Synchronization and application of delay-coupled semiconductor lasers

The work in this thesis is focused on the complex dynamics of semiconductor laser (SL) devices which receive time-delayed feedback from an external cavity or are delay-coupled with a second semiconductor laser. We investigate fundamental properties of the dynamics and study the utilization of transient complex dynamics of a single SL arising from delayed feedback and external signal injection for a neuro-inspired photonic data processing scheme. Based on experiments and numerical modelling, we investigate systems of two coupled SLs, gaining insights into the role of laser and coupling parameters for the synchronization characteristics of these systems. We link certain features of the synchronization dynamics, like intermittent desynchronization events, to the underlying nonlinear dynamics in the coupled laser system. Our research thus combines both fundamental insights into delay-coupled lasers as well as novel application perspectives. In order to explore the capabilities of a single SL with delayed feedback, we follow the concept of reservoir computing (RC) based on delay systems. In particular, we study two different tasks, which are computationally hard for traditional computing concepts. We explore several feedback configurations, data injection methods and operating regimes of the laser and identify the task-dependent optimal operating conditions. Our work demonstrates the potential of simple photonic setups and the RC concept for future computational paradigms. Furthermore, we study the synchronization properties in systems of two delay-coupled SLs with relay. We explore the consequences of asymmetries in this basic setup for the dynamics and synchronization properties. One key question is, how synchronization decays or is lost, which is of significant importance for applications in chaotic communications schemes and key-exchange protocols. We follow an event-based approach and connect changes in the synchronization levels for varying operating parameters or varying mismatches to the onset and characteristics of desynchronization events. Our results regarding synchronization levels and synchronizability underline the significance of symmetry and matching parameters for the identical synchronization of delay-coupled oscillators. We apply our findings regarding the possibility for identical synchronization to develop and implement an experimental method to identify determinism in the chaotic dynamics of a SL with delayed feedback. Our method is based on zero-lag synchronization of the laser with a twin system. We focus our investigation on power dropouts in the Low Frequency Fluctuations regime of a SL since they represent distinct dynamical features whose origin had been controversially discussed in the past. Our method can be adapted in principle to other nonlinear delay systems which exhibit intrinsic noise to test for traces of determinism. Our work is of general relevance for research in nonlinear dynamics, as many of our results and methods can be adapted for other delay systems and provide general insights into the characteristics of delay-coupled systems.Konstantin Hicke reconoce con gratitud la ayuda financiera concedida por el Govern de les Illes Balears (Conselleria d'Educació, Cultura i Universitats) para la formación de personal investigador. La ayuda ha sido seleccionada en el marco de un programa operativo cofinanciado por el Fondo Social Europeo. Tesis realizada en el Instituto de Física Interdisciplinar y Sistemas Complejos, IFISC (CSIC-UIB) para optar al título de Doctor, en el Programa de Física del Departamento de Física de la Universitat de les Illes Balears.Peer Reviewe

Synchronization and application of delay-coupled semiconductor lasers

The work in this thesis is focused on the complex dynamics of semiconductor laser (SL) devices which receive time-delayed feedback from an external cavity or are delay-coupled with a second semiconductor laser. We investigate fundamental properties of the dynamics and study the utilization of transient complex dynamics of a single SL arising from delayed feedback and external signal injection for a neuro-inspired photonic data processing scheme. Based on experiments and numerical modelling, we investigate systems of two coupled SLs, gaining insights into the role of laser and coupling parameters for the synchronization characteristics of these systems. We link certain features of the synchronization dynamics, like intermittent desynchronization events, to the underlying nonlinear dynamics in the coupled laser system. Our research thus combines both fundamental insights into delay-coupled lasers as well as novel application perspectives

Akustisches SpRK-Monitoring mit SEA und verteilten faseroptischen Sensoren

Im vorliegenden Bericht wurde untersucht, wie Spanndrahtbrüche in einem Brückenträger sowohl mittels Schallemissionsanalyse (SEA) als auch mit (eingebetteter) verteilter faseroptischer akustischer Sensorik (DAS) zu erkennen sind. Die Ergebnisse zeigen, dass die Bruchsignale anhand beider Messverfahren detektiert werden können. Die jeweils detektierten Drahtbrüche werden miteinander verglichen. Durch eine Gegenüberstellung werden SEA und DAS detailliert dargestellt

Different Effect of Proteasome Inhibition on Vesicular Stomatitis Virus and Poliovirus Replication

Proteasome activity is an important part of viral replication. In this study, we examined the effect of proteasome inhibitors on the replication of vesicular stomatitis virus (VSV) and poliovirus. We found that the proteasome inhibitors significantly suppressed VSV protein synthesis, virus accumulation, and protected infected cells from toxic effect of VSV replication. In contrast, poliovirus replication was delayed, but not diminished in the presence of the proteasome inhibitors MG132 and Bortezomib. We also found that inhibition of proteasomes stimulated stress-related processes, such as accumulation of chaperone hsp70, phosphorylation of eIF2α, and overall inhibition of translation. VSV replication was sensitive to this stress with significant decline in replication process. Poliovirus growth was less sensitive with only delay in replication. Inhibition of proteasome activity suppressed cellular and VSV protein synthesis, but did not reduce poliovirus protein synthesis. Protein kinase GCN2 supported the ability of proteasome inhibitors to attenuate general translation and to suppress VSV replication. We propose that different mechanisms of translational initiation by VSV and poliovirus determine their sensitivity to stress induced by the inhibition of proteasomes. To our knowledge, this is the first study that connects the effect of stress induced by proteasome inhibition with the efficiency of viral infection

