Plasmonic Quantum Dot Nanocavity Laser: Hybrid Modes

Propagation properties of Surface Plasmon Polariton (SPP) mode in AlGaAs/Ag/AlGaAs waveguide are presented. A two dimensional finite-difference time-domain (FDTD) based algorithm has been developed in order to analyze the dynamics of the waveguide numerically. The SPP mode is excited through a monochromatic point source embedded in the AlGaAs layer. The SPP wavelength in the waveguide and penetration depth of SPP in Ag and AlGaAs layers have been calculated both analytically and numerically. An excellent agreement has been observed between the analytical and numerical results. The electric field strength at different distances from top AlGaAs/Ag interface is also analyzed and presented.

We study the coupling of localized surface plasmon (LSP) and surface-plasmon polariton (SPP) modes in a system composed of a metallic nanoparticle chain separated from a thin metallic film by a dielectric spacer. The thickness of such a spacer influences the level of interaction between LSP and SPP modes and controls the electromagnetic enhancement in this system. An enhancement with narrow resonances can be observed for appropriate parameters. The high-resonance quality factor and tunability of this system make it a very promising candidate for biosensing and surface-enhanced spectroscopy applications.

The optical response of metal/dielectric interfaces is largely influenced by surface plasmon-polariton (SPP) modes. In the mid-infrared (IR) range, SPPs can probe the inner physicochemical properties of metal/dielectric systems, including interfaces with mid-IR polaritonic 2D crystals. Using advanced nanoscopy techniques, we characterize mid-IR SPP modes at air/gold and hexagonal boron nitride (hBN) 2D crystal/gold interfaces via synchrotron infrared nanospectroscopy (SINS) and scattering-scanning near-field optical microscopy (s-SNOM) imaging. SPPs in these systems show micrometer-sized wavelengths and propagation lengths over 20 micrometers at room temperature. In hBN/Au, both SPPs and hyperbolic phonon polaritons (HPhPs) coexist, creating SPP-HPhP wave superposition. The experimental momentum and damping of the SPP waves are determined from the s-SNOM imaging and the SINS spatio-spectral linescan. Thereby, we retrieve the experimental frequency-momentum dispersion relation, presenting excellent agreement with theory. Furthermore, we characterize an anti-crossing of the SPP dispersion near the in-plane transverse optical phonon frequency of hBN, indicating that SPP modes and phonon form a coupled system interacting in the strong coupling regime. Such an interaction of SPPs with phonons can be further explored to enhance the sensibility of mid-IR nanospectroscopy techniques.

The excitation conditions for surface plasmon polaritons (SPPs) on a silver-gold bilayer coated sinusoidal grating can be varied over a wide range by tuning the azimuthal grating orientation $(\ensuremath{\alpha})$. Grating coupling induces rotation of the SPP wave vector which, for specific conditions, can be directed perpendicular to the exciting light direction. Certain $\ensuremath{\alpha}$ orientations allow the excitation of two SPPs with the same frequency but different propagation directions. Other azimuthal orientations allow excitation of many SPP modes characterized by propagation over a large angular range. The kinematics of SPP propagation can be described by a model based on the wave-vector conservation law. Using this model, SPP dispersion relation, propagation direction, and mode density have been computed and shown to be in agreement with experimental measurements. The wave-vector dispersion is characterized by an energy threshold for the SPP excitation that increases as $\ensuremath{\alpha}$ increases. The angular spread is accompanied by an energy condensation of the SPP modes in correspondence to the energy threshold.

This chapter summarizes basic properties of the main Surface plasmon polariton (SPP) modes. SPPs are electromagnetic (EM) excitations that, being coupled to surface collective oscillations of free electrons in a metal, are bound to and propagate along metal-dielectric interfaces. Light-matter interactions in nanostructured materials give rise to nanostructured optical fields, implying that EM fields of SPP modes supported by metal nanostructures exhibit subwavelength spatial frequencies. The SPP electric field is thereby primarily transverse in the dielectric and longitudinal in the metal, reflecting the hybrid nature of SPPs that combine the features of both propagating EM waves in dielectrics and free electron oscillations in metals. The SPP waveguide configuration representing a finite-width metal stripe placed on a dielectric substrate is probably the most natural and certainly the best studied one to date. SPPs represent interface EM excitations, in which evanescent EM waves are coupled to surface collective oscillations of free electrons, propagating along metal-dielectric interfaces.

