Nonlinear dynamics of semiconductor laser arrays: a mean fieldmodel

An analysis of the spatiotemporal dynamics of single-emitter and multiemitter index-guided semiconductor laser arrays is presented. The results are based on a propagation model that involves a pair of coupled nonlinear partial differential equations. The model describes the space-time evolution of the mutually interacting lateral field and carrier density distributions. It includes the effect of carrier diffusion and the effect of carrier-induced antiguiding. Coupling between the emitters is provided by the overlapping evanescent fields of the emitters as well as by the exchange of carriers through carrier diffusion. We show that carrier diffusion plays a significant role in the stability and the nature of bifurcations. Also we show that carrier-induced antiguiding is the principal reason of instability for singleand two-emitter arrays. We illustrate a wide variety of instabilities that demonstrate the richness of the dynamics in these devices     

Nonlinear dynamics of a semiconductor laser with delayed negative optoelectronic feedback

Nonlinear dynamics of a semiconductor laser with delayed negative optoelectronic feedback are studied both numerically and experimentally. Mappings of the dynamic states and bifurcation diagrams are compared between a delayed negative optoelectronic feedback system and a delayed positive optoelectronic feedback system. Both systems follow a quasiperiodic route to chaos, where regular pulsing, quasiperiodic pulsing, and chaotic pulsing states are observed. Frequency-locked pulsing states are also found in a delayed negative optoelectronic feedback system, but not in a delayed positive optoelectronic feedback system. These frequency-locked pulsing states are experimentally observed to exhibit a harmonic frequency-locking phenomenon, where the pulsing frequency is locked to a harmonic of the delay loop frequency instead of the delay loop frequency itself. The rotation numbers of these frequency-locked pulsing states show a Devil's staircase structure.     

Theory of semiconductor quantum-dot laser dynamics

A theory for describing nonequilibrium dynamics in a semiconductor quantum-dot laser is presented. This theory is applied to a microcavity laser with a gain region consisting of an inhomogeneous distribution of quantum dots, a quantum-well wetting layer, and injection pumped bulk regions. Numerical results are presented and the effects of spectral hole burning, plasma heating, and many-body effects are analyzed.     

Rate equations analysis of phase-locked semiconductor laser arrays under steady state conditions

Rate equations analysis of phase-locked semiconductor laser arrays has been carried out. It was found that for given (Laser) current densities, the photon density distribution in the array elements is that particular one which maximizes the total photon density. The results of this analysis were then combined with the waveguiding properties of the laser array waveguide, yielding a basic model of phase-locked diode laser arrays. This model explains the effects of the variation of the current combination through the array elements on its mode structure that were observed recently.     

Spatio-temporal dynamics of gain-guided semiconductor laser arrays

A continuous model based on the coupled field-matter Maxwell-Bloch equations for a two-level homogeneously broadened single mode laser is developed. The model includes a Langevin formulation to model thermal and spontaneous emission noises and accounts for carrier diffusion, optical field diffraction and current spreading. Our model is flexible enough to simulate any gain-guided longitudinally uniform laser geometry and is applied to both a single-stripe and a four-stripe gain-guided semiconductor lasers where the influence of the injection current, the interstripe distance and carrier diffusion is discussed within the context of the laser dynamics. We show that an array operating with quasi-independent stripes may be achieved at low pumps and larger interstripe distances. However, as injection current is increased or the interstripe distance is decreased, the device passes through a variety of dynamical instabilities which can be analyzed in the context of lateral cavity modes. Moreover, we also show that the array dynamics is strongly influenced by carrier diffusion which may also lead to different thresholds for each element of the array     

Analysis of the emission efficiency of powerful semiconductor lasers under closed-mode threshold lasing conditions

A new model describing the decrease in the emission efficiency and optical output power of a semiconductor laser above the lasing threshold of the Fabry-Perot mode is suggested. The mechanism of deterioration of the output-power characteristics is described in the suggested model in terms of the achievement of closed-mode threshold conditions. Rate equations are used to analyze how the closed-mode threshold conditions are satisfied in semiconductor lasers.     

