Showing papers by "Giuseppe Coppola published in 2004"

Controlling image size as a function of distance and wavelength in Fresnel-transform reconstruction of digital holograms

Abstract: A method for controlling the size of amplitude and phase images reconstructed from digital holograms by the Fresnel-transform method is proposed and demonstrated. The method can provide a constant reconstruction pixel width in the reconstructed image plane, independent of the recording and reconstruction distance. The proposed method makes it possible to maintain the size of an object for a sequence of digital holograms recorded at different distances and, therefore, to subtract phase maps for an object recorded at different distances. Furthermore, the method solves the problem of superimposition in multiwavelength digital holography for color display and holographic interferometry applications.

A digital holographic microscope for complete characterization of microelectromechanical systems

Abstract: Digital holographic microscopy (DHM) can be described as a non-invasive metrological tool for inspection and characterization of microelectromechanical structures (MEMS). DHM is a quick, non-contact and non-invasive technique that can offer a high resolution in both lateral and vertical directions. It has been employed for the characterization of the undesired out-of-plane deformations due to the residual stresses introduced by technological processes. The characterization of these deformations is helpful in studying and understanding the effect of residual stress on the deformation of a single microstructure. To that end, MEMS with different geometries and shapes, such as cantilever beams, bridges and membranes, have been characterized. Moreover, DHM has been applied efficiently to evaluate variations of the structure profile due to some external effects. As an example, the characterization of a cantilever subjected to a thermal process has been described. The results reported show that DHM is a useful non-invasive method for characterizing and developing reliable MEMS.

Recovering image resolution in reconstructing digital off-axis holograms by Fresnel-transform method

Abstract: The resolution of amplitude and phase reconstruction of images from digital holograms by the Fresnel transformation method is limited by the pixel width in the reconstructed image plane. The reconstruction pixel depends on distance, wavelength, and number of pixels in the hologram. The spatial frequencies, in the reconstructed image, are band limited by the size of the reconstruction pixel. Undersampling can occur, in the image plane, in the reconstructed amplitude and/or wrapped phase maps. Recovery of reconstructed undersampled spatial frequencies, is possible by the fictitious enlargement of the digital hologram. Correct profile reconstruction of a silicon microelectromechanical structure is demonstrated, applying the proposed method.

Sexing river buffalo (Bubalus bubalis L.), sheep (Ovis aries L.), goat (Capra hircus L.), and cattle spermatozoa by double color FISH using bovine (Bos taurus L.) X- and Y-painting probes

Abstract: River buffalo, sheep, and goat spermatozoa were cross-hybridized using double color fluorescence in situ hybridization (FISH) with bovine Xcen- and Y-chromosome painting probes, prepared by DOP-PCR of laser-microdissected-catapulted chromosomes, to investigate the possibility of using bovine probes for sexing sperm of other members of the family Bovidae. Before sperm analysis, the probes were hybridized on metaphase chromosomes of each species, as control. Frozen-thawed spermatozoa of cattle, river buffalo, sheep, and goat were decondensed in suspension with 5 mM DTT. Sperm samples obtained from three individuals of each species were investigated, more than 1,000 spermatozoa were scored in each animal. FISH analysis of more than 12,000 sperm revealed high level of sperm with X- or Y-signals in all of the species investigated, indicating FISH efficiency over 99%. Significant interspecific differences were detected in the frequency of aberrant spermatozoa (aneuploid and diploid) between goat (0.393%) and sheep (0.033%) (P < 0.01), goat and cattle (0.096%) (P < 0.5), as well as between river buffalo (0.224%) and sheep (P < 0.5). There was no significant difference between river buffalo and cattle. The present study demonstrated that it is possible to use bovine X-Y painting probes for sexing and analyzing sperm of other species of the family, thus facilitating future studies on the incidence of chromosome abnormalities in sperm as well as on sex predetermination of embryos for the livestock industry. Mol. Reprod. Dev. 67: 108–115, 2004. © 2004 Wiley-Liss, Inc.

Surface topography of microstructures in lithium niobate by digital holographic microscopy

Abstract: We report here on the application of digital holographic microscopy as a metrological tool for the inspection and the micro-topography reconstruction of different microstructures fabricated in bulk lithium niobate by differential etching of reversed ferroelectric domain patterned crystals. These structures have a range of applications in optical ridge waveguides, alignment structures, V-grooves, micro-tips and micro-cantilever beams and precise control of the surface quality and topography is required. The technique allows us to obtain digitally a high-fidelity surface topography description of the specimen with only one image acquisition allowing us to have relatively simple and compact set-ups able to give quantitative information on object morphology. The advantages of this technique compared to traditional microscopy are discussed.

