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Beam self-imaging in nonlinear graded-index multimode optical fibers is of interest for many applications, such as implementing a fast saturable absorber mechanism in fiber lasers via multimode interference. We obtain a new exact solution for the nonlinear evolution of first and second order moments of a laser beam of arbitrary transverse shape carried by a graded-index multimode fiber. We have experimentally directly visualized the longitudinal evolution of beam self-imaging by means of femtosecond laser pulse propagation in both the anomalous and the normal dispersion regime of a standard telecom graded-index multimode optical fiber. Light scattering out of the fiber core via visible photo-luminescence emission permits us to directly measure the self-imaging period and the beam dynamics. Spatial shift and splitting of the self-imaging process under the action of self-focusing are also revealed. Funding Agencies|European Research Council (740355); Agence Nationale de la Recherche (ANR-18-CE080016-01); CILAS Company (ArianeGroup); Vetenskapsrådet (2017-05309); Russian Ministry of Science and Education (14.Y26.31.0017)

We study nonlinear self-imaging dynamics in graded-index multimode optical fibers. Side-scattering of light that accompanies the propagation of intense femtosecond pulses permits us to directly measure the self-imaging period.

Progress in MEMS Technology continuously stimulates new developments in the mechanical structure of micro systems, such as, for example, the new concept so-called CSFH (Conjugate Surfaces Flexural Hinge), which makes it possible, simultaneously, to minimize the internal stresses and to increase motion range and robustness. Such hinge may be actuated by means of a rotary comb-drive, provided that a proper set of simulations and tests are capable to assess its feasibility. In this paper, a CSFH has been analyzed with both theoretical and Finite Element (FEM) methods, in order to obtain the relation between voltage and generated torque. The FEM model, realized with an APDL code (ANSYS Parametric Design Language), considers also the fringe effect on the comb drive finger. Electromechanical couple field analysis is performed by means of both Direct and Load Transfer Methods. Experimental tests have been also performed on a CSFH embedded in a MEMS prototype, which has been fabricated starting from a SOI wafer and using D-RIE(Deep Reactive Ion Etching). Results showed that CSFH performs better than linear fexure hinges in terms of larger rotations and less stress for given applied voltage.

Although a certain amount of work has been presented in literature which concerns micro and nano tribology, few contributions have been dedicated to the development of experimental set up for friction assessment in MEMS. The present paper offers a contribution which attempts to fill this gap: the proposal of a new concept design of a micro-tribometer for testing silicon-silicon sliding in MEMS devices, particularly in those obtained via D-RIE process. Since the general contact conditions at the macro scale are very different from those which characterize MEMS, the proposed tribometer is very different from the classic pin-on-disk or block-on-ring. For this reason, a dedicated MEMS has been built, whose only purpose is recreating silicon-silicon sliding under prescribed loads and, then, assessing friction and wear. Since most of MEMS have planar relative motion, the tribometer presented in this article is able study only planar relative motions, and so it has been essentially based on a the creation of a pair of conjugate profiles, whose relative motion has been obtained by using Finite Element Analysis (FEA) simulations, rather than by the classical centrodes theory.Copyright © 2014 by ASME

A new selective processing technique based on a confined dynamic liquid drop\meniscus is presented. This approach is represented by the localized wet treatment of silicon wafers using dynamic liquid drop that while is in contact with the wafer forms a dynamic liquid meniscus. The main scientific innovation and relevance introduced by this work have been applied to industrial solar cell production and on silicon wafer metal bumps formation for the IC interconnection (i.e. copper pillars). Such new technique allows to touch in specific defined positions the silicon wafer in order to perform any kind of wet processing (e.g. etching, cleaning and/or plating) without the need of any protective resist. To investigate on pendant dynamic liquid drops and dynamic liquid meniscus use of computational fluid dynamic technique (i.e. numerical techniques to accurately predict fluid flows) was followed and is presented. An experimental setup has been built to validate the calculations. Numerical results showed a good agreement with experimental ones. Prototypes heads, using stereo-lithography systems, were developed and localized selective plating without the need of lithography step was performed on silicon.

In this work it is described an high-density contacting technology that can replace wire bonding in power electronic applications, to overcome known limitation of bond wires liftoff occurring after several power cycles due to the difference in the coefficient of thermal expansion of silicon and aluminum. In the presented technology, MEMS (micro-electro-mechanics systems) micro-fabrication processes are used to realize contact structures that, pressed against the silicon dice, provide a reliable compliant contact. One advantage of this technology is that the contacts can be hosted on a printed circuit board that integrates the control circuitry for the power devices. This will reduce the footprint of power systems, like Integrated High Power Modules (IHPM). Reduced footprints are beneficial in applications where space is a concern, like the automotive industry. The description of the technological steps for building the contacting assembly is reported together with process conditions and electrical performances of two test structures.

A novel topology for a micromachined acoustic speaker suitable for cellular phones is proposed in this paper. The membrane is composed of two materials, each of them with different function: a silicon moving part acting as a rigid piston, and polymer annulus acting only as suspension. The high ratio between Young moduli and masses of membrane and suspension leads to a simpler design of the mass-spring-damper system. This new topology can be obtained thanks to a new micromachining technology, that leads to an higher adhesion between polymer and silicon. Simulations presenting the main micro-loudspeaker parameters (e.g. SPL, frequency response) are presented in details as also the principal technological steps.

The electrochemotherapy is an effective treatment that requires the application of an intense electric field to the tumoral tissue to open the cellular membrane and deliver drugs. This work will present the results of the ongoing research project, showing a new technology and design geometry that allows to realize flexible electrodes able to wrap biological tissues bringing the necessary electric field intensity for the electroporation of cells to reach a unique penetration depth to the centimeter range. The flexible electrode is realized by conversion of porous silicon into nano-porous metals (copper and/or gold) filled by a biocompatible thermoplastic polymer.

In this work we present a composite nanostructure based on PS-Cu and obtained by a corrosive deposition of Cu from an aqueous solution containing copper ions. PS samples of different porosities ranging from 15% to 75% were immersed in a 0.025 M CuSO4-5H(2)O + 0.005 M HF solution for different times. Scanning electron microscopy analysis was carried out to study the structural form of the PS-Cu nano-composite samples. It was clearly observed that Cu was deposited into and onto PS as nanosized granular film. Characteristic of Cu distribution, structural features of Cu film and factors that influence Cu film structure are described. It is shown that variation of PS porosity and corrosive deposition time provides formation of new composite PS-Cu structures. (C) 2007 Elsevier Ltd. All rights reserved.

Microrobots are used nowadays in several fields of application, specially in mini invasive surgery. However, they are rather difficult to be constructed, and the traditional micro machining tools are not adequate yet to built the smaller parts. The construction of the microrobots is even harder if more than one D.O.F. are required for the mechanism, because these systems are more complicated. This paper deals with the development of a 3 D.O.F. planar micro platform with remote system of actuation. The new approach of design and manufacturing is based on two innovative solutions: a) the adoption of the technologies used to built MEMS, Micro Electro Mechanical Systems; b) the introduction of new flexural hinge to develop compliant micro mechanisms. The new concept of flexural hinge is described in the paper, also from a theoretical point of view. Several example of possible structures are proposed and analyzed, together with their remote wire actuation systems. Finite Element Analysis (FEA) has been also adopted to analyze the system performance under small deformations. The principle of fabrication is, then, described. The process consists of a sequence of single steps which have allowed to achieved an overall maximum size down to 3–4 mm and the minimum thickness of the smaller components down to 50µm.