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Distributed Bragg Reflector semiconductor lasers are ideally suited for quantum technology applications due to their high efficiency, small footprint, and tunability in combination with the frequency stability provided by an integrated frequency selective element. Here we present the design, fabrication, and electro-optical characterization of DBR lasers optimized for strontium-based quantum technology applications at 689.449 nm. The devices achieved an optical output power of up to 88 mW, four times more than previously reported, as well as a spectral linewidth of 0.4 MHz. [ABSTRACT FROM AUTHOR]

Coherent reception becomes an interesting option when data rates in time-division-multiplexed (TDM) passive optical networks (PONs) grow beyond 50 Gbit/s. Controlling the wavelength, i.e., the optical frequency, and the phase of the laser acting as local oscillator (LO) is one of the main technical challenges in the design of coherent TDM PONs. In the optical network units (ONUs), low-cost lasers are required, which come at the expense of wavelength variations and drifts over multiple nanometers due to fabrication imperfections, and temperature variations. This contradicts the requirement of wavelength-stable LOs in coherent receivers. The use of a wavelength locker circuit and a temperature controller is considered as too complex for applications in access networks. In this work, we propose a novel colorless coherent architecture with high resilience to ONU laser wavelength drifts of up to $\pm$ 4 nm ($\pm$ 0.5 THz) for future 100 Gbit/s PON. It allows the use of distributed feedback lasers at the ONU side. This is rendered possible by generating a frequency comb with carefully chosen free spectral range in a quantum-dash mode-locked laser diode at the optical line terminal. In upstream operation, the frequency comb serves as an LO, whereas the same information is modulated onto all comb lines for the case of downstream. As a result, the ONU laser can drift over the entire comb bandwidth without substantial performance penalty. We experimentally demonstrate downstream and upstream operation with an aggregated raw data rate of 96 Gbit/s, respectively. We further introduce advanced digital signal processing (DSP) methods including a coarse frequency offset compensation (CFOC) and a multiple-input multiple-output (MIMO) equalizer to improve the performance of our concept. We show that the receiver sensitivity can be increased by 3 dB for a high-bandwidth receiver when using a 6 × 2 MIMO equalizer scheme. A 4 × 2 MIMO equalizer scheme enables colorless reception even with a limited-bandwidth receiver. [ABSTRACT FROM AUTHOR]

A wavelength-division-multiplexing (WDM)-visible laser light communication (VLLC) and white-lighting ring network with a 150-Gbit/s accumulative transmission rate at central station (CS), a 50-Gbit/s transmission rate at optical node, and a 604-lux white-lighting at CS is successfully demonstrated. Red, green, and blue laser diodes employing two-stage injection locking and optoelectronic feedback techniques are utilized to afford the dual functions of high-speed VLLC links and white-light illumination at reading/writing-level. By deploying optical add-drop multiplexing scheme, this newly-built WDM-VLLC and white-lighting ring network is promising since it allows a point-to-multipoint link and a two-way operation in free-space transmission. Impressively low bit error rate of 10−9, clear PAM4 eye diagrams, and qualified white-lighting for reading and writing are achieved through 7.5 m/9 m/10.5 m/12 m VLLC link with 5 m plastic optical fiber transmission. Such constructed WDM-VLLC and white-lighting ring network shows a potential one for the evolution of high-speed VLLC with white-lighting for reading/writing. [ABSTRACT FROM AUTHOR]

A vertical-cavity surface-emitting laser (VCSEL) under polarization selected and rotated optical feedback has been proposed and numerically investigated to generate neuron-like spiking dynamics and to show the potential functionalities in spiking information processing. The proposed optical-feedback VCSEL-neuron employs only one laser to simulate one neuron, while conventional optical-injection VCSEL-neurons often require multiple lasers. The input stimulus is conducted by modulating the feedback strength while the output response is monitored by measuring the intensity in the initially non-lasing polarization. On the one hand, the generation of tonic spiking in the form of periodic pulses is related to the frequency difference between the laser's two orthogonal polarization modes. On the other hand, the generation of phasic spiking in the form of a single abrupt pulse is attributed to the transient response at the onset of self-injection locking. Systematically investigations reveal that the frequency of tonic spiking is roughly proportional to the stimulus strength of input, while the critical stimulus strength of phasic spiking is roughly proportional to the birefringence rate of laser. The potential functionalities of proposed VCSEL-neuron are further verified by single neuron information processing tasks. • A novel single-VCSEL spiking neuron is proposed. • The proposed neuron needs only one laser thanks to the light stored in feedback loop. • The tonic spiking is due to the cavity anisotropies of VCSEL. • The phasic spiking is due to transient response at onset of self-injection locking. • The single-VCSEL neuron has similar performances with multi-VCSEL neurons. [ABSTRACT FROM AUTHOR]

• It is theoretically proved that the −1st comb tooth power is related with the modulation depth and the frequency difference between f m (the modulation frequency) and f rep (the free-running repetition rate). • An optical closed-loop injection locking technology is realized using the −1st comb tooth as error signal for the soliton microcomb repetition rate (f rep) long-term stabilization. • The SSB phase noise of the closed-loop locked f rep have no obvious change in long-term, which is about 20 dB lower compared with the open-loop locking case. And the Allan deviation of the closed-loop locked f rep maintains at 1.8 × 10-13@0.1 s for a long time, which improves by three orders of magnitude compared with the open-loop locking case. We demonstrate an optical closed-loop injection locking technology for the soliton microcomb repetition rate (f rep) stabilization. Using the power of the −1st comb line (−1st represents the first comb tooth on the left side of the pump laser) as an error signal, the pump laser frequency is auto-tuned to ensure f rep locked at an optimal level. After injection locking for 2 h, the single-sideband (SSB) phase noise of the closed-loop locked f rep decreases by 20 dB compared with the open-loop locked f rep within the offset frequency range of 20 Hz to 30 kHz. After locking one and a half hours, the Allan deviation of the closed-loop locked f rep reaches 1.8 × 10−13@0.1 s, which improves by three orders of magnitude. The experimental results prove the feasibility of the optical closed-loop injection technology for long-term f rep stabilization. The proposed scheme has excellent locking performance, simple structure and low cost, which has the potential application for stable microwave generation, precision ranging, etc. [ABSTRACT FROM AUTHOR]