Plasmonics have been identified as an ideal platform for ultra-sensitive, label-free biosensors mainly due to the high field confinement on a metal-dielectric interface and the resulting strong light-matter interaction offered by surface plasmon resonances (SPRs) that can be entirely exposed to test analytes. Well-established SPR-based biosensors exploiting propagating SPRs yield superior specifications regarding bulk sensitivity compared to localized counterparts leading to already commercial available sensor devices. However, most of these systems require bulky prism-based configurations to couple light into the Surface Plasmon Polariton (SPP) mode impeding system miniaturization. In addition, SPR-based sensors suffer from intrinsic high propagation losses restricting the potential for multiple on-chip functionalities. In this context, co-integration of plasmonics with a low-loss photonic platform emerges as a viable solution towards highly sensitive, low-loss and small footprint optical sensors. In this work, we present an ultra-compact, interferometric plasmonic sensor co-integrated on a TiO2 photonic waveguide platform. The device consists of two access TiO2 photonic waveguides separated by a gold-based metal stripe which is located on top of an appropriately shorter TiO2 waveguide layer. Two metal/insulator interfaces are formed at the top (sensing arm) and bottom surfaces (reference arm) of the metal able to support SPP modes which upon excitation through the input photonic waveguide propagate along the two metal surfaces and interfere at the output waveguide realizing a single-arm Mach-Zehnder Interferometer. After optimization of the device in aqueous environment, we achieved sensitivity values as high as 2430 nm/RIU at near-infrared spectrum region for a 65 um long plasmonic stripe.

We explore the dispersion properties and optical gradient forces from mutual coupling of surface plasmon polariton (SPP) modes at two interfaces of nanoscale plasmonic waveguides with hyperbolic metamaterial cladding. With Maxwell’s equations and Maxwell stress tensor, we calculate and compare the dispersion relation and optical gradient force for symmetric and antisymmetric SPP modes in two kinds of nanoscale plasmonic waveguides. The numerical results show that the optical gradient force between two coupled hyperbolic metamaterial waveguides can be engineered flexibly by adjusting the waveguide structure parameters. Importantly, an alternative way to boost the optical gradient force is provided through engineering the hyperbolic metamaterial cladding of suitable orientation. These special optical properties will open the door for potential optomechanical applications, such as optical tweezers and actuators.

We investigate numerically, by means of the finite-difference time-domain method, the propagation characteristics of surface plasmon-polariton (SPP) modes excited in an optical nanowire consisting of a chain of Ag spheres embedded in dielectric shells made of materials with optical Kerr nonlinearity. It is demonstrated that, in the linear limit, the nanowire supports two SPP modes, a transverse and a longitudinal one, separated by Δλ = 20 nm. Furthermore, the dependence of the transmission characteristics of these SPP modes, on both the pulse peak power and Kerr coefficient of the dielectric shell, is investigated. Nonlinear optical phenomena, such as power dependence of mode frequency, switching, or optical limiting, are observed and discussed.

Excitation of surface plasmon polariton (SPP) modes results in the appearance of resonance line shapes observed in the attenuated total reflection spectra of layered structures in the Otto or Kretschman configurations. The sensitivity of the resonance characteristics of the propagating modes to changes in optical characteristics of the environment is widely used in sensor devices to determine qualitative and quantitative changes in the environment, as well as low concentrations of substances adsorbed on the surface. In the present work, we analyze the resonance characteristics of SPP modes based on the optical properties of plasmonic materials. Interfaces of metal-dielectric structures support the propagation of SPP modes. Estimation of the dispersion dependences of the propagation constant of the SPP mode, sensitivity to changes in external conditions, enhancement of the near field on the surface is carried out within the electromagnetic theory based on approximations of asymmetric shapes of spectral resonance lines of SPP by Fano formulas in the ultraviolet, visible, and infrared regions.

A metasurface consisting of a 2D periodic square lattice of metallic square ring resonators is considered for supporting spoof surface plasmon polariton (SSPP) modes. First, SSPP modes are highlighted by simulated dispersion curves. The dispersion curves are analyzed by considering hybridization of modes in either a patch or an aperture array with frequency shifts. Hybridization of modes is also supported by means of surface current and electric field mappings showing consistent symmetric and anti-symmetric fields. Second, it is shown that a dipole antenna located near the metasurface is able to generate SSPP modes. The transmission spectra between two antennas located at each extremity of the metasurface show transmission enhancements compared with propagation in free space. The transmission enhancements are shown for different locations of the antennas either facing each other or positioned in diagonal. Finally, the transmission enhancement is connected to SSPP modes by comparing the transmission spectra and the measured dispersion curves with each other. Specifically, two transmission windows measured for an embroidered metasurface are related to the cutoff frequency of the two SSPP modes supported by the metasurface as evidenced by the measured dispersion curves.

We consider the formation of the surface plasmon polariton (SPP) mode in the structure with a metallic torus and a metallic flat surface separated by a dielectric medium. The energy of the wave field is mainly concentrated in the dielectric medium at the vicinity of the minimum thickness of the gap between the metallic surfaces. The dependence of the resonant frequency on parameters of the structure was determined. The strongly localized SPP mode in the transverse direction contributes to the increase in the Purcell factor that is crucial for enhancement of the spontaneous emission rate.

