Roberto Diana

A Semiempirical SPICE Model for n-Type Conventional CNTFETs

We present a compact, semiempirical model of carbon nanotube field effect transistor easily implementable in simulation SPICE software to design analog and digital circuits. The model is based on analytical approximations and parameters extracted from quantum mechanical simulations, having compared the results with those of the numerical model online available and of experimental data.

Optical fiber Bragg gratings. Part I. Modeling of infinitely long gratings

We present an accurate numerical method based on the Floquet-Bloch formalism to analyze the propagation properties and the radiation loss in infinitely long uniform fiber Bragg gratings. The model allows us to find all the propagation characteristics including the propagation constants, the space harmonics and the total field distribution, the guided and radiated power, and the modal loss induced by the periodic structure. The influence of the geometrical and physical parameters on the performance of the Bragg gratings has been established. A clear explanation of the physical phenomena related to the index modulation amplitude changes is presented, including the photonic bandgap effect, which is not easily described by the finite-difference time-domain method and cannot be described by the widely used coupled-mode theory.

Optical fiber Bragg gratings. Part II. Modeling of finite-length gratings and grating arrays

A model of both uniform finite-length optical fiber Bragg gratings and grating arrays is presented. The model is based on the Floquet-Bloch formalism and allows rigorous investigation of all the physical aspects in either single- or multiple-periodic structures realized on the core of a monomodal fiber. Analytical expressions of reflectivity and transmittivity for both single gratings and grating arrays are derived. The influence of the grating length and the index modulation amplitude on the reflected and transmitted optical power for both sinusoidal and rectangular profiles is evaluated. Good agreement between our method and the well-known coupled-mode theory (CMT) approach has been observed for both single gratings and grating arrays only in the case of weak index perturbation. Significant discrepancies exist there in cases of strong index contrast because of the increasing approximation of the CMT approach. The effects of intragrating phase shift are also shown and discussed.

Novel integrated optical beam former for phased-array antennas

We present the theoretical investigation, including design criteria, of a new optical beam former for phased-array active antennas. The device is formed by a Z-cut LiNbO3 channel- planar composite waveguide, an array of interferometric modulators and a linear microlens array. The basic element of the new architecture is the array of Mach-Zehnder Ti:liNbO3 intensity modulators having asymmetric coplanar-strip traveling-wave electrodes in which a relatively thick SiO2 buffer layer is utilized to reduce the phase velocity mismatch between the microwaves and optical waves. A comparison with other optical and electronic architectures already proposed shows a number of significant advantages. In particular, our device can be used in multichannel optical computing systems as well as in optical communication and RF signal processing systems allowing to overcome severe frequency limitations typical of devices reported in literature since it can work at frequencies greater than 30 GHz. So the very large transmission rate typical of the optical fiber communication systems may be conveniently exploited.

A method to design DWDM filters on photonic crystals

A new very promising technology for dense wavelength division multiplexing (DWDM) systems seems to be the photonic crystals with forbidden bandgap (photonic band-gap, PBG). In this paper, we propose a method for the design of DWDM filters on PBG, based on a new model developed by the authors and already described.

Guided-wave photonic bandgap filters for space applications

In this paper a detailed analysis and design of guided-wave 2D photonic bandgap filters are presented by using the Floquet-Bloch approach. Significant performance has been obtained in one and three cavity PBG structures.

Optimal design of waveguiding periodic structures

The design of some 1D waveguiding photonic bandgap (PBG) devices and Fiber Bragg Gratings (FBG) for microstrain based sensing applications has been carried out by a model based on the Bloch-Floquet theorem. A lwo loss, very narrow passband GaAs PBG filter for the operating wavelength λ = 1.55 μm, having an air bridge configuration, was designed and simulated. Moreover, a resonant Si on glass PBG device has been designed to obtain the resonance condition at λ= 1.55 μm. Finally, a FBG-based microstrain sensor design has been carried out, having an array of 32 FBG. A complete analysis of the propagation characteristics, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, guided and raidated power, and total losses, enabled the optimization of the design in a very short CPU time.

Recent advances in guided-wave devices for optical signal processing

A great research effort has been spent in recent years for the use of guided-wave optoelectronic technologies for signal processing in space applications, because they allow to reduce size, weight, power consumption and system complexity with respect to electronic ones. Based on these motivations, we have conceived, designed and simulated a number of original integrated optical signal processors, such as 2D correlators for imaging reconstruction in SAR applications, both airborne and spaceborne, preprocessors for data classification and identification in satellite applications for remote sensing, beam formers and steerers in active phased array antennas, heterodyne spectrum analyzers, and so on. The substrate materials considered for these circuits are both ferroelectric and III-V semiconductor materials. Original modeling and numerical techniques have been developed to analyze and design the guided-wave components included in the optical architectures. In this paper, the most significant developments of this research activity are reviewed.

Optimization of Microwave PBG-based Hadron Accelerator with Square Cell

We present a theoretical investigation devoted to the optimization of a Photonic Band-Gap (PBG) based hadron accelerator having a square lattice. The approach, based on the rigorous Floquet-Bloch theory, allows to analyze without approximations the propagation of a wave inside a two- dimensional periodic structure. Our simulations have been performed to evaluate the geometrical parameters able to improving the features of the resonator in terms of bandgap width and field confinement. Photonic band diagram and leakage factor have been shown for the structure under investigation.

Design of a wireless digital measurement system for the blood arterial pressure control

A system to measure the blood arterial pressure is designed and presented. The device has been designed by using the very promising oscillometric method, which does not suffer from the limitations of the well-known auscultatory method. The device makes use of a microcontroller and a Sallen-Key active filter, and allows the evaluation of the systolic and diastolic pressure values. The system, which allows also the transmission of the collected data to a remote computer, has been designed, realized and tested.