Surface Plasmon Polariton Modes Research Articles

Photonic-plasmonic hot-electron-based photodetection with diffracted-order-resolved leaky plasmonic mechanisms

Abstract Although hot-carrier-based photodetection using plasmonic effects has been widely investigated, photodetectors of this type with an external quantum efficiency (EQE) > 1 % ${ >}1\%$ and an active area of < 1 ${< }1$ mm2 remain out of reach even in the visible frequencies. In this work, a novel hot-electron-based, non-trench-type photodetector exploiting pure photoexcitation in a thin aluminum (Al) film and leaky plasmonic modes at and between its heterojunctions is proposed, analyzed, and experimentally demonstrated. Combining diffracted-order-resolved analytical analysis and numerical computations unravels the optical absorption mechanism of the innovative design. Leaky surface plasmon resonance (with leakage radiation into the air) produced by a propagating diffracted order and quasibound supermodes (with power leakage via coupled gap plasmon polariton and bound surface plasmon polariton modes) excited by evanescent diffracted orders are shown to significantly contribute to the absorptance in the preferred thin Al film where hot electrons are generated. At 638.9 nm and electric bias −0.9951 V, the measured per-unit-area responsivity, detectivity, and the external quantum efficiency reach 298.1444 μA/mW/mm2, 4.3809 × 109 cm Hz1/2/W, and 2.6878%, respectively, from an active area of 4.6457 × 10−2 mm2. The performance is among the best of those previously reported operating at similar wavelengths and biases. The RC time constant is estimated to be about 1.673 μs from the current-voltage measurements. The physical insight into the innovative, experimentally demonstrated device could lay the groundwork for the practical use of low-voltage, metal-based photodetection.

Faraday effect in magnetoplasmonic nanostructures with spatial modulation of magnetization.

For the first time, to the best of our knowledge, the properties of the Faraday effect are addressed in a magnetoplasmonic nanostructure with nonuniform spatial distribution of the magnetization. It is shown that the coincidence in period and phase between magnetization modulation and the field of the optical mode provides the resonant enhancement of the Faraday effect. This effect is observed for both the surface plasmon polariton and waveguide modes.

Near-field radiative heat transfer in three-body Weyl semimetals.

We investigate the near-field radiative heat transfer in a three-body system made of Weyl semimetals. At infinitesimal temperature gradient, the rotation of the middle and the right bodies leads to heat transfer suppression, enabling thermal switching with considerably enhanced heat flux but slightly smaller ratio than two-body system without the middle body, due to stronger cavity surface plasmon polariton modes and their mismatch caused by relative rotation. By further moving the middle body to induce asymmetric cavity sizes, the three-body system can achieve a switching ratio exceeding the two-body counterpart due to asymmetric cavity modes coupling. As the temperature gradient increases to 200 K, the highest switching ratio by optimally tuning the rotation and cavity size asymmetry decreases slightly yet still outperforms the two-body system. Our results provide important understanding of the near-field radiative heat transfer in many-body systems consisting of Weyl semimetals.

Enhanced graphene surface plasmonics through incorporation into metallic nanostructures.

A methodology for enhancing the surface plasmon polariton (SPP) resonance associated with graphene, through nanoscale metal-dielectric-metal (MDM) gaps, is proposed. The modulation of the resonances, in the range of 0.7 µm to 1 µm was done through tuning the carrier density in graphene and has been shown to be of potential utility for surface analyte sensing. It was shown, from finite element simulations in the frequency domain, that the related hybrid SPP modes could be clearly delineated in far field spectroscopy.

Engineering the Dispersion of Surface Plasmon Polariton/Epsilon‐Near‐Zero Modes through Modal Separation and Optical Confinement

