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We experimentally demonstrate a scheme for generating massively parallel and real-time physical random bits (PRBs) by using weak-resonant-cavity Fabry-Perot laser diodes (WRC-FPLDs) with optical feedback. By using external optical feedback to modify the nonlinear dynamic behavior of the longitudinal modes in WRC-FPLDs, the chaotic behavior of each channel can be induced under suitable feedback strength. By filtering these longitudinal modes, a real-time PRBs at 10 Gbits/s can be generated by using field programmable gate array (FPGA) board for the real-time post-processing of a single-channel chaotic signal. Considering the presence of up to 70 longitudinal modes within a broad spectral range exceeding 40 nm, each of these modes can be used to extract chaotic time sequences for random number generation. Therefore, our PRB generation scheme has the potential to achieve a data throughput of over 700 Gbits/s. [ABSTRACT FROM AUTHOR]

Electrosurgical and ultrasonic devices are used in surgical procedures for hemostatic sealing and bisection of vascular tissues. Previous benchtop studies alternatively demonstrated successful infrared laser sealing and cutting of blood vessels, in a sequential, two-step approach. This study describes a smaller, laparoscopic device compatible design, and simultaneous approach to sealing and bisection of vessels, with potential optical feedback. A 1470-nm infrared diode laser sealed and bisected 40 porcine renal arteries, ex vivo. A reciprocating, side-firing, optical fiber, housed in a transparent square quartz optical chamber (2.7 × 2.7 × 25 mm outer dimensions), delivered laser energy over an 11 mm scan length, with a range of incident powers (41–59 W) and treatment times (5–21 s). Vessel diameters ranged from 2.5 to 4.8 mm. Vessel burst pressure measurements were performed on each cut end (n = 80) with success indicated by pressures exceeding 360 mmHg. All vessel ends were successfully sealed and bisected (80/80). The highest incident power, 59 W, yielded short treatment times of 5–6 s. Peak temperatures on the external chamber surface reached 103 oC. Time to cool down to body temperature measured 37 s. Infrared lasers simultaneously seal and bisect blood vessels, with treatment times comparable to, and temperatures and cooling times lower than reported for conventional devices. Future work will focus on integrating the fiber and chamber into a standard 5-mm-outer-diameter laparoscopic device. Customization of fiber scan length to match vessel size may also reduce laser energy deposition, enabling lower peak temperatures, treatment times, and cooling times. [ABSTRACT FROM AUTHOR]

An external-cavity laser with resonant optical feedback is a common and mature method to achieve narrow linewidth lasers. Since the proposal of optical feedback in 1964, a series of studies on resonant optical feedback have been reported. Although longer feedback length leads to narrower linewidth, it also introduces coupling of environmental noise and causes instability in the laser cavity, which is detrimental to high-speed tuning of the laser wavelength. With such a challenge, current research on resonant optical feedback primarily focuses on the static results of laser linewidth compression. In order to obtain narrow linewidth high-speed tuned external-cavity lasers, further research on the laser dynamics is required to obtain dynamic tuning of narrow linewidth external-cavity lasers. In this work, we construct an external-cavity laser based on resonant optical feedback, and utilize a coherent detection method to measure the dynamic process of laser linewidth compression and wavelength tuning. Based on resonant optical feedback from the external cavity, the linewidth of the main-cavity laser can be compressed from near 100 kHz to the 100 Hz level, with the frequency noise compressed from the order of 104 to the 102 Hz2/Hz level. Since the wavelength switching process includes frequency shift process, linewidth compression process, and frequency stabilization process, etc., we first conduct a research on laser linewidth compression dynamics. In the results of linewidth compression dynamics, we discover that using a shorter fiber ring results in shorter linewidth compression time, which is advantageous for laser dynamic tuning. We subsequently carry out the laser wavelength switching process with a main-cavity switching time in milliseconds. In the wavelength switching process, while undergoing the frequency shift process of fast tuning transient laser frequency, the laser first undergoes the linewidth broadening process, then enters the main-cavity laser frequency stabilization process and undergoes the linewidth compression process at the same time. The experimental results show that the 100 m feedback fiber ring will not significantly increase the external-cavity laser wavelength switching time under the condition that linewidth compression is faster than main-cavity laser switching, while a longer fiber ring will introduce a strong noise. Our work experimentally demonstrates that shorter feedback ring lengths lead to faster compression, which provides valuable insights for the development of high-speed and high-precision tunable narrow linewidth external-cavity lasers. [ABSTRACT FROM AUTHOR]

