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Terahertz (THz) external-cavity lasers based on quantum-cascade (QC) metasurfaces are emerging as widely-tunable, single-mode sources with the potential to cover the 1-6 THz range in discrete bands with watt-level output power. By operating on an ultra-short cavity with a length on the order of the wavelength, the QC vertical-external-cavity surface-emitting-laser (VECSEL) architecture enables continuous, broadband tuning while producing high quality beam patterns and scalable power output. These properties are favorable for spectroscopic applications that can benefit from large bandwidths and high output powers, such as serving as a local-oscillator (LO) for heterodyne receivers in astronomy. THz QC-lasers have garnered much attention in the past decade in the astrophysics community due to the lack of well-established THz LO sources above 3 THz. The QC-VECSEL has potential to fill this technological gap, and provide the power output levels necessary for next-generation heterodyne receiver arrays.In this thesis, we discuss the methods and challenges for designing the metasurface at various frequencies across the 1-6 THz bandwidth, and establish fundamental rules for VECSEL scaling. We discuss the methods and challenges for designing the metasurface at various frequencies across the THz bandwidth, and demonstrate single-mode lasing up to 5.72 THz. The device is enabled by a reflectarray metasurface composed of sub-wavelength metallic antennas loaded with quantum-cascade gain material. In theory, wavelength-scaling the metasurface is a matter of scaling up or down the geometric parameters proportionally, maintaining the electromagnetic properties of the structure. However, as the QC-VECSEL is scaled below 2 THz, the primary challenges are reduced gain from the QC active region, increased metasurface quality factor and its effect on tunable bandwidth, and larger power consumption due to a correspondingly scaled metasurface area. At frequencies above 4.5 THz, challenges

This article presents two dual-photodiode (PD) dif-ferential optical receivers that achieve double photodetection area to support gigabit-per-second optical wireless communication (OWC), while maintaining the receiver bandwidth. To enable differential light detection with a single incident light beam, a dual-PD OWC receiver architecture is proposed. In this architecture, two PDs are connected to the receiver complemen-tarily without sacrificing the receiver bandwidth, and meanwhile, remain properly reversely biased. In addition, an adaptive dc photocurrent cancellation (ADPC) circuit is employed to prevent the saturation of the receivers under strong and imbalanced incident light. Based on the proposed architecture, two OWC receivers are implemented, including a proposed receiver and a reference one. In the proposed receiver, a low-noise shunt-feedback transimpedance amplifier (SF-TIA) with differential-pair-based current reuse and cross-coupled resistive feedback is proposed to enhance the sensitivity. In contrast, the reference receiver employs positive capacitive feedback to improve the transimpedance amplifier (TIA) performance. Both receivers have been fabricated with a standard 180 nm CMOS process and have been wire-bonded to two PDs. Experimental results indicate that both receivers can detect optical signals with data rates up to 2 Gb/s, and the proposed receiver architecture has significantly improved the bit error rate (BER) at 1.5 Gb/s from worse than 10(-6)-10(-9) (error-free) with constrained optical power density. Moreover, the proposed receiver achieves an input sensitivity of 3.4 mu A(pp) due to the superior performance of the proposed TIA, which outperforms the sensitivity of 10.4 mu A(pp) from the reference receiver. Both sensitivities are measured at 1.5 Gb/s for a BER of 10(-9) (error-free). The power consumption of the proposed and the reference receiver are 24.3 and 19.1 mW, respectively, excluding the output driver.

We study the output of a semiconductor laser with optical feedback operated in the lowfrequency fluctuations (LFFs) regime and subject to weak sinusoidal current modulation. In the LFF regime, the laser intensity exhibits abrupt drops, after which it recovers gradually. Without modulation, the drops occur at irregular times, while, with weak modulation, they can lock to the external modulation and they can occur, depending on the parameters, every two or every three modulation cycles. Here, we characterize experimentally the locking regions and use the wellknown Lang–Kobayashi model to simulate the intensity dynamics. We analyze the effects of several parameters and find that the simulations are in good qualitative agreement with the experimental observations., This research was funded by the Spanish Ministerio de Ciencia, Innovacion y Universidades (PGC2018-099443-B-I00) and the ICREA ACADEMIA program of Generalitat de Catalunya., Postprint (published version)

As one of the most widely used light sources today, semiconductor lasers (SLs) are an important part of many optical systems, especially for sensing, communications, metrology, and storage applications. SLs have the advantages of small size, easy integration, and miniaturization. The massification of electronic devices has furthered this agenda, allowing the creation of portable systems capable of supporting optical sensing systems. Essentially, SLs are inherently nonlinear devices, in nonlinear systems, the folding and stretching behaviors of variables result in di↵erent dynamical routes. It is worth noting that under the conditions of a stable operation, an SL biased by constant current usually emits laser light with a constant intensity. However, with the introduction of external optical feedback (OF), the laser light can become unstable. SL will undergo from steady state, switching status, to period-one (P1) oscillation by crossing Hopf-bifurcation. In the P1 state, the system produces a modulation of the laser optical output power for the generation of microwave photonics (MWP) signals. In this thesis, we operate SL with OF scheme in P1 dynamics, and found that the proposed system has the great capability to achieve both displacement and absolute distance sensing applications with high resolution and wide measurement range, by using time-frequency information, relaxation oscillation information, and nonlinear dynamic characteristics carried in that SLs emit signals. The contributions of each chapter in this thesis are described in the following: In Chapter 3, we propose an SL with OF set at the P1 dynamics to generate the MWP signal for displacement sensing. Di↵erent from the traditional MWP generation method, the designed laser nonlinear dynamics are used by slightly perturbing the SL source with the help of external feedback light to make the system work in the P1 dynamic state, thereby generating regular microwave oscillation. By using the fourth-order Runge

