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To fulfill the demands of high-speed photonic applications, researchers, and engineers have been working to improve the modulation bandwidth (MBW) of semiconductor lasers. We extend our prior work on modeling a vertical-cavity surface-emitting laser (VCSEL) with multiple transverse-coupled-cavities (MTCCs) to evaluate the feasibility of boosting MBW beyond 100 GHz in this study. Because of the strong coupling of slow-light feedback from nearby lateral transverse coupled cavities (TCCs) into the VCSEL cavity, the laser has a high modulation performance. The intensity modulation response of the VCSEL design using one, two, four, and six TCCs is compared. Due to the optical-feedback (OFB) from short TCCs, which achieves 3 dB MBW reaching 170 GHz, photon–photon-resonance (PPR) is projected to occur at ultra-high frequencies beyond 145 GHz. In terms of the Fourier spectrum of the relative intensity noise (RIN), we characterize the noise features of the MTCC-VCSEL in the ultra-high bandwidth domain.

Low-coherence interferometry (LCI) is a widely used measurement technique. Typical applications of LCI range from optical low-coherence reflectometry (OLCR) to optical coherence tomography (OCT). The main advantages offered by LCI over coherent-interferometry (CI) are its usual greater capacity to spatially locating the region of the sample from where the interferometric signal came from (the volume under test — VUT), and the greater robustness to straylight. When the LCI technique is combined with the self-mixing (SM, or optical-feedback, OF) technique, it is possible to obtain additional benefits in terms of compactness, and signal to noise ratio (SNR) of the interferometric signal. Optical layouts based on guided lightwaves generally allow to further improve the robustness and performances of the system. In this review, we focus on metrological applications of guided LCI-SM and, in particular, on the use of LCI-SM to measure positions and absolute distances, flow rates, fluid velocity profiles, and thicknesses.

A tunable narrow-linewidth photonic terahertz (THz) carrier generation scheme using a distributed-Bragg-reflector-based mode-locked laser diode (MLLD) with optical feedback and mode filtering technique is proposed and experimentally demonstrated. Photonic terahertz carrier covering the D-band (110–170 GHz), and H-band (220–325 GHz) was obtained. With the assistance of the feedback loop, the optical linewidth of the MLLD was reduced from MHz to kHz level, and the heterodyning photonics carrier linewidth was reduced from 121.7 kHz to 2.1 kHz, satisfying the linewidth tolerance in the THz communication system with high-order modulation formats.

The new paradigm of parity-time symmetry in quantum mechanics has readily been applied in the field of optics with numerous demonstrations of exotic properties in photonic systems. In this work, we report on the implementation of single frequency electrically injected distributed feedback (DFB) laser diodes based on parity-time symmetric dual gratings in a standard ridge waveguide configuration. We demonstrate enhanced modal discrimination for these devices as compared with index or gain coupled ones, fabricated in the same technology run. Optical transmission probing experiments further show asymmetric amplification in the light propagation confirming the parity-time symmetry signature of unidirectional light behavior. Another asset of these complex coupled devices is further highlighted in terms of robustness to optical feedback.

International audience; Single section quantum dash (QDash) mode locked lasers (MLL) can provide a flat and broadband optical frequency comb with low energy consumption, operational simplicity and large-scale low-cost production possibilities. MLL longitudinal modes can be employed as single carriers with a regular spectral spacing in a dense wavelength division multiplexing (DWDM) link, making them promising components for next generation DWDM transceivers. However, individual modes of a MLL suffer from relatively high phase noise while high capacity coherent transmission requires carriers with low phase noise. Optical feedback, which is a well-known method to reduce the linewidth of a single mode laser, can be used to stabilize comb lasers. This paper reports on the investigation of phase noise properties of comb lines delivered from a single section QDash MLL under optical feedback and shows that each MLL longitudinal mode optical linewidth can be drastically narrowed. It enables coherent transmission with extended link budget over 50 km at Tbit/s line rates.

