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An investigation of angled flip-chip integration of a singlemode 850 nm vertical-cavity surface-emitting laser (VCSEL) on a silicon nitride photonic integrated circuit (PIC) is presented. Using numerical FDTD simulations, we consider the conditions under which the VCSEL can be integrated at an angle over a grating coupler with high coupling efficiency and low optical feedback. With both coupling efficiency and feedback decreasing with increasing angle, there is a trade-off. With co-directional coupling, first-order diffraction loss sets in at a critical angle, which further reduces the coupling efficiency. No such critical angle exists for contra-directional coupling. We also experimentally demonstrate angled flip-chip integration of GaAs-based 850 nm single transverse and polarization mode VCSELs over grating couplers on a silicon-nitride PIC. At the output grating coupler, light is either collected by an optical fiber or converted to a photocurrent using a flip-chip integrated GaAs-based photodetector. The latter forms an on-PIC optical link. We measured an insertion loss of 21.9, 17.6 and 20.1 dB with a singlemode fiber, multimode fiber and photodetector over the output grating coupler, respectively.

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.

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.

Practical needs related to infrastructure management are driving optical network operators to include Raman amplification in order to improve the performance of long fiber spans. Compared to standard erbium-doped fiber amplifier (EDFA) management, Raman amplifiers require a greater degree of control and monitoring due to their distributed nature. Inevitably, this update leads to a key consideration; the introduction of additional telemetry devices with respect to standard EDFA photodiodes, resulting in an increase in required investments. In this work, we present an embedded controller architecture in combination with an ad-hoc probing procedure to manage Raman amplification within disaggregated optical networks, using only standard integrated equipment, allowing an efficient implementation without the introduction of optical channel monitors (OCMs). This proposal is validated using a fully representative experimental campaign, testing both the probing procedure on a single fiber span and the operation of a Raman amplifier using the extracted information.

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 physical bottleneck of optical design and the complexity associated with the human visual system (HVS) limits the true potential of the head-up display (HUD) for use in vehicles. A full windscreen of visual information feedback is required for driving safety, and its implementation to enhance the driving experience is one of the most significant challenges. We present an immersive augmented reality (AR) HUD concept to support future vehicle design following a human-centric design approach. The limited field of view of contemporary optical solutions can be overcome by multiple display elements tiled to utilize images over the entire windscreen and so create an immersive experience. The design takes important human factors into account and improves the operator’s driving experience. Furthermore, the images are “distributed,” meaning that the physical interface generates the images via multiple optical apertures/image sources and displays these images according to HVS requirements. These configurations are tested in a laboratory environment with a replica of a real car interior and a prototype vehicle installed with distributed multiple HUD units. The proposed concept of an immersive human–machine interface (HMI) can be further extended in various forms to other parts of the vehicle interior, including surfaces and free space, which we envisage will take place in future car designs.

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.

International audience; Experimental Self-Mixing (SM) or optical feedback interferometric signals are usually affected by additive white Gaussian noise (AWGN) and impulsive noise. Depending on SM sensing setup , these noises can significantly reduce the signal to noise ratio (SNR) of SM signals which in turn affects the measurement performance of signal processing algorithms employed for metric information retrieval. In this paper, adaptive line enhancement (ALE) technique is proposed to remove AWGN and impulsive noise from SM signals. Specifically, a recursive least squares (RLS) based ALE algorithm has been designed and the results have been compared with established methods such as high-order digital low-pass filtering and discrete wavelet transform. The comparison indicates better precision in case of use of RLS-ALE even when significant variations occur in the operating optical feedback regime and remote target velocity as well as in presence of speckle. The proposed algorithm can also estimate the SNR of SM signals belonging to weak-, moderate-, and strong-optical feedback regime with SNR ranging from 0 dB to 40 dB, with a mean absolute error of 1.35 dB and a 1.09 dB precision. Statistical analysis of noise recovered from different experimental SM signals attests the Gaussian-and impulsive-nature of noise. Thus, the proposed method also enables a simple and reliable quantitative analysis and comparison of different laser diode based SM laser sensors operating under variable optical conditions.

