Plasmon Polariton Modes Research Articles

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.

Effects of electron transport layer thickness on light extraction in corrugated OLEDs.

This study reported the effects of electron transport layer (ETL) thickness on light extraction in corrugated organic light-emitting diodes (OLEDs) and each layer in OLEDs exhibited a periodical corrugated structure, which was determined by depositing thin films on a glass substrate with a nanoimprinted blazed grating structure. The insight is that light extraction in corrugated OLEDs significantly depends on the ETL thickness. Varying the ETL thickness changed the distribution of carrier recombination and led to exciton formation and optical interference, thereby resulting in different attribution of optical loss modes in OLEDs, which increased or even decreased light extraction and device efficiency. Trapped light extraction from the surface plasmon polariton (SPP) and waveguide (WG) modes was identified by splitting the light into transverse electric and transverse magnetic emissions. Thus, the contributions from the individual SPP and WG modes to the external quantum efficiency (EQE) were distinctly clarified by comparing the experimental results with the theoretical calculations. At the ETL thickness of 115 nm, the corrugated OLED exhibited a significantly enhanced (1.83-fold) EQE compared to the planar one due to the effective extraction of trapped light from the SPP and WG modes. The EQE was enhanced by 0.5%, wherein 0.39% came from the WG mode and 0.11% came from the SPP mode.

Plasmonic Biosensor With Gold and Titanium Dioxide Immobilized on Photonic Crystal Fiber for Blood Composition Detection

This paper proposes a photonic crystal fiber (PCF) based plasmonic biosensor for the detection of various blood compositions like red blood cells (RBCs), hemoglobin (HB), white blood cells (WBCs), plasma, and water. The finite element method (FEM) has been used to simulate and quantitatively evaluate this biosensor. The gold and titanium dioxide coated PCF operates on the surface plasmon resonance (SPR) theory, where the gold layer acts as a plasmonic material, and the titanium dioxide layer improves adhesion between the gold layer and the PCF surface. SPR occurs at the interface between gold and the sensing channel, when the core propagation mode is coupled with the surface plasmon polariton (SPP) mode in the vicinity of the phase-matching point. Due to the occurrence of SPR, the loss peak is noticed in the core propagation mode, and this loss peak is extremely sensitive to the various blood compositions that each have their unique refractive index (RI) poured into the sensing channel of the PCF. The proposed biosensor has maximum wavelength sensitivity of 12400 nm/RIU. However, the maximum amplitude sensitivity is −574.3 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . Furthermore, with the maximum detection limit of 0.02, the refractive index resolution varies from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.06\times {10}^{-6} {\mathrm {RIU}}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.0\times {10}^{-5} {\mathrm {RIU}}$ </tex-math></inline-formula> . As a result, it is safe to say that this biosensor will work admirably in terms of detecting blood compositions. Thus, the proposed biosensor will explore the broad realms of medical diagnostics.

Greedy-algorithm-empowered design of wideband achromatic beam deflector based on spoof surface plasmon polariton mode

Greedy-algorithm-empowered design of wideband achromatic beam deflector based on spoof surface plasmon polariton mode

Dual functional anode for organic light-emitting devices by directly imprinted nanostructured ultrathin Au film

The ultrathin metal film with excellent electrical conductivity and high visible-band transmittance has attracted considerable attention as a transparent electrode for the organic light-emitting devices (OLEDs). However, the deficient surface morphology and poor continuity of low thickness evaporated metal films and the surface plasmon-polaritons (SPPs) mode induced energy loss still seriously limit the actual efficiency of OLEDs. In this work, the thermal nanoimprint lithography has been further modified and directly applied to fabricate nanostructures onto the ultrathin Au film. During the imprinting process, the surface smoothness and conductivity of the Au film are obviously optimized with the formation of nanostructures. After integrating proper nanostructures into OLEDs, the photons that trapped by SPPs mode within the device were effectively out-coupled. The current efficiency and luminance have been enhanced 45.3% and 18.1%, respectively. Furthermore, the emitting properties of the OLEDs were also modified by the nanostructures, and the directional transmission capability of output light was significantly improved.

