Presence Of Surface Modes Research Articles

Narrow-core hollow optical waveguide with nanostructured SOI as ultra-low loss platform for efficient photodetection

A nanostructured hollow optical waveguide based on high-index contrast grating (HCG) embedded SOI is proposed. An ultra-low propagation loss of 1.22 dB/m even at narrow, 1- $$\upmu $$ m thick, air-core is reported. A high-performance photodetection is realized by the introduction of hollow core in form of intrinsic region in the photodetection (PIN) layer within HCG-assisted narrow-core waveguide. A sufficiently high responsivity of 0.8 A/W and quantum efficiency of 64% are obtained at 1550-nm which is possible because of the presence of surface modes within HCG which get coupled in the photodetection layer leading to a strong optical confinement in that layer. High reflectivity, small penetration length and coupling of lateral surface modes in HCG make it possible to offer improved waveguiding and hence photodetection.

Study of Surface-Active Modes and Defects in Single-Phase Li-Incorporated MgO Nanoparticles

Synthesis and detailed characterization of lithium-incorporated (0–20% of Li loading) MgO nanocrystals are presented. High surface reactivity arises due to the presence of facets and kinks at the surface of the particles. Fourier transform infrared spectroscopy (FTIR) showed that the presence of surface modes with peak shift related to the difference in the electronegativity of Li ions and the formation of extra modes for low loading of Li. For LiMgO particles, interband transitions due to the F+ centers and the surface LixO species are observed. Formation of F+ centers is consistent with a decrease in the lattice parameter as a function of Li loading. A significant increase in the magnetic moment of the LiMgO nanoparticles is discussed in terms of the presence of oxygen vacancies and Li-rich surface regions. Three new bands in the higher frequency range are observed for LiMgO nanoparticles. Overall, studies revealed that the surfaces of the particles are not the same for low and high loadings of Li.

On the limits of the effective description of hyperbolic materials in the presence of surface waves

Here, we address the question of the validity of an effective description for hyperbolic metamaterials in the near-field region. We show that the presence of localized modes such as surface waves drastically limits the validity of the effective description, and requires revisiting the concept of homogenization in the near-field. We demonstrate, from exact scattering matrix calculations for multilayer hyperbolic structures, that one can find surface modes in spectral regions where the effective approach predicts hyperbolic modes only. Hence, the presence of surface modes which are not accounted for in the effective description can lead to physical misinterpretations in the description of hyperbolic materials and their related properties. In particular, we discuss in detail how the choice of the topmost layer affects the validity of the effective medium approach for calculating the local density of states and the super-Planckian thermal radiation.

Colloquium: Light scattering by particle and hole arrays

This colloquium analyzes the interaction of light with two-dimensional periodic arrays of particles and holes. The enhanced optical transmission observed in the latter and the presence of surface modes in patterned metal surfaces are thoroughly discussed. A review of the most significant discoveries in this area is presented first. A simple tutorial model is then formulated to capture the essential physics involved in these phenomena, while allowing analytical derivations that provide deeper insight. Comparison with more elaborated calculations is offered as well. Finally, hole arrays in plasmon-supporting metals are compared to perforated perfect conductors, thus assessing the role of plasmons in these types of structures through analytical considerations.

Infrared study of the kinetics of oxidation in porous amorphous silicon

Infrared spectroscopy has been applied to the study of the kinetics of oxidation in high-pressure dc-sputtered amorphous silicon. The different spectra obtained during the evolution of the oxidation are processed by factor analysis. Two oxidation mechanisms have been found. Their associated infrared spectra and time evolution can be explained by a model that proposes the existence of a two-level microstructure. The spectra associated with each one of the oxidation mechanisms seems to correspond mainly to SiO2, modified by the presence of surface modes.