Agostino Giorgio

Very fast and accurate modeling of multilayer waveguiding photonic bandgap structures

A model of one-dimensional (1-D) waveguiding photonic bandgap (PBG) structures, based on leaky mode propagation (LMP) method, is proposed for the first time. A complete analysis of the propagation characteristics, including the determination of modal propagation constants, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, total forward and backward power flow in the structure, guided and radiated power, and total losses, has been carried out for a finite extension configuration. The numerical results have been compared with those obtained by using other methods, showing a very good agreement together with some significant advantages in terms of very low computational time, absence of any a priori theoretical assumptions and approximations, capability of simulating the actual behavior of the device as a reflector, and fast determination of the bandgap position.

Modeling of fully etched waveguiding photonic bandgap structures

Modeling of a 1-D finite-height, finite-length fully etched waveguiding photonic bandgap structures, based on the leaky mode propagation method, is proposed for the first time. So far only infinitely long gratings have been modeled by this approach. Finite extension structures having deep grooves, high refractive index contrast, and an arbitrary profile of the etched region can be modeled in very short computer time, starting from the infinitely-long photonic bandgap structure. Useful analytical and closed-form expressions for the reflection and transmission coefficients and out-of-plane losses are derived, which are valid for any operating conditions. One of the most important applications of the model relevant to 1-D photonic bandgap devices is to determine the losses occurring also in 2-D devices. Comparisons of results in terms of transmittance, losses, bandgap position and complex propagation constant with those obtained by the bi-directional mode expansion and propagation method and an exact vectorial method show an excellent agreement together with a strongly reduced CPU time for our method. Full investigations of three different etching profiles (i.e., rectangular, triangular and saw-tooth) are carried out. Particular attention is paid to the physical behavior around the first and second Bragg interaction regions. We demonstrate that the rectangular shape exhibits the highest losses and the widest bandgap, while the saw-tooth grating exhibits the lowest losses and the narrowest bandgap. Quick and accurate determination of the out-of-plane losses in a large variety of photonic bandgap devices is also demonstrated.

An analytical method for the thermal layout optimisation of multilayer structure solid-state devices

Abstract In this paper an analytical method for the electrothermal solution to the non-linear 3-D heat flow equation for multilayer structure electronic devices is proposed. Compared with previous models presented in literature, it is general and can be easily applied to a large variety of integrated devices, provided that their structure can be represented as an arbitrary number of superimposed layers with a 2-D embedded thermal source, so as to include the effect of the package. The proposed method is independent of the specific physical properties of the layers, hence GaAs MESFETs and HEMTs as well as silicon and silicon-on-insulator MOSFETs and heterostructure LASERs can be analysed. Moreover, it takes into account the dependence of the thermal conductivity of all the layers on the temperature; the heat equation is solved coupled with the device current–voltage relation in order to give physical consistence to the experimental evidence that a temperature increase causes a degradation of the electrical performances and that the electrical power is not uniformly distributed.

Optimized electrothermal design of integrated devices through the solution to the non-linear 3-D heat flow equation

In this paper, an optimized electrothermal design of integrated devices through the solution to the non-linear 3-D heat equation is presented. The thermal solution has been achieved by the Kirchhoff transform and the 2-D Fourier transform. The electrothermal feedback has been implemented by calculating the device current at the actual channel temperature. A multiple layer structure approximating the effect of the package has been considered as spatial domain in which the heat equation has been solved.

Multiple defect characterization in finite-size waveguiding photonic bandgap structures

A powerful and efficient model recently proposed by the authors based on the leaky mode propagation method is used to characterize photonic bandgap structures incorporating multiple defects, having arbitrary shape and geometrical parameter values. The importance of the defect-mode characterization in photonic bandgap materials is due to the intensive use of defects for light localization to design very promising optical devices. This paper provides a new, efficient method to model defects in waveguiding, finite-size photonic bandgap devices and analytical and closed-form expressions for the reflection and transmission coefficients and out-of-plane losses,which is very useful and easily implemented under any operating conditions. Moreover, the method has been applied to examine the capabilities of waveguiding photonic bandgap devices in dense wavelength division multiplexing filtering applications. Therefore, the design of two optical filters for such applications has been carried out and optimal design rules have been drawn using the new model.

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.

Design of guided-wave photonic bandgap devices by using the Bloch-Floquet theory

The design of some 1-D waveguiding photonic bandgap (PBG) devices has been carried out by utilizing a model based on the Bloch-Floquet theorem. A complete analysis of the propagation characteristics, including the modal propagation constants, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, total forward and backward power flow in the structure, guided and radiated power, and total losses, enable the optimization of the design in very short CPU time.

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.

DC thermal modelling of GaAs MESFETs based on a semiempirical approach

In this paper a new semiempirical large signal thermal model of GaAs MESFETs is proposed for DC characterization. The model includes a third order dependence of fitting parameters on bias conditions and three thermal fitting parameters. A number of GaAs MESFETs, each very different from a geometrical and technological point of view, have been characterized as a function of temperature and modelled with high accuracy. The CPU extraction time results are moderate in any example. Results have been compared with the Rodriguez–Tellez model, showing improvements in accuracy of better than 30%. The model can be successfully used in MMIC CAD applications.

Electrothermal model of multilayer structure for the design of GaAs integrated circuit devices

In this paper a mathematical model for the solution of the non-linear 3-D heat equation for GaAs MESFETs is presented. The electrothermal feedback has been implemented by calculating the FET drain current at the actual channel temperature. The thermal solution has been achieved by the Kirchhoff transformation, which accounts for the temperature-dependent thermal conductivity, and the 2-D Fourier transform method.