We measure the noise of the converted frequency-modulated (cFM) signal in a self-mixing interferometer (SMI) and confirm the theoretical prediction of a dependence of rms noise from ( $1+ C)^{-1}$ , where $C$ is the Acket feedback factor, up to a high value (i.e., $C=30$ ) in region III of Tkach and Chraplyvy feedback diagram. We also verify the minor dependence of noise from the phase factor 2 ks + atan $\alpha $ . Finally, we show that the cFM SMI easily attains an unprecedented limit of small-signal detection, with amplitudes down to 0.25 pm/ $\surd $ Hz.

The small-signal model of the incremental optical encoder introduced in this paper provides an insight on the impact of this sensor in the dynamics of the motion control loop of a motor drive. The model is derived and validated for the most commonly employed speed estimation methods: the pulse count and the elapsed time methods. Using the model, the reduction of the phase margin due to the encoder phase lag can be quantified at an early design stage. This model facilitates the design of control techniques to compensate for the phase margin reduction due to the associated feedback delays.

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.

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., We acknowledge the Spanish State Research Agency, through the Severo Ochoa and María de Maeztu Program for Centers and Units of Excellence in R&D, grant MDM-2017-0711 funded by MCIN/AEI/10.13039/501100011033. X.P. acknowledges funding from the European Union’s Horizon 2020 (713694) and the Volkswagen Foundation (NeuroQNet II).

Spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) with birefringence-induced polarization oscillations have been proposed to generate desired photonic microwave signals. Here, we numerically investigate the generation of photonic microwave signals in an optically pumped quantum dot (QD) spin-VCSEL. First, the influence of intrinsic key parameters on period-one (P1) oscillations and microwave properties is discussed. Second, the difference between microwave generation based on the quantum well (QW) and QD spin-VCSELs is analyzed by controlling the carrier capture rate that is described in the spin-flip model. The QD spin-VCSEL shows superior microwave quality in the low-frequency range (e.g., 10 GHz~20 GHz) compared with the QW spin-VCSEL. Finally, to boost the performance of the generated photonic microwave signal, optical feedback is introduced. The results show that dual-loop feedback can simultaneously narrow the microwave linewidth and suppress the side modes that are derived from the external cavity mode.

In this study, a novel distance sensing method is presented by using a semiconductor laser (SL) with optical feedback (OF) and operating the SL at a switching status happened between two nonlinear dynamic states (stable state and period-one state). In this case, without the need for any electronic or optical modulation devices, the laser intensity can be modulated in a square wave form due to the switching via utilizing the inherent SL dynamics. The periodicity in the switching enables us to develop a new approach for long-distance sensing compared to other SL with OF-based distance measurement systems and lift the relevant restrictions that existed in the systems. Moreover, the impact of system controllable parameters on the duty cycle of the square wave signals generated was investigated on how to maintain the proposed system robustly operating at the switching status. Both simulation and experiment verified the proposed sensing approach.

To further improve the performance of cavity-enhanced spectroscopy systems, a high-quality U-cavity system was established. In the process of the experiment, an asymmetric ripple effect, which is different from the previous etalon effect, was found, which seriously affects the performance of the spectral system. This unique phenomenon mainly manifests in the different amplitudes of the fluctuations of the spectral curves measured by the folding mirror and the end mirror in the U-cavity system. Based on multi-beam interference theory, we analyzed the characteristics of the transmission spectrum of each mirror in the presence of the etalon effect at the end mirror, and obtained the following conclusions: for the U-cavity system, the strength of the etalon effect of each mirror is inversely proportional to its transmission loss value, that is, the larger the loss, the smaller the ripple of the transmission spectrum, and vice versa. In order to eliminate this effect, the most effective way is to eliminate the etalon effect caused by the light feedback of the end mirror. After improving the system, the minimum detectable absorption coefficient of αmin=8.33×10−9cm−1 is obtained with this U-shape Optical Feedback Cavity-Enhanced Absorption Spectroscopy. These works are valuable references for the design of folded Cavity-Enhanced Absorption Spectroscopy systems and have potential for laser wavelength calibration and measurement of a mirror’s reflectance.

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.

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.

We propose a high-sensitivity fiber fault detection method using the feedback-delay signature of a modulated semiconductor laser. The modulated laser is directed to a fiber fault and then receives the fault echo, which, in principle, forms an external cavity feedback laser. The fault location, i.e., the external cavity length, is measured by the feedback-delay signature appearing on the laser modulation response curve. The resonance effect between the modulation frequency and external cavity frequency significantly enhanced the laser sensitivity to feedback light and then led to highly sensitive fault detection. Numerical simulations based on laser rate equations predicted that −118.1 dB sensitivity to fault echo light can be obtained.

