Antonello Cutolo

Silicon electro-optic modulator based on a three terminal device integrated in a low-loss single-mode SOI waveguide

We analyze, from a theoretical point of view, a novel silicon optical amplitude-phase modulator integrated into a SOI (silicon on insulator) optical waveguide and based on a three terminal electronic structure which gives rise to definite advantages in comparison with a classical p-i-n diode based modulator. The proposed device utilizes the free carrier dispersion effect to produce the desired refractive index and absorption coefficient variations. The MEDICI two-dimensional (2-D) semiconductor device simulator has been used to analyze the electrical operation, with reference to the free carrier concentration injected into the optical channel, its uniformity and the required current density and electrical power. The optical investigation was carried out by means of FDM (finite difference method), EIM (effective index method), and BPM (beam propagation method) tools, giving rise to a complete evaluation of the properties of our device. We report the results for both the amplitude and phase modulators, paying attention to the static and the dynamic behavior. In particular, an amplitude modulation of 20%, with an injection power of about 126 mW, and a switching time of 5.6 ns can be achieved theoretically, Furthermore, as a phase modulator, the device exhibits a very high figure of merit, predicting an induced phase shift per volt per millimeter of about 215/spl deg/, for a injection power of about 43 mW, and a switching time shorter than 3.5 ns.

AN ELECTRICALLY CONTROLLED BRAGG REFLECTOR INTEGRATED IN A RIB SILICON ON INSULATOR WAVEGUIDE

In this letter, we present a novel structure for light amplitude modulation based on a lateral p-i-n diode combined with a Bragg reflector which transforms the phase shift induced by the plasma dispersion effect in the intrinsic region of the diode into a voltage controlled variation of the reflectivity of the Bragg mirror. Numerical simulations show a modulation depth of 50% achieved in about 12 ns with a power dissipation of 4.0 mW and an insertion loss of 1.0 dB. The device is demonstrated to be very attractive in terms of power dissipation as compared to a Mach–Zehnder interferometer occupying the same area on chip.

An optoelectronic sensor for cure monitoring in thermoset-based composites

In this paper, we present the design and the experimental results of an optoelectronic fiber optic sensor able to monitor the polymerization reactions of thermoset polymer-matrix composite processing. These kinds of materials are now widely used in large industrial areas: aeronautical, aerospace, automotive and civil due to their low cost/low weight features. Unfortunately, their final properties are strongly dependent on the processing stage. In order to ensure the setting of correct processing parameters (i.e. temperature and pressure), it is crucial to monitor, during the reaction, the process variables such as degree of cure (DOC) and viscosity. In this work, we point out our attention upon the use of a fiber optic sensor, which can be embedded into the composite component, to monitor the cross-linking formation, occurring during the curing process. Based on the Fresnel refraction principles, the proposed sensor scheme is sensitive to refractive index variation. Experimental results are shown on sensor capability to monitor the cure kinetics, and a novel calibration method is proposed in order to link the optoelectronic response directly to the DOC of the reacting resin.

New possibilities for efficient silicon integrated electro-optical modulators

Abstract A new class of silicon electro-optical modulators for λ = 1.3 and 1.55 μm is proposed and analyzed. The devices, based on single- and multi-pass Fabry-Perot interferometry, can be built by standard microelectronic tecniques.

Analysis of feasibility on the use of fiber Bragg grating sensors as ultrasound detectors

The spectral response changing of a Fiber Bragg grating due to the interactions with an ultrasound wave have been numerically analyzed by a transfer matrix approach has been used, taking into account the geometrical and elasto-optic effects. Numerical analysis show that its possible to characterize the ultrasound wave, only if the ratio between the ultrasonic wavelength and the length of the used grating exceeds an established value, which depends on both the characteristics of the Bragg grating and the ultrasound amplitude itself.

An optical technique to measure the bulk lifetime and the surface recombination velocity in silicon samples based on a laser diode probe system

Abstract A high sensitivity, pump–probe optical method to measure the bulk minority-carrier lifetime and surface recombination velocity in silicon is proposed. A pig-tailed 1.55xa0μm CW laser diode is used to detect the transient of the excess carriers generated by a short Nd:YAG laser pulse. The probe beam is launched parallel to the sample surface while the pump beam uniformly illuminates the sample perpendicular to its surface. Separation between bulk lifetime and surface recombination velocity is achieved by performing the measurement on samples of different thickness. Experimental results indicate that separation of bulk and surface contribution is feasible in a wide range of surface recombination velocities thus making this method suitable to investigate the effects of surface passivation techniques.

