As a result of recent developments in nanofabrication techniques, the dimensions of metallic building blocks of plasmonic devices continue to shrink down to nanometer range thicknesses. The optical and electronic properties of ultra-thin plasmonic films are expected to have a strong dependence on the film thickness, composition, and strain, as well as an increased sensitivity to external optical and electrical perturbation. This unique tailorability establishes ultra-thin plasmonic films as an attractive material for the design of tailorable and dynamically switchable metasurfaces. Due to their epitaxial growth on lattice matched substrates, TiN is an ideal material to investigate the tailorable properties of plasmonic films with thicknesses of just a few monolayers. MXenes, a class of two-dimensional (2D) nanomaterials formed of transition metal carbides and carbon nitrides, are yet another promising material platform for tailorable plasmonic metamaterials. MXenes have been widely explored in a variety of applications, such as electromagnetic shielding and SERS. However, investigations of MXenes in the context of nanophotonics and plasmonics have been limited leading to this current exploration of MXenes as building blocks for plasmonic and metamaterial devices. In this study, we investigate these two emerging classes of materials, MXenes and ultra-thin transition metal nitrides, as potential material platforms for tailorable plasmonic metamaterials. We report on the strain and oxidation dependent optical properties of ultrathin TiN. Applications of MXenes as a broadband plasmonic metamaterial absorber and a random laser device are also discussed.
An explanation of bound states in the continuum (BICs) is offered. With particular attention to Friedrich–Wintgen BICs, the commentary presents a study by Bogdanov et al., which appears in the same issue of Advanced Photonics.
Over the last decade, there has been tremendous success in developing optical metasurfaces with desired properties using innovative nanopatterned metal-dielectric composite films. However, major problems towards the mass production and use of these metafilms include expensive and poorly-scalable nanofabrication along with ohmic losses in their nanostructured metallic elements. More advanced approaches in this area include designs providing for (i) electrical or all-optical control of the metasurface responses to get their switchable or multi-functional performance, and (ii) ability to compensate loss and achieve lasing by adding gain inclusions. In all these cases, modeling only light propagation in nanostructured and optically dispersive media is not sufficient to fully understand, control and optimize the performance of a given metadevice. Instead, 3D full-wave time-domain electrodynamics should be coupled to additional nanoscale equations describing complex light-matter interactions at ab-initio level, thus providing a designer with an advanced multiphysics and possibly multiscale numerical modeling framework.
Here, we present our multiphysics time-domain modeling framework for tunable and active photonics. First, we start with reviewing our efficient time-domain approach to modeling tunable graphene-based devices, where the integral multi-parametric surface conductivity is reformulated in time domain with physically interpretable and fast-to-compute integration-free terms. Then, we discuss a multiphysics approach to model optically tunable materials, where classical electrodynamics is coupled to non-equilibrium thermodynamics of electrons and lattice ions. Finally, we present our models of non-linear media built on carrier kinetics, including nanolasers and loss-compensated plasmonic metafilms, as well as metadevices with absorption saturation and reversed absorption saturation effects.
MXenes are a recently discovered family of two-dimensional nanomaterials formed of transition metal carbides and carbon nitrides with the general chemical form Mn+1XnTx, where ‘M’ is a transitional metal, ‘X’ is either C or N, and ‘T’ represents a surface functional group (O, -OH or -F). MXenes are derived from layered ternary carbides and nitrides known as MAX (Mn+1AXn) phases by selective chemical etching of the ‘A’ layers and addition of functional groups ‘T’.
In our work, we focus on one of the most well studied MXene, titanium carbide (Ti3C2Tx). Single to few layer flakes of Ti3C2Tx (in a solution dispersed form) are used to create a continuous film on a desired substrate by using spin coating technique. Losses inherent to the bulk MXene and existence of strong localized SP resonances in Ti3C2Tx disks/pillar-like nanostructures at near-IR frequencies are utilized to design an efficient broadband absorber. For Ti3C2Tx MXene disk array sitting on a bilayer stack of Au/Al2O3, high efficiency (>90%) absorption across visible to near-IR frequencies (bandwidth ~1.55 μm), is observed experimentally.
