Optimal Nonlinear Labor Income Taxation in Dynamic Economies

The aim of this paper is to explore the characteristics of the optimal nonlinear labor income tax in dynamic economies with information asymmetries and human capital accumulation. We develop a dynamic optimal income tax model in which agent’s productivity evolves over time according to two different factors: an exogenous component and a learning by doing process endogenous to the fiscal policy. The latter is determined by the government, maximizing in the initial period a social welfare function capturing some level of aversion to inequality. We characterize analytically the first order condition driving the optimal tax schedule in a model in which agents choose the consumption and labor supply patterns that maximize their lifetime utility function. We show that the inclusion of the endogenous evolution of productivities into the tax problem changes the results with respect to the static framework `a la Mirrlees (1971). We find that the optimal tax strategy balances social marginal costs of increasing marginal tax rates with social marginal benefits of doing so. The costs are related with the reduction of both past and future human capital accumulation, with the negative impact on aggregate social welfare due to the reduction of the individual utility of all the agents paying more taxes and with the increase of the necessity to redistribute more in the future (given that the spread among social marginal weights of each agents will be higher). The benefits derive from the increase of the instantaneous tax receipts with the consequent reduction of the overall tax burden all along the time horizon and from the reduction of present inequality of incomes and future inequality of the productivities. As a particular extreme result we find that it can be optimal to subsidize (instead of taxing) at the margin high productivity agents.Dynamic Optimal Income Taxation, Private Information, Learning by Doing.

Spatio-temporal modeling of the optical properties of VCSELs in presence of polarization effects

15 pages, 10 figures, 1 table, 1 appendix.We develop an optical dynamical model for vertical-cavity surface-emitting lasers (VCSELs) which describes, in an unified way, polarization and spatial effects. The model is based on equations for the lateral dependence of the slowly-varying amplitudes of the optical field in both circular polarizations, and equations for the carrier density in both spin orientations. This provides a natural generalization of the Spin Flip Model for the description of polarization properties of VCSELs extensively used in the literature. In its present form, the model assumes given functional dependence of the guiding mechanisms (built-in refractive index and thermal lensing) as well as the spatial dependence of the current density. We investigate the transverse mode behavior of gain-guided, bottom and top-emitter VCSELs by implementing the model with an analytical approximation to the susceptibility of quantum-well semiconductors. We demonstrate that the stronger the thermal lens, the stronger the tendency towards multimode operation, which indicates that high lateral uniformity of the temperature is required in order to maintain single mode operation in gain-guided VCSELs. We perform analytical calculations of the threshold curves in both types of VCSELs. Also, close-to-threshold numerical simulations show that, depending on the current shape, thermal lensing strength and relative detuning, different transverse modes can be selected.This work was supported by the European Commission under the VISTA HP-TRN and the Spanish MCyT under Projects TIC99-0645-C05-02 and BFM2000-1108.Peer reviewe

Excitable optical waves in semiconductor microcavities

4 pages, 4 figures.-- PACS nrs.: 05.45.-a, 42.65.Sf, 42.65.Tg.-- PMID: 15783966 [PubMed].We demonstrate experimentally and theoretically the existence of excitable optical waves in semiconductor microcavities. Although similar to those observed in biological and chemical systems, these excitable optical waves are self-confined. This is due to a new dynamical scenario, where a stationary Turing pattern controls the propagation of waves in an excitable medium, thus bringing together the two paradigms of dynamical behavior (waves and patterns) in active media.We acknowledge financial support from MCYT (Spain) through project TIC2002-04255-C04-03 and European project VISTA.Peer reviewe

Mode-Locking in Semiconductor Fabry-Pérot Lasers

We theoretically study the dynamics and the mode-locking properties of semiconductor Fabry-Perot lasers with intracavity saturable absorber by using a travelling-wave model and a time-domain description of the optical response of the semiconductor materials. Our description enables us to incorporate important features as for instance the abrupt spectral variations of the absorption in the saturable absorber. We analyze the influence of several key parameters that affect the stability of the mode-locking regime and show that this modelling approach can be used, upon proper fitting of the material parameters, for optimization of the design of semiconductor mode-locked lasers.Peer Reviewe

Excitability and optical pulse generation in semiconductor lasers driven by resonant tunneling diode photo-detectors

We demonstrate, experimentally and theoretically, excitable nanosecond optical pulses in optoelectronic integrated circuits operating at telecommunication wavelengths (1550 nm) comprising a nanoscale double barrier quantum well resonant tunneling diode (RTD) photo-detector driving a laser diode (LD). When perturbed either electrically or optically by an input signal above a certain threshold, the optoelectronic circuit generates short electrical and optical excitable pulses mimicking the spiking behavior of biological neurons. Interestingly, the asymmetric nonlinear characteristic of the RTD-LD allows for two different regimes where one obtain either single pulses or a burst of multiple pulses. The high-speed excitable response capabilities are promising for neurally inspired information applications in photonics. (C) 2013 Optical Society of AmericaFCT [PTDC/EEA-TEL/100755/2008]; FCT Portugal [SFRH/BPD/84466/2012]; Ramon y Cajal fellowship; project RANGER [TEC2012-38864-C03-01]; Direcci General de Recerca del Govern de les Illes Balears; EU FEDER funds; Ministry of Economics and Competitivity of Spain [FIS2010-22322-C02-01