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.

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.

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.

Quantum cascade lasers subject to tilted optical feedback produce periodic oscillations, quasi-periodic oscillations, and low-frequency oscillations. This work presents the modulation characteristics of period-one (P1) oscillations in a quantum cascade laser with tilted optical feedback. The electrical signal at the oscillation frequency is more than 50 dB higher than the noise level, and the electrical linewidth is less than 2.0 kHz. This electrical linewidth is about four orders of magnitude narrower than the optical linewidth (around 16 MHz) of the free-running laser, which suggests that the optical sidebands induced by the P1 oscillations are highly coherent with the main optical mode. In addition, the modulation depth of the optical signal is found to be in the range of 1% to 3.5%. In addition, it is verified in the simulations that the P1 oscillations induce not only amplitude modulation but also frequency modulation due to the phase-amplitude coupling effect.

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.

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 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

A brightness- and power-scalable polarization beam combining scheme for high-power, broadarea semiconductor laser diodes is investigated numerically and experimentally. To achieve the beam combining, we employ Lyot-filtered optical reinjection from an external cavity, which forces lasing of the individual diodes on interleaved frequency combs with overlapping envelopes and enables a high optical coupling efficiency. Unlike conventional spectral beam combining schemes with diffraction gratings, the optical coupling efficiency is insensitive to thermal drifts of laser wavelengths. This scheme can be used for efficient coupling of a large number of laser diodes and paves the way towards using broad-area laser diode arrays for cost-efficient material processing, which requires high-brilliance emission and optical powers in the kW-regime.

The second order photon correlation g(2)(&tau, ) of a chaotic optical-feedback semiconductor laser is precisely measured using a Hanbury Brown&ndash, Twiss interferometer. The accurate g(2)(&tau, ) with non-zero delay time is obtained experimentally from the photon pair time interval distribution through a ninth-order self-convolution correction. The experimental results agree well with the theoretical analysis. The relative error of g(2)(&tau, ) is no more than 5&permil, within 50 ns delay time. The bunching effect and coherence time of the chaotic laser are measured via the precise photon correlation technique. This technique provides a new tool to improve the accuracy of g(2)(&tau, ) measurement and boost applications of quantum statistics and correlation.

The nonlinear dynamics of semiconductor laser with coherent, as compared to incoherent, delayed optical feedback systems have been discussed and contrasted in prior research literature. Here, we report simulations of how the dynamics change as the coherence of the optical feedback is systematically varied from being coherent to incoherent. An increasing rate of phase disturbance is used to vary the coherence. An edge emitting, 830nm, Fabry Perot semiconductor laser with a long external cavity is simulated. Following this study, consideration of prior and future experimental studies should include evaluation of where on the continuum of partial coherence the delayed optical feedback sits. Partial coherence is a parameter that will affect the dynamics.

In this paper, the nonlinear dynamics of a novel model based on optically pumped spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) with optical feedback is investigated numerically. Due to optical feedback being the external disturbance component, the complex nonlinear dynamical behaviors can be enhanced and the regions of different nonlinear dynamics in size can be extended with appropriate parameters of spin-VCSELs. According to the equations of the modified spin-flip model (SFM), the comparison of bifurcation diagrams is first presented for the clear presentation of different routes to chaos. Meanwhile, numerous bifurcation diagrams in color are illustrated to demonstrate the rich dynamical regimes intuitively, and the crucial effects of optical feedback strength, feedback delay, linewidth enhancement factor, and spin-flip relaxation rate on the region evolvement of complex dynamics of the proposed model are revealed to investigate the dependence of dynamical behaviors on external and internal parameters when the optical feedback scheme is introduced. These parameters play a remarkable role in enhancing the mechanism of complex dynamic oscillations. Furthermore, utilizing combination with time series, power spectra, and phase portraits, the various dynamical behaviors observed in the bifurcation diagram are simulated numerically. Correspondingly, the powerful measure 0&ndash, 1 test is employed to distinguish between chaos and non-chaos.

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.

