Showing papers by "Pietro Ferraro published in 2003"
TL;DR: An approach is proposed for removing the wavefront curvature introduced by the microscope imaging objective in digital holography, which otherwise hinders the phase contrast imaging at reconstruction planes and it is shown that a correction effect can be obtained at all reconstruction planes.
Abstract: An approach is proposed for removing the wave front curvature introduced by the microscope imaging objective in digital holography, which otherwise hinders the phase contrast imaging at reconstruction planes. The unwanted curvature is compensated by evaluating a correcting wave front at the hologram plane with no need for knowledge of the optical parameters, focal length of the imaging lens, or distances in the setup. Most importantly it is shown that a correction effect can be obtained at all reconstruction planes. Three different methods have been applied to evaluate the correction wave front and the methods are discussed in detail. The proposed approach is demonstrated by applying digital holography as a method of coherent microscopy for imaging amplitude and phase contrast of microstructures.
406 citations
TL;DR: A new method for focus tracking during the recording of a sequence of digital holograms while the sample experiences axial displacement is proposed and can be applied as a quasi-real-time procedure.
Abstract: We propose a new method for focus tracking during the recording of a sequence of digital holograms while the sample experiences axial displacement. Corrected reconstruction distances can be automatically calculated, and well-focused amplitude and phase-contrast images can be obtained for each digitized hologram. The method is demonstrated for inspection of microelectromechanical systems subjected to thermal load. The method can be applied as a quasi-real-time procedure.
171 citations
TL;DR: A new method for measuring simultaneously the thickness and the refractive index of a transparent plate is proposed, based on a simple, variable lateral-shear, wavelength-scanning interferometer.
Abstract: A new method for measuring simultaneously the thickness and the refractive index of a transparent plate is proposed. The method is based on a simple, variable lateral-shear, wavelength-scanning interferometer. To achieve highly accurate measurements of both refractive index n and thickness d we use several means to determine these two quantities. We finely tune a distributed-feedback diode laser light source to introduce a phase shift into the detected signal, whereas we make the sample rotate to produce variable lateral shearing. Phase shifting permits precise determination of the optical thickness, nd, whereas refractive index n is obtained from the retrieved phase of the overall interference signal for all incidence angles.
98 citations
TL;DR: In this paper, a Mach-Zehnder interferometer with a pyroelectric type optoelectronic sensor array is used to record digital off-axis Fresnel holograms of an extended object.
71 citations
TL;DR: In this paper, the authors demonstrate fabrication of periodically poled lithium niobate samples by electric field poling, after patterning by interference lithography, and investigate the poling process at an overpoling regime which caused the appearance of submicron dot domains very similar to those induced by backswitch but different in nature.
Abstract: We demonstrate fabrication of periodically poled lithium niobate samples by electric field poling, after patterning by interference lithography. Furthermore we investigate the poling process at an overpoling regime which caused the appearance of submicron dot domains very similar to those induced by backswitch but different in nature. We show the possibility for realizing submicron-scaled threedimensional domain patterns that could be applied to the construction of photonic crystals and in nonlinear optics. We show that high etch-rate applied to such structures allows to obtain pyramidal-like submicron relief structures which in principle could find application for waveguide construction in photonic bandgap devices.
44 citations
TL;DR: In this article, the presence of a plane parallel plate along the path of the object beam, such as a beamsplitter cube, often used in interferometers, affects the actual reconstruction distance.
Abstract: In digital holography, it is necessary to know the distance of the object from the recording charge-coupled device camera to obtain a correct numerical reconstruction process. The presence of a plane parallel plate along the path of the object beam, such as a beamsplitter cube, often used in interferometers, affects the actual reconstruction distance. This effect, to our knowledge, has never been discussed in the literature despite the fact that it adds a contribution that cannot be ignored in the reconstruction process. We evaluate the effect for a spherical object wavefront as well as in the case of an extended object.
24 citations
TL;DR: An electro-optic device applied as an optical beam deflector and switch at different wavelengths has been built and tested and its operation has been visualized by an imaging camera for the first time.