Nonlinear dynamics at mid-infrared wavelength is of interest for various applications but has been mainly limited to quantum cascade lasers so far. In this article, we show that interband cascade lasers can generate complex optical chaos with bandwidth in the GHz range and this outperforms the performances of quantum cascade laser chaos. The chaos nature of our signal is confirmed by a thorough time-series analysis. Modeling of the semiconductor laser under short-cavity external optical feedback allows confirming the high bias chaos operation that we observe experimentally. These results pave the way for applications at mid-infrared wavelength, such as private free-space communication. [ABSTRACT FROM AUTHOR]

The development of a 1.65 µm cavity ringdown methane spectrometer for methane isotope analysis is reported. In order to reduce the laser linewidth, simple optical feedback with an 11 m external fiber cavity using a retroreflector was implemented and it improved the sensitivity. The detection limit at the ppt level for both 12CH4 and 13CH4 concentrations at 100 Torr gas pressure was evaluated from the Allan–Werle plot calculated from the dataset obtained at the fixed laser frequency. In contrast, the detection limit estimated from the baseline noise on the absorption spectrum was a few ppb for both methane isotopologues due to the periodic background oscillations that remained even after baseline correction. The system demonstrated the direct measurement of ambient methane in atmospheric room air, and the estimated 13CH4 ratio as well as the methane concentration were in good agreement with the reference values of ambient air. [ABSTRACT FROM AUTHOR]

Time-delayed optical feedback is known to trigger a wide variety of complex dynamical behavior in semiconductor lasers. Adding a second optical feedback loop is naturally expected to further increase the complexity of the system and its dynamics, but due to interference between the two feedback arms, it was also quickly identified as a way to improve the laser stability. While these two aspects have already been investigated, the influence of the feedback phases, i.e., sub-wavelength changes in the mirror positions, on the laser behavior still remains to be thoroughly studied, despite indications that this parameter could have a significant impact. Here, we analyze the effect of the feedback phase on the laser stability in a dual-feedback configuration. We show an increased sensitivity of the laser system to feedback phase changes when two-feedback loops are present and clarify the interplay between the frequency shift induced by the feedback and the interferometric effect between the two feedback arms. [ABSTRACT FROM AUTHOR]

Common-signal-induced synchronization of semiconductor lasers with optical feedback inspired a promising physical-layer key distribution with information-theoretic security and potential in high rate. A significant challenge is the requirement to shorten the synchronization recovery time for increasing the key rate without sacrificing the operation parameter space for security. Here, open-loop synchronization of wavelength-tunable multi-section distributed Bragg reflector lasers is proposed as a solution for physical-layer key distribution. Experiments show that the synchronization is sensitive to two operation parameters, i.e., currents of grating section and phase section. Furthermore, fast wavelength-shift keying synchronization can be achieved by direct modulation on one of the two currents. The synchronization recovery time is shortened by one order of magnitude compared to close-loop synchronization. An experimental implementation is demonstrated with a final key rate of 5.98 Mbit/s over 160 km optical fiber distance. It is thus believed that fast-tunable multi-section semiconductor lasers open a new avenue for a high-rate physical-layer key distribution using laser synchronization. [ABSTRACT FROM AUTHOR]

The study examines an extensive and complete synchronization of optimal feedback with quantum dot semiconductor laser mutual coupling system. This has been achieved by resolving the transmitter and receiver equations of the quantum dot lasers. Numerous crisis areas have been observed at the time of investigating the relationship between photon density and time. The authors have selected an optimal time delay for the optical feedback so as to render an appropriate situation for intermittent dynamics. The study analyses the impact created by a long external cavity of QDSL upon the synchronization process in this mutual coupling system, in the presence of the enhancement factor of (α =3). [ABSTRACT FROM AUTHOR]

