Mario Iodice

A digital holographic microscope for complete characterization of microelectromechanical systems

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.

Temperature dependence of the thermo-optic coefficient of InP, GaAs, and SiC from room temperature to 600 K at the wavelength of 1.5 μm

The thermo-optic coefficient ∂n/∂T has been measured from room temperature to 600 K at the wavelength of 1523 nm in three important semiconductors for fiber-optic device fabrication, namely, InP, GaAs, and 6H–SiC. The adopted technique is very simple and is based on the observation of the periodicity of the signal transmitted, at the desired wavelength, by an etalon made of the material under test, when it experiences a temperature variation. The values of ∂n/∂T measured in InP and GaAs at room temperature are in agreement with previously reported ones, but increase with temperature with a weak quadratic dependence. SiC conversely shows a lower thermo-optic coefficient (2.77×10−5 K−1) at 300 K, which, however, doubles for a 300 K temperature increase.

Near-Infrared Sub-Bandgap All-Silicon Photodetectors: State of the Art and Perspectives

Due to recent breakthroughs, silicon photonics is now the most active discipline within the field of integrated optics and, at the same time, a present reality with commercial products available on the market. Silicon photodiodes are excellent detectors at visible wavelengths, but the development of high-performance photodetectors on silicon CMOS platforms at wavelengths of interest for telecommunications has remained an imperative but unaccomplished task so far. In recent years, however, a number of near-infrared all-silicon photodetectors have been proposed and demonstrated for optical interconnect and power-monitoring applications. In this paper, a review of the state of the art is presented. Devices based on mid-bandgap absorption, surface-state absorption, internal photoemission absorption and two-photon absorption are reported, their working principles elucidated and their performance discussed and compared.

Advance in thermo-optical switches: principles, materials, design, and device structure

All-optical networking can be the sole approach to provide the huge bandwidth required for future networks. The essential elements in such an optical network are optical switches. A number of options have been proposed in order to implement them efficiently. We focus on thermo-optical switches. First, the physical principles of the thermo-optic effect are briefly introduced. A description of the most common technologies used for the fabrication of thermo-optic switches is provided along with the values of thermo-optic coefficient for a number of materials. The main steps useful in order to design thermo-optical switches are also briefly introduced. Finally, a birds-eye view of the main and recent proposals of switches based on the thermo-optic effect is reported and their performances compared.

Cu/p-Si Schottky barrier-based near infrared photodetector integrated with a silicon-on-insulator waveguide

In this letter, a near infrared all-silicon (all-Si) photodetector integrated into a silicon-on-insulator waveguide is demonstrated. The device is based on the internal photoemission effect through a metal/Si Schottky junction placed transversally to the optical field confined into the waveguide. The technological steps utilized to fabricate the device allow an efficiently monolithic integration with complementary metal-oxide semiconductor compatible structures. Preliminary results show a responsivity of 0.08 mA/W at 1550 nm with a reverse bias of 1 V and an efficient behavior both in C and L band. Finally, an estimation of bandwidth for GHz range is deduced.

Fabrication and characterization of a porous silicon based microarray for label-free optical monitoring of biomolecular interactions

We have fabricated a microarray of porous silicon Bragg reflectors on a crystalline silicon substrate using a technological process based on standard photolithography and electrochemical anodization of the silicon. The array density is of 170 elements/cm2 and each element has a diameter of 200 μm. The porous silicon structures have been used as platform to immobilize an amino terminated DNA single strand probe. All fabrication steps have been monitored by spectroscopic reflectometry, optical and electron microscopy, and Fourier transform infrared spectroscopy. A label-free detection method has been employed to investigate the hybridization between micromolar DNA probe and its complementary target. Due to fast and low cost production, good reproducibility, and high quality optical features, this platform could be adopted also for other different microarray applications such as proteomics and medical diagnostics.

A temperature all-silicon micro-sensor based on the thermo-optic effect

A new class of temperature silicon micro-sensors, based on an interferometric optical technique, is presented. The sensing element consists of a planar Fabry-Perot cavity defined on a silicon wafer by highly anisotropic reactive ion etching, and is therefore suitable for full integration with other standard opto- and micro-electronic devices. Preliminary temperature measurements have been performed with the temperature resolutions predicted by the theory. The limit performances, in terms of resolution, speed of operation and energy dissipation of this class of sensors are discussed in detail. In particular, a final temperature resolution of 0.064/spl deg/C is expected for a low loss interferometric cavity, with a settling time of 150 ns and a 0.2% readout error. An energy resolution as low as 30 nJ is also estimated.

All-silicon Fabry-Perot modulator based on the thermo-optic effect.

The operation at 1.5 μm of a silicon Fabry–Perot optical modulator is reported. The electrically driven device, which uses the thermo-optic effect to achieve as much as a 55% intensity modulation depth, has been realized by means of standard silicon microelectronic technology. This demonstrates that this new type of optical modulator can easily be integrated with electronic circuits. An accurate three-dimensional thermal analysis of the device has permitted the setup of a reliable numerical code aimed at the design of optimized integrated versions of it. The simulation outputs therefore predict operation frequencies of hundreds of kilohertz, remarkably superior to those previously reported in thermo-optic-effect-based modulators

Surface plasmon resonance optical cavity enhanced refractive index sensing

We report on a method for surface plasmon resonance (SPR) refractive index sensing based on direct time-domain measurements. An optical resonator is built around an SPR sensor, and its photon lifetime is measured as a function of loss induced by refractive index variations. The method does not rely on any spectroscopic analysis or direct intensity measurement. Time-domain measurements are practically immune to light intensity fluctuations and thus lead to high resolution. A proof of concept experiment is carried out in which a sensor response to liquid samples of different refractive indices is measured. A refractive index resolution of the current system, extrapolated from the reproducibility of cavity-decay time determinations over 133 s, is found to be about 10(-5) RIU. The possibility of long-term averaging suggests that measurements with a resolution better than 10(-7) RIU/√Hz are within reach.

Silicon Fabry-Perot filter for WDM systems channels monitoring

Abstract A simple and low-cost solution for tracking the frequency of WDM channels, based on the thermo-optic tuning of single-cavity Fabry–Perot silicon optical filters, is presented. High finesse and narrow bandwidth are obtained thanks to coating stacks deposited by e-beam evaporation on both facets of a previously thinned and polished silicon wafer. The filter, in a first prototypal version, resolves up to seven 50-GHz-spaced channels, at wavelengths around 1550 nm, with a crosstalk of −10 dB.