Synchronization and application of delay-coupled semiconductor lasers

The work in this thesis is focused on the complex dynamics of semiconductor laser (SL) devices which receive time-delayed feedback from an external cavity or are delay-coupled with a second semiconductor laser. We investigate fundamental properties of the dynamics and study the utilization of transient complex dynamics of a single SL arising from delayed feedback and external signal injection for a neuro-inspired photonic data processing scheme. Based on experiments and numerical modelling, we investigate systems of two coupled SLs, gaining insights into the role of laser and coupling parameters for the synchronization characteristics of these systems. We link certain features of the synchronization dynamics, like intermittent desynchronization events, to the underlying nonlinear dynamics in the coupled laser system. Our research thus combines both fundamental insights into delay-coupled lasers as well as novel application perspectives

Enhanced Distributed Fiber Optic Vibration Sensing and Simultaneous Temperature Gradient Sensing Using Traditional C-OTDR and Structured Fiber with Scattering Dots

We present results demonstrating several beneficial effects on distributed fiber optic vibration sensing (DVS) functionality and performance resulting from utilizing standard single mode optical fiber (SMF) with femtosecond laser-inscribed equally-spaced simple scattering dots. This modification is particularly useful when using traditional single-wavelength amplitude-based coherent optical time domain reflectometry (C-OTDR) as sensing method. Local sensitivity is increased in quasi-distributed interferometric sensing zones which are formed by the fiber segments between subsequent pairs of the scattering dots. The otherwise nonlinear transfer function is overwritten with that of an ordinary two-beam interferometer. This linearizes the phase response to monotonous temperature variations. Furthermore, sensitivity fading is mitigated and the demodulation of low-frequency signals is enabled. The modification also allows for the quantitative determination of local temperature gradients directly from the C-OTDR intensity traces. The dots’ reflectivities and thus the induced attenuation can be tuned via the inscription process parameters. Our approach is a simple, robust and cost-effective way to gain these sensing improvements without the need for more sophisticated interrogator technology or more complex fiber structuring, e.g., based on ultra-weak FBG arrays. Our claims are substantiated by experimental evidence

Characterizing the deterministic nature of individual power dropouts in semiconductor lasers subject to delayed feedback

We implement a method to identify the deterministic nature of specific events in the dynamics of a semiconductor laser subject to time-delayed optical feedback. Specifically, we study the power dropouts in the low-frequency fluctuations regime on an individual event basis and identify whether the underlying dominant mechanism is deterministic. Our approach is based on sychronization with a twin system in a symmetric relay configuration. We investigate the dependence of the fraction of deterministically driven (i.e., synchronized) dropouts on the laser's pump current as a key parameter. Our experimental results are corroborated by numerical modeling based on rate equations. Our numerical findings also provide insights into the influence of spontaneous emission noise. © 2013 American Physical Society.This work was supported by MICINN (Spain) under Project TEC2009-14101 (DeCoDicA), by MINECO (Spain) under Project TEC2012-36335 (TRIPHOP), by the Government of the Balearic Islands within Grups Competitius, and by the European Commission under EC FP7 Project PHOCUS (Grant No. 240763). K.H. acknowledges financial support from the Government of the Balearic Islands (Department of Education, Culture, and Universities), cofunded by the European Social Fund.Peer Reviewe

Distributed Fiberoptic Sensor for Simultaneous Humidity and Temperature Monitoring Based on Polyimide-Coated Optical Fibers

Along temperature, humidity is one of the principal environmental factors that plays an important role in various application areas. Presented work investigates possibility of distributed fiberoptic humidity monitoring based on humidity-induced strain measurement in polyimide (PI)-coated optical fibers. Characterization of relative humidity (RH) and temperature response of four different commercial PI- and one acrylate-coated fiber was performed using optical backscattering reflectometry (OBR). The study addresses issues of temperature-humidity cross-sensitivity, fiber response stability, repeatability, and the influence of annealing. Acrylate-coated fiber exhibited rather unfavorable nonlinear RH response with strong temperature dependence, which makes it unsuitable for humidity sensing applications. On the other hand, humidity response of PI-coated fibers showed good linearity with fiber sensitivity slightly decreasing at rising temperatures. In the tested range, temperature sensitivity of the fibers remained humidity independent. Thermal annealing was shown to considerably improve and stabilize fiber RH response. Based on performed analysis, a 20 m sensor using the optimal PI-coated fibers was proposed and constructed. The sensor uses dual sensing fiber configuration for mutual decoupling and simultaneous measurement of temperature and RH variations. Using OBR, distributed dual temperature-RH monitoring with cm spatial resolution was demonstrated for the first time

Time-Efficient Convolutional Neural Network-Assisted Brillouin Optical Frequency Domain Analysis

To our knowledge, this is the first report on a machine-learning-assisted Brillouin optical frequency domain analysis (BOFDA) for time-efficient temperature measurements. We propose a convolutional neural network (CNN)-based signal post-processing method that, compared to the conventional Lorentzian curve fitting approach, facilitates temperature extraction. Due to its robustness against noise, it can enhance the performance of the system. The CNN-assisted BOFDA is expected to shorten the measurement time by more than nine times and open the way for applications, where faster monitoring is essential

Akustisches SpRK-Monitoring mit SEA und verteilten faseroptischen Sensoren

Im vorliegenden Bericht wurde untersucht, wie Spanndrahtbrüche in einem Brückenträger sowohl mittels Schallemissionsanalyse (SEA) als auch mit (eingebetteter) verteilter faseroptischer akustischer Sensorik (DAS) zu erkennen sind. Die Ergebnisse zeigen, dass die Bruchsignale anhand beider Messverfahren detektiert werden können. Die jeweils detektierten Drahtbrüche werden miteinander verglichen. Durch eine Gegenüberstellung werden SEA und DAS detailliert dargestellt