wavelengths of the transmission peaks are related to the duty cycle in a nearly linear manner for three slit widths, which can be used to flexibly adjust the center wavelength of extraordinary optical transmission.

Quasi-bound states in the continuum in a metal nanograting metasurface for a high figure-of-merit refractive index sensor.

In this work, we investigate the bound states in the continuum (BICs) in a gold nanograting metal-insulator-metal metasurface structure at oblique angles of incidence. The nanograting metasurface consists of a gold nanograting patterned on a silicon dioxide dielectric film deposited on a thick gold film supported by a substrate. With rigorous full-wave finite difference time domain simulations, two bound states in the continuum are revealed upon transverse magnetic wave angular incidence. One BIC is formed by the interference between the surface plasmon polariton mode of the gold nanograting and the FP cavity mode. Another BIC mode is formed by the interference between the metal-dielectric hybrid structure guided mode resonance mode and the FP cavity mode. While true BIC modes cannot be observed, quasi-BIC modes are investigated at angles of incidence slightly off from the corresponding true BIC angles. It is shown that quasi-BIC modes can suppress radiation loss, resulting in narrow resonance spectral linewidths and high quality-factors. The quasi-BIC mode associated with the surface plasmon polariton mode is investigated for refractive index sensing. As a result, a high sensitivity refractive index sensor with a large figure-of-merit of 364 has been obtained.

Nanoscale Manipulation of Exciton-Trion Interconversion in a MoSe2 Monolayer via Tip-Enhanced Cavity-Spectroscopy.

Emerging light-matter interactions in metal-semiconductor hybrid platforms have attracted considerable attention due to their potential applications in optoelectronic devices. Here, we demonstrate plasmon-induced near-field manipulation of trionic responses in a MoSe2 monolayer using tip-enhanced cavity-spectroscopy (TECS). The surface plasmon-polariton mode on the Au nanowire can locally manipulate the exciton (X0) and trion (X-) populations of MoSe2. Furthermore, we reveal that surface charges significantly influence the emission and interconversion processes of X0 and X-. In the TECS configuration, the localized plasmon significantly affects the distributions of X0 and X- due to the modified radiative decay rate. Additionally, within the TECS cavity, the electric doping effect and hot electron generation enable dynamic interconversion between X0 and X- at the nanoscale. This work advances our understanding of plasmon-exciton-hot electron interactions in metal-semiconductor-metal hybrid structures, providing a foundation for an optimal trion-based nano-optoelectronic platform.

Bayesian optimization of periodic multilayered slabs for passive absorptivity control

A vanadium dioxide (VO2) film grown on a titanium oxide crystal shows a metal–insulator transition at room temperature with drastically changed optical properties. A multilayered slab with a sub-micron scale VO2 film was proposed to utilize its unique properties for passive intensity control of sunlight absorption and radiative cooling. Its optimal geometries were numerically explored using the Bayesian optimization (BO) method. BO was applied for three types of multilayered slabs, those having one, two, or three isolated slabs of different widths. For each type of multilayered slab, BO could optimize geometric variables with practical calculation times considering the total number of possible combinations of variables, which is subsequently referred to as the total number of candidates. Optimization results revealed that two isolated slabs had the most suitable spectral absorptivity in both hot and cold environments. The infrared absorptivity of the double slab was kept low in cold conditions to suppress radiative cooling. However, the double slab exhibited good radiative cooling performance under hot conditions. Electromagnetic energy density surrounding the slab illustrated that metallic VO2 and gold placed in a parallel manner excited the coupled mode of surface plasmon polaritons to enhance absorptivity. Radiative cooling faded for the triple slab because each slab could couple with radiation propagating only across a portion of the cross-sectional area. Through three BO trials, improvement of the VO2 visible reflectivity was recognized as a future issue for further development of passive sunlight absorption control.

Fabrication Process of Metal-Assisted Chemical Etched Curved Mirror Structure for Extracting Surface Plasmon Polariton Mode of Top-Emitting Organic LED

Fabrication Process of Metal-Assisted Chemical Etched Curved Mirror Structure for Extracting Surface Plasmon Polariton Mode of Top-Emitting Organic LED

High refractive index sensing highly sensitive and low loss SPR sensor based on hollow-core D-shaped optical fiber

A hollow-core D-shaped optical fiber-based surface plasmon resonance (SPR) sensor for low-loss and highly sensitive liquid analytes detection is theoretically investigated. The gold (Au) metal nanolayer is coated on the cladding etched D-shaped flat surface to develop the plasmonic effect. The nanolayer coating on the outer flat surface is very easy compared to the inside hollow-core, so our hollow-core sensor manufacturing is too easy compared to other hollow-core refractive indices (RIs) detection sensors. The resonance effect between analytes filled fundamental guided core mode and surface plasmon polariton mode of the D-shaped hollow-core optical fiber sensor is used to obtain the detections of analytes RIs variations. We have found good linear results ([Formula: see text]) in analytes RIs versus resonance wavelength for gold layers thicknesses for the analytes RIs range of 1.45–1.52. This hollow-core D-shaped optical fiber sensor achieves the maximum wavelength sensitivity of 23500[Formula: see text]nm RIU[Formula: see text] and a corresponding resolution of [Formula: see text] RIU. We have obtained the maximum figure of merit (FOM) of 228 1/RIU. The proposed sensor may be highly active in detecting the biological and chemical liquid analytes.