In this article, the dependence of the operation states, dynamics, and noise of laser diodes (LD) with external optical feedback (OFB) on the linewidth enhancement factor (LEF) and spontaneous emission factor (SEF) have been investigated. We systematically studied the classification of the laser dynamics based on the bifurcation diagrams (BDs) of the photon numbers and the relative intensity noise (RIN) spectra at different levels of OFB, LEF, and SEF. The simulation results show that variations in the LEF and SEF lead to significant changes in the laser operation states and dynamics, which vary from continuous wave (CW), pulsation, and chaos states. The Hopf bifurcation (HB) point moves toward increasing/decreasing OFB intensity by increasing/decreasing the SEF/LEF. The laser state becomes more stable through a wide range of OFB by increasing/decreasing the SEF/LEF. The RIN reduces the solitary laser noise level at higher/lower values of SEF/LEF when the laser is operated under OFB. The relaxation frequency of the laser shifts toward higher values by increasing/decreasing the SEF/LEF through most laser states, and the RIN peak is higher than solitary laser noise by four orders of magnitude, especially in the pulsation regions. In the low-frequency region, the RIN is enhanced from one to two orders by reducing the LEF and SEF through laser states. [ABSTRACT FROM AUTHOR]

Semiconductor lasers with optical feedback are stochastic nonlinear systems that can display complex dynamics and abrupt changes when their operation conditions change. Even very small changes can lead to large variations in the spatial and spectral properties of the laser emission. This makes a semiconductor laser with feedback an ideal system for conducting controlled experiments to test data analysis tools to detect and characterize transitions. Here, we identify feedback-induced transitions by analyzing speckle patterns that are generated after the laser light propagates in an optical fiber. Speckle patterns result from the interference of multiple modes, and their statistical properties are understood, but a direct mathematical model does not exist. Here we show the versatility of the correlation length and the permutation entropy as measures for characterizing speckle patterns. Combining entropy and correlation analysis with speckle contrast analysis, we uncover changes that occur when the laser current increases from below to well above the threshold, which unveils the effects of optical feedback on the coherence of the laser emission. [ABSTRACT FROM AUTHOR]

An investigation into the dynamic states and relative intensity noise of laser diodes subjected to double optical feedback has been conducted. We employed modified and improved time-delay rate equations to account for double external optical feedback. The dynamic states and noise of lasers will be investigated using bifurcation diagrams of the output photon number, its temporal variations, and the intensity noise of the laser. This analysis considers feedback strengths due to the double external cavity and their spacing from the front facet of the laser with and without phase due to feedback. The results reveal that considering phase causes significant variations in laser intensity and a phase shift in the temporal variations of the laser output. This results in relative intensity noise suppression and a frequency shift in the intensity noise spectrum. These findings represent new contributions to our understanding of the reliance of lasing frequency shift on the phase due to feedback, regardless of whether feedback originates from a single or double external cavity. We investigated the optimal conditions corresponding to stable dynamic states of the laser with the lowest noise level. Additionally, we identified conditions that result in chaotic dynamics, where the spectrum does not convey information about the laser system. These insights have potential applications in chaotic and secure optical data encryption. [ABSTRACT FROM AUTHOR]

A novel method for the generation of an optical frequency comb (OFC) is presented. The proposed approach uses a laser diode with optical feedback and operating at a specific nonlinear dynamic state named periodic window. In this case, the laser spectrum exhibits a feature with a series of discrete, equally spaced frequency components, and the repetition rate can be flexibly adjusted by varying the system parameters (e.g., external cavity length), which can provide many potential applications. As an application example, a dual-OFC system for distance measurement is presented. The results demonstrate the system's ability to achieve target distance detection, underscoring its potential for real-world applications in this field. [ABSTRACT FROM AUTHOR]

Organic semiconductor lasers have shown great application potential in various fields, such as low-cost sensing, high-performance lighting and display, and lab-on-a-chip devices. Since the introduction of organic lasers in the 1960s, research on semiconductor laser devices has expanded to include various materials and structures. The organic laser has attracted much attention due to its wide range of emission spectrum and simple synthesis and processing. Researchers constantly pursue the goal of using organic semiconductors to fabricate low-threshold thin-film organic laser devices while retaining the characteristics of a wide luminescence spectrum of organic materials, simple and portable structure, and low cost. However, organic semiconductor lasers face challenges due to material stability under optical pumping and large optical losses under electrical pumping, making commercialization difficult. Many scholars have put great efforts into enhancing the performance of materials and optimizing the structure to minimize the threshold of organic semiconductor lasers. Herein, based on the basic principles of organic lasers, the main factors affecting the excitation threshold are summarized. A comprehensive analysis of the relevant factors and threshold conditions is performed, considering both positive and negative aspects of modal gain and modal loss that need to be addressed. We expect to provide a wide range of ideas for reducing the threshold of organic lasers and offer theoretical guidance for the practical industrial production of organic lasers. [ABSTRACT FROM AUTHOR]