Quantum surface plasmon polaritons (SPPs) are a growing research area with many unknown phenomena. In this paper, the behavior of squeezed SPP modes on a metal slab is assessed. To begin with, a quantized form of the SPP modes propagating on the metal thin film based on Green’s tensor method is provided. Since the squeezing properties of the SPP modes are indeed transferred from incident photons, in the next step, different aspects of this phenomenon are studied. Obtaining an important direct relation between incident photons’ properties and SPP modes will allow for the effective factors on this phenomenon to be explored. Although the initial quantum properties will be changed or lost during the photon–surface plasmon interaction, it will be shown that some factors can improve the transfer process. Finally, the squeezing transfer from incident photons to the SPP modes and effective factors on it as a full quantum phenomenon will be investigated.

Recently, much attention has been paid to an interesting subject, i.e., the interactions between surface plasmon polaritons (SPPs) and molecules. The interactions between SPPs and molecules often appear in two opposite cases, namely weak and strong coupling. When the interaction is weak, the absorption maximum simply coincides with the electronic transition energy of the molecule. In the weak coupling regime, the wave functions of the molecule and the SPP modes are considered to be unperturbed, only leading to enhancement of the absorption or fluorescence of the molecules. On the other hand, when the interaction is strong enough, the SPPs and molecules can form a coherent hybrid object, thus the excitation energy is shared by and oscillates between the SPPs and molecular systems (Rabi oscillations), leading to vacuum Rabi splitting of energy levels at the resonance frequency. Due to the fact that both the SPPs and the molecule components can be confined into the nanometer scale, the work on strong coupling with SPPs offers a very good opportunity to realize nanoplasmonic devices, such as thresholdless laser and room temperature B-E condensates.In this work, we investigate a hybrid system formed by strong coupled gold nanodisk arrays and J-aggregate molecules. Smooth gold nanodisk arrays are fabricated by a template-stripping process. In such an experimentally simple replicate process, mass-production of gold nanodisk arrays with the same morphology can be transferred from patterned indium tin oxides (ITO) glass. The structures on ITO glass are milled with a focused ion beam. Periodic gold nanodisk arrays have the capability of converting light into SPPs modes, resulting in a significant field confinement at the patterned metal surface. In particular, the desired SPP mode can be chosen by changing the nanodisk array period to match the absorbance peak of the J-aggregate molecule. On the other hand, J-aggregate molecule is chosen due to its large dipole moments and absorption coefficient, which makes it attractive for designing the strong exciton-plasmon interaction system. The strong coupled system is formed when the J-aggregate molecule is spin-coated on the gold nanodisk arrays. Through reflection measurements, Rabi splitting energy value 200 meV is observed when the period of the nanodisk array is 350 nm. Through tuning the coupling strength by changing the lattice period from 250 nm to 450 nm, the typical signature of strong coupling:anticrossing of energies is found in reflection spectra. This simple replicate process for strong coupling hybrid system fabrication should play an important role in designing novel ultrafast nanoplasmonic devices with coherent functionalities.

Numerical investigation of finite thickness metal-insulator-metal structure for waveguide-based surface plasmon resonance biosensing

A novel surface plasmon resonance (SPR) refractive index (RI) sensor based on the D-type dual-mode photonic crystal fiber (PCF) is proposed. The sensor employs a side-polished few-mode PCF that facilitates the transmission of the fundamental and second-order modes, with an integrated microfluidic channel positioned directly above the fiber core. This design minimizes the distance to the analyte and maximizes the interaction between the optical field and the analyte, thereby enhancing the SPR effect and resonance loss for improved sensing performance. Au-TiO2 dual-layer material was coated on the surface of a microfluidic channel to enhance the penetration depth of the core evanescent field and tune the resonance wavelength to the near-infrared band, meeting the special needs of chemical and biomedical detection fields. The finite element method was utilized to systematically investigate the coupling characteristics between various modes and surface plasmon polariton (SPP) modes, as well as the impact of structural parameters on the sensor performance. The results indicate that the LP11b_y mode exhibits greater wavelength sensitivity than the HE11_y mode, with a maximum sensitivity of 33,000 nm/RIU and an average sensitivity of 8272.7 nm/RIU in the RI sensing range of 1.25-1.36, which is higher than the maximum sensitivity of 16,000 nm/RIU and average sensitivity of 5666.7 nm/RIU for the HE11b_y mode. It is believed that the proposed PCF-SPR sensor features both high sensitivity and high resolution, which will become a critical device for wide RI detection in mid-infrared fields.