Doped cadmium oxide (CdO) films support tunable, low‐loss surface plasmon polaritons (SPPs) and epsilon‐near‐zero (ENZ) modes throughout the mid‐infrared. Prior work demonstrated that polaritonic strong coupling could be realized in bilayer films of CdO supporting adjacent SPP and ENZ modes. The hybridized SPP‐ENZ dispersion displays a prominent anti‐crossing with an amplitude dependent on the spectral and spatial overlap of the modes. Here, we leverage the low carrier diffusivity, in concert with the broad tunability of the plasma frequency in CdO to control the SPP‐ENZ dispersion within monolithic, multilayer CdO structures featuring dielectric, unintentionally doped CdO coatings or spacer layers. In the case of the former, the coating induces further compression of the polaritonic fields, altering the dielectric environment. In contrast, when incorporated as a spacer layer, the spatial overlap of the constituent polaritonic near‐fields is reduced. In all cases, the anti‐crossing behavior of the hybrid SPP‐ENZ modes is maintained, thus inheriting the extreme light confinement of the ENZ mode and extended propagation length of the SPPs. Through simultaneous control over the SPP‐ENZ coupling strength and group velocities, significant tunability over the SPP‐ENZ dispersion is demonstrated, enabling applications such as in‐plane waveguiding, tailored thermal emission, and tunable near‐field heat transfer.

High-Efficiency Conversion From Rectangular Waveguide Mode to Spoof SPP Using Metasurface

In this letter, we propose a method to realize rectangular waveguide mode to spoof surface plasmon polaritons (SSPP) mode conversion using phase gradient metasurface (PGM). By applying a PGM with designed wavevector to the narrow wall of the rectangular waveguide, propagation mode and direction of the guided waves can be conversed and controlled due to wavevector matching. Such system can provide an excellent transition by matching the momentum of the rectangular waveguide mode and the SSPP mode. A smooth bridge between the rectangular waveguide system and the SSPP waveguiding system can be realized with potential advantages in conformal design, super-resolution imaging or signal manipulation. Simulated and experimental results, agreeing well with each other, validated the effectiveness of rectangular waveguide mode to SSPP mode conversion using PGM from 6.96-7.55 GHz. Furthermore, a dual channel rectangular waveguide to SSPP splitter is proposed and validated with applications for dual-channel power dividing and signal transmission, achieving an efficiency of 72.4%.

PS-b-PMMA templated ITO electrodes for improving the performance of non-fullerene organic photovoltaics

We have developed a block copolymer (BCP)-based patterned electrode with a periodic structure of 80 nm and investigated their application in organic photovoltaics. The indium tin oxide (ITO) electrodes with the thicknesses of 30, 50, 70, 90, and 120 nm were sputtered onto BCP-patterned templates and the morphology and optoelectronic properties were investigated. Using the finite difference in time domain method, the effect of different thickness electrodes on the light absorption of the active layer was studied. We found that the ITO thickness of 70 nm has an absorption enhancement effect in the visible wavelength band. Finally, we prepared organic photovoltaic devices based on the non-fullerene PBDB-T:ITIC system, the BCP-patterned templates enhance greatly the light absorption of the active layer through both light diffraction and coupling to surface plasmon polariton modes achieving a 12.9% increase in power conversion efficiency. • ITO electrodes with 80 nm periodic structure were developed by BCP self-assembly. • Patterned ITO greatly enhance the light absorption of the PBDB-T:ITIC active layer. • OPVs with patterned ITO achieve a 12.9% increase in power conversion efficiency.

An angle-tuned polarization-independent multi-narrowband perfect absorber

We propose and numerically investigate an angle-tuned polarization-independent multi-narrowband perfect absorber, which comprises a simple gold nanocube array on SiO2/oxidized aluminum mirror layers. The oxidized aluminum mirror is able to support the surface plasmon polariton mode on the SiO2/Al2O3 interface. The multi-narrowband absorption contributes to the simultaneously excited quasi-metal–insulator–metal guided modes and standing wave cavity mode in the thick insulator layer by the incident light normal to the structure in the wavelength range 1400–2400 nm. Moreover, the absorption can be actively modulated by adjusting the incidence angle, and it is polarization independent. The perfect absorber is also suitable for sensing, with the figure of merit reaching 102 RIU−1 within the refractive index range from 1.3 to 1.36.

Design of photonic crystal fiber to excite surface plasmon resonance for highly sensitive magnetic field sensing.