We investigate experimentally and numerically the existence of fast chaotic spiking in the dynamics of a semiconductor laser with ac-coupled optical feedback. The observed dynamics is chaotic in the explored range of both bias current optical feedback strength. The effects of a modulation applied to the bias current are also investigated. We eventually indicate that the observed chaotic dynamics is a good candidate to hide information to satisfy secure communications. Keywords: Chaos, Spiking, Optical feedback

An optical communication scheme based on the synchronization of two chaotic semiconductor lasers is investigated experimentally. Two schemes of optical feedback injection, bidirectional and unidirectional, have been used. Synchronization of the chaos is achieved by coupling a fraction of the transmitter’s output power to the driving current of the receiver. We present experimental results on the different routes of chaos synchronization. First is by using different current densities from master to slave-making synchronization, second is to apply different frequencies with fixed amplitude by using an external perturbation, and third is by applying a different amplitude white noises signals. Our results show that the third route has perfect results of synchronization. The last two routes are new methods and their experimental results are presented for the first time in making chaos synchronization. Finally, the quality of the synchronization was studied by different methods such as a Cross-Correlation Coefficient and Residual Chaos.

Taming laser instabilities Broad-area and high-power lasers often suffer from instabilities owing to the chaotic interference of multiple modes within the cavity. Such instabilities can ultimately limit the operation of the laser or damage the cavity. The usual approach to minimizing such instabilities is to limit the number of modes in the cavity. Bittner et al. designed a chaotic cavity that disrupts the formation of self-organized structures that lead to instabilities (see the Perspective by Yang). This approach of fighting chaos with chaos by using the boundary condition of the cavity shape may provide a robust route to stabilizing lasers at high operating powers. Science , this issue p. 1225 ; see also p. 1201

International audience; Silicon photonics has allowed cost reduction and performance improvement for optical interconnects for the past few years, and short-reach wavelength-division-multiplexed (WDM) links have recently emerged thanks to the introduction of microring modulators and filters [1-5]. Nevertheless, the promise of optical networks-on-chip foreseen in [1] has to face the integration challenges of scalable low-footprint elementary drivers and robust operation under heavy thermal stress due to self-heating of the cores with varying loads. This work presents a 3D-stacked CMOS-on-Si-photonic transceiver chip, which includes base building-blocks targeting die-to-die WDM optical communication for multicore processors: 10Gbps 2.5V pp OOK modulator driver, associated receiver, and digitally-supervised analog wavelength stabilization using microring heaters and remapping for 0-to-90°C operating range, for a total footprint of 0.01mm 2 per microring.

A single mode, tunable semiconductor laser is presented for the L band. This facetless, regrowth-free laser shows a tuning range extending from 1564nm to 1611nm, with side-mode suppression ratio values over 30dB.

We propose a method with high spatial resolution to detect fiber faults in a time-division multiplexing passive optical network (TDM-PON). A semiconductor laser serving as the probe light source is subjected to self-feedback caused by reflection at fiber faults. The feedback will induce the laser to generate chaos. Autocorrelation of the output time series shows the external cavity signature and, therefore, indicates the distance between the laser and the fiber fault. Each branch is identified by the marker that is formed by the inserted fiber Bragg grating (FBG) providing the feedback in each branch, and the faulty branch can be distinguished by the marker that has disappeared. Our proof-of-concept experiment demonstrates the identification of the faulty branch and the location of the fault point in an optical network simultaneously. This is achieved with a 6-km feeder fiber and realizes the 8-mm spatial resolution.

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., This work is supported by the National Science Foundation, USA, under the Grant no. PHY-1068789. A. Valle thanks support from Ministerio de Economía y Competitividad, Spain, under Project TEC2012-38864-C03-03 cofinanced by FEDER funds.

We experimentally achieve common-signal-induced synchronization in two photonic integrated circuits with short external cavities driven by a constant-amplitude random-phase light. The degree of synchronization can be controlled by changing the optical feedback phase of the two photonic integrated circuits. The change in the optical feedback phase leads to a significant redistribution of the spectral energy of optical and RF spectra, which is a unique characteristic of PICs with the short external cavity. The matching of the RF and optical spectra is necessary to achieve synchronization between the two PICs, and stable synchronization can be obtained over an hour in the presence of optical feedback. We succeed in generating information-theoretic secure keys and achieving the final key generation rate of 184 kb/s using the PICs. © 2017 Optical Society of America.