Surface Plasmon Resonance–Based Refractive Index Biosensor: an External Sensing Approach

A surface plasmon resonance (SPR)-based sensor founded on photonic crystal fiber (PCF) is suggested and numerically analyzed in the manuscript. The refractive index (RI) detecting SPR-based sensor has the ability to identify the analyte range from 1.33 to 1.4. Pure silica is used as a base material and it has high RI value than the analyte RI. Furthermore, an analyte layer and chemically stable gold (Au) layer are also placed at the sensor design. The simulations are done based on the finite element method (FEM). Here, the scaled-down approach has the necessity to increase phase matching point within the core mode and surface plasmon polariton (SPP) mode which tends to the sensor to reach high sensitivity response. At the intersect point of core and SPP mode, the loss curve shows a maximum peak value. The suggested sensor shows the highest wavelength sensitivity (WS) response of 35,943.22 nm/RIU, amplitude sensitivity (AS) response of 2321.36 RIU−1, sensor resolution of 9.04 × 10−6 RIU, and figure of merit (FOM) value of 600. It is noted that all the optical parameters show better performance analysis. Furthermore, an external sensing approach provides more fabrication feasibility which marks the offered sensor more suitable for practical experimentation. Besides, the investigated sensor provides the maximum and rapid sensing performance that will be helpful for microfluidic analyte detection, detection of biomolecules, medical diagnostics, virus detection, security, and bio-imaging.

Excitation of Surface Plasmon Polariton Modes with Double-Layer Gratings of Graphene.

A long-range surface plasmon polariton (SPP) waveguide, composed of double-layer graphene, can be pivotal in transferring and handling mid-infrared electromagnetic waves. However, one of the key challenges for this type of waveguide is how to excite the SPP modes through an incident light beam. In this study, our proposed design of a novel grating, consisting of a graphene-based cylindrical long-range SPP waveguide array, successfully addresses this issue using finite-difference time-domain simulations. The results show that two types of symmetric coupling modes (SCMs) are excited through a normal incident light. The transmission characteristics of the two SCMs can be manipulated by changing the interaction of the double-layer gratings of graphene as well as by varying various parameters of the device. Similarly, four SCMs can be excited and controlled by an oblique incident light because this light source is equivalent to two orthogonal beams of light. Furthermore, this grating can be utilized in the fabrication of mid-infrared optical devices, such as filters and refractive index sensors. This grating, with double-layer graphene arrays, has the potential to excite and manipulate the mid-infrared electromagnetic waves in future photonic integrated circuits.

Ultra-wideband surface plasmonic bandpass filter with extremely wide upper-band rejection

An ultra-wideband bandpass filter (BPF) with a wide out-of-band rejection based on a surface plasmonic waveguide (SPW) slotline with ring grooves is designed and analyzed. A paired microstrip-to-slotline transition is designed for quasi-TEM to TM mode conversion by using a microstrip line with a circular pad and the slotline with the same circular slot. The mode conversion between the TM and the surface plasmon polariton (SPP) mode is realized by using a gradient slotline with ring grooves and an impedance matching technique. The upper cut-off frequencies of the passband can be adjusted by using these proposed SPP units, while the lower frequencies of the passband are created by using the microstrip-to-slotline transitions to give an ultra-wideband BPF. The dispersion curves of SPP units, electric field distribution, and the transmission spectra of the proposed ultra-wideband bandpass filter are all calculated and analyzed by the finite-difference time-domain (FDTD) method. The simulated results show that the presented filter has good performance including a wide 3-dB bandwidth of 149% from 0.57 GHz to 3.93 GHz, an extremely wide 40-dB upper-band rejection from 4.2 GHz to 18.5 GHz, and low loss and high selectivity in the passband. To prove the design validity, a prototype of the BPF has been manufactured and measured, showing a reasonable agreement with simulation results. The unique features of the proposed BPF may make it applicable for integrated circuit and plasmonic devices in microwave or THz frequency ranges.