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., This work was supported by MINECO (Spain), through project TEC2016-80063-C3 (AEI/FEDER, UE) and by the Spanish State Research Agency, through the Severo Ochoa and María de Maeztu Program for Centers and Units of Excellence in R&D (MDM-2017-0711). The work of Dr. A. Argyris was supported by the Conselleria d’Innovació, Recerca i Turisme del Govern de les Illes Balears and the European Social Fund.

We present a design of a tunable hybrid laser based on III-V Reflective Semiconductor Optical Amplifier (RSOA) and Silicon Photonics (SiPh) external mirror that represents a good trade off between high Wall-Plug Efficiency (WPE) and high tolerance to optical feedback caused by unwanted back reflections from the rest of the SiPh chip. The sensitivity to optical feedback of different configurations, an important issue in many SiPh applications, is evaluated through the calculation of the critical feedback level based on an effective Lang-Kobayashi model and the main results are validated through numerical simulations of laser dynamics. We conclude that hybrid lasers with long effective external cavities typically designed to reduce the laser linewidth can be also exploited to improve the tolerance to spurious optical feedback.

A simple method to regulate the single-mode lasing intensity of semiconductor lasers without wavelength shift is demonstrated in this paper. The basic component is a digital micro-mirror device (DMD), which can be taken as an adjustable two-dimensional grating by its special structure. The lasing peak wavelength and peak intensity are respectively regulated by the DMD angular position and the DMD setting. The lasing peak wavelength could be tuned over by rotating the DMD. Meanwhile, the lasing peak intensity could be regulated by the DMD setting, which generates optical feedback digitally. The regulating speed is very high (up to 10 kHz) and has no wavelength shift in the lasing mode, which is more stable and faster than the conventional method.

The H2020 METRO-HAUL European project has architected a latency-aware, cost-effective, agile, and programmable optical metro network. This includes the design of semidisaggregated 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 European Telecommunications Standards Institute (ETSI) network function virtualization 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 800s and the service deployment time is under 180s., Comment: 10 pages

Non-contact absolute distance measurements are desirable in several industrial processes. For this purpose, the interferometric Self-Mixing Super Luminescent Diode technique represents a unique approach for simplicity and robustness. Thanks to optical feedback, large interference fringes, even with diffusive targets and without utilizing high-sensitivity detectors, can be obtained rejecting any stray-light. To establish the absolute target position, the most common approach is to process the interference fringes envelope by the zero-crossing technique. In this paper, we propose to process the photogenerated signal by a custom modified envelope detector to reduce the measurement uncertainty.

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.

