Showing papers by "Giuseppe Coppola 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: It is indicated that polyploidy affects a large percentage of IVP porcine embryos capable of developing to blastocysts and the incidence of chromosomal abnormalities is much higher than that reported previously in in vivo embryos in this species.
55 citations
TL;DR: In this article, a Si-based light modulator working at the standard communication wavelength of 1.5 /spl mu/m has been described, which consists of a threeterminal bipolar mode field effect transistor integrated with a silicon rib waveguide on epitaxial Si wafers.
Abstract: We have fabricated and characterized a novel Si-based light modulator working at the standard communication wavelength of 1.5 /spl mu/m. It consists of a three-terminal bipolar mode field effect transistor integrated with a silicon rib waveguide on epitaxial Si wafers. The modulator optical channel is embodied within its vertical electrical channel. Light modulation is achieved moving a plasma of carriers inside and outside the optical channel by properly biasing the control electrode. The carriers produce an increase of the Si absorption coefficient. The devices have been fabricated using clean-room processing. Detailed electrical characterization and device simulations confirm that strong conductivity modulation and plasma formation in the channel are achieved. The plasma distribution in the device under different bias conditions has been directly derived from emission microscopy analyses. The device performances in terms of modulation depth will be presented.
45 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, the performance of an electro-optical router, working at a wavelength of 1.55µm and based on multimode interference effects together with the electrooptic effect of smectic A liquid crystal, is theoretically and numerically discussed.
Abstract: In this paper, for the first time, the performance of an electro-optical router, working at a wavelength of 1.55µm and based on multimode interference effects together with the electro-optic effect of smectic A liquid crystal, is theoretically and numerically discussed. The device comprises: a single-mode input optical channel waveguide, a bimodal active region with a liquid crystal over-layer, and an output Y-branch to separate the two output channels. The active region is designed to allow a π shift between the two modes that it supports, by means of the electro-optic effect of smectic A, in order to steer light from one output channel to the other. The principal advantages of such a device include a fast tuning speed, low power consumption, low cost and small device size.
23 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
18 Nov 2003
TL;DR: In this article, an optoelectronic router integrated in a sol-gel waveguide with a liquid crystal over-layer, working at the wavelength of 1.55 μm, is theoretically discussed.
Abstract: An optoelectronic router integrated in a sol-gel waveguide with a liquid crystal over-layer, working at the wavelength of 1.55 μm, is theoretically discussed. Mode-mixing principle and electro-optic effect of a smectic A * liquid crystal have been employed to reach the optical shift between two output waveguides. The device is composed by: a single mode input optical channel waveguide; a bimodal active region, having a liquid crystal as over-layer; an output Y branch. The active region is designed to allow a π shift between the two supported modes, by means of electro-optic effect of smectic A*. By doing so it is possible to steer light from one output channel to the other one of output Y.
9 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
11 Mar 2003
TL;DR: In this article, a method for measuring simultaneously, thickness and refractive index of transparent plates is proposed, which is based on a very simple lateral variable shear wavelength scanning interferometer.
Abstract: In this paper a new method for measuring simultaneously, thickness and refractive index of transparent plates is proposed. The method is based on a very simple lateral variable shear wavelength scanning interferometer. The transparent plate is made to rotate at controlled and constant angular speed. Radiation from a laser diode propagates though the sample and experiences an even number of reflections at the sample-air interfaces. The emerging wave fronts are laterally sheared with a shear depending from the actual angle of incidence. Varying the emission wavelength of the laser source a variation of the phase of interference signal is obtained. In this way, interferometric signals as function of incidence angle for each laser wavelength λ were obtained. Evaluating phase variations in correspondence of normal incidence, by a simple non-linear fit, it is possible to determine the optical thickness n.d. Then, retrieving the phase of the overall interference signal for all available incidence angles and employing the previously evaluated optical thickness, the refractive index value can be determined. Finally, geometrical thickness d was obtained straightforwardly as end result. The effectiveness and straightforwardness of the method has been demonstrated for a silicon sample and also for a z-cut Lithium Niobate sample.
