Modulation instability in waveguides doped with anisotropic nanoparticles

Formation of Au, Pt, and bimetallic Au-Pt nanostructures from thermal dewetting of single-layer or bilayer thin films

Formation of Au, Pt, and bimetallic Au-Pt nanostructures by thermal dewetting of single-layer Au, Pt and bilayer Au-Pt thin films on Si substrates was systematically studied. The solid-state dewetting of both single-layer and bilayer metallic films was shown to go through heterogeneous void initiation followed by void growth via capillary agglomeration. For the single-layer of Au and Pt films, the void growth started at a temperature right above the Hüttig temperature, at which the atoms at the surface or at defects become mobile. Uniformly distributed Au (7 ± 1 nm to 33 ± 8 nm) and Pt (7 ± 1 nm) NPs with monodispersed size distributions were produced from complete dewetting achieved for thinner 1.7-5.5 nm thick Au and 1.4 nm thick Pt films, respectively. The NP size is strongly dependent on the initial thin film thickness, but less so on temperature and time. Thermal dewetting of Au-Pt bilayer films resulted in partial dewetting only, forming isolated nano-islands or large particles, regardless of sputtering order and total thin film thickness. The increased resistance to thermal dewetting shown in the Au-Pt bilayer films as compared to the individual Au or Pt layer is a reflection of the stabilizing effect that occurs upon adding Pt to Au in the bimetallic system. Energy dispersive x-ray spectroscopic analysis showed that the two metals in the bilayer films broke up together instead of dewetting individually. According to the x-ray diffraction analysis, the produced Au-Pt nanostructures are phase-segregated, consisting of an Au-rich phase and a Pt-rich phase.

A generic model for the study of supercontinuum generation in graphene-covered nanowires

We study supercontinuum (SC) generation in graphene-covered nanowires based on a generic model that correctly accounts for the evolution of the photon number under Kerr and two-photon absorption processes, and the influence of graphene is treated within the framework of saturable photoexcited-carrier refraction. We discuss the role of the various effects on the generation of SC by a thorough analysis of short-pulse propagation in two different kinds of graphene-covered nanowires, one made of silicon nitride and the other made of silicon. Finally, we discuss the effect of stacking graphene layers as a means to enhance SC generation with pulse powers compatible with those in integrated optical devices.

Role of frequency dependence of the nonlinearity on a soliton's evolution in photonic crystal fibers

We reveal the crucial role played by the frequency dependence of the nonlinear parameter on the evolution of femtosecond solitons inside photonic crystal fibers (PCFs). We show that the conventional approach based on the self-steepening effect is not appropriate when such fibers have two zero-dispersion wavelengths, and several higher-order nonlinear terms must be included for realistic modeling of the nonlinear phenomena in PCFs. These terms affect not only the Raman-induced wavelength shift of a soliton but also impact its shedding of dispersive radiation.