International audience; We report on the occurrence of extreme events (EEs) in the polarization dynamics of vertical cavity surface emitting lasers with optical feedback. We have identified two types of EEs based on numerical simulations: vectorial and scalar events corresponding, respectively, to the emission of a high-power pulse in both linear polarizations simultaneously and in single linear polarization. We show that these two types of events follow the typical statistics of rogue waves. Finally, we observe that an emission in both polarizations leads to a larger generation rate of EEs with a saturation over a wide range of feedback strength by comparison to a single-polarization mode emission

We study experimentally and theoretically a semiconductor ring laser with four filtering channels providing filtered delayed optical feedback. To describe and analyze the wavelength selection and tuning in this device, we exploit the traveling-wave model determining the evolution of optical fields and carrier density along the ring cavity and filtering branches. The numerical results agree with the experimental observations: we can reproduce the wavelength tuning, the multiple wavelength emission, and the wavelength switching speed measured in these devices. The traveling-wave model allows us to study in detail the effect of the different laser parameters and can be useful for designing the future devices.

The explosive growth of the internet during the last few decades has been enabled by two complementary innovations in optical communications: the use of multiple optical channels within a single optical fibre, and the increase in the bandwidth of individual channels to hundreds of Gbps. Further increases in overall bandwidth look to be provided by more spectrally efficient optical superchannels that use coherent sub-carriers generated using optical orthogonal frequency division multiplexing (OFDM). Yet, a cost effective way of generating these signals has not been demonstrated. One crucial, but missing piece is an effective means to separate the closely frequency spaced optical sub-carriers from the coherent optical comb before placing information on each sub-carrier, and thus creating the OFDM signal. Here, we demonstrate a flexible strategy implemented in a compact photonic integrated circuit (PIC) that is used to separate and amplify these sub-carriers using on-chip injection locking.

In this paper, we discuss the relations between the spatially-distributed traveling wave, Lang-Kobayashi, and a new multi-mode delay differential equation models for Fabry-Perot type semiconductor diode lasers with an external optical feedback. All these models govern the dynamics of the slowly varying complex amplitudes of the optical fields and carrier density. To compare the models, we calculate the cavity modes determined by the threshold carrier density and optical frequency of the steady states in all three models. These calculations show that the Lang-Kobayashi type model is in good agreement with the traveling wave model only for the small feedback regimes, whereas newly derived multi-mode delay differential equation model remains correct even at moderate and large optical feedback regimes.