Microwave photonic (MWP) sensing and measurement are envisioned to be a promising alternative to the conventional pure electronic or optical solutions. A semiconductor laser (SL) with external optical feedback (EOF) operating in a period-one (P1) dynamic state contributes a new implementation architecture for MWP systems. However, designing such a SL system to generate frequency-modulated MWP sensing signals through traditional Lang–Kobayashi (L–K) equations requires extensive computational effort to derive the system control parameters (SCP), making real-time adjustment of the SCP impossible in cases where it is needed. This paper proposes an effective design approach based on machine learning. A feedforward neural network (FNN), in conjunction with a gradient descent algorithm, is employed to fast and accurately ascertain the SCP, offering a solution readily applicable in the system design. Both simulation and experiment are conducted to validate the proposed approach. • Proposes a machine learning approach to optimize control for period-one state. • Solves computational bottlenecks of Lang–Kobayashi (L–K) equation method. • Uses a neural network with gradient descent to determine control parameters quickly. • Experimental validation confirmed the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Line intensities for carbon dioxide are measured with a novel spectroscopic approach, assisted by an optical frequency comb synthesizer for frequency calibration purposes. The main feature of the spectrometer consists in the exploitation of optical feedback from a V-shaped high-finesse optical resonator to effectively narrow a distributed feedback diode laser at the wavelength of 2 μm. Lasergas interaction takes place inside an isothermal cell, which is placed on the transmission from the cavity. High quality, self-calibrated, absorption spectra are observed in pure CO2 samples at different gas pressures, in coincidence with three lines of the R-branch of the ν1 + 2ν2 + ν3 band. Line intensities are determined using a global fitting approach in which a manifold of spectra are simultaneously analyzed across the range of pressures between 5 and 100 Torr, sharing a restricted number of unknown parameters. Various sources of uncertainty have been identified and carefully quantified, thus leading to an overall uncertainty ranging between 0.17% and 0.23%. The measured values are in a very good agreement with recent ab initio predictions. [ABSTRACT FROM AUTHOR]

We present the development of an interferometer capable of making contactless measurements of vibrations. The results show the we achieve micro- and/or nano-metric measurements without the stabilization of the laser. While there are multiple techniques to achieve this objective, in this case, we use a method whose main virtue is the low component count and the self-alignment capacity. The method is based on the optical feedback effect in a laser diode which relieson the use of an internal reference for calibration.

In allusion to the privacy and security problems, a secure multi-channel information protection scheme based on an integrated optical device is proposed in this paper. The information to be encrypted and shared is converted into a QR code. For supporting the multi-channel encryption, a 1- n w encryption algorithm is employed, which possesses the capability to map the original image information into n w seemingly random cipher images. In terms of hardware, an ultra-compact optical encryption device is designed, which consists of two rows of ring resonators coupled to the waveguide. This novel encryption device can output ten cipher images, each transmitted on a separate channel. Meanwhile, the vertical-cavity surface-emitting laser subject to optical injection and optical feedback is researched to generate optical chaos sequences, which are introduced for key generation and QR code encryption. Ultimately, combining the 1- n w encryption algorithm and optical chaos, information protection is implemented based on integrated optics. The simulation results demonstrate the practical feasibility and remarkable effectiveness of the proposed scheme. Furthermore, various security and robustness analyses are performed, and the results reveal that the proposed information protection scheme has a high level of security and robustness. This work is of great significance for the development of optical encryption chips and provides potential applications for secure data sharing. [ABSTRACT FROM AUTHOR]

This article presents a dual laser-based optical feedback cavity-enhanced absorption spectroscopy technique using polarization division multiplexing. The technique involves two laser beams with orthogonal polarization that enter a V-shaped cavity from two injection directions. This allows for independent control of feedback phase and eliminates the need for an optical component to combine the beams. The two lasers are detected separately at the two ends of the cavity. Additionally, a differential process is proposed to mitigate residual interference between the two lasers. By employing this technique, simultaneous detection of CH 4 , CO 2 and H 2 O is achieved, resulting in a detection sensitivity of approximately 2 × 10−11 cm−1. Despite using a moderate cavity finesse in our spectrometer, the minimal detectable concentration for the gases is comparable to that of superior gas analyzers using cavity ringdown spectroscopy (CRDS). • A dual laser-based optical feedback cavity-enhanced absorption spectroscopy technique using polarization division multiplexing is presented. • A differential process to mitigate residual interference between the two beams are proposed. • An excellent detection sensitivity of 2×10-11 cm-1 has been achieved, despite using a moderate cavity finesse. [ABSTRACT FROM AUTHOR]