Abstract: An electro-optic device applied as an optical beam deflector and switch at different wavelengths has been built and tested. The electro-optic device is based on domain-engineered lithium niobate (LiNbO3). In this paper, for the first time, its operation has been visualized by an imaging camera. The device has been characterized both at the visible wavelength (632.8 nm) and at a typical telecom wavelength (1532 nm). Furthermore, the device has been tested as an amplitude modulator in the mid-infrared region as well, at a wavelength of ~4.3 microm, where no Pockels cells are available. A detailed description of this device is given, and the experimental results are discussed.
23 citations
TL;DR: In this paper, a two-beam shearing interferometric technique for testing refractive conical lenses is described, which requires two mutually coherent plane wave fronts transmitted through the conical lens under test.
22 citations
24 Mar 2003
TL;DR: In this article, the use of digital holography (DH) as a metrological tool for inspection and characterization of MEMS structures was proposed, which can be efficiently employed to assess the fabrication process of micro structures as well as to test their behaviour in operative conditions.
Abstract: We propose the use of digital holography (DH) as a metrological tool for inspection and characterization of MEMS structures. We show that DH can be efficiently employed to assess the fabrication process of micro structures as well as to test their behaviour in operative conditions. DH allows reconstructing both the amplitude and phase of microscopic objects and, compared to traditional microscopy, it provides quantitative phase determination. We demonstrate that DH allows determination of full field deformation maps that can be compared with analytical and/or numerical models of the deformed microstructure. Application of DH on structures with several different geometries and shapes, like cantilever beams, bridges and membranes is reported and result will be discussed. Dimensions of the inspected microstructures ranging from 1 to 50µm. Examples of application are presented were DH allows determination with high accuracy out of plane deformations due to the residual stress introduced by the fabrication process. An optical set-up for recording digital holograms based on a Mach-Zehnder interferometer was adopted and a laser source which wavelength is =532 nm was employed. The light reflected by the object under investigation was made to interfere with a plane wave front. Holograms were recorded by a CCD array with 1024 x 1280 square pixels with 6.7 µm size. A mirror mounted on a piezo-actuator was inserted along the reference arm of the interferometric in order to introduce controlled phase steps and to employ phase shifting technique. This technique allows suppressing both the zeroth-order and the conjugate wave-front in the numerical holographic reconstruction process. A method for compensating numerically curvature of the wave front and introduced by the microscopic objective lens is proposed and discussed. Keywords: Digital Holography, Interferometry, MEMS characterization.
21 citations
03 Apr 2003
TL;DR: In this article, the authors report on the application of Digital Holography as metrological tool for the inspection and characterization of the domain structures in bulk Lithium Niobate samples.
Abstract: Ferroelectric domain micro structuring of bulk Lithium Niobate is very useful for optoelectronic applications such as non-linear optics employing Quasi-Phase-Matching for efficient harmonic and parametric conversion processes or for the fabrication route for production of novel MEMS devices, like micro-cantilever beams. Quasi-Phase-Matching based applications require periodically reversed ferroelectric structures with periods of the order of micrometers. Precise control of the surface quality and of the domain structure of the micro structured materials is required such as in the case of optical MEMS applications. We here report on the application of Digital Holography as metrological tool for the inspection and characterization of the domain structures in bulk Lithium Niobate samples. This technique allows reconstructing both the intensity and the phase of the microstructures under test and it allows determining quantitatively the phase distribution. Several examples of application of the Digital Holography technique for the numerical reconstruction of the micro-topography of domain structure are presented and discussed.
8 citations
28 May 2003
TL;DR: In this article, an interferometric analysis of a 0.5mm-thick lithium niobate crystal sample was performed using a reflective grating interferometer and a digital holographic technique.