Fano Resonance Hybrid Waveguide-Coupled Plasmonic Sensor Using Transparent Conductive Oxide in the Near-Infrared Range

We proposed an ultra-sensitive refractive index sensor by using indium-doped cadmium oxide as a plasmonic material operating in near-infrared based on Fano resonance. The proposed sensor has a hybrid multilayer waveguide structure that supports both a long-range surface plasmon polariton (LRSPP) mode and a dielectric waveguide (DWG) mode. The design strategy of the structure parameters of the inner layers is elaborated in detail through the numerical analysis of the two modes. By suitably tailoring the thickness of the coupling layer, a strong mode coupling between the two modes could be achieved, leading to a sharp asymmetric Fano resonance. With the designed optimal physical parameters, our proposed sensor could achieve a maximum intensity sensitivity of 19,909 RIU−1, a 193-fold enhancement than that of a conventional long-range SPR (LRSPR) based scheme. The proposed design can be a promising platform for biochemical sensing in the near-infrared region.

Highly sensitive double D-shaped channel photonic crystal fiber based plasmonic refractive index sensor

In this paper, a highly sensitive miniaturized surface plasmon resonance (SPR) based photonic crystal fiber (PCF) sensor is presented for a wide range of analyte sensing. Gold is selected as the plasmonic metal for its higher chemical stability and titanium oxide works as the adhesive layer for gold attachment on silica. The plasmonic metal and the sensing medium are placed exterior to the surface of the sensor design to make it fitting for practical applications. By a careful arrangement of the periodic arrangement of the refractive index in the design, the generation of the evanescent fields is fine-tuned to obtain the phase matching between the leaky core guided mode and the surface plasmon polariton (SPP) mode. Numerical simulations have been carried out by employing the finite element method (FEM) with the consideration of a perfectly matched layer (PML) to absorb surface radiations. The proposed sensor shows a maximum wavelength sensitivity of 34,000 nm/RIU (refractive index units) and a maximum amplitude sensitivity of 331 RIU−1, investigated by using the wavelength and the amplitude interrogation methods, respectively, for the analyte sensing range of 1.16 to 1.37 RI (refractive index). The sensor also exhibits a wavelength resolution of 2.94×10−6 RIU which indicates a high detection accuracy. On that, the proposed sensor would be an excellent candidate for a wide range of RI detection, applicable for various purposes such as chemical detections, medical diagnostics, bio-sensing, and other low RI analytes.

All-optical terahertz logic gates based on coupled surface plasmon polariton sub-wavelength waveguiding in bulk Dirac semimetal

Bulk Dirac semimetals (BDS) are quantum fermionic system also identified as three-dimensional counterpart of graphene exhibit rich plasmonic response at terahertz (THz) frequencies. In this work, we report THz waveguiding in the BDS curved geometries, which confine electromagnetic field in the form of symmetrically coupled surface plasmon polariton (SPP) modes. We demonstrate how the sub-wavelength BDS-Air-BDS multilayer system with various bending and corners efficiently confines THz beam with minimal bending losses. The realized sub-wavelength THz waveguiding in BDS system is advantageous than other approaches like zero-refractive index metamaterials. Based on the symmetric coupled SPP waveguiding in BDS multilayers, all-optical logic gates including OR, AND, XOR, NOR and NAND are realized at THz waveband. The realized THz logic gates exhibit optimal threshold transmission (at least 50%) for defining ON-OFF states. We anticipate that the illustrated waveguiding and logic gate applications in BDS system could open an avenue for optoelectronic applications at THz frequencies.

Plasmon-Enhanced Exciton Delocalization in Squaraine-Type Molecular Aggregates.