Numerical simulation of generation of a random fiber laser proves that a model, considering only major physical effects, is capable of reproducing the characteristic line spectrum consisting of narrow localized spectral modes near the generation threshold. Lifetime of narrow spectral modes is shown to amount to tens of full cavity pass times or 1 ms by order of magnitude, that well corresponds to experimental observations. It was ascertained that addition of technical noise by implementation of a random phase of backscattered wave does not change the generation regime significantly. Possibility of narrow generation well above the threshold is demonstrated in case of negligible nonlinear effects. Essential role of Rayleigh backscattering in its formation is emphasized by comparison with corresponding ideal fiber amplifier with no feedback, characterized under the same conditions by smooth spectrum. [Display omitted] • Narrow modes emerge in radiation of a random fiber laser due to optical feedback. • Random fiber laser's spectrum acquires line pattern beyond the impact of nonlinearity. [ABSTRACT FROM AUTHOR]

Reservoir Computing (RC), an evolution from Recurrent Neural Networks (RNN), not only represents a unique machine learning paradigm, but also serves as a neuromorphic framework that mirrors the intricate cortical circuits of the human brain. This paper proposes another new photonic RC system based on four basic photonic reservoir computing architectures (single photonic RC system, the parallel photonic RC system, the dual-feedback loop-based photonic RC system and the mutually coupled photonic RC system). System proposed uses optical injection for signal input and retains two parallel responsive semiconductor lasers (R -SLs) with self-feedback loops. Meanwhile, two relatively independent R -SLs are mutually coupled via two coupling lines. The new photonic RC system adds only two sections of fiber compared to the parallel photonic RC system and the mutually coupled photonic RC system. The experiments show that the system proposed has significant advantages on the nonlinear auto regressive moving average series tasks, the chaotic time series prediction tasks and the waveform classification task. More importantly, the memory capacity of system proposed can be adjust by controlling the delay time of the self-feedback loops, so it has higher memory capacity to handle the higher order nonlinear auto regressive moving average tasks (NARMA20 and NARMA30) after optimizing the parameters. • The proposed system integrates the advantages of the dual-feedback loop-based and mutually coupled photonic RC systems. • The proposed system can adjust its memory capacity to suit various short-term memory needs. • The inclusion of mutual coupling and self-feedback structures in the proposed system enriches its dynamic characterization. [ABSTRACT FROM AUTHOR]

Optical frequency combs in the terahertz frequency range are long-awaited frequency standards for spectroscopy of molecules and high-speed wireless communications. However, a terahertz frequency comb based on a low-cost, energy-efficient, and room-temperature-operating device remains unavailable especially in the frequency range of 0.1 to 3 THz. In this paper, we show that the resonant-tunneling-diode (RTD) oscillator can be passively mode-locked by optical feedback and generate a terahertz frequency comb. The standard deviation of the spacing between the comb lines, i.e., the repetition frequency, is reduced to less than 420 mHz by applying external bias modulation. A simulation model successfully reproduces the mode-locking behavior by including the nonlinear capacitance of RTD and multiple optical feedback. Since the mode-locked RTD oscillator is a simple semiconductor device that operates at room temperature and covers the frequency range of 0.1 to 2 THz (potentially up to 3 THz), it can be used as a frequency standard for future terahertz sensing and wireless communications. The authors report passive mode-locking and frequency-comb generation induced by optical feedback in the resonant-tunneling-diode terahertz oscillator, a semiconductor-based oscillator covering the frequency range of 0.1 to 2 THz. [ABSTRACT FROM AUTHOR]

Frequency modulated continuous wave laser ranging (FMCW LiDAR) enables distance mapping with simultaneous position and velocity information, is immune to stray light, can achieve long range, operate in the eye-safe region of 1550 nm and achieve high sensitivity. Despite its advantages, it is compounded by the simultaneous requirement of both narrow linewidth low noise lasers that can be precisely chirped. While integrated silicon-based lasers, compatible with wafer scale manufacturing in large volumes at low cost, have experienced major advances and are now employed on a commercial scale in data centers, and impressive progress has led to integrated lasers with (ultra) narrow sub-100 Hz-level intrinsic linewidth based on optical feedback from photonic circuits, these lasers presently lack fast nonthermal tuning, i.e. frequency agility as required for coherent ranging. Here, we demonstrate a hybrid photonic integrated laser that exhibits very narrow intrinsic linewidth of 25 Hz while offering linear, hysteresis-free, and mode-hop-free-tuning beyond 1 GHz with up to megahertz actuation bandwidth constituting 1.6 × 1015 Hz/s tuning speed. Our approach uses foundry-based technologies - ultralow-loss (1 dB/m) Si3N4 photonic microresonators, combined with aluminium nitride (AlN) or lead zirconium titanate (PZT) microelectromechanical systems (MEMS) based stress-optic actuation. Electrically driven low-phase-noise lasing is attained by self-injection locking of an Indium Phosphide (InP) laser chip and only limited by fundamental thermo-refractive noise at mid-range offsets. By utilizing difference-drive and apodization of the photonic chip to suppress mechanical vibrations of the chip, a flat actuation response up to 10 MHz is achieved. We leverage this capability to demonstrate a compact coherent LiDAR engine that can generate up to 800 kHz FMCW triangular optical chirp signals, requiring neither any active linearization nor predistortion compensation, and perform a 10 m optical ranging experiment, with a resolution of 12.5 cm. Our results constitute a photonic integrated laser system for scenarios where high compactness, fast frequency actuation, and high spectral purity are required. Stable and tunable integrated lasers are fundamental building blocks for applications from spectroscopy to imaging and communication. Here the authors present a narrow linewidth hybrid photonic integrated laser with low frequency noise and fast linear wavelength tuning. They then provide an efficient FMCW LIDAR demonstration. [ABSTRACT FROM AUTHOR]

