Nonequilibrium model for semiconductor laser modulation response (original) (raw)
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Approaching intraband relaxation rates in the high-speed modulation of semiconductor lasers
IEEE Journal of Quantum Electronics, 2000
This paper uses a nonequilibrium semiconductor laser model to investigate high-modulation bandwidth operation in semiconductor lasers. In particular, limitations to 100 GHz modulation response, which approaches the carrier-phonon scattering rate, are analyzed. It is found that plasma heating leads to a dynamic carrier population bottleneck, which limits scaling of modulation bandwidth. An optical injection scheme is proposed to verify this phenomenon experimentally.
Improved Semiconductor-Laser Dynamics From Induced Population Pulsation
IEEE Journal of Quantum Electronics, 2006
This paper investigates theoretically the modification of dynamical properties in a semiconductor laser by a strong injected signal. It is found that enhanced relaxation oscillations are governed by the pulsations of the intracavity field and population at frequencies determined by the injected field and cavity resonances. Furthermore, the bandwidth enhancement is associated with the undamping of the injection-induced relaxation oscillation and strong population pulsation effects. There are two limitations to the modulation-bandwidth enhancement: Overdamping of relaxation oscillation and degradation of flat response at low frequencies. The injected-laser rate-equations used in the investigation reproduce the relevant aspects of modulation-bandwidth enhancement found in the experiment on injection-locked vertical-cavity surface-emitting lasers.
Model calculation of the laser-semiconductor interaction in subpicosecond regime
Journal of Physics and Chemistry of Solids, 1986
We develop a model calculation to investigate the interaction of a subpicosecond laser pulse with a direct-gap semiconductor. In this problem, carrier distributions are extremely far from equilibrium and nonequilibrium LO phonons are generated at the center of the Brillouin zone. We solve numerically a system of three transport equations, namely one for the conduction band, one for the valence band and one for the LO phonons. Contrary to all previous work, we do not assume that carrier distributions are nondegenerate so that we can investigate the following problems: (a) conditions of internal thermalization in degenerate nonequilibrium plasma (thermalization time, influence of screening on the energy-loss rate, formation of nonequilibrium LO phonons) and (b) absorption saturation and transmission of the pump laser pulse. 1. INTRODUCIION During the last years, the interaction of ultrashort light pulses with semiconductors or insulators has been more and more experimentally investigated [l-8]. These researches are focused either on the properties of the laser pulse (as, for example, the conditions of transmission or reflection) or on the solid-state properties under strong optical excitation (as, for example, the processes of energy absorption, the occurrence of nonequilibrium phonons, etc.). Let us recall briefly now the conditions of the laser-semiconductor interaction. At this stage, the description remains more or less intuitive. One may attempt to distinguish three steps in the interaction kinetics as discussed in Parts 1, 2 and 3 of this section. 1.1 First step during the laser pulse The lase pulse generates electron-hole pairs. Because of the selection rules, all these pairs, when created, do have almost the same kinetic energy (we restrict mainly this discussion to direct-gap materials), so that neither
Spatio-temporal dynamics of semiconductor lasers: Theory, modelling and analysis
Progress in Quantum Electronics, 1996
The spatio-temporal dynamics of semiconductor lasers is studied theoretically on the basis of semiclassic laser theory. The carrier dynamics is described in a density-matrix approach and the coupled set of equations of motion for the active medium and the light field are derived. Several approximafions related to separations of length and time scales are discussed, resulting in a hierarchy of model equations leading from microscopic to macroscopic levels of description. By numerically solving space-dependent coupled partial differential equations for the (complex) optical fields, the interband polarization and the charge carrier distribution functions on the various levels of the hierarchy the formation and longitudinal propagation of unstable transverse optical filamentary structures is analyzed in a model configuration for typical doubleheterostructure multi-stripe and broad-area lasers. Spectral and spatial hole burning which is observed in the simulated carrier distributions reflects the interplay between stimulated emission and the relaxation dynamics of the carrier distributions as well as the polarization. Its details are strongly influenced by the momentum and density dependence of the microscopic relaxation rates. The transverse hole burning leads to complex spatio-temporal patterns in the macroscopic intensity picture. This complex spatio-temporal dynamic behavior in multi-stripe and broad-area lasers is analyzed by various theoretical tools which allows one to quantify the degree of complexity. CONTENTS * It should be mentioned that these assumptions break down if the the scattering probabilities are strongly peaked around a single final state as is the case in pure LO-phonon scattering or for carrier-carrier scattering at low densities, where most scattering processes are in the forward direction. (57,6s) In the present case of high densities with strong large-angle carrier-carrier scattering the assumptions are well satisfied. * Strictly speaking, p, is not exactly the linear part. Due do the band gap renormalization and the density dependent dephasing rate it includes already parts which are nonlinear in the field.