Optical feedback (OF) refers to the beating of the frequency shifted back reflected laser emission from the remote (vibrating) object with that of incident radiation in the laser cavity cause rapid fluctuation of the laser emission. This fluctuations (also known as fringes or optical feedback signal (OFS)) contain the relevant information regarding the vibrating object. Optical feedback, and its associated variants e.g. continuous wave frequency modulated OF (CWFM-OF) has been extensively used for non-contact, non-destructive and self-aligned photonic sensing applications such as displacement, vibrations, ranging and imaging to name few. Despite its advantages, the optical feedback signal (OFS) require processing them in time and/or frequency domain to extract the relevant parameters. In this article, we present detailed frequency domain analysis of OFS. Among the many parameters we thoroughly investigate the effect of intensity modulation index (m) and external distance (L ext ) on the bandwidth of OFS and then determine the (active) filter parameters required to process them. Finally we discuss the trade-off between different parameters for optimal performance and signal processing of OFS., Peer Reviewed, Postprint (published version)

Semiconductor lasers can exhibit complex dynamical behavior in the presence of external perturbations. Delayed optical feedback, re-injecting part of the emitted light back into the laser cavity, in particular, can destabilize the laser’s emission. We focus on the emission properties of a semiconductor laser subject to such optical feedback, where the delay of the light re-injection is large compared to the relaxation oscillations period. We present an overview of the main dynamical features that emerge in semiconductor lasers subject to delayed optical feedback, emphasizing how to experimentally characterize these features using intensity and high-resolution optical spectra measurements. The characterization of the system requires the experimentalist to be able to simultaneously measure multiple time scales that can be up to six orders of magnitude apart, from the picosecond to the microsecond range. We highlight some experimental observations that are particularly interesting from the fundamental point of view and, moreover, provide opportunities for future photonic applications.

The H2020 METRO-HAUL European project has architected a latency-aware, cost-effective, agile, and programmable optical metro network. This includes the design of semi-disaggregated metro nodes with compute and storage capabilities, which interface effectively with both 5G access and multi-Tbit/s elastic optical networks in the core. In this paper, we report the automated deployment of 5G services, in particular, a public safety video surveillance use case employing low-latency object detection and tracking using on-camera and on-the-edge analytics. The demonstration features flexible deployment of network slice instances, implemented in terms of ETSI NFV Network Services. We summarize the key findings in a detailed analysis of end-to-end quality of service, service setup time, and soft-failure detection time. The results show that the round-trip-time over an 80 km link is under 800 µs and the service deployment time under 180 seconds., Horizon 2020 Framework Programme (761727); Bundesministerium für Bildung und Forschung (16KIS0979K)., Peer Reviewed, Article signat per 25 autors/es: B. Shariati, Fraunhofer HHI, Berlin, Germany / L. Velasco, Universitat Politècnica de Catalunya, Barcelona, Spain / J.-J. Pedreno-Manresa, ADVA, Munich, Germany / A. Dochhan, ADVA, Munich, Germany / R. Casellas, Centre Tecnològic Telecomunicacions Catalunya, Castelldefels, Spain / A. Muqaddas, University of Bristol, Bristol, UK / O. Gonzalez de Dios, Telefónica, Madrid, Spain / L. Luque Canto, Telefónica, Madrid, Spain / B. Lent, Qognify GmbH, Bruchsal, Germany / J. E. Lopez de Vergara, Naudit HPCN, Madrid, Spain / S. Lopez-Buedo, Naudit HPCN, Madrid, Spain / F. Moreno, Universidad Politécnica de Cartagena, Cartagena, Spain / P. Pavon, Universidad Politécnica de Cartagena, Cartagena, Spain / M. Ruiz, Universitat Politècnica de Catalunya, Barcelona, Spain / S. K. Patri, ADVA, Munich, Germany / A. Giorgetti, CNIT, Pisa, Italy / F. Cugini, CNIT, Pisa, Italy / A. Sgambelluri, CNIT, Pisa, Italy / R. Nejabati, University of Bristol, Bristol, UK / D. Simeonidou, University of Bristol, Bristol, UK / R.-P. Braun, Deutsche Telekom, Germany / A. Autenrieth, ADVA, Munich, Germany / J.-P. Elbers, ADVA, Munich, Germany / J. K. Fischer, Fraunhofer HHI, Berlin, Germany / R. Freund, Fraunhofer HHI, Berlin, Germany, Postprint (author's final draft)

Both bacterial viability and concentration are significant metrics for bacterial detection. Existing miniaturized and cost-effective single-mode sensor, pH or optical, can only be skilled at detecting single information viability or concentration. This paper presents an inverter-based CMOS ion-sensitive-field-effect-transistor (ISFET) sensor array, featuring bacterial pH detection which is an indicator of viability. The proposed design realizes pH detection using the native passivation layer of CMOS process as a sensing layer and configuring an inverter-based front-end as a capacitive feedback amplifier. This sensor array is assisted by optical detection which reveals bacterial concentration, and temperature sensing. The optical detection is enabled using the leakage current of a reset switch as a response to a light source. While in reset mode, the inverter-based amplifier works as a temperature sensor that could help to reduce temperature influences on pH and optical detection. All the functionalities are realized using one single inverter-based amplifier, resulting in a compact pixel structure and largely relaxed design complexity for the sensor system. Fabricated in 0.18um standard CMOS process, the proposed CMOS sensor array system achieves an amplified pH sensitivity of 221mV/pH, an improved sensor resolution of 0.03pH through systematic noise optimization, a linear optical response, and a maximum temperature error of 0.69. The sensing capabilities of the proposed design are demonstrated through on-chip Escherichia coli (E. coli) detection. This study may be extended to a rapid and cost-effective platform that renders multiple information of bacterial samples. IEEE