We demonstrate real-time broadband multi-Gb/s electrical RF synthesizer-free millimeter-wave (MMW) signals generation and wireless transmission at the 5G new radio (NR) frequency band of 47 GHz based on analog radio-over-fiber (A-RoF) fronthaul. This is enabled by a low noise, highly correlated, monolithic C-band semiconductor InAs/InP quantum-dash (QDash) dual-wavelength distributed feedback (DW-DFB) laser. One laser mode is encoded using 4-/6-GBaud multilevel quadrature amplitude modulation (M-QAM) (16-/32-/64-QAM) baseband data signals, the other lasing mode is used as an optical local oscillator for optical-heterodyne remote up-conversion to a MMW carrier of 47.27 GHz. Consequently, optical baseband modulated data signals with data capacity up to 36 Gb/s (6-GBaud × 64-QAM) are transmitted through back-to-back (BtB) and 25-/50-km of standard single mode fiber (SSMF) before the MMW carrier is optically synthesized remotely for free space wireless data transmission and detection over up to 9-m. The end-to-end MMW-over-fiber (MMWoF) wireless link is thoroughly characterized exhibiting promising error-vector-magnitude (EVM) and bit-error-rate (BER) values. The 4-/6-GBaud 16-QAM MMWoF wireless links achieve EVMs down to 6.32%/7.33%, 6.71%/7.78%, and 7.35%/8.91% through BtB, 25-km, and 50-km SSMF, respectively. Similarly, the EVM for 32-QAM and 64-QAM links is observed to be 5.56%/6.56% and 6.05%/6.62%, respectively. Moreover, in each case, the calculated BER is below the forward error correction (FEC) limit of 3.8 × 10−3. The results corroborate the potential and viability of the QDash DW-DFB laser as a simple, efficient and cost-effective alternative to individual laser sources for deployment in broadband photonic MMWoF fronthaul systems of 5G wireless networks. [ABSTRACT FROM AUTHOR]

Laser emissions at 1.6–1.7 μm band have captured considerable attention in recent years. However, limited by the available emission spectrum of typical rare-earth-ion doped gain fibers, it is extremely difficult to realize highly stable laser output in this wavelength region with a simultaneous high spectral purity and high output power. To address these problems, a cost-effective robust random fiber lasing scheme is proposed to generate the high-power and high-spectral-purity laser output at 1.69 μm. The maximum output power is 7.55 W and the spectral contrast between the output lasing and the pump is as high as 24.3 dB. Both the short-time temporal characteristics and the long-time output power fluctuations are measured, which shows excellent stability and robustness of the laser configuration. This work provides an alternative approach to realize high-performance 1.6–1.7 μm band lasing output which is of particular significance for potential applications. [ABSTRACT FROM AUTHOR]

Ultra-stable lasers serve as the backbone for the most advanced optical metrology scientific experiments, enabling the ability to laser interferometry or atomic spectroscopy at the highest levels of precision, thanks to the rapid development of laser wavelength stabilization techniques based on optical or electrical feedback from an external reference such as absorption line or optical cavity. With the increasing interest in making these scientific systems portable and applying it outside of the laboratory, it still remains an open question as to how to realize a laser source that can reach the high wavelength stabilization and still remain sufficiently compact and portable for field use. Here, we describe a wavelength stabilization fiber laser with intracavity reference mechanism, by utilizing the beat note of dual modes inside the laser cavity as the laser wavelength drift reference signal. A laser wavelength drift less than 5 kHz and ADEV 10−13 level at integration time scales from 0.01s to 1000s is achieved, which is to-date the best results for the laser wavelength stabilization without the external frequency reference. The outcome of this work presents a new way to achieve an ultra-stable laser with a simpler, lower cost feature. It offers new insights to promote the highest precision optical metrology scientific application outside of the laboratory, and also gives the possibilities of applying the ultra-stable laser source into a wider range of industrial application. [ABSTRACT FROM AUTHOR]

Integrated polarization stabilizers along with corresponding stabilizing algorithms have been investigated for years to tackle the polarization fluctuation issue in polarization dependent systems such as photonics integrated circuits and coherent optical communication systems. Here, we propose and demonstrate a novel integrated polarization stabilizer which is composed of an in-line polarimeter and two cascaded Mach-Zehnder interferometers-based polarization converter, with a footprint of 2.8 mm × 0.8 mm. Benefitting from the integrated in-line polarimeter and two controlling algorithms, namely feed-forward tracking algorithm and feedback tracking algorithm, the stabilizer can track the incoming light with arbitrary state of polarization in one-time manipulation. The whole process consumes about 30 μs, which is approaching the limitation of the response time of the adopted thermal phase shifters, making the proposed device the fastest one with thermal phase shifters on silicon photonics platform. Meanwhile, the incoming light is endlessly tracked in real time and 99% converted to horizontal linear polarized light. [ABSTRACT FROM AUTHOR]

Interpolating video frames involving large motions remains an elusive challenge. In case that frames involve small and fast-moving objects, conventional feed-forward neural network-based approaches that estimate optical flow and synthesize in-between frames sequentially often result in loss of motion features and thus blurred boundaries. To address the problem, we propose a novel Recurrent Motion-Enhanced Interpolation Network (ReMEI-Net) by assigning attention to the motion features of small objects from both the intra-scale and inter-scale perspectives. Specifically, we add recurrent feedback blocks in the existing multi-scale autoencoder pipeline, aiming to iteratively enhance the motion information of small objects across different scales. Second, to further refine the motion features of the highly moving objects, we propose a Multi-Directional ConvLSTM (MD-ConvLSTM) block to capture the global spatial contextual information of motion from multiple directions. In this way, the coarse-scale features can be utilized to correct and enhance the fine-scale features through the feedback mechanism. Extensive experiments on various datasets demonstrate the superiority of our proposed method over state-of-the-art approaches in terms of clear locations and complete shape. [ABSTRACT FROM AUTHOR]