In this work, we propose to employ strong optical feedback to narrow the spectral linewidth of quantum cascade lasers without using any phase control. Rate equation analysis demonstrates that optical feedback beyond a certain level always reduces the laser linewidth for any feedback phase. It is also found that the linewidth becomes less sensitive to the feedback phase for higher feedback strength. Simulations show that optical feedback with a feedback ratio of −10 dB can suppress the laser linewidth by about two orders of magnitude. This is in contrast to near-infrared laser diodes, which can be easily destabilized by strong feedback. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Jilin University (Science Edition) / Jilin Daxue Xuebao (Lixue Ban) is the property of Zhongguo Xue shu qi Kan (Guang Pan Ban) Dian zi Za zhi She and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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

Photonic reservoir computing has been intensively investigated to solve machine learning tasks effectively. A simple learning procedure of output weights is used for reservoir computing. However, the lack of training of input-node and inter-node connection weights limits the performance of reservoir computing. The use of multiple reservoirs can be a solution to overcome this limitation of reservoir computing. In this study, we investigate parallel and deep configurations of delay-based all-optical reservoir computing using semiconductor lasers with optical feedback by combining multiple reservoirs to improve the performance of reservoir computing. Furthermore, we propose a hybrid configuration to maximize the benefits of parallel and deep reservoirs. We perform the chaotic time-series prediction task, nonlinear channel equalization task, and memory capacity measurement. Then, we compare the performance of single, parallel, deep, and hybrid reservoir configurations. We find that deep reservoirs are suitable for a chaotic time-series prediction task, whereas parallel reservoirs are suitable for a nonlinear channel equalization task. Hybrid reservoirs outperform other configurations for all three tasks. We further optimize the number of reservoirs for each reservoir configuration. Multiple reservoirs show great potential for the improvement of reservoir computing, which in turn can be applied for high-performance edge computing. [ABSTRACT FROM AUTHOR]

An investigation into the dynamic states and relative intensity noise of laser diodes subjected to double optical feedback has been conducted. We employed modified and improved time-delay rate equations to account for double external optical feedback. The dynamic states and noise of lasers will be investigated using bifurcation diagrams of the output photon number, its temporal variations, and the intensity noise of the laser. This analysis considers feedback strengths due to the double external cavity and their spacing from the front facet of the laser with and without phase due to feedback. The results reveal that considering phase causes significant variations in laser intensity and a phase shift in the temporal variations of the laser output. This results in relative intensity noise suppression and a frequency shift in the intensity noise spectrum. These findings represent new contributions to our understanding of the reliance of lasing frequency shift on the phase due to feedback, regardless of whether feedback originates from a single or double external cavity. We investigated the optimal conditions corresponding to stable dynamic states of the laser with the lowest noise level. Additionally, we identified conditions that result in chaotic dynamics, where the spectrum does not convey information about the laser system. These insights have potential applications in chaotic and secure optical data encryption.

We are delighted to present this Special Issue of "Advancements in Semiconductor Lasers", which features a remarkable collection of 14 papers that explore the diverse and cutting-edge aspects of semiconductor lasers. The first section of this Special Issue presents advancements in understanding the underlying determinism of semiconductor lasers, and a new method to distinguish chaotic regimes in a semiconductor laser with feedback is presented. Bian et al. proposed a simple method using mutually coupled free-running VCSELs to generate broadband polarization chaos [[9]], while the locking map of a semiconductor laser under the injection of a frequency comb was studied [[10]]. [Extracted from the article]

We numerically investigate the influence of an integrated filtered optical feedback on the behavior of a semiconductor ring laser subject to external optical injection. The optical injection is spectrally directed at one of the non-lasing longitudinal modes of the laser. This so-called side-mode injection can cause wavelength switching, directional switching, and changes in the dynamical regime of the semiconductor ring laser. Such changes are often unwanted as they can affect the stability and the performance of the semiconductor ring laser. We investigate to what extent these undesired effects can be avoided by stabilizing the laser using on-chip filtered feedback. A two-directional mode model is used to investigate the dynamical behavior of the semiconductor ring laser under the simultaneous effect of the external optical injection and the integrated feedback. The results show that on-chip filtered optical feedback can be used to reduce the sensitivity of the semiconductor ring laser to external optical injection. [ABSTRACT FROM AUTHOR]

The article offers information on the Photonic artificial intelligence which has attracted considerable interest in accelerating machine learning and its unique optical properties have not been fully used for achieving higher-order functionalities. It discusses a method for controlling the chaotic itinerancy in a multimode semiconductor laser to solve a machine learning task, namely, the multiarmed bandit problem, which is fundamental to reinforcement learning.