The dynamics of semiconductor lasers with optical feedback and current modulation has been extensively studied, and it is, by now, well known that the interplay of modulation and feedback can produce a rich variety of nonlinear phenomena. Near threshold, in the so-called low frequency fluctuations regime, the intensity emitted by the laser, without modulation, exhibits feedback-induced spikes, which occur at irregular times. When the laser current is sinusoidally modulated, under appropriate conditions, the spikes lock to the modulation and become periodic. In previous works, we studied experimentally the locked behavior and found sub-harmonic locking (regular spike timing such that a spike is emitted every two or three modulation cycles), but we did not find spikes with regular timing, emitted every modulation cycle. To understand why 1:1 regular locking was not observed, here, we perform simulations of the well-known Lang–Kobayashi model. We find a good qualitative agreement with the experiments: with small modulation amplitudes, we find wide parameter regions in which the spikes are sub-harmonically locked to the modulation, while 1:1 locking occurs at much higher modulation amplitudes., This research was funded by the Spanish Ministerio de Ciencia, Innovacion y Universidades (PGC2018-099443-B-I00) and the ICREA ACADEMIA program of Generalitat de Catalunya., Peer Reviewed, Postprint (published version)

The back-reflection of emitted laser beam (optical feedback, also know as selfmixing) from various external interfaces are sufficient to cause instability, and prohibiting its use in various fields such as communication, spectroscopy, imaging to name a few. So it is desirable to study the laser dynamics and the conditions causing it to be stable in spite of strong optical feedback. With the aid of mathematical formulation, simulation and backed by experimental evidences, it is demonstrated that the frequency deviation of the laser emission due to current (intensity) modulation alters the dynamic state and boundary conditions of the system such that even under large optical feedback strength, the laser may attain stability and retain single modal state. The frequency deviation resulting from former is shown to modify the phase of the system in opposite direction to that induced by the later, showing that there exists an optimal modulation current which compensates the effect of optical feedback and may be used to retain the laser in single modal stationary state. The method thus provides a methodology to avoid optical feedback-induced instability in semiconductor lasers by using the proper amplitude of current (intensity) modulation., Peer Reviewed, Postprint (published version)

Excitable lasers that mimic neuronal activity can be building blocks of ultra-fast neuro-inspired information processing systems, which can revolutionize the fields of optical signal processing, optical computing and artificial intelligence. To implement such photonic neurons, we must first identify low-cost and energy-efficient lasers whose excitable dynamics mimics neuronal dynamics. Here we conduct an experimental study of the dynamics of a diode laser with optical feedback from an external cavity. We focus on the response of the laser when is under weak periodic perturbations that are implemented via direct modulation of the laser pump current. We consider sinusoidal and pulsed waveforms. The dynamics of the laser intensity is compared with the dynamics of the membrane potential of a neuron, which is simulated with the FitzHugh-Nagumo (FHN) model. The analysis of the statistics of the time intervals between dropouts of the laser intensity (optical spikes) and of the time intervals between the neuron's action potentials (or spikes) unveils similarities, and also differences. The analysis of the spike rate reveals a variation with the amplitude and with the frequency of the external signal that is similar for both, the laser and the FHN neuron. Therefore, in terms of the spike rate, the laser response to a weak periodic signal mimics the response of a FHN neuron, and thus diode lasers with optical feedback can be used to implement photonic neurons. A drawback of this implementation is the length of the feedback cavity, which prevents on-chip integration., This work was supported in part by the Spanish Ministerio de Ciencia, Innovación y Universidades (PGC2018- 099443-B-I00). C. M. also acknowledges support of the ICREA ACADEMIA, Generalitat de Catalunya., Peer Reviewed, Postprint (author's final draft)

We show numerically and experimentally that strong optical injection can enhance the operating bandwidth of semiconductor lasers with optical feedback in a photonic time-delay reservoir computing configuration. Its operating conditions can be significantly expanded while maintaining competitive computational performance in a time-series prediction task.

Semiconductor lasers (SLs) that are subject to delayed optical feedback and external optical injection have been demonstrated to perform information processing using the photonic reservoir computing paradigm. Optical injection or optical feedback can under some conditions induce bandwidth-enhanced operation, expanding their modulation response up to several tens of GHz. However, these conditions may not always result in the best performance for computational tasks, since the dynamical and nonlinear properties of the reservoir might change as well. Here we show that by using strong optical injection we can obtain an increased frequency response and a significant acceleration in the information processing capability of this nonlinear system, without loss of performance. Specifically, we demonstrate numerically that the sampling time of the photonic reservoir can be as small as 12 ps while preserving the same computational performance when compared to a much slower sampling rate. We also show that strong optical injection expands the reservoir’s operating conditions for which we obtain improved task performance. The latter is validated experimentally for larger sampling times of 100 ps. The above attributes are demonstrated in a coherent optical communication decoding task.

We propose a new confocal device for flow profiling in microcapillaries. A viewfinder system is developed using a visible light microscope, allowing focusing with high precision an 830 nm Fabry-Perot laser diode on a microchannel. By means of a novel confocal approach, the Doppler shift produced by the particles of a turbid liquid moving in the focal plane can be measured in real time using the well-known self-mixing effect. The resolution of this device is characterized in function of the full width at half maximum of the Gaussian frequency peak related to the self-mixing signal in the frequency domain. Velocity measurements for flow rates from 0.2 to 1.6 mL/min are presented, and the results demonstrate that the method reduces the phase noise and the effects of the out-of-focus particles, allowing straightforward flow profiling in microchannel structures, Peer Reviewed, Postprint (published version)

Consistency is a powerful concept to characterize and classify the behavior of driven dynamical systems, therefore playing an essential role for the understanding of information processing in and by complex photonic systems. Here, we discuss two different experimental configurations of semiconductor laser systems with delayed optical feedback allowing for a unifying view via the detailed characterization and comparison of consistency and synchronization properties. The first configuration comprises two unidirectionally coupled semiconductor lasers, which has found considerable interest for applications in encrypted communication. The second configuration consists of a single laser with two optical delay loops of significantly different lengths, designed such that only one loop is active at a time and that allows to study replays of injected optical signals. We show that, in terms of three characteristic correlation measures-consistency correlation, transformation correlation, and spurious correlation-the dynamical features of the two different experiments are very similar and how the two configurations are connected. Our approach shows that consistency allows to understand and relate various chaos synchronization and stability properties. We particularly discuss the experimental results in the context of a previously established analytical framework, providing a common dynamical interpretation of consistency and chaos synchronization in delay-driven laser systems.