We demonstrate numerical analysis of the dynamics and noise of semiconductor laser (SL) with optical feedback (OFB) and nonlinear gain (NLG). The simulations are based on an improved time-delay rate equations model that takes into account the multiple round-trips of the lasing field in the external cavity. The temporal trajectory of the photon number, bifurcation diagrams, and relative intensity noise (RIN) is used to perform this analysis. The results show that when NLG included the Hopf bifurcation point moved towards the direction of increasing OFB strength. Period doubling, or sub-harmonics operation, is the route to chaos of SL depending on whether NLG is included or not. In the periodic oscillation (PO) and route to chaos regimes, including the NLG causes a significant frequency shift relative to the frequency in the case without NLG. Under strong OFB, the inclusion of NLG changes chaotic dynamics to continuous wave operation or PO depending on the OFB strength and characterized by RIN near to or higher than the RIN of the solitary laser. At high-frequency regime, the RIN is characterized by the compound cavity frequency or the external cavity frequency depending on the NLG whether included or not. [ABSTRACT FROM AUTHOR]

An active feedback network‐based bandwidth extension technique for CMOS differential transimpedance amplifier (TIA) is proposed in 0.18 µm CMOS process technology. The design consists of three stages in differential mode. The first stage is a common‐source amplifier that minimizes noise. A common collector stage is used for level shifting and buffering in the second stage. The third stage is a differential amplifier that provides additional gain. In addition to these three stages, an active CMOS negative feedback circuit is used for extending the bandwidth. The proposed design achieves a gain of 45.2 dBΩ with a 3 dB bandwidth of 21.23 GHz. The active feedback circuit provides an additional bandwidth of 7.3 GHz. The TIA achieves a data rate of 30 Gb/s with input‐referred noise current density of 63.1 pA/Hz $\sqrt{\mathrm{Hz}}$ and jitter of 9.07 ps. The TIA consumes a power of 10.3 mW with a supply voltage of 1.8 V. [ABSTRACT FROM AUTHOR]

Artificial intelligent skins hold the potential to revolutionize artificial intelligence, health monitoring, soft robotics, biomedicine, flexible, and wearable electronics. Present artificial skins can be characterized into electronic skins (e-skins) that convert external stimuli into electrical signals and photonic skins (p-skins) that convert deformations into intuitive optical feedback. Merging both electronic and photonic functions in a single skin is highly desirable, but challenging and remains yet unexplored. We report herein a brand-new type of artificial intelligent skin, an optoelectronic skin (o-skin), which combines the advantages of both e-skins and p-skins in a single skin device based on one-dimensional photonic crystal-based hydrogels. Taking advantage of its anisotropic characteristics, the resulting o-skin can easily distinguish vector stimuli such as stress type and movement direction to meet the needs of multi-dimensional perception. Furthermore, the o-skin also demonstrates advanced functions such as full-color displays and intelligent response to the environment in the form of self-adaptive camouflage. This work represents a substantial advance in using the molecular engineering strategy to achieve artificial intelligent skins with multiple anisotropic responses that can be integrated on the skin of a soft body to endow superior functions, just like the natural organisms that inspire us. [ABSTRACT FROM AUTHOR]

In this work, we experimentally investigate the nonlinear dynamics of an interband cascade laser (ICL) under variable-aperture optical feedback implemented by a gold mirror combining with a ring-actuated iris diaphragm (RAID). By continuously varying the diameter of RAID (DR), the evolution of the dynamical state of ICL with the aperture of the optical feedback can be inspected. The characteristics of each dynamical state are characterized by time series, power spectra, phase portraits, and Lyapunov exponents. The results show that, with the decrease of DR, the dynamical state of the ICL under variable-aperture optical feedback presents an evolution from complex, simple to stable. Diverse dynamical states including period one state (P1), period two state (P2), multi-period state (MP), quasi-period state (QP), low-frequency fluctuation (LFF), chaotic state (C), and hyperchaos have been observed. Through mapping the evolution of dynamical states with DR for the ICL biased at different currents, different evolved routes of the dynamical states are revealed. [ABSTRACT FROM AUTHOR]

We report feedback-induced frequency oscillations using a power-split-ratio through asymmetric dual-loop optical feedback (Loop I: ~2.2 km and Loop II: ~20 m) subject to a self-mode-locked two-section QDash laser emitting at 1550 nm and operating at 21 GHz repetition rate. To assess the suppression of frequency resonances, three chosen combinations of feedback power (Loop I: −27.27 dB and Loop II: −19.74 dB, Loop I: −22 dB and Loop II: −22 dB, and Loop I: −19.74 dB and Loop II: −27.27 dB) through asymmetric dual-loop optical feedback have been studied. Based on the chosen coupling strength, an optimum feedback ratio that yields better side-mode suppression has been identified. Our results demonstrate that side-mode suppression can be achieved by the fine adjustment of coupling power through either cavity of dual-loop feedback configurations. Furthermore, we have further demonstrated that frequency fluctuations from the RF spectra can be filtered by carefully selecting the delay phase of the second cavity. Our experimental findings suggest that semiconductor mode-locked lasers based on dual-loop feedback configurations can be used to develop noise oscillations free from integrated photonic oscillators for potential applications in telecommunications, multiplexing, and frequency-comb generation. [ABSTRACT FROM AUTHOR]

