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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.

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.

Miniaturized endoscopic scanners have had a significant impact on high-resolution optical imaging. Technological advancements in micro-electromechanical systems and optical fiber technology have resulted in various optical-mechanical configurations designed to fulfill specific requirements. However, it is still challenging to provide comprehensive, undistorted images with high-resolution images of target samples. This paper reviews the optical imaging techniques utilized in cantilever-based endoscopic scanners by analyzing and comparing their key performances, pros and cons, and corresponding optical components needed to develop the system. The concept of multimodal imaging is then highlighted by discussing its principle and current status in endoscopic scanners. We also reviewed the scanning configurations concerning their mechanical components, general structures, and drive signals for different scanning patterns. The feedback control aspect in endoscopic scanners is then highlighted. We discuss its role in mitigating undesired nonlinear vibration effects and provide a survey of the current implementations. Finally, we discuss the endoscopic scanners’ current and potential applications, artificial intelligence techniques in image reconstruction, and disease detection and provide recommendations on endoscopic scanner system design for future reference.

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.

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.

This paper presents the first vector network analyzer (VNA)-based sub-Terahertz (sub-THz) phase-compensated channel sounder at 220 330 GHz using radio-over-fiber (RoF) techniques that could enable long-range phase-coherent measurements. The optical cable solution enables long-range channel measurements at sub-THz bands, since it can effectively minimize the cable loss. This paper also proposes a novel phase compensation scheme to stabilize the phase variations introduced by optical fiber of the channel sounder to enable its application in multi-channel/antenna measurements. This proposed channel sounder is validated in back-to-back measurements under two optical cable conditions, i.e., with presence of thermal changes and mechanical stress. The phase variation introduced by the cable effects in the system is shown to be over 400_ in 220-330 GHz, compared to 15_ at 220-288 GHz and 37_ in 288-330 GHz after compensation, respectively, demonstrating the robustness and effectiveness of the developed channel sounder in practice. The developed system, which has a dynamic range of 106:7 dB, can support measurement range up to 300m (limited by the optical cable length in our system and subject to over-the-air signal transmission loss in practical environment).

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.

We present a theoretical study of the nonlinear dynamics of a long external cavity delayed optical feedback-induced interband cascade laser (ICL). Using the modified Lang–Kobayashi equations, we numerically investigate the effects of some key parameters on the first Hopf bifurcation point of ICL with optical feedback, such as the delay time (τf), pump current (I), linewidth enhancement factor (LEF), stage number (m) and feedback strength (fext). It is found that compared with τf, I, LEF and m have a significant effect on the stability of the ICL. Additionally, our results show that an ICL with few stage numbers subjected to external cavity optical feedback is more susceptible to exhibiting chaos. The chaos bandwidth dependences on m, I and fext are investigated, and 8 GHz bandwidth mid-infrared chaos is observed.

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.

The future-generation passive optical network (PON) physical layer, targeting 100 Gbps/wavelength, will have to deal with severe optoelectronics bandwidth and chromatic dispersion limitations. In this paper, largely extending our Optical Fiber Communication Conference (OFC) 2020 invited paper, we review 100 Gbps/wavelength PON downstream alternatives over standard single-mode fiber in the O- and C-bands, analyzing three modulation formats (PAM-4, partial-response PAM-4, and PAM-8), two types of direct-detection receivers (APD- and SOA + PIN-based), and three digital reception strategies (unequalized, feed-forward equalized, and decision-feedback equalized). We evaluate by means of simulations the performance of these alternatives under different optoelectronics bandwidth and dispersion scenarios, identifying O-band feasible solutions able to reach 20 km of fiber and an optical path loss of at least 29 dB over a wide wavelength range of operation. Finally, we compare two digitally precompensated modulation schemes that are highly tolerant of chromatic dispersion, showing a possible extension to C-band operation, preserving direct-detection and linear-impairment equalization at the optical network unit side.

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.

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.

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.

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.

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.

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.

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

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

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; We report experimentally and theoretically the emergence of sustained oscillations over a slow and periodic polarization switching in a laser subjected to polarization rotated optical feedback. This phenomenon originates from a clear bifurcation point that marks the transition between sustained and damped oscillations on the plateaus. Analytical study reveals also that the frequency of this new oscillatory dynamics is independent of the time delay.

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.

Laser diodes with optical feedback can exhibit periodic intensity oscillations at or near the relaxation-oscillation frequency. We demonstrate optoelectronic oscillators based on external-cavity semiconductor lasers in a periodic dynamical regime tunable over the entire $X$ -band. Moreover, unlike standard optoelectronic oscillators, we need not employ the time-dependent optical intensity incident on a photodiode to generate the microwave signal, but rather have the option of generating the electrical microwave signal directly as a voltage $V(t)$ at the laser-diode injection terminals under constant current operation; no photodiode need be involved, thus circumventing optical-to-electrical conversion. We achieve a timing jitter of $\lesssim 10$ ps and a quality factor of $\gtrsim 2\times 10^{5}$ across the entire $X$ -band, that ranges from 6.79 to 11.48 GHz. Tuning is achieved by varying the injection current $J$ .

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 demonstrate an asymmetric dual-loop feedback method to suppress external cavity side-modes induced in self-mode-locked quantum-dash lasers with conventional single-and dual-loop feedback. In this Letter, we report optimal suppression of spurious tones by optimizing the delay in the second loop. We observed that asymmetric dual-loop feedback, with large (similar to 8x) disparity in loop lengths, gives significant suppression in external-cavity side-modes and produces flat radio frequency (RF) spectra close to the main peak with a low timing jitter, compared to single-loop feedback. Significant reduction in RF linewidth and timing jitter was produced by optimizing the delay time in the second feedback loop. Experimental results based on this feedback configuration validate predictions of recently published numerical simulations. This asymmetric dual-loop feedback scheme provides simple, efficient, and cost-effective stabilization of optoelectronic oscillators based on mode-locked lasers. (C) 2017 Optical Society of America

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.

We theoretically demonstrate the possibility to synchronize polarization chaos generated by a free-running vertical-cavity surface-emitting laser (VCSEL). We highlight two distinct synchronization regimes: 1) a high-quality synchronization regime where all polarization modes and total intensity are synchronized, which shows good robustness against parameter mismatch, and 2) a "slow time-scale" synchronization where the slower part of the dynamics-that is, the random-like hopping between the two scrolls of the chaotic attractor-synchronizes while the faster oscillations remain unsynchronized. (C) 2016 Optical Society of America

The time-delay signature and the chaos bandwidth in three-cascaded vertical-cavity surface-emitting lasers have been investigated experimentally. A peak value of autocorrelation coefficient at the feedback round trip time and the ratio between this peak value and its background are used to quantitatively identify the time-delay (TD) signature of chaos. A new concept—peak to side-peak ratio is introduced for better quantification of the TD signature concealment. The peak to side-peak ratio is defined as the ratio between the peak value of autocorrelation coefficient at the TD and the peak value at a delay time other than the TD and zero delay time. Three injection cases, namely, small bandwidth, intermediate bandwidth, and wide bandwidth of the injecting chaos signals, have been used to study the effect of the bandwidth of the injecting chaos on the TD concealment. The experimental results show that the time-delay signature can be totally concealed in the slave laser subject to the intermediate bandwidth of chaotic optical injection over a wide frequency detuning range.

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.