Ecological interface design (EID) was originally developed in the context of process control but has been extended into many domains where technology has resulted in both changing work demands and increased opportunities for improved interface applications. This paper gives an overview of the application of the EID to the control of vehicle locomotion, either from within the vehicle, as a driver or a pilot, or from the outside, as an operator or a (air traffic) controller. It discusses lessons learned from the application of the EID for the vehicle locomotion control task and focuses on how the methodology can be applied to this domain. Specific issues identified are that the planning and control of a vehicle simultaneously spans multiple time scales and that the interface must be designed considering the format in which the control input is defined. Also, due to the extensive standardization of the instrumentation and training certification, changes introduced by the new displays must initially be additional to the existing displays. Chosen representations must also be shown in a format that matches the current instrumentation and the directly observable outside world., Control & Simulation, Control & Operations

External optical feedback can severely deteriorate the performance of semiconductor lasers. This paper proposes an integrated laser design that can withstand tens of percent of off-chip feedback, without requiring the integration of magneto-optic materials. The proposed laser consists of a ring cavity with a weak intracavity optical isolator. Sufficient gain difference between clockwise and counter-clockwise modes leads to unidirectional laser oscillation. Any reflected light is returned to a mode that is below threshold. This significantly reduces interactions between the feedback and the lasing mode. A rate-equation analysis is presented to show that the rin changes less than a factor 2 when less than -0.1 dB of the light is fed back into the laser and when intracavity isolation is 10 dB. Linewidth and optical output power change approximately 0.1% for these values.

An InP-based, monolithically integrated multiwavelength laser with optical feedback is presented. We demonstrate the performance of the dual-wavelength operation. Single-mode lasing is obtained for each of the two channels within a temperature range from 16 to $30$ °C and an injection current range from 30 to 70 mA without mode-hopping. This is due to the combined filtering functions of an arrayed waveguide grating and a distributed Bragg reflector. A method that makes use of weak optical feedback is demonstrated to improve the stability of each single-mode. With this method, sustained relaxation oscillations that are excited by on-chip parasitic reflections are damped and linewidths in both channels are narrowed to around 400 kHz compared to the linewidth of 1 MHz that is obtained when no feedback is applied. The suppression ratio of the relaxation-oscillation-induced side peaks is measured to be over 45 dB for two simultaneously operated channels.

Self-mixing interferometry (SMI), or also called optical feedback interferometry (OFI) is a promising non-contact sensing technology. It is based on the self-mixing effect which occurs when a fraction of light back-reflected or back-scattered by an external target re-enters the laser internal cavity. A sensing system by using SMI technique consists of a laser diode (LD), a photodiode (PD) packaged at the rear of the LD, a lens and a target. The LD is called self-mixing laser diode (SMLD). This configuration reflects a minimum part-count scheme, which is useful for engineering implementation. Compared to traditional interferometry, e.g., Michelson or Mach-Zehnder interferometry, SMI has the advantages of simplicity in system structure, low cost in implementation, and ease in optical alignment. Using these merits, SMI technology has been developed for various applications, such as measurement of displacement, vibration, velocity, imaging, material related parameters, laser related parameters, etc. Most of the SMI-based applications and behavior study on SMLD system are based on the analytical SMI model, which is derived from the steady-state solution of the Lang and Kobayashi (L-K) equations, or from the classical three-mirror model, by assuming the system operates in stable mode, i.e. both the electric field and carrier density in an LD with a stationary external cavity can reach constant state after transient period. However, undamped relaxation oscillation (RO) may occur under some operation conditions, e.g. it is found an SMLD in moderate feedback regime exhibits undamped RO. The moderate feedback regime is quite commonly employed by researchers. Based on our in-depth study, the behavior of an SMLD system with undamped RO cannot be described by the existing analytical SMI model. The laser intensity (called as sensing signal) from such SMLD system shows some new characteristics. In order to differentiate the conventional SMI signals, we name the SMI signals with un

In this paper, we investigate the possibility of using optical injection to efficiently suppress the time-delay (TD) signatures of chaotic signals in a large experimentally accessible parameter range of semiconductor ring lasers (SRLs). We also study how this optical injection can improve the signal bandwidths. The injection signal is obtained from a master SRL with either optical self- or cross-feedback. For optical self-feedback configurations, it is found that the suppression of TD signatures is similar to what has been found in injected Fabry–Perot semiconductor lasers, i.e. narrow range of parameters with respect to the detuning and injection strengths. For cross-feedback configurations, however, the TD signatures can be suppressed in a wide range of parameters; meanwhile, the bandwidths are significantly improved for the same range of parameters. This is particularly useful for the security in chaos-based communications and also for generating random bits with improved properties., SCOPUS: ar.j, info:eu-repo/semantics/published