Optical feedback for either the excitation or the signal is an effective approach to enhance the detection sensitivity of Raman scattering spectroscopy. A combination of plasmonic and optical feedback schemes may supply multifold enhancement mechanisms with further improved efficiency. Herein, a plasmonic Bragg grating (PBG) consisting of periodically distributed silver nanoslabs coated onto the sidewalls of the grating lines is reported. Localized surface plasmons excited in the silver nanoslabs with a large width/thickness ratio facilitate enhanced local field and Raman interaction. Asymmetric Bragg diffraction not only supplies optical feedback along the grating plane to extend largely the laser–molecule interaction distance but also enables efficient collection of the Raman signal through back‐diffraction into the detection system. Such a design accomplishes "volume" surface‐enhanced Raman scattering with a modulation depth of more than 500 nm and strong optical feedback, extending largely the limited interaction distance of surface plasmons. With respect to the scheme using Ag films for enhancement, a further enhancement factor larger than 2.8 × 103 has been achieved by the PBG device in the direct detection of the low‐concentration water solution of R6G molecules. The discovered photophysics is potentially important for practical applications in in situ water pollutant detection. [ABSTRACT FROM AUTHOR]

The current research work presents an evidence on overall synchronization of loosely bound strength in chaotic systems along with a new coupled design based on dual quantum dot light-emitting diodes (QDLEDs) in order to generate n-scroll attractors. To characterize these phenomena, the researchers used a theoretical approach on the basis of time series and phase space maps, i.e., attractors. In case of coupled QDLED attractors, the phases are generally locked during synchronous regime while the amplitudes are correlated. With the proposed construction scheme, both frequency detuning and coupling strength of two systems can be tuned independently. Further, chaotic attractors with even or else odd count of scrolls can also be easily generated. The study also demonstrated distinct attractors with n scrolls obtained using coupled design. [ABSTRACT FROM AUTHOR]

Active particles can self-propel by exploiting locally available energy resources. When powered by light, these resources can be distributed with high resolution allowing spatio-temporal modulation of motility. Here we show that the random walks of light-driven bacteria are rectified when they swim in a structured light field that is obtained by a simple geometric transformation of a previous system snapshot. The obtained currents achieve an optimal value that we establish by general theoretical arguments. This optical feedback is used to gather and confine bacteria in high-density and high-activity regions that can be dynamically relocated and reconfigured. Moving away from the boundaries of these optically confined states, the density decays to zero in a few tens of micrometers, exhibiting steep exponential tails that suppress cell escape and ensure long-term stability. Our method is general and scalable, providing a versatile tool to produce localized and tunable active baths for microengineering applications and systematic studies of non-equilibrium phenomena in active systems. Light can be used to precisely modulate the speed of active particles in space and time. Here, the authors rectify and confine bacteria using an optical feedback loop that couples bacteria topast configurations. [ABSTRACT FROM AUTHOR]

Decision making using photonic technologies has been intensively researched for solving the multi-armed bandit problem, which is fundamental to reinforcement learning. However, these technologies are yet to be extended to large-scale multi-armed bandit problems. In this study, we conduct a numerical investigation of decision making to solve large-scale multi-armed bandit problems by controlling the biases of chaotic temporal waveforms generated in semiconductor lasers with optical feedback. We generate chaotic temporal waveforms using the semiconductor lasers, and each waveform is assigned to a slot machine (or choice) in the multi-armed bandit problem. The biases in the amplitudes of the chaotic waveforms are adjusted based on rewards using the tug-of-war method. Subsequently, the slot machine that yields the maximum-amplitude chaotic temporal waveform with bias is selected. The scaling properties of the correct decision-making process are examined by increasing the number of slot machines to 1024, and the scaling exponent of the power-law distribution is 0.97. We demonstrate that the proposed method outperforms existing software algorithms in terms of the scaling exponent. This result paves the way for photonic decision making in large-scale multi-armed bandit problems using photonic accelerators. [ABSTRACT FROM AUTHOR]

In the current environment of the explosive growth in the amount of information, the demand for efficient information-processing methods has become increasingly urgent. We propose and numerically investigate a delay-based high-speed reservoir computing (RC) using a circular-side hexagonal resonator (CSHR) microlaser with optical feedback and injection. In this RC system, a smaller time interval can be obtained between virtual nodes, and a higher information processing rate (Rinf) can also be achieved, due to the ultra-short photon lifetime and wide bandwidth of the CSHR microlaser. The performance of the RC system was tested with three benchmark tasks (Santa-Fe chaotic time series prediction task, the 10th order Nonlinear Auto Regressive Moving Average task and Nonlinear channel equalization task). The results show that the system achieves high-accuracy prediction, even with a small number of virtual nodes (25), and is more feasible, with lower requirements for arbitrary waveform generators at the same rate. Significantly, at the high rate of 10 Gbps, low error predictions can be achieved over a large parameter space (e.g., frequency detuning in the interval 80 GHz, injected strength in the range of 0.9 variation and 2% range for feedback strength). Interestingly, it has the potential to achieve Rinf of 25 Gbps under technical advancements. Additionally, its shorter external cavity length and cubic micron scale size make it an excellent choice for large-scale photonic integration reservoir computing. [ABSTRACT FROM AUTHOR]

