Rate equation analysis of slow-light photonic crystal lasers

Slow-light (SL) in active photonic crystal (PhC) waveguides enhances the modal gain per unit length [1], with application to shorter lasers [2]. Recently, we have proposed a coupled-Bloch-mode (CBM) approach [4] to analyze active PhC structures. Essentially, the presence of material gain in a line-defect waveguide is viewed as a weak perturbation to a reference structure with purely real refractive index. In the SL regime, the optical gain induces a distributed feedback (DFB) between the counterpropagating Bloch modes of the reference waveguide. The active waveguide is efficiently described by a scattering matrix [5], which accounts for the SL gain enhancement and gain-induced DFB. In particular, this effect reveals that SL semiconductor optical amplifiers may benefit from a smaller linewidth enhancement factor (LEF) [5], as they would experience a weaker backscattering

Impact of carrier dynamics on the photovoltaic performance of quantum dot solar cells

The study presents a theoretical investigation of the impact of individual electron and hole dynamics on the photovoltaic characteristics of InAs/GaAs quantum dot solar cells. The analysis is carried out by exploiting a model which includes a detailed description of quantum dots (QD) kinetics within a drift-diffusion formalism. Steady-state and transient simulations show that hole thermal spreading across the closely spaced QD valence band states allows to extract the maximum achievable photocurrent from the QDs; on the other hand, slow hole dynamics turns QDs into efficient traps, impairing the short circuit current despite the extended light harvesting provided by the QDs

The cosmic dust rate across the Universe

We investigate the evolution of interstellar dust in the Universe by means of chemical evolution models of galaxies of different morphological types, reproducing the main observed features of present-day galaxies. We adopt the most updated prescriptions for dust production from supernovae and asymptotic giant branch stars as well as for dust accretion and destruction processes. Then, we study the cosmic dust rate in the framework of three different cosmological scenarios for galaxy formation: (i) a pure luminosity scenario, (ii) a number density evolution scenario, as suggested by the classical hierarchical clustering scenario and (iii) an alternative scenario, in which both spirals and ellipticals are allowed to evolve in number on an observationally motivated basis. Our results give predictions about the evolution of the dust content in different galaxies as well as the cosmic dust rate as a function of redshift. Concerning the cosmic dust rate, the best scenario is the alternative one, which predicts a peak at 2 < z < 3 and reproduces the cosmic star formation rate. We compute the evolution of the comoving dust density parameter \u3a9dust and find agreement with data for z < 0.5 in the framework of DE and alternative scenarios. Finally, the evolution of the average cosmic metallicity is presented and it shows a quite fast increase in each scenario, reaching the solar value at the present time, although most of the heavy elements are incorporated into solid grains, and therefore not observable in the gas phase

Numerical Study of Optical Frequency Combs in mid-IR Quantum Cascade Lasers: Effective Semiconductor Maxwell-Bloch Equations

In this paper a theoretical model based on Effective Semiconductor Maxwell-Bloch Equations (ESMBEs) is proposed for the description of the dynamics of a multi-mode mid-Infrared (mid-IR) Quantum Cascade Laser (QCL) in Fabry Perot (FP) configuration, in order to investigate the spontaneous generation of frequency combs in this device. In agreement with recent experimental results our numerical simulations show both chaotic and regular multimode regimes. In the latter case we identify self-confined structures travelling along the cavity, and furthermore the instantaneous frequency is characterized by a linear chirp behaviour

A new galactic chemical evolution model with dust: Results for dwarf irregular galaxies and DLA systems

We present a galactic chemical evolution model which adopts updated prescriptions for all the main processes governing the dust cycle. We follow in detail the evolution of the abundances of several chemical species (C, O, S, Si, Fe and Zn) in the gas and dust of a typical dwarf irregular galaxy. The dwarf irregular galaxy is assumed to evolve with a low but continuous level of star formation and experience galactic winds triggered by supernova (SN) explosions. We predict the evolution of the gas to dust ratio in such a galaxy and discuss critically the main processes involving dust, such as dust production by asymptotic giant branch stars and Type II SNe, destruction and accretion (gas condensation in clouds). We then apply our model to damped Lyman \u3b1 (DLA) systems which are believed to be dwarf irregulars, as witnessed by their abundance patterns. Our main conclusions are the following. (i) We can reproduce the observed gas to dust ratio in dwarf galaxies. (ii) We find that the process of dust accretion plays a fundamental role in the evolution of dust and in certain cases it becomes the dominant process in the dust cycle. On the other hand, dust destruction seems to be a negligible process in irregulars. (iii) Concerning DLA systems, we show that the observed gas-phase abundances of silicon, normalized to volatile elements (zinc and sulfur), are in agreement with our model. (iv) The abundances of iron and silicon in DLA systems suggest that the two elements undergo a different history of dust formation and evolution. Our work casts light on the nature of iron-rich dust: the observed depletion pattern of iron is well reproduced only when an additional source of iron dust is considered. Here we explore the possibility of a contribution from Type Ia SNe as well as an efficient accretion of iron nanoparticles

Modal properties of photonic crystal cavities and applications to lasers

Photonic crystal cavities enable strong light–matter interactions, with numerous applica-tions, such as ultra-small and energy-efficient semiconductor lasers, enhanced nonlinearities and single-photon sources. This paper reviews the properties of the modes of photonic crystal cavities, with a special focus on line-defect cavities. In particular, it is shown how the fundamental resonant mode in line-defect cavities gradually turns from Fabry–Perot-like to distributed-feedback-like with increasing cavity size. This peculiar behavior is directly traced back to the properties of the guided Bloch modes. Photonic crystal cavities based on Fano interference are also covered. This type of cavity is realized through coupling of a line-defect waveguide with an adjacent nanocavity, with applications to Fano lasers and optical switches. Finally, emerging cavities for extreme dielectric confinement are covered. These cavities promise extremely strong light–matter interactions by realizing deep sub-wavelength mode size while keeping a high quality factor

Dynamic regimes and damping of relaxation oscillations in III-V/Si external cavity lasers

We report how external cavity IIIV/Si hybrid lasers operate in regimes of ultradamped relaxation oscillations or in turbulent and selfpulsing regimes. The different regimes are reached by detuning the lasing wavelength respect to the mirror effective reflectivity peak and are the consequence of the dispersive narrow band reflectivity of the silicon photonics mirror, the linewidth enhancement factor and fourwave mixing in the gain medium

Dynamics and tolerance to external optical feedback of III-V/Si hybrid lasers with dispersive narrowband mirror

We report how external cavity III-V/Si hybrid lasers operate in regimes of ultra-damped relaxation oscillations or in unstable regimes as consequence to the dispersive mirror, non-zero linewidth enhancement factor and four-wave mixing in the gain medium. Tolerance to external optical feedback is also discussed