Проблематика. Особливості ефективного розпізнавання типів поверхонь при взаємодії пальців протеза з об’єктами маніпуляції та організація системи оптичного зворотного зв’язку в модулі керування біонічної кінцівки. Мета дослідження. Розробка й апробація методу організації оптичного зворотного зв’язку для систем біонічних протезів пальців рук людини. Методика реалізації. Створена система оптичного зворотного зв’язку базується на мікроконтролерному вимірювальному пристрої з інфрачервоним оптичним випромінювачем і сенсором, еліпсоїдальному рефлекторі та штучній нейронній мережі. Результати дослідження. Здійснено порівняння ефективності застосування системи оптичного зворотного зв’язку з використанням еліпсоїдального рефлектора та без нього. Аналіз проведено класифікацією набору із дванадцяти, одинадцяти та десяти видів поверхонь досліджуваних зразків за допомогою штучної нейронної мережі. Отримана точність розпізнавання поверхонь при використанні системи без еліпсоїдального рефлектора становила 77, 82 і 87 % відповідно. Своєю чергою точність розпізнавання зразків поверхонь при застосуванні еліпсоїдального рефлектора становила 94, 98 і 100 % відповідно, що засвідчує можливість подальшого використання системи на основі фотометрії еліпсоїдальними рефлекторами для організації складових частин або повноцінних модулів зворотного зв’язку біонічних пальців. Висновки. У роботі запропоновано систему організації оптичного зворотного зв’язку на базі оптичного випромінювача і сенсора, еліпсоїдального рефлектора та штучної нейронної мережі для розпізнавання виду окремих поверхонь, з якими можуть взаємодіяти пальці біонічного протеза. Запропонована система показала прийняту достовірність розпізнавання обмеженого набору досліджуваних зразків, а ефективність її застосування може бути підвищена завдяки використанню масиву сенсорів та більш широкої вибірки даних для тренування. Background. The investigation focus is the specificity of effective recognition of surface types during the interaction between finger prosthesis and manipulation objects, and organization of optical feedback system in the control module of bionic limb. Objective. The purpose of the paper is development and testing of method of optical feedback organization in the systems of bionic prostheses of human hand fingers. Methods. The developed system of optical feedback is based on the microcontroller measuring device with infrared (IR) optical emitter and sensor, ellipsoidal reflector, and artificial neural network. Results. During the research the comparison of application effectivity of optical feedback system with ellipsoidal reflector and without one was performed. The analysis was performed by classification of set with twelve, eleven, and ten types of surfaces of investigated specimens with the means of artificial neural network. The obtained accuracy of surface recognition for the system without an ellipsoidal reflector was 77%, 82% and 87%. In turn, the accuracy of surface recognition in the application of the ellipsoidal reflector was 94%, 98%, and 100%, correspondingly. Such results prove the possibility of further use of the photometry system by ellipsoidal reflectors for organization of constructive parts or complete feedback modules of the bionic fingers. Conclusions. The organization system of optical feedback based on optical emitter and sensor, ellipsoidal reflectors and artificial neural network for recognition of kinds of separate surfaces, with which can interact bionic prostheses fingers is proposed. The proposed system proved the certainty in recognition of limited set of investigated specimens. The efficiency of such system can be improved by using sensors array and wider data set for training. Проблематика. Особенности эффективного распознавания типов поверхностей при взаимодействии пальцев протеза с объектами манипуляции и организация системы оптической обратной связи в модуле управления бионической конечности. Цель исследования. Разработка и апробация метода организации оптической обратной связи для систем бионических протезов пальцев рук человека. Методика реализации. Созданная система оптической обратной связи базируется на микроконтроллерном измерительном устройстве с инфракрасным оптическим излучателем и сенсором, эллипсоидальном рефлекторе и искусственной нейронной сети. Результаты исследования. Проведено сравнение эффективности применения системы оптической обратной связи с использованием эллипсоидального рефлектора и без него. Анализ проведен путем классификации набора из двенадцати, одиннадцати и десяти видов поверхностей исследуемых образцов с помощью искусственной нейронной сети. Полученная точность распознавания поверхностей при использовании системы без эллипсоидального рефлектора составила 77, 82 и 87 % соответственно. В свою очередь точность распознавания образцов поверхностей при применении эллипсоидального рефлектора составила 94, 98 и 100 % соответственно, что свидетельствует о возможности дальнейшего использования системы на основе фотометрии эллипсоидальными рефлекторами для организации составных частей или полноценных модулей обратной связи бионических пальцев. Выводы. В работе предложена система организации оптической обратной связи на базе оптического излучателя и сенсора, эллипсоидального рефлектора и искусственной нейронной сети для распознавания типов отдельных поверхностей, с которыми могут взаимодействовать пальцы бионического протеза. Предложенная система показала достаточную достоверность распознавания ограниченного набора исследуемых образцов, а эффективность ее применения может быть повышена путем использования массива сенсоров и более широкой выборки данных для тренировки.

Near-field imaging techniques at terahertz frequencies (0.5-10 THz), conventionally rely on bulky laser sources and detectors. Here, we devise a compact configuration for scattering near-field nanoscopy based on quantum cascade lasers (QCL) that can simultaneously act as powerful THz source and phase-sensitive detector, exploiting optical feedback interferometry [1] , (see Fig 1a ). Self-detection is based on the reinjection of the field scattered by the AFM tip into the laser cavity causing coherent interference. The near-field scattering is measured through the induced changes in the contact voltage of the QCL. By changing the path length with a movable mirror, self-mixing interference fringes are acquired and allow to retrieve both the amplitude and phase of the scattered field giving access to the complex-valued dielectric response of the sample [2] . Interestingly for imaging applications, this detection approach is fundamentally limited only by electron transport in the QCL allowing for fast image acquisition.

