Pietro Ferraro

Bio: Pietro Ferraro is an academic researcher from National Research Council. The author has contributed to research in topics: Digital holography & Holography. The author has an hindex of 61, co-authored 653 publications receiving 12666 citations. Previous affiliations of Pietro Ferraro include Aeritalia & Centre national de la recherche scientifique.

An interferometric demodulation method for visualizing and determining quasi-static strain by FBG sensors

Abstract: In this paper, we propose an interferometric approach for visualizing and measuring the quasi-static strain experienced by fibre Bragg grating sensors. The method makes use of a simple bi-polished silicon sample acting like an etalon tuneable filter. The Bragg wavelength shift can be evaluated by analysing the overall interferometric signal achieved by tuning the etalon tuneable filter angularly. A fast Fourier transform method is applied for phase retrieval. The choice of the silicon sample is determined by the low-cost and well-developed silicon technology and fabrication, the easy design and tuneability of the spectral response, and the possibility of integrating on the same sample also the circuitry for electronic control. The principle of operation of this method is described and results obtained by employing such a configuration are reported.

Visual and Quantitative Characterization of Ferroelectric Crystals and Related Domain Engineering Processes by Interferometric Techniques

Abstract: Nonlinear crystals are, nowadays, key devices to build coherent sources emitting radiation from the UV to the IR spectral range. Applications of nonlinear optics are primarily based on frequency conversion, through harmonic generation or sum and difference frequency mixing. These nonlinear frequency conversion techniques make possible coherent light sources in spectral regions where laser sources are limited, or do not exist. Light sources based on nonlinear crystals, like optical parametric oscillators as well as harmonic and difference frequency generators, are finding increasing application in high sensitivity spectroscopy.

Sparsity promoting automatic focusing in digital holography

Abstract: Sparsity properties of digital holograms have been investigated for application in compressive holography, permitting the discovery of the sparsest reconstruction plane in which the recovery of digital holograms is suitable. Recent approaches for denoising and phase retrieval are also proposed exploiting the sparsity properties of digital holograms. Thus it can be shown a strong correlation between holograms sparsity and focal plane detection, making a sparsity measure coefficient as a candidate to be used for focus plane calculation. Here we implement different sparsity metrics, that are able to measure a degree of sparsity of reconstructed digital hologram and we investigate their relation with the automatic focusing criterions, highlighting the possibility to use a sparsity measure as refocusing metric as well as the contrary, i.e. using image contrast coefficients as sparsity measures. Our analysis will be reported for digital holograms recorded in both lensless and microscope configuration and for both amplitude and pure-phase objects.

A one-shot denoising method in Digital Holography based on numerical multi-look and 3D block matching filtering

Abstract: We introduce a novel method to totally suppress noise artifacts in Digital Holography (DH) with single-shot recording. This is based on concepts of numerical multi-look, non-local processing and 3D Block Matching filtering (BM3D).

Direct fabrication of polymer micro-lens array

Abstract: In order to break the rigidity of classic lithographic techniques, a flexible pyro-electric-electrohydrodynamic (EHD) inkjet printing is presented. In particular, here is showed a method able to manipulate highly viscous polymers, usable for optical integrated devices. The system proposed reaches spatial resolution up to the nano-scale and can print, for instance, nano-particles and high viscous polymer solutions. This technique allows writing patterns directly onto a substrate of interest in 2D or in 3D configuration and is studied in order to overcome limitations in terms of type of materials, geometry and thickness of the substrate. In the present work, we show the potential of pyro-EHD printing in fields as optics and micro-fluidics. A micro-channel chip is functionalized with a PDMS-made micro-lenses array, directly printed on the chip. The geometric properties and the quality of the lenses are evaluated by a Digital Holography (DH) analysis.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fiber grating sensors

Abstract: We review the recent developments in the area of optical fiber grating sensors, including quasi-distributed strain sensing using Bragg gratings, systems based on chirped gratings, intragrating sensing concepts, long period-based grating sensors, fiber grating laser-based systems, and interferometric sensor systems based on grating reflectors.