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Register a new userDiscrete Light Bullets in Passively Mode-Locked Semiconductor Lasers
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Added by
Svetlana V. Gurevich
Publication date
2020
fields
Physics
and research's language is
English
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In this paper, we analyze the formation and dynamical properties of discrete light bullets (dLBs) in an array of passively mode-locked lasers coupled via evanescent fields in a ring geometry. Using a generic model based upon a system of nearest-neighbor coupled Haus master equations we show numerically the existence of dLBs for different coupling strengths. In order to reduce the complexity of the analysis, we approximate the full problem by a reduced set of discrete equations governing the dynamics of the transverse profile of the dLBs. This effective theory allows us to perform a detailed bifurcation analysis via path-continuation methods. In particular, we show the existence of multistable branches of discrete localized states (dLSs), corresponding to different number of active elements in the array. These branches are either independent of each other or are organized into a snaking bifurcation diagram where the width of the dLS grows via a process of successive increase and decrease of the gain. Mechanisms are revealed by which the snaking branches can be created and destroyed as a second parameter, e.g., the linewidth enhancement factor or the coupling strength are varied. For increasing couplings, the existence of moving bright and dark dLSs is also demonstrated.
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We study the effect of noise on the dynamics of passively mode-locked semiconductor lasers both experimentally and theoretically. A method combining analytical and numerical approaches for estimation of pulse timing jitter is proposed. We investigate how the presence of dynamical features such as wavelength bistability affects timing jitter.
We consider design optimization of passively mode-locked two-section semiconductor lasers that incorporate intracavity grating spectral filters. Our goal is to develop a method for finding the optimal wavelength location for the filter in order to maximize the region of stable mode-locking as a function of drive current and reverse bias in the absorber section. In order to account for material dispersion in the two sections of the laser, we use analytic approximations for the gain and absorption as a function of carrier density and frequency. Fits to measured gain and absorption curves then provide inputs for numerical simulations based on a large signal accurate delay-differential model of the mode-locked laser. We show how a unique set of model parameters for each value of the drive current and reverse bias voltage can be selected based on the variation of the net gain along branches of steady-state solutions of the model. We demonstrate the validity of this approach by demonstrating qualitative agreement between numerical simulations and the measured current-voltage phase-space of a two-section Fabry-Perot laser. We then show how to adapt this method to determine an optimum location for the spectral filter in a notional device with the same material composition, based on the targeted locking range, and accounting for the modal selectivity of the filter.
The dynamics and stability of continuous-wave and multi-pulse structures are studied theoretically, for a generalized model of passively mode-locked fiber laser with an arbitrary nonlinearity. The model is characterized by a complex Ginzburg-Landau equation with saturable nonlinearity of a general form ($I^m/(1+Gamma I)^n$), where $I$ is the field intensity, $m$ and $n$ are two positive real numbers and $Gamma$ is the optical field saturation power. The analysis of fixed-point solutions of the governing equations, reveals an interesting loci of singular points in the amplitude-frequency plane consisting of zero, one or two fixed points depending upon the values of $m$ and $n$. The stability of continuous waves is analyzed within the framework of the modulational-instability theory, results demonstrate a bifurcation in the continuous-wave amplitude growth rate and propagation constant characteristic of multi-periodic wave structures. In the full nonlinear regime these multi-periodic wave structures turn out to be multi-pulse trains, unveiled via numerical simulations of the model nonlinear equation the rich variety of which is highlighted by considering different combinations of values for the pair ($m$,$n$). Results are consistent with previous analyses of the dynamics of multi-pulse structures in several contexts of passively mode-locked lasers with saturable absorber, as well as with predictions about the existence of multi-pulse structures and bound-state solitons in optical fibers with strong optical nonlinearity such as cubic-quintic and saturable nonlinearities.
We report on the characterization of the timing stability of passively mode-locked discrete mode diode laser sources. These are edge-emitting devices with a spatially varying refractive index profile for spectral filtering. Two devices with a mode-locking frequency of 100 GHz are characterized. The first device is designed to support a comb of six modes and generates near Fourier limited 1.9 ps pulses. The second supports four primary modes resulting in a sinusoidal modulation of the optical intensity. Using a cross-correlation technique, we measured a 20 fs pulse to pulse timing jitter for the first device, while, for the second device, a mode-beating (RF) linewidth of 1 MHz was measured using heterodyne mixing in a semiconductor optical amplifier. Comparison of these results with those obtained for an equivalent Fabry-Perot laser indicates that the spectral filtering mechanism employed does not adversely affect the timing properties of these passively mode-locked devices.
We report the unequivocal demonstration of mid-infrared mode-locked pulses from a semiconductor laser. The train of short pulses was generated by actively modulating the current and hence the optical gain in a small section of an edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch equations in an open two-level system. We anticipate our results to be a significant step toward a compact, electrically-pumped source generating ultrashort light pulses in the mid-infrared and terahertz spectral ranges.
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