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.

We propose a new sensing method based on the measurement of the second-order autocorrelation of the output of micro- and nanolasers with intensity feedback. The sensing function is implemented through the feedback-induced threshold shift, whose photon statistics is controlled by the feedback level in a characteristic way for different laser sizes. The specific response offers performances which can be adapted to different kinds of sensors. We propose the implementation of two schemes capable of providing a quantitative sensing signal and covering a broad range of feedback levels: one is utilizing the evolution of $\text{g}^{(2)}$ (0), the other one is the ratio between central and side peaks in $\text{g}^{(2)}$ ( $\tau $ ). Laser-threshold-based sensing could, thanks to its potential sensitivity, gain relevance in biomolecular diagnostics and security monitoring.

Trabajo presentado en la 46th European Conference on Optical Communication (ECOC), celebrada en Bruselas del 6 al 10 de diciembre de 2020., 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.

A novel Dual-frequency Doppler LiDAR (DFDL) is presented where the dual-frequency light source is generated by using external optical feedback (EOF) effect in a laser diode (LD). By operating a LD at period-one (P1) state and choosing suitable LD related parameters, a dual-frequency light source can be achieved. Such a dual-frequency source has advantages of the minimum part-count scheme, low cost in implementation, and ease in optical alignment. Theory and system design are presented for the proposed DFDL for velocity measurement with high measurement resolution. The proposed design has a potential contribution to the Light Detection And Ranging (LiDAR) in practical engineering applications.

Aiming to realize high-speed optical transmitters for isolator-free telecommunication systems, 1.3 &mu, m p-modulation doped InGaAs/GaAs quantum dot (QD) lasers with a 400 &mu, m long cavity have been reported. Compared with the un-doped QD laser as a reference, the p-doped QD laser emits at ground state, with an ultra-low threshold current and a high maximum output power. The p-doped QD laser also shows enhanced dynamic characteristics, with a 10 Gb/s large-signal direct modulation rate and a 7.8 GHz 3dB-bandwidth. In addition, the p-doped QD laser exhibits a strong coherent optical feedback resistance, which might be beyond &minus, 9 dB.

This work reports on an investigation of the optical feedback in an InAs/InGaAs passively mode-locked quantum dot (QD) laser epitaxially grown on silicon. Under the stably-resonant optical feedback condition, experiments demonstrate that the radio-frequency linewidth is narrowed whatever the bias voltage applied on the saturable absorber (SA) is; on the other hand, the effective linewidth enhancement factor of the device increases with the reverse bias voltage on the SA, hence it is observed that such an increase influences the mode-locking dynamic and the stability of device under optical feedback. This work gives insights for stabilizing epitaxial QD mode-locked lasers on silicon which is meaningful for their applications in future large-scale silicon electronic and photonic applications requiring low power consumption as well as for high-speed photonic analog-to-digital conversion, intrachip/interchip optical clock distribution and recovery.

International audience; Measurement and 3D imaging of acoustic waves through the acousto-optic effect has recently been demonstrated by means of Optical Feedback Interferometry (OFI). In this paper we study experimentally the lower limits of detection of an acoustic wave using an OFI sensor. We show that the OFI sensor exhibits a linear response to acoustic power variations, and we obtain a lower limit of detection of 83 dB rms for a planar acoustic wave at 3 kHz. We also determine the equivalent displacement, that is seen by the OFI sensor at this pressure level, to be 96 pm. A deeper understanding of the limits of the technology and the quantification of the acousto-optic effect shall help improve the applications already created for the measurement of acoustic pressure waves using OFI.