Talbot self-image effect in digital holography and its application to spectrometry.

Abstract: For the first time to the authors' knowledge, the Talbot effect has been observed and investigated in digital holography. By numerical reconstruction of holograms, the Talbot self-imaging phenomenon is observed by reconstruction of the amplitude of the image at different distances and (or) wavelengths. A simple spectrometer based on Talbot self-imaging in digital holography is proposed and demonstrated.

Controlling images parameters in the reconstruction process of digital holograms

Abstract: Digital holograms recorded with a charge-coupled device array are numerically reconstructed in amplitude and phase through calculation of the Fresnel-Kirchhoff integral. The flexibility offered by the reconstruction process in digital holography allows exploitation of new possibilities of application in microscopy. Through the reconstruction process we will show that it is possible to control image parameters as focus distance, image size, and image resolution. Those explored potentialities open further the novel prospective of application of digital holography in single- and multiwavelengths operation either for display or metrological applications. We demonstrate the concept of controlling parameters in image reconstruction of digital holograms in some real situations for inspecting silicon microelectronic-mechanical systems structures.

Identification of the homologue of the bovine Rob(1;29) in a captive gaur (Bos gaurus).

Abstract: Robertsonian translocations have been well documented in domestic cattle, with the most commonly occurring fusion involving chromosomes 1 and 29. The widespread nature of this translocation is indicative of its ancient origin. The gaur (Bos gaurus) is one of many wild cattle species currently listed as vulnerable or endangered. Due to the small founder stock and 50 years of restricted breeding, the captive herd is showing signs of inbreeding and reduced fertility. Recent cytogenetic analysis of a female gaur at Toronto Zoo found that the individual contained 2n=57 chromosomes instead of the normal 2n=58, with an extra submetacentric and the loss of two acrocentric chromosomes being observed. This study was undertaken to identify the translocation in this individual and to examine the karyotype of immediate family members. Chromosome analysis of fibroblast cell cultures was carried out using GTG-banding, C-banding and FISH (bovine 1 and 29 paints) techniques to characterize the translocation. Results from the GTG-banding and FISH analyses confirm that the two autosomes involved in the translocation are the bovine homologues 1 and 29. A monocentric centromere was observed by C-banding. Chromosome abnormalities have not been detected in other gaur tested to date. This study demonstrates the importance of cytogenetic analysis for the establishment of screening protocols for the assessment of reproductive potential in this and other exotic bovinae.

Thickness measurement of thin transparent plates with a broad-band wavelength scanning interferometer

Abstract: A novel broad-band telecom laser source is used to make a lateral-shear scanning-wavelength interferometer for measuring the thickness of thin plates. We show that the wide tunability range allows us to detect samples down to tens of microns with a relative uncertainty of less than 0.5%. A comparable accuracy in the thickness characterization of double-layer structures is also demonstrated. In turn, the wide tunability range needs the dispersion law of the materials to be taken into account in the model for correct thickness evaluation, although simultaneous measurement of dispersion and thickness are in principle possible with this technique.

Testing silicon MEMS structures subjected to thermal loading by digital holography

Abstract: We have applied digital holography (DH) as interferometric tool for measuring the out of plane deformation of Micro-Electro-Mechanical structures. DH has been adopted as method for determining with high accuracy deformations due to the residual stress introduced by fabrication process evaluating MEMS behavior subjected to thermal load. A thermal characterization of these structures requires to cope two fundamental problems. The first one regards the loss of the focus due to thermal expansion of the MEMS sample support. With an out-of-focus image, a correct reconstruction of the sample image can not be obtained. To overcome the problem an auto-tracking procedure has been adopted. The other problem regards the direct comparison of images reconstructed at two different distances. In fact, in DH the numerical reconstruction image is enlarged or contracted according to the reconstruction distance. To avoid this problem, we have adopted a novel but very simple method for keeping constant the image size by imposing the reconstruction pixel constant through the fictitious enlargement of the number of the pixel of the recorded digital holograms. These procedures have been employed in order to characterize MEMS with different shapes and dimensions. The measured profiles obtained by DH can be employed to evaluate both the residual stress induced during the fabrication processes and its dependence on the temperature.

