Giuseppe Coppola

Bio: Giuseppe Coppola 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 40, co-authored 256 publications receiving 5489 citations. Previous affiliations of Giuseppe Coppola include Seconda Università degli Studi di Napoli & University of Naples Federico II.

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.

Controlling Image Recostruction Process in Digital Holography

Abstract: The reconstruction of digital holograms is a full numeric process. Such peculiarity offers the possibility to control several parameters during the reconstruction process. In this chapter we will describe some recent advancements of Digital Holography and how it is possible to control the numerical reconstruction process by optimizing or regulating different parameters. By controlling the reconstruction process it is possible to overcome some problems arising during the optical tests of materials and devices or to improve the imaging capability of DH for example for color 3D imaging.

Thermo-optical switches

Abstract: In this chapter, we first introduce the physical principles of thermo-optic effect, providing also some basic details on the thermodynamic operation of an integrated optic device. Then, in the third section, we present a wide review of the most common materials utilized for the fabrication of thermo-optical switches, providing for each material an updated literature reporting the value of the thermo-optic coefficient. Finally, in the fourth section, recent proposals of thermo-optic-based switches are reviewed and their performances compared.

Simple interferometric method for measuring severally the refractive index and the thickness of transparent plates

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.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Micrometre-scale silicon electro-optic modulator

Abstract: Metal interconnections are expected to become the limiting factor for the performance of electronic systems as transistors continue to shrink in size. Replacing them by optical interconnections, at different levels ranging from rack-to-rack down to chip-to-chip and intra-chip interconnections, could provide the low power dissipation, low latencies and high bandwidths that are needed. The implementation of optical interconnections relies on the development of micro-optical devices that are integrated with the microelectronics on chips. Recent demonstrations of silicon low-loss waveguides, light emitters, amplifiers and lasers approach this goal, but a small silicon electro-optic modulator with a size small enough for chip-scale integration has not yet been demonstrated. Here we experimentally demonstrate a high-speed electro-optical modulator in compact silicon structures. The modulator is based on a resonant light-confining structure that enhances the sensitivity of light to small changes in refractive index of the silicon and also enables high-speed operation. The modulator is 12 micrometres in diameter, three orders of magnitude smaller than previously demonstrated. Electro-optic modulators are one of the most critical components in optoelectronic integration, and decreasing their size may enable novel chip architectures.

Silicon optical modulators

Abstract: Optical technology is poised to revolutionize short-reach interconnects. The leading candidate technology is silicon photonics, and the workhorse of such an interconnect is the optical modulator. Modulators have been improved dramatically in recent years, with a notable increase in bandwidth from the megahertz to the multigigahertz regime in just over half a decade. However, the demands of optical interconnects are significant, and many questions remain unanswered as to whether silicon can meet the required performance metrics. Minimizing metrics such as the device footprint and energy requirement per bit, while also maximizing bandwidth and modulation depth, is non-trivial. All of this must be achieved within an acceptable thermal tolerance and optical spectral width using CMOS-compatible fabrication processes. This Review discusses the techniques that have been (and will continue to be) used to implement silicon optical modulators, as well as providing an outlook for these devices and the candidate solutions of the future.

A high-speed silicon optical modulator based on a metal–oxide–semiconductor capacitor

Abstract: Silicon has long been the optimal material for electronics, but it is only relatively recently that it has been considered as a material option for photonics1. One of the key limitations for using silicon as a photonic material has been the relatively low speed of silicon optical modulators compared to those fabricated from III–V semiconductor compounds2,3,4,5,6 and/or electro-optic materials such as lithium niobate7,8,9. To date, the fastest silicon-waveguide-based optical modulator that has been demonstrated experimentally has a modulation frequency of only ∼20 MHz (refs 10, 11), although it has been predicted theoretically that a ∼1-GHz modulation frequency might be achievable in some device structures12,13. Here we describe an approach based on a metal–oxide–semiconductor (MOS) capacitor structure embedded in a silicon waveguide that can produce high-speed optical phase modulation: we demonstrate an all-silicon optical modulator with a modulation bandwidth exceeding 1 GHz. As this technology is compatible with conventional complementary MOS (CMOS) processing, monolithic integration of the silicon modulator with advanced electronics on a single silicon substrate becomes possible.