Rate-equation description of multi-mode semiconductor lasers
Physics and Simulation of Optoelectronic Devices XXII, 2014
We present a set of rate equations for the modal amplitudes and carrier-inversion moments that describe the deterministic multi-mode dynamics of a semiconductor laser due to spatial hole burning. Mutual interactions among the lasing modes, induced by high-frequency modulations of the carrier distribution, are included by carrier-inversion moments for which rate equations are given as well. We derive the Bogatov effect of asymmetric gain suppression in semiconductor lasers and illustrate the potential of the model for a two and three-mode laser by numerical and analytical methods.
MATERIALS TRANSACTIONS, 2006
This article investigates numerically carrier-phonon interaction and nonequilibrium energy transfer in direct and indirect bandgap semiconductors during sub-picosecond pulse laser irradiation and also examines the recombination effects on energy transport from the microscopic viewpoint. In addition, the influence of laser fluence and pulse duration is studied by using the self-consistent three-temperature model, which involves carriers, longitudinal optical phonons, and acoustic phonons. It is found that a substantial non-equilibrium state exists between carriers and phonons during short pulse laser irradiation because of time scale difference between the relaxation time and the pulse duration. It is clear that the two-peak structure in carrier temperature exists and it depends mainly on laser pulses, fluences, and recombination processes. During laser irradiation, in particular, the Auger recombination for Si becomes dominant due to the increase in the carrier number density, whereas for GaAs, the Auger recombination process can be ignored due to an abrupt increase in SRH recombination rates at the initial stages of laser exposure.
Nonlinear gain suppression in semiconductor lasers due to carrier heating
IEEE Photonics Technology Letters, 2000
We present a simple model for carrier heating in semiconductor lasers from which the temperature dynamics of the electron and hole distributions can be calculated. Analytical expressions for two new contributions to the nonlinear gain coefficient e are derived, which reflect carrier heating due to stimulated emission and free carrier absorption. In typical cases, carrier heating and spectral holeburning are found to give comparable contributions to nonlinear gain suppression. The results are in good agreement with recent measurements on InGaAsP laser diodes.
Analysis of semiconductor laser dynamics under gigabit rate modulation
A theoretical study of the dynamics of semiconductor lasers subjected to pseudorandom digital modulation at gigabit rates is presented. The eye diagram, turn-on jitter ͑TOJ͒, and power fluctuations in the modulated laser wave form are analyzed. The study is based on numerical large-signal analysis of the laser rate equations. Influences of the biasing and modulation currents on the eye diagram and TOJ are examined. The degree of eye opening is measured in terms of a Q factor of the laser signal analogous to the Q factor determining the bit-error rate in transmission systems. Influence of optimizing both the sampling and decision times on the signal Q factor is modeled. We show that the most eye opening corresponds to shortening the sampling time associated with lengthening the decision time. We also assess the relative contributions of the laser intrinsic noise and pseudorandom bit pattern to the TOJ. The results show that the bit pattern is the major contributor to the TOJ when the setting time of the relaxation oscillation is longer than the bit slot.
Effect of carrier heating on diffusion induced modulational instability in semiconductor plasmas
Indian Journal of Physics, 2010
The purpose of the present paper is to report the study on modulational amplification in diffusive semiconductors including hot carrier effects. Considering that the origin of modulational interaction lies in the third-order optical susceptibility c (3) arising from the nonlinear diffusion current density and using coupled mode theory, an analytical investigation of frequency modulational interaction between co-propagating laser beams and internally generated acoustic mode is presented. We have studied the steady state and transient amplification characteristics of modulated waves arising in diffusive semiconductor plasmas. The effect of carrier heating adds new dimensions to the present study. The heating effect reduces the required threshold amplitude of wave and enhances steady-state as well as transient gain of the generated acoustic mode.
IEEE Journal of Quantum Electronics, 1991
A density matrix equation for semiconductor lasers has been derived from the microscopic equation of motion for electrons using a projection operator method. The effect of non-Markovian intraband relaxation has been found to be described by the autocorrelation functions of electron scattering terms in the microscopic interaction Hamiltonian. The obtained density matrix equation provides a systematic treatment for dynamical properties of semiconductor lasers, and the treatment can be performed by calculating the autocorrelation functions from available material parameters. A gain formula for arbitrary light output power has been derived from a single-mode steady-state nonperturbative solution. A simplified estimation employing a stochastic model has shown that non-Markovian intraband relaxation enhances both linear gain and nonlinear gain. The reduction of nonlinear gain effects is also discussed.