Effect of fabrication errors in channel waveguide Bragg gratings

The spectral performances of nonideal rectangular Bragg gratings, integrated in a rib waveguide, are analyzed by a multilayer approach based on the effective-index method. The effects of errors on the photolithographic definition of the grating, that is, period and shape, and of errors on the control of etching depth are investigated. Also the influence of the stitching error, which is unavoidable when the grating is realized by means of electron-beam photolithography, is addressed. A novel analytical approach that extends coupled-mode theory to the analysis of real gratings is also presented.

Analytical and experimental analysis of the undulator radiation at finite distance as a function of the e-beam parameters

SummaryThe radiation emitted by the linear undulator installed on a straight section of the ADONE storage ring is studied both experimentally and theoretically. In particular, expressions are provided for the field at finite distance, based on the complex Fresnel integral. In addition, several expressions are derived for the average intensity pattern as a function of the electron beam divergence and energy spread. These formulae are used for analysing the spectral and angular patterns of the radiation measured from a distance of 20 m from the undulator origin. The excellent quality of the undulator and the negligible influence on the pattern of the electron beam divergence are confirmed by the satisfactory agreement of the measured radiation field with the computer-generated one.RiassuntoSi espone lo studio sperimentale e teorico della radiazione emessa dall’ondulatore lineare, installato su una sezione dritta dell’anello di accumulazione ADONE. In particolare, si illustra la possibilità di esprimere il campo a distanza finita utilizzando l’integrale complesso di Fresnel. Sono inoltre presentate varie espressioni dell’intensità media in funzione della divergenza angolare del fascio e della differenza di energia fra gli elettroni. Queste formula sono utilizzate per analizzare il profilo spettrale ed angolare della radiazione, misurata ad una distanza di 20 m dell’ondulatore. Leccellente qualità dell’ondulatore e l’influenza trascurabile che la divergenza del fascio ha sull’andamento dei parametri della radiazione sono confermate dal soddisfacente accordo fra le misure e le curve previste teoricamente.РезюмеТеоретически и экспериментально исследуется излучение, возникающее в линейном ондуляторе, помещенном в прямой секции накопительного кольца ADONE. В частности, выводятся выражения для поля на конечном расстоянии, на основе комплексного интеграла Френеля. Выводятся некоторые выражения для средней интенсивности в зависимости от расходимости электронного пучка и разброса энергии. Полугенные формулы используются для анализа спектральных и угловых характеристик излучения, измеренных на расстоянии 20 м от ондулятора. Высокое качество ондулятора и пренебрежимо малое влияние расходимости электронного пучка подтверждается удовлетворитебьным согласием измеренного поля излучения, полученного с помощью комьютера.

Optoelectronic technique for the characterization of high concentration gas–solid suspension

We describe a simple technique for measuring high (up to 0.16) time-averaged solids volumetric concentration in a two-phase flow. The technique is based on a properly modified version of the forward scattering of laser light. It is useful in a variety of practical configurations, and, in particular, it is instrumental in the diagnostics of particle flow in the free board of bubbling fluidized beds and in the circulating fluidized beds. A fallout of this work is the measurement of the extinction coefficient of the solid material tested.

Integrated fiber optic sensing system for in-situ characterization of the curing process of thermoset-based composites

In the last decade, in light of their superior mechanical properties advanced polymer matrix composites have been indicated as the most suitable candidates as Smart Materials and Structures. However, their final properties are strongly dependent on the processing stage and key points to improve the quality and the reliability of these materials that have been identified in the cure monitoring and the optimization of the manufacturing process. Based on this line of argument, an integrated fiber optic sensing system for simultaneous refractive index and temperature measurements has been designed and developed in order to monitor the curing process of thermoset based composites. A fiber optic refractometer has been designed by using the free end of the sensing optical fiber. A theoretical model has been developed for converting refractive index changes in detailed information on the extent of the curing. Its validation has been proved by comparison with calorimetric characterization. In addition, integrated fiber Bragg gratings has been used for local temperature measurements. The interrogation of the sensing Bragg grating has been implemented by using a different fiber Bragg grating able to convert the resonance wavelength shift in intensity changes. Preliminary results are presented.