Andrei Vladimirov

Model for mode locking in quantum dot lasers

We propose a model for passive mode locking in quantum dot lasers and report on specific dynamical properties of the regime which is characterized by a fast gain recovery. No Q-switching instability has been found accompanying the mode locking. Bistability can occur between the mode locking regime and the nonlasing state.

Delay differential equations for mode-locked semiconductor lasers

We propose a new model for passive mode locking that is a set of ordinary delay differential equations. We assume a ring-cavity geometry and Lorentzian spectral filtering of the pulses but do not use small gain and loss and weak saturation approximations. By means of a continuation method, we study mode-locking solutions and their stability. We find that stable mode locking can exist even when the nonlasing state between pulses becomes unstable.

Localized structures in dissipative media: from optics to plant ecology

Localized structures (LSs) in dissipative media appear in various fields of natural science such as biology, chemistry, plant ecology, optics and laser physics. The proposal for this Theme Issue was to gather specialists from various fields of nonlinear science towards a cross-fertilization among active areas of research. This is a cross-disciplinary area of research dominated by nonlinear optics due to potential applications for all-optical control of light, optical storage and information processing. This Theme Issue contains contributions from 18 active groups involved in the LS field and have all made significant contributions in recent years.

Delay-induced dynamics and jitter reduction of passively mode-locked semiconductor lasers subject to optical feedback

We study a passively mode-locked semiconductor ring laser subject to optical feedback from an external mirror. Using a delay differential equation model for the mode-locked laser, we are able to systematically investigate the resonance effects of the inter-spike interval time of the laser and the roundtrip time of the light in the external cavity (delay time) for intermediate and long delay times. We observe synchronization plateaus following the ordering of the well-known Farey sequence. Our results show that in agreement with the experimental results a reduction of the timing jitter is possible if the delay time is chosen close to an integer multiple of the inter-spike interval time of the laser without external feedback. Outside the main resonant regimes the timing jitter is drastically increased by the feedback.

Two-dimensional clusters of solitary structures in driven optical cavities

Interaction between localized structures in the transverse plane of a passive optical cavity containing a saturable medium is studied analytically and numerically. Stability properties of clusters of localized structures and their spontaneous motion are described.

Control and removal of modulational instabilities in low-dispersion photonic crystal fiber cavities

Taking up to fourth-order dispersion effects into account, we show that fiber resonators become stable for a large intensity regime. The range of pump intensities leading to modulational instability becomes finite and controllable. Moreover, by computing analytically the thresholds and frequencies of these instabilities, we demonstrate the existence of a new unstable frequency at the primary threshold. This frequency exists for an arbitrary small but nonzero fourth-order dispersion coefficient. Numerical simulations for a low and flattened dispersion photonic crystal fiber resonator confirm analytical predictions and open the way to experimental implementation.

On Vegetation Clustering, Localized Bare Soil Spots and Fairy Circles

We present a model and nonlinear analysis which account for the clustering behaviors of arid vegetation ecosystems, the formation of localized bare soil spots (sometimes also called fairy circles) in these systems and the attractive or repulsive interactions governing their spatio-temporal evolution. Numerical solutions of the model closely agree with analytical predictions.

Hybrid mode-locking in a 40 GHz monolithic quantum dot laser

Mode-locked semiconductor lasers are efficient sources of short optical pulses ideal for applications in high speed telecommunication systems. Especially promising for telecom applications is the new generation of quantum dot mode-locked lasers (QD-MLL) which demonstrate important advantages over the standard quantum well devices [1]. However, performance improvement is still an ongoing issue, in particular for the efficiency of hybrid mode-locking, — a commonly used technique to improve characteristics and synchronize the mode-locked pulses — namely the dependence of the locking regime on the frequency and power of the applied external signal. Based on our previous results on passive mode-locking in quantum dot lasers [2], we study experimentally and theoretically a monolithic two-section hybrid mode-locked quantum dot laser with periodically modulated reverse bias applied to the saturable absorber section.

Hybrid Mode Locking in Semiconductor Lasers: Simulations, Analysis, and Experiments

Hybrid mode locking in a two-section edge-emitting semiconductor laser is studied numerically and analytically using a set of three delay differential equations. In these equations, the external RF signal applied to the saturable-absorber section is modeled by the modulation of the carrier relaxation rate in this section. The estimation of the locking range where the pulse repetition frequency is synchronized with the frequency of the external modulation is performed numerically and the effect of the modulation shape and amplitude on this range is investigated. Asymptotic analysis of the dependence of the locking range width on the laser parameters is carried out in the limit of small-signal modulation. Our numerical simulations indicate that hybrid mode locking can be also achieved in the cases when the frequency of the external modulation is approximately twice and half of the pulse repetition frequency of the free-running passively mode-locked laser fP . Finally, we provide an experimental demonstration of hybrid mode locking in a 20-GHz quantum-dot laser with the modulation frequency of the reverse bias applied to the absorber section close to fP/2.

Stripe-array diode-laser in an off-axis external cavity: theory and experiment.

Stripe-array diode lasers naturally operate in an anti-phase supermode. This produces a sharp double lobe far field at angles +/-alpha depending on the period of the array. In this paper a 40 emitter gain guided stripe-array laterally coupled by off-axis filtered feedback is investigated experimentally and numerically. We predict theoretically and confirm experimentally that at doubled feedback angle 2alpha a stable higher order supermode exists with twice the number of emitters per array period. The theoretical model is based on time domain traveling wave equations for optical fields coupled to the carrier density equation taking into account diffusion of carriers. Feedback from the external reflector is modeled using Fresnel integration.