Non-linear dynamics and chaos in semiconductor laser devices

The theoretical and experimental aspects of non-linear dynamics and chaos in semiconductor lasers are surveyed. Three novel scenaria for complex dynamical behaviour in semiconductor lasers are proposed for experimental investigation.     

Multilongitudinal-mode dynamics in a semiconductor laser subject tooptical injection

Multilongitudinal-mode dynamics in a semiconductor laser subject to optical injection are investigated both experimentally and numerically. We found that there are parameter regimes for which the slave laser hops into an adjacent longitudinal mode as we vary the detuning of the optical frequencies between the master and slave laser. A traveling wave model is used to numerically investigate the mode hopping. Good qualitative agreement is found between the numerical computations and the experimental observations     

Nonlinear space-charge domain dynamics in a semiconductor with negative differential mobility

On a semiphenomenological level, the explanation of the Gunn effect is one in terms of a time-independent, negative differential, bulk conductivity. This mechanism is based on the conduction-band structure of GaAs, which provides for two kinds of electrons, light and heavy ones. Light electrons dominate at low fields, heavy ones at high fields. Since the mobility of the heavy electrons is much lower than that of the light ones, there is a range of current decrease with increasing field, i.e., a negative conductivity. This negative conductivity leads to an electrical breakup of the crystal into alternating traveling domains of high and low fields, accompanied by alternating current. In a "mathematically perfect" crystal this instability would take the form of traveling negatively charged electron accumulation layers, separating the domains of high and low fields. In real crystals the inevitable spatial fluctuations in the impurity distribution lead to the experimentally observed dipole mode, wherein both negatively charged electron accumulation layers and positively charged electron depletion layers occur.     

Transfer matrix analysis of the amplified spontaneous emission ofDFB semiconductor laser amplifiers

Analytical expressions are derived for the amplified spontaneous emission of a DFB (distributed-feedback) semiconductor laser amplifier with reflective cavity ends. The analysis is extended to a multisection DFB structure including a phase-shifted DFB semiconductor laser amplifier. It is shown that the spontaneous emission power per unit frequency bandwidth emitted from one facet is proportional to the transmission gain and to a quantity which at threshold becomes the inverse of the differential quantum efficiency of the other facet. The analysis is applied to two practical cases: (1) calculation of emission spectra of a DFB semiconductor laser biased below the threshold, and (2) assessment of the signal-to-noise ratio performance of DFB semiconductor laser amplifiers     

Nonlinear distortion performance of semiconductor laser diodes influenced by coherent reflected waves

The influence of the coherent reflected waves on the non-linear distortion performance of semiconductor laser diodes excited by an arbitrary number of input sinusoids with arbitrary amplitudes is analyzed by using the modified simple nonlinear rate equations. The special case of relatively small input amplitudes is considered, and closed-form expressions for the amplitudes of the resulting harmonics and intermodulation products of any order, as well as the differential gain, are obtained.     

Current oscillations in semiconductor diodes under streaming instability conditions

The current oscillations with frequency of the order of plasma frequency in the submicron GaAs n+-n-p-p+ structure are obtained by Monte Carlo particle simulation. The streaming plasma instability responsible for the current oscillations at near ballistic transport conditions is shown.     

Spatio-temporal dynamics of light amplification and amplifiedspontaneous emission in high-power tapered semiconductor laseramplifiers

We investigate the spatio-temporal light field dynamics in high-power semiconductor lasers with continuous-wave optical injection. The amplification processes that characterize this system occur during the propagation of the injected signal within the active area and can be attributed to spatially dependent gain and refractive index variations. Those are shown to be determined by dynamic interactions between the light fields and the active charge-carrier plasma. This microscopic light-matter-coupling is described by a spatially resolved microscopic theory based on Maxwell-Bloch-Langevin equations taking into account many-body interactions, energy transfer between the carrier and phonon system and, in particular, the spatio-temporal interplay of stimulated and amplified spontaneous emission and noise. Results of our numerical modeling visualize the dynamic spatio-spectral beam shaping experienced by the propagating light in amplifiers of tapered geometry. This reveals the microscopic physical processes that are responsible for the particular amplitude and spatial shape of the light beam at the output facet     