Enlarging exciton coherence lengths in molecular aggregates is critical for enhancing the collective optical and transport properties of molecular thin film nanostructures or devices. We demonstrate that the exciton coherence length of squaraine aggregates can be increased from 10 to 24 molecular units at room temperature when preparing the aggregated thin film on a metallic rather than a dielectric substrate. Two-dimensional electronic spectroscopy measurements reveal a much lower degree of inhomogeneous line broadening for aggregates on a gold film, pointing to a reduced disorder. The result is corroborated by simulations based on a Frenkel exciton model including exciton-plasmon coupling effects. The simulation shows that localized, energetically nearly resonant excitons on spatially well separated segments can be radiatively coupled via delocalized surface plasmon polariton modes at a planar molecule-gold interface. Such plasmon-enhanced delocalization of the exciton wave function is of high importance for improving the coherent transport properties of molecular aggregates on the nanoscale. Additionally, it may help tailor the collective optical response of organic materials for quantum optical applications.

Curved Mirror Arrays for Light Extraction in Top-Emitting Organic Light-Emitting Diodes.

The light outcoupling efficiency of a top-emitting organic light-emitting diode (OLED) is only about 20%, and the majority of the light is trapped in the waveguide modes and surface plasmon polariton (SPP) modes. Extracting the trapped modes can reduce the device power consumption and improve the operating lifetime. In this study, we demonstrate a top-emitting OLED structure with a dielectric spacer to suppress the SPP mode and with a patterned back mirror to extract the waveguide modes. We examine and compare several curved mirror arrays and conclude that a micromirror array (μMA) can efficiently extract the waveguide modes while minimizing the absorption loss. The optimized μMA device with a semi-transparent top electrode shows a 36% external quantum efficiency, 2 times higher than the referenced device. This optical design can be easily incorporated into a top-emitting device and has a great potential for displays and lighting applications.

Dual-mode independent detection of pressure and refractive index by miniature grating-coupled surface plasmon sensor.

Multiple parameters need to be monitored to analyze the kinetics of biological progresses. Surface plasmon polariton resonance sensors offer a non-invasive approach to continuously detect the local change of refractive index of molecules with high sensitivity. However, the fabrication of miniaturized, compact, and low-cost sensors is still challenging. In this paper, we propose and demonstrate a grating-coupled SPR sensor platform featuring dual mode operation for simultaneous sensing of pressure and refractive index, which can be fabricated using a highly-efficient low-cost method, allowing large-scale production. Both sensing functionalities are realized by optical means via monitoring the spectral positions of a surface plasmon polariton mode (for refractive index sensing) and Fabry-Perot or metal-insulator-metal modes (for pressure sensing), which are supported by the structure. Simultaneous measurement of refractive index with the sensitivity of 494 nm/RIU and pressure was demonstrated experimentally. The proposed platform is promising for biomonitoring that requires both high refractive index sensitivity and local pressure detection.

High-Sensitivity Refractive Index Sensing and Broadband Tunable Polarization Filtering Characteristics of D-Shaped Micro-Structured Fiber With Single-Layer Air-Holes and Gold Film Based on SPR

An easy-to-implement side-polished micro-structured fiber MSF)based on surface plasmon resonance (SPR) is proposed. The influence of fiber structure parameters on transmission performance is investigated by finite element method (FEM). The chemical stable gold is deposited on the side polished plane to provide the plasmonic material required for SPR. Ten cladding air-holes are used to confine light transmission and improve the coupling strength between the core mode and surface plasmon polaritons (SPP) mode. The optimization results show that the MSF integrates the characteristics of high refractive index (RI) sensing and broadband tunable polarization filtering. In addition, the RI detection range of the sensor can be further extended by depositing a <inline-formula><tex-math notation="LaTeX">$Si_{3}N_{4}$</tex-math></inline-formula> dielectric layer on the gold film. The RI detection range of the sensor with gold coating is 1.20--1.325 with the maximum sensitivity of 12,000 nm/RIU. The RI measurement range of the sensor with gold-<inline-formula><tex-math notation="LaTeX">$Si_{3}N_{4}$</tex-math></inline-formula> bilayer film can be extended to 1.20--1.37, and the maximum sensitivity is 10,000 nm/RIU. Furthermore, by changing the ambient RI of gold-coated fiber or the polishing depth of fiber, a broadband tunable filter with excellent performance can be obtained. Therefore, the proposed MSF not only has application value in the detection of biochemical liquid samples, but also has broad application potential in broadband communication networks, which is helpful to promote the development of miniaturization and integration of optical devices.