We demonstrate a narrow-linewidth, high side-mode suppression ratio (SMSR) semiconductor laser based on the external optical feedback injection locking technology of a femtosecond-apodized (Fs-apodized) fiber Bragg grating (FBG). A single frequency output is achieved by coupling and integrating a wide-gain quantum dot (QD) gain chip with a Fs-apodized FBG in a 1-μm band. We propose this low-cost and high-integration scheme for the preparation of a series of single-frequency seed sources in this wavelength range by characterizing the performance of 1030 nm and 1080 nm lasers. The lasers have a maximum SMSR of 66.3 dB and maximum output power of 134.6 mW. Additionally, the lasers have minimum Lorentzian linewidths that are measured to be 260.5 kHz; however, a minimum integral linewidth less than 180.4 kHz is observed by testing and analyzing the power spectra of the frequency noise values of the lasers. [ABSTRACT FROM AUTHOR]

This work describes an experimental method for measuring the speed of light in air. It uses optical feedback from a visible picosecond diode laser operated below the threshold and a voltage-controlled oscillator to determine the time required for a pulse to travel a known distance. The experimental setup is compact, fitting into a space of 1 × 0.5 m2, and at the same time, can determine the speed of light with an uncertainty of 0.03%. The method does not require fast detectors or oscilloscopes. [ABSTRACT FROM AUTHOR]

In this article, we revisit the concept of optical feedback regimes in diode lasers and explore each regime experimentally from a somewhat unconventional point of view by relating the feedback regimes to the laser bias current and its optical feedback level. The results enable setting the operating conditions of the diode laser in different applications requiring operation in different feedback regimes. We experimentally explored and theoretically supported this relationship from the standard Lang and Kobayashi rate equation model for a laser diode under optical feedback. All five regimes were explored for two major types of laser diodes: inplane lasers and vertical-cavity surface emitting lasers. For both lasers, we mapped the self-mixing strength vs. drive current and feedback level, observed the differences in the shape of the self-mixing fringes between the two laser architectures and a general simulation, and monitored other parameters of the lasers with changing optical feedback. [ABSTRACT FROM AUTHOR]

In this paper, we review the progress of wide tunable Bragg grating external cavity semiconductor lasers (BG-ECSLs). We concentrate on BG-ECSLs based on the wide tunable range for multicomponent detection. Wide tunable BG-ECSLs have many important applications, such as wavelength-division multiplexing (WDM) systems, coherent optical communications, gas detection and atom cooling. Wide tunability, narrow linewidth and a high side-mode suppression ratio BG-ECSLs have attracted much attention for their merits. In this paper, three main structures for achieving widely tunable, narrow linewidth, high side-mode suppression ratio BG-ECSLs are reviewed and compared in detail, such as the volume Bragg grating (VBG) structure, fiber Bragg grating (FBG) structure and waveguide Bragg grating (WBG) structure of ECSLs. The advantages and disadvantages of different structures of BG-ECSLs are analyzed. The results show that WBG-ECSLs are a potential way to realize the integration, small size, wide tuning range, stable spectral output and high side-mode suppression ratio laser output. Therefore, the use of WBG as optical feedback elements is still the mainstream direction of BG-ECSLs, and BG-ECSLs offer a further new option for multicomponent detection and multi-atoms cooling. [ABSTRACT FROM AUTHOR]

The diversity of observed nonlinear dynamics in laser diodes subjected to optical feedback shows promise as an excellent candidate for chaos-based commercial applications. Thus, works in the last decade have primarily focused on system performances, geometric configurations, and balancing their trade-offs. We demonstrate an optical feedback system operating on phase-conjugate feedback exhibiting state-of-the-art chaos bandwidth values reaching ≈ 30 GHz. We report numerous high-frequency, spatiotemporally complex, chaotic dynamics undocumented in the past four decades. We highlight the underlying physics involving a three-tier temporal interaction mechanism between laser relaxation oscillations, phase-conjugate feedback induced external cavity modes, and chaotic bursts repeating each delay time in the extended cavity. We show supporting real-time high-definition system outputs captured by modern large bandwidth oscilloscopes. The presented work shows to our knowledge, the highest bandwidth and complexity entropy to-date in an optical chaos from a single laser, thereby proving the unnecessary need for further complexity using cascading lasers. The chaotic behavior due to the non-linearity present in a time-delayed feedback system has potential applications for secure optical communication and encryption. Here, a laser diode with phase-conjugate feedback is reported with state-of-the-art broadband, spatiotemporally complex, and high-entropy chaos. [ABSTRACT FROM AUTHOR]