International audience; This work reports on the optical feedback dynamics of InAs/GaAs QD lasers epitaxially grown on silicon operating in both the short and long delay regimes. Both undoped and p-doped QD lasers are considered. Whatever the external cavity length, no chaotic oscillations are observed on both samples as a result of the small α-factor observed in the silicon QD lasers. Despite that, experiments conducted in the short-cavity region raise period-one oscillation for the undoped QD laser. In addition, the transition from the short to long delay regimes can be finely covered by varying the external cavity length from 5 cm to 50 cm, and the boundaries associated to the appearance of the periodic oscillation are identified. In the short-cavity region, boundaries show some residual undulations resulting from interferences between internal and external cavity modes; whereas in the long-delay regime, the feedback ratio delimiting the boundaries keeps decreasing, until it progressively becomes rather independent of the external cavity length. Overall, our results showed that the p-doped device clearly exhibits a much higher tolerance to the different external feedback conditions than the undoped one, seeing that its periodic oscillation boundaries are barely impossible to retrieve at the maximum feedback strength of-7 dB. These results show for the first time the p-modulation doping effect on the enhancement of feedback insensitivity in both short-and long-delay configurations, which is of paramount importance for the development of ultra-stable silicon transmitters for photonic technologies.

Currently, multiple photonic reservoir computing systems show great promise for providing a practical yet powerful hardware substrate for neuromorphic computing. Among those, delay-based systems offer a simple technological route to implement photonic neuromorphic computation. Its operation boils down to a time-multiplexing with the delay length limiting the processing speed. As most optical setups end up to be bulky employing long fiber loops or free-space optics, the processing speeds are ranging from kSa/s to tens of MSa/s. Therefore, we focus on external cavities which are far shorter than what has been realized before in such experiments. We present experimental results of reservoir computing based on a semiconductor laser, operating in a single mode regime around 1550nm, with a 10.8cm delay line. Both are integrated on an active/passive InP photonic chip built on the Jeppix platform. Using 23 virtual nodes spaced 50 ps apart in the integrated delay section, we increase the processing speed to 0.87GSa/s. The computational performance is benchmarked on a forecasting task applied to chaotic time samples. Competitive performance is observed for injection currents above threshold, with higher pumps having lower prediction errors. The feedback strength can be controlled by electrically pumping integrated amplifiers within the delay section. Nevertheless, we find good performance even when these amplifiers are unpumped. To proof the relevance and necessity of the external cavity on the computational capacity, we have analysed linear and nonlinear memory tasks. We also propose several post-processing methods, which increase the performance without a penalty to speed.

Practical deployment of elastic optical networks requires key enabling technologies supporting the miniaturization of flexible optical transponders for provisioning large-bandwidth services at low-cost per users. A silicon photonics (SiP) reconfigurable optical frequency comb (OFC) demultiplexer based on passive optical filtering exhibiting a minimum spurious tone rejection (STR) of nearly 30dB at 12.5GHz tone spacing is here reported. Low power penalty due to inter-channel crosstalk (IXT) originated by finite STR is observed. Improved filter designs for reduced IXT and/or operation at 6.25GHz comb spacing are experimentally and numerically verified. By monolithic integration with SiP OFC sources and I-Q modulators the scheme has potentials for realizing ultra-compact multiple-flow optical transmitters with adaptive bandwidth and channel spacing.

Photonic neuromorphic computing is attracting tremendous research interest now, catalyzed in no small part by the rise of deep learning in many applications. In this paper, we will review some of the exciting work that has been going in this area and then focus on one particular technology, namely, photonic reservoir computing.

International audience; This paper reviews experimental investigations of the route to chaos of a semiconductor laser subjected to optical feedback from a distant reflector. When the laser is biased close to threshold, as the feedback strength is increased, an alternation between stable continuous wave (CW) behavior and irregular, chaotic fluctuations, involving numerous external-cavity modes, is observed. CW operation occurs on an external-cavity mode whose optical frequency is significantly lower than that of the solitary laser. The scenario is significantly different for larger currents as the feedback level is increased. At low feedback, the laser displays periodic or quasiperiodic behavior, mostly around external-cavity modes whose frequency is slightly larger than that of the solitary laser. As the feedback level increases, the RF and optical frequencies involved progressively lock until complete locking is achieved in a mixed external-cavity mode state. In this regime, the optical intensity and voltage oscillate at a frequency that is also equal to the optical frequency spacing between the modes participating in the dynamics. For even higher feedback, the locking cannot be maintained and the laser displays fully developed coherence collapse.