Spectral delay algebraic equation approach to broad area laser diodes

In this study, we discuss an efficient modeling approach for the simulation of broad-area laser diodes. Our method is based on folding the longitudinal propagation dimension into time delays which extend to the lateral dimension and to the influence of diffractive terms the idea of mesh decimation as it is discussed in . We compare the results of the dynamics obtained with our improved model that consists of coupled delay algebraic equations with the results of a standard traveling wave description in the cases of straight current stripes as well as in the important configuration of high-power tapered antireflection coated devices. We obtain an excellent agreement and an improvement of the integration time between one and two orders of magnitudes which may alleviate in some cases the necessity of using complex parallel codes

Directional reversals and multimode dynamics in semiconductor ring lasers

We investigate the dynamics of longitudinal modes in quantum-well semiconductor ring lasers by means of a spatio-temporal travelling wave model. We report the existence of a novel multimode instability in such a system that provokes a periodic deterministic directional reversal involving jumps between consecutive longitudinal modes. The switching sequence follows the modal frequencies from blue to red, and every modal jump is accompanied by a reversal of the direction of emission. We characterize and analyze such instability via the bifurcation analysis of the full travelling wave model as well as by performing the linear stability analysis of the monochromatic solutions

Multi-channel wavelength conversion using four-wave mixing in semiconductor ring lasers

We theoretically study all-optical simultaneous wavelength conversion of multiple channels by four-wave mixing in semiconductor ring lasers. Locking the semiconductor ring laser to a holding beam allows to achieve large conversion efficiencies with good signal-tonoise ratio in several channels at multi-Gb/s bit rates. Cross-talk between signals, arising from the peculiar four-wave mixing cascade of modes in semiconductor ring lasers and their cross-gain saturation, is studied in detail. We show that it can be controlled by adjusting the intensity of the holding beam, the bias current of the laser and the number, intensity and wavelength of signals that one wants to convert

How lasing localized structures evolve out of passive mode locking

We investigate the relationship between passive mode locking and the formation of time-localized structures in the output intensity of a laser. We show how the mode-locked pulses transform into lasing localized structures, allowing for individual addressing and arbitrary low repetition rates. Our analysis reveals that this occurs when (i) the cavity round-trip is much larger than the slowest medium time scale, namely the gain recovery time, and (ii) the mode-locked solution coexists with the zero intensity (off) solution. These conditions enable the coexistence of a large quantity of stable solutions, each of them being characterized by a different number of pulses per round-trip and with different arrangements. Then, each mode-locked pulse becomes localized, i.e., individually addressable. © 2014 American Physical Society.J. J. acknowledges financial support from Ramón y Cajal program and CNRS for supporting a visit at the INLN where part of his work was developed. J. J. and S. B. acknowledge financial support from project RANGER (TEC2012-38864- C03-01) and from Direcció General de Recerca de les Illes Balears cofunded by the European Union FEDER funds. INLN group acknowledges funding from Région PACA with the Projet Volet Général 2011 GEDEPULSEPeer Reviewe

Bayesian state-space modelling of conventional acoustic tracking provides accurate descriptors of home range behavior in a small-bodied coastal fish species

State-space models (SSM) are increasingly applied in studies involving biotelemetry-generated positional data because they are able to estimate movement parameters from positions that are unobserved or have been observed with non-negligible observational error. Popular telemetry systems in marine coastal fish consist of arrays of omnidirectional acoustic receivers, which generate a multivariate time-series of detection events across the tracking period. Here we report a novel Bayesian fitting of a SSM application that couples mechanistic movement properties within a home range (a specific case of random walk weighted by an Ornstein-Uhlenbeck process) with a model of observational error typical for data obtained from acoustic receiver arrays. We explored the performance and accuracy of the approach through simulation modelling and extensive sensitivity analyses of the effects of various configurations of movement properties and time-steps among positions. Model results show an accurate and unbiased estimation of the movement parameters, and in most cases the simulated movement parameters were properly retrieved. Only in extreme situations (when fast swimming speeds are combined with pooling the number of detections over long time-steps) the model produced some bias that needs to be accounted for in field applications. Our method was subsequently applied to real acoustic tracking data collected from a small marine coastal fish species, the pearly razorfish, Xyrichtys novacula. The Bayesian SSM we present here constitutes an alternative for those used to the Bayesian way of reasoning. Our Bayesian SSM can be easily adapted and generalized to any species, thereby allowing studies in freely roaming animals on the ecological and evolutionary consequences of home ranges and territory establishment, both in fishes and in other taxa.This study was funded through a Marie Curie Post-Doc grant (FP7-PEOPLE-2012-IEF, grant no. 327160). MP received additional funding from the research project REC2 (grant no. CTM2011-23835) and the research project CONFLICT (grant no. CGL2008-00958) and JA from a Juan de la Cierva Post-doc grant (grant no. FJCI-2014-21239), all of them funded by the Spanish Ministry of Economy and Competiveness. The project also received additional funding from the B-Types project funded through Leibniz Competition (grant no. SAW-2013-IGB-2) to RA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer Reviewe