Nanoplasmonic Waveguides Research Articles

Collective quantum dynamics with distant quantum emitters in slow-wave nanoplasmonic waveguides

We consider a slow-wave nanoplasmonic waveguide system with spatially separated (distant) quantum emitters. Based on a nanoplasmonic waveguide quantum electrodynamic theory the emerging non-Markovian collective plasmon-polariton dynamics directly reflects the spatial positioning of the quantum emitters. A phase-space analysis allows us to distinguish between collectivity and cooperativity and the transition between these regimes. For distant emitters, temporal decoherence is reflected in anomalous phase-space evolution. In the spectral domain, collectivity emerges as a resonant single Lorentzian peak with two weak sidebands, while cooperativity manifests as a Fano-like resonance normal-mode splitting. Remarkably, even for distant quantum emitters, we achieve collective multiple quantum emitter dynamics with non-vanishing excitation and vanishing instantaneous emission, establishing an interaction-based quantum nanoplasmonic memory with key relevance in quantum nanoplasmonic networks.

Enhanced Green Light Emission from a Silicon-Based Metal-Encapsulated Nanoplasmonic Waveguide.

Integrated silicon plasmonic circuitry is becoming integral for communications and data processing. One key challenge in implementing such optical networks is the realization of optical sources on silicon platforms, due to silicon's indirect bandgap. Here, we present a silicon-based metal-encapsulated nanoplasmonic waveguide geometry that can mitigate this issue and efficiently generate light via third-harmonic generation (THG). Our waveguides are ideal for such applications, having strong power confinement and field enhancement, and an effective use of the nonlinear core area. This unique device was fabricated, and experimental results show efficient THG conversion efficiencies of η = 4.9 × 10-4, within a core footprint of only 0.24 μm2. Notably, this is the highest absolute silicon-based THG conversion efficiency presented to date. Furthermore, the nonlinear emission is not constrained by phase matching. These waveguides are envisioned to have crucial applications in signal generation within integrated nanoplasmonic circuits.

Ultrasensitive and Rapid Detection of Procalcitonin via Waveguide-Enhanced Nanogold-Linked Immunosorbent Assay for Early Sepsis Diagnosis.

Sepsis, a life-threatening inflammatory response, demands economical, accurate, and rapid detection of biomarkers during the critical "golden hour" to reduce the patient mortality rate. Here, we demonstrate a cost-effective waveguide-enhanced nanogold-linked immunosorbent assay (WENLISA) based on nanoplasmonic waveguide biosensors for the rapid and sensitive detection of procalcitonin (PCT), a sepsis-related inflammatory biomarker. To enhance the limit of detection (LOD), we employed sandwich assays using immobilized capture antibodies and detection antibodies conjugated to gold nanoparticles to bind the target analyte, leading to a significant evanescent wave redistribution and strong nanoplasmonic absorption near the waveguide surface. Experimentally, we detected PCT for a wide linear response range of 0.1 pg/mL to 1 ng/mL with a record-low LOD of 48.7 fg/mL (3.74 fM) in 8 min. Furthermore, WENLISA has successfully identified PCT levels in the blood plasma of patients with sepsis and healthy individuals, offering a promising technology for early sepsis diagnosis.

A nano-plasmonic HMIM waveguide based concurrent dual-band BPF using circular ring resonator

A nano-plasmonic HMIM waveguide based concurrent dual-band BPF using circular ring resonator

Electrically tunable grating metamaterials polarization-independent filter based on graphene–lithium niobate

In this paper, we propose an electrically tunable coupling filter that utilizes orthogonal gratings together with graphene. The position of the transmission valley can be altered by varying the gate voltage’s strength, and the electrotunable properties of lithium niobate are described. Under resonance conditions, monolayer graphene is comparable to a conductive electrode that completes all of this device’s absorption. By optimizing the substrate thickness and grating duty cycle, this device can achieve perfect filtering with an absorption rate of 99% at 801 nm. Coupled mode theory is also used to explain the spectrum response. Additionally, we discover that this serial filter exhibits polarization insensitive properties between 0 to 30 degree, such a filter with superior performance will play an significant role in fields such as plasmonic nanowaveguides.

Design of Graphene Hybrid Dielectric Plasmonic Nano-waveguide with Ultralow Propagation Loss

Design of Graphene Hybrid Dielectric Plasmonic Nano-waveguide with Ultralow Propagation Loss

One-way light flow by spatio-temporal modulation.