Magnetoplasmon-Polaritons in a Two-Dimensional Electron System with a Back Gate

Magnetoplasmon-polariton excitations in a two-dimensional (2D) electron system with a back gate are theoretically studied. The back gate is a metal layer that is parallel to the layer of 2D electrons and is separated from them by a dielectric substrate serving as a waveguide. In the absence of a magnetic field, the interaction of 2D plasmons with the modes of the waveguide limited by the gate from one side results in the formation of a family of waveguide plasmon-polariton modes. The two lowest of these modes are TM modes and have a gapless dispersion relation. As known, a static magnetic field B perpendicular to the plane of the system hybridizes different modes. The spectra and magnetodispersion of the found 2D modes are determined. The classification of all modes as longitudinal and transverse (ТМ–ТЕ classification), which is usually valid only in the absence of B, is recovered in the limit of high fields B. The magnetic field dependence of the cutoff frequencies of the considered modes significantly affects the results. Even a low magnetic field opens a frequency gap proportional to the magnetic field magnitude B in the spectrum of one of the lowest magnetoplasmon-polariton modes. As the magnetic field increases, the gap is saturated and the mode becomes waveguide.

Nanostructured Hyperbolic Metamaterials for Magnetoplasmonic Sensors

We demonstrate numerically a concept for highly integrated magnetoplasmonic biosensors made with nanostructured magnetooptical (MO) hyperbolic metamaterials (HMMs). The concept is based on the use of enhanced amplitudes of ultranarrow peaks of the transverse magnetooptical Kerr effect (TMOKE). In contrast to conventional magnetoplasmonic transducers that employ wide surface plasmon resonances, we use bulk plasmon polariton modes in HMMs. In sensing through changes in the refractive index of water, a figure of merit on the order of 8 × 102 was observed, to be compared with 590 for non-MO HMMs. This allows for improved resolution detection of low-molecular-weight analytes at concentrations on the order of picomolar.

Zeonex-based high sensitivity dual-channel SPR optical fiber sensor for gaseous analytes in terahertz regime

A Zeonex based dual-channel optical fiber Surface Plasmon Resonance (SPR) sensor has been proposed in this paper for gaseous analytes in terahertz regime. The subwavelength porous polymer fiber is surrounded by two semicircular air hole channels and the SPR effect can be excited by the ferroelectric polyvinylidene fluoride (PVDF) layer coated on the inner surface of the channels. A thin dielectric layer is used to enhance the coupling efficiency between the fundamental mode and the surface plasmon polariton mode. Using Finite Element Method, simulation results show that the sensitivity of the sensor can reach 110,000 nm/RIU, which is more than twice the sensitivity proposed by other existing THz optical fiber sensors. Moreover, the dual-channel design and the penetration of terahertz waves facilitate multi-channel detection, making it practical for biomedical and chemical fields.

Perspective on 2D material polaritons and innovative fabrication techniques

In this Perspective, we present that polariton modes hosted in two-dimensional (2D) materials can be used to increase and control light–matter interactions at the nanoscale. We analyze the optical response of the most used 2D material nanostructures that support plasmon, exciton, and phonon polariton modes. Polariton characteristic lengths are used to assess the hybrid light–matter modes of different 2D material monolayers and nanoribbons. We present that the 2D material nanodisk can act like a cavity that supports localized polariton modes, which can be excited by a nearby placed quantum system to present ultra-fast and ultra-bright operation. The key to achieve high quality 2D polariton modes is to reduce material losses. Thus, state-of-the-art exfoliation, chemical vapor deposition, and transferring techniques of 2D materials are introduced to fabricate nanostructures that fulfill the stringent requirements of applications in photonics, optoelectronics, and quantum technologies.