We also experimentally study random lasing behavior in a metamaterial constructed by randomly dispersing single layer nanosheets of Ti3C2Tx into a gain medium (rhodamine 101, R101). Sharp lasing peaks are observed when the pump energy reaches the threshold value of ~ 0.70 μJ/pulse. This active metamaterial holds a great potential to achieve tunable random lasing by changing the optical properties of Ti3C2Tx flakes.
A design of a transverse electric (TE)-pass polarizer based on hybrid plasmonic silicon-on-insulator (SOI) platform is reported and analyzed using full vectorial finite element method. The proposed design has gold nanorods that are injected into the silicon dioxide substrate to tolerate the function of the device, and hence the required polarizing state can be obtained. Detailed design principle is presented, taking advantage of the distinct confinements of the TE and transverse magnetic modes in the core region and their coupling with the surface plasmon modes around the metallic nanorods. According to the positions of the gold nanorods, the suggested plasmonic SOI can be used as a TE-pass polarizer with a compact device length of 1.85 μm with 0.1639 dB insertion losses and extinction ratio of 14.58 dB at wavelength of 1.55 μm. The optimized geometrical parameters offer 3 orders of magnitude smaller than similar devices previously demonstrated on the SOI platform. The proposed design has advantages in terms of simplicity and compactness, which makes it a good candidate to be used in integrated silicon photonics. Further, the compact device size and good performance could provide a simple yet satisfactory solution to the polarization-dependent performance drawback of the silicon photonics devices on the SOI platform.
In this paper, a novel design of hybrid silicon plasmonic transverse electric (TE) pass polarizer based on silicon-oninsulator (SOI) platform is reported and analyzed. The numerical results are obtained by using full vectorial finite element method. The suggested design depends on gold rods that are injected into the substrate in order to tolerate the function of the device and hence the required polarizing state can be obtained. The proposed SOI TE polarizer can achieve -0.19 dB insertion losses with compact device length of 18 μm. Further, the introduced device is easy for fabrication and is compatible with the standard CMOS fabrication process.
A theoretical analysis of plasmonic effects in a crystalline silicon-filled metallic nanohole is introduced. The dispersion properties of the guided modes of the silicon-filled silver nanohole are shown to have interesting characteristics such as negative dispersion, which is not normally observed in air-filled structures. Furthermore, the dispersion of the crystalline silicon material itself, when taken into consideration, significantly alters the dispersion characteristics of the guided modes. More interestingly, crystalline silicon is found to show metal-like properties at the edge of the UV/VIS spectrum; therefore, it is demonstrated that a silicon nanolayer surrounded by air is able to support surface plasmon polariton modes. The analysis is carried out using a full vectorial finite element method which can accurately detect the propagation properties of the structure under investigation.
A photonic crystal fiber (PCF) surface plasmon resonance (SPR) based sensor is proposed and analysed. The proposed sensor consists of microuidic slots enclosing a dodecagonal layer of air holes cladding and a central air hole. The sensor can perform analyte detection using both HE<sup>x </sup><sub>11 </sub>and HE<sup>y </sup><sub>11 </sub> modes with a relatively high sensitivities up to 4000 nm=RIU and 3000 nm=RIU and resolutions of 2.5×10<sup>-5</sup> RIU<sup>-1</sup> and 3.33×10<sup>-5</sup> RIU<sup>-1</sup> with HE<sup>x</sup><sub>11</sub> and HE<sup>y</sup><sub>11</sub>, respectively, with regards to spectral interrogation which to our knowledge are higher than those reported in the literature. Moreover, the structure of the suggested sensor is simple with no fabrication complexities which makes it easy to fabricate with standard PCF fabrication technologies.
A theoretical analysis of nanoscale metallic hole filled with a dielectric material is presented. The dispersion characteristics of the guided modes of a dielectric-filled metallic nanohole show interesting characteristics such as negative dispersion which is not normally observed in air-filled structures. Moreover, the material dispersion, taken fully into consideration, is shown to have a significant effect on the modal dispersion of guided modes, specially, at visible range of frequencies. The analysis is carried out using a full vectorial finite element method which can accurately detect the propagation properties of the structure under investigation.