The unidirectional flow of electrons that takes place in a conventional electronic diode has been a cornerstone in the development of the field of electronics. Achieving an equivalent one-way flow for light has been a long-standing problem. While a number of concepts have been suggested recently, attaining a unidirectional flow of light in a two-port system (e.g., a waveguiding configuration) is still challenging. Here, we present what we believe to be a novel approach for breaking reciprocity and achieving one-way flow of light. Taking a nanoplasmonic waveguide as an example, we show that a combination of time-dependent interband optical transitions, when in systems exhibiting a backward wave flow, can yield light transmission strictly in one direction. In our configuration, the energy flow is unidirectional: light is fully reflected in one direction of propagation, and is unperturbed in the other. The concept can find use in a range of applications including communications, smart windows, thermal radiation management, and solar energy harvesting.

Ultra-confined Propagating Exciton–Plasmon Polaritons Enabled by Cavity-Free Strong Coupling: Beating Plasmonic Trade-Offs

Hybrid coupling systems consisting of transition metal dichalcogenides (TMD) and plasmonic nanostructures have emerged as a promising platform to explore exciton–plasmon polaritons. However, the requisite cavity/resonator for strong coupling introduces extra complexities and challenges for waveguiding applications. Alternatively, plasmonic nano-waveguides can also be utilized to provide a non-resonant approach for strong coupling, while their utility is limited by the plasmonic confinement-loss and confinement-momentum trade-offs. Here, based on a cavity-free approach, we overcome these constraints by theoretically strong coupling of a monolayer TMD to a single metal nanowire, generating ultra-confined propagating exciton–plasmon polaritons (PEPPs) that beat the plasmonic trade-offs. By leveraging strong-coupling-induced reformations in energy distribution and combining favorable properties of surface plasmon polaritons (SPPs) and excitons, the generated PEPPs feature ultra-deep subwavelength confinement (down to 1-nm level with mode areas ~ 10–4 of λ2), long propagation length (up to ~ 60 µm), tunable dispersion with versatile mode characters (SPP- and exciton-like mode characters), and small momentum mismatch to free-space photons. With the capability to overcome the trade-offs of SPPs and the compatibility for waveguiding applications, our theoretical results suggest an attractive guided-wave platform to manipulate exciton–plasmon interactions at the ultra-deep subwavelength scale, opening new horizons for waveguiding nano-polaritonic components and devices.

Power Loss Reduction of Angled Metallic Wedge Plasmonic Waveguides via the Interplay between Near-Field Optical Coupling and Modal Coupling

Coupled metallic-wedge nano-plasmonic (CWP) waveguides were predicted as the best building blocks, which can realize ultra-compact and broadband integrated optical circuits (IOCs) due to the localized near-field distributions at the dielectric/metal interfaces. Our simulation results show that the manipulations of the near-field distribution and the near-field modal coupling in CWP waveguides can effectively minimize the power loss by varying the wedge angles, which can avoid the loss from the metallic structure and thereby improving the practical application in IOCs.

Cross-talk reduction in a graphene-based ultra-compact plasmonic encoder using an Au nano-ridge on a silicon substrate

Plasmonic waveguides have been widely studied in the rapid development of optically integrated circuits. The cross talk between plasmonic waveguides is a critical issue that should be considered. Nano-plasmonic waveguides with tunable graphene-free patterns on silicon ridge have very attractive features. Despite these attractive features, the low confinement in plasmonic waveguides reduces the coupling length. This issue results in high cross talk in optical integrated circuits. We present a solution to the mentioned problem. A metal ridge under the plasmonic channel helps to reduce the cross-talk value. A new graphene-based plasmonic waveguide has been proposed for achieving the switching operation at terahertz frequencies. Based on the designed waveguide, a 4-to-2 plasmonic encoder with the cross talk of -17.33dB has been presented. Using six waveguides, the encoder is designed with a contrast ratio of 14.44 dB and an area of 0.36µm2. Concerning the obtained results, the presented structure can be used in optical integrated circuits.