Thickness measurement of thin transparent plates with a broadband wavelength-scanning interferometer

Abstract: A novel broad-band telecom laser source is used to realize a lateral-shear scanning-wavelength interferometer for measuring the thickness of thin plates. We show that the wide tunability range allows to detect samples down to tens of microns with a relative uncertainty of less than 0.5% and a resolution of about 1 nm. A comparable accuracy in the thickness characterization of double-layer structures is also demonstrated. In turn, the wide tunability range needs the dispersion law of the materials to be taken into account in the model for correct thickness evaluation.

Recent advancements in digital holographic microscopy and its applications

Abstract: Digital holograms recorded with a charge coupled device camera array are numerically reconstructed in amplitude and phase through calculation of the Fresnel-Kirchhoff integral. The flexibility offered by the reconstruction process in digital holography allows exploitation of new possibilities of application in microscopy. Through the reconstruction process we will show that it is possible to control image parameters as focus distance, image size and image resolution. We report on recent developments obtained in the numerical reconstruction process of holograms. Novel prospective of application of digital holography in single and multi-wavelengths operation either for display and metrological applications can be explored by those recent achievements. Examples of applications of digital holographic microscopy for characterizing silicon MEMS structures by adopting new procedures are illustrated and discussed.

Method for modifying spatial resolution in the resolution in the reconstruction of images in digital holography

Abstract: The invention concerns a method Method for the reconstruction of holographic images, the holographic image being detected by an image detection device ( 9 ), the holographic image being transformed in a digitized hologram ( 10 ), the digitized hologram ( 10 ) being comprised of a number V r of elementary pixels, the size of which being equal to the holographic image sampling intervals, and of the V r values ( 51 ) respectively associated to the elementary pixels, the method comprising a first step ( 11,12 ) of processing the digitized hologram array, and a second step ( 13,15,16,17,18 ) of hologram reconstruction in the observation plane starting from the digitized hologram processed in the first step, the method being characterised in that the second step is carried out through discrete Fresnel Transform applied on an array of V e values corresponding to pixels having size equal to that of said elementary pixels, wherein said array of V e values ( 50, 51 ) includes said array of V r values and an integer number p=V e −V r >0 of constant values ( 50 ) equal to OS, said number V e of values being inversely proportional to the desired pixel size to be obtained for the reconstructed image ( 14 ). The invention further concerns the instruments necessary to the execution of the method and the apparatus executing it.

Controlling several image parameters in the digital holographic reconstruction process

Abstract: Recent developments in solid-state image sensors and digital computers have made it possible to directly record holograms by Charge Coupled Device (CCD) camera and numerical reconstruction of the object wave front by computer. Digital holograms recorded with a CCD array are numerically reconstructed in amplitude and phase through calculation of the Fresnel-Kirchhoff integral. Two methods are usually adopted to reconstruct digital holograms called Fresnel Transformation Method (FTM) and the Convolution Method (CM). In FTM, the reconstruction pixel increases with the reconstruction distance so that the size of image, in terms of number of pixels, is reduced for longer distances, limiting the resolution of amplitude and phase reconstruction. In CM, by contrast, the reconstruction pixel does not change, but remains equal to the pixel size of recording array. The CM is more appropriate for reconstruction at small distances whereas the FTM is useful for longer distances according to the paraxial approximation necessary to apply it. The flexibility offered by the reconstruction process in Digital Holography allows exploitation of new possibilities of application in different fields. Through the reconstruction process we will show that it is possible to control image parameters as focus distance, image size and image resolution. Those newly explored potentialities open further novel prospective of application of Digital Holography in single and multi-wavelengths operation either for display and metrological applications. We demonstrate the concept of controlling parameters in image reconstruction of digital holograms in some real situations for inspecting silicon MEMS structures.

MEMS inspection by Digital Holographic

Abstract: We employed Digital Holographic Microscope (DHM) as a useful method for determining, with high accuracy, the MEMS out-of-plane deformations due to the residual stress introduced by fabrication process and to understand the effect of a thermal load on MEMS profile. The measured profiles can be employed for a quantitative estimation of the residual stresses by mean of some analytical and numerical models. Moreover, DHM also allows determination of variation of the profile of the object due to some external dynamic load (e.g. change in temperature, pressure, electrostatic). In this paper, MEMS behavior subjected to thermal load has been evaluated. In particular, the variation of profiles of cantilever beams subjected to a thermal treatment from 23/spl deg/C to 130/spl deg/C has been measured.