IEEE Optical feedback interferometry (OFI) based flowmetry enables simple, robust, self-aligned and low cost systems to measure the fluid flow velocity with reasonable accuracy. The particle concentration in the fluid causes significant changes in the signal of OFI sensors. While the spectral analysis of the particle induced Doppler shift remains as the most usual approach to determine the flow properties, different processing algorithms have been proposed in order to evaluate the average flow velocity within the measurement volume. In this paper, the validity of the commonly used methods with regards to particle concentrations and flow rates is verified., Postprint (updated version)

Summary form only given. During the last decade reservoir computing (RC) has proven to be a powerful machine learning concept using recurrent networks to process sequential information streams [1]. Lately, the concept of RC was drastically simplified to reduce hardware requirements, thus making machine learning concepts more obtainable to apply in actual physical systems [2]. RC has been implemented in photonic configurations and has efficientìy processed analog optical signals following simple schemes and minimal training overhead. Especially the realization using a semiconductor laser with time-delayed optical feedback has shown the potential of all-optical machine learning, utilizing signals with transient states at the GHz regime [3].In this work we exploit the properties of a small-scale RC in order to improve the detection capabilities of lightwave communication signals of very low quality. The RC has a limited number of virtual nodes (N=33) and a total internal time-delay of 1.65ns in order to allow fast post-processing. Its design follows an all-optical configuration, including a discrete-mode semiconductor laser (SL) that emits at 1550nm and an optical feedback cavity, as presented in [3]. We numerically simulate the lightwave communication signals by considering an onoff keying modulated binary stream at 10Gb/s that has undergone 2000 km of fiber transmission (20 segments of 100-km spools including optical amplification and dispersion compensation). At such distances, direct threshold detection results in BER values higher than 0.1. Even when applying offline post-processing with a ridge regression training algorithm, which considers the patterns of the detected bits within the complete detection period, the detection BER value improves only slightly to 0.031. When we employ the RC, the transmitted signal is optically injected into the RC's SL, resulting in a nonlinearly transformed output which depends directly on the operating conditions of the reservoir

The length of quantum communication channels is limited by photons loss during their propagation in optical bres, which scales exponentially with the distance. Here we focus on a way to overcome this limitation: the quantum repeater. The communication channels are split into shorter segments connected by nodes. Each node consists of quantum memories and single photon sources. Entanglement is generated between neighbouring nodes and then extended to both ends of the communication channel via entanglement swapping operations. In the DLCZ protocol the quantum memory and the single photon source are combined into a heralded on-demand single photon source with memory. Our group is currently investigating such a photon source, at room temperature on the D2 line of Caesium-133: the DLCZ protocol. This protocol is based on atomic ensemble quantum memories in which a collective atomic excitation is created and retrieved on demand with high e ciency. The original proposal relies on cold atoms to achieve long memory time. However we follow a proposal by Borregaard et al. [5] based on a room temperature atomic vapour in a micro cell, enabling millisecond memory time, which is order of magnitudes longer than typical room temperature memories. This can be achieved by making use of motional averaging. The motional averaging requires that all atoms interact homogeneously with the beam. This is achieved by letting them cross the beam many times during the pulses and made possible by an anti-relaxation para n coating. The atoms are initially prepared in a stretched state by optical pumping. The writing step is realised by a weak laser transferring a single unknown atom of the ensemble to another ground state via spontaneous Raman scattering. The detection of a scattered photon heralds the creation of a delocalised atomic excitation. A reading step e ciently transfers the atomic excitation into a single photon which is detected. This scheme o ers the important advantages of co

We study experimentally a semiconductor laser operating in a feedback-induced regime known as low frequency fluctuations (LFFs), in which the laser emits a spiking output that resembles the spikes of biological neurons. We analyze the response to a weak periodic signal that is directly applied to the laser pump current, as a function of the frequency of the signal, and discuss the observations in relation to the response of sensory neurons., Peer Reviewed, Postprint (published version)

Gaze stabilization is a fundamental function for humanoid robots. Stabilizing the image being perceived facilitates the processing and thus the interpretation of visual data. In parallel, fixation should also guarantee that the visual target remains centered in the image. Several approaches exist to address the problem of gaze stabilization: closed-loop algorithms processing the visual data or inferring head movements from kinematic measurements, and feed-forward algorithms anticipating head movements from the lower-body commands. In this contribution, we develop a feed-forward controller addressing both image stabilization and target fixation into a unified framework. The addition of a virtual linkage between the robot eye and the visual target offers to elegantly rephrase the gaze control problem as the classical control of a redundant serial robot manipulator. Furthermore, a novel method to estimate the self-induced optical flow based on the robot kinematics - extended with this virtual linkage - is developed. It is then possible to solve the redundancy (i.e. guaranteeing target fixation) through a minimization of the optical flow (i.e. achieving image stabilization). This method is validated in simulation with a model of the head of the ARMAR IV humanoid. It is shown that the proposed controller offers to accurately estimate and minimize the optical flow, while keeping the visual target exactly in the center of the image.

We demonstrate a novel method that makes an efficient use of laser nonlinear dynamics when subject to optical self-injection for subwavelength displacement sensing purposes. The proposed methodology combines two different phenomena taking place inside the laser cavity: optical self-injection, which results in optical feedback interference, and laser continuous wave frequency modulation, giving rise to a wavelength sweeping effect in the laser's emission. We present a combination of these phenomena to measure vibration amplitudes below lambda/2 with the resolutions of a few nanometers, bandwidth dependent upon the distance of external target, amplitude, and frequency of current modulation. The basic theoretical details and a mathematical model are presented for the developed measurement principle. Experimental results with the system working as a vibrometer to measure a target vibration of amplitude lambda/5 (137.5 nm) with a mean peak-to-peak error of 2.4 nm just by pointing the laser diode onto the target and applying some signal processing are also demonstrated., Postprint (author's final draft)

