Andrea Irace

Temperature optical sensor based on a silicon bimodal Y branch

A novel temperature optical sensor configuration, based on mode mixing principle, is theoretically discussed. The sensing element consists of a single-mode all-silicon waveguide, followed by a two-modes section, which acts as sensing region, and an output Y branch to separate the two output channels. The fundamental mode coming from input waveguide excites both the fundamental mode and the first higher order mode in the sensing region. The interference between the two propagating modes in the sensing region produces a periodically repeated optical intensity distribution along the propagation axis. It is possible to observe a light steering from one output channel to the other caused by the temperature change of the structure itself. This fact is related to the variation of the material refractive index with the temperature, that is the thermo-optic effect, which implies a variation of the mode effective refractive indices, and, consequently, a phase shift between the modes themselves. In this way, a continuous variation of the power distribution on the two output waveguides as a function of the temperature can be observed. A simultaneous acquisition of both output signals, followed by a simple elaboration, allows obtaining a temperature evaluation independent on light source instability. Moreover, it is possible to design the device in order to obtain the desired initial output power distribution on two channels. This permits to design sensors characterized by greater accuracy, if we use the linear part of the optical transfer function, or larger measure range, if we utilize the whole output excursion.

Silicon-based optoelectronic filters based on a Bragg grating and P-i-N diode for DWDM optical networks

In this paper we propose an electrically controlled filter for the selection of channels in monitoring DWDM optical network. The highly selective filtering operation needed in this kind of communication systems is obtained with an all silicon device by combining the eletrical injection of free carriers in a forward biased P-i-N diode with a Bragg grating realized over the top of a Silicon on Insulator RIB waveguide. The combination of this fast electron device and the interference principle present under the periodic corrugation of the waveguide allows very fast reconfiguration of the filter. In order to increase filter performaces in terms of selectivity and crosstalk between adjacent channels, apodization of the duty-cycle of the grating is investigated; in this way the performances of the filter in terms of spectral bandwidth for 100 GHz and 50 GHz DWDM spacing become attractive and comparable to ITU specifications.

A calibration method based on look-up-table for cryogenic temperature fiber Bragg grating sensors

A calibration method for fiber Bragg grating (FBG) cryogenic temperature sensors based on look-up-table was proposed and demonstrated experimentally. The operating principles of different kind of FBG cryogenic temperature sensors are introduced. A statistical characterization of the data was carried out to verify the quasi-static condition of the measurement system by checking the stability of the measurement. Once verified this condition, the sensitivity curves of the sensors were determined by correlating the wavelength shift of the FBGs with the reference sensor measurements. On the basis of the sensitivity curves, the look-up-table (LUT) have been determined. The experimental data shows that the LUT fitting approach provides good and reliable performance in terms of accuracy and processing time.

Smart sensors and active adaptive control exploitation for vibration damping of a cantilever beam

In this work we present the first experimental results of a new multidisciplinary activity concerning active structural control. Specifically, exploiting Fiber Bragg Grating (FBG) sensors and Piezoelectric actuators, an adaptive control approach was adopted to damp the vibrations of a cantilever beam. The strain sensor used for the structural vibration detection is a Bragg Grating written on a single-mode optical fiber for telecom applications. The reading technique used to detect the variations in the &lgr;B of the grating due to the local strain variations, exploits a narrow band laser tuned to the mean wavelength of the grating reflectance spectrum roll-off, as it will be better explained in the following. The results obtained so far demonstrate how the combined application of novel strain sensors and a clever control approach can provide a benefit in terms of bandwidth, damping speed and reduced design effort.

Development of an electro-optic step-by-step sampling system for IC's close electro-magnetic field measurement

In this work we aim to realize a step-by-step electro-optical probe which exploits the linear (Pockels) electro-optic effect to survey the electromagnetic field on the surface of RF integrated circuits. This probe measures the variation of light polarization induced by a lithium niobate crystal immersed in the electric field provided by the DUT. The measurements will demonstrate the main features of this system which can be summarized in non-invasiveness, wide bandwidth, linearity and small spatial resolution. The LiNbO3 crystals have been developed by SELEX Sistemi Integrati S.p.A. Roma, and the whole research activity has been carried out under the sponsorship of the CRdC Nuove Tecnologie per le Attivita Produttive, the Campania Region Centre of Competence on New Technologies.

Experimental tests of a new multiplexing technique for fibre optical Bragg sensors array

In our previous papers we have introduced the Chirped-Pulsed Frequency Modulation technique (C-PFM); it has been used to allow the multiplexing capability of a multipoint Fiber Bragg Grating (FBG) sensor network. In this paper we report some preliminary experimental results, which confirm the theoretical analyses previously obtained. The innovative multiplexing approach, without to increase the complexity of the acquisition system, is able to address up to 10 independent sensing points on a single fiber. The C-PFM technique is based on the amplitude modulation of the emitted signal (pulsed) from the laser source by a chirped frequency signal and on the demodulation of the reflected signal by means of an adaptive filter (that is only a numerical elaboration). The experimental result are here shown and commented in order to define limitations and capabilities of the approach.

An ultrafast optical modulator based on SiGe HBT

In this paper a novel configuration of optical modulator is presented. It combines the effect of fast electron-hole plasma injection obtained with a SiGe HBT together with the usage of a distributed Bragg reflector. Numerical simulations performed on a non-optimized device shows that the presence of the SiGe HBT enhances significantly the performances obtained with a similar device realized with and all-silicon pin diode. Switching speed higher than 1 GHZ have been numerically simulated.

Experimental results of a three-terminal optical modulator based on a BMFET device

Optical switches and modulators are essential components in integrated optics applications. In this paper, we propose a three terminal optical amplitude modulator embedded in a silicon-on-silicon rib waveguide and we show new experimental results performed on a quasi optimized structure. The optimization of the optoelectronic behavior of the device is possible, by using both the two-dimensional electrical (2-D) semiconductor simulation package MEDICI and optical simulation codes.

Separation of bulk lifetime and surface recombination velocity by multi-wavelength technique

In this paper a contactless, all-optical and non-destructive technique for simultaneous measurement of minority carrier recombination lifetime and surface recombination velocity is presented. The principle is based upon measurement, at low injection level, of the free carrier optical absorption transient probed by an infrared beam following electron-hole pair excitation by a pulsed laser beam working at several wavelengths. Being contactless and non-destructive with respect to the surface to be analyzed, the method is appealing for routine lifetime characterization.

Infrared thermal imaging of SiNx membranes

In this paper we present preliminary experimental results of static thermal mapping for the characterization of thermal properties of single or multilayer thin film membranes. Based on direct radiometric measurement, the proposed system is able to acquire, with high spatial (less than 10 micrometers ) and quite good temperature (less than 0.1 degree(s)C) resolution, the temperature maps. The results, reported here, confirm its capability. We tested a low stress LPCVD SiN membrane heated by means of a LPCVD polysilicon (PS) resistor. The experimental results obtained are in qualitative agreement with theoretical previsions.