To improve the sensing performance of optical fiber magnetic field sensor based on magneto-refractive effect, a D-shaped photonic crystal fiber-surface plasmon resonance (PCF-SPR) sensor based on magneto-refractive effect is proposed and its magnetic field sensing characteristics are investigated. The designed D-shaped PCF has a core-analyte-gold structure. Within the D-shaped PCF, the side polishing surface is coated with the gold film and the special hole is sandwiched between the core and the gold film. To realize the high magnetic field sensitivity for the fiber SPR magnetic field sensor, the special hole is filled with magnetic fluid (MF). In this paper, we analyze the mode transmission characteristics and magnetic field sensing characteristics of this fiber sensor by finite element method. We also obtain a general rule for the optimization of PCF-SPR sensors by analyzing the dispersion curves, the energy of the surface plasmon polariton mode and the core mode on the sensing performance of the designed fiber sensor. The maximum refractive index sensitivity and magnetic field sensitivity of the optimized fiber are 59714.3 nm/RIU and 21750 pm/mT (50-130 Oe), respectively. Compared with optical fiber magnetic field sensors based on magneto-refractive effect reported previously, the magnetic field sensitivity in this paper is nearly two orders of magnitude higher and it can initially achieve nT magnitude magnetic field resolution and testing capability. The proposed fiber sensor has the advantages of simple structure, easy production, high sensitivity, and strong environmental adaptability. It not only improves the sensing performance of optical fiber magnetic field sensors, but also provides an ideal alternative platform for biosensors like microfluidics because of its high refractive index sensitivity and the special structure.

Correlations between incident and emission polarization in nanowire-particle coupled junctions.

Plasmonic nanostructures with subwavelength confinement are of great importance for the development of integrated nanophotonic circuits and devices. Here, we experimentally investigate how the polarization of the emitted light from nanowire-particle junction relies on the incident polarization. We demonstrate that the correlations can be effectively modulated by the particle position relative to the wire. By varying the wire-particle gap with only several nanometers, the nanowire-particle junction can be changed from polarization maintainer to rotator. Then, by moving the particle along the wire within half of the surface plasmon polariton (SPP) beat, the polarization behaviors can be tuned from positive to negative correlation. The mechanism can be well understood by the hybridization of wire-particle coupled mode and propagating SPP modes, which is verified by finite-difference time-domain simulations. These findings would provide a new degree of freedom for manipulating light polarization at the nanometer scale and additional flexibility for constructing nanophotonic devices.

Photonic crystal fiber modulator based on surface plasmon resonance

In this paper, a photonic crystal fiber (PCF) modulator based on surface plasmon resonance (SPR) is proposed. Two optical functional materials, liquid crystal and magnetic fluid, were filled in the air holes with aurum film of PCF to excite SPR. After applying electric and magnetic fields, the effective refractive index of the SPP (surface plasmon polaritons) mode in PCF would be changed by liquid crystals and magnetic fluids, which affected the resonance wavelength and loss peak. The modulation feasibility of the structure was verified by the full vector finite element method. The results show that the proposed modulator can independently realize electro-optical and magneto-optical modulation with a characteristic of wavelength tunability. At the wavelength of 1450 nm, the electro-optic modulation voltage reaches 2.5 V, and the extinction ratio reaches a maximum of 46.11 dB/mm. Only 0.43 mm length is required to meet communication requirements. At the same time, the magnetic field sensitivity and extinction ratio of the modulator reach 17.82 pm/Oe and 25.18 dB/mm, respectively, at the wavelength of 1682 nm. The modulator has the characteristics of high extinction ratio, low modulator voltage and miniaturization, which can be used in optical fiber transmission systems that need to be integrated.

Selectivity of dominant surface plasmon polariton modes using thin metal waveguides with grating structures

The conversion of incident light to surface plasmon polaritons (SPPs) was verified for a dielectric-metal-dielectric waveguide with a grating structure. The dominant SPP mode with respect to the propagation distance could be selected by adjusting the thickness of the gold film. To realize highly efficient light-to-SPPs conversion, the grating parameters for a realistic length of plasmonic waveguides were optimized using a recently developed numerical technique, FDCFD-FILT. This novel technique is the combination of finite-difference complex-frequency-domain (FDCFD) with fast inversion of laplace transform (FILT) and a powerful tool for designing plasmonic waveguides and investigating propagation characteristics efficiently.