A communication scheme based on the synchronization of two chaotic quantum dot light emitting diodes (QD-LEDs) is theoretically examined. The Chaos in the QD-LED is generated by means of an optical feedback. Synchronization of the chaos is achieved by varying coupling strength between the transmitter and the receiver as unidirectional coupling. The proposed communication schemes is test a by successfully transmitting messages.

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.

In this work, a novel optoelectronic oscillator (OEO) structure is proposed for generating widely tunable photonic microwave. In this structure, an optical injection semiconductor laser (OISL) functions as an active tunable microwave photonic filter (MPF). Through controlling the injection power and frequency detuning, the OISL is driven into period-one dynamics whose oscillation frequency can be widely tuned from 10.43 to 65.82 GHz. As a result, the OISL can be regarded as a widely tunable active MPF. By introducing an optical feedback loop, the filtered bandwidth of the widely tunable active MPF can be further reduced. Taking the OISL under optical feedback as a widely tunable narrow-bandwidth MPF and a seeding laser source to establish an OEO structure, widely tunable narrow-linewidth photonic microwave can be generated. The experimental results demonstrate that widely tunable photonic microwaves ranging from 10.43 to 39.10 GHz with linewidths below 0.1 MHz and phase variances below 10-2 (rad2) can be achieved.

We present a simple and straightforward method to determine the phase shift between the amplitude modulation (AM) and the frequency modulation (FM) of a laser diode. The approach is based on the measurement of AM and FM signals produced by the dynamical response of a laser diode exposed to weak optical feedback. The AM signal is measured directly on a photodiode detecting the emitted power, and the FM signal is demodulated to intensity modulation through the edge filtering techniques using: 1) a volumetric Bragg grating or 2) a Mach–Zehnder interferometer as filters prior to the signal detection. In this letter, we show experimentally that the phase shift determination unveils the linewidth enhancement factor of semiconductor lasers as predicted by the Lang and Kobayashi theory.

We propose a model for the oscillation of a single-frequency feedback semiconductor laser based on a ring fibre interferometer. It is shown that at a certain level of feedback, the semiconductor laser generation frequency is locked by the transmission peak of the fibre interferometer. The effect is accompanied by the narrowing of the spectral line and the reduction of noises. The described results are in qualitative agreement with the experimental data.

In a self-mixing interferometer based on a diode laser, the measurement of the external reflector displacement $s(t)$ is carried out by looking at the optical-phase signal $\cos 2ks(t)$ , a signal readily detected as an amplitude modulation (AM) of emitted power. In contrast, the other available signal, sin $2ks(t)$ , a frequency modulation (FM) of the emitted field at optical frequency, is never used because difficult to recover. Recently, Contreras et al. used a narrow-band acetylene cell to convert the FM into an amplitude signal, finding it is larger and has a better SNR than the AM. In this paper, we analyze the advantages of the new CFM (converted-FM) signal, calculating both amplitude and SNR, and compare theoretical results to published experimental evidence, finding good agreement. We then present options for realizing the selective filter in different configurations and technology. Finally, we evaluate the improvement offered by CFM in a number of measurements, like sub-wavelength vibrations, digital readout displacement, and diode laser alpha factor.

Optical techniques for information security have drawn a lot of attention in recent years. The development of cryptanalysis strategies will also have a positive promotion for the cryptosystems themselves. However, most of the present publications on cryptanalysis of optical cryptosystems are focusing only on theoretical analysis but not on experimental verification. In this paper, a practical optical cryptanalysis method using wavefront shaping is proposed. Considering that the confusion and diffusion of information in the optical cryptosystem are actually caused by scattering effect of random phase mask(s), the proposed method employs a point source function and the feedback-based optimization algorithm, which can obtain an equivalent key of the optical cryptosystem. In such a way, the confusion and diffusion of the random phase mask(s) in the cryptosystem could be removed successfully. To the best of our knowledge, this is the first time the attack strategy from the perspective of wavefront shaping can be seen, and one of the biggest advantages is that it could get an equivalent key of the cryptosystem without deducing its original keys.