Pairwise and Bipartite Entanglements of Three Non-Equally Separated Quantum Dots in Plasmonic Nanowaveguide System

We theoretically investigate properties of the pairwise and bipartite entanglements of three non-equally separated quantum dots (QDs) coupled to one-dimensional plasmonic nanowaveguide by means of the concurrence as a measure of entanglement. High concurrences of pairwise and bipartite entangled states for three QDs are obtained in wide range of the separation distances between the QDs. Moreover, the switching of maximally entangled state and unentangled state can be achieved by properly modulating the frequency detuning of the QDs from the plasmon field and the separation distances between the QDs.

Nanoscale All-Solid-State Plasmochromic Waveguide Nonresonant Modulator.

Plasmochromics, the interaction of plasmons with an electrochromic material, have spawned a new class of active plasmonic devices. By introducing electrochromic materials into the plasmon's dielectric environment, plasmons can be actively manipulated. We introduce inorganic WO3 and ion conducting LiNbO3 layers as the core materials in a solid-state plasmochromic waveguide (PCWG) to demonstrate light modulation in a nanoplasmonic waveguide. The PCWG takes advantage of the high plasmonic loss at the high field located at the WO3/Au interface, where the Li+ ions are intercalated into a thin WO3 plasmon modulating layer. Through careful PCWG design, the direction for ion diffusion and plasmon propagation are decoupled, leading to enhanced modulation depth and fast EC switching times. We show that at a bias voltage of 2.5 V, the fabricated PCWG modulator achieves modulation depths as high as 20 and 38 dB for 10 and 20 μm long devices, respectively.

Gold-induced photothermal background in on-chip surface enhanced stimulated Raman spectroscopy.

Surface enhanced Raman spectroscopy (SERS) and stimulated Raman spectroscopy (SRS) are well established techniques capable of boosting the strength of Raman scattering. The combination of both techniques (surface enhanced stimulated Raman spectroscopy, or SE-SRS) has been reported using plasmonic nanoparticles. In parallel, waveguide enhanced Raman spectroscopy has been developed using nanophotonic and nanoplasmonic waveguides. Here, we explore SE-SRS in nanoplasmonic waveguides. We demonstrate that a combined photothermal and thermo-optic effect in the gold material induces a strong background signal that limits the detection limit for the analyte. The experimental results are in line with theoretical estimates. We propose several methods to reduce or counteract this background.

Optical quantum yield in plasmonic nanowaveguide

We have developed a theory of the quantum yield for plasmonic nanowaveguide where the cladding layer is made of an ensemble of quantum dots and the core layer consists of an ensemble of metallic nanoparticles. The bound states of the confined probe photons in the plasmonic nanowaveguide are calculated using the transfer matrix method based on the Maxwell equations. It is shown that the number of bound states in the nanowaveguide depends on the dielectric properties of the core and cladding layers. The surface plasmon polaritons (SPPs) produced by the metallic nanoparticles interacts with the excitons of the quantum dots. The radiative and nonradiative linewidths of excitons in the quantum yield are calculated using the quantum mechanical perturbation theory. We have found that the quantum yield decreases as the dipole–dipole interaction between metallic nanoparticles increases. We have also calculated the photoluminescence and found that the enhancement in photoluminescence is due to the SPPs coupling. On the other hand, the quenching in the photoluminescence is due to the quantum yield. We compared our theory with experiments of a nanowaveguide where the core is fabricated from Ag- nanoparticles and the cladding is fabricated from the perovskite quantum dots. A good agreement between theory and experiments is found. Our analytical expressions of the quantum yield and photoluminescence can be used by experimentalists to proforma new types of experiments and for inventing new types of nanosensors and nanoswitches.

All optical logic gates based on nanoplasmonic MIM waveguides

In this paper, we propose and investigate some designs of basic plasmonic logic gates in two dimensional plasmonic waveguides with nanotube metal-insulator-metal waveguides using the numerical method of eigenmode expansion. These gates, including XOR, OR, NOT, and Feynman gate can be realized by changing geometrical parameters properly. Also, by cascading and combining these basic logic gates, any complex logic function can also be obtained providing the highly integrated optical logic circuits. The proposed logic gates have the broadband up to 300 nm and only spend the compact size as much as 2 µm×1.2 µm. Thus, the devices can be applied widely and significantly in optical computing and processing devices.

Mitigation of photon background in nanoplasmonic all-on-chip Raman sensors.