Nanowire Embedded Micro-Drilled Dual-Channel Approach to Develop Highly Sensitive Biosensor

In this letter, we propose a novel approach to develop a highly sensitive surface plasmon resonance (SPR) based fiber optics biosensor. The sensor comprises a dual-drilled channel (DDC) with gold-nanowire (AuNW) contained in each channel to excite the plasmon modes. The SPR effect between the core guided mode and the surface plasmon polariton (SPP) modes of the DDC is used to evaluate the sensing response with respect to different analytes. The sensing performance, coupling characteristics, and the fabrication tolerance of the sensor are numerically analyzed and characterized by using a full-vectorial Finite Element Method (FEM). The designed sensor shows a minimum sensitivity of 3150 nm/RIU for refractive index (RI) = 1.310. While, the sensor exhibits an extremely high sensitivity varying from 10250 nm/RIU to 90500 nm/RIU for RI varied over the range of 1.370 to 1.400. Various structural parameters, e.g., separation of the channel from the core, the radius of the AuNW, the fabrication tolerance, etc., have been studied in this work. In addition, the possible fabrication steps of such a design have been discussed indicating its simple practical realization.

Multi-band propagation of spoof surface plasmon polaritons by its high-order modes

Compact dual-band and tri-band bandpass filters (BPFs) based on high-order modes of spoof surface plasmon polaritons (SSPPs) are proposed. By using the meander line technique, the electrical size of the proposed SSPP structure was reduced by 68% compared with the traditional rectangular-grating SSPP structure. The high-efficiency passbands are excited by high-order modes of SSPPs. Therefore, dual-band and tri-band BPFs are designed by using two and three high-order modes of SSPPs, respectively. In addition, a notched band is obtained by loading three complementary split-ring resonators (CSRRs) on the bottom layer of the tri-band BPF. Thus, a quad-band BPF is achieved.

Flexible nanoparticle-on-mirror strategy for ultrasensitive molecule detection by directionally coupling surface plasmon polaritons

Applying local surface plasmon resonance (LSPR) to a nanoparticle-on-mirror (NPOM) configuration for realizing highly sensitive molecule detection using surface-enhanced Raman scattering (SERS) typically enhances the Raman signal by 106–1010 under limiting conditions. We propose a special nanoparticle-fishbone structure (NPFS) system, which incorporates the surfaceplasmon polariton (SPP) coupler of the fishbone structure into the NPOM configuration, to achieve ultra-high local electric field enhancement by plasmon hybridizing the LSPR mode of metallic nanoparticles and the SPP mode of the fishbone array structure. During the numerical simulation, the NPFS system exhibited a SERS enhancement factor of 1011, which is two orders of magnitude higher than that of the NPOM system; the SERS experimental results further demonstrated its outstanding performance. These findings indicate that introducing a well-designed SPP coupler on the metallic film can further improve the advantages of various NPOM configurations. The proposed approach can open new horizons for designing nanoscale photonic devices for ultrasensitive molecule detection.

Hybrid Nanowire-Rectangular Plasmonic Waveguide for Subwavelength Confinement at 1550 Nm.

This paper presents a hybrid waveguide based on metal surface plasmon polaritons (SPPs) at 1550 nm comprising two silver (Ag) nanowires and a rectangular silicon (Si) waveguide. Due to the strong coupling effect observed in both the metal SPP mode and Si waveguide mode, excellent waveguide characteristics, such as a small effective modal area and long transmission length, could be achieved. The research results revealed that the proposed hybrid waveguide could achieve an ultra-long transmission distance of 270 µm and normalized effective mode area of 0.01. Furthermore, the cross-sectional size of the waveguide was 500 nm × 500 nm, which helped in achieving a subwavelength size. In addition, the hybrid waveguide was resistant to manufacturing errors. These excellent performances indicate that the proposed waveguide has great application potential in optoelectronic integrated circuits.