We discuss the sensitivity to optical feedback of a semiconductor ring laser that is made to emit in a single-longitudinal mode by applying on-chip filtered optical feedback in one of the directional modes. The device is fabricated on a generic photonics integration platform using standard components. By varying the filtered feedback strength, we can tune the wavelength and directionality of the laser. Beside this, filtered optical feedback results in a limited reduction of the sensitivity for optical feedback from an off-chip optical reflection when the laser is operating in the unidirectional regime.

International audience; Dual-frequency fiber lasers (DFFL) are shown to provide high purity beat notes for microwave signal generation and distribution. We study the stabilization of the beat from DFB DFFLs by using optical frequency-shifted feedback loop containing an electro-optic modulator (EOM). As a proof-of-principle of the method efficiency, a stabilized beat note with a phase noise level of -104 dBc/Hz at 1 kHz from a 1 GHz carrier, and of -90 dBc/Hz at 1 kHz from a 10 GHz carrier, is demonstrated when the EOM is driven by a synthesizer. Furthermore, the scheme is extended to a self-referenced scheme: a hybrid opto-electronic oscillator is obtained when the delayed DFFL beat note itself drives the EOM. Low-frequency phase noise is reduced by about 20 dB. Applications are discussed.

We report on mirrorless laser operation of Nd:YVO4 single- and double-cladding waveguides fabricated by femtosecond laser direct writing. Fundamental- (LP01) and high-order-mode (LP03, LP05) guiding and lasing have been observed in waveguides with different geometries and sizes. Double-cladding waveguides exhibit good guiding and lasing performance via inheriting advantages respectively from individual single cladding. As a result, continuous-wave lasing with a threshold as low as 59 mW is obtained, depending on the optical feedback provided only by Fresnel reflections at the waveguide end faces. By using few-layer graphene as saturable absorber, passively Q-switched operation in fabricated waveguides is also achieved., National Natural Science Foundation of China (11704201, 61775120); Consejería de Educación, Junta de Castilla y León (SA287P18); Ministerio de Economía y Competitividad (FIS2017-87970R); Natural Science Foundation of Tianjin City (17JCQNJC01600).

Funding: European Research Council (ERC) under the European Union’s Seventh Framework ERC Grant Agreement No.615613 and from the German Science Foundation (DFG) via the collaborative research center CRC787, CRC910 and GRK1558. BL acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 404943123. Mutual coupling and injection locking of semiconductor lasers is of great interest in non-linear dynamics and its applications for instance in secure data communication and photonic reservoir computing. Despite its importance, it has hardly been studied in microlasers operating at μW light levels. In this context, vertically emitting quantum dot micropillar lasers are of high interest. Usually, their light emission is bimodal, and the gain competition of the associated linearly polarized fundamental emission modes results in complex switching dynamics. We report on selective optical injection into either one of the two fundamental mode components of a bimodal micropillar laser. Both modes can lock to the master laser and influence the non-injected mode by reducing the available gain. We demonstrate that the switching dynamics can be tailored externally via optical injection in very good agreement with our theory based on semi-classical rate equations. Publisher PDF

