S. Barland

Cavity Soliton Laser based on mutually coupled semiconductor microresonators

We report on experimental observation of localized structures in two mutually coupled broad-area semiconductor resonators, one of which acts as a saturable absorber. These structures coexist with a dark homogeneous background and they have the same properties as cavity solitons without requiring the presence of a driving beam into the system. They can be switched individually on and off by means of a local addressing beam.

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.

Excitable particles in an optical torque wrench

The optical torque wrench is a laser trapping technique capable of applying and directly measuring torque on microscopic birefringent particles using spin momentum transfer, and has found application in the measurement of static torsional properties of biological molecules such as single DNAs. Motivated by the potential of the optical torque wrench to access the fast rotational dynamics of biological systems, a result of its all-optical manipulation and detection, we focus on the angular dynamics of the trapped birefringent particle, demonstrating its excitability in the vicinity of a critical point. This links the optical torque wrench to nonlinear dynamical systems such as neuronal and cardiovascular tissues, nonlinear optics and chemical reactions, all of which display an excitable binary (‘all-or-none’) response to input perturbations. On the basis of this dynamical feature, we devise and implement a conceptually new sensing technique capable of detecting single perturbation events with high signal-to-noise ratio and continuously adjustable sensitivity.

Mapping local defects of extended media using localized structures

The stable positions of localized structures depend on spatial gradients in the system parameters and on the local defects of the hosting medium. We propose a general method to disclose and visualize the local defects of the medium structure, otherwise not detected. The method is based on the observation of the spatiotemporal behavior of localized structures in the presence of controlled gradients in the experimental parameters. We experimentally show an application of this method in a broad-area semiconductor vertical cavity surface emitting laser with optical injection. The comparison of the experimental results with numerical simulations shows a very good agreement.

Efficient Illumination for Microsecond Tracking Microscopy

The possibility to observe microsecond dynamics at the sub-micron scale, opened by recent technological advances in fast camera sensors, will affect many biophysical studies based on particle tracking in optical microscopy. A main limiting factor for further development of fast video microscopy remains the illumination of the sample, which must deliver sufficient light to the camera to allow microsecond exposure times. Here we systematically compare the main illumination systems employed in holographic tracking microscopy, and we show that a superluminescent diode and a modulated laser diode perform the best in terms of image quality and acquisition speed, respectively. In particular, we show that the simple and inexpensive laser illumination enables less than s camera exposure time at high magnification on a large field of view without coherence image artifacts, together with a good hologram quality that allows nm-tracking of microscopic beads to be performed. This comparison of sources can guide in choosing the most efficient illumination system with respect to the specific application.

Cavity Solitons in Semiconductor Devices

Cavity solitons represent a class of dissipative solitons which are generated inside an optical resonator. They have attracted considerable interest in the recent years due to their possible application to optical information processing. First of all, this review chapter illustrates the physics of cavity solitons in semiconductor devices. We discuss the experiments which demonstrated cavity solitons in vertical-cavity surface-emitting lasers, both below and above threshold, and all the theory which accompanied such experiments. Those features of the experimental results, which relate to prospective applications, are highlighted. The final part of the chapter deals with the theory of the cavity soliton laser.

Phase solitons and domain dynamics in an optically injected semiconductor laser

We analyze experimentally and theoretically the spatio-temporal dynamics of a highly multimode semiconductor laser with coherent optical injection. Due to the particular geometry of the device (a 1~m long ring cavity), the multimode dynamics can be resolved in real time and we observe stable chiral solitons and domain dynamics. The experiment is analyzed in the framework of a set of effective semiconductor Maxwell-Bloch equations. We analyze the stability of stationary solutions and simulate both the complete model and a reduced rate equation model. This allows us to predict domain shrinking and the stability of only one chiral charge that we ascribe to the finite active medium response time.

Control of excitable pulses in a laser with optical injection

We experimentally study the dynamics of a Vertical Cavity-Surface Emitting Laser (VCSEL) with an injected signal subject to an external perturbation, in excitable regime. The possibility to control the kind of response of the system, depending on the perturbation amplitude, is demonstrated. Our perturbation technique induces excitable pulse with 100% efficiency when perturbation is above threshold.

High-speed direct modulation of semiconductor lasers

Direct modulation of the injected current still represents an attractive and inexpensive technique for encoding information in the output of a semiconductor laser. The growing requirements in volume of information to be transmitted and their conflict with the progressive, and rapid, degradation of the signal at high speeds have made this simple technical solution less and less attractive. A brief analysis of the sources of the problem is offered. A viable and inexpensive way of improving DMs performance is discussed. High quality signals are predicted at data transmission speeds that exceed by over an order of magnitude those obtainable with DM.

Physics and Properties of Cavity Soliton Lasers

We show the appearance of cavity solitons in two mutually coupled broad area VCSEL’s. We describe the physical processes at their origin and we discuss their properties. We compare experimental with theoretical results.