Side-mode gain in semiconductor lasers (original) (raw)
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Spectral signature of relaxation oscillations in semiconductor lasers
IEEE Journal of Quantum Electronics, 1992
A new and relatively simple expression is given for the optical spectrum of a single-mode semiconductor laser which, due to the presence of relaxation oscillations, consists of a strong central line with a broad weak sideband at each side. The coupling between phase and amplitude fluctuations is included in this derivation and is shown to result in an asymmetry between the relaxation oscillation sidebands. This asymmetry can be used to determine the linewidth enhancement factor a. Using optical heterodyne detection we have accurately measured the spectrum of a Fahry-Perot-type AlGaAs laser as a function of output power. Information on the dynamics of the relaxation oscillations was thus obtained. The power dependence of the frequency and damping of the relaxation oscillations allowed us to separately determine the spontaneous lifetime and the dependence of the gain on both carrier density (differential gain) and intensity (gain saturation).
Journal of Applied Physics, 1996
A combined experimental and theoretical approach to measuring the variation in carrier density along the length of a semiconductor laser is developed. It is shown that by following the rate of increase of the principal spectral peak, rather than monitoring the optical power at a fixed energy, measurements can be made less susceptible to the effects of heating in the sample. Experimental results showing the development of the longitudinal carrier density profile with injected current are presented and, when compared with the results of self-consistent modeling, provide insights into the internal operating mechanisms of the laser.
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.
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.
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.
Semiconductors, 2006
It is shown that the reason why the maximum attainable optical power in semiconductor lasers is limited is the finite time of carrier energy relaxation via scattering by nonequilibrium optical phonons in the quantum-well active region. The power and spectral characteristics of semiconductor lasers are studied experimentally at high excitation levels (up to 100 kA/cm 2 ) in pulsed lasing mode (100 ns, 10 kHz). As the drive current increases, the maximum intensity of stimulated emission tends to a constant value ("saturates"), and the emitted power increases owing to extension of the spectrum to shorter wavelengths. The intensity saturation is due to limitation of the rate of stimulated recombination, caused by a finite time of the electron energy relaxation via scattering by polar optical phonons. It is found that the broadening of the stimulated emission spectrum is related to an increase in carrier concentration in the active region, which enhances the escape of electrons into the waveguide layers. As the drive current increases, the carrier concentration in the waveguide reaches its threshold value and there appears an effective channel of current leakage from the active region. The experiment shows that the appearance of a band of waveguide lasing correlates with a sharp drop in the differential quantum efficiency of a semiconductor laser.
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.
Journal of Optics B: Quantum and Semiclassical Optics, 2002
We study the multimode dynamics of a semiconductor laser with optical feedback operating in the low-frequency fluctuation regime. A multimode extension of the Lang-Kobayashi (LK) model shows, in agreement with experimental observations, that the low-frequency power dropouts exhibited by the main modes are accompanied by sudden, asymmetric, activations of dormant longitudinal side modes. Furthermore, these activations are delayed with respect to the dropouts of the active modes. In order to satisfactorily reproduce both the asymmetric activation of side modes and their delay with respect to the dropouts, the generalized LK model has to include a parabolic gain profile, together with a frequency shift of the gain curve with carrier population.
Applied Physics B, 2018
Comprehensive theoretical investigation of the influence of external optical feedback on the dynamics of semiconductor lasers are introduced. The analyses are based on numerical simulation of the multimode rate equations superposed by Langevin noise sources that are generated in such a way as to keep the correlation of the modal photon number with the injected electron number. The gain saturation effect which causes mode-competition phenomena among longitudinal modes are considered in our multimode rate equation model. The dynamics of modes and the characteristics of the output spectrum are investigated for strong external optical feedback strength. Numerically simulated results show that the mode-competition phenomena induce quasi-periodic hopping among several longitudinal modes which reveals multimode-like output spectra in lasers. This mode-hopping phenomena is described in terms of asymmetric gain saturation effect.