Low frequency fluctuations in a Vertical Cavity Lasers: experiments versus Lang-Kobayashi dynamics

The limits of applicability of the Lang-Kobayashi (LK) model for a semiconductor laser with optical feedback are analyzed. The model equations, equipped with realistic values of the parameters, are investigated below solitary laser threshold where Low Frequency Fluctuations (LFF) are usually observed. The numerical findings are compared with experimental data obtained for the selected polarization mode from a Vertical Cavity Surface Laser (VCSEL) subject to polarization selective external feedback. The comparison reveals the bounds within which the dynamics of the LK can be considered as realistic. In particular, it clearly demonstrates that the deterministic LK, for realistic values of the linewidth enhancement factor $\alpha$, reproduces the LFF only as a transient dynamics towards one of the stationary modes with maximal gain. A reasonable reproduction of real data from VCSEL can be obtained only by considering noisy LK or alternatively deterministic LK for extremely high $\alpha$-values

All-optical delay line using semiconductor cavity solitons (vol 92, 011101, 2008)

Correction of Pedaci, F. and Barland, S. and Caboche, E. and Firth, W.J. and Oppo, G.L. and Tredicce, J.R. and Ackemann, T. and Scroggie, A.J. (2008) All-optical delay line using semiconductor cavity solitons. Applied Physics Letters, 92 (1). ISSN 0003-695

Cavity-soliton motion in the presence of device defects

Cavity solitons (CSs) are localized structures appearing as single intensity peaks in the homogeneous background of the field emitted by a nonlinear (micro) resonator driven by a coherent field (holding beam). By introducing a phase gradient in the holding beam, it is possible to induce CS drift. This motion is strongly influenced by the presence of defects in the device structure. We analyze numerically two situations that appeared in the experiments. In the first one, a structure is self-generated on the defect and a regular sequence of moving CS originates from it. We investigate the properties of this \u201ctap\u201d of CS as a function of the defect characteristics and of the parameters values. The second situation corresponds to the interaction between a moving CS and a defect, which plays a fundamental role in CS applications such as the delay line or the shift register

All-optical delay line using semiconductor cavity solitons

An all-optical delay line based on the lateral drift of cavity solitons in semiconductor microresonators is proposed and experimentally demonstrated. The functionalities of the device proposed as well as its performance is analyzed and compared with recent alternative methods based on the decrease of group velocity in the vicinity of resonances. We show that the current limitations can be overcome using broader devices with tailored material responses

Microresonator defects as sources of drifting cavity solitons

Cavity solitons (CS) are localized structures appearing as single intensity peaks in the homogeneous background of the field emitted by a nonlinear (micro)resonator. In real devices, their position is strongly influenced by the presence of defects in the device structure. In this Letter we show that the interplay between these defects and a phase gradient in the driving field induces the spontaneous formation of a regular sequence of CSs moving in the gradient direction. Hence, defects behave as a device built-in CS source, where the CS generation rate can be set by controlling the system parameters

Vectorial dissipative solitons in vertical-cavity surface-emitting Lasers with delays

We show that the nonlinear polarization dynamics of a vertical-cavity surface-emitting laser placed into an external cavity leads to the formation of temporal vectorial dissipative solitons. These solitons arise as cycles in the polarization orientation, leaving the total intensity constant. When the cavity round-trip is much longer than their duration, several independent solitons as well as bound states (molecules) may be hosted in the cavity. All these solutions coexist together and with the background solution, i.e. the solution with zero soliton. The theoretical proof of localization is given by the analysis of the Floquet exponents. Finally, we reduce the dynamics to a single delayed equation for the polarization orientation allowing interpreting the vectorial solitons as polarization kinks.Comment: quasi final resubmission version, 12 pages, 9 figure

Interaction of two modulational instabilities in a semiconductor resonator

The interaction of two neighboring modulational instabilities in a coherently driven semiconductor cavity is investigated. First, an asymptotic reduction of the general equations is performed in the limit of a nearly vertical input-output characteristic. Next, a normal form is derived in the limit where the two instabilities are close to one other. An infinity of branches of periodic solutions are found to emerge from the unstable portion of the homogeneous branch. These branches have a nontrivial envelope in the bifurcation diagram that can either smoothly join the two instability points or form an isolated branch of solutions

Impact of Age and Body Site on Adult Female Skin Surface pH

Background: pH is known as an important parameter in epidermal barrier function and homeostasis. Aim: The impact of age and body site on skin surface pH (pH(SS)) of women was evaluated in vivo. Methods: Time domain dual lifetime referencing with luminescent sensor foils was used for pH(SS) measurements. pH(SS) was measured on the forehead, the temple, and the volar forearm of adult females (n = 97, 52.87 +/- 18.58 years, 20-97 years). Every single measurement contained 2,500 pH values due to the luminescence imaging technique used. Results: pH(SS) slightly increases with age on all three investigated body sites. There are no significant differences in pH(SS) between the three investigated body sites. Conclusion: Adult pH(SS) on the forehead, the temple and the volar forearm increases slightly with age. This knowledge is crucial for adapting medical skin care products. Copyright (C) 2012 S. Karger AG, Base

Extreme events generated in microcavity lasers and their predictions by reservoir computing

Extreme events generated by complex systems have been intensively studied in many fields due to their great impact on scientific research and our daily lives. However, their prediction is still a challenge in spite of the tremendous progress that model-free machine learning has brought to the field. We experimentally generate, and theoretically model, extreme events in a current-modulated, single-mode microcavity laser operating on orthogonal polarizations, where their strongly differing thresholds -- due to cavity birefringence -- give rise to giant light pulses initiated by spontaneous emission. Applying reservoir-computing techniques, we identify in advance the emergence of an extreme event from a time series, in spite of coarse sampling and limited sample length. Performance is optimized through new hybrid configurations that we introduce in this paper. Advance warning times can reach 5ns, i.e. approximately ten times the rise time of the individual extreme event