Francesco G. Della Corte

Effect of a Lung Protective Strategy for Organ Donors on Eligibility and Availability of Lungs for Transplantation A Randomized Controlled Trial

CONTEXT Many potential donor lungs deteriorate between the time of brain death and evaluation for transplantation suitability, possibly because of the ventilatory strategy used after brain death. OBJECTIVE To test whether a lung protective strategy increases the number of lungs available for transplantation. DESIGN, SETTING, AND PATIENTS Multicenter randomized controlled trial of patients with beating hearts who were potential organ donors conducted at 12 European intensive care units from September 2004 to May 2009 in the Protective Ventilatory Strategy in Potential Lung Donors Study. Interventions Potential donors were randomized to the conventional ventilatory strategy (with tidal volumes of 10-12 mL/kg of predicted body weight, positive end-expiratory pressure [PEEP] of 3-5 cm H(2)O, apnea tests performed by disconnecting the ventilator, and open circuit for airway suction) or the protective ventilatory strategy (with tidal volumes of 6-8 mL/kg of predicted body weight, PEEP of 8-10 cm H(2)O, apnea tests performed by using continuous positive airway pressure, and closed circuit for airway suction). MAIN OUTCOME MEASURES The number of organ donors meeting eligibility criteria for harvesting, number of lungs harvested, and 6-month survival of lung transplant recipients. RESULTS The trial was stopped after enrolling 118 patients (59 in the conventional ventilatory strategy and 59 in the protective ventilatory strategy) because of termination of funding. The number of patients who met lung donor eligibility criteria after the 6-hour observation period was 32 (54%) in the conventional strategy vs 56 (95%) in the protective strategy (difference of 41% [95% confidence interval {CI}, 26.5% to 54.8%]; P <.001). The number of patients in whom lungs were harvested was 16 (27%) in the conventional strategy vs 32 (54%) in the protective strategy (difference of 27% [95% CI, 10.0% to 44.5%]; P = .004). Six-month survival rates did not differ between recipients who received lungs from donors ventilated with the conventional strategy compared with the protective strategy (11/16 [69%] vs 24/32 [75%], respectively; difference of 6% [95% CI, -22% to 32%]). CONCLUSION Use of a lung protective strategy in potential organ donors with brain death increased the number of eligible and harvested lungs compared with a conventional strategy. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00260676.

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.

Temperature dependence analysis of the thermo-optic effect in silicon by single and double oscillator models

The thermo-optic coefficient (dn/dT) of crystalline silicon has been critically analyzed in the temperature range 300–600 K, at the fiber optic communication wavelength of 1.5 μm. The temperature dependence has been attributed to the variation of the interband transition energies at some critical points of the silicon band structure. The experimental data have been fitted using single and double oscillator models. In particular, the double oscillator model, which is physically correlated to the silicon band structure, has been exploited to extrapolate the temperature dependence of the interband transition energies at some points (critical points) of the combined density of states. The extracted parameters are in good agreement with the data reported in the literature. Finally, in connection with both of the oscillator approximations, an analysis based on thermodynamic considerations is carried out, and electron–hole formation entropy and specific heat are calculated. The consistency of the obtained result...

Electro-optically induced absorption in α-Si:H/α-SiCN waveguiding multistacks

Electro optical absorption in hydrogenated amorphous silicon (α-Si:H) - amorphous silicon carbonitride (α-SiCxNy) multilayers have been studied in two different planar multistacks waveguides. The waveguides were realized by plasma enhanced chemical vapour deposition (PECVD), a technology compatible with the standard microelectronic processes. Light absorption is induced at λ=1.55 µm through the application of an electric field which induces free carrier accumulation across the multiple insulator/ semiconductor device structure. The experimental performances have been compared to those obtained through calculations using combined two-dimensional (2-D) optical and electrical simulations.

Study of the thermo-optic effect in hydrogenated amorphous silicon and hydrogenated amorphous silicon carbide between 300 and 500 K at 1.55 μm

The thermo-optic coefficients of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon carbide (a-SiC:H)—two of the main amorphous semiconductors in optoelectronics—have been measured and critically analyzed in the practical device operation temperature range 300–500 K, at the communication wavelength of 1.55 μm. The experimental data have been fitted using a single-oscillator model that takes into account the shape of the e2 spectrum of the amorphous materials. In particular, for a-Si:H, the extracted parameters significantly extend, and are consistent with, the few data reported in the literature; an interesting analogy with crystalline silicon is also found and discussed. Complete results for a-SiC:H are finally reported.

Thermo-optic effect exploitation in silicon microstructures

The strong thermo-optic effect in silicon has been exploited for the fabrication of new sensing and communication devices. A temperature sensor, an electromagnetic energy sensor and an optical modulator are in particular presented. These devices, all working on interferometric principles, have been realized by means of the silicon standard microelectronic technologies, and are therefore suitable for full integration with on-chip circuitry. New thermo-optical materials are finally proposed with superior characteriztics, which still maintain the compatibility with VLSI technology.

Use of Amorphous Silicon for Active Photonic Devices

Silicon photonics is a new emerging and disruptive technology aimed at using cost-effective silicon-based materials for the generation, control, and detection of modulated light signals for optical communication. Hydrogenated amorphous silicon (a-Si:H) is a particularly promising platform for enabling the desired matching between electronics and on-chip photonics. Thin a-Si:H layers can be in fact deposited using the CMOS-compatible low-temperature plasma-enhanced chemical vapor deposition technique, with no impact at all on the microelectronic layers. This paper provides an overview of the progress and the state of the art of a-Si:H-based active photonic devices, focusing, in particular, on the low technological complexity required for an easy integration within a single photonic microchip. This paper consists of three main sections, in each of which the exploitable optoelectronic effects present in a-Si:H are presented. A comparison between some experimental a-Si:H and crystalline-Si photonic components available in the literature is presented.

Electro-optical modulation at 1550 nm in an as-deposited hydrogenated amorphous silicon p-i-n waveguiding device.

Hydrogenated amorphous silicon (a-Si:H) has been already considered for the objective of passive optical elements, like waveguides and ring resonators, within photonic integrated circuits at λ = 1.55 μm. However the study of its electro-optical properties is still at an early stage, therefore this semiconductor in practice is not considered for light modulation as yet. We demonstrated, for the first time, effective electro-optical modulation in a reverse biased a-Si:H p-i-n waveguiding structure. In particular, phase modulation was studied in a waveguide integrated Fabry-Perot resonator in which the V(π)⋅L(π) product was determined to be 63 V⋅cm. Characteristic switch-on and switch-off times of 14 ns were measured. The device employed a wider gap amorphous silicon carbide 
(a-SiC:H) film for the lower cladding layer instead of silicon oxide. In this way the highest temperature involved in the fabrication process was 170°C, which ensured the desired technological compatibility with CMOS processes.

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.

A 2.5 ns switching time Mach­Zehnder modulator in as-deposited a-Si:H

A very simple and fast Mach-Zehnder electro-optic modulator based on a p-i-n configuration, operating at λ = 1.55 μm, has been fabricated at 170 °C using the low cost technology of hydrogenated amorphous silicon (a-Si:H). In spite of the device simplicity, refractive index modulation was achieved through the free carrier dispersion effect resulting in characteristic rise and fall times of ~2.5 ns. By reverse biasing the p-i-n device, the voltage-length product was estimated to be V(π)∙L(π) = 40 V∙cm both from static and dynamic measurements. Such bandwidth performance in as-deposited a-Si:H demonstrates the potential of this material for the fabrication of fast active photonic devices integrated on standard microelectronic substrates.