We numerically study the behavior of a semiconductor ring laser subject to bidirectional delayed optical feedback, when the isolated laser is in the quasi-unidirectional regime. The optical feedback, provided by two external reflectors located in front of the ring output waveguides, can modify the laser regime produced by the cross-saturation between the clockwise and the counter-clockwise mode. Thus, the system exhibits new different regimes, most of which are asymmetric and bidirectional, with alternating dominant mode. Two of these regimes are of special interest in view of applications, because the laser switching period, between the clockwise and the counter-clockwise mode, is linearly related to the time of flight from the laser to one or both reflectors. In these operating conditions, the laser is thus suitable to implement a telemeter. A convenient electrical output signal is obtained by a photodiode located behind one (partially reflecting) fixed mirror, or by measuring the voltage drop across the laser junction. Simulations are performed by mathematical models based on rate-equations, assuming typical literature parameters for a 1 mW ring laser. [ABSTRACT FROM AUTHOR]

Spectroscopic gas sensing technologies based on absorption and Raman scattering are fast, nondestructive, long-term stable and highly selective. By making use of an optically resonant cavity, the sensitivity can be enhanced hundreds to thousands of times. However, frequency-locking technology is necessary to maintain a stable resonant condition. In this review, various applications of Pound-Drever-Hall (PDH) and optical feedback (OF) frequency-locking cavity-enhanced spectroscopy (cavity ring-down spectroscopy, cavity-enhanced absorption spectroscopy and cavity-enhanced Raman spectroscopy) for highly sensitive gas sensing are presented. The effect of frequency-locking cavity-enhanced spectroscopy for improving the sensitivity of gas sensing is demonstrated. In addition, the key parameters and advantages as well as limitations of different frequency-locking cavity-enhanced spectroscopy are summarized and discussed. [ABSTRACT FROM AUTHOR]

Free-electron lasers (FELs) are the most advanced class of light-sources, by virtue of their unique capability to lase high-brightness pulses characterized by wavelengths spanning the extreme-ultraviolet, the soft and hard X-ray spectral domains, as well as by temporal lengths lying in the femtosecond (fs) timescale. The next step to push the current standards in ultrafast X-ray science is strongly linked to the possibility of engineering and exploiting time-resolved experiments exclusively for FELs pulses, ideally having different colors tunable at specific electronic resonance of the chemical elements. At the seeded FERMI FEL (Trieste, Italy) this goal is committed to the optical device known as AC/DC, which stands for the auto correlator/delay creator. AC/DC is designed to double the incoming FEL pulse splitting the photon beam by inserting a grazing incidence flat mirror, thus preserving the spectral and temporal properties, and further delaying one of these two pulses in time. It can independently tune the FEL pulses fluence on the two optical paths by means of solid-state filters, too. Here, we present a detailed description about this optical device. Strong emphasis is dedicated to the AC/DC opto-mechanical design and to the laser-based feedback systems implemented to compensate for any mismatch affecting the FEL optical trajectory, ascribable to both mechanical imperfections and paraxial errors rising during a temporal delay scan. [ABSTRACT FROM AUTHOR]

A DBR-laser-based SOA-assisted extended-reach EML (AXEL) was investigated in order to improve the optical feedback tolerance. The performance was tested in relative intensity noise measurement and fiber transmission experiment. A superior optical feedback tolerance was obtained in comparison with a conventional AXEL. The excess RIN induced by optical feedback is suppressed at 3-dB higher feedback power for the DBR-AXEL. 40 km fiber transmission of 10-Gbit/s signal with a feedback factor of −15 dB was achieved. The power budget was 41.3 dB. The feedback-induced power penalty was 0.52 dB. [ABSTRACT FROM AUTHOR]

The paper is focused on a systematic investigation of the circuits for active stabilization of the frequency offset between two semiconductorn ultra-accurate fiber optic time transfer systems. The frequency offset is increased up to 50 GHz, which can be achieved not only with relatively low-noise integrated tunable laser assemblies, but also with ordinary, telecom-grade, distributed feedback lasers. The paper starts by determining the general frequency accuracy and stability, required to keep the uncertainty contribution of the stabilization circuit at a negligible level (assumed here as 1 ps) compared to other contributions of the overall uncertainty of the link calibration. Next, the technical details of the essential building block of the system discussed, which is required to convert the high-frequency offset to lower frequencies to allow convenient frequency measurement, are analyzed. Experimental circuits built with commercially available millimeter wave integrated circuits were tested with the frequency offset complying with telecom dense wavelength division multiplex standards, equal to 12.5 GHz, 25 GHz and 50 GHz. It was found that such stabilization circuits can cause substantial systematic errors, which are related to lasers’ phase noise and the operation with low input optical powers (below −39 dBm in evaluated circuits). These effects were investigated experimentally in detail and countermeasures were proposed. [ABSTRACT FROM AUTHOR]

Interrogating a remote passive-sensor with high fidelity is one of the biggest challenges in the sensing domain. Recently, random fiber laser (RFL) combined with remote fiber sensors was proposed for optical fiber sensing with high signal-to-noise ratio over ultra-long-distance fiber link. However, only quasi-static sensing has been demonstrated. In this work, a novel dynamic sensing scheme based on backward-pumped random fiber laser is proposed, and its sensing bandwidth is both theoretically and experimentally studied. Particularly, a Raman-gain-modulated power-balance model reveals that the RFL intensity has instantaneous and linear response to remote feedback disturbances, laying the ground for ultra-high-bandwidth sensing; in a proof-of-concept experiment, RFL with 100 km fiber and a far-end fiber Bragg grating is used for dynamic strain sensing, and 65 kHz dynamic sensing is achieved, the sensing bandwidth of which is two orders higher than that determined by the lightwave round-trip time as in the pulse-probing cases. This work paves the way for ultra-high-bandwidth and ultra-long-distance interrogation for optical fiber sensors. [ABSTRACT FROM AUTHOR]

