169,992 research outputs found
Optical modelling of a Si-based DBR laser source using a nanocrystal Si-sensitized Er-doped silica rib waveguide in the C-band
Full text linkThe availability of reliable silicon-based laser sources is at the basis of the integration of photonic and microelectronic devices on a single chip with consequent development of wavelength division multiplexing telecommunication systems. A high efficiency Si-based laser source with good stability at room temperature would encourage and push the large scale of integration of electronic and photonic devices within a single chip.
Several techniques have been proposed for generating light with an internal quantum efficiency some order of magnitude greater than that typical of silicon (10-6) by using either electrical or optical pumping. Among them we mention the improvement of some fabrication process steps, reduction of the channels of non-radiative recombination, quantum confinement, the use of silicon nanocrystals (Si-ncs) incorporated in a silica matrix. This last technique is used in combination with Er3+ doping to generate light emission around 1500 nm in silicon, since Er-doped Si-ncs behave as electron-hole pairs trap, and the presence of Er shifts the emission peak to around 1500 nm. In this paper we have pointed out the optical model of a Si-based DBR laser including a Si-ncs Er-doped SiO2 rib waveguide, working at a wavelength in C-band. In particular, after a brief description of the structural and optical properties of the silicon crystals, we report on the model and design of the Er:Si-nc/SiO2 rib waveguide, of the optical cavity and of the Bragg mirrors. Numerical results are in good agreement with the literature
Laser gyroscope precisely tracks the Earth’s rotation
No full textPrecise measurements of the length of an Earth day are essential for understanding global mass transport phenomena. A ring laser gyroscope provides absolute measurements of variations in the length of the day with a resolution of 5 parts per billion over a 14-day period
Il Bootstrap e le sue applicazioni nella tecnica attuariale delle assicurazioni contro i danni.
No full textin corso di stamp
PCM aided PICs: a Crucial Migration Towards Cutting-Edge Signal Processing
No full textAdvanced signal processing is paramount in different sectors, including wireless communications, neural networks, artificial intelligence, quantum computing, medical diagnosis, internet of things, etc. With its rapid growth, silicon photonic integrated circuit (PIC) based signal processors are established to be a strong competitor to their electronic counterparts, owing to various advantages like small footprint, low energy consumption, immunity to electromagnetic interference, high speed operation, CMOS compatibility, etc. However, traditional means of realizing programmability, such as thermo-optic and carrier dispersion often suffer from large footprints due to small modulation in refractive index. Further, the volatile nature of such a programming mechanism requires a continuous power supply. In this context, a new generation of low-loss, large index contrast, non-volatile phase change materials (PCMs) are showing great promise towards upscaling the silicon photonic signal processing units. Here, a compact resonator cavity-based signal processing unit is proposed through advantageous integration of a hybrid plasmonic mode in the silicon photonic domain and low-loss PCM. Excellent switching performance with extinction ratio > 30 dB and low energy consumption of 7.6 nJ, highlighting its promise towards different sectors such as telecommunications, neural networks, etc
The photoisomerization mechanism of azobenzene: a semiclassical simulation of nonadiabatic dynamics
No full textWe have simulated the photoisomerization dynamics of azobenzene, taking into account internal conversion and geometrical relaxation processes, by means of a semiclassical surface hopping approach. Both n->pi* and p->pi* excitations and both cis-trans and trans-cis conversions have been considered. We show that in all cases the torsion around the N=N double bond is the preferred mechanism. The quantum yields measured are correctly reproduced and the observed differences are explained as a result of the competition between the inertia of the torsional motion and the premature deactivation of the excited state. Recent time-resolved spectroscopic experiments are interpreted in the light of the simulated dynamics
Hybrid optical resonator for nanostructured virus detection and sizing
No full textWe investigate a method for the detection of influenza A virus in order to reduce the risks associated with its toxicity. Our work is based on the analysis of the optical properties of a whispering gallery mode microresonator interacting with a spherical nanoparticle modeling the virion. The microresonator shows a Q-factor quite high, of the order of 6104. Higher is the Q-factor, higher is the perturbation that the light propagating inside the resonator experiences when interacting with a scattering center, i.e. a nanoparticle. Thus, from the transmission spectrum of the resonator-virion system, we are able to derive the size of nanoparticles having a radius in the range 30 - 100 nm, with a small error with respect to the nanoparticle nominal radiu
Parametric analysis of 2D guided-wave photonic band gap structures
Full text linkThe parametric analysis of the electromagnetic properties of 2D guided wave photonic band gap structures is reported with the aim of providing a valid tool for the optimal design. The modelling approach is based on the Bloch-Floquet method. Different lattice configurations and geometrical parameters are considered. An optimum value for the ratio between the hole (or rod) radius and the lattice constant does exist and the calculation demonstrated that it is almost independent from the etching depth, only depending on the lattice type. The results are suitable for the design optimisation of photonic crystal reflectors to be used in integrated optical devices
Resonant optical gyro: Monolithic vs. hybrid integration
No full textSince several decades, angular velocity sensors are considered crucial devices in a wide range of vehicles such as military and civil airplanes, military ships, submarines, satellites, space launchers, and long-range ballistic missiles. The interest towards miniaturized gyroscopes for aerospace and defense industry has given rise to an increasing research effort aiming at the scaling of optical gyros through integrated optical technologies. In particular, the resonant optical gyro (ROG) has been identified as the ideal candidate for a new generation photonic angular velocity sensor. Two technological approaches are available to implement the ROGs, i.e., the hybrid integration of optoelectronic components manufactured on different substrates or the monolithic integration of all components on a single chip. The two options are critically discussed and compared in this paper with a special attention on integrated gyroscopes (gyro-on-a-chip, GoC) in silica on silicon and indium phosphide that have been recently theoretically and experimentally studied, demonstrating promising results
3D modelling of 2D guided-wave photonic crystals
No full textIn this paper, a 3D model for studying electromagnetic wave propagation in 2D guided-wave photonic crystals is presented. The model is based on the resolution of the integral-differential Green equation associated with the Helmholtz wave equation in cylindrical coordinates, in order to provide a simple and time-efficient vectorial representation of the field components. The model, used for the investigation of a photonic crystal waveguide which operates at a wavelength of 1300 nm, is validated through a comparison with other well-known algorithms. Results show a good agreement together with a significant reduction of computational time and memory requirements
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