Abstract: We report an interferometric analysis of 0.5mm thick lithium niobate crystal sample by making use of a reflective grating interferometer and a digital holographic technique. The lithium niobate wafer was subjected to electric field poling in order to obtain two antiparallel ferroelectric domains. The crystal was then mounted into one arm of the interferometer in order to study the phase map and consequently to evaluate the effects of domain reversion at the boundary. Engineering of periodically reversed domains in LN is extensively used for quasi-phase-matching applications while the ferroelectric structure investigated here is suitable for producing electro-optically controlled deflector or switch devices via total internal reflection at the domain interface. The above mentioned applications require deep knowledge of how the domain reversal process affects the optical properties of the ferroelectric crystals.
18 Nov 2003
TL;DR: In this paper, the authors investigate the domain structure obtained on overpoled both sides polished z-cut Lithium Niobate crystal sample by applying an electric field on periodic liquid electrodes.
Abstract: We investigate the domain structure obtained on overpoled both sides polished z-cut Lithium Niobate crystal sample by applying an electric field on periodic liquid electrodes. Lithium Niobate sample was spatially patterned with photoresist by use of interference photolithographic process. The sample was then etched in a mixture of hydrofluoric and nitric acid to reveal the reversed domains. The different etch rate of the two opposite z faces of the crystal domains allowed to measure the surface profile of the sample by using a profilometer. Overpoling the crystal caused the appearance of high density and submicrometer spacing single dot domains vertically aligned along the direction of the interference fringes in the patterned region. ( Summary only available )
01 Jul 2003
TL;DR: In this article, a new interferometric technique for measuring the ordinary and extraordinary refractive indices of uniaxial crystals was proposed based on the measurement of the rotation-dependent phase changes of the optical path length in crystal plates.
Abstract: We report a new interferometric technique for measuring the ordinary and extraordinary refractive indices of uniaxial crystals. The technique is based on the measurement of the rotation-dependent phase changes of the optical path length in crystal plates. Accurate measurement of the phase shift as a function of the rotation of the sample is achieved by using a fast-Fourier-transform based fringe analysis method for phase retrieval. The principle of the method is discussed and measurements of the ordinary and extraordinary refractive indices of a lithium niobate crystal are reported.
TL;DR: It is shown that accurate determination of the nonlinear refractive index can be obtained by analyzing the two-dimensional phase distribution of the modulated ring pattern and by comparison with the theoretical ring-pattern intensity distribution.
Abstract: We describe an infrared interferometric technique based on a two-dimensional spatial fringe analysis Fourier method for investigating the characteristic ring diffraction pattern generated by the self-phase-modulation effect induced in nematic liquid crystals (NLCs) by an infrared laser beam and for measuring the nonlinear refractive index of the NLCs. The experimental setup employs a Mach-Zehnder interferometer with a cw CO2 laser emitting at 10.6 µm and a pyroelectric optoelectronic sensor matrix to detect the modulated ring-pattern intensity distribution formed in the far field by a nematic E7 sample. A Fourier-transform-based analysis of the interference fringe pattern allows comparison of the measurements with the theoretical ring-pattern intensity distribution. We show that accurate determination of the nonlinear refractive index can be obtained by analyzing the two-dimensional phase distribution of the modulated ring pattern.
07 Apr 2003
TL;DR: In this article, a beam deflection technique that exploits electric-field controlled deflection and total internal reflection at the interface between two anti-parallel domains realized in a single crystal lithium niobate wafer is presented.
Abstract: We report a beam deflection technique that exploits electric-field controlled deflection and total internal reflection at the interface between two anti-parallel domains realized in a single crystal lithium niobate wafer. The LiNbO 3 z-cut sample was 500-µm-thick and was photolithographically patterned and poled by means of an applied electric field, in order to realize two adjacent regions of opposite domain orientation. The boundary between these domains should be very regular and free from residual stress, but in practice, a small residual index difference exists at the interface. An electric filed E z applied across the interface region, produces equal in magnitude, but opposite in sign, refractive index variations between the adjacent anti-parallel domains. For sufficiently large index variation, and for grazing incidence geometry, that is when the incidence angle is between 87° and 89°, we obtain a high efficient beam deflection. Furthermore, if the incidence angle approaches the limit angle, which is about 89°, the Total Internal Reflection (TIR) occurs, producing an abrupt beam switch from transmission to reflection, characterized with a theoretical 100% switching contrast. However, the residual interface stress generates significant Fresnel reflection from this interface at high grazing angles, limiting the switching contrast ratio achievable at 20 dB. We present data obtained for wavelengths of 632.8 nm and 4.5 m; at the latter wavelength we demonstrated the possibility to perform amplitude modulation faster than mechanical chopping, in a spectral region where no Pockels cells are available Keywords: Total internal reflection, Switching, Scanning, Electro-optic effect, Lithium niobate
27 May 2003
TL;DR: In this paper, a digital holography method was used as a metrological tool for inspection and characterization of MEMS structures, and the efficiency of the digital holographic method was demonstrated measuring out-of-plane deformations due to the intrinsic residual stress.
