Numerical analysis of optical vortices generation with nanostructured phase masks

We study the theoretical formation of optical vortices using a nanostructured gradient index phase mask. We consider structures composed of spatially distributed thermally matched glass nanorods with high and low refractive indices. Influence of effective refractive profile distribution, refractive index contrast of component glasses and charge value on the quality of generation of vortices are discussed. A trade-off between waveguiding and phase modulation effects for various refractive index contrast is presented and analysed.Qatar National Research Fund (NPRP12S-0205-190047); Fundacja na rzecz Nauki Polskiej (POIR.04.04.00-00-1C74/16)

A Numerical Model of Wet Isotropic Etching of Silicon Molds for Microlenses Fabrication

International audienceA numerical model is proposed to simulate the isotropic wet etching of silicon through an aperture of a mask to produce microlenses molds. The etching process is based on aqueous solutions of HF and HNO3 in the range of concentrations where etching rate depends mostly on mass-transfer effects. In the considered case the etching rate is defined by diffusion of F− ions to the (oxidized) silicon surface. The simulation is built with the finite element method (FEM) coupled with the level set method (LSM). Our model does not assume an infinite reaction rate on the etched surface. We investigate the influence of finite rate of the reaction on the shape of the etched structures. We investigate 2D and axis-symmetric geometrical cases, properly suited for microlenses fabrication applications. The fitting of the model parameters with experimental data is thus presented. A simplified method to simulate chaotic stirring of the etchant mixture is also proposed to study common experimental setups where the etching baker is agitated. The etching of prefabricated silicon structures is analysed in order to add the possibility of more flexible design of the fabricated structures

Low pump power coherent supercontinuum generation in heavy metal oxide solid-core photonic crystal fiber infiltrated with carbon tetrachloride covering 930 – 2500 nm

All-normal dispersion supercontinuum (ANDi SC) generation in a lead-bismuth- gallate glass solid-core photonic crystal fiber (PCF) with cladding air-holes infiltrated with carbon tetrachloride (CCl4) is experimentally investigated and numerically verified. The liquid infiltration results in additional degrees of freedom that are complimentary to conventional dispersion engineering techniques and that allow the design of soft-glass ANDi fibers with an exceptionally flat near-zero dispersion profile. The unique combination of high nonlinearity and low normal dispersion enables the generation of a coherent, low-noise SC covering 0.93–2.5 μm requiring only 12.5 kW of pump peak power delivered by a standard ultrafast erbium-fiber laser with 100 MHz pulse repetition rate (PRR). This is a much lower peak power level than has been previously required for the generation of ANDi SC with bandwidths exceeding one octave in silica- or soft-glass fibers. Our results show that liquid-composite fibers are a promising pathway for scaling the PRR of ANDi SC sources by making the concept accessible to pump lasers with hundreds of megahertz of gigahertz PRR that have limited peak power per pulse but are often required in applications such as high-speed nonlinear imaging, optical communications, or frequency metrology. Furthermore, due to the overlap of the SC with the major gain bands of many rare-earth fiber amplifiers, our source could serve as a coherent seed for low-noise ultrafast lasers operating in the short-wave infrared spectral region