Interband cascade lasers are power-efficient mid-infrared laser sources which usually exhibit a spectral linewidth of hundreds of kHz. However, narrower linewidth lasers are more desirable for high-resolution molecular spectroscopy applications. This work narrows the spectral linewidth of an interband cascade laser from about 530 kHz down to about 30 kHz by applying optical feedback from an external mirror. In contrast to common laser diodes, the linewidth reduction of interband cascade lasers does not require any feedback phase control, which significantly simplifies the experimental configuration, and hence, is highly favorable for practical applications. [ABSTRACT FROM AUTHOR]

We for the first time present an all-passive cascaded optical frequency transfer technique over a fiber link, in which the phase noise of the each fiber link introduced by environmental perturbation and the laser repeater station are simultaneously compensated by using passive phase noise cancellation. The laser repeater station consisting of a cavity-stabilized laser is employed as a regenerative amplifier with a 45 dB optical gain. We demonstrate a cascaded optical frequency transfer with two 100 km spooled fiber links and one laser repeater station, illustrating an instability of $4.8\times 10^{-15}$ at the integration of 1 s and $4.9\times 10^{-19}$ at 10,000 s improved by a factor of 2 compared to the single-span 200 km fiber link. Dividing the whole fiber link into sub-sections could significantly improve the bandwidth of the phase noise compensation. Additionally, all-passive phase noise cancellation has the advantage of avoiding the servo bumps in the transferred light relative to the conventional active technique. The proposed technique provides a promising solution for high-performance and robust long-distance optical frequency transfer. [ABSTRACT FROM AUTHOR]

In robots, nonprehensile manipulation operations such as pushing are a useful way of moving large, heavy, or unwieldy objects, moving multiple objects at once, or reducing uncertainty in the location or pose of objects. In this study, we propose a reactive and adaptive method for robotic pushing that uses rich feedback from a high-resolution optical tactile sensor to control push movements instead of relying on analytical or data-driven models of push interactions. Specifically, we use goal-driven tactile exploration to actively search for stable pushing configurations that cause the object to maintain its pose relative to the pusher while incrementally moving the pusher and object toward the target. We evaluate our method by pushing objects across planar and curved surfaces. For planar surfaces, we show that the method is accurate and robust to variations in initial contact position/angle, object shape, and start position; for curved surfaces, the performance is degraded slightly. An immediate consequence of our work is that it shows that explicit models of push interactions might be sufficient but are not necessary for this type of task. It also raises the interesting question of which aspects of the system should be modeled to achieve the best performance and generalization across a wide range of scenarios. Finally, it highlights the importance of testing on nonplanar surfaces and in other more complex environments when developing new methods for robotic pushing. [ABSTRACT FROM AUTHOR]

In this work the optical feedback generated by a tapered amplifier (TPA) emitting at 1120 nm is characterized at different operational conditions. The TPA is operated in a master oscillator power amplifier (MOPA) configuration, while the influence of pump current or seed power on the emitted feedback is investigated. Measurements are also performed with the TPA exposed to defined external optical feedback. For an estimation of the feedback from the TPA a simple formula is derived and the calculations are compared to the measurement results. With the experimental and theoretical results the required feedback resistance of the master oscillator seed source can be defined and the MOPA system optimized for certain applications with unwanted optical feedback. [ABSTRACT FROM AUTHOR]

A semiconductor laser with optical feedback and optical injection is an appealing scheme to construct the time-delay reservoir computing (TDRC) networks. Quantum dot (QD) lasers are compatible to the silicon platform, and hence is helpful to develop fully on-chip TDRCs. This work theoretically demonstrates a parallel TDRC based on a Fabry-Perot QD laser with multiple longitudinal modes. These modes act as connected physical neurons, which process the input signal in parallel. The interaction strength of the modes is characterized by the cross-gain saturation effect. We show that the neuron interaction strength affects the performance of various benchmark tasks, including the memory capacity, time series prediction, nonlinear channel equalization, and spoken digit recognition. In comparison with the one-channel TDRC with the same number of nodes, the parallel TDRC runs faster and its performance is improved on multiple benchmark tasks. [ABSTRACT FROM AUTHOR]

The past decade has witnessed major advances in the development and system-level applications of photonic integrated microcombs, that are coherent, broadband optical frequency combs with repetition rates in the millimeter-wave to terahertz domain. Most of these advances are based on harnessing of dissipative Kerr solitons (DKS) in microresonators with anomalous group velocity dispersion (GVD). However, microcombs can also be generated with normal GVD using localized structures that are referred to as dark pulses, switching waves or platicons. Compared with DKS microcombs that require specific designs and fabrication techniques for dispersion engineering, platicon microcombs can be readily built using CMOS-compatible platforms such as thin-film (i.e., thickness below 300 nm) silicon nitride with normal GVD. Here, we use laser self-injection locking to demonstrate a fully integrated platicon microcomb operating at a microwave K-band repetition rate. A distributed feedback (DFB) laser edge-coupled to a Si3N4 chip is self-injection-locked to a high-Q (> 107) microresonator with high confinement waveguides, and directly excites platicons without sophisticated active control. We demonstrate multi-platicon states and switching, perform optical feedback phase study and characterize the phase noise of the K-band platicon repetition rate and the pump laser. Laser self-injection-locked platicons could facilitate the wide adoption of microcombs as a building block in photonic integrated circuits via commercial foundry service. 'Here the authors provide the demonstration of platicon comb generation in an integrated photonic chip using laser self-injection locking, They take advantage of platicons generation in normal GVD resonators, which significantly relaxes the material and geometry design restrictions [ABSTRACT FROM AUTHOR]

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.

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

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

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.