The nonlinear dynamics of a semiconductor laser with optical feedback (OF) combined with direct current modulation of the laser is demonstrated to suffice for the measurement of subwavelength changes in the position of a vibrating object. So far, classical Optical Feedback Interferometry (OFI) has been used to measure the vibration of an object given its amplitude is greater than half the wavelength of emission, and the resolution of the measurement limited to some tenths of the wavelength after processing. We present here a methodology which takes advantage of the combination of two different phenomena: continuous wave frequency modulation (CWFM), induced by direct modulation of the laser, and non-linear dynamics inside of the laser cavity subject to optical self-injection (OSI). The methodology we propose shows how to detect vibration amplitudes smaller than half the emission wavelength with resolutions way beyond ¿/2, extending the typical performance of OFI setups to very small amplitudes. A detailed mathematical model and simulation results are presented to support the proposed methodology, showing its ability to perform such displacement measurements of frequencies in the MHz range, depending upon the modulation frequency. Such approach makes the technique a suitable candidate, among other applications, to economic laser-based ultrasound measurements, with applications in nondestructive testing of materials (thickness, flaws, density, stresses), among others. The results of simulations of the proposed approach confirm the merit of the figures as detection of amplitudes of vibration below ¿/2) with resolutions in the nanometer range., This work is partially supported by European Union and Spanish Ministry of Science and Innovation through project DPI2011-25525., Peer Reviewed, Postprint (published version)

Illumination in scattering media provides a general means to provide optical diagnosis in a noninvasive, painless and low cost approach, which has pushed forward the interest of the field both in biomedical and industrial applications. Several biophotonics techniques are based on the use of the therapeutic window of skin, where diffusion of light is dominant and the classical geometrical optics approach gets lost, with only radiometric methods being valid in practice. A comparable analysis is valid for industrial applications where the analysis of inclusions in scattering e, Self-mixing interferometry is a measurement technique based on the effect that in a laser the reinjection of emitted light back-reflected into its cavity has on the the properties of the laser itself. In diode lasers, optical feedback effects are particularly powerful, and can be employed as a powerful metrological tool. Due to its self-alignment and lack of any external elements, self-mixing interferometry is very robust and low cost, and can offer an adequate trade-off between performance and cost for a wide range of sensing applications. In this work, self-mixing interferometry has been proposed, studied and implemented for vibrometry and flowmetry in combination with conventional microscopy to provide the former technique with the lateral and axial resolution of the latter. Besides, the self-mixing interferometry phenomena has been extensively reviewed, and a model for complex interferometric external cavities has been developed.

We propose and demonstrate theoretically that vertical-external-cavity surface-emitting lasers (VECSELs) with external flat mirrors can be stabilized by applying a periodic spatiotemporal modulation of the pump current. Such pump modulation is shown to suppress the pattern-forming instabilities (modulation instabilities), which eventually results in stable beam emission. A modified Floquet linear stability analysis is used to characterize the dynamics of the modulated system and to evaluate its stabilization performance. Stability maps identify the regions in parameter space for complete and partial stabilization of VECSELs operating in different regimes depending on the external-cavity length. In particular, the stabilization method is shown to operate most efficiently in Class-A laser limit (for relatively long VECSEL resonators), while it becomes ineffective in Class-B laser limit (for relatively short resonators). The stabilization effect is further confirmed through direct integration of the dynamical equations., Peer Reviewed, Postprint (published version)

We investigate experimentally how changes in the external cavity length and dc current affect the mean interspike-interval (ISI) in a modulated semiconductor laser with optical feedback operating in the low-frequency fluctuations regime. The variation of the mean ISI with the modulation frequency is shown to be more pronounced when time delay and dc current allow for low spike rate. We use the method of ordinal symbolic analysis to examine how time correlations (among three, four and five consecutive laser spikes) change with the spike rate. This method is able to capture subtle changes, otherwise hidden in the dynamics. We find that higher spike rates wash out the effects of the modulation in the time correlations. Simulations using the Lang and Kobayashi model are in good qualitative agreement with the experimental observations., Peer Reviewed, Postprint (author's final draft)

Dynamics of a multi-transverse mode vertical-cavity surface-emitting laser is studied experimentally in a wide parameter range of optical feedback and current modulation. While the orthogonal polarizations manifest anticorrelated feedback dynamics, dynamics of different transverse modes with orthogonal polarizations do not exhibit a clear correlation property. This may be attributed to spatial hole burning effect. As the current modulation becomes strong, both polarization and modal dynamics are modulation dominated. When the modulation frequency is close to the external cavity resonance frequency or its harmonics, feedback dynamics is enhanced. For the modulation frequency close to half integer multiples of the external cavity resonance frequency, feedback feature can be suppressed. The minimum modulation amplitude for suppressing feedback dynamics is measured for each polarization and one of the transverse modes in the polarization, and the results are discussed. Interplay of relaxation oscillation, optical feedback, and current modulation is observed and measured. Our results are compared to the theoretical predictions.

Within the framework of this two-year project, detailed experimental and numerical studies have been performed, focusing on the interplay of noise and nonlinear dynamics. Specifically, we used a method of time-series analysis, referred to as symbolic ordinal analysis, to demonstrate that serial correlations present in the output intensity of a semiconductor laser with optical feedback operating in the low-frequency fluctuations regime share common features with serial correlations present in the inter-spike-intervals (ISIs) of biological neuronal systems. The symbolic dynamics underlying the sequence of inter-dropout-intervals in the laser intensity has the same statistical features, in terms of distribution of symbolic patterns, as in ISI sequences of biological neurons. Therefore, semiconductor laser-based optical neurons could provide a novel, inexpensive and controllable experimental set up that could allow for improving our understanding of neuronal activity. By establishing a direct connection between these different dynamical systems our research offers new perspectives, both, in photonics and in neuroscience. For example, the optical setup could be used to analyze the role of external forcing in neuronal spike sequences. On the hand, optical neurons constructed from inexpensive semiconductor lasers could lead to the development of novel neuro-inspired optical computing devices (threshold detectors, logic gates, signal recognition, etc.)., The original document contains color images.