We have recently reported the self-pulsation phenomenon under strong optical feedback in terahertz (THz) quantum cascade lasers (QCLs). One important issue, however, we left open: the effect of multiple round trips in the external cavity on the laser response to feedback. Our current analysis also casts additional light on the phenomenon of self-pulsations. Using only one external cavity round trip (ECRT) in the model has been the common approach following the seminal paper by Lang–Kobayashi in 1980. However, the conditions under which the Lang–Kobayashi model, in its original single-ECRT formulation, is applicable has been rarely explored. In this work, we investigate the self-pulsation phenomenon under multiple ECRTs. We found that the self-pulsation waveform changes when considering more than one ECRT. This we attribute to the combined effect of the extended external cavity length and the frequency modulation of the pulsation frequency by the optical feedback. Our findings add to the understanding of the optical feedback dynamics under multiple ECRTs and provide a pathway for selecting the appropriate numerical model to study the optical feedback dynamics in THz QCLs and semiconductor lasers in general. [ABSTRACT FROM AUTHOR]

We study improvements of the Self-Injection Locked (SIL) distributed feedback (DFB) semiconductor laser phase noise as well as integral linewidth on the amount of the SIL feedback and show that SIL reduces the laser noise nearly equally in a broad frequency range, spanning from 1 Hz to 10 MHz. In our experiment SIL operation is supported by a tunable resonant reflector consisting of a high quality factor (high-Q) monolithic whispering gallery mode resonator (WGMR) supplied with a controllable attenuator. Using the experimental setup we validated theoretical formula describing the SIL spectral purity and identified practical parameters of the system allowing reaching the phase noise limit resulting from the fundamental thermodynamic noise of the resonator. We show that the linewidth improvement due to SIL effect is drastically impacted by the frequency spectral dependence of the phase noise of the laser and that it drops significantly in a flickering laser. We also confirmed that the thermorefractive coefficient as well as mode volume of the WGMR imposes the major limitations on the SIL performance. Low intracavity absorption is needed to suppress the attenuation-related thermal effects in the cavity. [ABSTRACT FROM AUTHOR]

A systematic treatment of the influence of the optical feedback (OFB) and the ratio of the radiative and the non-radiative recombination lifetime (τr/τnr) on the relative intensity noise (RIN) and the system dynamics of a semiconductor laser (SL) is presented. We found that the ratio τr/τnr causes a significant change in the intensity of noise, states, and route to chaos of such a system. Laser transit from a continuous wave (CW) to a periodic oscillation (PO) becomes faster in terms of the OFB strength by increasing the ratio τr/τnr. The route to chaos was identified in three distinct operating regions, namely, PO, period doubling (PD), and sub-harmonics (SH), which are dependent on the ratio τr/τnr, and injection current. In the route to chaos regime, the ratio τr/τnr triggers a slight shift in the frequency with reference to the frequency of the solitary laser. At upmost levels of the current, the highest value of the ratio τr/τnr stabilizes the laser and stimulates it to operate in CW or PO. In the strong OFB region, when the ratio τr/τnr increases, the chaotic operation changed to CW or PO operation and RIN is suppressed close to the quantum noise level. [ABSTRACT FROM AUTHOR]

In this article, we propose an all-fiber self-mixing velocimeter based on a DBR fiber laser with adjustable injection intensity for the first time, and theoretically and experimentally explore the behavior of fiber lasers in detecting non-cooperative target under different injection intensities. When the ultra-strong injection level is attained, the linewidth of the DBR fiber laser will be narrowed to about 10 kHz, thus extending the coherence distance of laser tremendously. Simultaneously, the intensity noise can be also significantly suppressed. The non-cooperative target velocity measurement with 40 km single-channel transmission distance has been successfully achieved. This velocimeter is shown to be of great significance in the field of remote sensing with simple and compact configuration, and adjustable dynamical monitoring range. [ABSTRACT FROM AUTHOR]

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

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]

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]

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]

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]