A novel interferometric spectrometer obtained by imaging Talbot effect in digital holography

Abstract: We present here the observation of the Talbot effect in digital holography (DH). A self-imaging phenomena is observed by reconstructing the amplitude of the object wavefield by using different distances and different illumination wavelengths. The numerical reconstruction allows to determine the complex field amplitude at different wavelengths while maintaining constant the reconstruction distance. We investigate on the possibility to build a spectrometer based on the Talbot effect. In particular, the spectrometer proposed in this work can cover the whole visible spectrum ranging from 350 nm to 750 nm and, from the FWHM of the spectrograms with a resolution of about 20 nm

Method for modifying spatial resolution in the reconstruction of images in digital holography

Abstract: The invention concerns a method for the reconstruction of holographic images in digital holography, the holographic images being detected and transformed in a digitized hologram by an image detection device, the digitized hologram being made of an array having a number Vr of elementary pixels, the sizes of which being equal to the sampling intervals of the image detection device, the method comprising a first step of processing the digitized hologram array (e.g. zero-order elimination, aberration correction), and a second step of digitally reconstructing the complex object in an observation plane starting from the digitized hologram processed in the first step, the method being characterised in that the second step is carried out through discrete Fresnel Transform applied on an array of Ve pixels having sizes equal to that of said elementary pixels, wherein said array of Ve pixels (50, 51) includes said Vr pixels (51) and an interger number p=Ve-Vr>0 constant values (50). The invention further concerns the instruments necessary to the execution of the method and the apparatus executing it.

An integrated Si-based electro-optical modulator

Abstract: Optical interconnects are, nowadays, considered a promising alternative to electrical ones and monolithic integration in Si is the only choice when high volumes, low fabrication costs and reduced spaces are needed. We fabricated an electro-optic Si-based modulator working at 1.5 um using a Bipolar Mode Field-Effect transistor integrated within a Si rib waveguide. The principle of operation is the light absorption by a plasma of free carrier that can be opportunely moved inside or outside the device optical channel by properly changing the bias. The optical channel of the modulator is embodied within its vertical electrical channel. The devices were fabricated using epitaxial Si wafers and standard clean room processing. The optical characterization in static conditions shows a modulation depth, defined as M=(P Off -P On )/P Off , of ~ 90 %. It was measured at 1.48 um using a laser diode source coupled with the modulator through a silica optical fiber. The dynamic electrical characterization provides an electrical switching time of ≈10 ns. A modulation depth of 72 % is observed at 100kHz electrical modulation frequency.

Digital holographic microscope for thermal characterization of silicon microhotplates for gas sensor

Abstract: Digital Holographic Microscope has been employed to obtain an accurate characterization of a micro-hotplate for gas sensing applications. The fabrication of these sensors needs different materials, with different properties and different technological processes, which involve high temperature treatments. Consequently, the structure is affected by the presence of residual stresses, appearing in form of undesired bowing of the membrane. Moreover, when the temperature of the sensor increases, a further warpage of the structure is observed. DHM allows to evaluate, with high accuracy, deformations due to the residual stress and how these deformations are affected by thermal loads. In particular, profiles of the structure have been evaluated both in quasi-static condition and the profile variation due to the biasing of the heater resistor has been measured.

Interferometric visualization and demodulation method for measuring quasi-static strain in fiber Bragg grating sensors by a simple rotating etalon filter

Abstract: Optical fiber sensors are the ideal system to monitor "smart structures" and on-site/real time stress measurements: they can be in fact easily embedded or attached to the structures under test and are not affected by electro- magnetic noise. In particular a signal from a Fiber Bragg grating sensor (FBG) may be processed such that its information remains immune to optical power fluctuations. Different interrogation methods can be used for reading out Bragg wavelength shifts. In this paper we propose a very simple interferometric method for interrogating FBG sensors, based on bi-polished silicon sample acting like an etalon tuneable filter (ETF). The Bragg wavelength shift can be evaluated by analyzing the spectral response of signal reflected by the FBG sensor and filtered by the ETF that is continuously and rapidly tuned. Tuning was obtained by rotating the ETF. Variation in the strain at the FBG causes a phase shift in the analyzed signal. The overall spectral signal, collected with time, consists in an interferometric figure which finesse and fringe contrast depending on the geometrical sizes and facets reflectivity of the silicon sample. The fringe pattern, expressed by the Airy's formula, depends on the wavelength l of the incident radiation and on the angle of incidence. The phase of fringe pattern can be retrieved by a standard FFT method giving quantitative measurements of the quasi-static strain variation sensed by the FBG. In this way, the method allows a valuable visualization of the time-evolution of the incremental strain applied to the FBG. Principle of functioning of this method is described and first results obtained employing such configuration, are reported.