Dual‐polarised end‐fire antenna based on the high‐order mode of spoof surface plasmon polaritons

AbstractA planar antenna with dual‐linearly polarised end‐fire radiation is proposed. A tapered double‐sided symmetrical spoof surface plasmon polariton (SSPP) transmission line (TL) with tilted unit cells is proposed. The SSPP TL can operate in two types of first high‐order modes: the first high‐order even mode and the first high‐order odd mode. A two‐port feeding structure is designed to feed the SSPP TL. When the signal is fed from port 1, the energy travels through the substrate integrated waveguide and eventually excites the even mode on the SSPP TL, leading to vertically polarised radiation. Conversely, when the signal is input from port 2, the energy travels through the stripline‐to‐slotline transition and eventually excites the odd mode on the SSPP TL, generating horizontally polarised radiation. According to the measured results, a 54.6% overlapping bandwidth is obtained. The horizontal and the vertical polarisations achieve a maximum gain of 14.7 and 12.2 dBi, respectively.

Terahertz Generation through Coherent Excitation of Slow Surface Waves in an Array of Carbon Nanotubes

In this paper, we present a scheme for generating terahertz (THz) radiation using an array of parallel double-walled carbon nanotubes (DWCNTs) subjected to a direct current (DC). The longitudinal surface plasmon polaritons (SPPs) in the DWCNTs are coherently excited by two near-infrared laser beams with slightly different frequencies. Through numerical methods, we investigate the spectral characteristics of the SPPs in the presence of a DC current in the nanotubes. We identify high-quality plasmonic modes with a slowdown factor exceeding 300 in the terahertz frequency region. The amplification of these slow SPP modes is facilitated by the DC current in the DWCNTs, fulfilling a synchronism condition. This condition ensures that the phase velocity of the SPPs is closely matched to the drift velocity of the charge carriers, allowing for an efficient energy exchange between the current and the surface electromagnetic wave. The high-frequency currents on the nanotube walls in the DWCNT array enable the emission of THz radiation into the far field, owing to an antenna effect.

Dynamic construction of refractive index-dependent vibrations using surface plasmon-phonon polaritons

One of the fundamental hurdles in infrared spectroscopy is the failure of molecular identification when their infrared vibrational fingerprints overlap. Refractive index (RI) is another intrinsic property of molecules associated with electronic polarizability, but with limited contribution to molecular identification in mixed environments currently. Here, we investigate the coupling mode of localized surface plasmon and surface phonon polaritons for vibrational de-overlapping. The coupling mode is sensitive to the molecular refractive index, attributed to the RI-induced vibrational variations of surface phonon polaritons (SPhP) within the Reststrahlen band, referred to as RI-dependent SPhP vibrations. The RI-dependent SPhP vibrations are linked to molecular RI features. According to the deep-learning-augmented demonstration of bond-breaking-bond-making dynamic profiling in biological reaction, we substantiate that the RI-dependent SPhP vibrations effectively disentangle overlapping vibrational modes, achieving a 92% identification accuracy even for the strongly overlapping vibrational modes in the reaction. Our findings offer insights into the realm of light-matter interaction and provide a valuable toolkit for biomedicine applications.

Optimization of a Weyl-semimetal-based near-field heat transfer system

Near-field radiative heat transfer (NFRHT) is inherently limited by Lorentz reciprocity, which can be partially mitigated through the application of an external magnetic field. However, recent studies have discovered that Weyl semimetals (WSMs) possess the ability to achieve nonreciprocal surface plasmon polariton modes without relying on an external magnetic field. Building upon the nonreciprocal nature of WSMs, this study investigates NFRHT between two WSM slabs and compares different WSM materials. The primary focus of the comparison lies in analyzing the heat flux under varying emitter and receiver temperatures. Three of the selected WSM materials exhibit similar performance in NFRHT, showing sensitivity to a decrease in the receiver temperature due to their low dielectric tensor components. In contrast, Eu2IrO7 displays distinctive characteristics, being sensitive to changes in the emitter temperature as a result of its higher dielectric tensor components. Additionally, a reassessment of the nonreciprocity in Co2MnGa, Eu2IrO7 and Co3Sn2S2 is conducted. Furthermore, Bayesian optimization algorithms are employed to optimize parameters and address the challenge of low thermal radiation observed in existing WSM NFRHT systems. The results highlight the achievement of an optimal WSM material that achieves an impressive heat flux of 5.29 × 108 (W/m2) at an emitter temperature of 310 K and a receiver temperature of 290 K. Notably, this heat flux surpasses that of Co2MnGa by 2.5 times in the context of NFRHT. The discoveries presented in this study promises to offer practical implications for the development of nonreciprocal thermal energy management systems.

Crossed grating sensing refractive index change in the non-laboratory environment.

Surface plasmon polaritons (SPPs) have been widely applied to refractive index (RI) sensing for their extremely high sensitivity to the surrounding RI change. Many efforts have been devoted to narrowing the linewidth of the SPP mode and enhancing the sensitivity of SPP sensors. However, most reported SPP-based RI sensing platforms could only operate in a laboratory environment for their bulky volume or sophisticated measuring systems. In this context, we have developed a miniaturized and portable RI sensing platform based on a 2D crossed grating coupled SPP sensor that can work under a non-laboratory environment. The crossed grating is fabricated by the laser interference lithography (LIL) method, which is cost-effective and reproductive. A series of glucose solutions with different concentrations have been used as analytes to verify the sensing performance of the fabricated crossed grating.