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]

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]

10.1109/JQE.1980.1070479 4 Schunk N., Petermann K. Numerical analysis of the feedback regimes for a single-mode semiconductor laser with external feedback. Colored Optical Feedback Turns Down the Noise in Chaotic Lasers Optical feedback always pushes the laser emission to change instantaneous values of frequency and power. 10.1109/JSTQE.2012.2234445 11 Jumpertz L., Carras M., Schires K., Grillot F. Regimes of external optical feedback in 5.6 m distributed feedback mid-infrared quantum cascade lasers. [Extracted from the article]

An InP-based mode-locked laser photonic integrated circuit with a repetition rate of 10 GHz is optically synchronized to a SiN microresonator-based dissipative Kerr soliton with a repetition rate of 305 GHz. The synchronization is achieved through regenerative harmonic injection locking assisted with electro-optic division which results in an optical frequency division factor of 18. The repetition rate of the dissipative Kerr soliton is stabilized through electro-optic division and transferred to the mode-locked laser, where we measure a fractional frequency instability in the repetition rate of $10^{-10}$ at 1 s with a $1/\tau$ trend. Furthermore, we also stabilize the repetition rate of the dissipative Kerr soliton using the mode-locked laser’s repetition rate beat as a feedback point. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the effect of optical feedback on the dynamics of a passively mode-locked ring laser operating in the regime of temporal localized structures. This laser system is modeled by a set of delay differential equations, which include delay terms associated with the laser cavity and the feedback loop. Using a combination of direct numerical simulations and path-continuation techniques, we show that the feedback loop creates echoes of the main pulse whose position and size strongly depend on the feedback parameters. We demonstrate that in the long-cavity regime, these echoes can successively replace the main pulses, which defines their lifetime. This pulse instability mechanism originates from a global bifurcation of the saddle-node infinite-period type. In addition, we show that, under the influence of noise, the stable pulses exhibit forms of a behavior characteristic of excitable systems. Furthermore, for the harmonic solutions consisting of multiple equispaced pulses per round-trip, we show that if the location of the pulses coincides with the echo of another, the range of stability of these solutions is increased. Finally, it is shown that around these resonances, branches of different solutions are connected by period-doubling bifurcations. [ABSTRACT FROM AUTHOR]

An experiment for measuring the speed of light by measuring the distance between regularly generated optical pulses is described. The experiment utilizes optical feedback from a visible picosecond diode laser to accurately determine the distance between two successive laser pulses. The required setup is compact, and it does not implement either a fast detector or an oscilloscope. This experiment is suitable for an undergraduate physics instructional laboratory course or as an independent student project. [ABSTRACT FROM AUTHOR]

In this paper, microwave photonic signal generation based on the period-one dynamic of optically injected discrete mode (DM) semiconductor lasers has been experimentally demonstrated and numerically simulated. The results show that the frequency of the generated microwave increases linearly with the frequency detuning or optical injection ratio. In addition, a single optical feedback loop is sufficient to reduce the microwave linewidth without significantly deteriorating side mode suppression. The simulation results using a model considering the nonlinear dependencies of the carrier recombination agree well with the experimental results, which indicates that the nonlinear carrier recombination effect is important in determining the nonlinear dynamics of optically injected DM lasers. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate a novel multi-channel chaos generation scheme, which can simultaneously produce multiple chaotic signals with wideband spectrum and suppressed time-delay signature (TDS). In this scheme, we introduce an external self-phase-modulated feedback (ESPMF) to improve the optical bandwidth of the initial chaos generated by a conventional external-cavity semiconductor laser (ECSL), then optical tunable filters (OTFs) are utilized to simultaneously extract three-channel chaotic outputs. The experimental results show that the proposed scheme has three main advantages. Firstly, it can simultaneously generate multiple chaotic outputs with different central wavelengths and low correlations. Secondly, the bandwidth of original ECSL-based chaos can be improved by several times, and the undesired TDS characteristics in the original chaos can be completely suppressed to an indistinguishable level (lower than 0.02). Thirdly, the bandwidths of these chaotic outputs are flexible and can be adjusted within a wide range of 20 GHz by controlling the filter bandwidths. In addition, we demonstrate an application of the proposed chaos generation scheme in random bit generation (RBG), and multi-channel high-speed random bit sequences with a total generation rate over Tb/s and NIST verified randomness are simultaneously obtained. [ABSTRACT FROM AUTHOR]