In the quest for a more compact and cheaper Raman sensor, photonic integration and plasmonic enhancement are central. Nanoplasmonic slot waveguides exhibit the benefits of SERS substrates while being compatible with photonic integration and mass-scale (CMOS) fabrication. A difficulty in pursuing further integration of the Raman sensor with lasers, spectral filters, spectrometers and interconnecting waveguides lies in the presence of a photon background generated by the excitation laser field in any dielectric waveguide constituting those elements. Here, we show this problem can be mitigated by using a multi-mode interferometer and a nanoplasmonic slot waveguide operated in back-reflection to greatly suppress the excitation field behind the sensor while inducing very little photon background.

High performance vanadium dioxide based active nano plasmonic filter and switch

We have designed a compact active nano-plasmonic waveguide-based filter and switch in a Fabry Perot structure, in which Vanadium dioxide (VO2) is used as the active material to form an Au/VO2/Au tri-layer structure, which is based on the effect of the electrical-driven phase transformation from the VO2 layer. The largest modulation depth and lowest insertion loss of the Au/VO2/Au tri-layer based FP resonator are 44.77 dB and 1.43 dB respectively in the near-infrared wavelength range from 1400 nm to 2100 nm. In addition, a moderate quality factor of 146 and a high figure-of-merit of 33.31 can be achieved by using a short nano-plasmonic waveguide. The compact size, wavelength tunability, high modulation depth and low insertion loss indicate that the proposed active nano-plasmonic waveguide can be used in a high-density integrated optical circuit.

Wedge Angle-Dependent Propagation Characteristics of Two Coupled Semi-Infinite Au Rib Nanoplasmonic Waveguides

The wedge angle-dependent propagation characteristics of two coupled semi-infinite Au rib nanoplasmonic waveguides are investigated using the three-dimensional finite-difference time-domain (3D FDTD) method with the fast Fourier transform and curve fitting techniques. The simulation results show that the propagation loss and modal index of the fundamental mode are closely related to the field distribution of the supermode which can be manipulated by varying the wedge angle from 75° to 100°. Understanding of the nanostructure-induced enhancement of the propagation characteristics of nanoplasmonic waveguides helps us find the best way to optimize the metallic waveguiding structures.

Waveguide-based surface-enhanced Raman spectroscopy detection of protease activity using non-natural aromatic amino acids.

Surface enhanced Raman spectroscopy (SERS) is a selective and sensitive technique, which allows for the detection of protease activity by monitoring the cleavage of peptide substrates. Commonly used free-space based SERS substrates, however, require the use of bulky and expensive instrumentation, limiting their use to laboratory environments. An integrated photonics approach aims to implement various free-space optical components to a reliable, mass-reproducible and cheap photonic chip. We here demonstrate integrated SERS detection of trypsin activity using a nanoplasmonic slot waveguide as a waveguide-based SERS substrate. Despite the continuously improving SERS performance of the waveguide-based SERS substrates, they currently still do not reach the SERS enhancements of free-space substrates. To mitigate this, we developed an improved peptide substrate in which we incorporated the non-natural aromatic amino acid 4-cyano-phenylalanine, which provides a high intrinsic SERS signal. The use of non-natural aromatics is expected to extend the possibilities for multiplexing measurements, where the activity of several proteases can be detected simultaneously.

Tunable ultra-width bandgap U-shaped band-stop filters of chip scale based on periodic staggered double-side trapezoidal resonators in a metallic nanowaveguide

A chip-scale plasmonic band-stop filter (BSF) based on periodic staggered double-side trapezoidal resonators (PSDSTR) is proposed and investigated theoretically and numerically in this letter. A wide bandgap, derived from the interference superposition of the reflection and transmission waves from each periodic unit, is achieved. One periodic unit consists of two staggered double-side trapezoidal resonators (TSDSTR) which can be tunable by modifying the parameters of the trapezoids and the horizontal distance of two staggered trapezoids. Additionally, optimization and theoretical analysis of the periodic unit structure are also made in the letter. Based on the optimized periodic unit, a chip-scale metallic nanowaveguide embodying PSDSTR is discussed and analyzed to broaden the bandgap width and further improve filter functions. With an ultra-width bandgap and tunable characteristic, the plasmonic nanowaveguide filter presented here may find significant applications in ultrafine spectrum analysis and highly integrated photonic circuits.