Near-field properties of spin, Huygens and Janus sources in a narrow sandwiched structure

Near-field photonics has attracted extensive attention for its applications from classical to quantum fields, and near-field directionality is the core of many applications. Here, we use a sandwich structure to investigate the effects of waveguide width and source position on the behavior of spin, Huygens and Janus sources. Although the structure is very simple, the conclusions obtained through it can be extended to more complex structures. In a narrow waveguide, the surface modes on each interface can be coupled together to form symmetric and antisymmetric surface plasmon polaritons (SPPs) modes, connecting the evanescent fields at the two interfaces. The width of the waveguide determines the propagation constants of the two SPPs modes and will affect the near-field directional emission of the three sources. We find that the directionality of the three sources in the narrow waveguide is no longer perfect, but related to the position of the source. In addition, we also discuss the possibility of realizing near-field directional emission of three sources with only one electric dipole in different structures by selectively exciting the special SPPs mode. Our result increases the flexibility of controlling the direction of near-field emission of evanescent waves, having potential applications in nanophotonic propagation and multifunctional nanophotonic devices.

Terahertz hybrid optical-plasmonic modes: tunable resonant frequency, narrow linewidth, and strong local field enhancement.

Hybrid optical-plasmonic modes have the characteristics of low loss and small mode volume, which will result in the strong localization and enhancement of electromagnetic field. Such advantages of hybrid optical-plasmonic mode are important for the enhancement of light-matter interactions. Here, terahertz (THz) hybrid modes of Fabry-Perot resonances (FPRs) and spoof surface plasmon polaritons (SSPPs) in the modified Otto scheme are investigated both in theoretical and experimental aspects. The device structure is composed of a metal grating silicon waveguide (MGSW) and a metal slit grating (MSG). The two components are vertically stacked with a variable air gap between them. The THz hybrid modes are originated from the far-field coupling of the FPRs and the SSPP supported by the air gap and the MSG, respectively. By changing the thickness of the air gap, the resonant frequency of the FPR-SSPP modes can be tuned in a frequency range of about 0.1 THz. An anti-crossing behavior between two reflection dips corresponding to the guided-mode resonance in the MGSW and the FPR-SSPP mode is observed, which leads to the narrowing of the reflection dips in the anti-crossing region. Numerical simulations show that at the resonant frequencies of FPR-SSPP mode, there is a huge volume-averaged electromagnetic energy enhancement of about 1600 times in the grooves of the MSG, which is around 8.7 times larger than that induced by the SSPP directly launched by free-space electromagnetic field. The hybrid FPR-SSPP modes can be used to construct THz sensors and detectors with high sensitivity.

A novel photonic crystal fiber refractive index sensor with ultra wide detection range based on surface plasmon resonance effect

In this paper, a novel photonic crystal fiber (PCF) refractive index (RI) sensor based on surface plasmon resonance (SPR) effect is proposed. With the full vector finite element method, the SPR-PCF RI sensor is designed, and the mode coupling effects between the X-polarization (X-pol) and Y-polarization (Y-pol) core modes and second-order surface plasmon polariton modes are analyzed. The simulation results show that the structure parameters of the proposed PCF have significant influences on the resonance wavelength drift and wavelength sensitivity (WS). Finally, in the RI range of 1.32 ~ 1.48, the average WSs of the X-pol and Y-pol core modes can reach − 4735.83 nm/RIU and − 4525.83 nm/RIU, respectively. Moreover, the maximum resolution (R) and figure of merits (FOM) of the X-pol and Y-pol core modes are 4.71 × 10−6 and 4.65 × 10−6 RIU, and 134 and 177 RIU−1, respectively. Compared with other reported results, the proposed SPR-PCF RI sensor can achieve wide detection range, high average WS, good linearity, high R, and large FOM, so it will have important applications in the fields of biochemistry, medicine, and environmental science.

Coupled Optical Solitons in Microwave-Assisted Plasmonic Graphene Waveguide

The emergence of soliton in plasmonic graphene waveguide is investigated in the presence of optical and microwave fields. The considered configuration encompasses a monolayer graphene waveguide placed between parallel plate capacitor. The optical fields are launched as surface plasmon polariton modes, while the microwave field is applied to the capacitor. The governing nonlinear-Schrödinger equations of the propagating optical fields have been derived. It is shown that electronically controlled coupled optical solitons can be achieved by altering the corresponding self- (and cross-) modulation terms with proper electrical biasing and doping concentration. This present work paves the way towards soliton formation in the field of quantum technology.