Efficiency of vertical emission from a semiconductor laser waveguide with a diffraction grating

A model for calculating the spatial distribution and decay time of electromagnetic modes in laser structures with a dielectric or metal diffraction grating parallel to the active layer is developed. Self-consistent calculation of the efficiency of vertical emission is performed taking into account backscattering and the interaction of scattered waves with substrate modes. The possibility of longitudinal mode selection as a result of the frequency dependence of the decay time without the use of distributed feedback is discussed.     

Transient analysis of two semiconductor devices under circuit-loaded operation conditions

A new method of numerical analysis for semiconductor devices is described. The analysis is carried out by solving a set of fundamental equations which govern the device characteristics and the circuit equation which indicates the circuit condition, simultaneously. Here, instead of Poisson's equation used as one of the fundamental equations in most reported analyses, a "current equation" is used, which represents the device current consisting of conduction current and displacement current. Current equation can be directly substituted into the circuit equation, so the solution obtained from this analysis has self-consistency between device characteristics and circuit condition, Furthermore, the time variations for I-V characteristics, carrier concentration distribution, and electric field distribution for an individual device can be obtained. As a calculation example, the transient characteristics of two diodes with reverse biased condition are calculated. Avalanche oscillation is found for both diodes with opposite phase after avalanche breakdown.     

Optical characteristics of silicon semiconductor bridges under highcurrent density conditions

The optical emission spectra (180-700 nm) of plasma produced by a semiconductor bridge (SCB) with aluminum or tungsten electrodes have been measured and analyzed. The spatially and temporally resolved emission spectra of the SCB device have provided insights into the dynamic discharge of the bridge. The plasma electron temperature of the SCB device was measured using the comparison of the continuum emission of the bridge with the calculated optical emission spectra for a gray body source. Measured electron temperatures in the plasma produced by the bridges are related to the capacitor discharging voltage. The best estimates indicate that 4100-5500 K was measured for Al-electrode SCB device and 5650-6000 K for W-electrode SCB device     

Measurement of semiconductor laser gain and dispersion curvesutilizing Fourier transforms of the emission spectra

A new technique for the measurement of semiconductor laser gain and dispersion spectra is presented. The technique is based on an analysis of the subthreshold emission spectrum by Fourier transforms. Applications of this method to AlGaInP-based interband laser diodes and mid-infrared intersubband quantum cascade lasers are discussed. A good agreement between the measured dispersion of the refractive index and tabulated values in the literature was found     

Pulsed injection locking dynamics of passively mode-lockedexternal-cavity semiconductor laser systems for all-optical clockrecovery

The performance characteristics of a pulse injection locked, passively mode-locked (PML) external-cavity semiconductor laser system for all-optical clock recovery are investigated in detail. It is important to characterize the clock recovery dynamics to understand the fundamental capabilities and limitations of the clock recovery system. It is experimentally shown that these devices offer robust clock recovery with low phase and amplitude noise, low injected data power requirements, large frequency locking bandwidth, large phase tracking bandwidth, short lockup time, long dephasing time and immunity to bit-pattern-effects. Harmonic clock generation and subharmonic clock generation are demonstrated for data-rate conversion applications     

Nonlinear dynamics of the magnetization in a ferrite plate with magnetoelastic properties under the conditions for orientational transition

The nonlinear dynamics of the orientational phase transition of the magnetization vector in a magnetoelastic medium is analyzed. It is demonstrated that the transition involves the precession of the magnetization vector accompanied by the elastic oscillations at the same frequency. The critical constants of magnetoelasticity, elasticity, and magnetization needed for the transition are determined. It is shown that, in real materials, the magnetoelastic interaction leads to an increase in the field of transition by several or several tens of oersteds. The conditions for and the possibility of an increase in this field by hundreds of oersteds are revealed.