Diese Arbeit soll einen Beitrag leisten zur Entwicklung neuer Sensorstrategien, basierend auf Phänomenen der optischer Rückkopplung, in Kombination mit die Intensitätsmodulation des Lasers. Optische Rückkopplung, ein Phänomen, bei dem ein Teil des vom Laser emittierten Felds in die Kavität zurückgeleitet wird, wurde früher im Kontext der Glasfaserkommunikation aufgrund der Einführung von Laser-Instabilitäten als störend angesehen. Heutzutage wird optische Rückkopplung als leistungsfähiger photonischer Sensor für praxisorientierte Anwendungen in Betracht gezogen. Optische Rückkopplung beeinflusst einige Betriebsparameter des Lasers (wie den Facettenreflektionskoeffizienten, die Verstärkung oder die Photonen- und Ladungsträgerdichte) und verändert letztendlich die emittierte Intensität. Die Beziehung zwischen optischer Rückkopplung, Intensität und Frequenzmodulation ist interessant, weil sie einen günstigen Halbleiterlaser in einen kompletten interferometrischen Sensor konvertiert, in dem der Laser als Quelle, Detektor und Medium, in dem die Interferenz stattfindet, dient, was ihn tauglich macht für berührungslose und zerstörungsfreie Detektion. Die Untersuchung in dieser Arbeit soll einen Beitrag leisten zu verschiedenen Gebieten der optischen Rückkopplungs-Interferometrie, von der theoretischen Formalisierung des Verständnisses der Transferfunktion eines Lasers unter optischem Feedback basierend auf Streutheorie, bis zur Signalverarbeitung des optischen rückgekoppelten Signals (optical feedback signal, OFS) gleichzeitig in der Zeit- und Frequenzdomäne mittels Wavelet-Transformation, um Rauschen zu entfernen, Speckle zu regeln, und die vibrationsverwandten Parameter periodischer und transienter Vibrationen alle in einem einzigen Arbeitsschritt zuextrahieren. Außerdem werden, basierend auf der Lang-Kobayashi-Gleichung, die experimentellen Befunde zu den theoretischen Vorhersagen genutzt, um den Laser sogar bei starker Rückkopplung zu stabilisieren, indem Injektionsmodulation genutzt wird, und man sich die Tatsache zu Nutze macht, dass die Frequenzabweichung in der Laseremission durch optische Rückkopplung der Frequenzabweichung durch Injektionsmodulation entgegenläuft. So fügen Sie auf, jedoch hat sich der wichtigste Beitrag dieser Arbeit war in der Tiefe noch eine weitere Variante von OFI zu entwickeln, die wir Continuous Wave Frequency Modulation Differential Optical Feedback-Interferometrie (CWFM-DOFI) benannt, der die nichtlineare Dynamik kombiniert aufgrund oF und Injektionsmodulations Lichtwegdifferenzen unter die Hälfte der Emissionswellenlänge zu messen, mit Auflösungen unter im einzelnen nm-Bereich, unter Beibehaltung der Versuchsaufbau gleiche wie die der klassischen OFI. Unter den breiten Bereich von möglichen Anwendungen hat sich die vorgeschlagene Methode getestet worden, um die Schwingung der Membran eines akustischen Wandlers zu charakterisieren und die momentane Oberflächenverschiebung eines entfernten Ziels aufgrund von akustischen Strahlung zu detektieren tion Druck, um die akustische Feldmuster über die Soll-Verschiebungs zu dem optischen Strahl zu übertragen. Diese Arbeit erweitert den Anwendungsbereich von OFI im Allgemeinen auf Anwendungen als Sensor in der Laser-Ultraschall, akustischen Holographie und photoakustische Bildgebung, unter anderem., Paradoxically optical feedback (OF) (the phenomenon in which a fraction of the optical field emitted by a laser is fed back into its cavity), that was once considered an undesired phenomenon in the context of optical fibre communications because it introduces instabilities in the laser, has proven to be extremely useful in different real world photonic sensing applications. The optical feedback affects the internal parameters of the laser, such as the facet reflection coefficient, the laser gain, the photon and carrier density, and ultimately the emitted intensity from the laser. This direct relationship among the OF, intensity and frequency modulation is appealing because it transfigures the laser into a complete interferometric set-up where the laser itself acts as source, detector and interfering media all in one, suited for non-contact, non-destructive photonic sensing. The study in this Thesis contributes to different areas of optical feedback interferometry (OFI): from the theoretical formalization of understanding the transfer function of the laser under OF based on scattering theory, to signal processing of the optical feedback signal (OFS) in time and frequency domain simultaneously using the wavelet transform for combating noise, speckle management and extraction of the vibration related parameters of periodic and transient vibrations all in a single processing step. Furthermore, based on the Lang-Kobayashi formulation, experimental evidences are shown of the ability of injection modulation to stabilize the laser even under strong feedback conditions, taking advantage of the fact that the frequency deviation produced in the laser emission by OF is in opposite direction to that of injection modulation. To add on, however, the main contribution of this Thesis has been to develop yet another variant of OFI, continuous wave frequency modulated differential optical feedback (CWFM-DOF), that combines the non-linear dynamics due to OF and that due to injection modulation to measure the optical path difference (OPD) below half the emission wavelength with resolution way below the classical optical feedback (C-OF), while keeping the experimental setup the same as that of C-OF. Among the broad range applications which would benefit from such a sensor, such as Photo-acoustic tomography (PAT) or laser ultrasonic (LUS), the proposed methodology is tested to characterize the vibration of membrane of an acoustic transducer and to measure the displacement of a metallic target due to the acoustic pressure. Thus, the Thesis extends the performance of OFI sensors and covers in detail the theoretical and experimental aspects of CWFM-DOF, and its application to the detection of very small perturbations.

International audience; The onset of the coherence collapse (CC) regime, which is incompatible with data transmission, is investigated both theoretically and experimentally in a 1.55-um InAs/InP quantum dash semiconductor laser. It is numerically shown that the filling from the excited state produces an additional term, which accelerates the route to chaos. This contribution can be seen as a perturbation that reduces the overall CC threshold.