Quantum dot lasers have been shown to have greatly enhanced stability in the feedback configuration thanks to a high damping of the relaxation oscillations and they display different dynamics to those of conventional semiconductor lasers. For high feedback levels in conventional devices one obtains Low Frequency Fluctuations: sharp dropouts in intensity and subsequent gradual build-ups. Standard low frequency fluctuation-like traces are conspicuous by their absence in studies of feedback with quantum dot devices. We experimentally examine single mode quantum dot lasers at high feedback levels with a long delay and observe regular pulse-trains with a period equaling the external cavity round-trip time where each pulse features a distinctive broad trailing edge plateau. The distinctive pulse shape is very similar to the recently published strong pulse-asymmetry in two-section, passively mode-locked quantum dot lasers where this asymmetry was shown to result from the creation of different modal groups. We attribute the pulses in our experiment to the same phenomenon: each pulse corresponds to a simultaneous excitation of a number of the external cavity modes. We consider a model tailored specifically for quantum dot lasers with strong optical feedback and find it reproduces the experimentally observed trains extremely well. © 2014 SPIE., SCOPUS: cp.p, info:eu-repo/semantics/published

Semiconductor lasers with continuous-wave optical injection display a rich variety of behaviors, including stable locking, periodic or chaotic oscillations, excitable pulses, etc. Within the chaotic regime it has been shown that the laser intensity can display extreme pulses, which have been identified as optical rogue waves (RWs), and it has also been shown that such extreme pulses can be completely suppressed via direct modulation of the laser current, with appropriated modulation amplitude and frequency. Here we perform a numerical analysis of the RW statistics and show that, when RWs are not suppressed by current modulation, their probability of occurrence strongly depends on the phase of the modulation. If the modulation is slow (the modulation frequency, f(mod), is below the relaxation oscillation frequency, f(ro)), the RWs occur within a well-defined interval of values of the modulation phase, i.e., there is a, Peer Reviewed, Postprint (published version)

The increasing amount of data being generated in different areas of science and technology require novel and efficient techniques of processing, going beyond traditional concepts. In this paper, we numerically study the information processing capabilities of semiconductor lasers subject to delayed optical feedback. Based on the recent concept of reservoir computing, we show that certain tasks, which are inherently hard for traditional computers, can be efficiently tackled by such systems. Major advantages of this approach comprise the possibility of simple and low-cost hardware implementation of the reservoir and ultrafast processing speed. Experimental results corroborate the numerical predictions. © 1995-2012 IEEE.

Wavelength beam combining of diode lasers produces the intensity and brightness necessary for metal cutting and welding that previously required more powerful and more expensive laser systems. The wavelength beam-combining fiber-coupled diode laser is the first direct-diode laser that is bright enough to cut and weld metal. Although diode lasers are the highest efficiency lasers, until recently their brightness has been relatively low compared to that of other kW-class lasers used in industrial applications. Lincoln Laboratory's fundamental breakthrough in wavelength beam-combining (WBC) has enabled the development of a system that has the laser brightness necessary for industrial use., Published in Tech Notes, 2012. This technology won a 2012 R&D 100 Award.

This report results from a contract tasking Universite Libre de Bruxelles as follows: Quantum dot (QD) lasers have attracted a lot of attention because of their low threshold currents, low line width enhancement factors, and temperature insensitivity. Although the self-assembled dots have provided an enormous stimulus to work in this field, there remain a number of critical issues involving their growth and formation: greater uniformity of size, controllable achievement of higher quantum dot density, and closer dot-to-dot interaction range will further improve laser performance. Better understanding of carrier confinement dynamics and capture times, and better evaluation of loss mechanisms, will further improve device characteristics. Because of the large variety of QD lasers currently tested in laboratories, there are several obstacles in the characterization and modeling of these devices that need to be overcome. A delay-differential equation model of a passively mode-locked quantum-dot laser originally proposed by Vladimirov and Turaev has been used recently by AFRL/RYDP to simulate asymmetric pulse intensities which have been observed experimentally. The model equations for the passively mode-locked QD laser include delay and exponential nonlinearities and are too complicated for analytical studies. This has motivated very recently investigations of simpler experimental set-ups as turn-on experiments, the optically injected laser or the laser subject to a delayed optical feedback. In collaboration with N. Usechak and V. Kovanis at AFRL/RYDP and the experimental group of L.F. Lester (University of New Mexico), we propose a multi-disciplinary approach of the stability of QD lasers subject to optical feedback. The group of T. Erneux at the Universite Libre de Bruxelles (ULB) will be responsible for the modeling and analysis of rate equation models. Numerical simulations will be shared by the Brussels and AFRL groups., AFRL-AFOSR-UK-TR-2012-0002. The original document contains color images.