Abstract: We investigate digital holography method as metrological tool for inspection and characterization of MEMS structures. The efficiency of the digital holography is demonstrated measuring out of plane deformations due to the intrinsic residual stress. Microstructures under investigation are of two different types: the first are made of a single polysilicon layer, whereas the second are bimorph structures with a thin silicon nitride layer over the polysilicon one. These structures exhibit an out-of-plane deformation owing to residual stresses between the different layers. The characterization of these deformations is instrumental to study and understand the effect of residual stress on the deformation of the single microstructures. To this aim digital holography has been applied as metrological tool in order to obtain the profile of the microstructures. These data are employed in analytical and numerical model to evaluate residual stress inside the investigated structures. Moreover, digital holography has been employed to evaluate MEMS behavior when subjected to thermal load. Profile of cantilevers, with dimensions from 1 to 50 μm, has been measured.
03 Apr 2003
TL;DR: In this paper, one and two dimensional periodic ferroelectric domain structures obtained by an electric-field poling process applied to 500μm thick Lithium Niobate crystal samples patterned by means of interference lithography were realized using a Michelson interferometric set-up and a He-Cd laser.
Abstract: We realized one and two dimensional periodic ferroelectric domain structures obtained by an electric-field poling process applied to 500μm thick Lithium Niobate crystal samples patterned by means of interference lithography. The fringe pattern is realized using a Michelson interferometric set-up and a He-Cd laser. We report on the appearance of high density and micrometer-sized single dot domains aligned along the direction of the interference fringes, as consequence of overpoling procedures. These structures are similar to those induced by back-switching. The effect seems to be originating by inverted domains’ merging under the photoresist fringe pattern after spreading. We investigate the possibility to obtain a highly regular and homogeneous dot-structure which can find application for photonic crystals technology and nonlinear optics.
18 Nov 2003
TL;DR: In this article, a simple lateral shearing interferometer is proposed for measuring refractive index of thin parallel plate silicon sample, where the rotating sample works as lateral shear element and the recorded interferometric signal is Fourier transform analyzed and the phase change is determined as a function of the rotating angle.
Abstract: A simple lateral shearing interferometer is proposed for measuring refractive index of thin parallel plate silicon sample. The rotating sample works as lateral shearing element. As the sample rotates a continuous lateral shearing is obtained owing to the change of the optical path difference (OPD) between the transmitted beam and that first reflected by the surface sample. The recorded interferometric signal is Fourier-transform analyzed and the phase change is determined as a function of the rotating angle. If the thickness of the silicon sample is known the method provides accurate measurement of the refractive index. ( Summary only available )
01 Jul 2003
TL;DR: In this paper, a longwavelength Mach-Zehnder interferometer for digital off-axis Fresnel holography with a pyroelectric detector array was used to record digital holograms of an extended object.
Abstract: We describe a long-wavelength Mach-Zehnder interferometer for digital off-axis Fresnel holography with a pyro-electric detector array used to record digital holograms of an extended object at 10.6 μm. We show that, although the spatial resolution of the pyro-electric detector array is much less than that of typical CCD cameras working in the visible region, good reconstruction of the amplitude and phase of the object wavefield can be obtained. The principle of Fresnel reconstruction in digital holography is described and results of reconstruction process for object size of the order of 700 μm are presented and discussed.