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

The qualitative and quantitative analysis to trace gas in exhaled human breath has become a promising technique in biomedical applications such as disease diagnosis and health status monitoring. This paper describes an application of a high spectral resolution optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) for ammonia detection in exhaled human breath, and the main interference of gases such as CO2 and H2O are approximately eliminated at the same time. With appropriate optical feedback, a fibered distributed feedback (DFB) diode laser emitting at 1531.6 nm is locked to the resonance of a V-shaped cavity with a free spectral range (FSR) of 300 MHz and a finesse of 14,610. A minimum detectable absorption coefficient of &alpha, min = 2.3 &times, 10&minus, 9 cm&minus, 1 is achieved in a single scan within 5 s, yielding a detection limit of 17 ppb for NH3 in breath gas at low pressure, and this stable system allows the detection limit down to 4.5 ppb when the spectra to be averaged over 16 laser scans. Different from typical CEAS with a static cavity, which is limited by the FSR in frequency space, the attainable spectral resolution of our experimental setup can be up to 0.002 cm&minus, 1 owing to the simultaneous laser frequency tuning and cavity dither. Hence, the absorption line profile is more accurate, which is most suitable for low-pressure trace gas detection. This work has great potential for accurate selectivity and high sensitivity applications in human breath analysis and atmosphere sciences.

Distributed-feedback (DFB) fiber lasers can sustain the oscillation of two orthogonal polarizations at different frequencies, due to the fiber Bragg grating UV-induced birefringence [1]. Such dual-frequency fiber lasers (DFFL) are promising as heterodyne sources but, in the context of microwave photonics, the stabilization of the beat frequency becomes necessary. Locking the beat frequency of a dual-frequency laser to a local oscillator by optical frequency-shifted feedback (FSF) has been proved to be efficient [2], and can be applied in principle to any dual-polarization laser. Here we investigate this FSF method to an Er3+-doped DFB fiber laser, resulting in an all-fibered system emitting a stabilized beat note at 1 GHz.

International audience; The first InGaN-based LDs were reported in 1996 by Nakamura and co-workers [1] and commercialized from 1999 by the Nichia Corporation. Since then, huge efforts have been devoted to the optimization of the epitaxial layers (doping, defect concentration, shortening of the radiative lifetime, etc.). Nowadays, blue laser diodes emitting hundreds of mW are commercially available but they often exhibit multimode behaviors for both transverse and longitudinal directions. The InGaN-based laser diode technology is still in its infancy, compared to its long wavelength counterparts and only recently the first electrically pumped single mode blue laser diodes have been demonstrated [2] with a resolution limited linewidth of 11.7 GHz. At telecom wavelengths, a mature approach to force the laser diode in a single frequency regime consists in using an external feedback by means of Fiber Bragg Grating [3,4]. Nevertheless, to our knowledge, such a compact design has not been proposed for blue laser diodes yet.

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.

International audience; A relatively simple and stable microwave oscillator tunable across the full X-band is achieved. The microwave oscillations are self-generated limit-cycles produced by a laser diode subjected to optical feedback from a mirror. Further, the oscillations are stabilized utilizing two techniques in tandem, the first being a resonance effect based on locking the two inherent timescales of the laser, and the second being optoelectronic feedback. The resulting stable oscillations are fully tunable across the X-band from 5.5 to 12.1 GHz with typical phase noise performance of -107 dBc/Hz at 10 kHz offset. Further, the system is relatively simple by not requiring multiple lasers, radio-frequency filters, external RF sources, or any specialized equipment, thus, enabling a compact and low-cost microwave oscillator for applications in radar, radio over fiber, and telecommunications.

We observe the first evidence of self-mixing in THz frequency quantum cascade random lasers fabricated in both wire and irregularly squared resonator architectures with surface photonic patterns. By reflecting the emitted light back into the laser cavity and changing the external cavity length, we observe the interference fringes within the laser cavity, thereby proving evidence of self-mixing. This paves the way to detectorless speckle-free imaging applications in the far-infrared.

International audience; We explore experimentally and theoretically the dynamics of a DFB quantum well laser subject to external optical feedback from a mirror. With increasing feedback, the system exhibits the following dynamical scenario: an extremely small limit cycle appears first and is followed by a quasi-periodic regime, and then by three subsequent limit cycles with different repetition rates. This sequence of limit cycles can be associated with the change of phase of the reflected field which reveals translational symmetry and the fact of periodic solutions coexistence which we confirm numerically. The results can be useful for applications in reservoir computing with phase space of coexisting limit cycles acting as a nonlinear reservoir as well as for other applications.

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.