We study experimentally and numerically a new dynamical regime in the operation of semiconductor ring lasers (SRLs) subject to delayed optical feedback. When employing an asymmetric feedback scheme, we find experimentally that the SRL can show square-wave intensity oscillations with a 50 % duty cycle. In this scheme, where the output in one direction is delay-coupled to the other direction but not vice versa, the laser switches regularly between the clockwise (CW) and counter-clockwise (CCW) propagating modes. The measured period of the square-waves is slightly longer than twice the roundtrip time in the external cavity. We analyze the regularity and the shape of the square-waves as a function of the pumping current and the feedback strength. For higher pump currents on the SRL,the output displays stochastic mode hopping between the square waves attractor and stable unidirectional operation in the CW mode. To understand the origin of this dynamical regime, we rely on numerical simulations based on the Lang-Kobayashi equations. We demonstrate a novel mechanism leading to square wave oscillations based on the cross-feedback overcoming backscattering asymmetries present in the device's structure. Our numerical results are in close agreement with the experimental ones. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE)., SCOPUS: cp.p, info:eu-repo/semantics/published

SCOPUS: ch.b, info:eu-repo/semantics/published

[no abstract]

En este proyecto se presenta la caracterización de un sistema de láseres en configuración maestro-esclavo, llevados a comportamiento caótico mediante realimentación óptica y se estudiarán sus diagramas de sincronización. Se analizarán los efectos de los parámetros más importantes, tales como la realimentación, el detuning o la posición del espejo y su influencia en la correcta sincronización. Además se hará una rápida referencia a otros estudios y la posibilidad de una encriptación de datos en una portadora caótica

We analyze the intrinsic time scales of the chaotic dynamics of a semiconductor laser subject to optical feedback by estimating quantifiers derived from a permutation information approach. Based on numerically and experimentally obtained times series, we find that permutation entropy and permutation statistical complexity allow to extract important characteristics of the dynamics of the system. We provide evidence that permutation statistical complexity is complementary to permutation entropy, giving valuable insights into the role of the different time scales involved in the chaotic regime of the semiconductor laser dynamics subject to delay optical feedback. The results obtained confirm that this novel approach is a conceptually simple and computationally efficient method to identify the characteristic time scales of this relevant physical system.

We have experimentally studied polarization instabilities in the multi-transverse-mode regime of a vertical- cavity surface-emitting laser subject to polarized optical feedback. A dynamical regime that is similar to the transition from the so called low frequency fluctuation (LFF) to coherence collapse (CC) in the single-transverse-mode VCSEL is found and investigated. The role of higher order transverse modes is to increase the irregularity of the dynamics as shown experimentally and numerically.

We present a detailed numerical study of the dynamics of two unidirectionally coupled semiconductor lasers subject to filtered optical feedback. We show that this chaos-based communication scheme allows for an improvement in the decoding of encrypted messages in comparison with the conventional feedback scheme. We found that the performance of the system is optimal when the closed-loop configuration and similar filters are used in the emitter and receiver systems.

We numerically find that higher privacy and security in all-optical chaos-based communication systems can be achieved when the closed-loop scheme is used in the receiver architecture, instead of the more traditional open-loop scheme. Our results show that the extraction of the encoded message demands a larger amplitude of the message when the open-loop receiver is used than when the closed loop is implemented. A large amplitude of the encoded message compromises the performance and security of the system.

Microstructure manipulation is a fundamental process to the study of biology and medicine, as well as to advance micro- and nano-system applications. Manipulation of microstructures has been achieved through various microgripper devices developed recently, which lead to advances in micromachine assembly, and single cell manipulation, among others. Only two kinds of integrated feedback have been demonstrated so far, force sensing and optical binary feedback. As a result, the physical, mechanical, optical, and chemical information about the microstructure under study must be extracted from macroscopic instrumentation, such as confocal fluorescence microscopy and Raman spectroscopy. In this research work, novel Micro-Opto-Electro-Mechanical-System (MOEMS) microgrippers are presented. These devices utilize flexible optical waveguides as gripping arms, which provide the physical means for grasping a microobject, while simultaneously enabling light to be delivered and collected. This unique capability allows extensive optical characterization of the structure being held such as transmission, reflection, or fluorescence. The microgrippers require external actuation which was accomplished by two methods: initially with a micrometer screw, and later with a piezoelectric actuator. Thanks to a novel actuation mechanism, the “fishbone”, the gripping facets remain parallel within 1 degree. The design, simulation, fabrication, and characterization are systematically presented. The devices mechanical operation was verified by means of 3D finite element analysis simulations. Also, the optical performance and losses were simulated by the 3D-to-2D effective index (finite difference time domain FDTD) method as well as 3D Beam Propagation Method (3D-BPM). The microgrippers were designed to manipulate structures from submicron dimensions up to approximately 100 µm. The devices were implemented in SU-8 due to its suitable optical and mechanical properties. This work demonstrates two prac

This report results from a contract tasking Universite Libre de Bruxelles as follows: Lasers are ubiquitous today, mostly in the form of semiconductor lasers (SLs), which are characterized by smallness in size, weight, cost of production, and power requirements. Optical networks depend on SLs for generation, amplification, and distribution of the light that transmits voice, video, and data. However, an unfortunate property of these devices is their high susceptibility to unavoidable optical feedback, such as reflection from any optical element of the system surrounding the laser. Even tiny amounts of optical feedback (less than 0.01%) can cause the laser to enter a state of erratic pulsating instabilities and irregular chaotic transitions. Systematic experimental studies started recently. Fourier spectra measurements showed the gradual emergence of new frequencies as the feedback rate is progressively increased. But time series are still delicate to obtain because of the extremely small time scale of the intensity pulsations. Most of our understanding of these instabilities came from numerical simulations of simple model DDEs where the delay is the round-trip time of the light from the laser to the mirror and back to the laser. We propose to investigate the bifurcation possibilities of these lasers by combined analytical and numerical techniques. The goal is to find simple guidelines on the properties of the pulsating solutions and/or frequencies. The properties of several types of feedback will be compared. Finally, we shall investigate the case of two mutually injected lasers because of a series of experiments studied at Kirtland AFB.

This paper presents a novel neural network signal interpolation technique in order to eliminate the noise and disturbance associated with the self-mixing signal observed from optical feedback self- mixing interferometry (OFSMI). The proposed technique aims to improve the accuracy for displacement and moving track measurement of a target. The performance of the proposed approach is evaluated by both simulation and experimentation, with simulation revealing a measuring accuracy of A/25 for weak feedback and J20 for moderate feed back.