TL;DR: In this paper, the authors describe two different kind of optoelectronic devices based on a three terminals active device and exploit the plasma dispersion effect to achieve the desired working.
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.
Patent•
18 Jul 2003
TL;DR: In this paper, the authors employed an interferometer as a shear interferometers with the advantage of varying the wavelength of the luminous source to obtain the index of refraction and the thickness of transparent materials.
Abstract: Interferometric system for the simultaneous measurement of the index of refraction and of the thickness of transparent materials with a single measurement operation. In said system is employed an interferometer as a “shear interferometer” with the advantage of varying the wavelength of the luminous source. The index of refraction and the thickness are determined in two phases. Firstly it is determined the optical path analyzing the displacement of interferometric signal obtained by orthogonal incidence; successively, by means of phase recovery techniques and the previously determined optical path value, it is possible to obtain the index of refraction of the material. From the knowledge of the index and of the optical path it is obtained the material thickness. The system is made up of: a laser source ( 1 ), with variable emission wavelength, a collimator ( 4 ), a sample ( 5 ), a precision rotating base ( 7 ), aphotodiode ( 9 ), an oscilloscope ( 10 ), un bus IEEE- 488 ( 12 ) ed a PC ( 11 ). The invention is pertinent to the technical field of the optics and to the technical field of the characterization of materials and manufacturing of optical instruments.
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 )
14 Apr 2003
TL;DR: In this article, a new method for reading out Bragg wavelength shifts experienced by fiber Bragg gratings is described, which is based on a bi-polished silicon sample acting like a Fabry-Perot filter.
Abstract: In this paper a new method for reading out Bragg wavelength shifts experienced by fiber Bragg gratings is described. The system is based on a bi-polished silicon sample acting like a Fabry-Perot filter. The spectral response of the Silicon Fabry-Perot filter allows to convert the Bragg wavelength shift into a variation of the light intensity, which can be read by a photodiode. The method efficacy is proved monitoring dynamic strain characteristics of a simple structure. So, the vibration mode of an aluminium cantilever has been sensed by means a FBG sensor attached on the surface of the cantilever itself. In proposed demodulation method the sensitivity and accuracy depend on the spectral band width of the filter. The filter can be designed according to the range of the amplitude vibrations, assuring linear response of system, as function of the thickness of the silicon sample. Moreover, thank to great tuning capability of the Silicon Fabry-Perot filter, it is possible to place Bragg grating spectral response on the central portion of the linear region of the FP response.
11 Mar 2003
TL;DR: In this article, a three terminal optical amplitude modulator embedded in a silicon-on-silicon rib waveguide has been proposed and experimental results performed on a quasi optimized structure.
Abstract: Optical switches and modulators are essential components in integrated optics applications. In this paper, we propose a three terminal optical amplitude modulator embedded in a silicon-on-silicon rib waveguide and we show new experimental results performed on a quasi optimized structure. The optimization of the optoelectronic behavior of the device is possible, by using both the two-dimensional electrical (2-D) semiconductor simulation package MEDICI and optical simulation codes.
03 Oct 2003
TL;DR: In this article, a method with automatic focus tracking in Digital Holography is proposed allowing inspection of MEMS, under thermal loading, in real-time, in order to evaluate the deformation induced by the thermal loading.
Abstract: In this paper we study silicon MEMS (Microelectromechanical systems) structures subjected to thermal loading. Digital holography has been investigated as inspection tool to evaluate the deformation induced by the thermal loading. 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, varies in the range 1÷50μm. The experimental results shown that a "bimorph-effect" induces a deformation in MEMS structures. The difficulties encountered in performing the deformation analysis by digital holography in real-time will be afforded and discussed. A method with automatic focus tracking in Digital Holography is proposed allowing inspection of MEMS, under thermal loading, in real-time.